CHAPTER 20 Sound Isolation Upper structure Foam Re-reflected Air cavity energy reinforcing transmitted direct energy Weakened transmitted energy Plasterboard Incident energy FIGURE 20.13 Re-reflexion between layers. Resonant build-up in an air cavity can reduce isolation in a similar way to which the build-up of reverberant energy in a space can make a source louder than it would be in free-field conditions. for the neighbors to sleep easily. Similarly, if the acoustic control treatment were to be removed from the recording room, rendering it much more reverberant, the maximum SPL produced in the room by typical instruments would also increase. So many variables exist in acoustic control work, which is why it is often so difficult for acoustics engineers to give simple answers to what may appear to be simple questions.