There are six fundamental questions that must be answered by any sound system design:
1. Is it loud enough?
2. Can everyone hear?
3. Can everyone understand?
4. Will it feedback?
5. Does it sound natural?
6. Is it versatile and easy to operate?
Is it loud enough?
This is largely a matter of speaker efficiency, power amplifier size, and distance from speaker to listener. We start with a target sound pressure level (SPL) and frequency response at the furthest listener's ear and work forward.
Can everyone hear?
This is determined by the coverage provided by the various speakers within the speaker cluster(s). Computer aided design (CAD) programs provide us with excellent predictions of loudspeaker coverage. We use EASE (Enhanced Acoustic Simulator for Engineers) for this analysis.
Can everyone understand?
This is the most complicated question to answer because most people would equate hearing with understanding. Outdoors this is true, but indoors we must take into account reverberation. Reverberation is sound energy that takes time to decay. Often referred to as RT60, reverb is measured in seconds and can cause audible speech to become unintelligible when it becomes excessive. In the case of a building yet to be built or completed, we calculate the anticipated reverb time based on the coefficients of absorption of the finished surfaces and relative areas covered. All is well if the original finish schedule will result in an acceptable reverb time, but if we anticipate an RT60 that is either too long or too short then we negotiate changes with the architect. If the room is complete and we measure an undesirable RT60, we recommend the addition of acoustical material to either diffuse or absorb the sound as needed.
Will it feedback?
This is a very important question that is answered through careful analysis and computation. In this process we learn how many open microphones we can have at one time, how far we can work from a microphone, or how close to a speaker we can get.
Does it sound natural?
The first four questions are objective and measurable, however this question is highly subjective. When reinforcing the spoken word, our goal is to make the talker's voice louder and more intelligible than the non-reinforced voice without adding or subtracting anything. The listener should be unaware of the amplification.
When amplifying music our goals are different. The sound is subject to enhancements ranging from tone changes, dynamics manipulation, and frequency shifting to added reverberation. We need to think about issues such as frequency response, peak output capability, and sometimes even auditioning loudspeakers.
Is it versatile and easy to operate?
We need to have an interface between the operator and the electronics that is versatile enough to accommodate the many demands that the performers will place on the system, as well as keep it simple enough for everyone to use. Detailed discussions with prospective operators and performers are required to get the right blend of features.