R19 fiberglass and need opinions on my situation

[tomlinmgt]

I'm in the process of building bass traps and sound control panels for my garage listening area pictured below. For the traps I'm going to build floor to ceiling panels to triangulate the walls that form the two corners behind my speakers and will use R19 fiberglass batting as my absorption medium with the typical wood frame and burlap sandwich.

I studied the Bob Gold absorption coefficent chart (link below) and found that 6" of fiberglass battting, if given some air space behind, compares very favorably to 4" of 703. They have almost the same coefficient values across the frequency range with exception to 125hz where 6" ofthe R13 is actually 33% better than 4" thick 703. The value of the R19 is undeniable compared to the 703. To build my panels it'll take $35 to achieve the same level of performance as $210 worth of 703. And at that much value I intend to double the thickness of R19 in my panels from 6" to 12" which should add even better LF absorption.

Frequency (hz).................125...250...500..1000..2000..4000
703, plain 4" .........16" air 0.65...1.01..1.20..1.14..1.10....1.16..1.10

Unfaced 6.25" R19..16" air 0.96...1.03..1.13..1.02..1.04....1.13..1.05

http://www.bobgolds.com/AbsorptionCoefficients.htm

Now, I need some opinions wrt how to deal with the hot water heater I have in the corner. My plan is this...If I triangulate the two walls and put the hot water heater just behind the panel my panel width will be 5'. This creates a distance of 30" from the corner to the panel...or the height of the triangle formed by the panel and two walls. I expect the water heater will create reflection and RevMen suggested it would actually create some diffusion, but it's obvious it will consume some of the volumetric air space behind the panel. To balance this in the opposite corner I intend to stack some speaker boxes to create an eqivalent amount of surface area. I will then cover the water heater and speaker box stack with one 6" layer of R19. Hopefully the air space above the water heater/speaker stack will be sufficient to create the "buffer zone" that is represented on the chart by the 16" spacing from the wall. Please offer your opinions/observations.

One final question...is there any benefit to compressing the fiberglass batting as much as possible inside the burlap "sandwich"?

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[VolvoHeretic]

How about the fuse panel, it is illigal to hide it, even behind an access panel. Edit; maybe if you have a giant orange sign pointing it out?

 

[SaSi]

I'd like to point out that R19 is too "fluffy" and as such offers little density. And density (and spacing from the wall) is what offers absorption. Additionally, being fluffy, the compression it eventually gets when confined between burlap sheets will increase it's density giving an unknown (improved) absorption coefficient.

But unknown is bad...

 

[tomlinmgt]

How about the fuse panel, it is illigal to hide it, even behind an access panel. Edit; maybe if you have a giant orange sign pointing it out?

I'm way too libertarian to be concerned with that! Actually you make a very good point. Each corner trap will actually be made up of two 8'x2.5' panels butted up against one another side by side. I'll just move the panel that covers the, uh, panel out of the way when not listening.

 

[tomlinmgt]

I'd like to point out that R19 is too "fluffy" and as such offers little density. And density (and spacing from the wall) is what offers absorption. Additionally, being fluffy, the compression it eventually gets when confined between burlap sheets will increase it's density giving an unknown (improved) absorption coefficient.

But unknown is bad...

I can see your point and also feel that compressing for more density would be beneficial...which is why I asked. But "fluffy" or not, R19 has been assigned measured coefficient values based on a standardized testing method just like all the other materials on the Bob Gold chart I referenced. There is no stipulation that it has to be compressed to achieve the measured values. Certainly those measurements represent the material as supplied by the manufacturer, otherwise there would be deviation from a controlled scientific test.

 

[RevMen]

One final question...is there any benefit to compressing the fiberglass batting as much as possible inside the burlap "sandwich"?

In terms of space saved, yes. In terms of absorption, no. Your test data is for a 6" sample, so if you compress it down to 4" it won't perform the same. You might get better at high frequency but you could compromise your low frequency absorption.

The reason 703 et. al. are preferred for this application is their rigidity for easy mounting and their lower thickness requirements. Mounting batt insulation on a wall or ceiling requires support and containment, whereas the semi-rigid panels just need a skin for protection and a few connections to the wall.

But you're right, batt insulation is much cheaper. If you don't mind paying for and building frames for it, and you don't mind thicker, bulkier panels, then by all means, use the R19.

The thing that makes a corner bass trap work is the distance between the terminations (wall) and the absorptive surface. Unless you're actually sealing off the space behind the panel, the volume doesn't really matter since it's not independent of the volume of the room. I wouldn't bother trying to even out the opposite corner by placing items behind your screen.

 

[merrylander]

How about the rigid form of fiberglass panels? They did our playroom with this type of fiberglass covered with a fabric sorface. I know that the Polk 10Bs from the shop system that I have in here temporarily are putting out more low end than they ever did in the shop. Or maybe they were putting it out before but it just got lost.

 

[RevMen]

How about the rigid form of fiberglass panels?

That's what he's referring to by "703." He's talking about Owens Corning model 703 semi-rigid fiberglass, or one of the equivalents from the other fiberglass companies.

 

[Mike Sommer]

Though the fluffy insulation will provide absorption in the mid to upper frequencies (those above 125 Hz) it has a difficult time controlling low frequencies (those below 125 Hz).

One may not think that is does not matter to have bass control along the walls, it is in fact a very important part of the overall treatment of your room's acoustics, and obtaining a well balanced room. In other words you need wideband absorption along the walls as much as you need bass trapping in the corners. It takes the two working together to provide a well controlled listing or working space.

In most small rooms ( those under 1500 cubic feet) it has been my findings that one needs about 80% of the walls treated with 4" of medium density fiberglass at 3 lb. per cubic foot, and a minimum of 6" of rigid fiberglass straddled across the corners, 24" floor to ceiling to provide effective bass control.

One can achieve greater bass trapping in the corners using a denser product like OC 705 which is 6 lb. per cubic foot.

(I've found that the same amount of material that in required to build 6" thick corner bass traps, one can build more efficient Superchunk basstraps.)

Though this studio below was designed for Voice Over in mind (very dry and dead) this recording and production area was treated with with almost 95% wall treatment on the walls and Superchunks in the corners. The rear of the studio uses a primitive root diffuser to add a little diffusion to the room

As for the water heater, it may be best to move it to a different location, or inclose it and treat the new corners that the inclosure creates.

The rooms dimensions and layout would go a long way to help understand what is needed.

 

[merrylander]

That's what he's referring to by "703." He's talking about Owens Corning model 703 semi-rigid fiberglass, or one of the equivalents from the other fiberglass companies.

It was Owens Corning that did the walls of our playroom. Similar to their 703 but with a fabric surface.

 

[tomlinmgt]

Good info, Mike.....thanks. This is an evolving project so I'll keep your suggestions in mind as I progress.

Built the panels last night.

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I went with 6" of R19 rather than 12" as going that thick would necessitate compressing the bats and I wanted to minimize any compression as I noticed on the Bob Gold chart that increased density at the same thickness reduced the absorption coefficient at 125hz (just like you said, RevMen).

I also have two panels at first reflection held about 8" off wall that I built a month ago but they are 6' x 2.5' and use two 3.5" layers of somewhat compressed R13 rather than the one 6" inch layer of R19 in the bigger panels.

First impression.....mid bass is noticeably better. More forward and very musical although there is just a hint of mudiness (I'm getting pretty critical here) though overall a definite improvement in LF. Soundstage is not what I'd call huge...I mean, it doesn't go beyond the walls....but it did open up compared to before any treatments. Top end is more controlled and perhaps a bit softer. Imaging is very good. However, one big hurdle that I did not overcome (and the one I want to fix the most) is the slight drop in LF db when sitting in the listening position. If I'm standing in the listening position I have nice rich, robust and punchy bass well below 63hz. As soon as I sit down the punch and body of the very low end thins out just enough to begin to notice. The distance of my listening position from the speakers and distance between speakers is 7' (6' in the picture) and I have a very slight toe in. Perhaps I should play with the tilt of the Vandersteens as the Sound Anchor stands allow for this adjustment.

Mike, I like the idea of Superchunk corner traps and possibly boxing in the water heater and treating the created corners. Nested traps behind the corner panels have me intrigued as well. Maybe this will help that LF cut I experience when sitting in the listening position.

 

[Mike Sommer]

Firstly I'm going to tell you that you are almost wasting your time using the the R19.
The R19 will help with comb-filter ringing and some refections which is why your mids cleaned up a little bit. You're almost better off just hanging moving blankets 4-inches off the wall. Belive me when I tell you this, I eat and crap this stuff almost everyday.

What will bring total focus and depth to your rooms sound stage and image is the density of 703. Three Pound per Cubic Foot -- "3" is the magic number. Even Auralex foam has this density, the problem with foam is that you need 6-inches of foam to equal 2-inches of medium density rigid fiberglass- which 703 is.

Looking at you pictures, all you have done is place the equivalent of 4, 2-inch think 703 panels in your room.

The reason why your bass disappeared when you sat down is because you have not taken into account that you are possibly sitting in a null created between the floor and the ceiling. You will need at least a 4-inch thick cloud above your listening position.

You are also going to need a lot more bass trapping than you have provided. This means at minimum, you will need bass traps in all standing corners.

The reason the coefficient end at 125 Hz is became accurate testing at low frequencies is very expensive, and bass can be very unpredictable. A recently released 30 year old NASA white-paper has documented that 703 and 705 perform much better than published data has indicated. Your interpretation of what I said is wrong.

What you need is more compression (denser materiel or thicker) to control the low frequencies. After that initial loss of absorption at 125 Hz it actually gets better, and better yet the thicker and denser the material. An air gap between the wall and the treatment then centers the material in the frequency . General rule of him the air gap should be the same and the thickness of the material.

Besides 703 there is John Manville Insul-Shield
http://www.jm.com/insulation/building_insulation/products/hig1214dk_insul-shield.pdf

 

[tomlinmgt]

A guy that eats and craps this stuff is just what I need, Mike...so if you want to help a guy out then here's what I'm up against.....

[/IMG]

Right side wall (8.5' long)....lots of reflection from the bare sheetrock. First reflections is at the right hand side of the cd shelf.

Wall behind speakers (14' wide)

Left hand "wall" (9' of shelving). I guess I'm getting reflection off the hard surfaces (speaker boxes) and diffusion off the irregular shaped items on the shelves. Definitley not acoustically symmetrical. First reflection is where the Zildjian cymbal case is sitting.

Back "wall"....Eventually all the speakers will be relocated.

Lots of tidying up planned so just about all of the stuff on the floor will be removed. I'm open to covering the shelves with canvas tarps or moving blankets if that would benefit. I'm on a pretty tight budget so let's start with most bang for buck treatments. I have the four 2.5' x 8' panels with 6" of R19and two 2.5' x 6' panels with 7" of R13 to use wherever.

 

[Tubamark]

Firstly I'm going to tell you that you are almost wasting your time using the the R19.
. . . Looking at you pictures, all you have done is place the equivalent of 4, 2-inch think 703 panels in your room.
. . . What you need is more compression (denser materiel or thicker) to control the low frequencies. After that initial loss of absorption at 125 Hz it actually gets better, and better yet the thicker and denser the material. An air gap between the wall and the treatment then centers the material in the frequency .

Data, please.
In my experience, and based on data that I have seen, higher density is detrimental at lower frequencies. The one exception to this is when a 703 or 705 board -- which contains stiffening resins not used in batt insulation -- is suspended in such a manner (airspace) as to permit it to provide diaphragmatic absorption. This is functionally different than porous absorption, and would make any conclusions based on density alone a bit flawed. When adding an airspace, R-19 won't behave as a diaphragm absorber as readily as 703 or 705, because fiberglass board products contain additional resins which make the fiberglass stiff. It's not a fair comparison, because density is not the only variable that differs between the batts and boards.

Within some reasonable range of densities, depth has been shown to be far more important than density.
For surface-mounted material (I'm not advocating that application, just using it as a known point of reference), R-19 performs better than the same thickness of 703, which performs better than the same thickness of 705. 1-2 pound density is not an inferior bass absorber.

Please show me where R-19 is the same as 2" 703.

I'm open to new knowledge, but need more data or literature than has been provided. I think R-19 is a fine way to go for walls if one has the space for it, and in the case of deep traps, I would just suggest adding a 3 or 6 pound density face panel for its diaphragmatic and cosmetic benefits.

-- Mark

 

[RevMen]

Here's some data I found in our database. This is all the info I have on these unless I go looking for the test reports. Presumably the tests with similar names came from the same lab.

4" 703 Fiberglass
nrc 1.00
63 .90
125 .99
250 .99
500 .99
1k .99
2k .99
4k .99

4" 703 board
nrc 1.00
63 .75
125 .99
250 .99
500 .99
1k .99
2k .98
4k .98

4" 705 Fiberglass
nrc 1.00
63 0.64
125 0.75
250 0.99
500 0.99
1k 0.99
2k 0.97
4k 0.98

2" 703 Fiberglass
nrc 0.95
63 .10
125 .18
250 .76
500 .99
1k .99
2k .99
4k .99

2" 703 board
nrc 0.95
63 .10
125 .18
250 .76
500 .99
1k .99
2k .99
4k .99

2" 705 Fiberglass
nrc 0.95
63 .10
125 .19
250 .74
500 .99
1k .99
2k .99
4k .99

glass fiber 6" thick 0.7 pcf
nrc 1.15
63 --
125 0.94
250 1.19
500 1.27
1k 1.06
2k 1.10
4k 1.20

glass fiber 3.5" thick 0.7 pcf
nrc 0.95
63 --
125 0.63
250 0.85
500 1.00
1k 0.96
2k 0.96
4k 1.08

3.5" Glass Fiber, Denisty 0.7 pcf
nrc 0.95
63 --
125 0.63
250 0.85
500 1.00
1k 0.96
2k 0.96
4k 1.08

fiberglass lining 4" thick 3 lb/cuft
nrc 1.00
63 0.50
125 0.84
250 1.00
500 1.00
1k 1.00
2k 1.00
4k 1.00

fiberglass lining 2" thick 3 lb/cuft
nrc 0.95
63 0.10
125 0.17
250 0.86
500 1.00
1k 1.00
2k 1.00
4k 1.00

2x4 with plain R11 insulation
presumably this means a 2x4 stud wall, so 3.5" thickness
nrc 0.95
63 0.20
125 0.34
250 0.80
500 0.99
1k 0.97
2k 0.94
4k 0.92

 

[VolvoHeretic]

It looks like your access to the shelves on the left are through the overhead door? You could add a plywood backing to the room listening side of them to help the symmetry?

 

[dka56]

Have you considered Roxul Safe N Sound insulation? I was messing around with a generator enclosure and went with it because of it's fire-resistant properties and noise absorbtion.

Having some strips left over i'm now using it to experiment with helping with my room arrangement and noise reflections.

I'm not an expert on sound absorbtion... but would a less dense material like a speaker grill fabric work differently than the burlap as the covering of the insulation?

Also, I wouldn't block the panel...I believe you need 36" in most jurisdictions in all areas around the panel.

 

[tomlinmgt]

It looks like your access to the shelves on the left are through the overhead door? You could add a plywood backing to the room listening side of them to help the symmetry?

There's a doggie-door in the garage door on the other side of the shelves in question and the little space created between the shelves and door is there so the dogs can get out of the weather. To keep the pups from getttin' into the stuff on the shelves I put up a solid layer of pegboard on the backside. I'm sure this offers some reflection, but I would imagine there is more diffussion from the items on the shelves since that's what the soundwaves see first. Do you think the random diffussion I get from the items on the shelves is offering any sort of benefit to the room's acoustics or should I consider covering them with a reflective surface? If a reflective surface is the answer, then is there a type of canvas or tarp or some kind of non-rigid material that is reflective that could be used as a curtain so I don't have to move a big wood panel every time I need something off of the shelves?

 

[dka56]

Mass loaded vinyl works well to reflect sound.

Ideally a layer of MLV behind 3" of absorbing material works great..but MLV is heavy and pricey. This way the sound enters the insulation, gets reflected back into the insulation and also lowers the noise heard from outside the room.

 

[RevMen]

would a less dense material like a speaker grill fabric work differently than the burlap as the covering of the insulation?

Both burlap and speaker cloth are effectively transparently acoustic, so there should be no meaningful performance difference between them. The roll of the covering cloth is to hold the material in place while letting the sound pass through to be gobbled up inside.

Do you think the random diffussion I get from the items on the shelves is offering any sort of benefit to the room's acoustics

Yes, but it's unbalanced because you have diffusion on the left and a wall on the right. Maybe you can back those shelves with plywood or gyp-board to even out the room shape, then add more diffusion on the right side (another CD rack, maybe) to even out the diffusion.