Question about slat resinator

Hi, new here. First let me say how much I've enjoyed and learned here at the forum, thanks for putting this together and all the input from everyone. The only problem I think my brain is about to explode from all the info :lol: My question is more of an astetic vrs workability quary about slot resinators, I'm not a big fan of all the wood on the walls look, I don't mind it in an iso booth, and my floor has it, but I don't like it on the control room walls. I was wondering if anyone knows what the accustical differance would be to put the cloth on the outside of the slats? I'm sorry if this has been answered before but I couldn't find any refurance to it. Also, is $1 sqft a good price for 2in 703, or should I keep looking? Thanks again for all the help. Arthur

Hi, Arthur, welcome to the board - could you please take a minute and update your profile with a location? This is a worldwide resource, John is in Australia, I'm in Oregon, Barefoot is in the SF Bay area, and Aaron's in Tennessee - having a location posted just makes it easier to answer questions based more on the locale of the person asking, thanks... On the resonators - the cloth INSIDE the slats is necessary to the operation, it affects the bandwidth of the response, making it less "peaky" - you could add cloth to the outside as well, about all it would do (unless it's a really tight weave that's hard to blow through) would be to reflect a bit less highs and possibly diffuse a bit differently, but still usable for sure. The overall effect on sound in the room would be mainly a little less "sizzle", or whatever your favorite term for high frequency/treble response. $1 a square foot is typical for 703 in 2", once in a while someone finds it for less but usually it's a one-time "overstock" kind of deal. Since the stuff sells by weight, for some applications the lighter 701 or 702 may be more cost effective, but harder to find. One place where the lighter weight version can work as well as the heavier is in most broadband absorbers, especially for the surface layer in a solidly filled corner trap - When in doubt, the 703 is your safest bet though... Steve

Thanks Steve, How would Formica or some other type laminate work, you think it would be too reflective? Thanks for your time, Arthur

Thanks Steve, How would Formica or some other type laminate work, you think it would be too reflective? Thanks for your time, Arthur

I'm assuming you mean as a laminate over the slats, with the slots still there? Compared to wood, it would likely be a little brighter. If you don't like wood though, would you like formica any better? (That last was starting to sound like the old ditty, "if a woodchuck could, and a woodchuck would, how much wood would a woodchuck chuck?") Man, I must need to spend more time in the rubber room... :?

I know whatcha mean about the rubber room, that's where my wife said she was gonna put me if I don't get all this sorted out. :P I'm not sure that I'd like the laminate ether, I was just trying to think of something that might cure the sizzless problem, but your right it might be the wrong direction, I guess I could just paint :cry: course that might darken it some also, any suggestions? Thanks, Arthur

Would covering the exterior slat surface with acoustically transparent material help? I would imagine it would look good, at least. :)

Try a broadcloth type material.

Arthur, I'm not sure I understand what you're going for here - what kind of "look" do you envision for the room overall; and, are you trying to visually make the slats disappear without affecting the performance? Without more info on what you're after, we could be here for quite a while... Steve

it seems that is his goal steve. Of course I could be wrong. :) Sorta like this preacher I used to work for. Wnat to be heard but never let him see the speakers. we got real creative with hiding monitors and stacks :)

Right on Bryan, I like the cloth look, I don't mind having the wood on the back wall for say defusors, I just didn't want it on the front walls also. My room may not be big enough (17x14x8) for it to work like that, but I was just trying to seek out options before I start framing for my panels. Since my main goal is a mix room, wood may be my only option accustically. Like I said before, it's more of an astetic thing for me, since I'm the main engineer I want to be surrounded by a room that I like with both sound and looks. But my size may dictate some of that. Steve,I hope that helps clearify a little better, sorry. :? Thanks again for all the input. Arthur

Hey guys, what is the yellow insulation in these pictures? http://www.johnlsayers.com/Studio/Pages ... ions_3.htm Is that Duck Board? I thought I had a handle on building these, but the picture of the back wall shows this material about half way up, and I don't quite understand why it's there and not just the rockwool. Am I missing something :?: Thanks, Arthur

The yellow stuff is Owens Corning 703 - http://www.owenscorning.com/comminsul/p ... &system=80 The other stuff is apparently one of the mineral based products, similar in performance but made either from "spun rock" or slag from a steel mill, sometimes a mixture of the two... Steve

Thanks Steve, sorry I guess I wasn't thinking in terms of mixing the products, duhhh. :oops:

Hi great tread again as usual. I saw the pic´s from Silvia Studio project, see short cut. http://www.johnlsayers.com/Studio/Pages ... ions_3.htm My questions are is there any limit on the length of slats over the wall studs, (the inner frame)?? Thought normally a CC 600 mm with 2"X4" studs. Second is it recommendable to have the slot width as tiny as 0.5 mm (just ask to get a more LF absorber and save on the depth). Third, Any idea if it is any good idea for me to calculate with different slat depth in the same slat resonator, f ex. 12 mm, 22 mm, 28 mm, 45 mm. Just want to know what I have not seen yet at this forum, I might be here but too hard to read it all, (brain overload collapse). Last if the slat width alter from one end to the other in a slat resonator on the same slat, f. ex 45 mm up to 145 mm at oposit end of the slat. Any idea if this is tested and posible to make it work as the normal design, (nearly), I just want to know this as I can se eastethic opportunities with that option. If I´m clear as mud please bear with me, just using my second language. But in acoustic area of engineering think the techincal Swedish language is equally hard to understand for me anyway. Thanks for any easy explanation if any of above things are known to you. I will make a sketch of my designs after any positive feedback, re: eastetic look, in my opinion. PS Down loaded the Slat Hz calculator and noticed that the Insulation was mounted flush to inside of the Slat Resonator slats, in the drawings from SAE, (guess it is Johns design) are the insulations left with a air cavity between slat and bottom (back of trap), Are there any improved performance or is this neglectible in reality.

Slat length unsupported should be kept down, 600mm is probably plenty long - although slats can be felt to vibrate during use, this is NOT the goal but a side effect. Longer spans may conceivably aggravate this "side effect" into a problem of ringing, but I've not done any experiments in this so at the moment it's conjecture on my part. In actuality, a helmholtz absorber, whether perforated or slatted, is calculated on just the parameters listed in the spreadsheet and any flexing of materials is ignored in calculations - ideally, the frame and slats would be made of marble or concrete and would not flex at all - the effect is gotten through the dimensions of the air space, the restricted entry INTO the air space, the cloth behind the restriction, and the insulation smoothing out the response so that it's less "peaky" - I've got a whole lot more study to do before I can explain much more on this part; I did see briefly in Cox/D'Antonio's new absorber book that the cloth behind the slats is fairly critical, both in positioning (up against the slats) and in gasflow resistance (need more research time on that one) As to 0.5mm slots, I've not tried that either - I did ask John a similar question, and his experience has been that slots don't work well at that low frequencies. Besides, considering wood's tendency to change dimensions with aging, it would be nearly impossible to maintain such a narrow gap within workable percentages (if a 3mm gap changes by .5mm, it's less than one musical note change - if a .5mm gap changes to 1.0mm, it's more like half an OCTAVE. Add to that the difficulty of finding spacers and installing with that close a gap, and it becomes pretty impractical. On variable depth of air space - Barefoot brought up what I think is a valid point - unless the absorber is large relative to the wavelength of the sound, it would tend to average out. So realistically, the main advantage of a variable depth absorber would be its RFZ enhancement, with a secondary effect of probably a bit of smoothing (lower "Q") of the response, which generally is a good thing. Barefoot suggest that if more variation was wanted we might add sealed dividers between sections of such an absorber, so this averaging was limited to within the section. Generally, I just take the average depth and use that in the calculator. Variable slat width - this would fall into the same category as variable depth - two things come to mind; one, most control rooms are small enough that you're getting into "pressure mode" at mid-bass frequencies, where the entire room is effectively at the same pressure everywhere, instead of a passing "wave" of pressure variation - because of this, the absorber will tend to average - this in addition to the reasons above regarding the size of the absorber itself - in fact this could be considered one effect, caused by wavelength exceeding the device size. I'm still looking for info on the importance of insulation positioning - I believe most have been tested with insulation touching neither slats or back wall, but I'm sure many have been built using other methods, either from lack of info or ease of construction - I've seen no actual tests of different approaches however - Keep in mind just how expensive, time consuming and difficult acoustic tests are - I think this is the main reason there is so little hard fact available on things like slot resonators. I'm hoping the new book I mentioned above will shed more light, but it appears woefully thin on this particular subject so far... Steve

Steve, Thanks, I think I was out of the mud, you hit the nail on all my quest. I have an background as an house builder, and also has an arsenal available of machinery to machine any shape or form that required but, as you mentioned it is a huge area to cover, and a few serious tests has condenced into standard practice. And none in normal easy understandable language. My next move would be to ask you what´s your opinion about this: I use a machine cutter and slant the slat edge by f. ex 30 deg (reduced opening), (like the reversed idea of an Horn speaker) (thighter as sound penetrate the trap)..... You name it! Another idea your reply gave me, are that it is very important to get the slats steady (unwanted resonance) (maybe not bad sounding in all locations). What if I machine cutting a T track into my wood slats backside, (preferred hard wood, Oak?) and fit a T steel beam into each slat to re-inforce its rigidly (was that right spelled?) I mean that I can produce very solid (vibrationwise) slats by mixing Steel and hard wood, or even soft wood and steel. Is this last idea, a thread to give time to mature over a period of time? Know I pushing too far, but I´m just soo fulfilled of thiss Studio thing, since I found this forum, addictive??? Steve after all I´m soo happy with your feedback. I will learn to walk after this crawl. Thanks.

Steve sorry, even after screening my reply (previous) did not remember to ask about the "Pressure mode" is this related to room mode? :oops: admitting my greenish level here!!!! You can find my first post under Acoustics "Room modes" there is more upfront details, size etc. Have a nice day,.

Beveling the slats so that the slot between them is not parallel is not a good idea from the standpoint that the spreadsheet is designed to calculate an EFFECTIVE slot depth based on the actual slot depth - also, when air passes through the slot it immediately starts to spread out once clear of the slot - the cloth behind the slot is there as a flow resistance, and because of this laminar flow through the slot, the cloth can be considered to be effectively INSIDE the slot, because it is close enough to the rear edge of the slot to affect flow BEFORE the air column has a chance to spread out. Stiffening with splines, provided they are not too close to the edges of the slats (perhaps centered on the inside of a slat) would work - although if framing is kept to no wider spacing that 600 mm, we've not seen any reportable problems caused by this flexing. I guess it would depend on what material you used for slats - typically no less than 19mm thickness is used, sometimes much thicker. There is much more to this than I'm yet aware of; I'm still learning, and probably will be when my heart stops - I'm just getting started on a newly published book by two PhD's in the field, and hopefully can add to this thread more as I get time to read - Meantime, be happy that this design apparently has a lot of lattitude for error - there have been a large number of these absorbers built by our membership in the past few years, and I've not seen any negative comments that I recall. Hope that helps... Steve

Sorry, I guess we're both getting forgetful - here is an animation of sound radiation - use the top example (monopole) for purposes of explanation - http://www.kettering.edu/~drussell/Demos/rad2/mdq.html Note that as a sound wave reaches the edge of the square (this is our "wall", for this explanation) that quite a large area of the wall can get the same part of the sound wave (the pressure part) at almost the same time? This means that if any element in the room is small enough, and the frequency of the sound is low enough, that all points on a small object would see the same pressure at the same time. In practice, if I remember correctly, (couldn't find the link) this happens at approximately 1/4 wavelength of the longest dimension of the room - below that frequency, the pressure at a given time from a sound wave will be essentially the same along the entire length of the wall, and wave theory can't be used when doing calculation. What this means with typically sized slat resonators, is that unless they are tuned to relatively high frequencies (say, above 400 hZ or so) their entire surface would be at the same pressure at the same time, causing them to AVERAGE their absorptive characteristics over the entire unit. This would negate any variations in either slot width, slat width, or depth from wall. At higher than design frequency, they would still exhibit shifts in response depending on the LOCAL dimensions of slat/slot width, depth of slats and depth from wall - but these would be minimally important, since the devices peak at design frequency. This would also be true because the majority of the surface is reflective, so wouldn't absorb as much at these higher frequencies. I've already told more than I know and most of what I surmise, so I should probably shut up and go read more... Steve