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Summation With Others: Focus On Loudspeaker Arrayability
The primary goal of any array is to behave as a larger version of its individual elements....
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ar•ray•a•bil•i•ty [uh-ray-a-bil-i-tee]: 1. The properties of a transducer, or a transducer system, that permits summation with others of like kind, thereby providing an overall increase in energy.

While this definition includes devices such as microwave and sonar antenna arrays, here I’m specifically referring to an increase in acoustical energy.

And with that, it’s fitting to say that it’s hard to find “arrayability” in most dictionaries. That’s because it’s a word that I made up in 1984 when I started my loudspeaker company, Apogee Sound. Even “arrayable” isn’t in most dictionaries, but both terms show up incessantly in today’s loudspeaker marketing claims.

Essence Of The Issue
Sound travels quite slowly in air. This makes the arrival time, which dictate the relative phase relationship among two or more sonic sources, a critical issue in respect to how they will interact when more than one wavefront meets another.

So what makes a loudspeaker arrayable? “Any loudspeaker that is intended to be used in multiples must be carefully designed and thoroughly tested with like units to establish its viability as a member of an array that collectively provides reasonably flat constructive summation.” Well, that’s a mouthful. And unfortunately, careful design and thorough testing is not always the case.

There is a significant cost involved in building multiple prototypes, then possibly re-engineering the initial design, and then re-building and re-testing additional iterations until optimal acoustic summation has been achieved. It’s far easier (and cheaper) to predict what the array will do, rather than construct it in the physical domain and actually measure the response of various groupings of loudspeakers. And predicted response is precisely what most manufacturers concentrate on.

Let’s keep in mind that the goal of any loudspeaker array is to behave as a larger version of its individual elements. This doesn’t mean that the array cannot possess new properties of its own (and indeed it will) but rather, that the fundamental response of each array element should be constructively incorporated into the overall array response.

Sound Meets Light
It’s easy to think of sonic energy in the same way that we think of light sources: aim two or more luminaires at an object and they will collectively brighten the object more than a single lamp. Lights don’t care if they are of equal intensity, differing intensity, or widely varying distances from the subject that they are illuminating. That’s because of how incredibly fast light waves travel.

A copious quantity of loudspeaker arrays.

Not so with sound. In the audio domain, two or more loudspeakers focused on a given point in space may or may not produce a greater level of intensity. And even if multiple loudspeakers do increase the overall intensity, they are likely to cause all sorts of unevenness in the spectral response, thus degrading the sonic quality from that of a single loudspeaker. And that leads us to arrayability…

First, let’s establish that loudspeakers are not so easily defined as arrayable or not arrayable. In a manner of speaking, all loudspeakers possess both characteristics to some degree. In practice the issue is complex, and involves an understanding of wavelengths, pressure, and acoustic power. (See “Understanding Wavelengths” for more).

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