5
Technology

Although noise can be generated by turbulence in highspeed flows, most noise is generated by mechanical motion caused by forces acting on structures. The motion can be very complex—for example, in the case of a panel on a machine. Consequently, the coupling between the moving structure and air, required to generate noise, depends on details of the motion as well as frequency. Generally, low-frequency vibration is less efficient in generating sound than high-frequency vibration. Sound reaches the ear by propagation from the source to the receiver and can be complicated by reflections from nearby surfaces as well as atmospheric conditions outdoors. Some motion is unavoidable; for example, fan blades must move and vehicle tires must rotate. In many cases the function of the machine is unrelated to the noise generated. An example is the mechanical suspensions that attach airplane engines to an airplane but also allow the transmission of vibrations to the fuselage. This transmission into the fuselage and subsequent radiation of sound can be (and is) minimized by good design—which can also save money by reducing wear and fatigue.

This chapter is concerned with new technologies in materials and systems to reduce noise, the modeling and analytical tools used to design products for reduced noise, and experimental methods of gathering and interpreting data to test and determine how much noise is generated by different product designs. It will be immediately obvious that there are enormous disparities among programs, facilities, and resources for addressing noises of different types. For example, although engineering tools may be available for reducing aircraft noise and highway noise, the former has been deemed a national priority, while the latter has received less attention. Resources allocated for noise reduction are not always commensurate with noise exposures and impacts.

Many tools for designing and developing quieter products have become available in the past few decades, driven largely by increases in computational power and reductions in computational costs. Even so, access to new tools is as uneven as the allocation of resources; corporate budgets for capital equipment are generally tight and there is competition between departments for available funds. Furthermore, organizations that are doing only routine testing of products according to national and international standards find expensive new tools hard to justify. Thus, even though noise mechanisms in aircraft, automobiles, rapid transit and trains, consumer products, and industrial machinery are fundamentally similar, the availability and application of tools for addressing them are not. The question is whether ways can be found to give industry and academia access to these tools for the benefit of manufacturers, workers, and the public.

AEROSPACE AND AEROACOUSTICS

SOURCES OF AIRCRAFT NOISE

Noise from aircraft includes both noise from airplanes and noise from helicopters. At commercial airports, airplanes are the major noise source and will be emphasized here because of the widespread annoyance issues that have affected the quality of life for many persons. Noise from helicopters is also an important issue and affects people living near heliports and in densely populated areas where helicopter flights are not uncommon. The Federal Aviation Administration was asked to prepare a report to Congress on nonmilitary helicopter noise (FAA, 2004). One important issue relates to noise metrics; the impulsive character of the noise requires that metrics in addition to the widely used day-night average sound level (DNL) be used to assess its effects on people.

The noise heard when an airplane flies overhead comes from many sources, but the main contributors are engine noise and airframe noise. Engine noise comes from the fan/propeller, compressor, turbine, combustor, and jet exhaust. Airframe noise is produced mostly by airflows around lifting and control surfaces, such as flaps and slats, and around landing gears.



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 55
5 Technology Although noise can be generated by turbulence in high- uneven as the allocation of resources; corporate budgets for speed flows, most noise is generated by mechanical motion capital equipment are generally tight and there is competi- caused by forces acting on structures. The motion can be very tion between departments for available funds. Furthermore, complex—for example, in the case of a panel on a machine. organizations that are doing only routine testing of products Consequently, the coupling between the moving structure according to national and international standards find ex- and air, required to generate noise, depends on details of the pensive new tools hard to justify. Thus, even though noise motion as well as frequency. Generally, low-frequency vibra- mechanisms in aircraft, automobiles, rapid transit and trains, tion is less efficient in generating sound than high-frequency consumer products, and industrial machinery are fundamen- vibration. Sound reaches the ear by propagation from the tally similar, the availability and application of tools for ad- source to the receiver and can be complicated by reflections dressing them are not. The question is whether ways can be from nearby surfaces as well as atmospheric conditions out- found to give industry and academia access to these tools for doors. Some motion is unavoidable; for example, fan blades the benefit of manufacturers, workers, and the public. must move and vehicle tires must rotate. In many cases the function of the machine is unrelated to the noise generated. AEROSPACE AND AEROACOuSTICS An example is the mechanical suspensions that attach air- plane engines to an airplane but also allow the transmission of vibrations to the fuselage. This transmission into the SOuRCES OF AIRCRAFT NOISE fuselage and subsequent radiation of sound can be (and is) Noise from aircraft includes both noise from airplanes and minimized by good design—which can also save money by noise from helicopters. At commercial airports, airplanes are reducing wear and fatigue. the major noise source and will be emphasized here because This chapter is concerned with new technologies in of the widespread annoyance issues that have affected the materials and systems to reduce noise, the modeling and quality of life for many persons. Noise from helicopters is analytical tools used to design products for reduced noise, also an important issue and affects people living near heli- and experimental methods of gathering and interpreting ports and in densely populated areas where helicopter flights data to test and determine how much noise is generated are not uncommon. The Federal Aviation Administration by different product designs. It will be immediately obvi - was asked to prepare a report to Congress on nonmilitary ous that there are enormous disparities among programs, helicopter noise (FAA, 2004). One important issue relates to facilities, and resources for addressing noises of different noise metrics; the impulsive character of the noise requires types. For example, although engineering tools may be that metrics in addition to the widely used day-night average available for reducing aircraft noise and highway noise, sound level (DNL) be used to assess its effects on people. the former has been deemed a national priority, while the The noise heard when an airplane flies overhead comes latter has received less attention. Resources allocated for from many sources, but the main contributors are engine noise reduction are not always commensurate with noise noise and airframe noise. Engine noise comes from the fan/ exposures and impacts. propeller, compressor, turbine, combustor, and jet exhaust. Many tools for designing and developing quieter prod- Airframe noise is produced mostly by airflows around lift- ucts have become available in the past few decades, driven ing and control surfaces, such as flaps and slats, and around largely by increases in computational power and reductions landing gears. in computational costs. Even so, access to new tools is as 

OCR for page 55
6 TECHNOLOGY FOR A QUIETER AMERICA The relative contribution of these sources depends on heavy road traffic, a lower noise level than in an underground the engine and airframe designs and the operating condi- train. The noise footprint of the A380 is about half that of tions. For example, during takeoff, when the engines are at older, large commercial aircraft (Rolls-Royce, 2005b). full thrust, jet noise is the largest contributor to the noise Despite these impressive results, airport community noise signature of an aircraft. At approach, when the engine is continues to be a significant environmental problem, and re- throttled back, noise comes more from the airframe. Other search and development (R&D) continue in the United States sources, such as the fan, are significant contributors during and Europe to meet increasingly stringent noise require- both takeoff and landing. ments set by regulatory bodies, such as the Federal Avia- Typical noise sources for a fixed-wing aircraft are shown tion Administration (FAA), the International Civil Aviation in Figure 5-1. The noise received by an observer depends on Organization (ICAO), and individual airports (Rolls-Royce, the sources and propagation effects. The noise sources for a 2005b). Over the years, the FAA and ICAO have required propeller-driven aircraft are shown in Figure 5-2. comparable reductions. RESEARCH IN AEROACOuSTICS INFRASTRuCTuRE AND PROgRAMS THAT SuPPORT RESEARCH AND APPLICATIONS The aeroacoustics community has made significant prog- ress over the years in understanding and reducing aircraft A Note on Test Facilities noise. Figure 5-3 shows comparative contributions from different noise sources for 1960s and 1990s engines. The Both the United States and Europe have first-class aero- figure, which originally appeared in Rolls-Royce (2005a), acoustics test facilities. Anechoic flight simulation facilities, shows that the development of the turbofan engine and re- the most useful for testing both jet noise and airframe noise, duction in noise from individual engine components resulted are available on both sides of the Atlantic on a rental basis. in smaller, more evenly matched noise contributions from In the United States, high-quality anechoic chambers for engine sources (SBAC, 2009). model-scale testing are available at the National Aeronau- Over a period of 30 years, these improvements, coupled tics and Space Administration (NASA) Langley and Glenn with advances in aircraft aerodynamics and weight tech- Research Centers, as well as at Boeing, General Electric, nologies, have reduced aircraft noise by about 20 dB, which United Technologies, and some U.S. universities, such as corresponds to a reduction in noise annoyance of about 75 Georgia Institute of Technology, which inherited Lockheed percent (EU, 2007). The new Airbus A380, the largest com- Georgia’s aeroacoustics facilities. Rolls Royce in England mercial aircraft ever produced (average of 525 passengers), has used the NASA Glenn jet noise acoustic chambers, and has takeoff and approach noise levels comparable to those of Boeing researchers have used facilities in England. NASA Aircraft Noise: Source, Propagation, and Noise Impact FIGURE 5-1 Breakdown of typical noise sources for fixed-wing aircraft. Source: Posey (2008). Figure_5-1.eps bitmap with vector title

OCR for page 55
7 TECHNOLOGY Blade thickness and loading Engine Blade/wing interaction Transmission Fountain flow Blade/vortex interaction Key Noise Sources: • Blade thickness • Blade loading Blade/fuselage interaction • Blade/vortex interaction High-speed impulsive noise • Engine • Blade/fuselage interaction FIGURE 5-2 Breakdown of typical noise sources for a rotorcraft configuration. Source: Burley (2008). Figure_5-2.eps Langley researchers have also used the Dutch anechoic wind vector labelingof noise on communities, while NASA fo- bitmap with on the impacts tunnel to make helicopter noise measurements. Both the cuses on noise at its source—namely, aircraft engines and United States and Europe also have access to state-of-the-art airframes. A recent congressionally requested report on avia- flow measurement equipment (including particle imaging tion noise addresses (1) how well the FAA and NASA’s R&D velocimetry) and modern phased microphone array systems. plans are aligned and (2) the likelihood that noise reduction Most of these facilities have been described in great detail goals will be met (FAA, 2008). by Ahuja (1995). The FAA and NASA’s R&D plans, aligned through part- nerships and planning and coordinating mechanisms, include a wide range of projects for addressing aviation noise. The u.S. NOISE REDuCTION PROgRAMS FAA sponsors aviation noise R&D in noise measurement, The FAA and NASA have primary responsibility in the noise effects, interrelationships between noise and pollutant United States for R&D on aviation noise. The FAA focuses emissions, and flight procedures and technologies to mitigate 1960s 1990s Compressor Fan Compressor Turbine & Turbine & Jet Combustor Combustor Jet FIGURE 5-3 Noise sources for 1960s and 1990s jet engines. Source: Rolls-Royce (2005a). Figure_5-3.eps

OCR for page 55
8 TECHNOLOGY FOR A QUIETER AMERICA the impact of noise on communities. Much of this R&D is After rigorous testing, including measurements taken funded through partnerships with universities, other federal on the ground, in the passenger cabin, and on the airframe agencies (including NASA), and industry. NASA’s R&D can (Herkes, 2006), many noise reduction technologies, includ- eventually lead to new technologies for substantially quieter ing nozzle chevrons, spliceless inlet linings, extended lining aircraft. However, industry will have to integrate the research locations, and redesigned wing anti-icing systems (see Fig- results into production-ready aircraft designs. ure 5-4), as well as smooth fairings to reduce landing gear The FAA and NASA have worked with interagency noise (see Figure 5-5), have been incorporated into existing planning and coordinating groups to establish objectives airplanes and designs for future Boeing airplanes. Thus, for the nation’s aeronautical R&D and for specific research Boeing’s newer airplanes are significantly quieter for both on the environmental impacts of next-generation aviation passengers and airport communities (Herkes et al., 2006). A technologies. The strategic plans for the National Airspace third phase, QTD3, is in the planning stages at Boeing. System indicate how each agency’s R&D will contribute Over the years the FAA has defined requirements for to meeting noise reduction goals, which are designed to the reduction of aircraft noise emissions in terms of stages reduce public exposure to aviation noise primarily by re - (1–4). The metric for describing the noise emissions is the ducing noise at its source (GAO, 2008). effective perceived noise level in decibels (EPNdB), and In 1994, NASA initiated a seven-year program, the Ad- well-defined microphone positions are used for the measure- vanced Subsonic Transport (AST) Noise Reduction Program, ment. Note that this is quite different from the immission to develop technology to reduce jet transport noise by 10 dB metric (DNL) used to describe the effects of aircraft noise relative to 1992 levels. Most of the goals of AST were met on communities. by 2001. However, because of an anticipated annual increase The goal of NASA’s current Subsonic Fixed Wing Project of 3 to 8 percent in passenger and cargo operations well into is to reduce aircraft noise by 42 EPNdB cumulative below the twenty-first century and the slow introduction of new Stage 3 for conventional, small, tube-with-wing twin-jet air- noise reduction technology into the fleet, the global impact of craft, what NASA calls “N + 1 generation” aircraft, by 2012 world aircraft noise is expected to remain essentially constant to 2015 (Collier and Huff, 2007). An even more ambitious until 2020 (or perhaps 2030) and thereafter begin to increase. goal, set for the 2018 to 2020 period, is to reduce aircraft Therefore, NASA has begun planning with FAA, industry, noise by 52 EPNdB cumulative below Stage 3 for N + 2 universities, and environmental interest groups in the United generation aircraft, which NASA envisions as an unconven- States for a new noise reduction initiative. tional hybrid wing-body aircraft (see Figure 5-6). In addition One of the most important noise reduction technol - to reducing noise, NASA expects dramatic improvements in ogy programs in the United States is the so-called Quiet the emission and performance of these aircraft. Technology Demonstrator (QTD1) Program, a partner- ship among Boeing, Rolls Royce, and American Airlines EuROPEAN NOISE REDuCTION PROgRAMS initiated in 2000 (Bartlett et al., 2004). A second phase, Q TD2, a partnership among NASA, General Electric, Driven by increasingly stringent noise requirements and Goodrich, and ANA, was begun in 2005. These programs strong competition from the United States, Europe has set have validated new, advanced noise reduction technologies, including nacelle inlet acoustical treatments and chevrons on engine exhaust ducts. FIGURE 5-5 Toboggan landing gear fairings for reducing landing FIGURE 5-4 QTD2 noise reduction technologies. Source: Herkes gear noise tested in QTD2. Source: Herkes (2006). Copyright Boe- ing. All rights reserved. Figure_5-5.eps (2006). Copyright Boeing.igure_5-4.eps F All rights reserved. bitmap bitmap

OCR for page 55
 TECHNOLOGY Noise (cumulative below Stage 3) FIGURE 5-6 Goals of the N+1 and N+2 generation aircraft. Source: Collier and Huff (2007). very ambitious goals for reducing aircraft noise by Figure_5-6.epsinto service in 2020. This is equivalent to a 10-EPNdB 2020 entering (Collier and Huff, 2007). For example, as shown in Figure 5-7, reduction in the day-evening-night averaged sound level from bitmap the Advisory Council for Aeronautical Research in Europe fixed-wing airplanes. Along with the noise reduction, there (ACARE) has set a goal of a 50 percent reduction in noise must be a 50 percent reduction in specific fuel consumption annoyance (relative to their 2000 counterparts) for aircraft (again relative to engines introduced into service in 2000). Noise Reduction Objectives and Technology Paths FIGURE 5-7 Noise reduction objectives and technology plans set by ACARE. Source: EU (2007). Figure_5-7.eps bitmap with vector type change in title

OCR for page 55
60 TECHNOLOGY FOR A QUIETER AMERICA Over the years a number of ambitious programs for reduc- nance. However, a continuous, zero-splice design greatly ing aircraft noise and, more recently, reducing aircraft emis- improved the absorption of fan noise, and the new technol- sions have been launched in Europe. Significant investments ogy is now being used in Rolls-Royce’s Trent 900 engine have been made under the so-called Framework Programs on the Airbus A380. The change has resulted in a 4- to 7-dB in which European Union (EU) industry and researchers reduction in fan-tone noise on takeoff and a 2-dB reduction in in many countries work together to perform well-funded, fan noise on approach (Coppinger, 2007). (A similar device coordinated R&D. A total of 20 aircraft noise R&D initia- was demonstrated by QTD2 in the United States.) tives were launched in Europe between 1998 and 2006 with An active noise control system was also successfully considerable participation by industry, small and medium demonstrated (SBAC, 2009). The system consisted of micro- enterprises (SMEs), research establishments, and govern- phones mounted in the fan duct and actuators mounted on the ment agencies (see Figure 5-8). stator vanes. The microphones measured fan noise and sent Four of the most noteworthy programs are (1) the Silence(R) signals to the actuators, which generated “antinoise” (sound Program, (2) the Silent Aircraft Initiative (SAX-40), (3) the waves that were out of phase with the sound waves generated EnVIronmenTALly (VITAL) Friendly Aero Engine, and by the fan), canceling out the fan noise. (4) the EU Clean Sky Initiative. Each program is described in To reduce landing gear noise, some new low-noise de- detail in a Society of British Aerospace Companies (SBAC) signs for the nose and main landing gears were investigated. Aviation and Environment Briefing Paper (SBAC, 2009).1 Ultimately, the noise was reduced by shielding the gears The summaries that follow are based on the SBAC briefing from each other and aligning them in the direction of the paper, a discussion at a Council of Academies of Engineer- flow. Two aligned nose landing gears were demonstrated ing and Technical Sciences workshop in June 2008 (CAETS, to be as much as 3 dB quieter than two independent gears 2008), and a presentation at the Workshop on Technologies (Coppinger, 2007). for a Quieter America (Ahuja, 2008).2 Some of the noise technologies validated in SILENCE(R) are now in production engines. Others are either undergoing further work in R&D programs by individual manufacturers The SILENCE(R) Program or have been carried over to other projects (e.g., VITAL, SILENCE(R), the largest European aircraft noise research described below). project ever undertaken, was a six-year program that began in 2001. Coordinated by Snecma, a French company, the Silent Aircraft Initiative (SAX-40) €112 million program was a collaboration of 51 partners, including all major European airframe and engine manu- The Silent Aircraft Initiative (2006) (SAX-40) was a facturers, major research institutes, and universities. The £2.3 million three-year research project run by Cambridge program addressed both engine noise (including jet noise, University and the Massachusetts Institute of Technology— fan noise, compressor noise) (see Figure 5-9) and landing with input from industry and government. SAX-40 cul- gear noise and airframe noise (see Figure 5-10). minated in a revolutionary concept design for a very quiet Technologies for reducing jet noise included the ultra high aircraft (see Figures 5-12 and 5-13). The concept design bypass ratio fan; low-noise core and fan nozzles designed to includes an airframe and engines designed specifically for improve the mixing of exhaust and bypass flows; internal a steep, low-speed climb and a low-noise approach that re- and external exhaust plugs; and technologies to attenuate duces both the amount of noise generated and the ground area fan noise, including a zero-splice passive liner, active noise of noise exposure. Some of the noise reduction technologies control technologies, and a negatively scarfed intake design are listed below: to reflect fan noise away from the ground (see Figure 5-11). In flight tests the negatively scarfed fan was shown to reduce • a novel three-fan design that allows UHBR and hence perceived noise by about 2.5 dB for an observer at a 60 de- lower jet noise gree angle to the engine (Rolls-Royce, 2005a). • low fan speeds that emit less noise Acoustical liners have traditionally been constructed from • extensive use of acoustic liners to absorb fan noise two or three pieces to facilitate manufacturing and mainte- • engines embedded in the fuselage, with intakes above the wings, to shield much of the engine noise from the 1 SBAC is the Society of British Aerospace Companies. After a merger of ground three companies, it is now A|D|S, which is Aerospace|Defence|Security. • variable area nozzles that allow engines to operate 2Ahuja, K.K. 2008. Summary of the Aircraft Noise Day of the CAETS with low-speed, low-noise exhaust jets at takeoff and Workshop on Transportation Noise Sources in Europe, June 2–4, 2008, on ascent and then can be optimized for minimum fuel Southampton, United Kingdom. Presentation at the Workshop on New burn and carbon dioxide emissions at cruise Technologies for a Quieter America, National Academy of Engineering, Washington, DC, June 11–12, 2008. Unpublished. A summary of the • elimination of flaps and slats CAETS workshop is available online at http://www.noisenewsinternational. • low-noise fairing on the undercarriage net/docs/caets-008.pdf.

OCR for page 55
6 TECHNOLOGY Organizations par ticipating in at least one Aircraft Noise Research Project Proposal FIGURE 5-8 Aircraft noise research initiatives undertaken in Europe under the Framework Programs. Source: LEMA (2008). Zero-Splice Passive Liner Ultra High Bypass Ratio Gear Box FIGURE 5-9 Engine/nacelle noise reduction technologies. UHBR = ultra high bypass ratio. Source: SBAC (2009). Figure_5-9.eps bitmap

OCR for page 55
6 TECHNOLOGY FOR A QUIETER AMERICA FIGURE 5-10 Aircraft noise reduction technologies. Source: SBAC (2009). Figure_5-10.eps bitmap FIGURE 5-11 Negatively scarfed intake reflects fan noise away from the ground. Source: The Jet Engine, 2005. Reprinted with permission from Rolls Royce, 2005. Figure_5-11.eps bitmap FIGURE 5-12 SAX-40 silent aircraft. Source: SBAC (2009). Copyright Silent Aircraft Initiative. Figure_5-12.eps bitmap

OCR for page 55
6 TECHNOLOGY 1. Axial-radial compressor 2 2. Extensive acoustics liners 3 6 3. Variable area nozzle 2 1 2 4. Low-noise, 5-stage, 6 low-pressure turbine 4 2 5. Transmission system to transit power from low- 5 6 pressure turbine to fans 5 6. High-capacity, low-speed fans FIGURE 5-13 SAX-40 engine design. Source: SBAC (2009). Copyright Silent Aircraft Initiative. Figure_5-13.eps Eu Clean Sky Initiative SAX-40 is predicted to achieve a reduction in noise of 25 dB based on current standards and also a reduction in The goal of the Clean Sky Initiative is to create a radically fuel consumption of about 25 percent for a typical flight. innovative air transport system with a reduced environmen- Although these results are impressive, the SAX-40 is a con- tal impact based on less noise and gaseous emissions and cept design only. Further work must be done to confirm the better fuel economy. The specific objective is to reduce feasibility and develop and validate the novel technologies. carbon dioxide emissions by about 40 percent, nitrogen oxide emissions by 60 percent, and noise by 50 percent in EnVIronmenTALly (VITAL) Friendly Aero Engine time for a major fleet renewal in 2015. The approach is to conduct an overall assessment of individual technologies at The VITAL program is a four-year, €90 million, EU- wide R&D program that began in January 2005 and has 53 partners. The partners, major stakeholders in the European aviation industry, include all major engine manufacturers, Airbus, and equipment makers, as well as innovative small businesses, universities, and research centers. The goal of this Snecma-led program is to integrate the results and benefits in noise reductions of the SILENCE(R) program with the emission reductions achieved in the Af- fordable Near Term Low Emissions and Component vaLi- dator for ENvironmentally friendly Aero Engine programs. By the end of VITAL, there should be a noise reduction of 8 dB per aircraft operation and an 18 percent reduction in carbon dioxide emissions, compared to engines in service prior to 2000. To reduce engine noise, very high bypass ratio engines with novel low-noise, low-speed fan designs are being stud- ied. One of these designs, the contrarotating turbo fan, is shown in Figure 5-14. VITAL also plans to demonstrate a low-pressure com- pressor and turbine technologies designed for low noise and weight and compatible with the novel fan designs. An overview of the VITAL project was given by Bone (2009) at a European Engine Technology Workshop in Warsaw, FIGURE 5-14 Schematic drawing of contrarotating turbo fan Poland. design to be studied in VITAL. Source: EU (2007). Figure_5-14.eps

OCR for page 55
64 TECHNOLOGY FOR A QUIETER AMERICA the fleet level to ensure the earliest possible deployment of in noise and carbon emissions. In the longer term (beyond research results. 2025), further reductions in noise and carbon emissions are The budget for Clean Sky is up to €800 million from the likely to require the development of entirely new aircraft and 7th Research Framework Program, which will be matched by engine configurations. funds from industry. The total budget could be as high as €1.6 The enabling technologies for both phases of develop- billion. The research partners include all major aeronautical ment are becoming apparent. It appears that one version players in Europe, almost 100 organizations that are active o f the futurist aircraft, based on lessons learned from in aeronautical R&D and many SMEs, research centers, and SILENCE(R) and SAX-40, will mimic a hybrid wing/body universities. The technical and geographical scope of a typi- (HWB) configuration. As NASA continues to work toward cal team is shown in Table 5-1. the introduction of a new generation of highly fuel efficient The program is organized around six technical areas, called large aircraft as early as 2020, it is already planning wind integrated technology demonstrators (ITDs), that will (1) per- tunnel tests of low-noise HWB aircraft (Figure 5-15 shows form preliminary studies, (2) select research areas, and (3) lead a typical HWB). Convinced that the HWB is the only way large-scale demonstrations either on the ground or in flight. it can meet its goals, NASA is providing funding for Boeing The ITDs are “smart” fixed-wing aircraft, “green” regional to study improvements to the configuration to further reduce aircraft, “green” rotorcraft, sustainable and “green” engine noise and improve fuel burn. systems for “green” operations, and eco-design. NASA’s subsonic N+2 research is now focused on a cargo version of the HWB, and if all goes well, an HWB freighter could be available by 2020, with a passenger version to follow OVERALL OBJECTIVES OF ALL AERONAuTICS within 10 years. According to a report in Aiation Weekly (2009), RESEARCH PROgRAMS Boeing, with funding from NASA and the U.S. Air Force, will The goal of all of the programs described above is to have test two low-noise HWB configurations—N2A and N2B—in a a “silent” aircraft in the future, that is, for the average sound wind tunnel in 2011. N2A has padded engines mounted above pressure levels from all aircraft noise sources not to exceed the aft fuselage. N2B has embedded engines and S-duct inlets sound pressure levels from other sources beyond airport for lower drag. Both designs incorporate hybrid laminar flow boundaries during departure and arrival operations. In the control to further reduce drag. next 20 years, newly designed aircraft are likely to be intro- For NASA to achieve its goals of aircraft noise of 42 duced at a rapid rate. These aircraft will likely be based on EPNdB cumulative below Stage 3 for the N+1 generation current aircraft but designed to achieve significant reductions aircraft, considerable research will be needed in the follow- ing areas: • target next-generation single aisle • ultra-high-bypass engines TABLE 5-1 Team Members Available to Work on • noise reduction technologies for fans, landing gears, European Noise Reduction Programs and propulsion airframe aeroacoustics X-3 Team Partners Country • l ightweight acoustic treatment in multifunctional structures Ain Shams University Egypt Alenia Italy ANOTEC Spain A2 Acoustics Sweden Budapest University of Technology and Hungary Economics (U.T.E.) COMOTI Romania Czech Technical University (T.U.) Czech Republic EADS CRC Denmark EPLF (Ecole Polytechnique Fédérale de Switzerland Lausanne) Federal University of Santa Catarina Brazil FFT (Free Field Technologies) Belgium Gediminas T.U. (Technical University) Republic of Lithuania INASCO Greece Institute of Aviation Poland Instituto Superior Tecnico Portugal ISVR United Kingdom National Aviation University Ukraine NLR Holland ONERA France FIGURE 5-15 Hybrid wing/body aircraft with vertical tails on either Trinity College Ireland side of the engines to shield jet noise. Source: NASA (2002). Figure_5-15.eps bitmap

OCR for page 55
6 TECHNOLOGY To meet the goal of aircraft noise of 52 EPNdB cumulative which it is no longer a nuisance beyond airport boundaries below Stage 3 for the N+2 generation aircraft, considerable and that airports be free of operational restrictions related to research will be needed in the following areas: noise. The European Aeronautics vision highlights two areas not emphasized in any U.S. visions: (1) the quality and afford- • noise reduction from wing shielding of engines ability of air transportation and (2) the global primacy of the • drooped leading edge aeronautics industry (FTAG, 2002a; NRC, 2002). • continuous-mold line flaps According to the GAO report, by including quality and • landing gear fairings affordability issues, the European vision acknowledges the • long-duct, low-drag acoustic liners importance of structuring R&D programs to focus on provid- • distortion-tolerant fans with active noise control ing air transportation services that users want to buy and can afford. NASA’s original goals issued in 1997 included reduc- ing the cost of air travel by 50 percent in 20 years. However, Objectives for the Air Transport System this goal fell out of favor with Congress, which argued that meeting customer demands is an industry responsibility and Meeting NASA’s Goals not an appropriate goal for NASA’s research. Congress then If NASA can meet its targets for the next three genera- reduced NASA’s aeronautics budget to eliminate research tions of aircraft, successively quieter aircraft would enter related to this goal (GAO, 2002). into service by 2015, 2020–2025, and 2030–2035, respec- The European Aeronautics document foresees the future tively (GAO, 2002). The likelihood of meeting these targets in the following way: depends on a number of factors. First, federal funding will In 2020, European Aeronautics is the world’s number one. have to be available not only for NASA’s research but also Its companies are winning more than 50% shares of world for later-stage R&D, which NASA expects will be conducted markets for aircraft, engines, and equipment. The public sec- by others. tor plays an invaluable role in this success story. Crucially, Second, even if funding is available, the development of they are coordinating a highly effective European framework noise reduction technologies may be limited by concerns for research cooperation, while funding programs that put the industry on more equal terms with its main rivals. about global warming, because advances in noise reduc- tion technologies could make it more difficult to achieve reductions in aircraft emissions of greenhouse gases. Third, Future Operational Procedures manufacturers must be willing to integrate newly developed Limiting—on a yearly basis—the cumulative noise foot- technologies into aircraft and engine designs. Finally, air- print in areas surrounding airports will effectively limit the lines must purchase new aircraft or retrofit existing aircraft capacity of the national aerospace system. Present departure with the new technologies in sufficient numbers to achieve and arrival procedures, which were developed when a lim- targeted reductions in exposure to aviation noise. ited range of navigational aids was available, are far from If the FAA and NASA’s noise reduction goals are not met, optimal from an environmental point of view. Therefore, in this could impede efforts to reduce congestion by expanding combination with new “silent” aircraft, the introduction of the capacity of the National Airspace System (FAA, 2007). new approach, navigation, and flight management systems will make environmentally friendly procedures feasible. U.S. and European Visions of the Future In 2002 the Federal Transportation Advisory Group FINDINgS AND RECOMMENDATIONS published Aeronautics Research and Technology for 00: A generation ago, “Higher, Farther, Faster” was the im- Assessing Visions and Goals, which compares civil aeronau- perative for the future of air transport. Today, it is “More tics in Europe and the United States. Although the United Affordable, Safer, Cleaner, and Quieter.” This change reflects States recognizes that its national well-being depends on the new emphasis on combining cost effectiveness with a national transportation system with a strong aviation ele- safety and environmental objectives. Significant investment ment, there is no explicit goal to ensure the primacy of the is being made on both sides of the Atlantic to meet the de- U.S. aeronautics industry. On the contrary, competitiveness mands of the market as well as the needs of the community. is central to the European vision, so much so that it appears In the United States much of this effort has been led by in the title of the document that defines this vision: European NASA; in Europe significant investments have been made Aeronautics: A Vision for 00—Meeting Society’s Needs under the Framework Programs, in which EU industry and and Winning Global Leadership (DG Energie et Transport researchers in many countries work together in well-funded, and DG Recherche, 2001). coordinated R&D programs. NASA’s Blueprint (2002) and the European Aeronautics The major challenge in the development of noise reduc- vision both specify that the ultimate goal in terms of opera - tion technology for the future is that the design requirements tional impact is that aircraft noise be reduced to the point at

OCR for page 55
78 TECHNOLOGY FOR A QUIETER AMERICA blies than common-wall assemblies, and it would be helpful Most of these are one-way systems; the teacher speaks into if the NRC of Canada provided data on the wide range of a microphone and students wear hearing assistance devices. floor/ceiling assemblies in the built environment. These systems generally do not work for student-to-student The housing industry would also benefit from the devel- communication or student-to-teacher communication. The opment of theory and testing to characterize improvements to use of electroacoustical solutions to architectural acoustics the design of acoustical materials such as the dynamic stiff- problems is hotly disputed in the architectural acoustics pro- ness of resilient underlayers and how this information can fession. However, there may be a place for electroacoustical be used to evaluate the IIC rating of floor/ceiling assemblies. devices in classrooms, particularly for hearing-disabled stu- Recent advances in the incorporation of damping into panel- dents or those who have different learning styles. ized building materials such as drywall should also be rated to provide a better understanding of how damping works in gREEN ACOuSTICAL DESIgN building sound isolation systems; this would also encourage product development. New material concepts should also be The importance of Leadership in Energy and Environ- mental Design (LEED) certification5 for newly constructed explored, such as distributed absorbers composed of heavy lumped masses embedded in a lossy sheet binder, which has buildings and for the reuse/rehabilitation of existing build- been shown to improve the sound isolation of low-frequency ings is rapidly becoming a focal point of building design. airborne noise, and nanogels that offer high sound absorption Whereas only two years ago little attention was paid to green and partial translucency. design, including acoustics in the green design of buildings, it is now being addressed in some cases, notably in class- rooms and hospitals. Up to now, acoustics has played a minor CLASSROOMS role in the LEED rating of a building, although significant American National Standard S12.60, Acoustical Per- contributions to LEED ratings have been possible through formance, Criteria, Design Requirements, and Guidelines high-recycled-content products, such as acoustical ceilings, for Schools is the first widely used standard for acoustical duct silencer fill, and the use of acoustical products produced conditions in classrooms (available online at http://asastore. near project sites. It is expected that the availability of green aip.org). This standard establishes limits for sound isolation acoustical products will increase over time. between spaces; background sound produced by mechani- Green factors affect all building systems, which in turn cal, electrical, and plumbing equipment and systems; and affect the acoustics of a building. In a post-occupancy survey reverberation time. of building acoustics (see Muehleisen, 2009), it was found For the most part, sound isolation and reverberation con- that bad acoustics was at the top of the list of undesirable fea- trol methods and materials are well known. However, this is tures (acoustics, thermal comfort, air quality, lighting, etc.) not true for in-room unitary HVAC (heating, ventilation, and for all buildings and was considered even more undesirable air-conditioning) units or classroom ventilation units. Cur- for green buildings. Some features of green buildings that are rently, sound produced by these units exceeds the American considered important for reasons other than acoustics include National Standards Institute (ANSI) recommended maxi - more use of natural lighting, natural ventilating systems, use mum sound pressure level of 35 dB(A), thus requiring the of hard interior surfaces, maximum use of windows (espe- use of central air distribution using air handlers, air heating cially when they must open), and the lack of conventional and cooling methods, and air distribution terminal units. The (porous) acoustical materials. All of these features tend to cost of these systems, according to manufacturers, school degrade the acoustical quality of workspaces. building owners, and designers, is considerably higher than Some green features include lower partial-height parti- the cost of typical classroom ventilation units. tions, which may be used to extend natural light farther Arguments by classroom equipment manufacturers to into an open-plan building space. However, this can reduce exclude or significantly raise permitted sound levels in or- speech privacy between workstations. Another feature is the der to permit the use of noisier conventional units have not use of green materials that, in many cases, absorb less sound persuaded the standards and education communities; the than conventional materials. However, this can result in an standard has not been modified. Nevertheless, the cost of excessively reverberant environment and reflections from the school buildings and the need for flexibility are important is- ceiling can compromise speech privacy in open-plan offices. sues. Hence, quiet design concepts for classroom ventilation Natural ventilating systems are considered to be desirable units should be investigated. So far, manufacturers have had in green buildings, but they can transmit noise throughout a only limited success in developing units that are comparable building. The ability to open windows is considered desir- in cost to more conventional central system equipment. able but can result in transportation noise entering a building Certain manufacturers of electroacoustical products (mi- and being transmitted through the ventilation system. Lack crophones, loudspeakers, etc.) have argued that their systems of conventional acoustical materials in buildings can affect can be used in place of more expensive architectural solutions to background sound, sound isolation, and reverberation. 5 LEED is an initiative of the U.S. Green Building Council.

OCR for page 55
7 TECHNOLOGY speech privacy, as mentioned above, and can also affect additional theory and testing, and include new information speech intelligibility in conference rooms. in the ASHRAE Guide. This would reinforce the tools used Electronic sound masking, widely used in open- and by the mechanical engineering profession to address sound closed-plan offices since the 1960s, is now necessary as a produced by new green mechanical systems, such as numer- means of maximizing speech privacy. But, although elec- ous small fans operating in parallel in lieu of a single large tronic sound masking can go a long way toward ensuring ac- fan, new concepts in passive induction units that replace fan- ceptable speech privacy, it is usually not a sufficient solution. powered terminal units, and the development of new, quiet Green solutions to office workstation partition height and classroom ventilators (discussed above). sound absorption will have to be developed. The requirement for more natural ventilation, including opening of windows, ENTERTAINMENT VENuES just adds to the challenge. Razavi (2009) has reported on some acoustical improve- The rapid increase in multifamily urban dwellings is like- ments in green building ventilation systems, but the noise ly to increase demand for public entertainment venues, both control engineering and architectural acoustics community inside and outside buildings, particularly small venues that face a major challenge in integrating good acoustical condi- can nurture a sense of community. Small venues can pro- tions into green buildings. The Green Guide for Health Care vide opportunities for the performing arts in intimate, at- and the Green Guide for Schools establish design objectives tractive performance spaces. Entertainment in the broadest for acoustical building characteristics, including reverbera- sense includes music, cinema, and theater but also dining tion, sound isolation, and ambient sound in building spaces and parks. (http://www.gghc.org; http://www.buildgreenschools.org). The proliferation of small entertainment venues would LEED points6 are added if these objectives are met using open the door to commercial opportunities in lighting, sound green materials and methods. system equipment, and computer-controlled software, all of which have been addressed in the marketplace. However, the proximity of entertainment venues to living spaces, and AIR DISTRIBuTION SySTEMS community annoyance from sound that sometimes results, The American Society of Heating, Refrigerating and Air- can be a significant challenge. Rather than prohibiting such Conditioning Engineers (ASHRAE) has been the pioneer proximity, communities and developers should be guided by and sole standard bearer in the development of standards planning guidelines and codes that protect residences with and estimation methods for sound produced by air distri- only minimal compromises in performance or entertainment. bution systems. Much to the organization’s credit, it has Conflicts that arise between performers and the public were funded most of the research that is now the exclusive basis discussed and resolved in a decision by the U.S. Supreme for estimating and evaluating sound produced by building Court in 1989 (Ward, 1989). ventilation systems. Designers of building mechanical systems rely on the FINDINgS AND RECOMMENDATIONS ASHRAE Guide (ASHRAE, 2007), a handbook updated every five years that covers all aspects of the design of More people are probably affected by noise inside build- building mechanical systems (thermal and ventilation). The ings—such as sound transmission in multifamily buildings, ASHRAE Guide includes a chapter on design goals for sound noise (and reverberation) in classrooms, noise in residences produced by building mechanical systems. The design goals from road, rail, and air traffic, and noise in hospitals—than are divided into noise criteria, room criteria ratings, and A- in any other environment. Clearly, trade associations and weighted sound pressure levels. The algorithms for estimat- professional societies will play important roles in the design ing sound in building spaces are based on work by Reynolds and construction of quieter interior spaces. and Bledsoe (1989). Recommendation 5-5: The acoustics and noise control Little progress has been made since 1989, when the a lgorithms were published, despite efforts by TC 2.6 communities should actively promote the inclusion of noise (the ASHRAE committee on sound and vibration) to im- criteria in requirements for Leadership in Energy and En- prove the situation. In fact, it has been generally agreed that vironmental Design (LEED) certification of buildings, not the previously used general method of estimating the sound only to improve the noise environment but also to ensure power level of ventilation fans should be dropped from the that the acoustical environment is not degraded. Design Guide because of its unreliability. standards (e.g., building codes) must be improved to ensure It would be beneficial if industry and academia formed a that good acoustical practices are followed in the construc- partnership to study the acoustical literature, produce some tion of buildings. Recommendation 5-6: The National Institutes of Health 6 LEED certification involves awarding points for various aspects of and/or the Facilities Guidelines Institute should fund the de- green designs.

OCR for page 55
80 TECHNOLOGY FOR A QUIETER AMERICA velopment of improved materials for hospital environments, ers, and other components, enable computation of forces at where traditionally used materials may harbor and promote supporting points, combined with structural finite element the growth of bacteria and other harmful biological agents. analysis, to predict vibrations of the structure. Other software packages can use information about structure and vibration to compute radiated sound. Although at one time these ca- MODELINg, SIMuLATION, AND DATA pabilities were available only in distinct packages, software companies today offer them as an integrated package. MANAgEMENT In some products, airflow and heat transfer, accompanied by noise from fans and airflow, represent a different kind Perhaps the greatest change in technologies for noise reduc- of interaction between mechanisms, product geometry, and tion has occurred because of increased computational power, sound production. Progress toward an integrated procedure is which has changed the way products are designed, tested, and not as advanced as in the example cited above, but there is little analyzed. We now have tools for defining and manipulating doubt that integration will be achieved in the near future. structures and mechanisms, for modeling and simulation, for laboratory measurements on prototypes, and for processing and interpreting voluminous amounts of data. DATA MANAgEMENT AND ANALySIS Mechanism analysis programs compute the motions and Microphone arrays are now commonly used to character- forces of gears, cams and followers, cranks, and sliders that ize radiation from a structure. The analysis of these data can are the sources of audible energy in many products. It is said take the form of acoustic intensity or acoustical near-field that a sewing machine contains more interesting mechanisms holography. Data rates are typically 50 kilobits per second for per dollar than any other product. The forces that these 24-bit words; thus, a 10-second recording is 1.2 megabits of mechanisms place on their supports lead to vibrations in data and a 100-microphone array will generate 120 megabits the product structure that are analyzed using finite element of data per experiment. This kind of data collection can be analysis. These vibrations in turn cause radiated sound, ana- done with modern (even ordinary) computers, but keeping lyzed by boundary element analysis. track of all of these data for later processing can be a chal - The computer also has just as important a role in the exper- lenge. Generating the intensity and/or hologram graphs for imental testing that is part of the product engineering process. N channels of data may require as many as N(N – 1)/2 cross Accelerometer arrays allow the measurement and display of spectra for these data records of a simple 10-second experi- the natural modes of structural vibration, and postprocessing ment that will be repeated many times. using modal analysis programs is used to test the validity of Similar issues arise in collecting and processing vibration both the measured modes and those computed using finite data to correlate with acoustical data. Accelerometers are element analysis. Microphone arrays allow the quantification the most widely used sensors, but new scanning, three-axis and display of the radiation of sound from the product using laser vibrometers are increasingly being used. The latter have software for acoustic intensity and acoustical holography. signal processing, in the form of cross spectra between chan - As discussed below, the existence of these technologies nels, “built in” to the system. A laser vibrometer channel is does not mean that product companies are able to take ad- much more expensive than an accelerometer channel, but in vantage of them. Cost—in terms of the acquisition of the some situations being able to analyze data without physical software/ hardware and the commitment to the training and contact between the sensor and the structure or the airflow retention of specialized personnel—can be a problem, par- can be valuable. ticularly to smaller companies. Making these new methods more affordable and available to companies is a challenge to be met. CONSuMER PRODuCTS MODELINg AND SIMuLATION MAKINg PRODuCTS QuIETER AND SELLINg QuIET Traditional modeling for sound has been based on “ca- nonical problems” representing different aspects of a sound U.S.-made white goods (major household appliances such source. Simple examples include radiation from bending as refrigerators, dishwashers, and cookers), health care de- waves on a plate to estimate sound from machine or equip- vices, personal care products, and other products are mostly ment housing and a simple monopole source of sound to sold on the domestic market; the export sector is relatively represent the radiation of sound from the unsilenced inlet of small. In addition, foreign competitors are moving into U.S. a compressor. These models can be useful aids to understand- markets and challenging U.S. companies abroad. The sound ing, but they cannot deal with all aspects of design. and sound quality of products is important for market accep- Some modeling procedures are oriented toward describ- tance, and technology for improving sound and/or producing ing and analyzing mechanisms. These models, which can quieter products is important for maintaining U.S. competi- compute motions and forces attributable to cams, follow- tiveness. (See Chapter 6.)

OCR for page 55
8 TECHNOLOGY Although the current economic situation may slow reduc- Jury (listening panel) studies are a useful mechanism for tions in product noise, there is little doubt that consumers designing for better sound quality. Listeners are presented have concluded that quieter products are better built and have with a group of sounds from real or virtual products and “real quality” and not just better “sound quality.” On the asked to rate them in terms of acceptability. The number of other hand, the market has not favored developments that sounds, their order, the number of listeners, and the scaling result in increased prices. Thus many consumer products of responses are all part of the experimental design. In a become commodities with different manufacturers meeting sense the jury is a measuring instrument, the output of which the same price points and offering very similar products. is a measure of sound quality. But to anticipate the effect of In some product sectors, however, consumers are willing future design changes on sound quality, either the jury study to pay more for products with extra features or materials. must be repeated or a correlation must be found between For example, new countertop cookers and refrigerators with physical metrics and the jury’s response. brushed steel exteriors and countertops made of granite Historically, acousticians have associated perceptual have become status symbols and statements of achievement. aspects of sound with individual physical metrics. Thus, the Kitchens are becoming gathering places where these prod- perception of loudness correlates well with the physical met- ucts are displayed. These upscale products (made both in ric of “loudness.” A similar correlation between the percep- the United States and abroad) are generally quieter and have tion of annoyance and the metric “noisiness” was developed profit margins sufficient to support extra engineering and for jet aircraft and later applied to other noise sources. But as manufacturing costs. But these products, although growing, the perceptions become more complex, involving expected, remain a smaller part of the market. There is still a need to informative, and hedonistic dimensions, the correlation make the technology for better noise control more available between any single physical metric and perception breaks in the manufacturing environment where cost constraints are down, and one is required to look for patterns of acceptability very important. or sound quality of a product, and that correlation will be dif- ferent for each product. This has been expressed as “a good lawnmower does not sound like a good washing machine.” PRODuCT SOuND QuALITy Physical metrics in use include tonality (the presence of Metrics for product sound are important for controlling tones in the signal), spectral balance (high-frequency versus noise exposure, measuring customer satisfaction, and guid- low-frequency content), fluctuation strength (presence of ing design. The acceptability of the sound of a product is modulation), and roughness (nonharmonic dissonant compo- influenced by user expectations, context, and signal content nents) as well as loudness and noisiness. One sound quality or information. Unfortunately, noise control professionals program evaluates nearly 20 such physical metrics to form a have labeled product sound as “product noise,” implying that profile of values to correlate with jury judgments of product any sound from a product is undesirable. Perhaps as a reac- sounds. Products for which such metrics profiles have been tion to the notion of product sound as product noise, the most used to correlate with jury study judgments of sound quality attention has been paid to metrics, such as A-weighted sound include washing machines, dishwashers, vacuum cleaners, pressure level, that measure noise exposure, annoyance, and cookers, and room air cleaners. hearing impairment and reflect negative reactions to sound. The metrics profile that best correlates with good sound However, hearing scientists (psychologists and engineers) quality (or most acceptable) will be different for different and product designers are aware that A-weighted sound level products, but there are certain features of the sound that are is an imperfect measure for predicting product sound accept- undesirable for any product. Loudness, noisiness, tonality, ability. Recent work has focused on defining physical metrics and fluctuation strength are all undesirable if too strong. that can select out certain sound signal features that are sepa- Modulation is an interesting example because it is very rately audible and are likely to be associated with positive or desirable in music as vibrato or tremolo but undesirable in negative reactions to sound. a product sound. The reason seems to be that modulation In some cases the link between metrics and design is very captures our attention—desirable in music, undesirable in strong. Product engineers in the automotive industry can sit a product. at a workstation, manipulate signals by filtering and other There is little cost to generating a profile of 20 or more means, and decide that certain signal features (tones, modu- metrics since this only requires running the same sound lation, and transients) should be changed to achieve a more samples that are to be presented to a jury through the signal desirable sound for the driver and passengers in a car. The processing algorithm for each metric. Using a larger set of “sound quality” programs used allow them to modify sig- physical metrics can give some reassurance that nothing has nals and process the resulting signals to determine changes been missed, but making sense of the profiles can be difficult. in 20 to 30 physical metrics. The changes in values are an If the metrics profile for each sound is labeled with the jury indication of how the sound should be evaluated as design evaluation for that sound, it is possible to combine the metrics changes are made. In this case the first evaluation is made into a smaller set of variables using the method of principal by an engineer or a product designer. component analysis.

OCR for page 55
8 TECHNOLOGY FOR A QUIETER AMERICA Manufacturers would like to have a single metric such the supporting structure in a sequence that minimizes the as A-weighted sound level that would enable them to claim need for reconfiguring the assembly. When this method was their products have better sound than their competitors and applied to a popular electric mixer, its noisiness was signifi- can also be used in product development. Organizations cantly increased because of the increased tolerances in the such as Consumers Union that routinely evaluate products drive train gearing inherent in this method of assembly. for sound would also like such a metric. Unfortunately, the The basic message is that issues of product sound are very correlation between any single metric and sound quality and complex and do not become simpler and easier to handle the outcome of jury studies has not been generally accepted because a product is simpler and less costly. Indeed, the by the acoustics community, so claims that one product has situation may be quite the opposite. But there are good tools “better sound” than another cannot be supported by physical for meeting the need. The question is: are they being used metrics, even though improvement in the sound quality of a and, if not, why not? particular product in a particular organization is possible. For more information on product sound quality, see Lyon (2000, TOOLS FOR QuIET PRODuCT DESIgN AND TESTINg 2004) and Lyon and Bowen (2007). Most companies now use computer-aided design (CAD) software to visualize their product designs and to anticipate R&D IN SuPPORT OF QuIETER PRODuCTS problems of parts interference and fit before a prototype is Sound is very important for some products (e.g., automo- built. These CAD programs can be interfaced with certain biles), and companies spend heavily in terms of facilities and computer-aided engineering programs like finite element personnel to make these products quiet and pleasing. But in analysis for structural analysis (stiffness, resonant modes, the past 40 years or so, the price of an automobile has risen mass distribution) or dynamic analysis for mechanism forces. by a factor of more than 10, while the price of a dishwasher But these programs (discussed above) while useful, are lim- has risen by a factor of 3 to 4. One result is that while the ited in their assistance in designing for quiet function. automobile companies have developed large staffs and good For example, a fan can be analyzed using a computer facilities for sound, most appliance companies have not fluid dynamics (CFD) program, which most likely does not (with one notable exception). In typical appliance and health reflect the actual flow environment of a typical product. Also, care products companies, engineers are “jacks of all trades,” these programs are very expensive to run, and considerable working one day on problems of airflow or heat transfer and expertise is needed to run them. Most consumer products the next on product sound. Also, these engineers may have companies will not make the investment in personnel or significant motivation to move around in a company where funds to have their products analyzed in this way. Some CFD the path upward is through management and not technical providers will work with manufacturers on a consulting basis expertise. to provide such analyses, but the process remains expensive Another factor that affects nonautomotive producers is the and the idealized calculations may not provide the informa- pace of model changes. Appliances, health care, and personal tion needed for design decisions. care products go through much more frequent changes, so Manufacturers are more likely to invest in experimental consumers will replace older products or choose to buy a facilities than software for analysis for several reasons. First, newer product because of a desired feature. The effect of the cost of experimental equipment has been coming down this is to compress development schedules and to limit the and its capabilities are increasing. Multichannel systems transfer of a new development (e.g., a quieter way to support of microphones and vibration sensors (accelerometers) a small motor) into the new model. involving dozens of sensors are now commonplace, and It would appear that simpler products such as a sleep the software to analyze the patterns of sound and vibration, apnea device should have noise issues that are simpler. But such as acoustical near-field holography and modal analysis, this product has a couple of brushless DC motors, a fan, an is widely available. Also, experimental work is generally air pump, and valves, each of which produces audible sound more relied on in product development than is analysis. The in a device that is in someone’s bedroom at night. In addition, ability to keep engineers in place long enough to become cost and utility constraints mean the enclosure is lightweight proficient in the use of both hardware and software remains and stiff, a perfect construction for the efficient radiation of an issue but seems to be much less of an issue than for the sound. The manufacturer probably buys the motors from a analytic software. manufacturer in China and finds it impossible to convince his supplier to do the engineering to make the motor quieter. WHAT’S NEXT? There are other trends that are not helpful in terms of product sound. Design for manufacturing has a cachet that Although the current economic situation may slow sound is attractive to industry because of lower assembly costs and improvements, there seems little doubt that consumers have easier model changes. One such method is “layering,” in become convinced that quiet products are better built and which an assembly is achieved by placing components into have “real quality” and not just better “sound quality.” So

OCR for page 55
8 TECHNOLOGY the issue of better sound as a marketing feature will not go almost all cases, is inferior to the first strategy because away, and the need to support the industry in its attempts to its effectiveness is limited to a single area. Because meet this marketing and technical challenge will not go away. this strategy does not affect the sound power output Thus the technology for better sound must be more available of the primary source and creates a secondary source, in the manufacturing environment where cost constraints are the overall noise level is increased in locations where very important. cancellation does not occur. A good practical applica- tion of this strategy are noise-canceling headphones, such as those manufactured by the Bose Corporation ACTIVE NOISE CONTROL that achieve a significant reduction in sound pressure level in the ear canal. The most efficient and cost-effective way of reducing 3. Increasing the low-frequency sound attenuation of noise is to design equipment to produce less noise. If this tuned dissipative silencers by placing actuators (loud- strategy has been fully implemented and additional noise speakers) in the cavity behind the thin porous lining as reduction is needed, add-on measures must be applied. Ac- described by Vér (2000). The sound pressure is sensed tive noise control is one of these measures. behind the porous lining by a microphone and entered Most noise sources produce noise in a wide frequency into a control system that feeds the loudspeaker with range. Passive noise control measures (such as silencers, a signal so that for a wide frequency band it produces acoustic enclosures, wrappings, barriers, etc.) usually pro - (nearly) zero sound pressure immediately behind the vide sufficient noise reduction at middle and high frequen- porous liner. This condition maximizes the sound cies (approximately 200 Hz and above), and they are robust, pressure gradient across the liner and consequently its reliable, and cost effective. However, they are ineffective at ability to absorb sound. In a passive silencer this condi- low frequencies (below about 200 Hz). At these low frequen- tion occurs only at single frequencies where the depth cies, active control becomes an alternative; it may be the only of the airspace is one-quarter the acoustic wavelength solution for frequencies below 100 Hz. and at odd multiples of that frequency (frequency, f, Noise sources such as gas turbines and large reciprocat- and wavelength, l, are related by f = c / l, where c is ing compressors produce high levels of low-frequency noise. the speed of sound). Almost without exception, the noise control of such sources 4. When the noise is produced by the sound radiation of requires a combination of both passive and active measures. a structure exited to vibration by localized dynamic The passive measures attenuate the mid and high frequencies, forces (such as the attachment points of the wing of and the active measure attenuates the low frequencies. an airplane to a ring frame), the most efficient way to There are four major active noise control strategies: obtain global noise reduction is to mount a shaker at the attachment point and feed it by a control system to 1. Reducing the sound radiation efficiency of the sound produce nearly zero vibration (i.e., render nearly zero source by placing a secondary source (loudspeaker in power input to the structure). Here, again, the noise an enclosure) in its immediate vicinity and driving it that is attributable to the vibration force is reduced at with an electric signal that produces the same mag- all locations. nitude but opposite phase fluctuating volume flow as the primary noise source. In this case the air volume One early example of active control was the electronic pushed out of the primary source during the positive sound absorber (Olson and May, 1953), which was a micro- cycle fills the void generated by the receding volume phone, phase inverter, and loudspeaker that could be used of the secondary source and, conversely, the reced- to create a “zone of silence” around the head of a factory ing volume flow of the primary source is supplied by worker. At that time all of the circuits were analog, and phase the outflow from the secondary source. This strategy, shift through the system was critical. It was not until digital which reduces the radiation efficiency of the original signal processing became feasible that applications began source and effectively reduces the noise level at all to be developed. locations, is sometimes referred to as “global” noise Active control of sound is effective only when the wave- reduction. length of the sound is long compared with the dimensions 2. Creating a limited “zone of silence” in the vicinity of of the volume in which cancellation is desired. For example, the receiver (the person to be protected) by sensing the the most successful application of the technology is in active local sound pressures, driving the loudspeaker with headsets where cancellation of sound in the (small-volume) an electric signal (located as near to the receiver as ear canal is desired. Another example is cancellation in the practicable) that produces a sound pressure of the same cabin of a turboprop commuter airplane, which requires a magnitude and opposite in phase as the primary signal. large number of microphones and loudspeakers and is only This is the only situation where “noise cancellation” effective at low frequencies. is appropriate. This active noise control strategy, in This limitation of cancellation to low frequencies also

OCR for page 55
84 TECHNOLOGY FOR A QUIETER AMERICA has implications for sound perception, sound quality, and fiers and special loudspeakers may be required. There is hazard to hearing. A listener may perceive the sound as also the problem that the materials used for transducers lacking in low frequencies. Hence, it may sound “hissy.” (microphones, accelerometers, loudspeakers, force transduc- The A-frequency weighting network already attenuates ers) must, in many cases, withstand hostile environments. low-frequency sound, and therefore additional attenuation Examples are hot exhaust gases and turbulent flow. through active control may not produce a significant decrease There is a rich literature on active control of sound and in the A-weighted sound level. According to current stan- vibration. This includes books (Hansen and Snyder, 1997; dards, a small decrease in A-weighted sound level produces Nelson and Elliott, 1993), technical articles (Nelson and only a small decrease in the hazard to hearing. Elliott, 1993; Tichy, 1996), and conference proceedings papers (ACTIVE, 2009; Fuller, 2002). APPLICATIONS OF ACTIVE CONTROL Recommendation 5-7: Research agencies should fund Despite the complexity of active control and the above university research on active noise control to address situa- limitations, the technology has been applied in a number tions where the use of traditional noise-control materials is of cases. Some examples are given below. Active headsets problematic or where they are not suitable for attenuating provide noise reduction and both comfort and protection noise in the appropriate frequency range. Investigations into from hazardous noise for the user. The Federal Railroad hybrid active-passive and adaptive-passive noise control Administration has demonstrated both active control in systems and the development of low-cost microphones and locomotive cabs and proof of principle for active control of loudspeakers that can be used in hostile environments should exhaust stack noise from idling locomotives. Hansen (2005) also be funded. developed an active control system to control sound propa- gation in the exhaust stack of a spray dryer unit in a dairy SuMMARy factory. Scheuren (2005) discussed a number of engineering applications of active control, including wind tunnel buff- Active controls of sound and vibration have been under ering, control of combustion burners, noise control in gas development for many years, but few products on the mar- turbines, and modification of sound in the cabin of automo- ket have incorporated them, and many barriers must still be biles. Cancellation of the blade passage tone in a small axial overcome. flow fan was achieved by Sommerfeldt and Gee (2003) by In this chapter, technologies for controlling noise from a using four small cancellation loudspeakers placed around the large variety of sources have been described. Clearly, aircraft fan. There are a number of applications of active control in noise control technology is much more advanced than tech- the aerospace industry; these have been described by Maier nologies for addressing other noise sources, and the funds ex- (2009). Gorman et al. (2004) produced noise reduction on pended to reduce the noise of airplanes themselves as well as the flight deck of an airplane, and Cabell et al. (2004) have mitigation measures around airports are far greater than for shown how active control can be used to control chevrons other noise sources. Road traffic noise has been controlled and produce noise reduction of a jet engine exhaust. Finally, mostly by constructing noise barriers, but work is being done Fuller et al. (2009) reduced noise from a portable generator on promising technologies for reducing noise generated by set by using active control. tire/road interaction. Technologies are available for reducing noise from rail-guided vehicles, and these will become more important as the nation develops light rail systems and high- Impediments to Commercial Development speed trains. Technologies for the built environment will also Despite the long history of the development of active become more important as building construction is driven by control technology and digital processing systems, there are LEED certification and “green” principles. few devices (except for active headsets) on the market today. Some of the barriers to commercial development are expense REFERENCES and reliability as well as the materials used and characteris- tics of transducers, amplifiers, and materials. 23 CFR 772. Procedures for Abatement of Highway Traffic Noise and Active control systems are expensive to implement Construction Noise. Available online at http://www.fhwa.dot.go/ hep/cfr77.htm. because of the required microphones (or accelerometers), ACTIVE. 2009. Collected papers from the ACTIVE series of international loudspeakers (or force transducers), and electronic control symposia on active control of sound and vibration: 1995, 1997, 1999, systems. If a universal control system were to be developed, 2002, 2004, 2006, and 2009. Available online at http://www.atlasbooks. it would have to be versatile because the control algorithm com/marktplc/0076.htm. will depend on the type of noise being canceled (e.g., a Ahuja, K.K. 1995. Aeroacoustic Performance of Open-Jet Wind Tunnels with Particular Reference to Jet/Collector Interactions. Final Report single-frequency tone, a tone in noise, or broadband noise). AEDC-SBIR-94-02. Reston, VA: American Institute of Aeronautics Reliability is also an issue in complex systems. and Astronautics. For high-intensity noise sources, high-powered ampli- Anjali, J., and R. Ulrich. 2007. Sound Control for Improved Outcomes in

OCR for page 55
8 TECHNOLOGY Healthcare Settings. Issue Paper 4. Concord, CA: Center for Health MI, May. Warrendale, PA: SAE International. Design. Donavan, P. 2005. Quieting of Portland Cement Concrete Highway Surfaces AREMA (American Railway Engineering and Maintenance-of-Way As- with Texture Modifications. Proceedings of NOISE-CON 05, The 2005 sociation). 2009. Rail Transit. Chapter 12, Table 12-2-6, in Manual National Conference on Noise Control Engineering, Minneapolis, MN, for Railway Engineering. Lanham, MD: AREMA. Available online October 17–19. Available online at http://www.bookmasters.com/markt at http://www.arema.org/eseries/scriptcontent/custom/e_arema/pubs/ plc/0076.htm. pubs.cfm?actiesection=pubs. Donavan, P. 2006. Comparative Measurements of Tire/Pavement Noise in ASHE (American Society for Healthcare Engineering). 2010. 2010 Guide - Europe and the United States—NITE Study. Report No. FHWA/CA/MI- lines for the Design and Construction of Health Care Facilities. Dallas, 2006/09. Sacramento, CA: California Department of Transportation. TX: Facilities Guidelines Institute. Available online at http://www. Donavan, P., and B. Rymer. 2009. Measurements of the Vertical Distribution fgiguidelines.org/index.html. of Truck Noise Sources During Highway Cruise Pass-bys Using Acous- ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning tic Beam-Forming. Compendium of Papers, Transportation Research Engineers). 2007. ASHRAE Handbook—HVAC Applications. Atlanta, Board 88th Annual Meeting, Washington, DC, January. GA: ASHRAE. Donavan, P., and R. Schumacher. 2007. Exterior Noise of Vehicles—Traffic Aviation Weekly. 2009. NASA Pushes Blended Wing/Body. January 13. Noise Prediction and Control. Chapter 120 in Handbook of Noise and Available online at http://www.aiationweek.com/aw/generic/story. Vibration Control, edited by M. Crocker. Hoboken, NJ: John Wiley & Sons. jsp?id=news/Body00.xml&headline=NASA%0Pushes%0Blend ed%0Wing/Body%0&channel=space. Donavan, P.R., R.F. Schumacher, and J.R. Stott. 1998. Assessment of tire/ Bartlett. P., N. Humphreys, N., and P. Phillipson. 2004. The Joint Rolls- pavement interaction noise under vehicle passby test conditions using Royce/Boeing Quiet Technology Demonstrator Programme. American sound intensity measurement methods (A). Journal of the Acoustical Institute of Aeronautics and Astronautics (AIAA) 2004-2869. Presented Society of America 103(5): 2919. at the 10th AIAA/CEAS Aeroacoustics Conference, Manchester, United DOT (U.S. Department of Transportation). 2002. Final Environmental Kingdom, May 10–12. Impact Statement: Final Rule for the Use of Locomotive Horns at Berendt, R.D., E.L.R. Corliss, and M.S. Ojalvo. 1976. Quieting: A Practical Highway-Rail Grade Crossings. Washington, DC: Office of Railroad Guide to Noise Control. National Bureau of Standards Handbook 119. Development, Federal Railroad Administration. Washington, DC: U.S. Department of Commerce. EPA (U.S. Environmental Protection Agency). 1974. Information on Levels Bone, D. 2009. VITAL Project Overview. Presentation at the European of Environmental Noise Requisite to Protect Public Health and Welfare Engine Technology Workshop, Warsaw, Poland, June 2–3. Available with an Adequate Margin of Safety. Report No. 550/9-74-004. Arling- online at http://www.newac.eu/6..html. ton, VA: EPA Office of Noise Abatement and Control. Bowlby, W. 1998. Highway Noise Prediction and Control. Pp. 48.1–48.23 EPA. 1981. Noise in America: The Extent of the Noise Problem. EPA/ in Handbook of Acoustical Measurements and Noise Control, edited by ONAC Report No. 550/9-81-101. Washington, DC: EPA. C. Harris. Melville, NY: Acoustical Society of America. EU (European Union). 2007. “Silence(R)” Aircraft Noise Reduction Project Cabell, R.H., N. Schiller, J.H. Mabe, R.T. Ruggeri, and G.W. Butler. 2004. Holds Final Meeting. Available online at http://ec.europa.eu/research/ Feedback Control of a Morphing Chevron for Takeoff and Cruise transport/news/article_67_en.html. Noise Reduction. Proceedings of ACTIVE 04, The 2004 International FAA (Federal Aviation Administration). 2004. Report to Congress—Non - Symposium on Active Control on Sound and Vibration, Williamsburg, military Helicopter Urban Noise Study. Available online at http://www. VA, September 20–22. Available online on the ACTIVE 2009 CD at faa.go/regulations_policies/policy_guidance/enir_policy/media/ http://www.bookmasters.com/marktplc/0076.htm. 04No-0-RTC.pdf. CAETS (International Council of Academies of Engineering and Techno- FAA. 2007. Capacity Needs in the National Airspace System. Available logical Sciences). 2008. The Design of Low-Noise Vehicles for Road, online at http://www.faa.go/airports/resources/publications/reports/ Rail, and Air Transportation. Sponsored by the Royal Swedish Academy media/fact_.pdf. of Engineering Sciences and the Royal Academy of Engineering (U.K.), FAA. 2008. Aviation and the Environment: FAA’s and NASA’s Research and Institute of Sound and Vibration Research, Southampton, U.K., June Development Plans for Noise Reduction Are Aligned But the Prospects 2–4. Available online at http://www.noisenewsinternational.net/docs/ of Achieving Noise Reduction Goals Are Uncertain. GAO-08-384. caets-008.pdf. Available online at http://www.gao.go/new.items/d0884.pdf. Cavanaugh, W.J., and J.A. Wilkes. 1998. Architectural Acoustics: Principles FGI (Facilities Guidelines Institute). 2009. Interim Sound and Vibration De- and Practice. New York: John Wiley & Sons. sign Guidelines for Hospital and Healthcare Facilities. Draft, November Cavanaugh, W.J., G.C. Tocci, and J.A. Wilkes, eds. 2010. Architectural 1, 2006. Available online at http://www.fgiguidelines.org/pdfs/Interim% Acoustics: Principles and Practice, 2nd ed. Hoboken, NJ: John Wiley 0Sound%0and%0Vibration%0Design%0Guidelines%0for%0 & Sons. Hosp%0and%0Healthcare%0Fac.PD-Watermark.pdf. Collier, F.S., and D.L. Huff. 2007. NASA’s Subsonic Fixed Wing Project. FHWA (Federal Highway Administration). 2009. Tire Pavement Noise. Presented at Revolutionary Aircraft for Quiet Communities Workshop, Available online at http://www.fhwa.dot.go/enironment/noise/tire- Hampton, VA, July 24–26. Available online at http://www.nianet.org/ paement_noise/. workshops/docs/QA/presentations/KFS/Huff.pdf. Fleming, G., A. Rapoza, and C. Lee. 1996. Development of National Refer- Coppinger, R. 2007. Quietly does it. Flight International 172(5104):11– ence Energy Mean Emission Levels for the FHWA Traffic Noise Model 17. (FHEA TNM), Version 1.0. Report No. DOT-VNTSC-FHWA-96-2. De Camp, U. 1979. Measurement of sound levels in hospitals. Noise Control Washington, DC: U.S. Department of Transportation. Engineering Journal 13(1):24–27. FRA (Federal Railroad Administration). 2002. Final Environmental Impact DG Energie et Transport and DG Recherche. 2001. European Aeronautics: Statement: Final Rule for the Use of Locomotive Horns at Highway-Rail A Vision for 2020—Meeting Society’s Needs and Winning Global Grade Crossings. Washington, DC: FRA. Leadership. Luxembourg: Office for Official Publications of the Eu - FRA. 2005. High-Speed Ground Transportation Noise and Vibration Im- ropean Communities. Available online at http://www.eurosfaire.prd. pact Assessment. HMMH Report No. 293. October. Washington, DC: fr/7pc/bibliotheque/consulter.php?id=0. FRA. Donavan, P. 1993. Tire/Pavement Interaction Noise Under Vehicle Operating FRA. 2006. Use of Locomotive Horns at Highway-Rail Grade Crossings; Conditions of Cruise and Acceleration. Document No. 931276. Proceed- Final Rule. 49 CFR § 222 and 229 (FR 71, 159, August 17, 2006). ings of the Noise & Vibration Conference and Exposition, Traverse City, Washington, DC: FRA.

OCR for page 55
86 TECHNOLOGY FOR A QUIETER AMERICA FTA (Federal Transit Administration). 2006. Transit Noise and Vibration HUD. Undated. The Noise Guidebook. Washington, DC: HUD. Avail- Impact Assessment. FTA-VA-90-1003-06. Washington, DC: FTA. able online at http://www.hud.go/offices/cpd/enironment/training/ Available online at http://www.hmmh.com/cmsdocuments/FTA_coer_ guidebooks/noise/index.cfm. sec0.pdf. IOM (Institute of Medicine). 2000. To Err Is Human: Building a Safer FTAG (Federal Transportation Advisory Group). 2002a. Vision 2050: An Health System. Washington, DC: National Academy Press. Integrated Transportation System. Available online at http://scitech.dot. Johnson, T., et al. 2009. Development of Passive and Active Noise Control go/polplan/ision00/index.html. for Next-Generation Locomotive Cabs. Proceedings of INTER-NOISE FTAG. 2002b. Aeronautics Research and Technology for 2050: Assessing 09, The 2009 International Congress on Noise Control Engineering, Visions and Goals. Available online at http://scitech.dot.go/polplan/ Ottawa, Canada, August 23–26. Kinetics (Kinetics Noise Control). 2009. Kinetics Model IsoMax: Resilient ision00/index.html. Fuller, C.R. 2002. Active Control of Sound Radiation from Structures, Sound Isolation Wall and Ceiling Clip. Patent No. 7,093, 814. Available Progress and Future Directions. Paper P236. Proceedings of ACTIVE online at http://www.kineticsnoise.com/arch/isomax/index.aspx. 02, The 2002 International Symposium on Active Control of Sound and LEMA (Laboratory of Electromagnetics and Acoustics). 2008. Overview Vibration, Southampton, United Kingdom, July 15–17. Available online o f EC Funded Aircraft Noise Research: Networks and Research at http://www.bookmasters.com/marktplc/0076.htm. Projects. Available online at http://lema.epfl.ch/images/stories/LEMA/ Fuller, C.R., C. Papenfuss, and T.D. Saux. 2009. Active Control of Portable AC/X_noise_workshop/presentation/0807_xnoise%0workshop_ Generator Set Noise: Heuristic Verses Design. Proceedings of ACTIVE 0_collin.pdf. 09, The 2009 International Symposium on Active Control of Sound and Lilly, J. 2002. Resilient Channel Update (December). Available online at Vibration, Ottawa, Canada, August 20–22. Available online at http:// http://www.jglacoustics.com/acoustics-rc_.html. www.bookmasters.com/marktplc/0076.htm. Lodico, D., and J. Reyff. 2009. Long-term noise performance of open graded GAO (U.S. Government Accountability Office). 2002. Aviation and the asphalt concrete (OGAC)—Results of 10-year long study. Noise Control Environment: Impact of Aviation Noise on Communities Presents Engineering Journal 56(2):84–93. Challenges for Airport Operations and Future Growth of the National Lyon, R.H. 2000. Designing for Product Sound Quality. New York: Marcel Airspace System. Testimony before the Subcommittee on Aviation, Dekker. Committee on Transportation and Infrastructure, U.S. House of Repre - Lyon, R.H. 2004. Product Sound Quality—From Design to Perception. sentatives. GAO-08-216T. Available online at http://www.gao.go/new. Proceedings of INTER-NOISE 04 207(1):4417–4420. Available online items/d086t.pdf. at http://www.noisenewsinternational.net/docs/lyon-004.pdf. GAO. 2008. Aviation and the Environment: FAA’s and NASA’s Research Lyon, R.H., and D.L. Bowen. 2007. Designing quiet products. The Bridge and Development Plans for Noise Reduction Are Aligned But the Pros - 37(3):13–17. pects of Achieving Noise Reduction Goals Are Uncertain. GAO-08-384. MacLeod, M., J. Dunn, I.J. Busch-Vishniac, J.E. West, and A. Reedy. 2007. Washington, DC: U.S. Government Printing Office. Quieting Weinberg 5C: A case study in hospital noise control. Journal Gorman, J., R. Hinchliffe, and I. Stothers. 2004. Active Sound Control on of the Acoustical Society of America 121(6):3501–3508. the Flight Deck of a C130 Hercules. Proceedings of ACTIVE 04, The Maier, T. 2009. Challenges and Applications for Active Noise and Vibration 2004 International Symposium on Active Control on Sound and Vibra- Control in Aerospace. Proceedings of ACTIVE 09, The 2009 Interna- tion, Williamsburg, VA, September 20–22. tional Symposium on Active Control of Sound and Vibration, Ottawa, Greene, M. 2002. Typical Diurnal Traffic Noise Patterns for a Variety of Canada, August 20–22. Available online at http://www.bookmasters. Roadway Types. Proceedings of INTER-NOISE 02, The 2002 Interna- com/marktplc/0076.htm. tional Congress and Exposition on Noise Control Engineering, Dear- McNeer, R.R., J. Bohorquez, O. Ozcan, A.J. Varon, and P. Barach. 2007. born, MI, August 19–21. Available online at http://www.bookmasters. A new paradigm for the design of audible alarms that convey ur- com/marktplc/0076.htm. gency information. Journal of Clinical Monitoring and Computing Hansen, C.H. 2005. Current and future industrial applications of active noise 21(6):353–363. control. Noise Control Engineering Journal 53(5):181–196. Muehleisen, R.T. 2009. Noise Problems and Opportunities in “Green Build- Hansen, C.H., and S.D. Snyder. 1997. Active Control of Noise and Vibra- ings.” Presentation at the Second CAETS Forum on Worldwide Noise tion. Boca Raton, FL: Taylor & Francis. Sources, Ottawa, Canada, August 25. Available online at http://www. Harris, C.M. 1994. Noise Control in Buildings: A Practical Guide for noisenewsinternational.net/docs/caets-00.pdf. Architects and Engineers. New York: McGraw Hill. Available online at NASA (National Aeronautics and Space Administration). 2002. Aeronautics http://www.atlasbooks.com/marktplc/0076.htm. Blueprint, 2002. Washington, DC: NASA. Available online at http:// Herkes, B. 2006. Quiet Technology Demonstrator 2 Flight Test. Presented www.nasa.go/pdf/40main_0%0AT.pdf. at the Aviation Noise & Air Quality Symposium, Palm Springs, CA, Neergaard, C.F. 1930. Are Acoustical Materials a Menace in Hospitals? March 7. Available online at http://www.techtransfer.berkeley.edu/ Third Meeting of the Acoustical Society of America, New York, May aiation06downloads/herkes.pdf. 9–10. Herkes, W.H., R.F. Olsen, and S. Uellenberg. 2006. The Quiet Technology Neergaard, C.F. 1941. What Can the Hospital Do About Noise? Twenty- Demonstrator Program: Flight Validation of Airplane Noise-Reduction Sixth Meeting of the Acoustical Society of America, New York, October C oncepts. AIAA 2006-2720. Presented at the 12th AIAA/CEAS 24–25. Aeroacoustics Conference (27th AIAA Aeroacoustics Conference), Nelson, P.A., and S.J. Elliott. 1993. Active Control of Sound. San Diego, Cambridge, MA, May 8–10. CA: Academic Press. Herman, L., and J. Withers. 2005. Effectiveness of Tire/Road Noise Abate- Nightingale, F. 1860. Noise. Chapter 4 in Notes on Nursing: What It Is, and ment Through Surface Retexturing by Diamond Grinding. Report No. What It Is Not. New York: D. Appelton. Available online at http://digital. FHWA/OH-2005/009. Columbus: Ohio Department of Transportation. library.upenn.edu/women/nightingale/nursing/nursing.html. HUD (U.S. Department of Housing and Urban Development). 1967. NRC (National Research Council). 2002. Aeronautics Research and Tech- A irborne, Impact, and Structure Borne Noise—Noise Con - nology for 2050: Assessing Visions and Goals—Letter Report. Wash- trol in Multifamily Dwellings. Washington, DC: HUD. Avail - ington, DC: National Academies Press. able online at h ttp://www.eric.ed.go/ERICWebPortal/custom/ Olson, H.F., and E.G. May. 1953. Electronic sound absorber. Journal of the Acoustical Society of America 25(6):1130–1136. portlets/recordDetails/detailmini.jsp?_nfpb=true&_&ERICExtSearch PAC International. 2009. Resilient Sound Isolation Clip (RSIC-1™). Avail - _SearchValue_0=ED04&ERICExtSearch_SearchType_ 0=no&accno=ED04. able online at http://www.pac-intl.com/products.html.

OCR for page 55
87 TECHNOLOGY Pelton, H.K., E. Ryherd, and M. Martin. 2009. Acoustical design of a burn Sandberg, U. 2001. Noise Emissions of Road Vehicles: Effectiveness of acute care unit for enhanced patient comfort. Noise Control Engineering Regulations. Final Report from the Working Party on Noise Emissions Journal 57(1):32–41. of Road Vehicles. International Institute of Noise Control Engineering. Polcak, K. 2003. Highway traffic noise barriers in the U.S.—construc - Available online at http://www.i-ince.org/data/iince0.pdf. tion trends and cost analysis. Noise/News International 11(3):96–108. Sandberg, U., and J. Ejsmont. 2002. Tire/Road Noise Sources and Genera- Available online at http://www.noisenewsinternational.net/archies_idx. tion Mechanisms. Pp. 127–138 and 147 in Tire/Road Noise Reference htm. Book. Kisa, Sweden: Informex. Quirt, J.D. 2009. Controlling Air-Borne and Structure-Borne Sound in SBAC (Society of British Aerospace Companies). 2009. SBAC Aviation Buildings. Proceedings of INTER-NOISE 2009, The 2009 International and Environment Briefing Papers: 1. Aircraft Noise. Available online at Congress on Noise Control Engineering, Ottawa, Canada, August 23–26. www.sbac.co.uk/community/dms/download.asp?txtFilePK=8. Available online at http://www.bookmasters.com/marktplc/0076.htm. Scheuren, J. 2005. Engineering applications of active sound and vibration Rasmussen, R., R. Bernhard, U. Sandberg, and E. Mun. 2007. The Little control. Noise Control Engineering Journal 53(5):197–210. Book of Quieter Pavements. Report No. FHWA-IF-08-004. Washington, Silent Aircraft Initiative. 2006. Silent Aircraft Creeps Closer to Real- DC: Federal Highway Administration. Available online at http://www. ity. Available online at http://silentaircraft.org/news/article/default. tcpsc.com/LittleBookQuieterPaements.pdf. aspx?objid=60. Razavi, Z. 2009. Acoustical Improvements with Natural Air Ventilations Sommerfeldt, S.D., and K.L. Gee. 2003. A compact active control imple- in the Liu Institute at the University of British Columbia. Proceedings mentation for axial cooling fan noise. Noise Control Engineering Journal of INTER-NOISE 2009, The 2009 International Congress on Noise 51:325–344. Control Engineering, Ottawa, Canada, August 23–26. Available online Sykes, D.M., and G.C. Tocci. 2008. Speech privacy: Momentum grows in at http://www.bookmasters.com/marktplc/0076.htm. healthcare. Acoustics Today 4(4):30–33. Remington, P.J. 1983. Control of Wheel/Rail Noise and Vibration. Final Taylor, F.B. 1958. Noise control in a research hospital. Noise Control Report No. TOT-TSC-UMTA-82-57. Washington, D.C: Urban Mass 4(5):9–62. Transit Administration, U.S. Department of Transportation. Tichy, J. 1996. Applications for active control of sound and vibration. Remington, P.J., S.J. Knight, D. Hanna, and C. Rowley. 2005. A hybrid Noise/News International 4: 73–86. Available online at http://www. active/passive exhaust noise control system for locomotives. Journal of noisenewsinternational.net/docs/tichy-6.pdf. the Acoustical Society of America 117(1):68–78. Vér, I.L. 2000. Active Muffler, United States Patent 6,160,892. Issued Reyff, J.A., and P.R. Donavan. 2005. Reduction of Traffic Noise and Tire/ December 12. Pavement Noise: First Year Results of the Arizona Quiet Pavement Pro- Waitz, I., R.J. Bernhard, and C.E. Hanson. 2007. Challenges and promises gram. Proceedings of NOISE-CON 05, The 2005 National Conference in mitigating transportation noise. The Bridge 37(3):25–32. on Noise Control Engineering, Minneapolis, Minnesota, October 17–19. Ward. 1989. Ward v. Rock Against Racism, 491 U.S. 781 (1989). Available Available online at http://www.bookmasters.com/marktplc/0076.htm. online at http://www.oyez.org/cases/80-8/88/88_88_6. Reynolds, D.R., and J.M. Bledsoe. 1989. Algorithms for HVAC Engineers. Warnock, A.C.C., and J.A. Birta. 2000. Detailed Report for Consortium on Atlanta, GA: ASHRAE. Fire Resistance and Sound Insulation of Floors: Sound Transmission Rolls-Royce. 2005a. The Jet Engine. Stamford, U.K.: Key Publishing Ltd. and Impact Insulation Data in 1/3 Octave Bands. Internal Report IRC Rolls-Royce. 2005b. Noise Facts Leaflet. Stamford, U.K.: Key Publishing IR-811. Ottawa, Canada: National Research Council of Canada. Ltd.

OCR for page 55