John Sayers' Recording Studio Design Forum Archive

Hashbrown,

I just kind of quickly glanced over the thread. Here's a quick pic of what I did w/ wall braces: http://johnlsayers.com/phpBB2/viewtopic ... &start=215

For Insulation, I'm using Roxul AFB http://www.roxul.com/sw34142.asp

Or there's also the Owens Corning 703 http://www.owenscorning.com/comminsul/d ... Series.pdf

For Acoustical Sealant, there are several mfg's that make it: Boss, Grabber, etc, etc. I'm paying $3.25 for a 29oz tube when I buy it by the case (12 tubes).

Find out who the suppliers are for construction materials in your area for (eg: steel studs, drywall, insulation, etc). One of them are bound to carry it.

As far as SPL, in a CR, you're probably not going to want to go over 100db.

Hope this helps.

Aaron

Aaron, I've read your thread a few times, it's a great one! My concern was doing those anti-sway brackets with angled walls. But I suppose I could just angle the entire bracket the same amount. I would have to drill the holes for the joist as I was fitting each one, so I'd know where along the bracket I was aligned with a joist. Now did you secure those into any joists or did you always put another span in between, like in the picture?

Ok, so I see that the bracket wraps around the top of the frame, how did you attach the sheetrock to the frame where this bracket would interfere? It looks like you used RC on your walls, so maybe that gave you the space you needed to clear the brackets at the top? I won't be using RC on the walls so I'm not sure how that would work for me.

Hey thanks for responding!

Hey Hashbrown,

I did use RC on the control room side of the walls, This gave me the clearance I needed. However, I also, before putting up the drywall, shaved about a 1/4" piece of 703 and liquid nailed to the the side of the bracket that was facing the drywall, as kind of a perimeter board concept, just in case the bracket shifted and rubbed up against the drywall. This way it would give a little cushion to reduce any vibrations.

Several of the brackets are attached directly to the joists where they run parallel to the wall. On the perpendicular walls, I just put a 2x4 in between the joists so I'd have something to mount the mounts to. Same thing for the angled wall. If the joist just happened to be where I could put the mount, I used the joist, if the bracket location was between joists, I did the same as the perpendicular wall situation.

The other question you had about "not using RC". I didn't use RC in my iso booth. Here's what I did, but I'm not sure if it has worked well or not. I did the same mounting method as above. Except on the first layer where the brackets were, I cut out the drywall. Used some acoustical sealant, and also did the 703 padding. The second layer went over it just fine. Providing you're using 5/8" drywall on the first layer.

Aaron

Thanks Aaron. It seems that your technique for the non-rc walls would certainly work, good enough for me at least. Especially since that 2nd layer goes over without problem (yes I'm using 5/8"). So now I have to re-read some of that thread and take a look at those designs again.

So now I have options from both you and Andrew that allow me to build the wall first or the ceiling first. What to do, what to do.

I'm building my walls first, and then hanging the ceiling from RC "Inside" the walls.

Your comment about 85 dB levels tells me you already know what works, to answer your PM - what kind of monitor system do you have that can play clean at 110 dB? And, if it's not clean, it won't show off anything but instead stands a good chance of losing customers ("what's that? Sounds like crap...")

Yeah, the "wow" factor can be impressive if kept under control, but I doubt you'll find many nearfields that will sound good at over 100 dB (which is still pretty loud) - if you want to go much louder, you're talking pretty expensive and large mains or quite a bit of distortion - anyway, as I said you already know how to get your mixes to translate.

Insulation - If you're using a single layer of drywall on all your concrete backed walls for the increased bass trapping, you could go to a lot of work and keep your insulation off the insides of the panels, or you could allow it to touch a bit and broaden the panel's response, making for a smoother absorption curve. This would also, however, lower your absorption coefficient at resonance from about .9 to around .7 or so, so if you're calculating ALL your absorption figures for ALL your walls, ceiling, and acoustic treatments, you need to take that into account.

One other thing to consider - your room dimensions. If they are going to cause modal problems anywhere in the 50 to 100 hZ range, that's your target frequency for calculations on panel cavity depth - this would override just placing studs next to the wall; panel trap frequency is calculated by the mass of the panel and the depth of the air space (including insulation) - the formula is

Fo=170/sqrt of m*d,
where
Fo is the resonant frequency in hZ,
m = surface density of the panel in lb/sq ft, and
d = depth of air space in inches.

for example, 5/8 drywall with a 3.5" air gap works out to around 60 hZ - with no insulation inside, this peak will be only about an octave wide; with insulation, it should broaden out to around 2-3 octaves usable, with its peak about 20% less than without insulation.

The standard way of building panel traps is to use rigid fiberglass - this improves absorption over the fluffy kind, where in regular sound isolation walls the fluffy stuff is almost as good as the rigid. Reason for this is the way panel traps work - externally, they are a pressure device which is why they work best with no air space behind the trap assembly, and placed against a wall or ceiling. Inside the trap, however, different things are happening - the moving panel (caused by external bass wave pressure) tries to move the air inside the trap - in order for the air to move much, it has to pass through the rigid fiberglass insulation, which has a fairly high resistance to gas flow - the bass energy is first absorbed by the work required to flex the outer panel; then, by the air trying to get through the absorbent - sort of a "double whammy" effect.

Bottom line - probably the best way for you to use your 3 basement walls for trapping would be to first measure all your room dimensions, then calculate modal frequencies (at least the axial ones), and finally pick a frequency where there are a couple of modes bunched up around 50-120 hZ or so, and choose your air gap depth based on that frequency and the above formula - in almost all cases, resonance of wall panels will cause no discernible ringing, so just gluing rigid fiberglass to the concrete will keep it from contacting the panels and you'll get the most absorption.

Speaking of basements, have you come across the "basement from hell" PDF here yet? If not, yell; I forget where it's hiding at the moment.

Hope that helped some... Steve

I did a quick search on "basement AND from AND hell", but didn't find anything relevent. I'm curious.

Fourth post down, on this page -

http://www.johnlsayers.com/phpBB2/viewtopic.php?t=839

HTH... Steve

Thanks Knightfly. I call that "The Famous Mold PDF".

Thanks Steve, an excellent response! I appreciate you taking the time to explain it. Yep I read "The famous Mold PDF" a couple times a few months ago, it was before I moved into the new house so I couldn't apply it to my situation at the time, better read again. The basement wall insulation was covered in plastic, so I definitely want to get rid of that. I thought about using that landscaping fabric to cover it, so it can still breath, but should keep in the fibers. Its a moot point once I get the sheetrock on anyway (still removing the plastic of course.)

Gluing 703 to the brick definitely seems the way to go, but I'm guessing I might want to treat that brick first? I'll re-read the pdf and look for an answer.

Modal problems - Since I'm using splayed walls, will that take care of the modal problems? The framing is already up on the exterior walls, I suppose if I need to increase the cavity depth, I could attach some kind of battons(not sure what they be called) to the face of the 2x4 frame and attach the sheetrock to that? Essentially creating 2x6 or whatever depth I need.

I think I'm to the point where I just need to start working on it. Probably start a new thread with some pics and questions as I encounter specific issues.

Thanks alot guys. Lets see if I can get this 2 month project done by next summer!

-HB

Splayed walls won't get rid of modal problems, it will only shift them to unknown variables The good news is, it WILL help things like flutter echo, and early reflections - it will also make modal problems (between the splayed walls, not between still-parallel ones) less violent in response, because the distance between those walls is constantly changing so the frequency will change as well.

Be sure to thoroughly understand all the ramifications in that basement PDF before you finalize your plans - dunno about you, but tearing out walls and redoing them isn't on my list of favored things to do over and over and over - it's a short list, consisting of pizza, sex, beer, music, reading whodunnits, and...... nope, no wall-tearing out, sorry... Steve

I plan on using the design on p13, fig15 of the BSC pdf. So I would put 2" XPS board aginst the cement wall, then put in 1" 703 then 1 layer of 1/2" sheetrock. I'll have to use 1" 703 instead of 2-3" so that I can fit it in the stud cavity and leave a slight gap before the sheetrock. I think if I went with 2" I'd be stuffing it in there too much? I know slight damping has some benefits, but this seems like it may be too much?

The only question is 703 a semi-permeable vapor barrier? (My limited understanding)The XPS insulation will allow some moisture through and allowing it to vent to the room. Because you want moisture to escape either to the outside or the inside, and I'm almost totally below ground so I need it to escape into tthe room. If the 703 is not permeable, then I would only be able to cover 1/2 to 3/4 of the wall height with the 703, leaving some are for vapor to escape. Don't know what effect that would have on my bass trapping, but it can't be good.

So is this what you would derive from that pdf as well, or am I looking at it wrong? From the Owens Corning 700 pdf it appears that the 703 will not act as a vapor barrier (desired) unless faced with FRK. Which menas I should be able to cover the enitre height of the wall.

I think I'll start a new thread on interpeting results of those calculators. I used a few and still couldn't tell what I was looking at. Didn't seem like I had any modal problems below 250 khz. Wouldn't that be lucky. But are you suggesting that with splayed walls modal problems will exist, but calculating them would be impossible?

Thanks Steve!

-HB

From the Owens Corning 700 pdf it appears that the 703 will not act as a vapor barrier (desired) unless faced with FRK

Yes.
Plain (unfaced) 703 will let moisture through it.

There's two types of faced 703, one of which is the FRK. I'm not sure how much of a vapor barier it is though. I think FRK is Kraft, which is mostly paper, so it's more of a vapor retarder than a barier. But I don't know.

Thanks for the confirm z.

Everything I know about construction I learned here in the last 6 months, so no practical experience whatsoever. So making decisions that can impact the structure or performance of my new house is nerve racking.

Should have seen my nerves when I pulled that load bearing post out of the basement...

Replaced it w/ a steel beam. So far so good, but it still makes me nervous...It's been nearly a year now.

Aaron