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Insulation density vs acoustical performance
Old 17th July 2020
  #1
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Insulation density vs acoustical performance

Hi,

seeing parameters of the following products I would like you to ask you to help with their interpretation:

Rockwool SAFE’N’SOUND, thickness 3" (75 mm), density 2.4 lb/ft³ (38 kg/m³), acustical performance:
(this product is not available in Europe, listed for reference)
125 Hz - 0.52
250 Hz - 0.96
500 Hz - 1
1000 Hz - 1
2000 Hz - 1
4000 Hz - 1

Knauf Akustik Board, thickness 3" (80 mm), density 1 lb/ft³ (16 kg/m³), acustical performance:
125 Hz - 0.28
250 Hz - 0.75
500 Hz - 0.99
1000 Hz - 1
2000 Hz - 1
4000 Hz - 1

Isover Akuplat+, thickness 3" (75 mm), density 1 lb/ft³ (16 kg/m³), acustical performance:
125 Hz - 0.30
250 Hz - 0.85
500 Hz - 1
1000 Hz - 1
2000 Hz - 1
4000 Hz - 1


1) Higher density = better soundproofing. SAFE’N’SOUND outperforms other two at 125 and 250 Hz. Is this simply because of having almost 2.4x higher density?

2) I am building "existing wall - air gap - 75 mm steel wall frame with 75 mm insulation - two layers of 12,5 mm (1/2") drywall" system. While listed Knauf and Isover products have very similiar acoustical performance, the Isover is 30% more expensive than Knauf. Any reason why to choose more expensive Isover product?

3) Higher density products are available here, but their listed (if at all) acoustical properties for thickness of 75 mm (3") are lower than listed Knauf and Isover products above. Should I consider them?

This is all about soundproofing my new workshop - with power tools (drill, saws, vacuum cleaner, router, small lathe...); no drum kits neither recording studio.

Thanks.

Boris
Old 17th July 2020
  #2
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Kyle P. Gushue's Avatar
Use the cheapest available fluffy insulation. Wall insulation is good for about 3-5db of sound reduction. Insulation just has to be there and its fine. Any real significant differences in isolation happen with decoupling, and mass.
Old 18th July 2020
  #3
Hi Boris,

It is a confusing subject, I know.

These are absorption materials, so the right approach is to understand first the function that they cover within a soundproofing system, and the words “system” and “within” are key to understand the whole thing.

So first thing is: those numbers are alpha coefficients measuring absorption, not literally soundproofing levels.
I can tell you one thing out of experience, most of the times it is as important how you design and execute your solution than the materials themselves. Well, I would say without any doubt, that correct execution outperforms materials’ expectations, in fact you can easily ruin your whole investment in materials with the wrong execution providing that the design is up to the function of your system.
Anyway and to simplify, what is really giving you the main levels of soundproofing, as a barrier, are mainly your hard and dense materials not these soft materials.

1) Higher density = better soundproofing. SAFE’N’SOUND outperforms other two at 125 and 250 Hz. Is this simply because of having almost 2.4x higher density?

The easy answer is a yes and the complex answer is it depends. You would relate this to one of the foundational concepts of soundproofing that is mass. But, think that out of all the elements of your soundproofing system the mass of these materials is ridiculous compared to the mass and density of your plasterboard, plywood or any other hard material. Since the function of these materials is absorption within the cavity, and not to act as a soundproofing barrier, you would be surprise with the variations in sound absorption based on thickness and density that sometimes are counter-intuitive. For your case and to simplify this post, all densities of the materials that you propose would not be of much relevance. All of them could be categorize as low density for a high performance soundproofing system, usually 40, 60 Kg/m3 or even more deppending on the case of application. But everything depends on what is the frequency distribution and sound pressure of your noise, Depending on the frequencies that we want to stop or absorb and depending on the type of fibrous materials we sometimes choose different densities, not necessary higher.

2) I am building "existing wall - air gap - 75 mm steel wall frame with 75 mm insulation - two layers of 12,5 mm (1/2") drywall" system. While listed Knauf and Isover products have very similiar acoustical performance, the Isover is 30% more expensive than Knauf. Any reason why to choose more expensive Isover product?

Well I would say no, save that 30% for other things that can massively improve the performance of your system. It is probably more important to decouple your wall, to add a MLV to your system, and many other things that will be more beneficial for achieving your goals.

3) Higher density products are available here, but their listed (if at all) acoustical properties for thickness of 75 mm (3") are lower than listed Knauf and Isover products above. Should I consider them?

Again, and for your case do not get caught with manufacturers specs and snake oil. Keep this in mind, first it comes mass of your hard components, distance (air gap), decoupling and finally the absorption that you put in the cavity. The main reason to use mineral wool or glass fibre in a system is damping, that helps with soundproofing, specially to tune the response of your system to certain frequencies. And there is the key, first you need to know the characteristics of your noise in terms of sound pressure and frequency so you can design the best solution and pick your materials.

Other note about this numbers, number 1 would mean a perfect absorber, 100% of the energy being eaten by the panel. Well, you don’t need to be an acoustic engineer to know that in reality, that is not possible, that is just a misleading figure coming from the methods of measurement that they use. You can sometimes see spec sheets where numbers go even above 1, it is a good marketing tool to sell panels and it is backed by the standards of measurement but it is completely misleading. In the same page, if 1 is unattainable you can imagine that all the other numbers does not give you an accurate representation of the reality.

Don’t get me wrong, absorption is a key and vital component in soundproofing but in order of priority on where you put your money, there are other things that come first.

And finally another big consideration in your case. It seems that you are trying to achieve a barrier for airborne sound but you should consider too, and very carefully, vibration noise. What I mean is that a drill, a circular saw or a sanding machine will produce an airborne sound in the mid-high range of frequencies, quite loud but stoppable by a well designed wall. The problem is that depending on how you are using these tools in connection with the structure of your building the effects can be dissastrous in neighbouring spaces/rooms. The type of noise that could be annoying your neighbour is very different, and even opposite in terms of frequencies, to the one that you hear inside of your workshop directly from the machine. As an analogy, if someone is walking upstairs with high-heels, you would hear some sort of amplified impact noise quite in the mid-low and low frequencies while the person walking upstairs is probably hearing his own steps as mid-high frequency.
So depending on the tasks that you are performing with your tools, and as a general advice try always to decouple or damp by any means your work benches, tools supports, the table where you are laying a board that you are cutting or sanding and so on.

Hope this helps and did not confuse you more.
Good luck, and please use ear protection when working in such an enclosed space with that type of noisy machinery, you just have a pair of ears and you can permanently damage your hearing in just one session of work.
Old 18th July 2020
  #4
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Kyle P. Gushue's Avatar
MLV is incredibly expensive mass, and very rarely a good choice. 5/8" drywall is often the king for bang for the buck mass.
Old 18th July 2020
  #5
Quote:
Originally Posted by Kyle P. Gushue View Post
MLV is incredibly expensive mass, and very rarely a good choice. 5/8" drywall is often the king for bang for the buck mass.
I 100% agree with that. I would never use MLV just for the sake of adding mass to a wall, and just to clarify I would not prioritize its use sandwiched between plasterboard sheets in many low budget applications. Anyway, there are very effective uses of MLV in a soundproofing system. Workshops and industrial facilities and the type of noise and acoustic issues that they produce are very often good candidates for its use when correctly designed and installed.
Old 9th August 2020
  #6
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Guys, thank you very much for you advice and detailed explanation. MLV cannot be sourced localy. OK, I will focus on mass, maximizing the air gap and decoupling the system. I will pay attention to vibrations and get some antivibration pads for stationary equipment. Considering variety of tools I expect full sound spectrum. I will focus on low range preferably. Btw, the floor is a solid concrete.
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