A good system designer will look at achieving coverage from smaller loudspeakers placed closer to the audience, versus larger loudspeakers placed at a greater distance.
The role of the client is to decide which approach will work best with regard to cost, aesthetics, and a host of other issues. Once this decision is made, it is the architect’s job to integrate the loudspeakers aesthetically in a way that does not impair the operation of the loudspeaker (no loudspeakers in cavities, please!).
Complicating The Process
It all seems pretty simple, right? It’s not. Two things complicate the selection and placement of loudspeakers with regard to coverage:
1) Their directivity characteristics tend to differ significantly with frequency. We say that the directivity is “frequency dependent.” So, a placement that works well for the woofer (low frequencies) may not for the tweeter (mid and high frequencies).
2) When two loudspeakers are placed in close proximity, it produces an entirely different directivity that almost never follows the intuitive expectation. For example, it’s common practice to place two loudspeakers side-by-side in an attempt to achieve wider coverage.
In fact, this will actually narrow the coverage for some ranges of the loudspeakers response. It may also cause interference effects that produce “drop outs” in areas of the audience.
The poor performance of many sound systems can be traced directly to loudspeakers placed by intuition with no regard for the physics of the acoustic interaction between multiple sound sources. When loudspeakers are placed in close proximity, they form an array – like it or not. Arrays are very complex in behavior and require careful design to produce an intended result.
As with other engineering problems, loudspeaker selection and placement is a matter of trade-offs. Improvements made in one aspect of performance come at the expense of some other performance benchmark. For instance, adding loudspeakers to cover additional seating areas will likely reduce the sound quality elsewhere in the room.
Using Powerful Tools
The good news is that loudspeaker selection and placement need not be left to chance or trusted to intuition. There are tools available for evaluating performance in advance.
Very powerful computer modeling programs can map the sound coverage onto the audience, allowing the system designer to evaluate the trade-offs. These same programs can model the interaction between loudspeakers to allow for the optimal design of arrays.
The bad news is that you probably don’t own one of these programs. They are rightfully expensive, and once acquired have very long, steep learning curves – their effectiveness is limited by the knowledge of the user. In short, loudspeaker selection and placement is a task for someone who is tooled up to do it AND has a lot of experience in doing it.
The audio system consultant is second in importance only to the acoustical consultant. Successful professionals have made a life-long study of their trade, and the value of what both bring to a project means that they always pay for themselves.
Some sound system projects of a smaller nature can benefit from the services of a design-build contractor. However, make sure that they have the necessary measurement and prediction tools to fully assess your room’s acoustics and provide predictions regarding the response of the proposed sound system.
Further, take the time to check out other church projects that they’ve done in both acoustically live and dead architectural spaces. Listen to the sound systems, and talk to the technical staff. Attend a service or two and evaluate the sound quality , especially with regard to speech intelligibility.
Some churches sound great from day one, while others never sound good. The difference is in the planning, and that should be done under the direction of qualified audio consultant and contractor to determine the appropriate selection and placement of loudspeakers.
After that, it’s a matter of providing them with the latitude and budget that needed to satisfy the “Big 5.”