Cavity Resonance?

[Jack Russell]

I am putting up drywall at last in my studio, but I have a cavity between my concrete foundation and the back wall, which is angled (to avoid direct reflections). So, I have two 9' x 7' walls joined at an angle of about 175 degrees, with a 10-inch space behind where the drywall will be and the concrete wall. There is a 2-inch house wrap insulation next to the wall.

Will I have problems with resonance? If so, should I fill the space with something?

[Dang. It won't let me upload my plan. You can find my plan on the thread "Lighting versus Clouds"]

[Jack Russell]

Yipee! Post number 392.

[Jack Russell]

Post number 393.

[Jack Russell]

My cavity is really resonating now, baby!
Post 394. 400 is within reach!

[Jack Russell]

Links to stuff about 'cavity resonance'. None of which I really understand.

http://hyperphysics.phy-astr.gsu.edu...ab/cavity.html

http://www.downeastmicrowave.com/cavity.htm

http://www.eccosorb.com/principles/M...e_RFDesign.pdf

None of these really help much...













...but I am able to post number 395!!

[apl]

Originally Posted by Jack Russell

Will I have problems with resonance? If so, should I fill the space with something?

It's quite possible. You could put some pink fiberglass bats in it, you don't need to fill it.

[Jack Russell]

Originally Posted by apl

It's quite possible. You could put some pink fiberglass bats in it, you don't need to fill it.

Thanks, man. That is what I figured I'd do--just chuck in a few bats of pink stuff.

You know I was just being sarcastic on the other thread today, don't you?

And obnoxious.

[apl]

Originally Posted by Jack Russell

You know I was just being sarcastic on the other thread today, don't you?

And obnoxious.

It's The Cave, man! Of course I know.

[TexRoadkill]

I don't think resonance will be an issue but you could make better use of the space as a bass trap. If the purpose of the space was to function as an air space for sound proofing then you would want to leave it empty or just put some insulation on the walls inside.

I would use it as a bass trap. Instead of drywalling that wall you could put up some wood slats and leave some gaps, float some 703 behind it and you have a slot resonator. If you want a more live feel you could fill the gap with insulation and cover the wall with pegboard and/or fabric or to really deaden it just use fabric.

[apl]

Originally Posted by TexRoadkill

I don't think resonance will be an issue but you could make better use of the space as a bass trap.

Brilliant idea!

[Jack Russell]

Originally Posted by TexRoadkill

I don't think resonance will be an issue but you could make better use of the space as a bass trap. If the purpose of the space was to function as an air space for sound proofing then you would want to leave it empty or just put some insulation on the walls inside.

I would use it as a bass trap. Instead of drywalling that wall you could put up some wood slats and leave some gaps, float some 703 behind it and you have a slot resonator. If you want a more live feel you could fill the gap with insulation and cover the wall with pegboard and/or fabric or to really deaden it just use fabric.

Wow. Can you guys be more specific? I know what a bass trap is, but what kind of wood? How large the slats and spaces between? space the slat over the entire surface or just the bottom? I'll post a shot of what I have. It is studs at the moment.

I'm a novice at studio building. So please speak to me like I'm a third grader.

Thanks,
JR

[Jack Russell]

Here is the wall. I have placed a drywall ruler (48 inches long) for size reference. Two views of it.

[Jack Russell]

Post 400!!! At last!!!

Now, do I get money sent to me or something?

[apl]

Have you read www.ethanwiner.com/acoustics.html ?

[Jack Russell]

Originally Posted by apl

Have you read www.ethanwiner.com/acoustics.html ?

Yep. More than once. It sort of goes over my head, unfortunately. I understand the basic theories, but I don't know what a "slot resonator" is.

Not only that, but getting 2" wide 703 in my area has proven difficult. Any idea for a good on-line source?

Edit: I'll read it again though. Maybe it will sink in?

[Jack Russell]

Here's the wall I run into a lot while building a home studio:

Most people like me have a limited budget to begin with. Hence, the term "home studio". The more I get into the details of sound technology, the more I run into cost barriers. There are ideal room dimensions to start from, but if you don't have enough space, what can you do?

At some point one just has to throw up their hands and say, "I have to wing it a bit!"

Another example: I could get all kinds of exact measurements for the angled wall, which is the topic of this thread, and I could carry out calculations (or hire someone to calculate) nodes, hum, etc. etc., and then I could go purchase just the right materials (ouch!), and do it to perfection.

Or I could just chuck some pink insulation into the cavity and wall it up. Or "wing it" and make it into a crude bass trap. It is hard to know what the end result will be.

IOWs, I'm not sure the gain in technical nuance really offsets the money spent.
???

[apl]

Originally Posted by Jack Russell

Or "wing it" and make it into a crude bass trap.

How 'bout leaving every third space between the studs undrywalled and covering those openings with burlap, after putting a bunch of pink in the cavity? The one thing you've got going for you is a lot of space for absorption, and this may be a cheap way of exploiting it.

[Jack Russell]

Originally Posted by apl

How 'bout leaving every third space between the studs undrywalled and covering those openings with burlap, after putting a bunch of pink in the cavity? The one thing you've got going for you is a lot of space for absorption, and this may be a cheap way of exploiting it.

That sounds good. Is there something I can use besides burlap, though, that would look a little less cheesey? I could prbably afford to construct some sort of wood slats that would be attractive.

And would you leave the entire space open from floor to ceiling between the stud? Or just near the floor? Doesn't the bass travel mostly on the floor?

Another question: Is the ultimate goal to have a trap that essentially gathers ALL the bass frequencies or just to attenuate them to a degree? I am hoping to a RFZ at the console, for the highs and mids, but the bass is unknown without bass traps of some sort. Am I right?

[RICK FITZPATRICK]

I understand the basic theories, but I don't know what a "slot resonator" is.

Here ya go Jack. Its quite easy and looks fantastic. One thing though, the interior gap must be sealed at the ends, floor and cieling(like a bottle).

http://www.saecollege.de/reference_material/index.html

[apl]

Originally Posted by Jack Russell

That sounds good. Is there something I can use besides burlap, though, that would look a little less cheesey? I could prbably afford to construct some sort of wood slats that would be attractive.

Yeah, the open part just needs to be acoustically open.

Originally Posted by Jack Russell

And would you leave the entire space open from floor to ceiling between the stud? Or just near the floor? Doesn't the bass travel mostly on the floor?

It doesn't matter too much. Around 1/3 of the area being open into the absorber would be plenty.

No, the wavelengths are large, so they tend to be everywhere. Corners focus them, though.

Originally Posted by Jack Russell

Another question: Is the ultimate goal to have a trap that essentially gathers ALL the bass frequencies or just to attenuate them to a degree?

Yes. That's what I don't like about slot resonators, they are essentially a tuned device with a little damping to increase their effective bandwidth. Plus they gotta be sealed and are a lot of extra work.

Originally Posted by Jack Russell

I am hoping to a RFZ at the console, for the highs and mids, but the bass is unknown without bass traps of some sort. Am I right?

You could put a stack o' 703 triangles in the corners behind the mixing desk.

[Jack Russell]

Originally Posted by RICK FITZPATRICK

Here ya go Jack. Its quite easy and looks fantastic. One thing though, the interior gap must be sealed at the ends, floor and cieling(like a bottle).

http://www.saecollege.de/reference_material/index.html

Aha! Bingo, I figured it out. A slot resonator is also known as a Helmholtz resonator. That might be the answer!

Thanks, man!

Also: I assume a slot resonator is the same thing as a slat resonator. Yes?

Now, if I can just resonate my slut....

[RICK FITZPATRICK]

Aha! Bingo, I figured it out. A slot resonator is also known as a Helmholtz resonator. That might be the answer!

How bout a wall of Broadband Slot resonator-Panel Absorber-Polycurve Slat Diffuser instead?
fitZ

[Jack Russell]

Originally Posted by RICK FITZPATRICK

How bout a wall of Broadband Slot resonator-Panel Absorber-Polycurve Slat Diffuser instead?
fitZ

Good god, man. You must be obsessed!

That is really frikkin' cool though. Thanks for taking the time to spec that out. I will have to think about it awhile. That would do the trick for sure.

Cheers,
JR

[TexRoadkill]

A quick and dirty way if you don't want to do all the math is just put some 703 in the space between the studs. Cover the wall with frabric. Then rip up some 8' strips of 1/4" or 1/2" plywood in 6" widths. Nail them up going horizontally across the studs. Leave a random gap between slats of about 1/4"-1". If you make the gaps into a pattern it won't look like your just a sloppy carpenter.

Check out the walls at Blue Bear's studio http://www.bluebearsound.com/gallery_studio.htm

[Jack Russell]

Thanks, Tex. That is a great idea also.

At this point, due to pretty significant time and money pressure in my life (life sucks...then you die ), and the fact that I need to "finish" my studio/rehearsal room soon so I can get by band to start using it, here's what I'm doing:

1) I filled the space with CertaSound insulation, made my Certainteed. This appears to be cheaper than 703, or at least it is what I can get locally today.

2) I have laid burlap over every other stud, from 6 inches to 60 inches up from the floor. So I have four 15" by 54" burlap-covered openings. The rest I will just go ahead and cover with drywall.

It isn't ideal, but I could revisit this later and upgrade it.

What do you think? I wonder if the 4 holes are enough space though. Apl said it should be one-third (see above).