Dropped Ceiling and Subs

[KdAgain]

In another thread on dropped ceilings it was suggested not to use a "Potent Sub" in a room with a dropped ceiling. Unfortunately our Khorn room has a dropped ceiling (7') and we are stuck with it. I'm interested in the effects it has on low bass as we plan to get a large sub in the future?

Thanks,

Rod

[picky]

KdAgain: We have a huge, Klipsch RSW-15 Sub and RF-7s in our tiny 10.5' x 19' x 7' theater with a suspended ceiling and we have no buzzing or rattles at all. In fact, our ceiling provides 90% absorption. The trick is to avoid the use of typical ceiling tiles and go with acoustic foam tiles that are made for sound-proofing rooms. In our case, we went with flat black, 2" thick melamine foam (has a Class 1 commercial fire rating) ceiling tiles made by Illbruck Sonex. The are called Contour Harmoni Ceiling tiles and come in a varierty of colors and patterns. I've attached a PDF brouchure for you to download. I hope this helps. They make our room sound awesome and no noise from the ceiling at all and we have lots of bass in our room! I don't feel "stuck" with the drop ceiling; I prefer it! -Glenn

Contour-Tiles.pdf

[KdAgain]

Glenn - Thanks very much for the informative response and the link to the good tiles. I guess the two issues with typical dropped ceilings are 1. Rattles at the support connection points and 2. Very nonlinear frequency absorption. I'm not sure how you avoided the rattles, unless it's a result of the extra weight of your panels. In looking at the absorption characteristics of your panels they don't appear to be very linear, but perhaps much more so than the typical panels.

Glad to hear that you are very pleased with this approach. It looks a little pricey, but you must feel the extra cost is justified. With so much absorption in the ceiling does the room sound at all dead? Also with our Khorns, I think it's recommended to have high ceilings. I have been concerned about any effect our present panels (at 7') may be giving, and wonder if the sound-proofing panels might lessen the ability of the Khorn to 'fill' the room. BTW, our room is only slightly larger than yours.

Rod

[formica]

I guess the two issues with typical dropped ceilings are 1. Rattles at the support connection points

Generally that would be my main concern at higher listening volumes... but you can purchase spring clips (installed above the tiles) which reduce this problem... as well as the fact that not all tiles react the same way.

2. Very nonlinear frequency absorption.

I don't know about being "very non-linear".... it's normal for the absorption coefficient to drop as frequency drops, as it is for any accoustical treatement of limited thickness. I don't know your room responce... but with tall kHorns and low ceilings, i'm guessing you'd be getting quite a bit of mid - high frequency relections off you ceiling... which happen to be the frequencies accoustical tiles could treat quite well. With the right tiles... your accoustical ceiling probably helps in making your ceiling appear accoustically taller.

ROb

[WMcD]

For what it is worth.

The elevator bay outside the office where I work had a dropped ceiling and carpet.

I've read that typical ceiling tiles and carpet don't have enough acoustic properties to solve problems.

But, recently the landlord is redecorating and the dropped ceiling and carpet were torn out during construction. Gosh. that area became an echo chamber of impressive power. So I conclude that they were solving treble issues.

My overall thought our hard rooms have such poor treble that anything makes them a bit better. That is a much bigger problem than bass.

Wm McD

[picky]

Rod: The extra expense was warranted in our case. The tiles, coupled with membranes I installed in the walls, made our room really work. In fact, the tiles helped more significantly than anything else to improve the sound. The ceiling works so well and no, the room is not dead. The sound comes right at you without being too bright and the ambience implied by the movie's surround channels really creates a believeable, virtual environment; which is what the producers intend to happen. It simply works even at very high volumes where I have measured up to 124 db peaks during the movie 'Behind Enemy Lines' at 12 feet from the front array. The tiles are made to slightly protrude down below the grid. That, coupled with their weight, eliminates all rattles at any volume in the ceiling. No clips or springs needed in our case. -Glenn

[WMcD]

Continuing here with some two cents.

I am assigned to to a fairly small office at work which has a suspended ceiling with glass on the east wall overlooking the Chicago El. But it is a very big suite. The somewhat beat up Forte II's sound great with solid bass (only played on weekends of course).

The very favorable performance seems at odds with "small room" theory. But then I stood on the desk and poked around up above the tiles and considered the actual physical structure of the "room."

The sheet rock walls go up eight feet. There is a three foot tall area above the suspended ceiling up to the slab of the floor above. The ceiling area extends about 25 feet north; extends only to the wall of the building to the east at the windows; extends about 45 feet to the west, and then extends probably more than 100 feet to the south.

So for bass purposes, I'm not in small room at all. More like in a cubical formed by the sheetrock walls up to 8 feet. Then there is a huge volume.above. If it is possible to calculate room modes, the dimensions are very large.

My thought is that anyone with a suspended ceiling might consider similar issues. Just what is above and how far does it extends.

Wm McD

[LarryC]

Gil, a few decades ago, I read that the SPACE above a suspended ceiliing has frequency absorption qualities of its own, namely the lower middle range and/or upper bass. And, indeed, a SUSPENDED ceiling takes out reverberant chesty sounds, which goes a long way toward cutting down the strong echo effect. The tiles themselves only handle the highs.

The difference is heard when tiles are glued directly to the ceiling surface without the space above them. The LMR/upper bass resonance is not knocked out the way it is with suspended tiles. The highs reduction seems almost irrelevant.

I think the same kind of absorption may occur in a car with a separate trunk compartment. A wagon without a separate compartment seems to have a boomy quality.

Larry

[picky]

In adding to what Gil and Larry have expressed, our room's "large volume" happens to be an adjacent open stairway up to the side door landing and first floor kitchen and the remainder of the house. Below is the room's response curve measured by Dr. Who. Measurements were taken at the room's primary listening position (sweet spot) approximately 10 feet from the front array and slightly off-center. All sealed doors to adjacent rooms (they have exterior, bulb-type weather stripping and the utility room also has an industrial, noise-blocking brush along its bottom gap) such as the bathroom, office and utility room were closed and the stairwell was open during measurements. Measurements were taken again with the doors open and there was barely much difference in response noted but the changes were in the bass region as expected. Sorry, I do not have a copy to display for comparison.

Room driver complement: 2-RF7s (front), 1 RC-7 (center), 2 RS7s (sides), 2 RCW-5s (rear) and 1 RSW-15 (sub). Room dimensions are 10.5' W x 19' D x 7' H (6.6' average H). -Glenn

[garyrc]

I have heard that the problem with low ceilings and Klipschorns is that the low ceiling provides a too early reflection of the tweeter sound, which is ahead of (closer than) the midrange to begin with. Heyser (?) alluded to this in his otherwise positive review in Audio a couple of decades ago. With a high ceiling, the other good qualities of the Khorns outweigh the drawback of the midrange and tweeter not having their diaphragms aligned (i.e., not in the same plane), but with a low, bright ceiling the early reflection plus the nonalignment add up to a small loss of clarity. Heyser recommended a high ceiling plus a thick rug to alleviate this problem.

Now, I imagine that if you were to find those first reflection points on the ceiling as seen by having someone stand on a ladder and press a mirror on your suspended ceiling and move it around until you see the reflection of the tweeter/midrange unit in the mirror from all your listening positions, then attach some highly absorbing material on the ceiling in those places, that might lick the problem. The 4" thick Sonex foam made of many anechoic wedges comes in many colors and works from 400Hz (where your Khorn mid starts) on up to the top ... thinner Sonex would start absorbing at a higher frequency on up, and might be fine for absorbing the tweeter bounce only -- either 4.5K up or 6K up, depending on what vintage K-horns you have. For one basic listening area you would need the two relevant areas on the ceiling covered (one for the line from each Khorn), and for several, several.

Another solution I've heard of (that does not take up space in the room) is to remove some of the panels from the suspended ceiling (the ones in the early reflection spots) and replace them with some highly absorbing pads covered with acoustically transparent fabric either of the color of the ceiling, or some other color of your choice ... one guy had a sort of checkerboard pattern on his ceiling. The pads themselves might need to be attached to some kind of backing to avoid sagging and just placed up there in the space just above the ceiling, sitting on it, or spaced (hanging) above if you have a way to do that. The pads could be made of the Sonex anechoic wedge material, or on of the competing absorbers, or ____?

While the above and a thick rug might be helpful, you would want to be sure the room as a whole is not too dead .... a dead listing room sounds terrible. The good news is that Khorns (due to their corner position and "controlled directivity" horns deliver a little less midrange and treble to the side walls than many speakers, so you might not need absorption there. For the rest of the room, you might want diffusion, rather than absorption .... Commercial or home made diffusers, 3 D decor, artifacts, sculptures, bookcases, whatever.

[jacksonbart]

Well that is a heavy load to carry all by yourself, Hope they didn't land on your foot.

[KdAgain]

Glen, Rob, William, Larry, Gary, & Jackson,

Thanks very much for all your interesting and informative posts on this topic. I'm still trying to digest it all, but it seems that the dropped ceilings may not be a negative as I had thought. Or as Glen said it may be a real benefit! Glen you mentioned that your room doesn't sound dead and with the surround speakers it sounds great. Have you done much two channel listening in that room? I am wonderingif it may be a bit dead without the surrounds. BTW I checked your website - what a fantastic job you have done!

Interesting observations about the space above the tiles being helpful. In my case the ceiling is 7' 3" up and about a foot more to the bottom of the joists. Then another 10 or12" up to the subfloor. Way less than the space above Williams office, but probably much more helpful than if I had a sheetrocked 7' 3" ceiling. As far as the mid and treble early reflections, it would seem that this system would absorb some (even with my standard tiles) and then diffuse most of the rest at the joists. If this is the case i wonder how beneficial more absorbent tiles would be?

As frequency drops the tiles probably become more transparent and I am then only getting diffusion at the joists. Then some diffusors on the walls would make sense.

It would be great to hear from some Khorn owners with dropped ceilings and their take on all this.

And finally, JacksonBart - what can I say.......

Rod

[WMcD]

It is very interesting to read all of these comments.

I can believe that ceiling reflections of treble events per Garyrc.

It is intersting that the earlier CW with a vertical horn are favored. It seems to me that the exit angle takes some of the mid signal off the ceiling and floor.

Also I had posted the Audio article on the tractrix horn by Klipsch engineers. It seemed to me that the larger vertical size cut the pattern headed toward the floor and ceiling.

- - - -

I like Picky's decription which describes that rooms have added volume for bass. And Larry has some very good observations. I wonder if he is describing the suspended ceiling as a diaphragm type absorber. We see bass traps like that on a smaller scale.

- - - -

I'll again comment on my questions about how room node (mode) calculators can predict much of anything if there is a big passage way communicating to a big room volume which could triple the effective volume and really mess up an elementry theory of parallel walls.

- - -

At the risk of repetition. I have a bathtub enclousure with sliding glass doors about 4 feet tall. All hard surfaces of course. With the doors closed, it is an echo chamber when listening to the Sony tap tunes. If I slide open a door about 12 to 18 inches, there is a very radical change for the better.

The opening created is probably 10 percent of the surface area of the echo chamber. It is probably a totally anechoic opening for our purposes. .

My thought is that we can scale the experiment to larger rooms and bass freqs.

Wm McD

[garyrc]

If a small area of the ceiling -- a first reflection point re the tweeter -- needs more absorption than the rest of the ceiling, than I would think something softer & thicker than tiles would be better, especially if it has small anechoic wedges to catch & trap the high frequencies.

As to diffusion, what is diffused depends on the relationship between the dimensions of the protrusions, wells, what-have-you and the wavelength of the sound to be diffused --- at least that's what I've read; I'm no expert. The treble wavelengths that may account for the Klipschorns' preference for high ceilings are short, and might be diffused by objects ranging from less than an inch deep to about 8" (I think 8" may be the maximum depth of the "buildings" on the famous "cityscape" diffuser -- or not). You want the first reflections from the tweeter to be either absorbed or to go all over the place so that each little splinter of a reflection is much less intense, and so most of them don't come at you, but go elsewhere and return to you -- if at all -- via a much longer path, bouncing off other surfaces, becoming softer each time, and becoming more random in spectral characteristics over whatever band is reflected.

I think only the bass and mid frequencies are going to get to your joists and get back, having to pass through your ceiling tiles twice. Bass can go through practically anything .... when we used a RadioShack sound pressure level meter measure the intensity of the timpani, large bass drum, and huge Tam Tam on Crystal Clear Recordings version of Copeland's Fanfare for the Common Man (the best version I've heard), the needle peaked briefly at 110 dB (which may mean there were unread peaks up to 13 dB higher according to PWK), and DID NOT CHANGE when a fleshy hand was pressed over the microphone totally sealing it ... using two hands did not lower the reading either!

We used to have our Klipschorns in room with a ceiling that went from 9 feet to 14 feet in height. They sounded gorgeous. We moved, and the Khorns are in a room with slightly less than 8' ceilings. The music did not sound as good. Putting absorption at first reflection points on the ceiling DID help but the room sounds a little too dead now. Since we are finally going to make it into a Home Theater, as well as a two channel room, and we are renovating any way, we are going to raise the ceiling.

[LarryC]

I wonder if [Larry] is describing the suspended ceiling as a diaphragm type absorber.

I don't think so, as I was thinking of the standard ceiling of acoustical tile held up by T-xsection runners. Perhaps auto trunks have a diaphragm effect. Subjectively, it feels more like a resonator effect to me.

[picky]

Glen you mentioned that your room doesn't sound dead and with the surround speakers it sounds great. Have you done much two channel listening in that room? I am wonderingif it may be a bit dead without the surrounds. BTW I checked your website - what a fantastic job you have done!

Rod: Because the ceiling is surrounded by drywalled soffets along most of its outside border (except for in the area of the screen) there is sufficient reflection to prevent the room from sounding dead, even when doing some two-channel listening. I still enjoy spinning my vinyls once in a while, too. I do know because the room is small, it could use a but more echo time, but no; it never sounds dead. I am sure the tiled, concrete floor helps with that. -Glenn

[picky]

If a small area of the ceiling -- a first reflection point re the tweeter -- needs more absorption than the rest of the ceiling, than I would think something softer & thicker than tiles would be better, especially if it has small anechoic wedges to catch & trap the high frequencies.

Gary: In reference to my suspended ceiling: The only real similarity it has to typical ceiling "tiles" is the name. The "tiles" in our ceiling are 2" or 2-1/2" thick, soft, melamine foam. They are more like thick inserts than tiles and work beautifully without the room sounding dead. The company that makes our tiles does offer designs with various protusions. We prefered a smooth look and they are still very effective without the contours.

The room also benefits from some diffusion provided by at built-in, 4-shelf bookcase I built on the adjacent, right-side wall. I have the books dressed near shelf edges to provide varying voids behind all of the books; thus providing some diffusion I suspect. -Glenn

[KdAgain]

Gary, Glenn, Gil & Larry,

Thanks very much for your well thought out and helpful posts. And sorry for the belated appreciation here!

I'm a few months away from rearranging our listening room to put the Khorns on the long wall. We are presently using the room for other purposes and will have to postpone any acoustic improvements until the change.

But you all have given me lots of food for thought. I may want to try some of Glenns panels for the first reflection points per Garys suggestions. Perhaps will also experiment with some diffusion. Later when we get a subwoofer some bass trapping will probably be needed to control room nodes.

Overall it has been really good to hear that the suspended ceiling is not the big negative I feared it was.

Rod

[colterphoto1]

I will remember to my dying day Glenn saying, as he shut the doors to his theater 'you're going to feel a change in the air pressure'!

Then he played that IndyCar bit with the Andretti's with me in the chair right in front of the RSW15 and my insides got all jellified.

[ka7niq]

have suspended ceilings, with ceramic tile recently instelled.

Room sounded WAY better with carpet.

Question ???

Will placing or stuffing fibergass above the ceilinng tiles help deaden the room ?

Things sound echoey now. almost like processor is stuck in a surround mode ??

Dont the ceiling tiles have to be porous for sound to go through them ?

If so, what good will fiberglass do ?

Thoughts ??