What Rooms Do To Sound

Author: N.H. Crowhurst

Most of the sounds that we are concerned with in audio exist in rooms. But to understand what happens to sound in rooms, remember that echo that can be heard in the mountains. Every sound made comes back a few seconds later, like a perfect mimic. A wall-like face of rock reflects the sound waves that are generated, and sends them back one or more times.

The echo

Because of the large open spaces in mountain areas and the time it takes sound to travel (about 4.75 seconds for each mile of travel), the reflected sound is heard so long after the original sound that it sounds quite separate from it. However, all surfaces reflect sound in the same way, even the walls in your living room. The difference is that the sound does not take so long in going to the reflecting surface and coming back, so the reflected sound does not get completely separated from the original sound.

You must have noticed at some time the difference in a room when all the furniture and rugs are removed (before moving into a new apartment or in preparation for the painters). Without the furniture and carpeting, the room sounds "hollow." When the furniture is in it, the room becomes pleasant to talk in. The hollow effect is due to the echo in the room from the wall surfaces. When the room is empty, the echo goes on bouncing from wall to wall a great many times; when the furniture is in, the echo is deadened.