by Curt Taipale

One of our ChurchSoundcheck members wrote to the group recently 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?

We took a look at the technical specifications for that loudspeaker and it is a fairly tall cabinet. The spec says that it has a “75° axisymmetric” pattern. At first I read that as asymmetric, so my initial response was no, it would not work well. One of our more astute CSC members corrected me to realize that it was instead “axisymmetric”, which means “symmetrical about its axis”. Shows that we need to always be learning, because I’ve made my living in pro audio for nearly 40 years and I had never heard that term before. (Where would we be without marketing guys?)

Methinks to myself “Well, we’ll just see about that.” Don’t get excited. I wasn’t upset. I was intrigued by what on this meant. So I took a moment, created a simple room in EASE, dropped in that particular loudspeaker model, first in its intended vertical orientation, and examined the coverage at several frequencies. Not bad. Seemed to behave itself nicely.

The loudspeaker appears to be a 3-way box, although I wasn't sure what the frequency range of each section was. So I "guessed" and did direct sound coverage maps at 4000 Hz, 2000 Hz, 1250 Hz and 315 Hz.

Then I rotated the loudspeaker to a horizontal orientation to compare the coverage at those same frequencies, and the results were surprising to say the least. Not what I imagined when I read those words “symmetrical about its axis”. Maybe it doesn’t mean what I think it means?

What this shows is at least at those upper frequencies the sound coverage in the vertical orientation is fairly smooth. Almost impressive. 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. (Remember 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.)

So consider the results – instead of a nice wide coverage pattern at 4 kHz, the “good seats” are now confined to a small swath over to the side. 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 them 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. There are several loudspeakers that have good correlation between the horizontal and vertical polar patterns. It is a good reason to review the technical specifications for any loudspeaker you are considering 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.

The moral of this story? 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.