Rough/simple calculators for dB reduction of a particular wall buildup?

[YodhrinForge]

There are a few decent calculators out there online that let you get a very rough ballpark u-value for whatever your wall buildups are going to be, I'm wondering if there's anything similar for wall buildups designed for acoustic mitigation? I'm a big fan of over-designing rather than dancing on thin margins so I'm less interested in the exact precise values for a specific actual wall than I am in whether the general buildups I'm considering(current lead contender is existing brick partition wall>40mm rigid wood fibre boards with adhesive & hammer fixings, CLS stud wall in contact with previous, further 40mm wood fibre depth between studs bonded to initial insulation layer, then some kind of decoupling system with acoustic plasterboard mounted to it)  will be sufficiently excessive.

[Nickfromwales]

1 hour ago, YodhrinForge said:

There are a few decent calculators out there online that let you get a very rough ballpark u-value for whatever your wall buildups are going to be, I'm wondering if there's anything similar for wall buildups designed for acoustic mitigation? I'm a big fan of over-designing rather than dancing on thin margins so I'm less interested in the exact precise values for a specific actual wall than I am in whether the general buildups I'm considering(current lead contender is existing brick partition wall>40mm rigid wood fibre boards with adhesive & hammer fixings, CLS stud wall in contact with previous, further 40mm wood fibre depth between studs bonded to initial insulation layer, then some kind of decoupling system with acoustic plasterboard mounted to it)  will be sufficiently excessive.

If there's no physical decoupling from outside to inside, then no. It's rudimentary not excessive.

 

Are you saying you are peeling back the interior to the brick walls, still standing, and are building backwards > inwards?

 

Can you post a drawing of room/walls/layout/etc plz?

[Nick Laslett]

Insul have a trial version of their software you can use, but this is a professional tool. 
 

https://www.insul.co.nz

[SteamyTea]

R = 20 Log₁₀(mf) -47

 

Where:

m = kg/m²

f = Hz

 

 

[YodhrinForge]

20 hours ago, Nickfromwales said:

If there's no physical decoupling from outside to inside, then no. It's rudimentary not excessive.

 

Are you saying you are peeling back the interior to the brick walls, still standing, and are building backwards > inwards?

 

Can you post a drawing of room/walls/layout/etc plz?

 The physical decoupling occurs in the decoupling system I mentioned, one of the polymer mount & channel type systems for fixing your plasterboard to, the insulation layers are for thermal performance and mass(rigid wood fiber has a similar or better kg/m3 than the best acoustic-rated rockwool and I'm using it on my exterior wall interior facings for insulation anyway). I'll be stripping all exterior and adjoining walls to the masonry to add vapour open airtightness, insulation and, for the adjoining walls, soundproofing. Here's a shitty MSpaint of what I've been discussing with the architect. Top to bottom on the buildup is existing wall, lime adhesive, wood fibre, stud wall, decoupling system, acoustic plasterboard. The variations are just different thicknesses of wood fibre(top to bottom 80mm, 40+40 between studs, same, and 20+40 between studs) and sizes & layouts of CLS(top two 38x63, bottom two 38x98), which I end up with will depend on space constraints of the final designs and what the structural engineer wants. Second one down seems the best compromise of depth, mass, & thermal performance to me. Oh and for clarity I say excessive because the existing wall is two rows of brick in a circa 1900 stone building, so you already have to pretty much be *trying* to be loud to annoy each other, I just figure that since I'm pulling everything down for airtightness & insulation work anyway I might as well see how I can tweak it to maximise acoustic performance too.

Edited August 2 by YodhrinForge

[Nick Laslett]

@YodhrinForge, are you going to use something like genie clips for decoupling?

 

 

Soundstop show their decoupled sound proof wall buildup having a sound reduction of 56 decibels. This is with a 36 db single skin brick wall despite what the picture shows. 
 

 

Metal has much better acoustic reduction properties than wood. You would need to adjust the gap to suit your insulation requirements as 50mm of rockwool is probably not enough. E.g. you would add timber battens to the wall first, then the genie clip with furring channel. 

Edited August 3 by Nick Laslett

[Mike]

On 02/08/2025 at 01:36, YodhrinForge said:

existing brick partition wall>40mm rigid wood fibre boards with adhesive & hammer fixings, CLS stud wall in contact with previous, further 40mm wood fibre depth between studs bonded to initial insulation layer, then some kind of decoupling system with acoustic plasterboard mounted to it)  will be sufficiently excessive.

Swap the rigid wood fibre boards with adhesive & hammer fixings for a semi-flexible wood-fibre boards friction-fitted into place. That will be quicker and easier, and the insulation will prevent impact noise being transmitted..

The CLS stud can keep the insulation in place, though I prefer to use metal studwork (fixed only to the floor & ceiling).

No need for extra decoupling; the semi-flexible wood-fibre provides that.

 

Noise takes the easiest path, and one of those will be the doors & door frames, so you'll need to buy them accordingly. Another will be flanking sound via the ceiling and floor, but since you don't mention them as a problem, maybe they're not.

 

 

 

[YodhrinForge]

40 minutes ago, Mike said:

Swap the rigid wood fibre boards with adhesive & hammer fixings for a semi-flexible wood-fibre boards friction-fitted into place. That will be quicker and easier, and the insulation will prevent impact noise being transmitted..

The CLS stud can keep the insulation in place, though I prefer to use metal studwork (fixed only to the floor & ceiling).

No need for extra decoupling; the semi-flexible wood-fibre provides that.

 

Noise takes the easiest path, and one of those will be the doors & door frames, so you'll need to buy them accordingly. Another will be flanking sound via the ceiling and floor, but since you don't mention them as a problem, maybe they're not.

 

 

 

I'd considered using flexible batts, but the wall will be getting coated with some kind of lime-based material anyway as that will form my airtight layer(using enerPHit principles, just not fussed about getting the certification), I also have to be careful about managing dew point and avoiding unintended cavities. How about the pictured; lime parge/adhesive > 20mm rigid wood fibre(thermal break) > stud wall w/ 50mm flexible wood fibre between > clip & rail system > acoustic plasterboard.

 

When it comes to the floors, whichever solution I go with will be carried through the floor as much as possible to achieve continuity of insulation and airtightness, and I was intending to use a sound dampening subfloor for any suspended timber flooring. There's also the benefit that the run of the joists is front-to-back while the neighbouring property is to one side.

[SteamyTea]

1 hour ago, Mike said:

Noise takes the easiest path

But you also get constructive and destructive interference which can vary the local energy intensity.

Why my little, 5W, radio, when down stairs on volume 2 (of 11 of cause) can seem quite loud upstairs in the bedroom.

[YodhrinForge]

Having finally found some more detailed reference material, I've amended my buildup again(turns out Diathonite Thermactive has a final density of 250kg/m3 +/- 15%, which is basically double rigid wood fibre, so pushing that from a ~30mm parge/levelling coat to a ~40mm base layer will do both the extra mass and thermal decoupling adequately).

[Mike]

1 hour ago, YodhrinForge said:

the wall will be getting coated with some kind of lime-based material anyway as that will form my airtight layer...

Yes, you certainly need that.

 

51 minutes ago, YodhrinForge said:

a ~30mm parge/levelling coat

A parge coat is normally only a few mm thick. If your wall is so uneven that it requires 30mm, that's 2 or 3 coats of lime plaster - or the Diathonite Thermactive. Nether of them are cheap, though you'll need it pretty flat, especially for rigid insulation.

 

BTW, when balancing dB reductions against cost, remember that it's a logarithmic scale. 3dB is only just perceptible, 5dB is noticeable, 10dB halves the noise (at the frequencies measured).

 

[YodhrinForge]

4 hours ago, Mike said:

Yes, you certainly need that.

 

A parge coat is normally only a few mm thick. If your wall is so uneven that it requires 30mm, that's 2 or 3 coats of lime plaster - or the Diathonite Thermactive. Nether of them are cheap, though you'll need it pretty flat, especially for rigid insulation.

 

BTW, when balancing dB reductions against cost, remember that it's a logarithmic scale. 3dB is only just perceptible, 5dB is noticeable, 10dB halves the noise (at the frequencies measured).

 

I'm aware. The Diathonite was planned anyway for the exterior walls inner face, and to be applied thicky both to level, decrease the chances of cracking in future which would compromise the airtight layer, and for its excellent wicking and moisture management properties. And while the cost isn't small, in this plan for the adjoining walls it would be somewhat offset by dropping the inner layer of rigid insulation I had thought to add behind the stud wall. Anyway in the end it's all subject to WUFI/PHPP modelling anyway, I'm just trying to get an idea of how to balance everything optimally.