Good sound absorption does not imply good sound isolation

Evidence

The first thing to note is that just because a material is a good absorber of sound doesn’t mean that it is a good isolator of sound. In fact, most absorbing materials are terrible at sound isolation. This is because, in the sound isolation case, we are interested in the amount of sound that travels through a structure rather than the amount that is absorbed by it, as shown in Figure 6.53. A poor value of sound isolation would be around 20 dB, yet it corresponds to only one hundredth of the sound being transmitted. A good absorber with an absorption coefficient of 0.9 would let one tenth of the sound through, which corresponds to a sound isolation of only 10 dB! — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2112

Categorization

• XREF: Connects to the reader’s broader project on silence and sound management — explains why noise-blocking materials often disappoint. — connects to: Sound absorption and sound isolation are confounded but behave inversely in materials — David Howard, Jamie Angus, coustics and Psychoacoustics, 2159; Sound isolation depends on flanking paths more than the barrier itself — David Howard, Jamie Angus, coustics and Psychoacoustics, 2169
• DEFINE: Clarifies the critical distinction between absorption and isolation coefficients in acoustics.
• CANDY: The fact that even a poor 20 dB isolation is better than the best absorber’s 10 dB is a striking, tweetable number.