SPS Post 2: System Design - Speakers

Pat Brown: Illuminating The Audience With Beautiful, Consistent Audio Coverage

As human perception of sound is highly subjective and differs from person to person, there is no true standard on how to make a room sound right.

However, Pat Brown has a list of items that are a must for a sound system, his "Big 5".

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

He suggests that for existing sound reproduction systems, the best way to find out if there are problems is by listening to the complaints of the audience. There is likely to be an issue with something on the list when there are problems such as inability to hear, loss of intelligibility, or imbalances within frequency response at various locations within the house.

The sources of problems are often the transducers - the microphones and speakers. These are the "weakest links" in the signal flow chain.

Speaker selection and placement is highly important for two reasons:
1) Among the two transducers, more is budgeted for speakers than microphones when designing a system.
2) Speakers are the next most important thing to room acoustics in the way elements of the sound system affect the sound in a field.

In a permanent install, speaker selection and placement is of extreme importance, as there is little that can be done to correct issues if these are not first done right. Coverage should be as equal as possible across all seats, in terms of amplitude over distance/position. The best way to check is by playing back speech over the system, and walking around to listen, instead of using metering tools.

As for directivity or coverage angle, the farther away the speaker is from the listener, the more confined the angle must be. This can be determined, in general, by physical size of the speaker  larger speakers have more directivity. This can be observed with lights, as changing distance and focus work the same way as distance and directivity of a speaker.

Directivity is also important in ensuring sound does not spill onto areas without audience, especially back onto the stage.

First determine possible placements, which will determine required directivity, and thus determine if a larger or smaller speaker is required. Look for the closest possible placement, so that smaller speakers can be used.

The problem is that directivity is "frequency dependent", so suitable placements for subs versus high cabs will differ. Also, with multiple speakers, the sources interfere with each other to produce "drop outs" and narrow coverage. Much care has to be taken in calculating the way in which arrays, closely placed speakers, will interact.

There are tools such as modeling programs, but these are not effective if the user does not have the required experience and knowledge. Besides the acoustical consultant, hiring an audio system consultant is also important.

For quality sound and speech intelligibility, at an even level across all seating areas, much planning is required, such that each element in the system is selected and placed right, satisfying the "Big 5".

I feel that this article points out the importance of getting the system right instead of trying to fix issues later, and also the importance of getting a specialist for each area when planning and designing a system. Getting a system installed right will cost more at first, but will minimize future issues.