FOH planning


2007-04-20 9:19 pm
I had a thread last year, but want to ask a different question this time. Our church auditorium is a 70' wide octagon that seats about 350. Speakers are flown at about 15' high, about 15' inside the walls. Coverage required is roughly 3/4 of a 70' diameter circle.


I would like to build (or buy, I guess) speakers to cover this area from 100Hz and up. I'm looking at each enclosure housing two 8" speakers on either side of a 90*x60* horn. The 8" would share a sealed enclosure, isolated from the horn.

I'm looking to build option A below, one (or possibly two) per side. From the diagram below, assume the top, bottom, sides and rear panels are identical, only the front baffle will change to give the 8" speakers a slight horn loading effect. Would there be any advantage to B over A? Option A would be easier to construct.


Speakers would be bi-amped horns separate from mids, and actively crossed over before the 8"s start beaming.

Is there another/better option I should consider besides an arrangement like this?



2013-09-08 10:58 am
I would strongly suggest looking into columns. A room like this always shows reverberation issues, so you need to have a very controlled pattern. Your solution will only provide controlled patterns if used as a well controlled Line Array. I guess that's not what you want (OR NEED!!)

I build 4x 4" columns, they handle 300 watts easily and can cover your area. The big advantage of a column is that the higher the column is, the narrower the vertical beam. Horizontal is no problem for a column (nor most other speakers).
So either make one large column (12 - 16 4" drivers in 1 column), or make a set of small columns that you can stack as required.

It is not difficult to build, just closed boxes with just enough internal volume to let the 4" driver roll of at the frequency you aim for. I roll them of at 180Hz, with an internal volume of 1 liter per 4" driver, so a 4 liter enclosure. Paint them in a colour of your church and you end with an invisible very nice sounding DIY PA.:p

I guess you have 2 options;

1 - put 2 columns of 2 - 3 enclosures at the wall your picture is aiming at (the stage I guess). Hang them High and aim them DOWN to cover front to back seats (optional angle them per box a few degrees). The beauty of columns speakers is they carry a LONG distance, as opposed to "traditional" setup speakers. This means you concentrate more energy in the target area, and spil almost NO energy to area's where there will be NO ears (and areas that cause reverberations / echo's) :D

2 - put 2 - 3 enclosures at each side of the room, 2 meters high, 5 meters apart, slightly tilted downwards. This way you can keep the volume down even more and have a nice consistent sound area. This way you will further reduce the room reverberation.

I added a picture of one of my own products as an example. They are really easy to build. 1 challenge, find the right driver, full range with enough power (go for at least 30 watts, since you roll off the lows, they will be able to handle at least double the power).


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FOH planing

Instead of pitching the 8's outwards I angled them inwards from the rear of my enclosure on a V shaped baffle so I got some horn loading without a hole in the middle. I mounted the speakers on the sides of the extended baffles and got about 130 degrees of coverage with a very flat response and about 6 db of acoustic gain. I used a pair of B and C DE16 horns and mounted them on the front edge at right angles. I would gladly include an image but for some reason this forum wont let me copy paste or drag and drop an image here. My enclosure is installed in a theater and the manager is delighted with the result. From hard left to hard right the sound is identicle. I'm hoping to use the same design again as it worked so well.