OC703 vs OC705 in bass traps

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DrewPeterson7

DrewPeterson7

Sage of the Order
Ok, long story short, one of my roommates is moving out so I'm moving from my room to his (bigger) room. Additionally, we're taking an upstairs hallway we'd previously used mostly for storage and filling it with bookcases, and since most of the pictures hanging on our walls downstairs were his, I'll be taking most of mine and moving them down to the common space of the apartment as well. Since most of my room's walls were previously covered with bookcases (hey, I read a lot) and picture frames, suddenly I'll have a LOT of available wall space, which I plan on using for bass traps - the bigger room is maybe not ideal, acoustically, but it's a better space to record drums in and I'll be tracking them in a couple months for this album I'm working on, so I want to get the room ready for tracking drums and mixing before then.

I know, way more detail than you need, but this is going to be the first of many threads on acoustic treatment, so... :D

So, my first question... As I understand, OC705 is quite a bit denser and 2" of insulation provides approximately the same bass trapping as 4" of 703. Is this true, at least within reason? I was thinking of starting with six panels, and six 2" sheets of 705 are both a bit cheaper than 12 2" sheets of 703, and would also take less physical space, which would make it a bit more practical to (at least temporarily, for drum tracking) hang one or two from the ceiling, which I haven't measured but I'd guestimate at around 9', which as a 6' guy I don't want to lose TOO much height.

If it matters, my plan is to make fairly thin wooden rectangular frames on the back side, glue or otherwise fasten the insulation to the front of the frame, and cover them in fabric, something vaguely burlap-y. I plan on enlisting my fabric-handy mom to help with the fabric part, so they don't look absolutely horrid. :D

I'll also post another thread after I've measured the room to discuss orientation and speaker placement and whatnot. This has to serve first and foremost as a bedroom, but I'm hoping I can find some way to make it work relatively well as both a bedroom and a good acoustic space for mixing.
 
May have answered my own question, doing some *gasp* research. :eek:

http://johnlsayers.com/Stuff/AbsorptionCoefficients.htm

705, plain 2" (51mm) on wall 6.0 pcf (96 kg/m3) 0.16 0.71 1.02 1.01 0.99 0.99 0.95

703, plain 4" (102mm) on wall 3.0 pcf (48 kg/m3) 0.84 1.24 1.24 1.08 1.00 0.97 1.15
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So, basically, they're pretty comparable above 1k, but below that 4" of OC703 theoretically should provide far superior trapping vs 2" of OC705, and it's almost certainly worth the extra $20-30 or so and the extra couple inches of space.
 
Sounds like a plan. I know RickF has mentioned several times that 3.0 pcf is the target density and thicker is better.

For the fabric, if you like burlap, then good, but you're not limited to it. I find my fabric in the clearance bin at Walmart. $1/linear yard. Cheap stuff. Just look for a lightweight fabric. If you can blow through it easily, it's good for acoustics. I used a spray on adhesive to hold it to the OC703. Be sure to get the fabric on correctly the first try. If you spray the panel with adhesive then lay the fabric down and pull it back off to reposition, you might pull chunks of the 703 with it.

We will need pics of the new room!!! :D
 
Chili said:
Sounds like a plan. I know RickF has mentioned several times that 3.0 pcf is the target density and thicker is better.

For the fabric, if you like burlap, then good, but you're not limited to it. I find my fabric in the clearance bin at Walmart. $1/linear yard. Cheap stuff. Just look for a lightweight fabric. If you can blow through it easily, it's good for acoustics. I used a spray on adhesive to hold it to the OC703. Be sure to get the fabric on correctly the first try. If you spray the panel with adhesive then lay the fabric down and pull it back off to reposition, you might pull chunks of the 703 with it.

We will need pics of the new room!!! :D
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:laughings: I'll be painting over the weekend. Once I finish, sure thing. I'll try to clean and straighten my current room to photographable condition, and give you before/after shots. It's an old house, but not without it's charm. :)

I was thinking of not bothering with adhesive on the cloth, but simply staple it to the wooden frame. One sheet across the back of the frame trimmed to size and pulled tight, then a second wrapped around from the front and sort of folded down like, oh, like a properly tucked in sheet on a bed or something, and then stapled to the back. Then, a wire across the back a la a picture frame, and simply hang them off the walls (maybe trying to space them an inch or so off the walls, as a compromise for a little extra absorption without looking too weird for a bedroom).

I remember hearing that "if you can blow through it, you're probably fine" thing before here. I think we have a fabric store in town, and my mom was kind of all gung-ho about going fabric shopping with me so I'll probably go there. She also isn't really as musical or as into music as I am (I inherited that from my dad), so it's a way for her to involve herself a bit in a hobby/passion of mine and I think she's looking forward to that. You know how parents are. :D
 
Check the link in this thread.

As well as CIRO's comments and the link he provided in there.

From what I've been gathering, for thicker panels, less dense material has better performance in LF.
 
noisewreck said:
Check the link in this thread.

As well as CIRO's comments and the link he provided in there.

From what I've been gathering, for thicker panels, less dense material has better performance in LF.
Click to expand...

Yep, that was the thread I found when I started digging around on my own. :)

When you say "thicker panels," you mean thicker than 4", right? I think that's about the thickest I can get away, given that this has to be primarily a living space, and only secondarily a 'studio.'
 
DrewPeterson7 said:
Yep, that was the thread I found when I started digging around on my own. :)

When you say "thicker panels," you mean thicker than 4", right? I think that's about the thickest I can get away, given that this has to be primarily a living space, and only secondarily a 'studio.'
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Yeah for the panels 4" is pretty much all most of us can do. I was more referring to corner "superchunk" type stuff, where you get a lot more thickness in the center section.

Although, it seems no one really knows what the hell is going on in the corners, and I haven't been able to find test data with less dense (such as RHT 40) material as superchunk. Everybody seems to be going to the OC 703 by default.
 
Hrm. Corners are going to be tough for me - I'll do something a bit more exact in Google Sketchup tonight, but this is roughly the floorplan, attached.

The dotted lines are where an angled wall meets the ceiling, and there's a little alcove with a window - the other side has a door. I could probably fit my desk in there, but somehow putting it intentionally in the smallest section of the room seems like a bad idea, somehow, so I've been thinking of putting my bed against the wall at the bottom, and setting my desk up on the far wall, centered, facing my bed.

I'll start a proper thread about that tonight though.
 

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Don't jam your desk into that little alcove. You'll want to be 30% of the way into the room anyhow, which will put you well back behind it anyway.
 
Weasel9992 said:
Don't jam your desk into that little alcove. You'll want to be 30% of the way into the room anyhow, which will put you well back behind it anyway.
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Wasn't planning on it - see above.

Also, 30% into the room is simply not going to happen. Again see above - this is first and foremost a bedroom that I'm acoustically treating to make it double a bit better is a studio. I COULD put a desk 30% into the room... but if I was to do so, I'd lose (including the desk) something like 50% of my floor space, and rooms in old Boston houses are small enough as it is.

It's theoretically correct, yes. It's also a practical impossibility.
 
703 and 705 are not interchangeable. I forgot the technical term for it, but higher density 'glass can actually reflect sounds coming at extreme angles.

In either case, you will get the most bang for your buck by mounting the panels a distance away from the wall equal or greater to their thickness.

You might also want to consider mixing it up and using lower and heavier density materials. Check out mineral/rock wool in the 3-8pcf range.
 
One observation/question, since the subject is bass traps.... :)

I notice some guys here who build and/or buy bass traps end up attaching them flat up against the side walls.
Maybe Ethan or one of the other pro acousticians can comment...but as I’ve always understood it…you're supposed to have some space behind the traps (a few inches at least) for them to fully realize their bass trapping potential...otherwise when they are flat against the wall, they end up being more mid/high absorbers rather than bass traps.

???
 
miroslav said:
One observation/question, since the subject is bass traps.... :)

I notice some guys here who build and/or buy bass traps end up attaching them flat up against the side walls.
Maybe Ethan or one of the other pro acousticians can comment...but as I’ve always understood it…you're supposed to have some space behind the traps (a few inches at least) for them to fully realize their bass trapping potential...otherwise when they are flat against the wall, they end up being more mid/high absorbers rather than bass traps.

???
Click to expand...

I think this is technically the best way to go, but again many of us have other constraints to work against rather than the theoretically most pure. In my case, I simply don't have the space necessary to leave even 6" of dead air behind my bass traps, even though that would definitely increase absorbtion.

...though, it's possible I could jerry-rig something such that whenever I wanted to mix or record something that would require room mics, I could put "spacers" under them, angling them out from the wall or something, to increase low-frequency absorbption.

Anyway, my roommate's only half done moving out, but I went in there this morning and did a couple preliminary measurements. It looks like the room's about 12' by 12', with that corner cut out of one side and the slanted ceiling on the other, plus the alcove. Ceiling's maybe 7'2", so I have even less space than I thought, and being 6' and all I might not want to take another 4-5" off the ceilings with ceiling mounted bass traps (or, maybe I ought to just make the best of it and only put 2" panels on the ceiling so I at least get some absorbption, even if it's not entirely broadband).
 
DrewPeterson7 said:
Wasn't planning on it - see above.

Also, 30% into the room is simply not going to happen. Again see above - this is first and foremost a bedroom that I'm acoustically treating to make it double a bit better is a studio. I COULD put a desk 30% into the room... but if I was to do so, I'd lose (including the desk) something like 50% of my floor space, and rooms in old Boston houses are small enough as it is.

It's theoretically correct, yes. It's also a practical impossibility.
Click to expand...

Your EARS have to be at the 38% mark, not the desk...
 
Weasel9992 said:
Your EARS have to be at the 38% mark, not the desk...
Click to expand...

Which brings up a question for me. Is this calculated from the actual wall? What if you have a full wall covered with acoustic treatment, absorbers, diffusers, etc? Do you still calculate the distance from the actual wall?
 
noisewreck said:
Which brings up a question for me. Is this calculated from the actual wall? What if you have a full wall covered with acoustic treatment, absorbers, diffusers, etc? Do you still calculate the distance from the actual wall?
Click to expand...

It's calculated from the hard boundary surface itself, not from whatever you have installed on it.
 
Chili said:
I have a 10'x10' room and my head is right about there with the desk up against the wall. :o
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:lol: You were able to make it work, though?

I've got ceilings that are about 7 1/3 feet tall, IIRC - how do yours compare? Have you tried tracking drums in your space yet?

I grabbed paint and supplies on my lunch break today, so I'll be starting the prep process tonight. :D
 
DrewPeterson7 said:
:lol: You were able to make it work, though?

I've got ceilings that are about 7 1/3 feet tall, IIRC - how do yours compare? Have you tried tracking drums in your space yet?

I grabbed paint and supplies on my lunch break today, so I'll be starting the prep process tonight. :D
Click to expand...

Yeah, It sounds pretty good. I tried taking official sound measurements with an audio analyzer, but it didn't have the resolution to provide an accurate graph. I think it was only capable of 1/3 octave and Ethan Winer said I needed something better. So, my only assessment is by listening to commercial material and compare. I like what I hear and I think my mixes come out okay.

My ceiling is about 10' tall, so I have a near cube, the worst shape for a room. lol. But 703 in the corners, 1st reflection points, behind a subwoofer, on the front and back walls, a cloud, speakers detached from mounts; I think I've got it covered.

Really, I only record vocals and acoustic guitar live. The rest is DI, modelers, or VSTi's; all in the box. Because of that, I'm not as concerned about the tracking properties of the room as I am about the mixing. I also don't crank my monitors up too loud, so not as much energy to attenuate. I think that's why I can get by with what I've got.

HTH,
 
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