Noise—(a) Undesired sound, by extension is any unwarranted disturbance in a useful frequency band, such as undesired electric waves in a transmission channel or device. (b) Erratic, intermittent, or statistically random oscillation.

NOTES:

1. If ambiguity exists as to the nature of the noise, a term such as “acoustic noise” or “electric noise” should be used.

2. Since definitions 3.25 (a) and (b) are not mutually exclusive, it is usually necessary to depend on context for the distinction.

*Noise-induced hearing lossSee hearing loss.

Noise-induced permanent threshold shift—Permanent hearing loss resulting from noise exposure. Abbreviation: NIPTS.

Noise-induced temporary threshold shift—Temporary hearing loss resulting from noise exposure. Abbreviation: NITTS.

*Octave band—A frequency band with upper and lower frequency limits in the ratio of 2. See one-third octave band.

*One-third octave band—A frequency band with upper and lower frequency limits in the ratio of 21/3.

*One-third octave filter—A filter with upper and lower passband limits in the ratio of 21/3 centered at one of the preferred frequencies given in ISO 266. Should meet the attenuation characteristics of IEC 61260 and ANSI S1.11–1986.

*Pascal (Pa)—unit of pressure corresponding to a force of 1 Newton acting uniformly on an area of 1 square meter. 1 Pa = 1 N/m2.

Perceived noise level—Frequency-weighted sound pressure level obtained by a stated procedure that combines the sound pressure levels in the 24 one-third octave bands with midband frequencies from 50 to 10 kHz. Unit, decibel (dB); abbreviation, PNL; symbol, LPN.

NOTE: Procedures for computing perceived noise level are stated in Federal Aviation Regulation Part 36, Noise Standards: Aircraft Type and Airworthiness Certification, Appendix B, and in International Civil Aviation Organization Annex 16, Volume 1, Aircraft Noise, 3rd ed., July 1993.

Perceived noisiness—Prescribed function of sound pressure levels in the 24 one-third octave bands with nominal midband frequencies from 50 to 10 kHz used in the calculation of perceived noise level. Unit, noy; abbreviation, n.

NOTE: The prescribed function is given in Federal Aviation Regulation Part 36, Noise Standards: Aircraft Type and Airworthiness Certification, Appendix B, and in International Civil Aviation Organization Annex 16, Volume 1, Aircraft Noise, 3rd ed., July 1993.

*Permissible exposure level (PEL)—Regulatory limit of sound exposure. The OSHA (Occupational Safety and Health Administration) PEL is a noise dose of 1.0 based on an 8-hour A-weighted sound exposure level at 90 dB with a 5-dB exchange rate. European PEL is generally an 8-hour A-weighted sound exposure level at 85 dB with a 3-dB exchange rate.

Phon—Unit of loudness, judged or calculated.

*Radiation efficiency; radiation factor—The ratio of the sound power radiated by a vibrating surface, with a given time-mean-square velocity, to the sound power, which would be emitted as a plane wave by the same vibrating surface with the same vibration velocity. The radiation factor is given by the following equation:

where Ps is the airborne sound power emitted by the vibrating surface, ρc is the characteristic impedance of air, Ss is the area of the vibrating surface, and is the squared rms value of the vibratory velocity averaged over the area Ss. Unit; none; symbol, σ. See sound power.

*Single-event sound pressure level—Time-integrated sound pressure level of an isolated single sound event of specified duration T (or specified measurement time T) normalized to T0 = 1 s. It is given by the formula:

where p(t) is the instantaneous sound pressure, p0 is the reference sound pressure, and Lpeq.T is the equivalent continuous sound pressure level. Unit, decibel (dB); symbol: Lp,1s.

Sound exposureTime integral of squared instantaneous frequency-weighted sound pressure over a stated time interval or event. Unit, pascal-squared second; symbol, E.



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