Is a non airtight wall part of an MAM

[Bastiaan]

These penetrations will not improve the isolation, of course.
If the contractor insists on venting the airgap you can eventually think of a system you can close 'm when you're working.
For maximum isolation you should consider to place the outer and inner leaf of the wall on seperate foundations.
And don't use ties, you should build without them (ankerloos).

A 120mm limestone - 50mm gap - 120 mm kalkzandsteen wall that is coupled by the foundation will have a sound reduction of (Jellema, Bouwkunde):
125 Hz - 52 dB
250 - 55
500 - 65
1000 - 89
2000 - 100

A 120mm limestone - 50mm gap - 120 mm kalkzandsteen wall that is decoupled will have a sound reduction of:
125 Hz - 45 dB
250 - 47
500 - 54
1000 - 63
2000 - 71

A 100mm limestone - 50mm gap filled with mineral wool - 100 mm kalkzandsteen wall that is decoupled on the foundation will have a sound reduction of:
125 Hz - 56 dB
250 - 54
500 - 62
1000 - 87
2000 - 99

A 100mm limestone - 50mm gap filled with mineral wool - 100 mm kalkzandsteen wall that is coupled by 20 ties per square meter will have a sound reduction of:
125 Hz - 50 dB
250 - 52
500 - 60
1000 - 79
2000 - 93

At lower frequencies these trends will continue to resonance.

The next challenge is to design a roof, doors, windows and a ventilation system that performs ass well as the walls.

Hi Bert, I think you are referring to this post

The third configuration (decoupled foundation, mineral wool) has the best performance at 125 Hz, but the first configuration (coupled foundation, no mineral wool) has a slightly better performance for frequencies > 125 Hz.

I'm surprised that the second configuration (decounpled foundation, no mineral wool) performs worse than the third configuration. Should you only decouple the foundations if you also use mineral wool?

Is the expectation that at 63 Hz, the third configuration will outshine the other configurations even more than 4 dB?

Which Jellema did you take this info from by the way?

[bert Stoltenborg]

I have a big mouth about Greg and then I screw up my own data

A 120mm limestone - 50mm gap - 120 mm kalkzandsteen wall that is DEcoupled by the foundation will have a sound reduction of (Jellema, Bouwkunde):
125 Hz - 52 dB
250 - 55
500 - 65
1000 - 89
2000 - 100

A 120mm limestone - 50mm gap - 120 mm kalkzandsteen wall that is coupled will have a sound reduction of:
125 Hz - 45 dB
250 - 47
500 - 54
1000 - 63
2000 - 71

A 100mm limestone - 50mm gap filled with mineral wool - 100 mm kalkzandsteen wall that is decoupled on the foundation will have a sound reduction of:
125 Hz - 56 dB
250 - 54
500 - 62
1000 - 87
2000 - 99

A 100mm limestone - 50mm gap filled with mineral wool - 100 mm kalkzandsteen wall that is coupled by 20 ties per square meter will have a sound reduction of:
125 Hz - 50 dB
250 - 52
500 - 60
1000 - 79
2000 - 93

At lower frequencies these trends will continue to resonance.

The data are from Jellema, Bouwkunde 7a, from the '80.
The newer Jellema doesn't have this detailled course on acoustics.

I don't know exactly where these data are coming from; data between labs on the same samples can differ quit a bit, data from the same lab between different samples are fairly trustworthy. Measurements are only above 125 Hz because under these frequencies you have no diffuse soundfield.
Some labs, like the KU Leuven, measure below to 20 Hz with the restriction taht LF data are not diffuse.

[Bastiaan]

Thanks Bert, so this means a 6-9 dB improvement in LF for the isolated floor. This should be enough confirmation

Next challenge: the ceiling!

[Bastiaan]

I have been looking at a ceiling to match up with the wall. I have used my TL calculator spreadsheet for a comparison.
I came up with the following basis:

ceiling doorsnede forum.jpg

The inner leaf is relatively simple, I plan to pour 8 - 10cm of reinforced concrete on top of the studio walls. This will give me a surface density of ~220 kg/m2. The wooden construction below serves the purpose to carry the load of the concrete while it is curing. On the inside, I can fill the space between the joists with rockwool and then finish it with fabric. The space between the outer and inner leaf will be fairly limited, so construction wise this will be a nice challenge

In order to come close to the TL of the walls, I need a surface density of about 70- 80 kg/m2 on the outer leaf. The building is only for 1/4 for the studio, and I would like the outer surface of the roof to be one surface (i.e. no differences in thickness of the leaf).

Underlayment is only ~10kg/m2, and 12.5mm gypsum board is 9.1kg/m2. In my current proposal I have 29.1 kg/m2. If I add more gypsum board to the inside, the gap between the inner and outer leaf decreases, which brings up the resonance frequency, and reduces the LF TL.

I have considered a sheet of lead of 3 mm, which has a mass of 34 kg/m2, but the cost is €1800 if I use it locally above the studio, e.g. 15 m2. Another option would be the cover the full roof with 5 sheets of gypsum board between the underlayment and the PIR. The roof is ~75 m2, so that means I need 50 boards of 1.5m2 per layer. One board is €2,5 so if I add 5 layers that comes down to 5 x 50 x 2,5 = €625.

Any suggestions?

[Paulus87]

I have been looking at a ceiling to match up with the wall. I have used my TL calculator spreadsheet for a comparison.
I came up with the following basis:

ceiling doorsnede forum.jpg

The inner leaf is relatively simple, I plan to pour 8 - 10cm of reinforced concrete on top of the studio walls. This will give me a surface density of ~220 kg/m2. The wooden construction below serves the purpose to carry the load of the concrete while it is curing. On the inside, I can fill the space between the joists with rockwool and then finish it with fabric. The space between the outer and inner leaf will be fairly limited, so construction wise this will be a nice challenge

In order to come close to the TL of the walls, I need a surface density of about 70- 80 kg/m2 on the outer leaf. The building is only for 1/4 for the studio, and I would like the outer surface of the roof to be one surface (i.e. no differences in thickness of the leaf).

Underlayment is only ~10kg/m2, and 12.5mm gypsum board is 9.1kg/m2. In my current proposal I have 29.1 kg/m2. If I add more gypsum board to the inside, the gap between the inner and outer leaf decreases, which brings up the resonance frequency, and reduces the LF TL.

I have considered a sheet of lead of 3 mm, which has a mass of 34 kg/m2, but the cost is €1800 if I use it locally above the studio, e.g. 15 m2. Another option would be the cover the full roof with 5 sheets of gypsum board between the underlayment and the PIR. The roof is ~75 m2, so that means I need 50 boards of 1.5m2 per layer. One board is €2,5 so if I add 5 layers that comes down to 5 x 50 x 2,5 = €625.

Any suggestions?

I'm sorry for joining this discussion late, but do you have a height restriction? If not then increasing the size of the cavity will dramatically improve your TL. You could also use layers of cement board instead of drywall, they have a surface density of 15-16kg/m2 @ 12mm thickness.

Paul

[Bastiaan]

Hi Paul,

Thanks for your reply. I do have a height restriction, the maximum building height is 3 m above ground level. I see in my calculator that if I increase the distance between inner and outer leaf from 20 to 40 cm, there is an improvement of 6 dB in TL below fknee, and at the same time fknee decreases from 237 Hz to 137 Hz.

Earlier suggestions have pointed me in the direction of a separate foundation for the studio, which means I can lower the level of the studio with respect to the rest of the building to create extra distance between inner and outer leaf as shown below:

hoogte detail forum.jpg

Great suggestion, thank you!

[Paulus87]

Hi Paul,

Thanks for your reply. I do have a height restriction, the maximum building height is 3 m above ground level. I see in my calculator that if I increase the distance between inner and outer leaf from 20 to 40 cm, there is an improvement of 6 dB in TL below fknee, and at the same time fknee decreases from 237 Hz to 137 Hz.

Earlier suggestions have pointed me in the direction of a separate foundation for the studio, which means I can lower the level of the studio with respect to the rest of the building to create extra distance between inner and outer leaf as shown below:

hoogte detail forum.jpg

Great suggestion, thank you!

You’re welcome, also if the foundations and slabs have not been poured yet then why not just dig down deeper into the ground? Then you wouldn’t have a height restriction anymore as you could make the internal height as high as you like.

Paul

Edit: I should really have read your post properly, I can see this has already been suggested. Sorry for repeating! Carry on...

[bert Stoltenborg]

If you maintain a gap like in the earlier post I made your roof will be balanced with the walls as they are comparable.

[Bastiaan]

Hi Bert,

My outer brick wall has a surface density of ~150 kg/m2 whereas the outer roof has a surface density of ~70 kg/m2. According to the MAM formula's, increasing the air gap would compensate slightly for this in LF. Would you advice against increasing the air gap? Or do you think it just does not have much benefit?

Kind regards,

Bastiaan

[bert Stoltenborg]

If you have an outer leaf with a heavy (brick wall) and a lighter part (roof) and an inner leaf where the wall is lighter and the roof is heavier you should create a situation where the sound entering the gap through the lighter leaf part can not escape through the other lighter leaf part.
So take care the gap is interrupted at the edges of where the leafs change of composition.

[Bastiaan]

We finally started building! There are two foundations, 1 to bear the outer shell of the building, and a separate foundation for the studio/music room within that outer shell. The studio foundation was cast this afternoon.

DSC_1055.JPG

The studio foundation rests on its own 4 piles.

The outer and inner beams are made by casting concrete into an EPS shell. The outer and inner beam shells touch. Since these are made for 99% out of air, I suppose that this is not a problem. Does anyone see a problem with this?

[gullfo]

it shouldn't be a problem - test with a stethoscope to be sure - if there is enough contact, dig out the EPS once the concrete is full set.

[Bastiaan]

Great suggestion! Just ordered one
I'll keep you guys posted!

[Bastiaan]

Today I used the stethoscope to check the isolation between the two foundations. I gently tapped with a hammer on the concrete. If I tapped on the same foundation I had the stethoscope on, I could hear the impact loud and clear. If I tapped on the other foundation, I only heard the noise through the air. I asked my wife to tap with the hammer on the two foundations on the other side of the building from where I was sitting, and there the difference was the same.

My conclusion is that the isolation is fine. I suppose I will use this trick more often later on in the building process. Interesting exercise!

IMG-20210418-WA0001.jpg

[gullfo]

definitely worth keep handy as construction progresses to check that isolated assemblies are truly decoupled - framing, ducts, wiring (stretched tight between frames) etc. also keep an eye on debris falling into the gaps between the pads to ensure they don't end up connecting them.