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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
4,778 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.
theaudiotweak
2,801 posts
 
I recently have fixed a room such as the one you describe.You probably have a foam pad under your carpet. Replace the foam pad with a natural fiber pad. The panels can be made to look like large eyebrows high up on the wall behind the speakers. They can be designed to follow the angle of the roof line and can be covered with cloth to match the painted wall. You can do much the same for the rear panels as well. These panels need to be about 6ft in height and 24 to 36 inches in width, the bottom of which should be placed slightly above the television that is compounding your problem. Better than fiberglass is natural longhair carded wool. The wool is much more linear in its absorption rate than fiberglass..Wool has less suckout and will give you smoother overall response. The problem is on your walls and not your ceiling. The problem is above 4 ft and beyond. Tom
mejames
986 posts
 
its the upper corners of the room where the walls meet the ceiling causing the majority of the echo you are hearing trust me get the MICHAEL GREEN DESIGNS PZC corner controllers which are easily adjusted will totally alleviate the echo. Believe their is a review on Audio asylum
theaudiotweak
2,801 posts
 
Pzc controllers do not have enough surface area to even budge the problem. The angled ceiling is reflecting energy back into the listening room which is also a good thing. The problem lies between the front flat wall surface and the rear flat wall surface. Other than designing a multi angular cantilevered attachment to both front and rear walls the dampening panels offer the most cost effective approach..Tom
gnobber OP
44 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
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