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Design Principles For Distributed Sound Systems
Enhancing the atmosphere with well-designed distributed systems for business spaces...
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Before beginning the design process for a business sound system, identify what the customer needs and expects:

Fidelity Expectations. Does the client want a good, basic system; something a little better than average; or maximum bandwidth and maximum fidelity?

Sound-Level Requirements. Will the system be used strictly for background music, or does it really need to rock?

Usage. What kind of music will be played through it? For example, if it’s urban funk, then you’re going to have to think about the bass quality and SPL capability.

Form. Do they want in-ceiling or on-wall loudspeakers?

Coverage Requirements. How even do they want the coverage to be? Is it OK for it to perceptibly vary in volume within the space, or do they want it even throughout? Are there areas that don’t need to be covered at all, or where they might want lower SPL, such as the cash register area in a store?

Low-Frequency Coverage. How even does low-frequency coverage need to be? If you’re using subwoofers, is it okay to use a small number, meaning the sound will be loudest close to the sub(s) and softer elsewhere, or do the subs need to cover evenly?

Paging. Do they need paging? If so, how important is paging intelligibility?

Zones. How many zones need separate volume controls, different source controls or paging assignment?

Benchmarking. Do they want this system in order to keep up with a key competitor? If so, this can give you a benchmark.

Cost. Does the system they want fit into their cost requirements? If not, which functions can be adjusted to meet the budget, or is a budget reassessment advisable?

Collect this information and confirm your understanding with your customer before you start designing. You’ll have a much clearer idea of how to proceed when you know what your customer needs.

As we start thinking about the design, we need to then translate our client’s requirements into specific goals for coverage, sound levels and bandwidth. Once these requirements are identified, we can start thinking about loudspeaker and component selection, speaker layout patterns and speaker density.

We need to be able to correctly commission the system after it is installed, ensuring proper settings and optimal performance. Let’s start here with loudspeakers, and in future installments, I’ll look at other issues, such as loudspeaker layout, as well as SPL and equalization.

Ceiling Loudspeakers
Have you ever heard, or followed, rules of thumb like “space ceiling loudspeakers as far apart as the ceiling is high” or “as far apart as the distance from the listener’s ear to the ceiling?” While they are simple to follow, they aren’t very practical. The conditions upon which these rules were supposedly based—the needs of commodity-grade systems—just aren’t what’s required today. No hard-and-fast rule is going to apply in all cases. You need to find out what the customer needs before you start making plans around loudspeakers.

The main objectives in deciding about the placement pattern and density of loudspeakers in a distributed system are covering the area effectively, providing sound that is audible and intelligible over the entire area, and making sure the system is capable of sustaining whatever sound pressure level the application requires.

A Common Misunderstanding
The following misunderstanding about the coverage angle specification of loudspeakers can easily result in system design mistakes. First, let me clarify that the term “coverage angle” is the angle at which the sound level is 6 dB down from the on-axis sound level.

It’s very common to see a polar coverage spec of the “coverage angle” on a spec sheet and assume that the speaker will actually cover this angle when installed. It seems like it would be the case, doesn’t it? But the truth is that loudspeakers actually cover less area than their spec sheets would imply.


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