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Sound insulation and acoustic panels from rock wool or fiberglass wool?

nas

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Hello,

I try to insulate kind of a wardrobe, where is heat recovery unit is hidden. That is - to absorb as much sound inside it as possible on tight budget. Heat recovery unit is a mechanical air ventilation device built from steel with rotational heat exchanger, which has 3 electric motors inside: 2 for moving the air and one for rotating the heat exchanger itself. That last motor is connected with gearbox and both of them are VERY noisy. Think as a half of washing machine noise or more. That motor was changed by the seller of the device couple of times during warranty, the new ones were silent just for couple of weeks, then again: weird noises. The type of noise is vibrational-mechanical type, like a small drill or slow washing or drying machine.

I am on-topic, as we can treat wardrobe as a small room :)

What I did to lessen the sound:
  • I built a wardrobe type box for it. Result: now there is definitely less sound amount, but some resonances are more pronounced. Overall still a positive thing
  • 5+% of total surface of machine including near that noisy motor, glued with antivibrational butyl rubber sound and vibration deadening material for automotive soundproofing. Maybe will glue some more, as only small amount had at hand from last project. Possitive impact, but expected more. I have a feeling, that it dampened the lowest freq sounds, or raised main ones
  • 50+% of total surface glued with some 6mm rubbery foam, also from automotive industry. Not much impact
  • Front panel on the inside glued 2 layers of dense synthetic 2mm felt, so 4mm total. Not much impact.
  • Inside panels and doors of the wardrobe near the machine glued with pyramid shaped foam. A lot of impact, did not expected much, but it worked well!
I have no measures before and after, just subjective feeling.
The butyl rubber is glued on inside, foam - on the outside. In front there are double panels, the foam is between them. Can post more photos if necessary.

Photos:


IMG20230209144256.jpg
IMG20230209144219.jpg



Sound profile 1m in front of wardrobe with doors closed and open:


Screenshot_2023-02-09-14-46-51-43_c4254a393c570ad5ee05d45c0b30d817.jpg
Screenshot_2023-02-09-14-47-39-61_c4254a393c570ad5ee05d45c0b30d817.jpg


Wardrobe is not air tight and there is no way I can make it.

There is still too much noise coming out, and if we think machine is a noise source, then we also can think that inside of a wardrobe is like a small room.

What I want to do is to glue some additional automotive soundproofing material, of felt type but... specialized is both expensive and supply chain issues also present.

Plan B is to glue some homemade rockwool acoustic panel on the front of machine as sound blocker and there is also a room for 1 another acoustic panel type absorber on 1 of the inside walls of closet. Around 10-12cm thickness is most space in front for noise blocker and 5-6cm on the side wall absorber. I am using term "rockwool" as a general term, we can say basalt fiber wool to make it more correct

Questions:
  • Can they be built the same?
  • Is dense stiff rockwool the right material?

My doubts about the rockwool got stronger after seeing this video:



Whyyyy???? How????
Because glassfibers are longer than rockwool? Because of flufyness? Because fibers are thinner? Will dense glassfiber work too?
It is a sound of 1000Hz, and not much science behind it, but... the result is way too good for glassfibers.

Both materials are sold in bulk, and I do not want to waste money and material which will be not used after, so if someone already tried both, please share your findings.
Btw, there are some industrial type sound absorption panels on sale, but... again, there are supply chain issues or/and I have to buy bulk

The most I want to block 160-220Hz spectrum.
Thank you all in advance.
 

sarumbear

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The most I want to block 160-220Hz spectrum.
Thank you all in advance.
There are very few products that absorb sound at such low frequencies, efficiently. You may need a box in a box with mechanical filtering in between walls of each box along with acoustical isolation materials. A very difficult job.
 

AudiOhm

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To bad she did not try towels...

Ohms
 

Philbo King

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You need absorbers of 1/4 wavelength thickness.
250 Hz : 12 inches
125 Hz : 24 inches
The other thing important for soundproofing is making the enclosure air tight, which will probably not work well for a heat exchanger unless it uses outside air.
Fluffy fiberglass bats wrapped in permeable cloth would be the cheapest. Its gas flow resistivity (which is the controlling factor in sound absorption) is slightly less than rigid fiberglass /roxul /mineral wool but it is cheap enough you could 'overdo' it for less total cost.
 

AudiOhm

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nas

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I cannot do box in a box. As a machine is pretty tight in there, also - the closet is with doors with some natural gaps. Washing and drying machine is there. It will not change.
Also, here, in Eastern EU - supply and assortment is pretty bad. Heat exhchanger is central, so there are pipes going outside, but they are with sound silencers, and only very little sound is traveling through the pipes.

The question was more about fiberglass vs stone/rock/basalt wool...

Now the towels video... I am scratching my head. Literally.
 

sarumbear

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You need absorbers of 1/4 wavelength thickness.
250 Hz : 12 inches
125 Hz : 24 inches
That’s not true. Such a relation doesn’t exist.
 

sarumbear

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nas

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Then you have no solution.
I don't want to make it background noise level. I already got ~5dB less sound than were before, so another 5dB is all I want to.

Pls, focus on that video, now the question is - basalt fiber wool or glass fiber wool.
 
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nas

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Next post: "I burned up my heat recovery unit"
:) as it is ventilation heat recovery unit - it cools itself kinda. Half of it is literally the same temperature as outside (-5 Celsius ATM)
 

Justin Zazzi

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Seems like the absorption coefficients are a little higher for fiberglass. If they are similar cost and you don't mind the additional precautions of working with the tiny fiberglass pieces in your home, seems like it would be the better material choice. I would choose the rockwool simply because I hate working with fiberglass, but that's just me.

source for rockwool data <--
source for fiberglass data <--

If you are not having great success with absorption treatments, you can also try blocking the noise by adding a "heavy" layer of something. Mass loaded vinyl is made specifically for this, and can work exceptionally well if you can make a single continuous (airtight) shape out of it by gluing multiple pieces together. It's really easy to do, uses contact cement which is easy to work it, and it's not super expensive. I made a bathtub shape to line the floorboards of my car to reduce the road noise and it's fantastic.

MLV is rated using sound transmission loss (STC) whereas fiberglass and rockwool are rated using sound absorption coefficients. MLV is a sound barrier that prevents sound energy from moving through it, whereas fiberglass is an absorber that removes acoustic energy from the air an converts it into tiny bits of heat. The "towels" test in the video above is a test for sound transmission from one side to the other, and towels are much more heavy than the foam and fiberglass samples, so the towels have better sound blocking. The acoustic foam and fiberglass, however, are used for sound absorption which is a different use case. The towels video is a little misleading because it's measuring the performance of a sound-absorber by using a sound-blocking test.
 
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nas

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Seems like the absorption coefficients are a little higher for fiberglass. If they are similar cost and you don't mind the additional precautions of working with the tiny fiberglass pieces in your home, seems like it would be the better material choice. I would choose the rockwool simply because I hate working with fiberglass, but that's just me.

source for rockwool data <--
source for fiberglass data <--

If you are not having great success with absorption treatments, you can also try blocking the noise by adding a "heavy" layer of something. Mass loaded vinyl is made specifically for this, and can work exceptionally well if you can make a single continuous (airtight) shape out of it by gluing multiple pieces together. It's really easy to do, uses contact cement which is easy to work it, and it's not super expensive. I made a bathtub shape to line the floorboards of my car to reduce the road noise and it's fantastic.

MLV is rated using sound transmission loss (STC) whereas fiberglass and rockwool are rated using sound absorption coefficients. MLV is a sound barrier that prevents sound energy from moving through it, whereas fiberglass is an absorber that removes acoustic energy from the air an converts it into tiny bits of heat. The "towels" test in the video above is a test for sound transmission from one side to the other, and towels are much more heavy than the foam and fiberglass samples, so the towels have better sound blocking. The acoustic foam and fiberglass, however, are used for sound absorption which is a different use case. The towels video is a little misleading because it's measuring the performance of a sound-absorber by using a sound-blocking test.
Hi Justin,

Thank you for reply.

That second table is really nice, but I don't know the methodology of the measurements. The most surprised data were perforated metal ceiling and various concrete surfaces.
Seems that I have to do some kind composite, as I already have some simple light foam, 2mm industrial felt, I think I go to the nearest shop and buy what is there: glass wool or stone wool. Yes, I also don't like to work with glass fibers, but it is nothing for couple hours.

No, there is no way I can do airtight box, but can do some decoupling with foam-rigid material(MLV alternative, as there are no such thing here)-felt-foam layers.

Towels video has both examples, sound blocking and sound absorption. Just sound absorption was not measured - less echo in his bedroom.

In the video I posted: fiberglass is really light so I guess it is doing absorption thing.
 
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wjp007

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I put in 4 12"x48" rockwool panels in my 15'x14' room. My room is carpeted and I have a fairly large cloth sofa in their. I put one panel behind each speaker and two on the opposite walls. I can't put them on the side walls for first reflection control as I have furniture and doors that interfere. While I can't put my finger on it, but my system just doesn't sound as dynamic as it did before. Is it possible to have too much sound absorption material? I use Dirac Live with the Bass Control Beta. From the graphs there was some reduction in bass peaks and nulls, but I wouldn't call them significant.
 
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nas

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I put in 4 12"x48" rockwool panels in my 15'x14' room. My room is carpeted and I have a fairly large cloth sofa in their. I put one panel behind each speaker and two on the opposite walls. I can't put them on the side walls for first reflection control as I have furniture and doors that interfere. While I can't put my finger on it, but my system just doesn't sound as dynamic as it did before. Is it possible to have too much sound absorption material? I use Dirac Live with the Bass Control Beta. From the graphs there was some reduction in bass peaks and nulls, but I wouldn't call them significant.
From my couple days experience - rock wool is really light ant fluffy. In a bad way: fibers are not very thin, but just rare, hard and not much compressible. Glass wool is the opposite - heavy, tight, soft, you can compress it a lot. Sound absorption from simple "voice" test seems much bigger with glass fibers, but maybe it is because the weight difference. Yes probably you have to double stone wool to equal glass wool layer. I am not sure about mass though.
 
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nas

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So, my little experiment results:

With open doors before and after
open_doors_before.jpg
open_doors_after.jpg


Witch closed doors (as it will be) before and after:

closed_doors_before_GOOD.jpg
closed_doors_after.jpg



How it is made
viber_image_2023-02-18_19-57-43-893.jpg
viber_image_2023-02-18_19-57-44-014.jpg
viber_image_2023-02-18_19-57-44-155.jpg


It is a sandwitch of

1x2mm felt
1x frame of 20mm EPS on perimeter
3x stone wool of 20mm with glass wool pretty dense filling
1x frame of 20mm EPS on perimeter
1x2mm felt
Everything covered with pretty light breathable fabric

The overall result is kinda disappointment... I expected more :(
Subjectively it feels the difference is in 2dB range, sound just a bit softer. But there are still some resonances which... may be even stronger.
The bad part is that I am not sure, if I not lost one of the files with closed doors before... :(
Closed doors measurements is right.

The next step is box-in-box kind of thing with 12mm MDF, as 19mm will not fit in some places.
 
Last edited:

ozzy9832001

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I put in 4 12"x48" rockwool panels in my 15'x14' room. My room is carpeted and I have a fairly large cloth sofa in their. I put one panel behind each speaker and two on the opposite walls. I can't put them on the side walls for first reflection control as I have furniture and doors that interfere. While I can't put my finger on it, but my system just doesn't sound as dynamic as it did before. Is it possible to have too much sound absorption material? I use Dirac Live with the Bass Control Beta. From the graphs there was some reduction in bass peaks and nulls, but I wouldn't call them significant.

This happened to me as well when I placed treatment behind the speakers. Mine are rear ported so it definitely helped, though 4" panels won't really do anything for frequencies lower than 500hz. I have 3 x 24"x48"x4" panels on the front wall plus 4x 12" corner bass traps. I wouldn't say it's lost dynamics although your speakers may react differently, but I would say it's a flatter response, so it sounds like it has.

You may need to tweak the eq to add some of the dynamics back or eq other parts of the spectrum that maybe are too loud or quiet. I don't treat SW reflections. I'm in the school of thought that they add more than they take away. Plus one reflection point is a door and the other a window.
 
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