Fiber Glass Insulation Questions

[Alex2507]

I'm on a job where Johns Manville semi rigid insulation is being used. After looking it up I discovered that it's only 1 lb/cu.ft. but saw that Johns Manville makes 3 and 6 lb/cu.ft products like Owens Corning 703 and 705.

The sound absorption data puts JM in the lead. I thought that was odd and question whether or not that might be a matter of test methods or maybe a matter claimed vs. actual NRC's. (Noise reduction coefficients).

Which brings me to my next knuckle head question. What is done with that coefficient and what does it mean? Maybe somebody can provide a link that explains all that.

Is the 6 lb/cu.ft. product preferred over the 3 lb/cu.ft. product? I might be able to get the Johns Manville product delivered to my job for my personal use. Is there any reason to seek out Owens Corning over them?

Here are links to there product data.

http://www.owenscorning.com/comminsul/documents/Fiberglas700Series.pdf

http://www.jm.com/insulation/building_insulation/products/hig1214dk_insul-shield.pdf

I'm bent on this rigid fiber glass because I really hate mineral wool. Sound panels and WmAx recommended speaker mods are what I would be using this stuff for.

 

[mike c]

basically, the denser the fg, the lower frequencies it can absorb.

the coefficients for example 1.0 for x frequency means it can absorb 100% of the sound that reaches it. the denser and thicker the FG, the x frequency it can attenuate goes down.

what is the purpose of your install? temperature insulation or sound insulation?

i might not be exactly correct (might even be wrong) but the general idea is there ...

 

[Alex2507]

what is the purpose of your install? temperature insulation or sound insulation?

Sound panels and a WmAx speaker mod.

Thanks for your reply. If you take a look at the links you'll see that some of the coefficients are above 1.0. I can't remember where I read it but the test procedure was stated and it was explained that the impossible coefficient of more than 1.0 was the result show by the test method and it had not had a correction factor applied to it. Interesting stuff to the ignorant and nerdy.

 

[WmAx]

Sound panels and a WmAx speaker mod.

Thanks for your reply. If you take a look at the links you'll see that some of the coefficients are above 1.0. I can't remember where I read it but the test procedure was stated and it was explained that the impossible coefficient of more than 1.0 was the result show by the test method and it had not had a correction factor applied to it. Interesting stuff to the ignorant and nerdy.

The above 1.0 factors are mainly possible because the test standard requires only the front face of the device under test be factored into the calculations. However, in many products, the sides are also substantial surface area that has absorption. The standard for the calculations does not allow this to be used in the calculation, as silly as that might sound. As a result, more surface area is present for absorption than is used in the calculation formulas, and the co-efficient can go over 1.0 as a result.

As for the meaning of the calculation, it does not deal with transmission through, just remember that. It deals only with reverberation/reflection, and the co-efficients can easily vary 20 percent due to testing error and differences between labs, and even more variation, possibly for some labs, if memory serves. The co-efficients are published should correlate very closely to the use in speaker cabinets as long as the material is installed directly to the walls of the cabinet.

-Chris

 

[mike c]

Sound panels and a WmAx speaker mod.

in that case, get the higher density FG

 

[Alex2507]

As for the meaning of the calculation, it does not deal with transmission through, just remember that. It deals only with reverberation/reflection,
-Chris

in that case, get the higher density FG

High density FG it is then. Today I'll see if I can get 1", 1 1/2" and 2" dropped off for little ole me. The supplier is providing 200,000 sq.ft. of insulation for the job. I just want 3 bags for Pete's sake.

I just read on the JM site that density has virtually no effect on sound transmission (STC) in a wall cavity application. It seems to be all about the thickness (volume) of the insulation. I thought that was interesting too.

 

[Alex2507]

in that case, get the higher density FG

Okay, I get that higher density means that lower frequencies will be absorbed. But if you look at the Sound Absorption Coefficients on the Owens Corning site:

http://www.owenscorning.com/comminsul/documents/Fiberglas700Series.pdf

you can see that the thinner low density faced insulation does the best job with the lowest frequency the tests list (125 Hz). There is a trade off with the high frequencies though.

I do understand that O.C. 705 is recommended again and again. I believe that there is a good reason and am not trying to re-invent the wheel here. But I would like to understand the mechanics of it. I am aware and have a vague comprehension of the term, 'pushing resonant frequencies above the pass band'. My interest lies in 3 areas.

1. Speaker modification
2. DIY subs
3. Sound absorbing panels

Edit: When it comes to cabinet resonance, what is it that that I'm trying to reduce, the sound bouncing around inside the cabinet or the sound comming out of the cabinet walls? I'm really trying to develop an understanding of the subject matter.

 

[mike c]

it might be because we are trying to prevent killing too much of the highs just to control the low end

or i could be talking out of my ...

 

[Rickster71]

Edit: When it comes to cabinet resonance, what is it that that I'm trying to reduce, the sound bouncing around inside the cabinet or the sound comming out of the cabinet walls? I'm really trying to develop an understanding of the subject matter.

Hi Alex,
if I may offer the little that I know; while you wait for the speaker experts to reply.

The answer is yes to both; one begets the other.

I've always meant to ask Chris and / or TLS about applying Ice and Water shield to the inside of a cabinet? Since it's a lot like DynaMat, I often thought about trying it.

I wonder if fiberglass would be a problem with a ported speaker, with the fibers blowing out of the port? Poly fill doesn't behave the same way.

IMHO,
Rick

 

[Alex2507]

it might be because we are trying to prevent killing too much of the highs just to control the low end

or i could be talking out of my ...

The highs are being killed more than the lows until the faced low density stuff is used.

I've always meant to ask Chris and / or TLS about applying Ice and Water shield to the inside of a cabinet? Since it's a lot like DynaMat, I often thought about trying it.

I wonder if fiberglass would be a problem with a ported speaker, with the fibers blowing out of the port? Poly fill doesn't behave the same way.

Peel & Seal from Lowe's is like Dynamat. My problem is that Lowe's up here doesn't carry Peal & Seal. What they do carry as 6" wide flashing for roofing is just like Ice & Water Shield. I was given an entire 36" wide roll of it at work. For me that's a done deal.

A new study has shown that fiberglass is good for you. No, really.
Actually wrapping the fiberglass in acoustically transparent cloth is the answer to not having it blow out the port. I kind of wondered about placing the acoustically transparent cloth on the port and letting that and the grill cloth do the work of catching fibers. But I'm sure there's a reason not to do that too. I get more fiberglass at work than you can imagine. You know you got it good when you can feel it crunch in between your teeth.

TLS loves polyfill and WmAx loves mineral wool. I already know that I detest mineral wool so I'm interested in fiberglass. To each his own, right?

 

[WmAx]

Hi Alex,


I've always meant to ask Chris and / or TLS about applying Ice and Water shield to the inside of a cabinet? Since it's a lot like DynaMat, I often thought about trying it.

I am familar with the Ice And Water Sheild branded product. It is inferior to Dynamat or Peel N' Seal for single sided cabinet resonance reduction. It does not appear to have ideal mechanical impedance matching with the substrate it is being used upon(solid wood/plywood/similar). That is, the material is too viscous. Now, this material does work wonderfully as the constrained layer(damping core between two stiff plates), but different factors are at play in that type of application.

A very good cheap material is asphalt based standard roofing tiles for single sided application. However, as you can imagine, it can be a pain to install them compared a simple adhesive backed roll of material like Peel N' Seal.

I wonder if fiberglass would be a problem with a ported speaker, with the fibers blowing out of the port? Poly fill doesn't behave the same way.

Besides the issue of the fiber glass fibers blowing out the port(a potential lung and eye irritant), the fibers can also potentially end up in the driver motor gap, rubbing between the voice coil and motor, due to the large air vent on the back of subwoofer drivers.


-Chris

 

[WmAx]

O
you can see that the thinner low density faced insulation does the best job with the lowest frequency the tests list (125 Hz). There is a trade off with the high frequencies though.

Yes, it is well known that applying a membrane of appropriate stiffness/mass to fiber glass insulation panels will increase the absorption at lower frequencies. However, the trade off is obvious. It may be possible to mount the faced material in a frame, with the facing against the wall, and leave a space behind the facing so it does not touch the wall, and have the material absorb more LF and without HF co-efficient reduction. But I am not sure, and you should ask a qualified authority about the validity of that assumption.

-Chris

 

[WmAx]

Edit: When it comes to cabinet resonance, what is it that that I'm trying to reduce, the sound bouncing around inside the cabinet or the sound comming out of the cabinet walls? I'm really trying to develop an understanding of the subject matter.

Many speakers have problems with both: sound coming from the panels and sound 'bouncing' around inside, due to insufficient acoustic absorption materials.

You can easily fix the internal 'bouncing' issue with proper materials being installed in place of the stock ones.

It is not so easy to fix the panel vibration/output problem. You can improve it by some degree by installing materials like Dynamat or similar in sufficient thickness. But if you actually want to eliminate it's audibility entirely, you would have to do extreme modifications(essentially re-building the interior).

-Chris

 

[Alex2507]

I am familar with the Ice And Water Sheild branded product. It is inferior to Dynamat or Peel N' Seal for single sided cabinet resonance reduction. It does not appear to have ideal mechanical impedance matching with the substrate it is being used upon(solid wood/plywood/similar). That is, the material is too viscous. Now, this material does work wonderfully as the constrained layer(damping core between two stiff plates), but different factors are at play in that type of application.

A very good cheap material is asphalt based standard roofing tiles for single sided application. However, as you can imagine, it can be a pain to install them compared a simple adhesive backed roll of material like Peel N' Seal.



Besides the issue of the fiber glass fibers blowing out the port(a potential lung and eye irritant), the fibers can also potentially end up in the driver motor gap, rubbing between the voice coil and motor, due to the large air vent on the back of subwoofer drivers.


-Chris

How inferior? Like, way inferior or like 10% inferior?

When you say 'single sided application', I take it you mean the 'inside'?

I always wondered about that foam in the hole in the middle of the magnet. A vent, huh? Thanks for that too.

 

[WmAx]

How inferior? Like, way inferior or like 10% inferior?

I would say, probably 1/2 as effective.

When you say 'single sided application', I take it you mean the 'inside'?

I mean, a single sided application, inside, as opposed to a constrained layer application(with two wall layers and the dampening material contained between them in a sandwich construction; this is a constrained layer).

-Chris

 

[Alex2507]

I give up. OC 705 can not be bought by me in between New York and Boston.

WmAx,

Would you be good enough to ship me enough Fiberglas or rock wool to modify two (2) Infinity Primus 360's and one (1) PC350 center channel?

Thank you,
Alex