Perhaps it would be an idea to involve an acoustic engineer in your case.
Firstly, regarding very targeted, calculated measures to change the potentially unfavorable building acoustics.
But also regarding the possible use of more suitable loudspeaker systems.
Especially in acoustically challenging environments, such as churches, it is very important to reach only the audience in a very targeted manner while disturbing the room as little as possible.
Unfortunately, this is usually not possible with conventional loudspeakers; instead, it requires “line radiators” (keyword: cylindrical wave).
In this regard, much more is possible today than most people think.
You really just need to involve the right specialists.
Yes, agreed. Good pointer in general practice. Appreciate the comment.
I’ve had a pro representative from a local acoustic panel manufacturer in to do measurements. That’s how I know our room reverb is 4.5 seconds. He said a goal is to reduce it down to 2 seconds.
There was a certain square foot of acoustic panels he said would do that for my Sanctuary. I’ve forgotten the number he said, but it’s in notes from the meeting.
One possible benefit we have is that currently the 2 speakers seem to cover every area well. We don’t need high output dB gain to allow all the attendees to be able to hear. We don’t have a band accompaniment, drums, etc. There is a baby grand piano and organ, and some church members play acoustic guitar, occasionally one plays a flute, and infrequently other random instruments.
Not recently, but several years ago I had an old Radio Shack dB meter that I used to measure sound within about every area in the Sanctuary. Though not guaranteed to be accurate, it showed just a slight dB spread of I think 1.2 dB between highest and lowest readings. I walked the whole Sanctuary with recorded music playing at the normal church service levels I’d encounter. Surprising almost uniform coverage it seemed.
It’s basically lower level sound reinforcement that I’m doing.
Maybe it’s telling by what the feedback suppression is cutting, by that it’s mid, upper mid, and highs that gets cut most. A range of 500 hz to 10k has certain hot frequencies.
Just proof audio nerds like me always have something to do.
PS: I think I saw a series of YouTube discussions from Kyle Audio University about what specs to use. There was another that the guy built panels himself, wouldn’t mind giving that a go.
OK just for the record, I found the info for the reverb decay time (I’m assuming RT60), the treated goal, and square foot acoustic treatment needed.
I was off in my 4.5 second decay time. It’s actually 3.35 seconds untreated, suggested goal down to 1.88 seconds, treatment needed is 320 sq. ft.
That sounds very good!
And with his hundredths of a second, he also seems to be very conscientious.
He’ll certainly also consider that damping very low frequencies, like those your organ might produce, is much more difficult than the rest.
But it’s good to have such an expert on board.
And if it doesn’t live up to expectations in the end, you also have someone to blame. 
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We were about to get the pro to make the panels, but I think some other thing regarding the church building required repairs first. Such as we need to empty the Sanctuary to get the concrete slab leveled. “Minor stuff”.
When I mean local, they’re in Chambersburg, PA 25 minutes away, same county as the church. Soundproof cow actually makes the panels to their sales guys specs. They do have an install team too.
Some large large very tall domed ceiling churches have an of RT60 4+ seconds. Two people standing 10 feet and just talking is hard to understand one another.
In those cases just about any sound source introduced into the room is hard to understand. The best approach there since industrial acoustical treatment is out of the question is to use small speakers placed as close to the seating areas as possible and running them at a lower level.
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Thank you for pointing this out to me, and you’re right, of course.
If possible, and common practice in large churches, it’s wonderful to use (delay-) support speakers to get as close to the audience as possible - for example, in the galleries.
But this naturally requires a lot of installation effort, often in listed buildings.
In the nave, however, there’s usually no way to do this anyway, and so you’re often forced to “light up” larger distances at the most precise angles possible.
For this there are now even systems that can be installed parallel to columns in a standard way and subsequently electronically focus the sound on the desired areas.
This all is, of course, of no interest for the OP.
But simply replacing two traditional 15" speakers in similar positions with more suitable “line array” speakers would probably be comparatively easy, which is why I mentioned it.
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Line array would be fine, I’ve actually looked a bit into some.
Myself, I think the simplest is actually treat the room. With the treatment square foot of 320, that should equal 32 12x12 panels or larger panel equal derivatives of that.
I’m thinking a lot of audio is bouncing off the back wall. It is made up of untreatable areas, but there’s some that can be addressed. Drywall material wall, with double wood and glass doors centered. Then left and right of this are 2 glass panels each side. I think with treatment, I might as well get the pro to build and install being best answer. Then they can place them where it counts most, giving most bang for buck.
Hitting up pastor now after buying the mixer and stage box is a sound tech solo I’d rather avoid.
I’ve researched line array setup and it would be helpful. I’ve also entertained an edit to my current 2 speakers with adding a third flying upside-down for better perceived front coverage.
Probably will treat first then edit speakers if needed is going to be the approach most appealing to pastor. Helpful is he was a main sound guy when we first built this church. So he’s not deaf to sound needs.
Happy Labor Day weekend.
Dave B.