Could I literally just put boxes of fiberglass in corners instead of taking them out?

C

crimsonhawk47

New member
Owens offers 24''x48''x'2'' 703 rock wool in packs of 6. I was wondering if it'd be even more effective to just leave these in the box and stack them in the whole corner? It sounds like they're tightly packed. The only issue I have with it is an understanding about treatment that some people seem to disagree with. I've heard that if you straddle a corner with 703 and leave space behind it, it's almost as good as filling the whole thing. Basically saying a 2'' 703 panel straddling the corner, with the middle of it being about a foot away from the corner, it is almost as good as having all that space filled with more 703 (essentially a soundwave hitting that corner at 45 Degrees has close to 14" of absorption. If that is true, then it would be redundant and a waste of money to stack a 6 pack there. Can anyone confirm that phenomenon?
 
no

the idea behind the rock wool is that the air meets the rock wool and dissipates its energy as it tries to move through it

leaving the rock wool in the boxes means that the air simply bounces off the less porous surface of the box, effectively reflecting instead of absorbing the air flow
 
the phenomenon is real as you are creating impedance mismatches with an air-rock wool-air boundary differential

i.e the movement of the sound through the rock wool is different through air and each boundary layer improves absorption simply because the air moves differently

however whether the benefit is the same as having several layers of the rock wool and only one air interface either side or having multiple air interfaces between each layer is only something that listening can tell you for sure
 
bandcoach said:
the phenomenon is real as you are creating impedance mismatches with an air-rock wool-air boundary differential

i.e the movement of the sound through the rock wool is different through air and each boundary layer improves absorption simply because the air moves differently

however whether the benefit is the same as having several layers of the rock wool and only one air interface either side or having multiple air interfaces between each layer is only something that listening can tell you for sure
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Good to know! Thanks for the help. I think I'll just wrap each panel in burlap like most people do and individually replace the Auralex I did years ago. Should pan out to 1.412 distance on each side of a corner and I have conveniently enough room for that. Thanks a lot.
 
Actually it'd be helpful if you could clear up a few more things.

1) I heard that standing waves don't just cause problems in low frequencies but create positive and negative pressure THROUGHOUT the frequency spectrum. Because of this, it's been said that broadband absorption can also keep your room from being boxy at some areas and harsh at others. Is this true?
2) I can't seem to find 4 inch 703 panels. I know at a certain point a problem room is still a problem room, but it sounds like I won't be able to absorb farther any lower than 70 HZ with a 14" gap (except for all the soundwaves hitting at angles of course. Theoretically I could get a few feet between the time it hits the 703 and the time it leaves). Is there anyway to remedy this? Like is it better to hang the panel suspended slightly away from the wall than against it? Or maybe I can find some places to do the 4' side across instead of 2'? Or is it just better to do what I originally was going to do but with even more traps: Vertically aligning all the 703's. This is the same room I record vocals in.

Edit: And when people say they need a quarter wavelength thick, is the quarter calculation supposed to compensate for distance traveled TO the panel? This article on Ethan's Real Traps says 41.2 HZ have a 1/4 wavelength of 6' 10-5/16". Does that mean that if a soundwave that size traveled 2 feet to the panel, then bounced at such an angle that it traveled another 4 feet by the time it came out, that I've essentially resolved it in open air? The chart is on the left hand side of the article RealTraps - Bass Waves in the Control Room
 
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crimsonhawk47 said:
Actually it'd be helpful if you could clear up a few more things.

1) I heard that standing waves don't just cause problems in low frequencies but create positive and negative pressure THROUGHOUT the frequency spectrum. Because of this, it's been said that broadband absorption can also keep your room from being boxy at some areas and harsh at others. Is this true?
Click to expand...

yes it is true this is why room treatment is not just a case of absorption at early reflection points or in handling low freqs with bass traps

of more importance, though, is the overall balance of the room mode resonances and their integer multiples if they have an even spread then the room may require less treatment than one where the dimensions actually add to make some freqs have more prominence

2) I can't seem to find 4 inch 703 panels. I know at a certain point a problem room is still a problem room, but it sounds like I won't be able to absorb farther any lower than 70 HZ with a 14" gap (except for all the soundwaves hitting at angles of course. Theoretically I could get a few feet between the time it hits the 703 and the time it leaves). Is there anyway to remedy this? Like is it better to hang the panel suspended slightly away from the wall than against it? Or maybe I can find some places to do the 4' side across instead of 2'? Or is it just better to do what I originally was going to do but with even more traps: Vertically aligning all the 703's. This is the same room I record vocals in.
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to make 4" panels simply put 2 2" panels together; I know it sounds obvious but it really is as simple as that -

as for panel hanging the air gap between the rear of the panel and the wall is probably just as crucial as the rock wool itself - the change in acoustic impedance as the wave moves from the rock wool to free air is significant and adds to the absorptive qualities of the panel overall
 
bandcoach said:
yes it is true this is why room treatment is not just a case of absorption at early reflection points or in handling low freqs with bass traps
Click to expand...

Is that also to say broadband absorption isn't just a "low shelf for the room" and the problem isn't necessarily too much bass?

bandcoach said:
of more importance, though, is the overall balance of the room mode resonances and their integer multiples if they have an even spread then the room may require less treatment than one where the dimensions actually add to make some freqs have more prominence
Click to expand...

That's a little complex for me. What I hear is that the construction and layout of the room is more important than the treatment? Much like tracking/arranging > mixing? If so, I hear there isn't such a thing as too much broadband absorption unless you use material that takes out too many reflections and make the room dead, or too close to an anechoic chamber (and I'm guessing it's damn near impossible for me too make it too dead with 703?


bandcoach said:
to make 4" panels simply put 2 2" panels together; I know it sounds obvious but it really is as simple as that -

as for panel hanging the air gap between the rear of the panel and the wall is probably just as crucial as the rock wool itself - the change in acoustic impedance as the wave moves from the rock wool to free air is significant and adds to the absorptive qualities of the panel overall
Click to expand...

Well I feel very silly for not thinking of that.

Is there a point of drawbacks I should be concerned about when backing off the panel from the corner? If I press a 2x4 against a corner then the distance between the corner and the panel's sides is 1.4142', and the distance between the corner and the middle of the panel is 1'. If I back that off I'll have more room for absorption, but the panels sides won't be pressed against the wall anymore. Are the amount of soundwaves that miss the 703 on the way in and only hit it on the way out, or even maybe not on the way out, going to be a problem?

Again, thank you. Very helpful.
 
And Lastly, in a roughly 12x10 room with a 7 foot ceiling and some 2 feet deep resonant slots in the ceiling, do I need to worry about too much 703 wrapped in burlap killing the highs?
 
the burlap is effectively transparent at most freqs (which is why you can use it as a cover)

the riockwool is a broadband absorber

from bobs coefficients

Productthicknessmountingdensity125hz250hz500hz1000hz2000hz4000hzNRC
703, plain[/th[td]2" (51mm)[/td][td]16" air[/td][td]3.0 pcf[/td][td](48 kg/m3)[/td][td]0.66[/td][td]0.95[/td][td]1.06[/td][td]1.11[/td][td]1.09[/td][td]1.18[/td][td]1.05[/td]
703, plain[/th[td]4" (102mm)[/td][td]16" air[/td][td]3.0 pcf[/td][td](48 kg/m3)[/td][td]0.65[/td][td]1.01[/td][td]1.20[/td][td]1.14[/td][td]1.10[/td][td]1.16[/td][td]1.10[/td]
[th]
[th]

it is apparent that it will be a strong absorber above 250Hz whether as a 2" or 4" panel. Note that these are single panels with an air gap behind not huge constructions as most diy sites show

also consider that you are probably looking at the distance (air gap or air gap + rockwool thickness) being 1/4 wavelength of what you are trying to trap, so 16" off the wall equates to 64" of trapped wavelength (at maximum in a corner) which is roughly 200Hz; i.e. nothing below 200Hz is being affected; if we add in teh depth of the rockwool the numbers become a little bigger and smaller 18" - 72" - 185HZ or 20" - 80" - 170Hz consider this Why Your Bass Traps Don’t Work | Home Recording Blog
 
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bandcoach said:
the burlap is effectively transparent at most freqs (which is why you can use it as a cover)

the riockwool is a broadband absorber

from bobs coefficients

Productthicknessmountingdensity125hz250hz500hz1000hz2000hz4000hzNRC
2" (51mm)16" air3.0 pcf(48 kg/m3)0.660.951.061.111.091.181.05
4" (102mm)16" air3.0 pcf(48 kg/m3)0.651.011.201.141.101.161.10

it is apparent that it will be a strong absorber above 250Hz whether as a 2" or 4" panel. Note that these are single panels with an air gap behind not huge constructions as most diy sites show

also consider that you are probably looking at the distance (air gap or air gap + rockwool thickness) being 1/4 wavelength of what you are trying to trap, so 16" off the wall equates to 64" of trapped wavelength (at maximum in a corner) which is roughly 200Hz; i.e. nothing below 200Hz is being affected; if we add in teh depth of the rockwool the numbers become a little bigger and smaller 18" - 72" - 185HZ or 20" - 80" - 170Hz consider this Why Your Bass Traps Don’t Work | Home Recording Blog
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Damnit... I was reading the wrong number on one of the Realtrap articles... I thought I was absorbing much lower than that. So really I just need to shell out money for real traps? I don't really have room for anything else.
 
building membrane or Helmholtz resonators are still viable options just a different approach - putting the rock wool into the resonators is also a viable way forward giving you action at two fronts instead of 1

go back and read Sound Proofing vs. Sound Treatment and go to the John L Sayers linked site to look into Helmholtz resonators
 
ACtually, I also misread the price on realtraps. I was looking at 2x4, not 2x2, which are cheaper and fit my room better. The only issue is the ceiling (you remember this from back when I had the shelf). I can treat a lot of my corners well but the ceiling is a whole different fiasco.

For a reminder, there are 6 slots in the ceiling and those slots extend halfway over the room (around 5 feet in length). They are 19.5" wide in space, and then the actual beam is 3.5". The beams are 9" deep and the distance from the bottom of a beam to the floor is 6'8''.

I looked into helmholtz resonators, and while I can give it a shot, that seems like a much bigger project and my craftsmanship is shoddy at best.

I'm thinking about ordering a few minitraps and seeing if I can hear them work, and if it's noticeable I can order more. But still, not sure what to do about the other corners in that ceiling.
 

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flying some clouds in those slots would work - 2 x 18" x 24" x 2" per slot would do the trick - a frame that is covered with burlap or similar and filled with rockwool
 
Any reason I'd need a frame? Couldn't I just wrap rockwool in burlap? I've never heard the term cloud before.

I met with someone today who developed a method with the guy that did prince's studio. He said he bought soundboard, put two fiberglass panels around it, wrapped that in a blanket and suspended it from the ceiling. He said because it isn't pressed against the wall it can absorb really far down. Is that true? Because thats essentially what I was going to do with fiberglass. Is it the soundboard that's really absorbent?
 
the board itself is simply a stiff/rigid membrane that causes the sound to change speed as it passes through the rockwool to the board to the rockwool and to the air behind - three acoustic impedance changes leading to lots of absorption over a broadband. the low freq energy will be mostly absorbed by the changes in impedance and the tuning of the cavity behind it

the frame is simply a means of ensuring that you stick to the dimensions required as well as providing a partial Helmholtz resonator
 
Ok, that really helps. I'm just trying to make sure this guy is right, because I don't know how much of the acoustic design was him and how much it was prince's guy. Will it absorb lower than just 2" Fiberglass suspended from a corner? I mean, enough that it will be preferable to do it his way? Otherwise I'm gonna order 2 real traps and see how I feel about those.

And do you say rockwool because it's more effective or will it essentially work the same way as fiberglass?
 
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