An outer wall, a hallway, and a double-leaf assembly walked into a bar...

[SoWhat]

Greetings all,

So, after TOO much searching and reading on this subject over many months, can anyone provide a (semi)definitive answer to this:

How much space (read: a hallway) between a wall and a double-leaf assembly must there be for the wall to NOT be considered a third leaf?

My reading has turned up the following answers: 1 foot (methinks that's not right at all, and yes, I really saw this), 2 feet (I can sort of believe that), 3 feet (seems like a very safe bet), and 4 feet or more (no problem at all).

Thanks in advance for your thoughts.

All the best,

Paul

[Starlight]

Like you, Paul, I have read a lot and cannot give a definitive answer. This is where Andre (avare) excels because A, he knows this stuff, and B, he would point you to a technical book or PDF that demonstrates the point.

Are you trying to find an answer for a specific situation or is this just a case of wanting to understand the principle?

Source of the postAn outer wall, a hallway, and a double-leaf assembly walked into a bar...

I thought this was going to be a humorous topic!

[SoWhat]

Greetings Starlight,

It is indeed for my project. I have had to scale scale back the size of my standalone studio in order to save thousands of dollars in survey/construction costs which would satisfy local codes. On the upside, I will be able to adapt some space INSIDE my house for a "supplemental" studio. Although I would have rather had a single large space, I am happy that I've found a compromise that won't break the bank.

Perhaps Andre will see the thread and respond.

I thought this was going to be a humorous topic!

I just had to find a way to sublimate my frustration. What better way than to come up with a catchy thread title!

All the best,

Paul

[bert stoltenborg]

Source of the post Like you, Paul, I have read a lot and cannot give a definitive answer. This is where Andre (avare) excels because A, he knows this stuff, and B, he would point you to a technical book or PDF that demonstrates the point.

Are you trying to find an answer for a specific situation or is this just a case of wanting to understand the principle?

Source of the postAn outer wall, a hallway, and a double-leaf assembly walked into a bar...

I thought this was going to be a humorous topic!

It is a matter of proportion.
Double windows, for example can have something like a 6-25-6 double pane, a gap of 200 mm and a single pane and you don't see much difference with regards to sound reduction when the double pane is made singe with the same mass. It is like a X-over filter where the airspring is the capacitor; if you have a large cap and a very small one you won't notice the small one. But it all depends, also on the masses of the constructions.

[terminator1987]

Source of the post

It is a matter of proportion.
Double windows, for example can have something like a 6-25-6 double pane, a gap of 200 mm and a single pane and you don't see much difference with regards to sound reduction when the double pane is made singe with the same mass. It is like a X-over filter where the airspring is the capacitor; if you have a large cap and a very small one you won't notice the small one. But it all depends, also on the masses of the constructions.

I am no specialist, but from what I've gathered in my research this is correct, and I will try to elaborate.

1) Every mass-air-mass barierr has its own resonance frequency, which will transmit MORE through it; The ideal for sound isolation is to design it below 20 Hz using a calculator;

2) triple-leaf effect means that when you are struggling for space, it is a much better option to expand the airspace between the two leaves than to add another leaf with smaller airspace, so especially if you are renovating to soundproof a wall that has e.g. 5 cm of airspace and a drywall on both sides as leaves, you have two reasonable options: a) add mass on both sides (another drywall sheet) which will perform poorly but noticeably and is the easiest way, b) remove one layer and extend the airspace, and ideally also add insulation and mass to the leaves. DO NOT add another leaf with same airspace of 5cm and a drywall sheet - this is the worst one could do, especially beacause identicall airspaces will resonate together and will be even worse than before for that frequency and not much better for others.

3) if you have a brick wall, half a meter of loosely insulated space and another brick wall, adding a third leaf of any kind should not practically matter at all, especially a small one. Even if it would produce a 1-2dB dent on a spectrum of sound isolation in that particular frequency, such a massive barrier will most probably isolate this frequency with something like 90-100 dB efficiency, so it won't matter

4) the real problem occurs only when you are using relatively lightweight leaves such as drywall and you cannot afford a large airspace, then just remember that two leaves of the same mass and with the same total thickness of the barrier will always perform better than three leaves arranged in the same total thickness

Was that helpful?

[Starlight]

Source of the postWas that helpful?

It is helpful, terminator1987. Bert is one of the professionals and so his reply was not in doubt but you have helpfully explained it in more detail. Thank you.