Hello,
I try to insulate kind of a wardrobe, where is heat recovery unit is hidden. 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.
What I did to lessen the sound:
I have no measures before and after.
Photos:
Sound profile 1m form wardrobe with doors closed and open:
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
Questions:
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.
The most I want to block 160-220Hz spectrum.
I try to insulate kind of a wardrobe, where is heat recovery unit is hidden. 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.
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 from automotive soundproofing industry. 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
- 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.
Photos:
Sound profile 1m form wardrobe with doors closed and open:
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
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.
The most I want to block 160-220Hz spectrum.
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The 'container' must be of high mass and must be airtight, or with labyrinth absorbers if ventilation is required. An inordinate of noise can leak through air gaps. Focusing on absorption is not the best strategy here, especially given the low frequencies you wish to reduce, where absorption is least effective and a sound barrier is required. A foam/MLV/foam sandwich might be a good solution.
Hi, did you look into the Rockfon sound treatment products from Rockwool? E.g. from Swedish site https://www.rockfon.se/produkter/rockfon-koral-100-mm/
Looks quite good. They have a specialised Bass Plus product, for LF absorbtion https://www.rockfon.se/produkter/rockfon-bass-plus-a51d102b/. They have many more materials, different from regular Rockwool. I rebuilt a wall in my bathroom (next to my music room), using some inwall, higher density stuff similar to Bass Plus, with good results
.
Regards,
Dagfinn
Looks quite good. They have a specialised Bass Plus product, for LF absorbtion https://www.rockfon.se/produkter/rockfon-bass-plus-a51d102b/. They have many more materials, different from regular Rockwool. I rebuilt a wall in my bathroom (next to my music room), using some inwall, higher density stuff similar to Bass Plus, with good results
. Regards,
Dagfinn
I looked at some of the other products. I never heard about Rockfon, only about Rockwool brand products. They are not freely available in my country. I have a feeling, that they are pretty much... the same glass fiber or basalt fiber which is just covered with smth extra and given extra marketing weight and fancy brand name.
p.s. have built today some DIY panel from EPS frame and crumbly unpressed glass fiber wool inside. Glue is drying out, so tomorrow will see how it performs
p.s. have built today some DIY panel from EPS frame and crumbly unpressed glass fiber wool inside. Glue is drying out, so tomorrow will see how it performs
You can look up the datasheets for materials and properties, but if you can't get them it doesn't help much
https://www.rockfon.com/products/rockfon-koral/#Documents&Resources .Exactly. I tried to use the same "Constrained layer damping" as you call technique on small scale and on almost 0 budget. It works on big structures, can work here too.
This, in short is wise advice. Although you wrote you will not be able to make the wardrobe airtight, you don't want gaps. Budgetwise a drywall metal stud construction with gypsum board on both sides is a no-brainer. That will bring the mass that you need to reduce sound transmission at low cost. But that requires at least 70mm wall thickness (12-46-12) and preferably 82mm (12/12-46-12). The constrained layer approach is worth investigating, but you still need mass (every doubling of mass per surface will give about 5dB higher insulation)
You likely will have a lot of sound transmission through the air ducts. That might need attention too. Look for flexible air ducts with sound absorption, those are quite common. Any supplier of ventilation hardware should be able to deliver those.
Absolutely, however be careful of adding mass to already somewhat flexible enclosure panels, as this can sometimes reduce the natural resonant frequency and actually make LF attenuation worse.
https://www.jochenschulz.me/en/blog/rockwool-glasswool-hemp-best-absorber-material
Basically, the lower the frequencies you are trying to absorb, the more you want damping material with less airflow resistivity but in greater thickness. Otherwise the LF sound bounces off. Now, in the case of a fully sealed enclosure, that's not necessarily problem, but you also would have to deal with vibration as you are finding out. Generally, the solution to vibration is CLD when you can afford it (cost, complexity, space).
Basically, the lower the frequencies you are trying to absorb, the more you want damping material with less airflow resistivity but in greater thickness. Otherwise the LF sound bounces off. Now, in the case of a fully sealed enclosure, that's not necessarily problem, but you also would have to deal with vibration as you are finding out. Generally, the solution to vibration is CLD when you can afford it (cost, complexity, space).
The resonances in wall panels almost always are in an audible range, unless you can push them out of the problematic bandwidth (say<50Hz). The reason you add mass is partly because you want to change the ratio between mass and stiffness. The famous acoustic mass law is only valid for panels that are not stiff (if it's valid at all in real life).
Just to clarify (since the edit is timed out), it’s not that the LF sound will bounce off if there is not enough thickness. If the flow resistivity is too high (compared to the “ideal” for damping at those frequencies), there will be a significant change in acoustic impedance which means more of the incident sound turns into reflected sound.
Agreed and apologies for my unclear post. I should have explained that I was referring to products like 'sound deadening panels' on an already lightweight and flexible structure where reducing transmission in one part of the spectrum can lead to increased transmission in another.
Yes. This is the very first option I opted, but... due to the space and connection constraints during purchase of initial HE there were only like 4-5 options which suited and most of them were rotational type out of 100-200 different models in the market. I made tubing and space for the exact model... Now it is too late to do reconstruction (too expensive). The exact model I chose was far from cheapest
Yes, the decision was bad as counter-current type with enthalpic type heat exchange unit would be quiet and still return moisture to the rooms.
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So, my little experiment results:
With open doors before and after
With closed doors (as it will be) before and after:
How it is made:
It is a
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
It is **** and sticks... Budget of around 20EUR, as most of the materials I had as leftovers.
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. Especially in low freq
The bad part is that I am not sure, if I not lost one of the files with closed doors before...
With open doors measurements are as they should be.
The next step is box-in-box kind of thing with 12mm MDF, as 19mm will not fit in some places.
With open doors before and after
With closed doors (as it will be) before and after:
How it is made:
It is a
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
It is **** and sticks... Budget of around 20EUR, as most of the materials I had as leftovers.
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. Especially in low freq
The bad part is that I am not sure, if I not lost one of the files with closed doors before...
With open doors measurements are as they should be.
The next step is box-in-box kind of thing with 12mm MDF, as 19mm will not fit in some places.