Why Don’t We Make Our Rooms Totally Reflective?

In theory, this all sounds terrific. So why don’t we make our playback rooms totally reflective? Why, we could just set up a room of totally reflective acoustic surfaces (how about polished marble?). A veritable auditory fun-house!

The problem, of course, is what happens AFTER the early reflections have occurred, AFTER 50 milliseconds have gone by. At that point in time, reverberance starts.

Reverberance is the part of the playback sound event that carries perceptually audible information about the playback room. It commences at 50 milliseconds and can run on for many seconds in a large reverberant room. In small rooms, it usually doesn’t go on for more than a second. Interestingly, the reverberance that exists between 50 and 150 milliseconds especially tends to interfere with clarity and intelligibility of sound.

This is why we need to absorb sound in a playback room. We need to shorten the sound decay to a point where the reverberance of the playback room never gets a chance to build up.

Happily, it turns out that it is extremely cheap and easy to make a small room highly reflective at almost all frequencies for a brief period (50-100 ms.) and highly absorbent after that. Without going into actual design details (I’ve actually worked out a topology based on this thinking I call a Moulton Room), we simply make the end of the room behind the loudspeakers highly absorbent at all frequencies, and the other walls highly reflective. All the energy from the speakers propagates along the length of the room and back and is then absorbed. All early reflections are broadband, and all reverberance is absorbed. It really is almost that straightforward!