What does this mean? Read on as ASC founder, president and TubeTrap inventor, Art Noxon, PE discusses auditorium acoustics 101 pertaining to audio performance.
The architect designs…
…a great-looking and comfortable auditorium. The people attend the grand opening and are impressed with what they see, but they have gathered for more than a dazzling display of architecture, lighting, electronics, carpets, glass, surface textures and paint. They have come to be in an auditorium, a place to hear and, moreover, a place to listen to and learn from the lecture or, as the case may be, the sermon.
The outer beauty of an auditorium is recognized by how it looks, but the inner more lasting beauty of the auditorium is truly known by how it sounds. And with this we mark our journey into auditorium acoustics.
Lots of sound, but little is heard
A sound wave starts at the loudspeaker, which is suspended high overhead in the front of the hall. Seated way below, are the many people who came to hear that sound. The greater the size of the audience, the farther from the speaker they have to sit. An audience of 1,000 people would occupy about 8,000 square feet of floor space. A member of that audience typically might be seated some 50 feet away from the loudspeaker. The sound wave emitted by the loudspeaker spreads out in the shape of an expanding quarter sphere. By the time this wave reaches the audience, it has expanded out to a radius of about 50 feet. It has spread out over a quarter sphere surface area of 7,850 square feet or about 1.13 million square inches.
ASC TubeTraps controlling acoustics throughout the auditorium.
Each ear of a person collects about one square inch of sound, funneling it down into the eardrum. A person in the audience of an auditorium collects about two square inches of the sound wave, that’s just about 0.00017 percent of the total sound emitted by the central cluster loudspeaker. This tiny fraction of sound is called the “direct sound” because it goes directly from the loudspeaker to the listeners’ ears. (Figure-1).
If 1,000 people are in the audience, their combined ears collect only 0.17 percent of the direct sound emitted by the loudspeaker. The rest of the sound, the other 99.83 percent of the sound, is called “indirect sound”. What happens to all this indirect sound is what auditorium acoustics is all about. If the indirect sound is neglected or mishandled, the auditorium will sound bad, and if it is well handled, the auditorium will sound good.
To recap, auditorium design or renovation can be understood to involve three consecutive areas of expertise. The architect designs a building that is attractive, comfortable and allows people to see what is going on. The sound contractor supplies a sound system to the auditorium that makes a direct sound loud enough so people can hear what is going on. However, nearly all of the sound generated by the sound equipment misses its intended target, the ears of the people. Picking up and handling the stray sound is the responsibility of the acoustical engineer. How it is collected and processed makes all the difference between a good and a bad-sounding auditorium.