John Sayers' Recording Studio Design Forum Archive

Hi all

First Post! probably should have got on this earlier, starting in about 8 weeks. Although I've been researching (dreaming) for years

This is not exactly the dream though. I'm building these under 4m by under 3m computer producer units, they don't need to be up to recording studio spec, I want to get the best isolation i can without the budget for green glue or three layers of gyproc, so can't skimp on precision of build and seal and getting the design right. they are sitting on a vast mass of concrete btw (& will support their own ceilings)

I'm realising there are a couple of issues that are stopping me from getting into the detail of the plans for the units.
And they are both about whether in this building I am actually able to get the isolation benefit of a well designed 2 leaf

The first one is whether, when I am building close to the (concrete) boundary walls I can consider them to be the second leaf, when I don't think the air in the cavity is 'sprung' / 'tuned' (or maybe is such a loose spring / is tuned to such a low frequency as to be irrelevant) due to the large open space in the building. It's rather a lot of air

Then you add this to the mix:

The walls are 2 layers of concrete block with a 200mm cavity filled by 2 layers of 100mm insulation board. So already a 2 leaf system. I'm sure this has been dealt with before, but I can't find it. Plus, I don't know their mass.

Where does that leave me?

confused is where

Ah I did find a post that pointed out that as the two layers of the concrete wall are not decoupled they pretty much act as one boundary, so that's a chunk of the confusion out of the way.

Now as to the resonant response of the air gap in a large space i really do think I need some help.

And I'd better find a way to discover the mass of those blocks short of removing one and weighing it!

From the reference section: a hollow block wall will act as TWO leaves, unless the hollow spaces are filled with mortar, grout, concrete or sand

In which case my concrete wall is definitely 2 leaves then

Hi " legezer", and Welcome!

Five freestanding units in one high roof warehouse space

I'm not really sure at all what it is you are trying to accomplish! What are the "units"? Are the live rooms? Control rooms? Iso booths? Rehearsal rooms? Something else? How big are they? How much isolation do you need?

computer producer units

I'm not sure what that term means either. Is that some sort of pre-fabricated system?

I want to get the best isolation i can

Fine, but you'll need to put a number to that! How much isolation do you NEED, in decibels? That's what should define the build. If you plan on having a Grateful Dead copycat band rehearsing full bore in one room, and someone else recording soft breathy romantic ballad vocals next door, then you need a LOT of isolation. But if you only ever have people reciting poetry in adjacent rooms, even a simple wall will suffice. You aren't giving us much to go on!

The first one is whether, when I am building close to the (concrete) boundary walls I can consider them to be the second leaf,

Do the math: There's a very simple set of equations that will allow you to figure out the MSM resonant frequency, and also predict the isolation for each of the spectrum regions. Here's what you need:


The equations for calculating total isolation of a two-leaf wall are simple:

First, for a single-leaf barrier you need the Mass Law equation:

TL = 14.5 log (M * 0.205) + 23 dB

Where: M = Surface density in kg/m2

For a two-leaf wall, you need to calculate the above for EACH leaf separately (call the results "R1" and "R2").

Then you need to know the resonant frequency of the system, using the MSM resonance equation:

f0 = C [ (m1 + m2) / (m1 x m2 x d)]^0.5

Where:
C=constant (60 if the cavity is empty, 43 if you fill it with suitable insulation)
m1=mass of first leaf (kg/m^2)
m2 mass of second leaf (kg/m^2)
d=depth of cavity (m)

Then you use the following three equations to determine the isolation that your wall will provide for each of the three frequency ranges:

R = 20log(f (m1 + m2)) - 47 ...[for the region where f < f0]
R = R1 + R2 + 20log(f x d) - 29 ...[for the region where f0 < f < f1]
R = R1 + R2 + 6 ...[for the region where f > f1]

Where:
f0 is the resonant frequency from the MSM resonant equation,
f1 is 55/d Hz
R1 and R2 are the transmission loss numbers you calculated first, using the mass law equation

And that's it! Nothing complex. Any high school student can do that. It's just simple addition, subtraction, multiplication, division, square roots, and logarithms.

The walls are 2 layers of concrete block with a 200mm cavity filled by 2 layers of 100mm insulation board. So already a 2 leaf system. I'm sure this has been dealt with before, but I can't find it. Plus, I don't know their mass.

That is, indeed, very likely a two-leaf system. However, it does have a lot of mass, so you should be reasonably OK when you build your single-leaf structures for each "unit". Just make sure there's a decent sized air gap and plenty of mass on that leaf.

Ah I did find a post that pointed out that as the two layers of the concrete wall are not decoupled they pretty much act as one boundary, so that's a chunk of the confusion out of the way.

Do you know for sure if they are decoupled or not?

And I'd better find a way to discover the mass of those blocks short of removing one and weighing it!

If you know the dimensions of each block, and they are solid (no internal cavities), then it's simple to calculate the surface mass of each leaf. All you need to know is that the density of concrete is around 2400 kg/m3. Based on that, and the dimensions, you can easily figure out the surface density.

From the reference section: a hollow block wall will act as TWO leaves

You did not say that your wall is built with hollow blocks! You said it was two layers of concrete block! That's a very different thing. Hollow blocks and solid blocks are not the same.

... will act as TWO leaves, unless the hollow spaces are filled with mortar, grout, concrete or sand

I'm not sure where you saw that, but hollow concrete blocks, such as breeze blocks, besser bricks, and suchlike should be considered as single-leaf with resonant cavities in them, but not two leaf. The concrete webbing of the blocks firmly couples the sides of the brick together, regardless of any fill in the hollow interior of the block.

- Stuart -