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Making A Splay: A Simple Asymmetric Coupled Point Source Loudspeaker Calculator

Loudspeakers coupled as tightly as possible with a ratchet strap might be structurally sound, but isn’t an optimum electroacoustic approach.

By Michael Reed February 7, 2019

A view of the recent application discussed by the author.

The venue had a 24-foot-wide stage, with two 75-degree main loudspeakers per side. Since the event was a rave, I knew that, by the end of the night, the audience would be all around the stage – not just in front of it – so I positioned the loudspeakers at unity splay (Figure 3).

As usual, things changed. The boss showed up and expressed concern with leakage from the tent to a nearby hotel. (We were in an urban city center on an ice rink.) I was able to quickly re-calculate the splay, as well as the drive levels that go with it, and the new configuration would keep the line of minimum variance along the tent walls rather than blasting out through them.

The math is simple: coverage of loudspeaker A plus (+) coverage of loudspeaker B, divided (÷) by 2, times (x) the distance ratio.

Figure 3

The distance ratio is easy to calculate as well: determine the farthest distance the inside loudspeaker will cover (in this case 65 feet), then determine the distance from the outside loudspeaker to the closest point of the coverage edge (in this case, the tent wall about 20 feet away.

The reason I chose to use the shortest distance (within my desired coverage area) to create the distance ratio for this particular job is that a smaller ratio will result in a tighter splay, lower drive level, and in this case, will have the minimum amount of leakage outside the tent wall while still covering the audience.

Divide the smaller distance by the longer distance, and it provides a decimal ratio. This math provides a new splay angle, in degrees, for the coupled mains. In this case the new splay was 23 degrees.

Hold on, we’re not quite done – we also need to determine the new drive level of the outer loudspeaker. Because it’s not throwing as far, we’ll need to turn it down to have consistent coverage across the area. Take 20*LOG (distance ratio) and you get the drive level in dB. In our example it’s 10.25 dB less than the inside loudspeaker.

Figure 4

Now take a look at the minimum variance line (Figure 4); instead of a half circle, now it runs along the edge of the tent. Everybody wins with this new configuration (shown in the photo that opens this article), and it’s easily repeatable.

Note that the data in the Figures with this article were captured with Meyer Sound MAPP XT (Figure 1 and 2) and EASE Focus 3 (Figure 3 and 4).


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About Michael

Michael Reed
Michael Reed

Michael Reed, a member of the Audio Engineering Society (AES), is an audio engineer and entrepreneur based in southern New England, where he heads up Marathon Audio Systems. Read more of his articles here.
https://www.marathonaudiosystems.com/

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