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PostPosted: Mon Aug 31, 2020 12:25 am 
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Hi team. My first post, and it might seem a silly question but it's got me intrigued.
I gather that double stud and staggered stud walls have larger air volumes between the leaves, and the more (mitigated) air volume the better.
But consider a single stud wall - you have multiple sealed cavities approx 540 mm x 1100 mm rather than the single much larger air volume you'd have on double or staggered walls. On a 2.4M x 2.4M single stud wall you would have 8 small cavities, each sealed from the other, with no air movement between them.
THE QUESTION - would there be any benefit in deliberately breaching the studs and joists laterally with a hole saw, jigsaw etc to allow air to flow between those small cavities?
I'm thinking it would affect resonance of the wall rather than reduce sound propagation. Please school me :)
Cheers, Mick.

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PostPosted: Mon Aug 31, 2020 4:22 am 
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Hi Mick,

It's an interesting question. I haven't seen any research into it myself though.

But logically thinking about it:

The resonant frequency formulae for MAM walls (that I've seen and use) do not take volume of the air cavity as a parameter, but rather the depth of the cavity.

In the case of your wall idea. It would be akin to having two panel absorbers screwed to each other, then drilling some holes in the shared side. This reminds me of an article Paul shared with me here: https://www.acousticsciences.com/art-noxon/limp-mass-membrane-bass-traps

This article shows that increased air volume can indeed lower resonant frequency of panel absorbers, but what you have described isn't quite the same.

You don't have 1 membrane vibrating over a sealed box, that has additional volume added. You have a membrane vibrating over each stud cavity. So when you drill through the stud between, any additional air volume is already damping that cavity and isn't available to "soften" the resonance and lower the frequency.

It's more likely to act like a back to back double sided membrane absorber described in the article. Each stud cavity acts against the other.

I would expect no lowering of resonant frequency.

A better way to lower the resonant frequency of any wall would be to increase the distance between the studs by using deeper studs. Eg. 600mm centres instead of 400mm centres. This will leave more panel to vibrate freely, and reduce edge effects increasing the resonant frequency.

Dan

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PostPosted: Mon Aug 31, 2020 5:18 am 
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I think the main problem with such an idea is that you'd severely weaken your studs.

But that aside, walls do act as either membrane absorbers, or panel absorbers and Andre from gearslutz coined the name "invisible alpha" to describe this.

You might want to research that on gearslutz to have a better understanding of how it works.

Paul

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PostPosted: Mon Aug 31, 2020 10:04 am 
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Quote:
I think the main problem with such an idea is that you'd severely weaken your studs.


I was going to say the exact same thing. Talk about "deadening" properties...

All the best,

Paul


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PostPosted: Tue Sep 01, 2020 10:39 pm 
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SoWhat wrote:
Quote:
I think the main problem with such an idea is that you'd severely weaken your studs.


I was going to say the exact same thing. Talk about "deadening" properties...

All the best,

Paul


Thanks SoWhat and Paulus87

I thought Musos were supposed to suffer for their art? Poverty, ostracism, bad reviews, walls and roofs collapsing on them :P
The wall in in question is 2.4 M high and 1.8 M wide with a hefty top beam and a concrete floor.
It's part of a vocal booth within an office within a commercial workshop.
So no carnage to be had here, sorry :D

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PostPosted: Tue Sep 01, 2020 11:12 pm 
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Waka wrote:
You have a membrane vibrating over each stud cavity. So when you drill through the stud between, any additional air volume is already damping that cavity and isn't available to "soften" the resonance and lower the frequency.

It's more likely to act like a back to back double sided membrane absorber described in the article. Each stud cavity acts against the other.

I would expect no lowering of resonant frequency.



Thanks Dan, you explained that well enough for a novice to understand.
When I posted the question I had just finished skimming a New Zealand Uni proposition paper about using Helmholtz resonators to lessen low frequency transfer between dwellings in medium rise blocks of flats without resorting to bigger wall gaps, double layers of plasterboard, expensive caulking etc. Here's a link if you're interested -
https://www.acoustics.asn.au/conference_proceedings/AAS2019/papers/p97.pdf
Short version, they're looking into using resonators in narrow stud walls. I don't need them but again, I was intrigued by the idea.
Cheers, Mick.

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PostPosted: Wed Sep 02, 2020 2:58 am 
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Ironstone Tech wrote:
When I posted the question I had just finished skimming a New Zealand Uni proposition paper about using Helmholtz resonators to lessen low frequency transfer between dwellings in medium rise blocks of flats without resorting to bigger wall gaps, double layers of plasterboard, expensive caulking etc. Here's a link if you're interested -
https://www.acoustics.asn.au/conference ... rs/p97.pdf
Short version, they're looking into using resonators in narrow stud walls. I don't need them but again, I was intrigued by the idea.


I had a skim of the article. It looks like an interesting concept. I don't think it will work, mind you :lol:

Helmholtz are most effective when they consist of a completely sealed container. Their idea to use helmholtz resonators instead of expensive caulking doesn't quite stand up, they would probably need to caulk all around the studs anyway in order get any helmholtz effect!

Also they would need to use the correct amount/GFR of insulation/absorption in the cavity (ie. NOT fully filled) to produce desirable Helmholtz absorption. But by NOT fully filling the cavity, they hinder the absorption they would usually get by damping the panel resonance of the wall. This would reduce their low frequency isolation.

I'm not convinced they would get enough movement through the Helmholtz slots either, due to the openings being within the cavity of the wall, and not exposed to the room producing the sound waves.

I can't see this working. And I definitely can't see this being cheaper than an extra layer of plasterboard...

It would be interesting to see what they come up with though.

Dan

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PostPosted: Wed Sep 02, 2020 3:02 am 
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I looked a little more into their research, and it appears they are actually using small plastic helmholtz devices slotted through holes in the walls of the cavity.
Not just drilling holes in the studs.

It's interesting. Mass producing the little resonators could be simple enough for the specific frequencies they need to target.

I'll have to read it more thoroughly later.

Dan

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PostPosted: Wed Sep 02, 2020 3:36 am 
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Waka wrote:
I looked a little more into their research, and it appears they are actually using small plastic helmholtz devices slotted through holes in the walls of the cavity.
Not just drilling holes in the studs.

It's interesting. Mass producing the little resonators could be simple enough for the specific frequencies they need to target.

I'll have to read it more thoroughly later.

Dan


I read the article as well, I may have read it wrong but from what I understand the double leaf assemblies they are referring to are actually not decoupled assemblies but just what we would call a partition wall in the UK (timber frame panelled both sides). It's interesting that according to the article the in fill of insulation does not seem to increase TL.

I think the idea will work, but it'll only provide a small reduction. Probably under 10db or so. would be interesting to build a life size assembly and try to target lower frequencies.

The device with the added membrane sound more promising, would like more details about that. I wonder if this is something similar to Northward's top secret membrane devices? I read somewhere that they may or may not be constructed from plexiglass (acrylic). Who knows.

Paul

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PostPosted: Wed Sep 02, 2020 4:47 am 
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Ask Aunty..... I remember reading of a criss cross of hardboard of even cardboard being installed in modular LF traps to increase the damping of the installed fibre.
There have been subsequent tests which show that a full fill of light fibre, touching the boundaries, but not compressed, is optimum, leading to say 10dB improvement in TL, very cheaply.
Such fill would IMO eliminate Helmholtz resonance by a similar amount or more. More importantly I thin mitigation of the much higher bending resonance, around 3KHz is vital. So although the linked process surely works as described, a whole brood of babies have been thrown out with the bathwater!

The LF resonant absorption peak of a stud/plasterboard Invisible Alpha structure is low LF. Typically employed in the region below all the other trapping.
This has been done by everybody forever using any thing that will contain and flex at LF. Newell's Limp Bag.
Again, asking Aunty, she used Steel sheet.

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PostPosted: Wed Sep 02, 2020 5:05 am 
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DanDan wrote:
Ask Aunty..... I remember reading of a criss cross of hardboard of even cardboard being installed in modular LF traps to increase the damping of the installed fibre.
There have been subsequent tests which show that a full fill of light fibre, touching the boundaries, but not compressed, is optimum, leading to say 10dB improvement in TL, very cheaply.
Such fill would IMO eliminate Helmholtz resonance by a similar amount or more. More importantly I thin mitigation of the much higher bending resonance, around 3KHz is vital. So although the linked process surely works as described, a whole brood of babies have been thrown out with the bathwater!

The LF resonant absorption peak of a stud/plasterboard Invisible Alpha structure is low LF. Typically employed in the region below all the other trapping.
This has been done by everybody forever using any thing that will contain and flex at LF. Newell's Limp Bag.
Again, asking Aunty, she used Steel sheet.


Dan, who is Aunty? :D

Paul

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PostPosted: Sat Sep 05, 2020 12:26 am 
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Paulus87 wrote:
Dan, who is Aunty? :D



Paul, without resorting to Google Search I'm fairly sure that Dan's Aunty is the BBC.
Apparently they did a lot of research and testing to improve their studios.
Only to find out that the dull boring flatness of their broadcasts was not because of the acoustics.
I could be wrong though :D

Cheers, Mick.

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PostPosted: Thu Oct 08, 2020 4:36 am 
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Waka wrote:
I looked a little more into their research isolation 1 euros conditions, and it appears they are actually using small plastic helmholtz devices slotted through holes in the walls of the cavity.
Not just drilling holes in the studs.

It's interesting. Mass producing the little resonators could be simple enough for the specific frequencies they need to target.

I'll have to read it more thoroughly later.

Dan

I've been looking for the name of this little thing for quite a while. Now I know it thanks to you.


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