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Clearing Up Certain Line Array and Point Source Loudspeaker Misconceptions
Let’s not let what these loudspeakers should be on paper get in the way of what they can be in the real world
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There is some misinformation floating about regarding the benefits and detriments of line array and point source loudspeaker technology.

The industry seems to be split down the middle with dogmatic “traditionalists” on one side, “new-fangled” line source users on the other, with seemingly fewer of us who just use whichever is most applicable and don’t worry about it.

Neither technology needs defending, neither technology is inherently superior at all tasks, and to be honest, there isn’t that much difference at a base level between the two anyway.

Most of the ammunition used by either side seems to be from examples of poor design or poor application, neither fault having anything to do with the concepts involved. Physics is physics.

Both models must adhere to it, and with a little bit of compromise thrown in due to real world limitations both models can create one hell of a loudspeaker system.

It is our job as professionals to look past the marketing, forget what we think we’ve learned about how things should be, and bring it back to the basics: the physics of good design and the right application.

I’m going to start off by eliminating three myths that have encumbered this “debate” for some time.

Number One: No loudspeaker array is a point source. Sure, a single loudspeaker can approximate a point source pretty well (most of them don’t), but once you build an array of those, you’ve got nothing of the sort, especially if that array isn’t built correctly; i.e., with no pattern overlap between sources more than 1/4 wavelength apart.

Just look at it and do the math: if you have four 60- degree horizontal enclosures covering less than 240 degrees of audience area, you don’t have a point source anymore.

Further, even if you set your loudspeakers up properly, you don’t have a point source at the intersections of their patterns where, by definition, a listener hears the output of more than one driver. Better designs handle this better, but this is the bête noir of arraying point source loudspeakers.

Number Two: No line array is a line source. It is so wildly impractical to build and deploy a true (wide bandwidth) line source in the real world that I’m almost positive nobody has ever done it.

A true line source has to be infinitely long, with all radiating elements within 1/4 wavelength of each other. This is impossible outdoors, and impractical in (where one may stack elements between two boundaries and emulate an infinite line).

Modern line arrays behave enough like a line source to be very useful, depending on how long the array is (I look at 10 feet as a minimum hang length), and how well the manufacturer has dealt with getting the higher frequencies to behave like a line (where it’s very hard to get sources within 1/4 wavelength of each other).

Number Three: Line arrays do not create cylindrical wavefronts. This sort of behavior is impossible as we understand linear acoustics.

What appears to be a cylindrical wavefront is the result of a large number of spherical wavefronts intersecting (Figure 1).

Figure 1 (click to enlarge)

Cylindrical wavefronts are possible in other disciplines, such as shallow water waves (which are non-linear and do not pass through each other undisturbed), but not in ours until the sort of extreme SPL that we don’t see out of any normal loudspeaker.

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Cylindrical wavefronts are also possible in antennas, but again that has little to do with us.

The reasons why, and the reasons it doesn’t matter, are well beyond the scope of this article.


Source: Live Sound International

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