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23 Table 4. Tests of the 5900 truck at the with eight Michelin XZE tires on the drive axles; (2) bobtail low-speed track. with eight Goodyear G164 RTD aggressive tread, high-traction (noisy) tires on the drive axles; and (3) loaded trailer with the Speed (mph) rpm Gear Notes 0 650 Neutral same aggressive tread tires on the drive axles. Figures 20 and 21 0 1500 Neutral Stationary show the truck without and with the trailer, respectively. 0 2000 Neutral 14 1500 4th Unlike the truck of this type (5900 PAYSTAR) tested at the Constant rpm, low-speed track, the 5900i tested at the high-speed track was 25 1500 5th varied gear 28 1500 6th equipped with a more powerful engine, but had a single muf- 10 650 5th 20 1500 5th Constant gear, fler and a tailpipe. varied rpm 26 2000 5th Tables 6 through 11 summarize the tests performed for each 30 Coast down Neutral truck at the high-speed track. The tables present the test con- 30 Cruise 7th8th From 14 From 1500 4th Acceleration ditions of the trucks, including the speed, engine rpm, and gear. Also shown in the tables is the overall A-weighted sound level (LA) measured with a single microphone at the distances a distance of 20 ft (6 m) from the edge of the nearest driving of 25 and 50 ft (7.5 and 15 m) from the track for each truck run, lane of unsealed, dense-graded asphalt. First, the stationary as described in Section 3.4.3. For the stationary tests, LA is the CESVA omni-directional speaker tests were performed at this measured time-averaged sound level; for the passby tests, LA is location for initial check-out and additional array perfor- the maximum sound level measured during the single truck mance validation. After that, the truck passby tests were carried run. No tests were performed at this track with a loudspeaker out in 3 days. The trucks (all by International) tested at the mounted on a truck. high-speed endurance track are listed in Table 5 (not in the order of testing). 3.4.3 Passby and Intensity Measurements The International 4400 truck was the same as the one tested before at the low-speed track. The other trucks tested at the In addition to the array measurements of the test trucks for high-speed track were not tested at the low-speed track. The the stationary and passby truck conditions, conventional 9200i truck with a 450 hp engine, shown in Figure 18, had front single-microphone and sound intensity measurements were and rear Goodyear G395 tires and a short vertical tailpipe, conducted. These measurements are described in this section. unlike the truck of the same type tested at the low-speed track To complement the beamforming results, single-micro- (compare with Figure 16). This 9200i truck also was not phone sound pressure level measurements were performed at equipped with aero skirts covering a fuel tank and a horizontal distances of 25 ft (7.5 m) and 50 ft (15 m) from the centerline part of the exhaust pipe under the cabin. of vehicle travel. These microphones were set on a line perpen- To test a truck with no muffler, the exhaust system of dicular to the direction of travel offset 5 ft 8 in. (1.7 m) from another 9200i Eagle truck (with 370 hp engine) was modi- the center of the array, as shown in Figure 22. The micro- fied by replacing its vertical muffler with a pipe, as seen in phones were adjusted to a height of 5 ft (1.5 m) above the pave- Figure 19. This truck was also equipped with an aerodynamic ment. The microphones were 0.5 in. (12.5 mm) Larson-Davis wind fairing over the cabin. (LD) Model 2541 fitted onto 0.5 in. (12.5 mm) LD Model The International 5900i tractor truck was tested at the PRM900C microphone preamplifiers. The signals from these high-speed track in three different configurations: (1) bobtail microphones were fed into an LD 3000 two-channel real-time Table 5. Trucks tested at the high-speed track. Truck Type Front/Rear Engine Type Exhaust Configuration (model year) Tires (no.) 4400 International DT466 G159 (2) Single horizontal muffler (2002) 250 hp G124 (4) & horizontal tailpipe 9200i Cummins ISX G395 (2) Single horizontal muffler (2006) 450 hp G395 (8) & short vertical tailpipe 9200i Eagle Cummins ISM G395 (2) Single modified vertical (2004) 370 hp G372 (8) tailpipe with no muffler 5900i Cummins ISX G286 (2) Single vertical muffler (2006) 600 hp Michelin XZE (8) & vertical tailpipe 5900i w/o and Cummins ISX G286 (2) Single vertical muffler with loaded 600 hp G164 RTD (8) & vertical tailpipe trailer (2006)

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24 Figure 18. The 9200i truck with short vertical tailpipe Figure 20. The 5900i truck with no trailer at the at the high-speed track. high-speed track. analyzer. The signals were also recorded on a Sony TCD D-100 A-weighted sound levels measured for the truck passby condi- two-channel DAT recorder for data backup and any further tions on the high-speed track were also given in Tables 6 data reduction required later. through 11. For the stationary tests of either the trucks or the loud- Note that the 25 and 50 ft measurements in Tables 6 through speaker, linear time averages of the sound pressure levels were 11 are generally consistent with inverse square law, but there obtained for a 15 s time period. These were analyzed in one- are some variations. Near-field effects associated with source third octave frequency bands from 20 to 20,000 Hz. The size may be a factor in the variations. This phenomenon is par- average overall A-weighted sound levels measured for the ticularly likely for the data in Table 8, where the modified stationary conditions on the high-speed track were given pre- exhaust resulted in a strong exhaust source significantly above viously in Tables 6 through 11 for both the 25 and 50 ft micro- the engine source. Near-field effects are a concern for passby phone positions. For the passby truck tests, one-third octave measurements with a single microphone. They are not, how- band spectra were captured every 0.100 s with a 0.125 s expo- ever, an issue for beamforming measurements which are nential (fast response) averaging time applied to the signals for intended to discriminate among a distribution of sources. a period of 10 s. These data were then used to examine the over- For each of the test trucks under no-load stationary condi- all A-weighted time history of the passby event, as well as the tions, sound intensity averaged over areas to the side of the one-third octave band spectrum at the time of maximum over- all A-weighted level during the passby. The maximum overall Figure 19. The 9200i Eagle truck with drag fairing Figure 21. The 5900i truck with trailer at the and no muffler at the high-speed track. high-speed track.

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25 Table 6. Tests of the 4400 truck at the high-speed track. Speed LA (dBA) at rpm Gear Notes (mph) 25 ft 50 ft 0 740 (idle) Neutral 69.1 62.7 0 1150 Neutral 72.4 65.7 Stationary 0 1400 Neutral 73.7 66.6 0 2100 Neutral 79.3 72.6 35 2100 Drive Automatic 80.4 74.3 50 1400 Drive transmission 83.6 77.6 35 2100 3rd Constant rpm, 80.3 74.7 50 2100 4th varied gear 84.3 78.0 From 50 * Throttle off Coast down 80.9 73.3 From 10 to 15 1500 to 2450 2nd Acceleration 81.9 76.2 From 22 to 31 1800 to 2450 2nd Acceleration 83.7 78.7 * Not recorded Table 7. Tests of the 9200i truck at the high-speed track. Speed LA (dBA) at rpm Gear Notes (mph) 25 ft 50 ft 0 Idle Neutral ** ** 0 1100 Neutral 74.6 68.2 0 1400 Neutral Stationary 78.7 72.2 0 1500 Neutral 78.6 71.7 0 1800 Neutral 81.1 74.1 35 1400 8th 77.8 72.3 46 1800 8th 84.2 77.9 50 1500 9th 83.0 77.5 50 1100 10th 82.6 76.5 35 2100 3rd Constant rpm, ** ** 50 2100 4th varied gear ** ** From 50 * 9th Coast down 81.4 74.7 Compression From 50 * 9th 83.6 77.3 brake From 900 46 8th Per SAE J366 84.5 78.5 to 1800 * Not recorded **Missing data trucks was measured. The sound intensity probe used for this phones were input to a LD 3000 two-channel analyzer for purpose consisted of two 0.5 in. (12.5 mm) phase-matched immediate sound intensity measurement in one-third octave condenser microphones spaced 0.625 in. (16 mm) apart in a bands. To determine the average sound intensity for an area in side-by-side configuration. The microphones were a G.R.A.S. the plane parallel to the side of a vehicle, the probe was manu- 40AI intensity microphone pair fitted to LD Model PRM900C ally swept over specific subareas, as shown in Figures 23 and 24, 0.5 in. (12.5 mm) preamplifiers. Signals from these micro- several times as linear averaging was performed over a period Table 8. Tests of the 9200i Eagle truck (modified exhaust, no muffler) at the high-speed track. LA (dBA) at Speed (mph) rpm Gear Notes 25 ft 50 ft 0 Idle Neutral 68.6 63.5 0 1500 Neutral 77.6 72.8 Stationary 0 1600 Neutral 79.6 74.9 0 1900 Neutral 81.7 76.7 35 1900 7th 85.2 79.9 35 1500 8th 82.6 76.7 45 1900 8th 89.2 84.3 50 1600 9th 89.6 82.1 From 50 * * Coast down 80.0 75.6 From 50 1400 9th Compression brake 96.2 90.9 * * * Low-speed acceleration 89.2 85.9 * Not recorded

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26 Table 9. Tests of the 5900i truck (standard tires) at the high-speed track. LA (dBA) at Speed (mph) rpm Gear Notes 25 ft 50 ft 0 Idle Neutral 66.5 60.3 0 1400 Neutral 76.2 68.7 Stationary 0 1800 Neutral 79.9 74.7 0 2000 Neutral 81.1 74.2 35 1800 6th 81.0 75.3 35 1400 7th 79.6 73.8 50 2000 7th 84.3 78.5 50 1400 8th 84.7 78.9 From 50 * * Coast down 81.8 76.2 From 50 1400 8th Compression brake 83.3 77.6 * Not recorded Table 10. Tests of the 5900i truck (aggressive tread rear tires) at the high-speed track. LA (dBA) at Speed (mph) rpm Gear Notes 25 ft 50 ft 35 1800 6th 81.4 76.1 35 1400 7th 79.3 73.7 50 2000 7th 85.5 79.9 50 1400 8th 83.5 77.8 From 50 * Neutral Coast down 81.8 77.1 From 50 1400 8th Compression brake 83.4 78.2 13 to 16 From 1300 4th Per SAE J366 80.5 75.2 * Not recorded Table 11. Tests of the 5900i truck (aggressive tread rear tires) with trailer at the high-speed track. LA (dBA) at Speed (mph) rpm Gear Notes 25 ft 50 ft 35 1800 6th 82.7 77.2 35 1400 7th 82.2 76.7 50 2000 7th 88.0 82.8 50 1400 8th 87.2 82.4 From 50 * Neutral Coast down 86.9 81.4 From 50 * Neutral Compression brake 87.4 81.3 50 1400 8th - Full throttle 87.9 82.4 th 35 1400 8 - Full throttle 84.2 78.5 * Not recorded 50 ft Microphone 25 ft Microphone 6 5 4 2 1 3 Figure 22. Positioning of passby measurement Figure 23. Sound intensity scan areas for the 9200i microphones. truck.

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27 3 1 2 4 5 6 5 Figure 26. Sound intensity scan areas for the 4400 truck with loudspeaker. for the areas indicated in Figure 26. From these data, it is appar- Figure 24. Sound intensity scan of muffler ent that the subareas corresponding to the hood and upper cab (subarea 3) for the 9200i truck. produce lower levels of sound power, and the sound intensity is negative at the lower frequencies. The latter is an indication that in these subareas the sound energy flows in the opposite of 40 s. Once the average intensity was determined for each direction (toward the structure rather than from it) because of subarea, the sound power radiated through each surface was the presence of the other, more powerful sound source(s) in calculated. These calculations were then summed to deter- the vicinity. As a result, for subsequent trucks the hood and mine the total sound power radiated on the side of the truck upper cab subareas were excluded from the analysis. For the facing the array. In this manner, the contribution of each sub- 4400 truck, the sound power contribution was also determined area to the total sound power radiated to the side of the truck for the loudspeaker, and its relationship to the total for the was evaluated. truck only is given in Figure 27. This methodology was initially applied to the 4400 truck The sound power breakdown for the stock 9200i truck for when tested at the low-speed track with the loudspeaker the subareas of Figure 23 is shown in Figure 28. For this truck installed. The results for the truck alone are shown in Figure 25 the contributions from the muffler and exhaust outlet are quite 100 Upper Cab - 2 Hood - 3 95 Muffler - 4 Lower Cab - 5 Wheel Well - 6 Total Truck A-weighted Sound Power Level, dBA 90 85 80 75 70 65 60 55 1000 1250 1600 2000 2500 3150 4000 5000 100 125 160 200 250 315 400 500 630 800 1/3-Octave Band Center Frequency, Hz Figure 25. Sound power levels for subareas and total of the 4400 truck at 2000 rpm.

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28 100 Speaker 95 Truck Total A-weighted Sound Power Level, dBA 90 85 80 75 70 65 60 55 1000 1250 1600 2000 2500 3150 4000 5000 100 125 160 200 250 315 400 500 630 800 1/3-Octave Band Center Frequency, Hz Figure 27. Sound power levels of the 4400 truck and loudspeaker. low compared to the sound power coming from underneath more contribution from the muffler. For the case of the 9200i the truck and through the wheel well. Only at very low frequen- Eagle truck with the modified "straight-through" exhaust (no cies of 100 to 160 Hz is there a significant contribution of the muffler), a significantly different contribution of subareas exhaust outlet. can be seen in Figures 31 and 32. In this case, radiation from For the 5900i truck, trends similar to the stock 9200i truck the exhaust pipe still remains low; however, sound radiation are seen in Figures 29 and 30, except that there is somewhat from the exhaust outlet subarea dominates the total radiation 95 Wheel Well - 1 Gas Tank - 2 Muffler - 3 Muffler Area - 4 90 Exhaust Pipe - 5 Exhaust Outlet - 6 A-weighted Sound Power Level, dBA Total 85 80 75 70 65 60 55 50 1000 1250 1600 2000 2500 3150 4000 5000 100 125 160 200 250 315 400 500 630 800 1/3-Octave Band Center Frequency, Hz Figure 28. Sound power levels for subareas and total of the 9200i truck at 1800 rpm.

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29 5 4 4 1 3 1 3 2 2 Figure 29. Sound intensity scan areas for the 5900i truck. Figure 31. Sound intensity scans areas for the 9200i Eagle truck with straight-through exhaust (no muffler). between 160 and 500 Hz, with the sound levels 6 to 15 dB array microphones, however, the study team determined that greater than any of the other subareas. Even at the higher increasing the number of microphones to 73 or 77, by adding frequencies, the contribution of the exhaust outlet remains units at and near the center of the array, was beneficial for the high. array's beamforming performance and resulting noise source Upon completion of testing at IT's high-speed track, the mapping. Also, assembling the array in the field, which measurement data collected was post-processed and analyzed involved handling multiple cable connections between the in the laboratory. The key results of the analysis are presented microphones and PXI unit, was found to be labor intensive and and discussed in Section 3.5. Again, the microphone array and time consuming. These aspects of the first field experience were data acquisition system performed as expected and required no addressed prior to subsequent application of the array for the major adjustments. From experimenting with the number of roadside truck noise measurements. 95 Front Wheel Well - 1 Between Fender & Gas Tank - 2 Gas Tank Area - 3 Muffler - 4 90 Exhaust Outlet - 5 Total A-weighted Sound Power Level, dBA 85 80 75 70 65 60 55 50 100 125 160 200 250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000 1/3-Octave Band Center Frequency, Hz Figure 30. Sound power levels for subareas and total of the 5900i truck at 1400 rpm.

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30 95 Front Wheel Well -1 Gas Tank Area - 2 Exhaust Pipe - 3 90 Exhaust Outlet - 4 Total A-weighted Sound Power Level, dBA 85 80 75 70 65 60 55 50 1000 1250 1600 2000 2500 3150 4000 5000 100 125 160 200 250 315 400 500 630 800 1/3-Octave Band Center Frequency, Hz Figure 32. Sound power levels for subareas and total of the 9200i Eagle truck with straight-through exhaust (no muffler) at 1500 rpm.