Slat wall question

Steve: Starting from top, down. 2x10 ceiling joists with R-30 (10") insulation - next is a layer of 1/2" drywall screwed into the joists spackled and finished. (This was already there prior to my start of the control room) Then we screwed furring strips (2-1/4") on edge, 16" o.c. across the ceiling with blue 1/2" styrofoam at the screw points (in order to help isolate the wood from the drywall) through the previous layer of drywall and into the ceiling joists. We drilled each of the furring strips (3/32" holes close to the bottom of each furring strip) at (+ -) 2' intervals so that we could string lengths of ceiling grid wire through the holes, across the room and as we installed 3" Roxul in the cavities, pulled the wire tight at each cavity until we got the entire ceiling filled. The wire supported the Roxul in the previous cavity so we could continue installing in next one. Then, with the Roxul being held in place in each cavity by the wire, we installed 3/8" drywall into the bottom of the furring strips, spackled, primed, painted and caulked the edges with clear silicone. BTW all surfaces in the room are pretty much parallel. However, like I said, all of the walls (except the front wall) are built out with the framework and 1" Roxul and covered fiberglass screen (like window and door screen) to help keep the Roxul from sagging over time and on top of that, cloth. I originally figured the Roxul would eliminate a lot of reflections. PAULIII

What's ABOVE the 2x10 joists - is there an upper floor, a roof, an attic, or??? Steve

Steve: There is a bedroom upstairs. A couple of questions: Wewill be installing the framework and 4" Roxul on the front wall tomorrow and Thursday I would like to also build a 4'x4' cloud since we have 2 free days. Does the cloud go directly over the mix position or do we use a mirror at ceiling height and install the cloud over the spot where the first view of the monitors shows in the mirror from mix position? Since I don't have a lot of ceiling height, will 1" Roxul framed and suspended from the ceiling 1" work at absorbing early reflections as well as 3" Roxul? I am a bit confused by the standing wave calculator. After putting in the calculations then drawing the chart where the frequencies intersect (I believe on the 1st page of this post), it shows that the "dead center" spot is the wrong spot to mix from, even though that's where I will be sitting. But by analyzing the room and putting in the appropriate treatments, will this be alright when we're finished? Thanks, PAULIII

OK, this may cause you problems - there's a bedroom upstairs, which suggests a FLOOR - then, you said "2x10 ceiling joists with R-30 (10") insulation - next is a layer of 1/2" drywall screwed into the joists spackled and finished. (This was already there prior to my start of the control room) Then we screwed furring strips (2-1/4") on edge, 16" o.c. across the ceiling with blue 1/2" styrofoam at the screw points (in order to help isolate the wood from the drywall) through the previous layer of drywall and into the ceiling joists. We drilled each of the furring strips (3/32" holes close to the bottom of each furring strip) at (+ -) 2' intervals so that we could string lengths of ceiling grid wire through the holes, across the room and as we installed 3" Roxul in the cavities, pulled the wire tight at each cavity until we got the entire ceiling filled. The wire supported the Roxul in the previous cavity so we could continue installing in next one. Then, with the Roxul being held in place in each cavity by the wire, we installed 3/8" drywall into the bottom of the furring strips" I've bolded each layer that is mass; note that there are three leaves of mass in this construction; none is very massive, so I would doubt you have ANY serious isolation to the upstairs, especially at lower frequencies. I hope this won't be a problem, because the fix is to remove everything you've done below the joists and start over. Wewill be installing the framework and 4" Roxul on the front wall tomorrow and Thursday I would like to also build a 4'x4' cloud since we have 2 free days. Does the cloud go directly over the mix position or do we use a mirror at ceiling height and install the cloud over the spot where the first view of the monitors shows in the mirror from mix position? The cloud needs to be centered left/right between the speakers, and centered front/back between a line intersecting both speaker fronts and your head; in other words, equidistant between the speakers and your head. If you can still place a mirror on the ceiling in any position that's NOT covered by the cloud and see either speaker, the cloud isn't big enough. You want at least 6-8" of absorption beyond the "visibile speaker" point for each side of the cloud; in other words, the cloud should MORE than cover the reflection points by at least that much. Since I don't have a lot of ceiling height, will 1" Roxul framed and suspended from the ceiling 1" work at absorbing early reflections as well as 3" Roxul? That's like asking "will a 6 ounce steak fill me up as much as an 18-ounce steak?" - With your decreased ceiling height, if you can only afford to lose 2" of headroom I would make it ALL rockwool, no air gap. I am a bit confused by the standing wave calculator. After putting in the calculations then drawing the chart where the frequencies intersect (I believe on the 1st page of this post), it shows that the "dead center" spot is the wrong spot to mix from, even though that's where I will be sitting. But by analyzing the room and putting in the appropriate treatments, will this be alright when we're finished? No, it won't; in your room (11'11" front to back) your head (ears) should be as close to 54" from the front wall (solid part) as you can get it; you're already dead center sideways, so may run into some modal problems from that source; adding ANOTHER null/peak to your listening position is just ASKING for it. Yes, treatment will HELP - but minimising the KNOWN problems BEFORE treatment will make less treatment necessary for an ACCURATE sounding mix position... Steve

Steve: Thanks so much for the answers to these questions. The isolation from CR to bedroom upstairs is not a problem. Cloud Actually, since I will be seated at 54" from front wall and there will be minimum walkable space under the cloud, I will install 3" Roxul and no air space at the areas you said. Question....Since we are installing the 4" roxul across the entire front wall, around the window, absorbing all the frequencies, will this make any difference to the 54" head/ear position or do those particular standing waves apply to a room of my dimensions regardless of what the wall covering is made of? Explaination of what I'm trying to say: I'm under the impression that these standing waves are caused by direct sound reflections (coming from the front of the speaker and bouncing off the back wall) and delayed sound reflections (resonating from the rear of the speaker cabinet and bouncing off the front wall) slaming into each other from opposite directions somewhere more toward the center of the room with the same amount of forward energy, but not being able to go forward any longer because they are facing against one another, thereby causing a particular frequency wave to stand still and cancel itself out. If there is absorbent material on the walls, eliminating most of the reflection, will the same standing wave calculations apply? Thanks again, Sincerely, PAULIII

4" Roxul won't even come CLOSE to absorbing ALL frequencies, especially not first harmonics in all three axes. It will, however, TAME them a bit; For most purposes, when calculating modes you can use the SOLID wall surfaces; these are lower frequencies, which won't be heavily affected by such treatment anyway. Also, even tho the speed of sound can be affected somewhat by passing through an absorbent, it's so thin with respect to the full room dimensions that you can generally disregard the change. The above is why you STILL need to get your listening position and speaker positions out of peaks/nulls - it takes both positioning AND treatment (in most rooms) to smooth out the response of a mix position so your mixes translate... Steve

I thought so, but I wasn't sure. Ok, we now have the entire front wall around the window framed and filled with 4" roxul, vinyl screen to help keep the roxul from sagging and cloth. Concerning the Cloud.... we got the mirror out, moved it across the ceiling and, seated in the 54" position that you recommended, found the outer most visable points of the monitors (which by the way I placed in the front corners of the room, 16" to the front center of the monitor from both the front and side walls , angled toward the mix position), then went 10" beyond these points in both directions toward the center and width of the room. Actually, the entire cloud is 34" wide x 88" long, centered on the width of the room and is 14-3/4" from the front wall drywall (10" from the 4" front wall roxul cloth). Instead of using the 1" roxul (6 oz steak), I decided that since the console will be sitting there and there really won't be any walkable space between there and the front wall, I decided to go ahead and build the cloud with 4" of roxul (18oz steak) and still suspend it from the ceiling 1". It still leaves about 3" of space between the cloud and a 6' person standing under it. Great! Now.... I am planning on moving all of the equiptment back into the room again over the weekend to hear how everything sounds from the new position. Next step? New frequency measurements from the previous positions in the room after everything is back in? I'm really looking forward to hearing this room sound the best possible with what we have to work with. Thanks for all your help, Sincerely, PAULIII

You're welcome; one more thing - you will want to keep a second location in mind for speakers. Having them the same distance from front walls as they are from side walls may cause SBIR anomalies to show up. If you run freq response tests at listening position and can't explain a particular dip or peak, it may well be these two distances being the same. If you're using the method of "ballparking" I explained using Harmon's axial mode calculator, you may want to use an alternate "green band" for either width or length position. Of course, listening/testing should be done first to see if this is even a problem; it won't always be. Mainly a "heads up" for now... Steve

Steve: I got the room back together and it sounds much better from the new 54" position. I am hearing bass now from the mix position that I didn't hear previously. I ran new freq. responce tests from listening position as you said, in auto EQ / Room correction mode. Frequency responces tested were from 40Hz to 20K and also from only 100Hz to 20K: The analyzer readings needed to correct the room are as follows: What do you suggest as the next step? PAULIII

Am I interpreting correctly that you have mainly peaks centered around 50-100 hZ, and again at around 200 and 400 hZ? If so, does moving your head(mic) forward or back change anything? Sideways? According to dimensions, the room itself may be responsible for the 200 hZ and 400 hZ regions but probably NOT the lower ones - can you do a fairly accurate sketch of the room including dim's from each speaker's woofer center to each surface, also including your head? I need all three dimensions for each... Steve

Steve: You are interpreting it correctly. Moving my head back does change the sound a little, however, that's getting pretty close to the spot where everything crosses in the center of the room, so I took new measurements......centered side to side (74 1/8") 48" from front wall (6" forward) and 60" from front wall (6" backward). Also from the listening position - 54" from front wall left @ 68-1/8" and right @ 80-1/8". Here are the new readings; Here is a diagram of the room. I forgot to show that the walls on the interior side of the room have 1/2" drywall over the 2x4s before the air gap, Roxul and cloth. Listening position is 72" perpendicular to the monitors and 54" from the front wall as you advised. BTW the cloud made a very noticable difference to the sterio imaging. Wow! Thanks so much, PAULIII

Glad the cloud is helping; can you re-post your charts, two to a pic (instead of 4), and large enough to read? Steve

Sorry about that. The first pic is head centered side to side - forward 6" and rearward 6"... The second pic is head @ 54" mix position 6" right and 6" left... PAULIII

:oops: :oops: :oops: :oops: :oops: :oops: :oops: :oops: :oops: Paul, I'm so sorry; not sure how this got sidetracked, but if one of your posts ever gets to the second page again please PM me - there's such a thing as TOO much patience... Looking at your figures, I'd give the 6" back position a good shot; maybe even further, you could check and see if it evens out more. BTW, 8 dB isn't a huge amount of difference for a room/speaker combination, this should be sounding pretty good by now. On the 20 hZ "problem" - you are kidding, right? You do know that there are $50,000 speakers (each) that aren't quite flat down there, right??!? Anyway, what I would do now is put up at least half a dozen different CD's that you KNOW are mixed well, that sound good on anything/anywhere you play them, and LISTEN in your room; BTW, from my experiences with the Truth monitors, they are a little over-enthusiastic on the bottom end; you might try using their low end controls to cut back a few dB and see if they translate better... Steve

Steve: Thanks. I forgot about the rear switches on the Truths. While taking new readings from the 54" position, I cut the room compensation switch 2 db at a time and when I got to the -6 position, everything flatened out to within 3 db except 50Hz (needs a cut of -9.5 db) and 80 Hz (needs a cut of -11.5 db). Aside from that, everything looks fairly flat across the board (within 2 - 3 db) all the way to 20K and it sounds GREAT! I'm hearing detail in the various CDs that I never heard before. Even mistakes that got recorded! Here I thought they were all perfected before release. Oh well, I'm really enjoying this. What do I need to do concerning the 50 and 80 Hz? We'll just forget about the 20Hz thing.....ha ha PAULIII

I just realized I forgot to mention that aside from the two cuts required for 50 & 80 hz listed in previous post, that 40Hz needs a 5.5db boost. I am most likely missing some of the punch of 40 Hz and getting too much of the 50 & 80. If I can correct these 3 frequencies in the room, I would rather do that than by using the an outboard eq. I do remember though, from another post, that you said slat absorbers don't work below 100Hz. What type of room treatment will work with those freq.'s? Thanks, PAULIII

I just (finally) looked for info on freq response of the Truth's - found it interesting that they call it "system" response, and that they list the same response for the 2030 as for the 2031, yet one has a 6-3/4" woofer and the other an 8-3/4" woofer - also, no TOLERANCE is given for the response; this is pure BS - there is no such thing as a measurement without a tolerance, only people who list them because they don't know any better. Most speakers are rated between -3dB points, Behringer makes no statement whatever on this. Their "50-21 kHz" response could just as easily be plus or minus 9 db, or whatever. Here's more on this - http://forum.ecoustics.com/bbs/messages ... 31062.html My main point is, you don't know what these speakers will do in a free field, there are no real specifications, but I would suspect that 40 hZ is NOT within their reach at anywhere near the same level as higher frequencies; I think the peaks you're seeing just above that may well be room modes or SBIR or something OTHER than the speaker's ability to reproduce that much SPL at that low a frequency. IF further tests at slightly different head/speaker locations don't get any better than you have now, I would start looking at more room treatments instead - for your lower frequencies, Properly tuned panel traps in specific locations (yet another marathon, BTW :=) would be the way to go... Steve

Steve: Wow, thanks for the link. That opens up a whole new world. Especially the point of the time factor in speakers that no one tells us about. I guess what I have really isn't too bad for what I have to work with. I have a set of NS 10Ms that I haven't put into play here yet. I think before I build any tuned panel traps and do the measurement marathon, I'm going to hook up the Yamaha's and see how they sit in this picture. I really appreciate all your help, especially on your limited time as I've been reading in the other posts. And I thought my schedule was bad. Good luck with all you're doing. I'll get back in here after I do some more measurements with the NS-10ms. Thanks again, Sincerely, PAULIII

Steve: I'm back in here again. I ran some measurements using my NS-10Ms so as to compare the results to the Behringer 2031A's. I copied the results onto a graph. (These are the room corrected results from the Ultra Curve Pro Analyzer) The low end results are quite different. I was concerned with the cut needed @ 50Hz and 80Hz on the Behringers, but with the Yamaha's, those freq's are just fine. Is this because of difference in monitors or the room. I have been moving the Yamaha's around to find the best position and this is about the best I could find. I am just trying to figure out if this is the best I can get out of my room. You mentioned the use of tuned panels, but now that I see the variation in results from the two different monitors, I'm not really sure what freq.(s) I would even correct. Or aren't my results really that bad. Somewhat Confused :roll: PAULIII Thanks, Steve.

NS-10's won't go as low as the Behringers; smaller woofs, active vs. passive, etc - your different results at low end may be largely the fact that the Behringers are exciting modes your NS-10's can't touch. The only way I know of that might actually WORK to determine what JUST the speakers are doing (without taking either manufacturer's WORD on it) is to go outside, make the world quiet :? , dig a pit, place a heavy plywood baffle across the mouth of the pit, mount your speakers flush with the plywood facing up, place a microphone straight above the speakers (at least 6 feet or so away), and test the speakers for response in 2 pi space - then, you'd need to come as close to that mode as possible in your studio (soffit mounting correctly), etc - little of which is very practical. I'm too short on time to see how much variance your NS-10's show, for some reason the pix don't come up without coaxing and I'm due to leave for work - but I agree that you should't re-do anything because of the way the Behringer's respond; better the other way 'round (get them as close as possible to flat with positioning, then maybe EQ things just a bit on the bottom if necessary) Sorry I don't have more time, I'd much rather be doing this than where I'm off to next... Steve

Wow! I don't know how I did that, but somehow erased all my pics from the host. Oh well, I got the graph back (2 posts up) so you can see the variation between the Yamaha and Behringer monitors. As far as EQing...A cut is required on the Behringers at 63Hz to get to "0", but a boost is called for on the NS 10s. They're both directly opposite. The same for 630Hz. How do you find the happy EQ medium. Still Confused :? PAULIII

How do you find the happy EQ medium - Maybe run both speaks in parallel?? (JK; I would suspect something in the Behringer analyzer may be causing this. Are you testing with the speaker woofers at the exact same position in all three axes? Steve

knightfly wrote:

Then, and ONLY then, if the room still had problems, would I reach for "surgical" tools such as panel, Helmholtz, etc - otherwise, you stand almost as good a chance a DAMAGING the room's response as FIXING it.... ..Bottom line - I'd wait til you HEAR and MEASURE before you get excited about building any treatments - Steve

I'm a bit confused here. I'm sure you are right Steve, but why there are slatresonators drawn in allmost all John's designs for a small control rooms if there is a good chance to damage the sound rather than make it better? I'm sure there are plenty of people (including me) building small rooms, that dont have access to any measuring equipment. So only way to decide the slot widths etc. is to use the Exel calculators to find out the problem frequencies. Or maybe in mixing the the wall absorber in johns site and slat resonator, alltough they look same to me. I'm talking about these: http://www.johnlsayers.com/HR/index1.htm http://www.johnlsayers.com/Pages/Bluebear.htm I'm just starting finally build my basement and i was going to make 10degree splayed 255cm long slat-wall-units to both sides of the mixing position. I'm using the exel calculator and modecalc to find out the frequencies where to target the slot widths. Will the splaying be enough to create RFZ? I dont want put plain 703 to the side walls as i dont like too dead sound. My front wall will be covered with 10cm 703 and also the ceiling is sloped towards the front with 5cm 703 so there is quite a lot absortion around the mixing position. Also i was wondering if i could put the cloth TOP of the slats not under like it usually should be. Reason for this is that i dont want to leave the wood visible. I want to create solid looking surfaces for aesthetic reasons by putting large coloured cloth over the slat wall. Maxx

Anyone?

You bring up a valid point; it's my belief that one of the reasons John's rooms work is the VARYING depth of the slots; I think that, since most rooms tend to have too much mids anyway, just pulling out a wider frequency range in that band works well enough not to cause noticeable problems (at least, not very often) - I would still prefer for most cases to only add treatment after the room is complete, and only after listening/measuring. Building things takes time and material, so I tend not to rush into things til I know it's needed. A splayed slat wall would need to be QUITE angled to perform RFZ in most rooms - but to know how MUCH of an angle, you would need to do a basic ray trace diagram (CAD program at least) to see where reflections are going. Somewhere I posted a drawing of a way to do ray tracing, but gotta get to bed now - if you do a search on those words, you should find it. Cloth OVER a slat is fine, but NOT as a replacement for the INNER cloth - that will be necessary whether or not you cover the absorber, it's part of the way they work. You want the cloth AND the insulation up against the slats, and usually about half of the total depth should be insulation. HTH... Steve