The Greeks had the idea, way back in the day. They placed their theatres on steep hillsides and quiet rural locations, trying to avoid gusty winds as well as urban noise. The circular seating plan allowed more of the audience to be closer to the stage, the actors. Raising the seats in the back allowed all the audience to hear the actors with increased clarity than before. Still this can be improved upon heavily using up-to-date production techniques.

There are three basic uses of the reflectivity of sound in a room acoustics environment :

After these, angles and the dreaded trigonometry come into play. A flat reflector huge from the ceiling with no angle will simply reflect sound waves evenly to an entire audience, which is nice, but can be improved upon. If we were to angle the reflector at a convex angle (to the perspective of the speaker) then the sound energy is distributed for a better listening experience for those in the back. The converse of this example, were we to have a concave reflector, would focus sound energy on a specific area, which would not be good for people outside said area and would cause echoes as well.

A rough way of finding if a room will echo or not is using a ray-diagram analysis. By charting sound wave rays from speaker to listener in key points around the room, one will be able to tell if a room will have a strong echo or not.

We have the direct line-of-sight sound wave ray for each listener, 12ft and 33ft. Then we have the reflected rays, which add up to a distance of (11+18 = 29ft) and (16 + 26 = 42 ft). If we find the difference of these numbers, they end up being 17ft for the closer person, and 9 ft for the far away person. We then apply those numbers to a table of sound-path difference, and we see if the 'echoes' produced are small enough that they may be neglected.


Sound Path Difference Listening Conditions
Less than 28 Excellent for speech
28-40 Good for speech
40-50 Marginal
50-68 Negative
Greater than 68 Strong Echoes

Since our largest number is 17ft, we are under 28 and excellent for speech.This particular example only works for situations where there is one origin of noise - in multiple origin contexts, such as a meeting/board room, the entire room must be optomized for participants to be able to hear a speaker from anywhere in the room Or for our dance club, where speakers are placed everywhere in the room.

Now that we have a working knowledge of how the shape of the structure affects acoustics, we can work on...

Designing a quality Concert Hall