DIY - Room Acoustics..

[elangoas]

There seem to be perforated acoustic gypsum board, that has some absorption co-efficient.. Were you referring to these boards (or) the plain one?..

Link for perforated acoustic gypsum board - https://www.gyproc.ae/products/perforated-acoustic-gypsum-products

Here is a snapshot from data sheet..

Approx 500 rupees per sqft
We should forget it

Ditch it..

What's your budget?

20K (or) lesser the better..

That's the most important part of this project.

To reduce the decay time, and get it under suggested 300ms (or) less for modal responses..

Option 4 is total guess work.. I'm not considering it.

Guess was only for the density of the material, which the supplier is yet to update me.. The method has been tried by a FM with results.. Have shared it in this thread earlier..

2 inches space should be left between the panel and wall for better absorption.
With space left, 4 inches will act as 8 inches.

The idea is to have more thickness without airgap..

 

[prateekatasniya]

There seem to be perforated acoustic gypsum board, that has some absorption co-efficient.. Were you referring to these boards (or) the plain one?..

Link for perforated acoustic gypsum board - https://www.gyproc.ae/products/perforated-acoustic-gypsum-products

Here is a snapshot from data sheet..

Ditch it..



20K (or) lesser the better..



To reduce the decay time, and get it under suggested 300ms (or) less for modal responses..



Guess was only for the density of the material, which the supplier is yet to update me.. The method has been tried by a FM with results.. Have shared it in this thread earlier..



The idea is to have more thickness without airgap..

No.. 2 inches should be left behind the panel. Then the effective thickness will become double.

I guess you will have to increase the budget.. it will be difficult in this budget . Or else go phase wise.

 

[prateekatasniya]

There seem to be perforated acoustic gypsum board, that has some absorption co-efficient.. Were you referring to these boards (or) the plain one?..

Link for perforated acoustic gypsum board - https://www.gyproc.ae/products/perforated-acoustic-gypsum-products

Here is a snapshot from data sheet..

Ditch it..



20K (or) lesser the better..



To reduce the decay time, and get it under suggested 300ms (or) less for modal responses..



Guess was only for the density of the material, which the supplier is yet to update me.. The method has been tried by a FM with results.. Have shared it in this thread earlier..



The idea is to have more thickness without airgap..

I was referring to the plain one for Rockwool as it's particles aren't safe.

How about putting Rockwool behind 3 mm ply?
That will surely let the low frequencies pass..

 

[elangoas]

No.. 2 inches should be left behind the panel. Then the effective thickness will become double.

Am thinking of 12inch traps.. Either square (or) circular one.. Don't think will be able to accomodate 2 inch gap.. Let me see how this will shape-up..

I guess you will have to increase the budget.. it will be difficult in this budget . Or else go phase wise.

Increase?.. why?.. The supplier said, he might revise the prices if i go for 100mm thickness panels.. However am leaning towards loose wool.. Waiting for him to update the density..

I was referring to the plain one for Rockwool as it's particles aren't safe.

Ok.. Yup read that too.. Will also check for fibreglass..

How about putting Rockwool behind 3 mm ply?
That will surely let the low frequencies pass..

Am not sure if it will pass.. Also have a different plan for ceiling to accomodate 4 heights (so cramped on ceiling space).. Already have subs there.. The ceiling corners is what will be free now.. So using them..

 

[prateekatasniya]

Am thinking of 12inch traps.. Either square (or) circular one.. Don't think will be able to accomodate 2 inch gap.. Let me see how this will shape-up..



Increase?.. why?.. The supplier said, he might revise the prices if i go for 100mm thickness panels.. However am leaning towards loose wool.. Waiting for him to update the density..



Ok.. Yup read that too.. Will also check for fibreglass..



Am not sure if it will pass.. Also have a different plan for ceiling to accomodate 4 heights (so cramped on ceiling space).. Already have subs there.. The ceiling corners is what will be free now.. So using them..

2 inch Gap+ 6 inches Rockwool almost equals 12 inches Rockwool stuck to wall without Gap.

 

[sound_cycle]

2 inch Gap+ 6 inches Rockwool almost equals 12 inches Rockwool stuck to wall without Gap.

Acoustics

20 September 2018
08:00

http://ethanwiner.com/acoustics.html

One important way to improve the low frequency performance of any absorbent material - besides making it thicker - is to space it away from the wall or ceiling. For a given material thickness, increasing the depth of the air gap lowers the frequency range it absorbs. For example, 703 that is two inches thick and mounted directly against a wall has an absorption coefficient of 0.17 at 125 Hz. Spacing the same material 16 inches away from the wall increases that to 0.40 - a nearly three-fold improvement

Ciao
Gr

 

[sud98]

Acoustics

20 September 2018
08:00

http://ethanwiner.com/acoustics.html

One important way to improve the low frequency performance of any absorbent material - besides making it thicker - is to space it away from the wall or ceiling. For a given material thickness, increasing the depth of the air gap lowers the frequency range it absorbs. For example, 703 that is two inches thick and mounted directly against a wall has an absorption coefficient of 0.17 at 125 Hz. Spacing the same material 16 inches away from the wall increases that to 0.40 - a nearly three-fold improvement

Ciao
Gr

Going by this link, how about this material.
http://kwalityproducts.in/7_50-mm-X-40-m3-Fiber-Glass-Wool-Slab.html
The tech specs are as below
http://kwalityproducts.in/uploads/pdf/Kwality_50 mm X 40 m3 Fiber Glass Wool Slab_7.pdf

or this one
https://www.indiamart.com/proddetail/akostika-acoustic-fiberglass-ceiling-panel-18958581788.html

 

[prateekatasniya]

Going by this link, how about this material.
http://kwalityproducts.in/7_50-mm-X-40-m3-Fiber-Glass-Wool-Slab.html
The tech specs are as below
http://kwalityproducts.in/uploads/pdf/Kwality_50 mm X 40 m3 Fiber Glass Wool Slab_7.pdf

Average nrc is useless in our context

 

[elangoas]

2 inch Gap+ 6 inches Rockwool almost equals 12 inches Rockwool stuck to wall without Gap.

How can 2 inch gap be a substitute for thickness?.. = 12inches seems a tall claim.. Probably 8 (or) 9 inch inch at best..

Am trying to interpret the absorption co-efficient from the table that was shared earlier..

From the the above table, as the thickness increases for the same density, absorption at low freq (below 250) seems higher..

On wall for same density (48 Kg/m3) - 3 inch panel has 0.53 for 125 Hz and 1.19 for 250Hz, but at 6 inches it is 1.19 for 125Hz and 1.21 for 250Hz..

If a 6inch panel can absorb more lows, then why use airgap for 3 (or) 4 inch panel?.. Drawing inferences from the table, an 8 inch panel on wall with same density would absorb even more lows, negating the airgap required..

For example, 703 that is two inches thick and mounted directly against a wall has an absorption coefficient of 0.17 at 125 Hz. Spacing the same material 16 inches away from the wall increases that to 0.40 - a nearly three-fold improvement

Hmm.. I think it would be impractical to have it 16 inches away from wall..

Just for calculation & reasoning :

2 inch panel onwall (48kg/m3)+ 16 inch airgap makes 0.40 at 125Hz.. But, 3 inch thickness onwall of (48kg/m3) does 0.53 at 125Hz.. I think you would save 15inch of space..

 

[sound_cycle]

Hmm.. I think it would be impractical to have it 16 inches away from wall..

Just for calculation & reasoning :

2 inch panel onwall (48kg/m3)+ 16 inch airgap makes 0.40 at 125Hz.. But, 3 inch thickness onwall of (48kg/m3) does 0.53 at 125Hz.. I think you would save 15inch of space..

NO ! (in caps)

BTW there is no recommendation to keep it 16" away, it was merely an illustrative example.

Please read the linked article for a clearer understanding, there is lots of interesting stuff there in how NRC is measured, why it is likely an overestimate and that since we are not using all surfaces it much be lesser than what was measured.

Sound waves pass through your traps/ absorbers *twice*. in and back out again. So you are exposing the surface you have twice. Having an air gap lowers the effective frequency you can manage for a given thickness of foam. AFAIK there are no differences across frequencies.

As always glad to be corrected if wrong, I am only trying to figure things out and improve my understanding.

ciao
gr

 

[sound_cycle]

Going by this link, how about this material.
http://kwalityproducts.in/7_50-mm-X-40-m3-Fiber-Glass-Wool-Slab.html
The tech specs are as below
http://kwalityproducts.in/uploads/pdf/Kwality_50 mm X 40 m3 Fiber Glass Wool Slab_7.pdf

or this one
https://www.indiamart.com/proddetail/akostika-acoustic-fiberglass-ceiling-panel-18958581788.html

Nothing specific for/ against. I opted for rockwool which I thought would be less irritating to the touch or likely to crumble.

ciao
gr

 

[sud98]

How can 2 inch gap be a substitute for thickness?.. = 12inches seems a tall claim.. Probably 8 (or) 9 inch inch at best..

Hmm.. I think it would be impractical to have it 16 inches away from wall..

If you are planning to cover the ceiling, then you can keep a frame on which these panels can rest and then have air gap from there to your actual ceiling.

Found another interesting product
https://www.indiamart.com/proddetail/akostika-acoustic-fiberglass-ceiling-panel-18958581788.html

 

[sud98]

Nothing specific for/ against. I opted for rockwool which I thought would be less irritating to the touch or likely to crumble.

ciao
gr

Thats why more inclined towards rigid fibre glass panels.

 

[sound_cycle]

Thats why more inclined towards rigid fibre glass panels.

I am sorry but I think I misunderstood. You are saying that you would opt for something that is more itchy and irritating to the touch and more likely to crumble OR are your saying that my interpretation of rockwool vs fiberglass was wrong

ciao
gr

 

[sound_cycle]

Sound waves pass through your traps/ absorbers *twice*. in and back out again. So you are exposing the surface you have twice. Having an air gap lowers the effective frequency you can manage for a given thickness of foam. AFAIK there are no differences across frequencies.

Muhammad, M., Sa’at, N., Naim, H., Isa, M., Yussof, H., Yati, M., 2012. The effect of air gap thickness on sound absorption coefficient of polyurethane foam. Def. ST Tech. Bull 5, 176–187.

(from the paper)

The main function of acoustical materials is to reduce the acoustic energy of sound waves that pass through it.

This can be performed using resistive materials that consist of porous structure which change sound energy into heat.

This can happen when energy is changed due to frictional forces between sound waves and the cell walls in the pore structure (Fang et al., 2007).

In other words, the further the distance sound waves travel through the medium of porous structure, the higher the amount of sound energy which is dissipated.

In practice, there are two methods used to install acoustical materials; either using an air gap or not.

By introducing an air gap behind an acoustical material any residues of incident sound waves that are not absorbed or transformed into heat energy after transmission through the acoustical material will face additional resistance through the air medium.

The mechanism of sound waves dissipating in the air medium is known as the Helmoltz resonance effect.

It excites some of the sound waves’ frequencies, causing them to oscillate at greater amplitude. When the energy reaches the maximum level, the sound waves become weak due to friction with air particles, which converts sound energy into heat (Zhang et al., 2012; Norton & Karszub, 2003; Crocker, 2007).

Previous studies show that the combination of acoustical materials and air gap thickness has significant impacts on the sound absorption coefficient.

See Figure 7 for a graph showing sound absorption coefficient and wave frequency for the different air gap thickness sound absorbing characteristics of polyurethane foam (the paper is on researchgate if you are interested)

Their results showed that the air gaps reduced the sound absorption capability at high frequencies of sound waves.

Both methods, with and without air gap, were not able to absorb the low frequencies of sound waves, particularly below than 250 Hz.

The implementation of combination polyurethane foam with air gaps was able to enhance the sound absorption coefficient in the medium frequency range without changing the thickness of acoustical materials.

ciao
gr

 

[sud98]

The itchiness is higher in Fibre glass wools. These AFAIK are different from fiberglass boards which are smoother. That's why your link was recommending these as also have better acoustics

 

[elangoas]

I am only trying to figure things out and improve my understanding.

Same here..

BTW there is no recommendation to keep it 16" away, it was merely an illustrative example.

Please read the linked article for a clearer understanding, there is lots of interesting stuff there in how NRC is measured, why it is likely an overestimate and that since we are not using all surfaces it much be lesser than what was measured.

Sure.. I get it.. Will read thru..

Having an air gap lowers the effective frequency you can manage for a given thickness of foam

Their results showed that the air gaps reduced the sound absorption capability at high frequencies of sound waves.

Both methods, with and without air gap, were not able to absorb the low frequencies of sound waves, particularly below than 250 Hz.

See Figure 7 for a graph showing sound absorption coefficient and wave frequency for the different air gap thickness sound absorbing characteristics of polyurethane foam (the paper is on researchgate if you are interested)

So this article refers to polyurethane foams absorption co-efficient for low frequency.. I hope these are the one that are aval locally, black in colour and sponge type..

I opted for rockwool which I thought would be less irritating to the touch or likely to crumble.

I believe you have had the rockwool panels in your living room, covered with fabric for few years.. Have you faced any discomfort during this time?.. I ask because, am also considering rockwool..

 

[sound_cycle]

So this article refers to polyurethane foams absorption co-efficient for low frequency.. I hope these are the one that are aval locally, black in colour and sponge type..
<snip>
I believe you have had the rockwool panels in your living room, covered with fabric for few years.. Have you faced any discomfort during this time?.. I ask because, am also considering rockwool..

I read that paper with a goal to understanding what the air gap does (it happened to be a paper that used PUF, but that does not matter)

I said upthread that sound passes through your material twice. But it would do that irrespective of the presence of an airgap. So what does the air do. I guess the paper had a reasonable explanation.

Rockwool has not inconvenienced me, family and pets in any manner. No smell, no crumbling, no dust, no itchiness.

BTW I have taken every thing off from the walls in in order to answer your question on the effectiveness of my DIY panels before and t get before after treatment measurements

https://photos.app.goo.gl/dTAdtZK29kmmCnfL9

https://photos.app.goo.gl/jXPeAZRoZouYwBG77

ciao
gr

 

[elangoas]

If you are planning to cover the ceiling, then you can keep a frame on which these panels can rest and then have air gap from there to your actual ceiling.

I started with the idea of ceiling, but now, with all these conversations am kind of rethinking..

Rockwool has not inconvenienced me, family and pets in any manner. No smell, no crumbling, no dust, no itchiness.

Ok.. Great..Perfect.. Kind of reassures, when someone has actual feedback..

BTW I have taken every thing off from the walls in in order to answer your question on the effectiveness of my DIY panels before and t get before after treatment measurements

 

[prateekatasniya]

I think you should build simple corner bass traps.. More corners you treat better the sound will get.. tried and tested method..