When it comes to room acoustics, definitions of “correct” or “appropriate” can be largely dependent upon the musical tastes of the listeners, often making it a sensitive subject. The decisions made are significant in terms of cost as well as the listening experience.
Fortunately, not all of the aspects of auditorium sound are so subjective. Large rooms require a sound system, and the criteria for performance are more universally accepted. All successful sound systems must:
1) Provide even sound coverage of all audience areas
2) Provide adequate loudness before distortion
3) Provide adequate loudness before acoustic feedback
4) Be easy to understand
5) Reproduce musical sources with adequate clarity and fidelity
I call these the “Big 5.” While there are numerous other criteria that can be used to judge a sound system, these are the ones that aren’t negotiable. Regardless of the proposed design of the system, if the system doesn’t fulfill the Big 5, there will be ongoing problems with sound reproduction.
For an existing system, the best instrument for determining if the sound system meets these criteria is the audience. Listen to them. Complaints such as: “I can’t hear when I sit over there” or “Why does the system squeal so much?” or “I can’t understand the words” often mean that a system is in violation of one or more of the Big 5.
Most of these problems can ultimately be traced back to the system’s transducers. A transducer is a device that converts energy from one form to another. The two types of transducers in a sound system are microphones and loudspeakers.
The microphone converts acoustical energy into electrical energy. The electrical signal flows through the system’s electronics on its way to the loudspeaker, which converts the electrical signal back into an acoustical signal. The acoustical signal flows through the air to the listeners’ ears.
Both electrical and acoustical signals are vital to the operation of the system. It should be pretty obvious that deficiencies in one will bring out the worst in the other. The transducers are always its weakest links. Never forget that.
Between the two, the loudspeakers get priority with regard to investment dollars. They are second in importance only to room acoustics in determining the sonic performance of the space, and therefore, it’s vital to understand some basic principles regarding the selection and placement of loudspeakers in a room.
The goal is to help you sort through the sundry opinions that are often expressed by those around you. The principles are general, but physically defensible and time-proven.
Limits Of Performance
There are two critical factors regarding loudspeaker deployment into an auditorium - selection and placement. They are of equal importance – when loudspeakers are selected and placed, the limits of performance have been established for the sound system in terms of the Big 5.
Further, the majority of common sound system ailments can be traced back to loudspeaker issues. Unfortunately there is relatively little that can be done with electronics to remedy the problems caused by the improper selection and placement of loudspeakers.
If someone walks into your church and asks “Where should I sit for the best sound?” the answer should ideally be “It doesn’t matter, sit anywhere you like.” In a permanently installed sound system, the sound coverage should be as uniform as possible over all seating areas – no overpowering the audience members in the front to achieve adequate level for those in the back.
Coverage is best checked by listening to speech over the system. Don’t waste time wandering around with a sound level meter in an evaluation of this type. Sound level meters display the total sound field level present at a given position, but the information needed by the listener is the early sound energy, with special instrumentation required to measure it.
Therefore, the best way to check coverage is to play speech tracks (usually from a CD) that is unfamiliar with and simply walk around and listen.