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PostPosted: Thu Aug 01, 2019 8:13 am 
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Joined: Sat May 20, 2017 7:47 am
Posts: 291
Location: Surfleet, UK
Hi there,

With regards to the Rockwool, is it for within the MSM walls or within the room for acoustic treatments you're asking about?

Within your MSM walls go for low density, low GFR. Anything around 5000KPa*s/m2 is good.

If you're taking about acoustic treatments, you should tailor the density/GFR depending on requirements.

Deep low density affects lower frequencies and is generally the best, if you can fit it in the room.

Use this acoustic absorber calculator to estimate the affected frequencies:

Absorber calculator

Dan


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PostPosted: Thu Aug 01, 2019 7:13 pm 
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Joined: Fri May 10, 2019 5:29 pm
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Location: Madrid, Spain
Hey Dan! Thanks for giving some input.

Quote:
With regards to the Rockwool, is it for within the MSM walls or within the room for acoustic treatments you're asking about?


This Rockwool is for within the MSM walls.

Quote:
Within your MSM walls go for low density, low GFR. Anything around 5000KPa*s/m2 is good.


Quote:
Deep low density affects lower frequencies and is generally the best, if you can fit it in the room.


So what's the logic behind this? Also, when you say "if you can fit it in the room"... how deep are we talking? I only have about 10cm between each of the leafs in the MSM wall, and I thought I'd do something along the lines of 4cm Rockwool, 2cm air cavity, 4cm Rockwool. Would this be enough depth to go for low density and low GFR and still perform better than high density high GFR for reducing low frequencies?

Before going deeper into that question, I've used the calculator link you have provided (thanks btw, great tool!) and obtained these results:

Attachment:
screen-shot-2019-08-01-at-11-0.png


It seems that the Alpharock 225 product performs best at lower frequencies, while Rocksol and Rockalm are similar and better at the higher end. Since I'll be playing drums and there will be plenty of low frequency involved (kick drum), it might make sense to go for the Alpharock 225. What do you think?

Here's the link to the parameters I used in case anyone is curious: http://www.acousticmodelling.com/mlink. ... &v44=20000


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PostPosted: Fri Aug 02, 2019 9:47 am 
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Location: Surfleet, UK
vdegou wrote:
So what's the logic behind this?


Within an MSM wall you don't need to calculate frequencies. The absorber is not exposed to the room, you're not going to get isolation via absorption.
You gain isolation by mass and damping.
MSM stands for mass - spring - mass.
Mass is your plasterboard / concrete /wooden surface. The spring is your cavity. The second mass is your second leaf of plasterboard etc.

This cavity must be damped, in the same way placing a blanket in a bass drum damps the sound. Completely (yes completely) fill the cavity with insulation (no empty airgaps). The only reason you would have an airgap, would be because you accidentally bought too dense insulation and need to avoid creating a flanking path.

The research tells us (sorry I can't find the link to the paper, maybe someone will find it) that the very best isolation is achieved by having the cavity completely filled from surface to surface with low density insulation, the same sort of thing you would put in a loft/attic.

Only use the absorber calculator for internal acoustic treatments. It's only useful when the absorber is exposed to the room.

vdegou wrote:
I only have about 10cm between each of the leafs in the MSM wall, and I thought I'd do something along the lines of 4cm Rockwool, 2cm air cavity, 4cm Rockwool


Have your calculated whether that will give you enough isolation?
Drums are ridiculously hard to isolate against. You have massive sound energy at low frequencies.
How much mass are you attaching to each leaf?

Dan


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PostPosted: Sat Aug 17, 2019 10:56 pm 
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Quote:
Within an MSM wall you don't need to calculate frequencies. The absorber is not exposed to the room, you're not going to get isolation via absorption.

Quote:
Only use the absorber calculator for internal acoustic treatments. It's only useful when the absorber is exposed to the room.

Oh, I didn't know that! That's very good to know Dan, thank you for that insight.

Quote:
This cavity must be damped, in the same way placing a blanket in a bass drum damps the sound. Completely (yes completely) fill the cavity with insulation (no empty airgaps). The only reason you would have an airgap, would be because you accidentally bought too dense insulation and need to avoid creating a flanking path.

Makes sense.

This advice regarding damping came just in time. I was about to shell out an unnecessary amount of money for high density rockwool. In the end, I went with the lowest density/cheapest I could find at my local hardware store, and good thing too, because I ended up drastically underestimating the amount I would need. Due to some irregularities in the original room construction (roof isn't completely parallel to the floor, walls are not perpendicular to floor/ceiling at certain points, which make them bulge out and cave in at some points), I ended up having to fill up a lot more than the original 60m^2 of surface area I had estimated.

Quote:
How much mass are you attaching to each leaf?

The outer leaves are mostly made up of concrete foundation. I'm not sure of the thickness, so unfortunately I wasn't able to get a proper density value from there, but the inner leaves which I do have control over are made up of 3cm thick MDF boards, which are quite dense sitting at around 700-800kg/m^3.

I'll post some update pictures in a few minutes, as I am about 90% done with the assembly :)

Thanks again for you insight Dan, seriously! You saved me a lot of money on damping!


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PostPosted: Sat Aug 17, 2019 11:32 pm 
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Hello all!

After a long two weeks of work and a lot of help from my father with the actual build, we are pretty much done with the assembly. For having close to no previous experience with DIY, construction, and woodworking, we are pretty excited with the results! I'll attach some pictures to this post for those of you who have been keeping an eye on this build. Also, thank you everyone who commented! All of this information has been of massive use to this project.

Without further ado, a very quick glimpse of the build process:

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Along the way there were some big changes in the design. For example, we decided to leave one of the water pipes inside of the studio and box it up, unlike the original idea of leaving it completely outside. The studio definitely has more space with the pipe inside, but now we have that awkward shelf across the length of it. No big deal, really, although it was one of the most challenging parts of the build.

I have to go back in and try to improve on some mistakes where we couldn't get the boards to align 100% with each other. Lots of filler, sanding, and patience should do the trick.

Also, this wouldn't make much sense without the data to accompany it! (Note: I got a better sound level meter and retook the base measurements, so they are not the same as the previous ones in this thread)

Attachment:
before_after_assembly_graph.PNG


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before_after_assembly_table.PNG


Since the door is still not ready, I simulated one by temporarily covering the place where it would go with the same MDF boards I used for the walls.

I hope to put together a timelapse of the whole build, but there is still lots to go. I need to finish covering up some sections of the shelf, correct for any mistakes, paint, and then treat the acoustics.

Hope you enjoyed!


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