Atmospheric absorption of sound: Further developments

Abstract

This Letter is an extension of an earlier Letter by Bass et al., ‘‘Atmospheric absorption of sound: Update’’ [J. Acoust. Soc. Am. 88, 2019–2021 (1990)]. Errors in a formula for saturation vapor pressure are corrected, and an alternative, much simpler formula is given. The role of atmospheric pressure is emphasized by giving formulas in which the absorption, frequency, and relative humidity are all scaled with respect to atmospheric pressure. Also presented are new, more readable and useful figures showing atmospheric absorption as a function of frequency, relative humidity, and atmospheric pressure. The new figures make it possible to estimate accurately the absorption at any value of atmospheric pressure.

Acoustic waveforms produced by a laboratory scale supersonic jet

“…where the absorption length scale (ℓ α ) is simply the inverse of the absorption coefficient (α) which is evaluated in Table 4.1 using an expression from Bass et al (1996) [6]. We evaluate α using the characteristic frequency f 0 = 3.6 kHz and for a relative humidity determined by the average value recorded during the 45 .…”

Imaging of directional distributed noise sources

“…C fr and C ff are the corrections for the actuator response and free-field response, respectively; they are based on data provided by the manufacturer of the microphone and are practically the same for all the microphones. α is the atmospheric absorption coefficient (dB/m), computed using the formulas proposed by Bass et al 13 for the measured values of relative humidity and temperature of the ambient air.…”

Impact of chevron spacing and asymmetric distribution on supersonic jet acoustics and flow

“…Pressure data was acquired for five seconds at approximately 205 kHz and then converted into frequency space following Bartlett's method [28]. The resulting averaged spectrum was then propagated to a radial distance of 100D d with non-standard day atmospheric attenuation corrections applied using the method of Bass et al [29]. Employing the above mentioned facility uncertainties, Lighthill's eighth power law [30] as well as additional sources of error, the OASPL values represented here were calculated to be within 70.8 dB of the true value with 95 percent confidence.…”