A-weighted decibels are a rough practical approximation of perceived loudness
Evidence
These effects make it difficult to design a meter that will give a reading that truly relates to the perceived loudness of a sound, so an instrument that gives an approximate result is usually used. This is achieved by using the sound pressure level but frequency weighting it to compensate for the variation of sensitivity of the ear as a function of frequency. Clearly the optimum compensation will depend on the absolute value of the sound pressure level being measured, and so some form of compromise is necessary. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 633
In order to have a better, yet relatively simple, measure of the perceived level of sound, the concept of sound level is defined as a measure that is weighted with frequency so that the level roughly approximates the frequency sensitivity of hearing. Four different weighting curves are defined: A, B, C, and D, as shown in Figure 9.3. The A-weighted sound level is commonly used in noise measurements to characterize the perceived level and the risk of hearing loss. The A weighting slightly emphasizes the levels at mid frequencies and attenuates them at low and high frequencies. When the weighting curve is compared with the inverted equal-loudness curves, it is easy to see that the A weighting is just a very rough estimate. Technical simplicity and extensive use in practice are its advantages. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 988
A comparison of circles and stars in Fig. 16.6 reveals that the subjective evaluation can be predicted by physical measurements with a loudness meter. On the other hand, A-weighted sound power overestimates the differences drastically. … For example it is stated frequently in advertisings that the noise emission of printer G is by 90% less than that of printer F. This is correct in physical terms of A-weighted sound power. However, the loudness difference perceived by the customer is only about 35%, in line with the indications by a loudness meter. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1777
Categorization
- DEFINE: Explains the purpose and design logic behind frequency-weighted sound level meters (A and C weightings introduced right after).
- ADDENDUM: Connects to the reader’s noise-exposure interests in the silence and acoustic-body chapters.
- XREF: Connects to the well-known psychoacoustic finding that A-weighting is a poor predictor of loudness, related to earlier discussion in this book of loudness models vs. sound level meters. — connects to: A-weighted dB values misrepresent perceived loudness for complex sounds. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1176; A-weighted sound pressure level misrepresents the loudness of broadband noises; ISO standardized loudness-based noise metrics because A-weighting proved inadequate (+15 more)
- SEED: Angle: how ‘90% quieter’ marketing claims mislead consumers because A-weighted power ratios exaggerate perceived differences by ~2.5x — a consumer-advice piece with real data.
- corroborated: 5 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 633; Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 988; Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1777
Broader Connections
- Perceived loudness and physical sound intensity follow different, non-intuitive mathematical scales
#expands(0.85) — George Michelsen Foy, Zero Decibels, 53 - Equal-loudness-contour weighting schemes failed as loudness meters
#contradicts(0.80) - Loudness perception is essentially logarithmic
#qualifies(0.75) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 611 - A-weighted decibels better predict hearing damage than unweighted sound pressure level.
#expands(0.75) — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 757 - Equal-loudness contours vary greatly across individual listeners
#qualifies(0.75)