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Guidelines for treating cathedral ceilings

My listening room is 18' wide x 18.5' deep, with a cathedral ceiling symmetrically over the room.
I have done the 'standard' room treatments (absorption behind the speakers and listening seats, and absorption at the first reflection points on the side walls). Absorption is 2" thick Owens Corning 703 fiberglass.

However, I am still hearing a sharp slap echo when I clap my hands in the room. I am beginning to suspect some sort of ceiling or upper corner interaction. Is there any rule of thumb for where to first start with a treating a cathedral ceiling? I am a little bit surprised, since the ceiling is angled and does not present two parallel surfaces for sound to bounce off of.

The practical concern is some sibillance when playing certain CDs at high volumes (possibly exciting something in the room and exaggerating the treble?).

thanks in advance,
Bill

(I hope this drawing comes through OK- the A is the top of the ceiling, and the two S are the speakers).

.......................A
.................... /....\
................./.............\
............../...................\
.........../..........................\
...........|...........................|
...........|...........................|
...........|...........................|
...........|.....S...............S.....|
............ --------------------------
gnobber

Showing 4 responses by gnobber

gnobber OP
46 posts
 
To answer Newbee's question, I get the flutter echo pretty much everywhere in the room. I did have my wife clap at the speakers while I sat in the listening chair- pretty much the same results as anywhere else.

I have a plush carpet with 1/2" pad througout, so no hardwood floor interactions.

I haven't been able to pinpoint the source. I have some 1" styrofoam sheets (4'x4') that I can hold up in various places to do a 'clapping' experiment. So far no smoking gun, although I used this technique in another room and was able to tame it almost completely. I guess my next move is to try climbing a ladder and blocking various spots up near the peak, or maybe the high corners . . .
gnobber OP
46 posts
 
Theaudiotweak, it looks like you were right on with your suggestion about treating the upper walls. I just got finished building more panels for the front wall behind the speakers. These run along the border between the angled ceiling and the wall, are 18 ft wide, 33" high in the middle, and taper down to nothing as you go left or right. Height is 9-12' above the ground. Great results: this totally killed the rising ringing sound I was hearing with hand claps.

I am now able to hear a little more depth and detail, and some of the sibilance in my favorite recordings seem to strike quickly and not linger on like they used to. Thanks for the advice, everybody!
Bill
gnobber OP
46 posts
 
the panel looks something like a roof truss- 18' wide, because that is the width of the room. 33" high, because that is the distance from the lowest part of the ceiling (9' above ground) to the peak of the cathedral part. I looked at your photo, and your speakers are 90 degrees away from where mine are (i.e. the peak of your ceiling is between your listening spot and the speakers, and my peak runs along the axis between my speakers and my listening spot). So, I might still advise trying this tweak if you have a symmetric cathedral ceiling. This stuff might be hard to visualize, so feel free to write back if you have more questions.
gnobber OP
46 posts
 
My advice would be to start with some inexpensive foam panels, just to experiment. You can get 4 x 8 sheets at Home Depot, 1.5" thick, for around $10. This would allow you to temporarily hold or nail the panels in different areas and test the results. You might cut some of the panels into 2x4 and 4x4 pieces, depending on your room's corners, etc.

Overall there are better materials (some fiberglass, etc.) but I've found that you won't know what you need or where you need it until you've done a fair amount of experimentation.
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