Wall Units - Build Question

Hi all - I am working on building from John's specified wall unit's my own modified versions - but, pretty much the same... as found here: http://www.johnlsayers.com/HR/index1.htm Mine are being built to be fairly portable and modular. I will post photos as soon as I get my camera back. But, I have questions - 1. Who has the dimensions for the spaces and size of slats? Each calc I find and the link to the one John mentioned doesn't work. 2. Isn't low freq absorp. better on Rockwool vs. Rigid? So if it can be made to be secure and stood up in these designs wouldn't it be better than rigid? I have both - but wondering what to do as the plans don't closely specify. 3. What sizes and thicknesses should the insulation be? He shows in the corner traps - insulation doubled up - is that suppose to be 2" Rigid or what? 4. How is the rigid being stood up or held in place for these wall units? The room I am doing my first install of these portable wall units is 13x13x8... pretty close to what John shows in the picture at that above link... does that matter in terms of what slat sizes and spaces get determined in terms of what the freq trouble spots are? thanks - DK

Moved to Acoustics forum.

that's a square room. There are going to be some seriously problematic resonances in it. The 13' measurement corresponds to about 87Hz, so you are going to have lots of buildup there and at all octaves of that (ie, 43.5Hz, 21.75Hz, as well as 174Hz, 348Hz, and all other multiples). The fact that 2 dimensions of the room have that same measurement makes your problem doubly worse. Bottom line, you will need a ton of bass trapping in that room. That should be priority 1a. I'd personally go with superchunks, which will give you a lot of bass trapping as well as more broadband absorption, in as many corners of the room as you can manage. Priority 1b would be to manage the first reflection points from your listening position, ie, creating a Reflection-Free-Zone, to manage all first reflections on the ceiling, side walls, and rear wall at the listening position.

Thanks JWL - Yeah, I am really aware of that and wasn't really asking that at all... the room is temporary and meant more as a basic production/composing room. The whole room is going to be treated pretty indepthly with modular constructed units based on John's initial wall unit designs. Also, building ceiling clouds with 703 to help with the RFZ over mix center. Anyhow, my questions as listed were quite specific around those wall units of John's - and very specific to if the Slats and dimensions and spacings of those were in direct connect to the resonant freq's of the room. And really, how do I determine sizings of slats, spaces between each etc. And are they the same dimensions for the corner traps as well as side wall units? Do you know anything specific to those questions? thanks kindly - David

Let me state it a different way. If it were me, I would not build John's slat resonators. I could be wrong, but my understanding is that they are most effective in the upper bass/lower midrange areas, about 100-800Hz. If you build them, they won't have much affect on the areas where your room needs the most treatment. That's why I recommended a strategy that does have an effect below 100Hz. But to answer your specific question, you can download a calculator here (it's in the stickys of this forum): http://www.johnlsayers.com/phpBB2/viewtopic.php?t=1363

Interesting.. thanks for the discussion here.. So, just for reference in determining slot size and slat size - you work from the core resonance for the room like you said: 87hz Plugging #'s into the Helmholtz calculator (in inches): Slot width. 0.195 Slat width. 6.5 Depth from wall. 20 (it's a triangular corner trap--- guessing here) Slat Depth. 0.75 Effective depth of Slot: 0.9 Absorption Frequency. 87 So - 1. Are all slats and slots (just for sake of example) the same size and spacing? If not - as most I have seen vary these measurements - how do you determine the variation? and do so with that calculator? 2. Does aiming at 87hz then handle the multiples automatically: 43.5Hz, 21.75Hz, as well as 174Hz, 348Hz, and all other multiples? thanks - David ps - pictures forthcoming of the traps and the room

To answer #1, I don' know. #2, for a small room, in general, I think it is much simpler and ultimately more effective to build broadband absorbers (like superchunks) rather than tune narrow-band resonators. In a small room there are so many problematic frequencies, that I just think you'd get better results that way. In this regard, I pretty much agree with Ethan Winer, read his Acoustics FAQ for really good info about small rooms. Furthermore, it would be simpler and cheaper to build modular broadband absorber units than John's wall units.....

Yeah, I never wanted to tune individual absorbers and nor never thought a small room would be a good place to do this. But, I took John's ideas off that page as more of a "complete system" that when combined would balance out a room of about 14'x12' as those drawings appear to be about that in scale. That article does leave a lot to variation and thought... so not sure what he was thinking overall or how much "tuning" was needed. Other than my initial cube dimensions - I don't see why if done correctly, based on what he is depicting, I wouldnt obtain enough low end absorption etc. Interesting final effective space dimensions such as: 12.5'x10.25'x8' = 1:1.28:1.56 = specific stacked freqs @ around 275hz, 220hz only; everything pretty nicely spaced Which means? Do you build and tune around controlling those 2 freq. areas? and do everything else equally with broadband absorbers... seems easy enough... vs. 13'x13'x8' = 43hz and every multiple thereafter seems problematic ... be easier for me to frame in the width dimensions of this room or if the side wall units eat up 2.75' (1.375' each side) ... isn't that the same thing? The effective space then being down to 10.25' by doing so? David

Virtually all "helmholtz" calculators on the web are wrong, even the original one at the SAE site, for one reason - they were all copied from a MISTAKE that's present in a fairly recent version of the Audio Cyclopedia, otherwise known as the Handbook for Sound Engineers, pub. by Howard Sams. Even the correct one(s) are usually based on Owens Corning's 703 product, because that was the "stuff du jour" at the time - if you're more of a math wiz than I am, you might find a calculator that actually takes into account the flow resistivity of your specific absorption material - otherwise, I'd stick with 703 if you wanna be close. And "close" is the best you can expect, without a fair amount of experimentation... The thing that helps John's version of a "slat resonator" the most is the varying depth - this widens the effective response a bit, although likely not as much as if each slot had its own separate, DIVIDED air space behind. Still, that "feature" makes for a pretty useful wall in a live room - here's a quote from Len Morgan (from page 15 of his thread in the stickies - "A friend of mine brought his guitar over yesterday afternoon and we went all around the big room with him playing and me listening to how the sound changed. Wow!!! It sounded great everywhere but very different in different parts of the room. A real nice discovery was with the wooden(slat) wall. As I've said before, that wall is divided into three different sized cavities behind the wood and therefore, should sound different depending on which cavity you're in front of. I'm happy to report that that is EXACTLY what happens. As he played facing the wall, about two feet away and angled about 45 degrees to it, walking down the wall sounds like adjusting the tone controls on a stereo! Thanks for suggesting this, Knightfly!!!! " As for building the angled slats in a temporary space - if you build them slightly less than half-height(stack two for full height), and choose slat/slot widths that will get 250-300 hZ values at the CENTER of the splayed enclosure, they will be about as portable as you can make them. Good in a CR for RFZ control without losing brightness, good in a drum room (predominant modal freq for a kick drum is around 300 hZ) without losing the "sizzle" from cymbals... But for your "semi-cube", I agree you're gonna need specific frequency help knocking down those stacked modes... Steve

Thanks Steve... that is very useful info etc. But, can I ask - does anyone really understand how to space the slats and size the slats? They are suppose to vary right? The calculator doesnt do that. And Steve - based on John's wall units (forgetting my space is a cube) was that a complete system aimed at lows, low mids and overall absorportion or what for what seems to be a room 14 ft in length? Seems like the corner traps are deep enough to the wall to get down pretty low, front and back wall doing more broadband things and sidewalls again doing a tuning but general low end absorption too... So, then with appropriate slat/slat gap dimensions for side and corner units tuned accordingly to the problem freqs of the room... seems like a good systematic strategy. His notes on that page don't suggest tuning specifics etc. though. I need an omni-directional mic! - If I had one I would do some room readings on the empty room.. to get this outta theory and see what happens adding wall units into the room pieces at a time, even with varying degrees of insulation in each etc. etc. ... would make for interesting discussion at least... David

I don't think it's necessary to vary slat/slot widths, since you're doing that with the variable depth in this instance. Besides, from a purely aesthetic standpoint varied sizes just makes me think a guy doesn't know how to use a tape measure :lol: In a so-called "standard" room (they don't exist) I would tend to make the REAR corner absorbers, and possibly even the front ones, super chunk types and build side absorbers like the angled slats - I think it'd even a room out more, and be easier to build. The problem with using those designs in a cube is that they ARE broader-band than a constant depth trap, and won't do as much toward knocking down the stacked modes found in a "less-than-ideal" shaped room. If you go to the thread in this forum titled "are my speakers in a null" it will help you find the exact modes your room would exhibit, as well as WHERE along each wall would be the effective location for a PANEL resonator trap - these can be tuned to be centered on specific problem frequencies, and need to be located at maximum sound PRESSURE instead of VELOCITY - this location depends on whether the problem is a first, second or third harmonic and which pair of boundaries are causing it. I don't have time ATM to get much deeper into this, but will help you along - First order of biz would be to do all the "generic" things to your room - corner traps (chunks, IMO) a cloud (see the stickies for DIY stuff) first reflection points, rear trap. Next would come finding out what the room's doing in THAT condition - you can get FREE PC software that'll do this, here http://www.hometheatershack.com/roomeq/ If, after doing all the general things, you still have too many bumps in the response, we can get into more "surgical" methods and where they need to be placed. This is what I call "cut and try", and it's how I work. Please keep in mind that all the stuff I do on this site is based on my own quest for decent sounding/sound proof spaces, and in "real" life I'm an industrial instrumentation tech/videographer/songwriter/jack-of-all-trades sorta guy, if you need more than that you'll probably end up paying RBDG or similar, and if so ya better start saving, 'cause that's why I started studying this stuff 25 years ago; it ain't cheap, or even reasonable :cry: Omni mic - for this, cheapest one you'll find is the Rat Shack Sound Level Meter - it has an RCA output that's approx. consumer line level, isn't flat above about 8 k but is fine for modal work. Even has a 1/4"-20 tripod screw thread on the back for mounting, and will prove itself invaluable later when you wanna keep your SPL at a constant 85 during mixing... Steve

knightfly wrote:

First order of biz would be to do all the "generic" things to your room - corner traps (chunks, IMO) a cloud (see the stickies for DIY stuff) first reflection points, rear trap. Next would come finding out what the room's doing in THAT condition - If, after doing all the general things, you still have too many bumps in the response, we can get into more "surgical" methods and where they need to be placed.

Thanks for stating that so succinctly, knightfly. That's what I was trying to convey in my original posts above. I think building resonators first is not the best way to go, particularly in a small room.

Thanks Knightfly - it is more succint. It would be great if John's wall unit designs specified what size room he was intending that overall system to be used in. Its rectangular so got me there, but longest dimension can't be more than 14 feet in that picture in the above link. I understand the narrow approach of resonators. Just seemed alittle mislead on what John was going after in that original link. I am sure it makes sense - just seems to be missing details as to why you would take that overall approach - if each of you are recommending something totally different. am not exactly on a low no dough budget or anything... and I got bags of Rockwool - just think... I am not big on those chunk things - seems cheezy to me. 8) Would definately go with an Ethan advised panel closing off the corners and traping low end that way if slat resonators even at John's advised sizings are just NOT gonna work at all. So, if my room was not a cube - would you each recommend something different? and say a room dimension could be made to be alittle bit bigger so as to get alittle bit better room mode ratio... I feel like I am re-inventing the wheel, maybe its how I write, or what I have been asking cause of John's article - which I thought was a good balanced direction for most rooms :-( ... I guess I's thought's a wrong... thanks - David

BTW, thanks you guys - I am enjoying the process here and appreciating the constructive and experienced input... thanks... Just wondering - if I take John's sealed corner units, don't put slats on them and instead line them with rockwool and have a piece of 703 at the front of them with fabric on the outside... would that make for the best non-surgical wood-built non-super-chunk type corner bass trap? I guess I could do the same per Ethan's design of lining furring strips vertically and attaching the 703 to those in the corners (triangular) to seal the corners up.... but, I have a bunch of these units already built... just the shells, nothing in them, or on the fronts of them... I am willing to give up 20 - 25" across the corners as needed... David ps - I got one of those Radio Shack units, so with the ETF software which I have too - I can do a room reading and post that??

OK, first off John's slatted corner absorbers are not all THAT different from superchunk types, mainly just brighter due to the slats - of course this would also depend on slat spacing - wider the slots, the less helmholtz effect you would see. Corner units- yes, you could build 'em without slats and it would do nearly as much as superchunks, especially if the faces are 4" thick. You could even do slats across the top and bottom parts and keep the centers broadband - this would leave the room a bit brighter with little else changed. "I am willing to give up 20 - 25" across the corners as needed" By that, I'm hoping you mean DEPTH and not total width of the trap face? Keep in mind that this is a "percentage" game, and too low a percentage of total surface won't make much difference. 3 feet wide is usually the minimum that will do much for a corner trap, although slightly less than that across all the wall/ceiling corners of a smaller room makes a noticeable improvement. If your room were not a cube, the only change might be that you'd be done tuning it sooner and it'd sound better. What's cheesy about a super chunk, BTW? It's not like you're gonna leave EITHER unit uncovered showing bare fiberglass or MW - And yes, if you have the option of moving a wall I'd do it NOW - changing just one of the 13's to 11' will make a LOT of difference, as in ZERO coincident modes and a pretty smooth Bonello distribution. Maybe if you did that you could use the 2 foot strip for instrument storage, machine closet, etc - placing that closet at the rear of the room with lightweight hollow core doors could work - you could face them with 3-4" of 703 and keep 'em closed during mixes (and recordings if this will also be your live room) - that would make the closet act similar to a (damped) panel bass trap with the added advantage of killing higher frequency rear wall reflections - even lightweight doors will re-shape your modal response - also, I'd line the closet everywhere possible with more absorbent, including BOTH sides of the doors. I would NOT try to actually SEAL your doors like they were entrances - some leakage will just increase bass trapping, and won't hurt the effect you're after (modal balance) I know this sounds like I'm advocating firing your speakers down the SHORT way - can't really be helped in this case because the front or rear of the room is the only place you should put such a trap - otherwise, you'll have a non-symmetrical mix position because that trap wall will act differently than your opposite wall. Besides, it's only a couple of feet and a small room, I doubt you could tell the difference - especially compared to the difference a non-symmetrical mix position will cause. HTH... Steve

It totally helps think this through, thanks for the input and ideas... before I either start demolitioning this closet (see below)... which is fine by me... take a look, here is the room: cube dimensions are: 12'11" x 12'x11" x 8" add the closet etc. and we actually have: 15'3" x 12'x11" x 8' need to run the room mode app again... and might setup and run a few tests tonight to see what the room response is leaving the room as is, with doorless closet... ... and I could demo' the drywalled ceiling to get whatever additional 8" are up there in the joists :-) ... pretty much willing to rip whatever out and down... to start from the best possible situation for this little production/writing/mix room. thx - David

Hey again, Here are the start of the 1) corner traps and 2) the side wall units.. Steve, per your notes above... these corner traps are about 33" across, and each inner side dimension is about 23", so only 16" or so deep... I could use these for the front corners and I still need to build another set of (4) for the other 2 corners... and could make those closer to 36" across or greater... They are built solid, awaiting to be USG acoustically cauked, and then determine insulation and slats or no slats based on final room dimensions and other meanderings etc. etc. They all stack really nicely and easy to pickup and move around... David

Here are the mode calculations for: 12'11"x12'11"x8' and 15'3"x12'11"x8'

Hey again, Tonight, performed some measurements using the Room Eq Wizard. Been many years since I first thought I would be fiddling with such things... so pretty cool stuff to check out... Anyhow, 3 readings - 1. Mustard/Tan = unsmoothed reading (only to 200hz) 2. Purple = smoothed at 1/3 octaves (to 700hz) 3. Teal = smoothed at 1/3 octaves (to 700hz) -- just to doublecheck #2 Pretty cool. You can really check out the mathematical mode calculations to some degree and see the real-world check out against the science... not much is different in the settings for each reading, though an earlier reading not shown had the return vent on which is just outside the room and that definately impacted things. Room is not really a cube, since the closet doors are off, but the slight divide does exist between the main part of the room and the closet area. Be interesting to do a reading with the closet doors on (for the sake of getting a reading on a cubed room, but kinda lazy for that)... I am assuming I am calibrated and doing this at the right level and spl and all that... any pointers from anyone would be good... Additionally, my laptop is in the room as I couldn't find enough connectors and RCA and 1/8th inch jacks to get my laptop (and its fan!) outside the room. Surely, it and my own body is disrupting the readings (I laid flat on the floor and am thin enough that maybe I went undetected, doubtful)... will get to the Shack tomorrow and get another extension cable so I can move myself and my laptop outside the room. It's interesting... doesn't say much except the room is crappy as is... :D (Russ Berger doesn't have to worry yet) David

I hope this thread is still alive two days later, because I'm facing the same decisions, i.e. about to put the slats on some resonators and need to know about spacing and slat size. I've attached a jpeg of my room (courtesy of John S. who came up with the modifications). It is not a cube (though it used to be). The only thing not shown in the pic is that the front of the room between the monitors is also a slat resonator (about 8" deep). Both of the angled walls on either side of the speaker soffits are also slat resonators. John had mentioned that it was not as important what sort of insulation went into them, so I used 6" thick standard fiberglass house insulation (is this a mistake?). I have not yet put the slats on, and I'd definitely want to know if I need something else before I seal it in. I had a bunch of 705 Owens Corning panels that I had previously wrapped in fabric (individual packages) and framed the outside edge. I attached these to the back wall of the room as shown in the picture. My question is: Given that my room is not a cube, is there anything I need to know/do regarding the width and spacing of the slats or the insulation that I've used inside? Oh, by the way, the ceiling is only 7' high, but I pulled down the boards that it was made from (it was tongue and groove pine). Above the ceiling are 2x12s that support the roof (which is flat) and between them is very thick insulation. I flipped the insulation around, putting the paper side toward the roof and the fuzzy stuff facing the room and then covered the ceiling with cloth. So the ceiling is a 7' x 11' box that is 12" deep and full of fiberglass. I would greatly appreciate any input! Thanks, Geoffrey

Hey there - well, it seems like no one really knows how to do the math or there is no straightforward way. Easy to kinda determine to get 1 size, but beyond that doesnt seem straightforward. Even in the super excellent you shoulda get a copy Rod Gervais book - he doesn't go into the specifics of varied slat and slot sizes. He too mentions it, but shows some examples where there actually is no variation. He even shows a corner trap that has the slats going vertically. Certainly, in small rooms and all that there is much that is easy to be said about what to do and what not to do. But, if John helped with your design and its originally John's page here on this site I was inquiring about -- maybe and certainly he would know how you determine the slat and slot dimensions. There is the question of narrow or broadband absorber design here. But, I must say as opposed to some of the drive to build SuperChunk things - Rod in his book points out that a Helmholtz trap can work effectively at the dreaded low end freqs that small rooms MUST deal with. Building SuperChunks w/ 703 is and can get more expensive then doing so with Rockwool stacked up. But, frankly, if a Helmholtz trap can cover the dreaded freq range (maybe 50hz - 150hz, not exactly what I think most consider BROADBAND, but I wouldnt actually think we are trying to tune these slated/slotted traps in a small room any narrower than that) and do so really well, I bet I can build it cheaper than a SuperChunk made with stacked 703 boards. Plus, with all the other trapping going on - alittle more wood from the slats can introduce back in "alittle" natural reverb to the room to make it "feel" alittle more comfortable to be in and work in - not so freakin dead. Small rooms need alittle reverb too. We humans like that. Hence, why I personally am trying to get good low end trapping done throughout the room but not panel the whole place in foam, 703 etc. I think John had an idea with his page I mentioned above in my first entry on this thread - it was a systematic tuning and balancing of the whole room together - not just focusing on 2 corners and then haphazardly doing something in another part and work completely trial and error. He seemed to be taking his experience and knowledge and putting that into a general idea around how to get a small-ish room working, balanced, easily, without too much guesswork. So, which leads me back to slots and slats... What is your room size? and the center frequency of it? I think somehow the slots and slats are based on that center freq. of the room if you are tuning for the whole of the room vs. trying to be very narrow and deal with 1 specific frequency. The fact that the corner traps are variable depths too - makes them potentially deal with a wider band of frequencies. I just really like the ideas John was putting forth... and would like to keep the thread going to prove how well his "idea" works... I should just email and pay him for some consultating time. That would solve this :-) (by now, he is sitting back reading and laughing at us, joke) David

Hi! My room is not that much different from yours, but narrower along one dimension, and the treatment I'm planning looks pretty much like yours does. However my room makes it awkward to put bass traps all the way in the corners because of structural pillars and beams. I wonder if having the bass traps off the wall causes problems with resonating behind the bass trap, or if they are less effective if they are not up against a hard wall, or if i can just use the wall as the back of bass trap. Then there is the argument over super-chunk vs 4" of 703 across the corner. and do the bass traps need to reach the ceiling corner? would the space above the top of the bass trap cause resonating problems? And for a lot of small rooms like mine, with non-sofit mounted monitors, the backs of the monitors will be facing the bass traps. will that mean strange reflections back from wooden slats to the listening possition? can the wooden slats be missed out at the height of the monitors? will this effect the bass traps in a bad way? aaargh so many questions :)

there is a graph of superchunk vs corner trap here.. for price it seems better to make a thicker corner trap (6" or something) http://forum.studiotips.com/viewtopic.p ... hunks+test and a price comparison here: http://forum.studiotips.com/viewtopic.php?t=534

This has been a very interesting thread. I've learned a lot. Since it began, my copy of Rod's book arrived, and I've been reading up on slot resonators. I've learned that I was wrong about the effective frequency ranges of slot resonators; they absorb lower than I thought they did. To answer an earlier thread question about calculating slot width.... all I can get out of Rod's book is that to calculate it, you would simply take the average of all the slot widths, and include that single figure in your calculations. He does not seem to elaborate on the effects of varying slot widths, from what I can see. This thread is also making more clear the serious need in the acoustics community for some testing. It would be very, very interesting to have a room, and treat it in different ways, measuring/listening to the results. How well do slot resonators perform compared to superchunks, or 4" of 703 across the corner, etc.? Part of the difficulty of such a test is that slot resonators completely depend on how they are constructed.

Hi JWL - I have been thinking the same thing regarding rooms and testing devices. The last few days I have spent hours doing testing -- in a really bad room. This has been for the sake of just having something to reference against once I: 1. Rip out the ceiling drywall - exposing another 8 - 9" 2. Rip out the open closet area (2'4" x approx. 9') One thing discovered and validated - Even if the new dimensions don't hit a best room mode ratio (still) - I see 3 things are going to happen with converting this room - 1. Overall total volume of room goes up, and even a little bit bigger room will give a wider room for error in treating it 2. Dimensions will be closer to a rectangle and less of a cube 3. Ceiling surface will be gone and be able to be treated deep in the joists with something absorbent (thinking maybe ADULT Depends(tm))... so, no ceiling bounce and generally again, just more height to work with Current dimensions again are: 12'11" x 12'11" x 8' New starting room dimension will be: 15'3" x 12'11" x 8'9" An amazing tool I have used to once again determine even the new room dimensions (suck) as a starting point and offer little option but to frame-in the width of the room and find another 2 feet in length (not physically possible)... is the iRoom Beta room mode calculator. But, my testing of the bad room proves one major point - 1. Treatment this or that, superchunks this or that, slat resonators probably too - NO LOW END ABSORBING TREATMENT IN A BADLY SHAPED SMALL ROOM (CUBE PROBABLY THE WORST cause of all the stacking resonant frequencies) REALLY HELPS THAT MUCH AT ALL -- ESPECIALLY AT THE ROOM'S RESONANCE FREQUENCY. Only doing "caps" - for sake of what might be a known understood fact by everyone... but, wasn't exactly apparent to me. This has been the clearest thing to come out "testing an empty bad room" vs. "testing a very quick superchunked bad room"... But, JWL and everyone else - take a look at the results, maybe its the start of something we could all collaborate on - a room somewhere dedicated to really being able accurately test all these things (make some slot resonators at all sorts of widths and gaps and see what the real deal is here anyhow :roll:)... Personally, I think after reading so many posts from people using small rooms who treat it like crazy (foam or this diy trap etc.) basically create a really dead-room and think they are hearing things - good bad or otherwise - but, think that they have done magic or something and really think they have "widened their stereo images" or "balanced the entire room". I think without even just a few hours of scientific testing - most of that is bs and is more perception than anything. Though the science falls down too - since sound and listening is about perception somewhat. But, I think to really see the true numbers is quite interesting, running tests over and over and seeing how sound is basically "erratic" in many ways and very "consistent" in others - yet, all at the sametime :-) I will post my final test results for the "bad cube room" and also document what the horrifying resonant frequencies are of this bad little room in one at a glance graph. Best - David