Good sound absorbers make terrible sound isolators

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! As we are more interested in sound isolations of 40 dB as a minimum, absorption is clearly not the answer. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2112

Categorization

• DEFINE: Clearly distinguishes absorption (sound energy taken in) from isolation (sound transmitted through a structure), a distinction the reader needs for grasping psychoacoustics vocabulary.
• SHARE: Perfect nerdy correction for a home-studio or hi-fi friend who blankets a room in foam expecting to silence the neighbours.