without the some more specific info (check the sticky of the construction forum), i can say that a thicker panel w/ a space behind it will absorb a lower frequency than any other suggested. i have a lot of doubts as to how much 33hz would get effected, so i'll assume where talking 66/99hz. massive traps are needed to hit low as 33, and wall mount stuff generally is pretty minimal in that range, unless you get into resonators. at my old home room i just used 4" rockwool and some door stop spacers, and built 2 resonators tuned to 77hz. the results were'nt optimal, but workable and predictable.

you need mass to absorb lows, so i'd keep expectations low for the capabilities of 2" fiberglass. but spacing will maximize the effect.

your best bet w/ the 33hz is to hpf

Follow-up - More difussion

Thanks kmetal. Yeah, my guess is that the only thing of reasonable physical size that could make a dent in 33Hz would be a spring trap device. Thankfully, the resonance of its harmonics are small enough to not be as big a problem. Now I'm grappling with if I should go with the typically 25% (or so) mid-range coverage (fiberglass type absoptive panels), wondering if it will deaden too much mid and high stuff. wondering if I should include just a bit more diffusion instead of absorption. right now, I only have diffusors planned for the back wall. (Of course, I have absorption located at all the first reflection points.)

Again, thanks.

i've never found 25% to be too much, especially in average residential type spaces. it usually ends up being about what you need to take care of the 1st reflection points. don't forget your ceiling cloud, mucho importante.

you have the right idea about location if the diffusion. but to achieve "true"diffusion requires alot of space. so w/ a 12ft depth, i'd experiment w/ both absorption and diffusion. or more specifically finding a good balance of low trapping, and mid/high scattering. the axial mode of concern, on a 12ft depth somewhere around 95hz, 62hz for 18ft width. Based on your dimensions my main concern would be that since the ceiling height is a multiple of the width you end up exciting the harmonics between in those boundaries, because they are multiples of each other. so these 2 areas are reinforcing each other, exaggerating the same peaks and dips. also the 12ft dimension is gonna have some modes in common as well, like 188, and 376.

i'd personally experiment w/ the orientation of the room, and see which way sounds better, and more accurate. having the speakers 'throw' down the longest dimension yealds a lower mode, and allows room for thicker treatment. but that's all in theory so i'd just try both and do some basic test w/ the mirror points covered, and see what ya like the best. glad i could help a little.

p.s i'd much rather deal w/ a slightly more dead room, than one that has slightly more comb filtering, but thats just me if i have to compromise.

we can help

Ars Nova, post: 396134 wrote: I have wrestled with the equations, and manufacturers' data, but would like some informed, practical advice.

I am acoustically treating my newly completed project studio - including extra thick and damped drywalls. My room measures 18' x 12' x 9'. Those dimensions, though either a Sepmeyer or Louden (can't remember) preferred ratio, still exhibit a 33 Hz mode. I may not be able to completely get that, but hope to lessen its higher multiple frequencies. So...the obvious...bass traps and some fiberglass acoustic panels.

My questions are specifically about fiberglass acoustic panels: Which is superior in overall performance? And which is superior in low bass mitigation?...a 2" fiberglass panel mounted to the wall, or a 1" panel mounted with a bit of space behind it, or a 2" panel mounted with some space behind it?

My reason for the question -- In some cases I have adequate mounting room to mount the panels a bit off the walls / ceilings, and in others it would be a bad idea.

Many thanks.

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As an aside, and just curious, where in the room are you planning on monitoring/mixing from?

I have preliminarily placed the mix position (the standard starting place) 38% of the length of the room from the West Wall. The monitors, again in a preliminary position, are set to form an equilateral triangle with the mix position. Those are set so that they are not obstructed by the computer monitors at the back of the desk. (By the way, I have my monitors set as flat as possible, while still making sure that reflections off of them from the monitors bounce back, not up to the mix position.

Thanks for your interest.

I was just curious as to how close to the center of the room you planned on placing your production center. It's been my personal experience that the closer I am to the center of the room in which I'm mixing, the better results I get. My best guess is that it has to do with the various frequencies in relation to the time that they are hitting my ears. Centering the mix position seems to allow the freq's to hit me at roughly the same time; this is, of course, all relative to the sound of the room itself, various absorbers, diffusors and live areas...

I don't have my pro studio anymore, these days I'm doing hired gun work as a walk-in engineer at various Northeast Ohio facilities... some are very nice, others not so, LOL... Some of the things that make me cringe are 1. walking into a control room and seeing 1" sonex on every square inch of wall space and 2. finding the production center jammed up against a control room window or shoved up against a wall.

I've tried explaining to these guys that 1" absorbers don't do anything for much below 1 k or so, but, they've got it in their heads that in placing this material all over the room that the room, that the room is "tuned".

Tough to crack that nut when people have preconceived notions based on what they've seen in a music video or what one of their friends has told them. It's also difficult to tell them that the money and time spent hasn't resulted in what they thought it would... kinda like telling someone their baby is ugly. LOL

Thank you for your interest and input.

Preliminarily, I have placed the mix position 38% of the length of the room off of one of those ends, and smack dap in the middle of the width of the room...so centered on the width. BUT...this is a preliminary position, I am going to have to test to see if moving slightly forward or backward along the length will yield better results. First, I have to work through some low freq mode stuff (as you probably read above)...around 32Hz and its multiples. But confirming your experience, I am pretty sure, even without setting a mic and test measures to prove it (that is, just by my ears) that smashed up against a wall or window is DEFINITELY NOT going to yield good results.

I have a vacation week coming up where testing, bass trap building, furniture moving will be on the agenda!

Again thanks for the input.