Can I Rotate My Loudspeaker?

Seems simple enough. But dig deeper and you realize that it's more wishful thinking than reality.

One of our ChurchSoundcheck members wrote to the group asking for help with a dilemma. His church had purchased some loudspeakers that they like the sound of. That particular loudspeaker is taller than most, and yet they have a low ceiling. Suspending those tall speakers in their intended vertical orientation would pose sightline issues.

So he asked the next logical question – could they suspend those loudspeakers horizontally without creating a coverage issue?

I checked the technical specifications for that loudspeaker. The spec says that it has a 90H x 50V coverage pattern.  

So I took a moment to create a simple room model in EASE, dropped in that particular loudspeaker model, first in its intended vertical orientation, and examined the coverage at several frequencies. Not bad. Looking at the direct sound coverage, it seemed to behave itself nicely at 4 kHz and at 2 kHz.

Next, I rotated the loudspeaker to a horizontal orientation to compare the coverage at those same frequencies, and the results were predictably surprising to say the least.

What this shows is at least at those upper frequencies the sound coverage in the vertical orientation is fairly smooth. Yet rotating the boxes to a horizontal orientation flips those coverage patterns. The vertical coverage becomes the horizontal, while the horizontal coverage becomes the vertical.

(Note that in each of these sound coverage maps, each isoline represents a 1 dB SPL change. The fewer the number of isolines, the smoother the coverage. And the brighter the color, the louder the sound.)

So consider the results – instead of a nice wide coverage pattern at 4 kHz, the “good seats” are now confined to a small swath in the middle.

Then consider what isn’t shown – that same pattern is now spraying that energy towards the ceiling as well, creating a very strong reflection (think phase cancellations) which is something we try to avoid in designing a loudspeaker system.

While sound will still come out and rotating the loudspeaker to a horizontal orientation won't stop you from having church, clearly the coverage across the seating areas will be uneven at best.

The natural next question might be is this to be expected with any loudspeaker? That of course depends on the loudspeaker. For example, coaxial loudspeakers can have good correlation between the horizontal and vertical polar patterns.

But there's another possibility. A couple of years ago I was at a church tuning their loudspeaker system. Their system at the time comprised three high quality main loudspeakers spread in an arc across the front of the platform.

As I always do, one of my first steps is to walk the room and listen to the sound coverage. It quickly became obvious that there was a major coverage issue with two of those three loudspeakers.

I shared my discovery with the client, and you could see their eyes light up. As it turns out, they had blown the high frequency drivers in two of their main loudspeakers. So they ordered replacement compression drivers and replaced them themselves.

What they didn't realize is that the horns in those particular loudspeakers are square, specifically so that they can be rotated ninety degrees. That allows the loudspeaker to be flown in either a vertical or horizontal orientation, yet still maintain the intended horizontal and vertical coverage pattern.

They had a 50/50 chance to reinstall the high frequency horns in the correct orientation, and they chose wrong for both of those repair jobs. It happens.

I think you can see why it's important to carefully review the technical specifications for any loudspeaker you are considering to use and compare the horizontal and vertical polar patterns. The manufacturers have an intended orientation for any loudspeaker they design, and in general it is best to use them in that orientation unless you have a very specific need.

Getting back to where this story started. Ceiling height should have been factored into the original decision before the church bought those loudspeakers. Ceiling height is your friend when it comes to designing loudspeaker systems. But in this case, if suspending them vertically is out of the question, our advice to this church is to consider new loudspeakers that are better suited to the realities of their application.

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