Can I disrupt "A " shaped ceiling's focus with diffusion, or ___?

[garyrc]

To Artto, and all who have knowledge in this area:

I'm looking for acoustical advice, re raising ceiling ...

We found out that we can't afford to raise the ceiling of our music room the way we really want to (we would prefer a high ceiling, with a > 1foot/10feet slope, a la Jeff Cooper), because that would involve tearing off some of the roof, building a new, higher roof, taller walls, ad nauseam, ad nightmarium.

But ... the 7' 7" flat ceiling must go. It sounds terrible, claustrophobic, compared to the music room in our old house (same speakers, but with a high ceiling -- length to width ratio much the same). The room has adequate length (25 feet) and width (17 feet). I believe the reviewer who said Klipschorns sound best with a high ceiling (Klipsch is now recommending 8.5 feet or more).

Various contractors looking at it have offered to remove the sheet rock ceiling, and rebuild the underside of the roof by putting in a gargantuan ridge beam (15" or more ... they're off to consult their engineering software), removing the joists, placing insulation in-between the roof rafters, and covering all with Visqueen (the plastic membrane, not the band), 5/8 sheetrock and a plaster coat over the sheetrock.

This would leave us with an "A" shaped pitched ceiling, of moderate slope, with the Klipschorns and Belle Klipsch center channel on the short wall (of necessity, but the sound stage is wide enough, and not bad) looking down the long dimension of the room, down the channel of the proposed A shaped ceiling.

Good news and Bad News (issues):

1) The new ceiling would be be non-parallel to everything, and its average height would put the room dimensions closer to being within Bolt's contour (but not within it, because most of the ceiling would not be high enough), and the modes would be better, we think (we'll run the software, using the average Ht).

2) The ceiling would be higher, hitting 8' high about 1' out from the wall (apex of the corners with the Khorns), hitting the recommended minimum 8.5 ' at a little less than 3 ' out from the corner, and then rising to > 10.5' at the peak without the difusser/redirector I'm about to talk about, and rising to about 9' to 9.5' with it in place.

3) I'm aware that a concave ceiling is a "no-no," with the underside of a dome being the worst, because such shapes tend to focus, rather than disperse or diffuse, the sound. I can see how that would be true with a speaker in center the floor, aimed straight up, but I'm wondering if it would be less of a problem with the main Khorns in the front corners? The Belle, dead center of the short wall, might still be a problem, right?

4) I'm toying with some ploys that might or might not be solutions:

a) Covering the ridge beam (the lower part of it would protrude into the room 9" or more) with a giant convex curved diffuser/redirector -- a "Bonner" that would be maybe three feet wide, and run the full length of the ceiling, right down the center, between the crossing radiating paths of the Khorns, and directly above the path of the Belle. Are you online Artto? What, with your extensive experience with Bonner-like curved surfaces, do you think of that? Would it disrupt the unwanted focus? Do you use bent masonite? How thick?

Or ... create a Bonner shaped surface, as described above, that, for part of its length, is really Acoustone acoustically transparent grille cloth (perhaps FR 94, which is only about 1 or 2 dB below complete transmissibility @ 15 Hz), wrapped around spaced, strong and non-resonant curved wood surfaces (several spaced Bonners, with large gaps between them with the same span across the ridge beam, and the underside of the point of the "A," as above) then put all kinds of diffusers in the gaps, behind the grille cloth, perhaps with some mounted askew, aimed at the speakers. I'm thinking of RPG skylines, &/or Flutterfrees, or near clones, or similar diffusers, alternating these with Bonners over the ridge beam. The direct sound from the speakers would be at grazing incidence to the grille cloth, rather than going straight through, so I'm assuming that some would be reflected by the vinyl coated fiberglass grille cloth (at least it'll be curved), some absorbed, and some transmitted to the diffusers beyond the grille cloth.

What do you folks think? Would any of these solutions adequately disrupt the focus, and give us enough diffusion (there will be open ended shelves attached to some of the walls, with books and art objects, and a few wall mounted diffusers, and absorbers if necessary)? If we had to choose, we would prefer slightly live (and diffuse) to slightly dead (and diffuse).

Any other ideas? We are open to suggestions, reactions, articles relating to what to do about "A" shaped ceilings, etc.

Thanks,

[gaspr]

Hi Gary

Ther is a forum at www.musicplayer.com where a bunch of acoustics gurus hang out. bet you could get lots of good advice there.

Garth

[mas]

While it may not directly address your particular need and/or desired aesthetic result, may I suggest the use of a particular technology that is elegant in both design and results.

Russ Berger has designed a spatial diffraction grating that has several useful applications.

As marketed in conjunction with Aurelex, the SpaceArray diffusor is based on a quasi-random series that provides superior performance without visual patterning. It is a very effective for its intended purpose. And an even more useful design is the Space Coupler - essentially a SpaceArray minus the filler in each cubicle.

These frames (the Space Coupler diffraction grating) could be easily made for home use and the Arrays could be easily constructed using the grating filled with pieces of styrofoam cut to snugly fit into the individual cubicles at their corresponding heights to create the appropriate well depths.

The usefulness and effectiveness of the grating as a diffraction grating was discussed by Russ and measured this past February in Dallas at the TEF seminar. And they work amazingly well! This grating, which is simply panels of empty squares ~2in x 2in x 2indeep are not filled with any absorbtive or reflective material. You might think of this as being similar to a larger scale grating used for overhead flourescent lights.

It allows 90 degree waves to pass unimpeded, but waves with incident angles greater or less than 90 degrees are reflected in the well and are either diffused into the coupled space (creating a very diffuse 'manufactured reverberant field' for a small acoustical space), or diffused back into the environment. This presents myriad uses as either a surface treatment (as most of the incident waves would be >< 90 degrees) or as a simple diffraction grating that is excellent for use as a suspended ceiling that allows for the use of the coupled space above while minimizing beaming and uncontrolled reflected sound.

It is a treatment that can be used without allot of discrimination, UNLIKE other absorptive materials whose use is very specific in order to achieve a desired result. Meaning, that it has allot of beneficial uses without many potential negative affects! Additionally, the pass-through characterisitics of a suspended grating present MANY potential uses, and if the asthetics of your application allow it, it would easily tame many mid-high frequency problem areas.

This concept is a welcome and very practical tool that has many applications. And it is also rather easily reproduced in a home shop.

Of course, LF treatment modes still require the use of traps and more fundamental techniques not addressed by simple absorption and/or diffusion techniques.

More details regardiing the concept and the commercial product are available at http://www.auralex.com/partscience/spacecoupler.asp

SpaceArray&SpaceCoupler.pdf

[DrWho]

It's cool to see more people getting involved with acoustical treatment - it certainly makes a world of difference.

Are you expressing concern with the proposed cieling redesign? I am confident that it would be a huge improvement over your current situation. I have also been in many dedicated listening rooms with a similar cieling shape and there was nothing inherrant about it that made things sound bad. In fact, the listening room at the Klipsch facility in Hope, Arkansas has a cieling very similar to what you describe.

As far as actual acoustic treatment...I would wait until you can hear what needs to change. Better yet would be to obtain an ETF and measure what needs to change. Aim for a flat power response and an RT60 around 300ms. I wouldn't worry so much about the peak itself, but rather the large flat cieling that is going to reflect sounds down from the other side of the room; the front right speaker will bounce off the left side of the cieling and hit you in your left ear (tis a rather crude analogy).

welcome to the forum.

[garyrc]

Thanks, everyone!

Mas, you mentioned that the effectiveness of the Berger gratings was measured at the TEF seminar in Dallas. I would love to take a look at those results. In fact, since it is impractical to get a large enough number of diffusers into our room to assess their effect by ear (before buying or building them), it would be great to get copies of test results (or verbal descriptions of same) of the range of frequencies diffused, and the pattern or angle of coverage and dispersion of the diffusion, for a few contenders, like the Berger diffraction gratings, the RPG skylights, Flutterfree, etc. Do people test these things the way some people test speakers? I guess I'm looking for information something like "at least xxx degrees of dispersion of frequencies from yK Hz to zzK Hz, when the angle if incidence is between aa and bbb degrees.

Any idea where I would look for this information?

The Berger gratings certainly look less obtrusive than the skylines, so it would be neat if they did as good a job. Hope so.

Does anyone know if the Space Coupler can be used successfully when it is only spaced a little way out from a surface, rather than over a cavity, or in the door aperture of a closet? I'm thinking of mounting a few with about a 1" or 2" space between them and the wall, and others about 15" from another wall.

[PrestonTom]

Gary,

You are asking a tough one.

I assume there are aesthetic issues regarding how you treat the space. Absorbtion, esp at the low, and very low, frequencies is probably out of the question. So diffusion is certainly appropriate. You are on the right path, but let me suggest that you also consider using pendants that hang from the ceiling. They can be oddly shaped and made of reflective materials. Hang several of them, at different heights (relative to the ceiling). This can help break up the waveform so you are no longer getting a coherent reflection. Importantly, with a bit of creativity you can probably get something that will blend into the room's decor.

Good luck & post some pics,

-Tom

[mas]

Regarding the Space Coupler style phase grating...<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

I have to admit that I have become quite enamored with this design. It is elegant in its simplicity and quite effective in a wide range of applications to achieve a variety of desired affects. Plus they can be more easily emplyed so that your home does not end up looking like the Museum of Modern art.

Garyrc: They can be applied directly to a surface for diffusion. It can be applied with spacing away from a surface and the diffusive effects increase, as a portion of the signal is reflected through the grating and it bounces about until the incident angle is such that it reemerges - darn this sounds like doubletalk without a simple draw tool!

And here is an ingeneous technique pioneered by Russ especially in such venues as the ever shrinking home studio. If the coupled space is larger (such as a crawl space, adjoining room, 'attic' space above a suspended or fixed ceiling, the additional time that the waveforms 'bounce around' and finally reemerge through the phase grating results in a 'longer' trailing (and correspondingly lower intensity) diffused field - thus, depending upon the volue of the adjoining space, effectively creating an artificial reverberant field that is impossible to achieve in a small acoustical space. The result is an acoustic space that performs as if it were a larger space, while utilizing otherwise 'unusable' space.

And while my intent is not to sell anything nor to tell you to avoid buying these products, an ingenious individual could easily fabricate many of the RPG and space coupler/array designs for their own use....as they are quite expensive! (figure ~$200 retail for one 2'x2'x3" space coupler!!!! Cheaper than many, but ouch!)

Just like making plantation shutters, a few hours fabricating a router jig and an hour more routing and wella! And its prime for a first time hobbyist! Also, a CNC would make short work of these, and they could be made in a myriad solid, veneered, MDF formats for natural finishing or painting. And for home use, readily available inexpensive 4x8 sheets of luan would be ideal. And I would use Styrofoam blacks cut and inserted into the grating with a pressure fit to complete the arrays. The blocks could easily be faced with any number of maerials, be they veneer, fabric, or other desired finishes.

...Regarding the measured specs - we were playing with a variety of toys and Russ happened to pull out a few of the then soon to be announced arrays and couplers. And we had the opportunity to shoot a mess of configurations in the demo & workshop as well as shoot the breeze over lunches and dinners for several days...so I don't have them recorded in any coherent fashion. Suffice it to say that the empiracal results were great! they are sufficient in themselves, leaving only LF traps as a missing piece. Please allow me to digress from my digression and elaborate just a little bit here. The diffusers work great where one would normally install absorption. In all but the nastiest situation, the diffuser will diffuse a hard reflected signal so that the result is no longer of sufficient intensity to require absorption. Of course, if the signal is of sufficient intensity to still require absorption, that is always an option. But it is rare in general applications.

But you raise a very good point. Let me check into what I can do to obtain them! (They are most generally available in a library form for importation into such programs as EASE or CATT as opposed to being stand alone.)

And yes, the measurements are taken just like the polar measurements are taken for a speaker...in degree increments over an ~ 180 degree arc. In the case of pass-through, the reflected response (reverse side) will be a mirror image of the front. This can become much more complex than it sounds depending upon the precise resolution you desire as you are adjusting not only the incident angle of the source signal, but also the angle of the reflected measurement mic - so a sound field array is a NICE tool to have if you don't have 6 months to measure each sample![]

But it is very easy to dial them in with a few measurements and extrapolate between them in order to establish a useable trend analysis.

The neat thing about the coupler and arrays is that, unlike many treatments - and I refer especially to absorptive treatments, it is hard to screw anything up with them. No mean feat! You may reach a point of maximum effectiveness and then, if more are applied, a point of diminishing ROI, but you are not going to negatively impact the room acoustical response! And its not often that you run into that scenario! The reason is that a well behaved diffuse sound field is a very nice thing! In such an environment, (assuming a nice decay - hence 'well behaved') you really only need to identify and address 'hard' (focused) reflections. These can be diffused or absorbed as necessary. And time based measurement tools make this a very hit and run affair.

Oh, and one more thing...These can be covered with an acoustically transparent fire retardant membrane if you desired to hide the slightly modern art appearance. And if a natural finished wood or painted 'textured' surface appeals to you, the grating could be applied directly to the extended ceiling surfaces, leaving only the LF modes to worry about.

Let me do a bit of checking and I will report back. But if you are considering such diffusive 'tools', I would not hesistate to tell you to go ahead.

Oh, and yes, I emphatically agree with the Doc. Time based measurements such as are afforded by such tools as ETF, TEF and Easera are definately worth their weight in gold! Not only do they offer you tools that can take you even further in this porcess then just the surface treatments, but it is certainly easier to get where you want to go when you have precise reliable tools to tell you where you are as well as to confirm when you have arrived! Although they may take away some of the fun [][][]

[mas]

OK...regarding the measurements for Russ' baby...

The exhaustive lab results were expected mid-August,soooo...hopefully within the next couple of weeks... Ron Sauro is doing the elaborate tests at NWAA, so they should be forthcoming soon, and apparently Ron is in the middle of debating how absorption testing should be conducted and whether one or multiple dodecs should be used to stimulate the materials...so...'ain't acoustics grand!? Unlike so many other sciences where most of the characteristics have been well understood for 100+ years, acoustics is still in an ongoing period of discovery!

We have kind of jumped the gun on the grating and arrays, as they are that new. Although Russ has been employing them for some time now in his designs. So they are proven.

And as I realized that I did not address at least one important aspect that should be rather obvious...[], the gratings can be use as diffusors where the angle of incidence is primarily greater or less, but not equal to 90 degrees! This should be pretty common sensical as they act as a pass through at that angle (90 deg)! Thus putting them on the back wall to act as a diffusor would be rather silly. Here you would definately want to use a broadband diffusor such as the array. []

And RPG is closed for the week, so I will followup with them next week..

I guess I should shut up and get back to the work I am supposed to be doing!

[garyrc]

Thanks, mas!

I'll look forward to hearing about the results of the tests that are being done now. If you are enjoying it, stay in the loop, but I don't mean to ask you to keep watch on this research just to meet my needs. If you have any websites or shareable email addresses I can use to check on the results in September, or later, I'd be glad to do so.

Thanks again

[mas]

Here is the link to Auralex and the specific products:

http://www.auralex.com/partscience/spacearray.asp

http://www.auralex.com/partscience/spacecoupler.asp (Application Note: Please notice the picture of them being used as a part of a suspended ceiling application as a space coupler - just be aware that they work great on wall/ceiling surfaces as well, as long as the incident waves are not at near 90 degree angles - so you don't want to use them on back wals or immediately adjacent to the speakers - the array configuration is optimal for that, with absorption needed Only for intense focused reflections. And that could easily be surgically applied After the room was nearly finished and a few measurements were available.)

Regarding the data: I have an interest in the test results as I am waiting for the importable data library for use in EASE.

And for a bit of my rambling:

But as far as the practical aspect, they are already well proven with years of use in Russ's projects. And they are as effective as the alternatives from RPG, etc. - and that is meant as HIGH praise! ...As like Russ, Peter D'Antonio's work is Always first rate!

Bottom line, they are effective as broadband diffusors and intended for use as part of an 'integrated system/package'.. For LF you Want to use bass traps, and there are a number of topologies for traps that you can chose from ranging from panels to wedges to tubes, as no wall surface treatment is going to effectively address them. OK, let me qualify that and save the Doc from having to do so...[], no reasonable wall surface treatment that anyone desires in their home is going to effectively treat the LF modal issues!

The test results are not needed to validate the actual effectiveness of the product...as they have been employed in real world high end applications for sometime. Rather they are for marketing purposes for the commercial product on the one hand, and more comprehensively, they are needed as data libraries for their incorporation into room modeling programs such as EASE (or CATT), as the data will be provided in 3D volumetric cloud form, thus allowing accurate modeling of very complex large acoustical space integrated room/speaker systems.

Who cares, I can hear most saying...and you are right! The point is, I would not hesitate to personally use the techniques now as they are a proven commodity that has simply not been heretofore commercially available at the retail level, but you are most certainly entitled to see the results for yourselves!

But if someone had the initiative, they could be easily fabricated yourself at a very high level of craftsmanship for a very small cost, thus saving ALOT of money! Hint hint! Was that 'subtle' enough! And who can't benefit from 'alittle' cost savings!

OK, I think I got the rambling bug out, at least for the moment...[][]

If anyone has questions or more ideas, please feel free to PM me. I can also be reached by IM or phone if I haven't already scared you away![]

[artto]

While a ceiling height of 7-7 is not good, sometimes the mind can be fooled, and when the mind can be fooled visually, I can usually be fooled aurally as well.

<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

A number of tall guys like Forum member John Malotky who have visited my music room have been surprised when I told them the rooms ceiling height, and they reached up and found they could actually touch it! The visual illusion can be a very powerful thing. Light, reflections and shadows, and how objects in the room are arranged can contribute greatly to our perception of the space and sound.

In my room, (arttos klipschorn room thread, Architectural section) youll notice that in its current incarnation there are numerous vertically orientated convex polycylinder diffusors. Their vertical orientation, in combination with recessed lighting highlighting the curves and a plain white ceiling make the room appear much higher than it actually is. Most people seem to think the ceiling is between 9 & 10 high when in reality it is a standard 8 ceiling. However, because of the heavy carpeting/pad and thicker ceiling drywall and additional Celotex rigid insulation to reduce sound transmission from the rooms above it actually comes it at around 7-10.

The other thing to consider here is that because of the polycylinders, sound is diffused in an essentially random manner in all directions, including the ceiling, thereby reducing the need for substantial ceiling treatment or modification (angle). The main issue here is the height and radiation angle (polar response) of the tweeter, which in the Khorn, is close enough to the ceiling in the typical 8 high room to cause some interference anomalies between the direct sound from the tweeter and the reflections off the ceiling. Probably the best way to spot treat this would be to use one of the more recent sophisticated diffusor designs like the RPG Skyline 2-dimensional diffusors which are relatively shallow (7 and 4 depth) or, since we are concerned primarily with treble frequencies here, a thinner open cell acoustic foam product such as those from Auralex, or even small acoustic tiles made from Celotex or Homosote rigid insulation could be used. These would be placed on the ceiling at the location where you can see the speakers reflection from your listening position in a mirror placed/held on the ceiling.

Will the angled ceiling produce the best sound result? Of course it will! If youre lucky enough to be able to make the modifications without structural changes then it might be worth it. If you have to make structural changes, but you have the space, you might be better off just building another room (addition) which will add more property value in the long run.

http://www.silentsource.com/diffusors-rpg-skyline-lp.html

[artto]

Regarding the Space Coupler style phase grating...<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

Plus they can be more easily emplyed so that your home does not end up looking like the Museum of Modern art.

As an architect, musician, and audiophile, I can think of nothing better that I'd want my home, especially my music room, to look like. []