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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
newbee
4,751 posts
 
Dumb question time - Where are you standing when you slap your hands? If your not at your listening position it probably doesn't make a difference. Have someone stand where you have placed your speakers and clap their hands while you are seated in the listening position and see what happens.
flex
292 posts
 
I don't agree with Newbee. Flutter echo makes a difference anywhere in the room, since sound reflects from all of the surfaces and combines into what reaches your ears.

The source of flutter echo is usually easy to locate. If you walk carefully around clapping, you may pinpoint the exact place where it begins and ends. Open hallways, or reflections between ceiling edges and untreated hardwood floors are typical sources. You can check floor-ceiling bounces by putting thick towels or rugs down on the floor and see if that kills it.

In my setup, I've found that foams and absorbers on the ceiling can do too much absorbing. Diffusors at either reflection point work equally well and, in fact, better than absorbers. So you might experiment with RPG or other diffusors, as well as rugs, bookcases and the like when you identify the source.
flex
292 posts
 
One other possibility for your room shape might be reflections between the back and front walls (behind the speakers vs. behind the listener) up near the ceiling. You can tape towels or cloth on the walls to check.
gnobber OP
43 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 . . .
newbee
4,751 posts
 
I'm not sure I have a solution, but I have an experience to share which might bare some light - I worked in an office with a high pyramid ceiling. The sound all along the outside walls (the executives offices) followed the roof line and focused at the cented and beamed down in to the center of the office (the secretarial pool). Boy was that fun!. So its possible your hand clap is bouncing off the ceiling and due to the distance travelled it would be clearly heard. Try the hand clap experiment with a piece of deadening materiel held between the clapper and the ceiling. If you don't have an echo you've found your problem and can focus on what you can do to fix it....keep us posted.
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