# Room Acoustics -> Questions



## Sam Ash (Aug 23, 2009)

Any help / input will be appreciated:-

1. I have a slightly L- shaped room and the ceiling on one long-side of the room slopes at the edge. For better acoustics, I am thinking of turning the room into a rectangle and incorporating the exact same slope on the opposite corner of the ceiling. This will give my theatre room complete symmetry - Any views from acoustic pros and those who have gone through a similar exercise is welcome.

2. Can anyone suggest any reasonably priced hazardous-fibre-free material (no fibre-glass or mineral-fibre/wool) that I can use to build my own absorption panels ? The material can be up to 4inch thick and should have an excellent low-frequency absorption capability too. I have been on the search for such a material but have not been able to locate anything suitable. Any DIY acoustic gurus that have found a way to do this using easily available materials that can be bought from local hardware or home interiors shops ? Any results with creating a sandwich of materials e.g. high-densiy foam panels, wool & polyester blankets and thick felt material. Please feel free to suggest or provide advice.


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## bpape (Sep 14, 2006)

I would want to know a bit more about the room, how much space you'd lose, etc. A sketch/pics would help a lot.

For the other, good luck with that. If NO fibers, that leaves only foam which is not going to do much of anything when restricted to a 4" thickness.


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## Sam Ash (Aug 23, 2009)

bpape said:


> I would want to know a bit more about the room, how much space you'd lose, etc. A sketch/pics would help a lot.
> 
> For the other, good luck with that. If NO fibers, that leaves only foam which is not going to do much of anything when restricted to a 4" thickness.


Thank you for your input Bryan, I have attached a pdf file with two drawings (a floor plan and an elevation). I suppose I could accommodate thicker material as long as it works effectively.


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## phazewolf (Feb 5, 2012)

Foam is not going to help much at all. Why no mineral wool is there a reason you want to avoid it? I would not call foam non toxic the stuff even if it does not burn will release toxic smoke.


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## Sam Ash (Aug 23, 2009)

phazewolf said:


> Foam is not going to help much at all. Why no mineral wool is there a reason you want to avoid it? I would not call foam non toxic the stuff even if it does not burn will release toxic smoke.


Well, my wife is allergic to dust and from what I've read, mineral wool contains fibres (glass etc) that can become airborne and is not good to breathe-in over time. Low frequency vibration could facilitate this and the thought of breathing-in harmful / invisible fibres is frightening.

I have been searching endlessly for alternatives but their performance below 500Hz is just not as good as Mineral wool/fibre. Plus, all these alternative (natural/safe) solutions are so expensive - not to mention that you have to go much thicker (e.g.) 8"-12" to achieve what Mineral fibre can achieve in 4".

I too am not fully confident using foams and am being super cautious about all sorts of claims being made on the internet.

Is there any effective DIY method out there that does not use the pink-stuff, Mineral Fibre products used in dry walls for temperature insulation ? I found a 4" Mineral Fibre material has excellent sound insulation performance but again it contains hazardous material.

I have built a false fabric wall and my speakers sit behind an AT screen and AT fabric, I need to insulate the actual back wall and was initially going to use this proven 4" Mineral Fibre material until I found out about the possible long term health risks. Apart from that, I definitely need some absorption panels.

Has anyone out there tried using different readily available materials. Example make a sandwich using high-density-foam, cotton & polyester blanket, felt pad ?

I am currently building my dedicated home theatre room and am in a dilemma as I need a good alternative but affordable solution onder:


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## Sam Ash (Aug 23, 2009)

bpape said:


> I would want to know a bit more about the room, how much space you'd lose, etc. A sketch/pics would help a lot.
> 
> For the other, good luck with that. If NO fibers, that leaves only foam which is not going to do much of anything when restricted to a 4" thickness.


Bryan - you seem to be a knowlegeable guy (Acoustician) working for a reputable firm. 

Any suggestions ???

I need to come up with a solution.


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## bpape (Sep 14, 2006)

Sorry - out of the country on vacation. Limited time the rest of this week. The new wall looks good. How far down do the angles come and shorten the side walls to? Looks like the center is 12'?

I would consider 3lb fiberglass and wrap in thin plastic. That will contain fibers and only limit high absorbtion above say maybe 8-10k? Then add some foam to do what it does best, suck up only highs.


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## Sam Ash (Aug 23, 2009)

bpape said:


> Sorry - out of the country on vacation. Limited time the rest of this week. The new wall looks good. How far down do the angles come and shorten the side walls to? Looks like the center is 12'?
> 
> I would consider 3lb fiberglass and wrap in thin plastic. That will contain fibers and only limit high absorbtion above say maybe 8-10k? Then add some foam to do what it does best, suck up only highs.


Hi Bryan, Very kind of you to have responded even though you are on vacation. Hope you're having load of fun.

Ok, floor to middle ceiling height is 12 feet, the angles on both sides come and shorten the side walls to about 6 feet.

Thank you for the suggestion, it makes sense. I've been looking for fibre-free products that are just as good as fibre-glass or mineral-fibre but they are expensive.


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## bpape (Sep 14, 2006)

Also in general for most products that are not fibrous, you'll need 2-3x the thickness for the same low frequency extension.


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## Sam Ash (Aug 23, 2009)

bpape said:


> Also in general for most products that are not fibrous, you'll need 2-3x the thickness for the same low frequency extension.


Yes, I understand that Bryan and that is an issue because I really don't want to sacrifice more space behind my false fabric wall. I mean, there are safe alternatives that come close to or have similar NRC values as traditional fibre products even in terms of thickness but they are expensive.

I am thinking of using 4" mineral fibre panels, sealing them in thick cotton fabric and then encapsulating it with 1" high density foam so that it is completely sealed all around. I will then insert the panels in wooden or aluminium frames with AT fabric on the faces.

Is there any alternative to thin plastic bags that would let sound in and prevent fibre dust from becoming airborne ? What about thin latex or rubber like material ?


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## Sam Ash (Aug 23, 2009)

It would be nice if GIK Acoustics did a reasonably priced product like that since it is already in the business of manufacturing acoustic absorption panels and has the infrastructure to achieve it.

4" Mineral fibre, encapsulated in thick AT fabric (cotton) and then re-encapsulated in good quality long lasting foam to guarantee safety by ensuring that non of the fibre becomes airborne.

If the price for such a product was equal to or just slightly higher than a DIY initiative, I would buy directly from GIK Acoustics.

This is something you should consider seriously Bryan because there are a lot of people out there like me that do not want the air they breathe infested with invisible fibre particles. Regardless of whether or not it is harmful in the long term, just the thought of it puts me off. It's almost like working at a nuclear power plant, you kind of know it's safe but you're always worried about the possibility of leakages and hazardous exposure by something you cannot see.


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## bpape (Sep 14, 2006)

Understand that NRC is an average and tells you nothing about performance below 125Hz and very little specifically about 250Hz and down.

You can use something like a disposable drop cloth stapled to framing over the material. That will limit the high frequencies very little.


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## Sam Ash (Aug 23, 2009)

bpape said:


> Understand that NRC is an average and tells you nothing about performance below 125Hz and very little specifically about 250Hz and down.
> 
> You can use something like a disposable drop cloth stapled to framing over the material. That will limit the high frequencies very little.


Thanks Bryan - whats a disposable drop cloth ?


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## bpape (Sep 14, 2006)

http://www.homedepot.com/p/HDX-9-ft-x-12-ft-0-7-mil-Drop-Cloth-6-Pack-DCHD-07-6/204711647

That one is only 0.007" thick so it will block very little sound but will stop any dust transfer.


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## phazewolf (Feb 5, 2012)

If the panel is built right the fabric should not let the fiber out in the first place. Most people that build their own at least the ones I have seen and have built use 3 to 7 mill thick plastic just to make sure. 

There should be no issue with mineral wool. Foam when it burns releases toxic gas and some of it can leach out toxic fumes even when it's not being burned. Most things that your home is built with if newer uses things that are toxic and will release it over many many years unless you have a old home with no carpet no plywood or anything else.

The panel's maybe the least of your worries.


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## bpape (Sep 14, 2006)

He was more worried about dust. I would agree though that short of beating on the panels, it really shouldn't be releasing anything anyway but just to be safe.... Regular vacuuming should take care of any dust issues.


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