Is a non airtight wall part of an MAM

Bastiaan wrote:

I have been thinking about a good floor this weekend. I still intend to use a floor like this:

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The easiest way to have the studiofloor decoupled from the rest of the building would be like this:

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This comes with no cost adder. However, the foundations are shared, and therefore there is a flanking path from one floor to another: floor1 surface -> Tbeam floor 1 -> common foundation Tbeam floor 2 -> floor 2 surface. This technique is used for townhouses/terraced houses. Bert suggested earlier that a decent floor should have a separate foundation. So the second option is this:

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This option comes with a cost adder in additional concrete for the foundation beams, and some additional piles. Also, it is a bit more difficult to build. I have limited real estate, so the distance between the foundations must be very small, I took 4 cm in the drawing. Therefore I think I cannot pour both foundations in one go. On the other hand, I like engineering challenges :D Is there any way to predict the difference in TL with the two options? I think option 2 will cost me about 2k euro's more, so it would be nice if I could justify this cost.

Didn't I post the differences? :-)

Almost all of my work is remedial or treating existing structures. For one green field build I ticked every box possible, with approval from all 4 Criteria in ModeWiz. I optimised to within centimetres of the planning limits. Modal pattern of the finished space bore no relationship with the predicted. Pondering this I note probable systemic errors in other predictors/calculators. For example:- Sound travels on average 20% slower through fibre, but this has a spectrum and some see it as low as 80m/S at some frequencies. So the modal pattern of a strongly treated room will be quite different to that of a concrete shoebox. Porous absorption calculators do not deal with the corner situation, which if we extrapolate from speakers, can be a x8 factor. Same calculators treat a layer as infinite or full surface. I do not believe the theoretical quarter wave absorption peak will hold up when a fibre trap is tiny compared to the boundary. And what happens when we distribute such tiny traps, do we bunch them together to form a bigger sheet, or strategically gap them? And how does this interact with the air gap to boundary distance? At studiotips we see a Corner Straddling batt of 703. Touching the wall it has a pretty massive absorption peak around 80Hz or so. Moved out a bit from the wall about 2 inches this collapses? Was this a fully sealed straddler, floor to ceiling? Or do single traps benefit this much in this position. Again, full surface/corner or gaps between panels? IMO, it is audible, denser fibres have a damped resonant effect. Calculators frequently predict little or no LF absorption as they use GFR only. Different types of fibre appear more damped e.g. Fibreglass 705 is quite ringy while Rockwool not. Also and by all means correct me if I am wrong, but some fibres appear to have vastly different absorption, not so related to GFR only. e.g. Caruso Isobond, Autex. Lastly, and maybe on point here..... A large surface area, even concrete, will flex a whole lot more than a smaller one. Do our TL predictors take this into account?

Dan, you're awesome.

But a calculator that calculates such numbers should really not be on a respectable forum.

Bert, the calculator uses basic well known formulas that any forum member here would have to do by hand in order to figure out what materials to use in their builds. It was built so that people could spend 20 seconds calculating different scenarios. The drop down boxes and conversion section make it easy to use. It takes out the research time a person would spend looking up the density of their materials. With all of that said, I'm not sure why you're so concerned with it being on here. If you build a better one that is as easy to understand and use for newcomers and post it for free, I'll gladly remove mine and sticky yours. Greg

Gregwor wrote:

Dan, you're awesome.

But a calculator that calculates such numbers should really not be on a respectable forum.

Bert, the calculator uses basic well known formulas that any forum member here would have to do by hand in order to figure out what materials to use in their builds. It was built so that people could spend 20 seconds calculating different scenarios. The drop down boxes and conversion section make it easy to use. It takes out the research time a person would spend looking up the density of their materials. With all of that said, I'm not sure why you're so concerned with it being on here. If you build a better one that is as easy to understand and use for newcomers and post it for free, I'll gladly remove mine and sticky yours. Greg

What are you talking about? 73 dB @ 20 Hz is ridiculous.

What are you talking about? 73 dB @ 20 Hz is ridiculous.

I've stated that the calculator 2.04 is fixed and releasing soon. It has taken a year and a half of version 2 out for this to come to fruition. Greg

bert Stoltenborg wrote:

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 :oops: 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?

I have a big mouth about Greg and then I screw up my own data :x :mrgreen: 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.

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

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: 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 :D 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?

Bastiaan wrote:

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:

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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 :D 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

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: Great suggestion, thank you!

Bastiaan wrote:

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:

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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...

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

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

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.

We finally started building! :yahoo: 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. 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?

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.

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

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!

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.

Hi Bastiaan and All, I am particularly interested in the subject line of this thread and how you are dealing with the following from your initial post: "Humidity is an attention point in the dutch climate, and therefore a brick wall will have several openings in it for ventilation, and possible water drainage. The purpose of those openings are to prevent that moisture enters the inner building. Should I still consider the brick wall one of the leaves in a MAM even if it is not airtight?" "I think I can come away with omitting the openings, as the current insight is that it is not necessary. So that will define my first leaf" In Australia our building regulations require that we include these "weep holes" for the reason you described. As I am proposing a brick (concrete block) outer leaf and a timber stud wall inner leaf for my studio build in a new home, I am interested to know how you came to the conclusion that the weep holes are not necessary to prevent moisture buildup? As was stated, leaving weep holes in the brickwork compromises the acoustic integrity of the two leaf structure, so is not an option, however once I have complied with building regulations, if I seal these holes I want to ensure I am not going to have wall cavity moisture issues in the future.

Should I still consider the brick wall one of the leaves in a MAM even if it is not airtight?"

No - to achieve a soundproof room you must have two totally sealed rooms, an inner and an outer. Remember, sound is air pressure. cheers john

So in Melbourne's more temperate climate, you would advise NOT sealing an outer brick wall built with say Besser blocks to act as an outer leaf, but rather construct a standard brick veneer cavity wall with weep holes, then air gap, then another stud wall with 2 sheets of gyprock for the internal structure? This would obviously reduce the internal studio dimensions somewhat, but would function as a two leaf system while preventing moisture retention?

as John noted - the MAM works if there are two sealed rooms - in the case of the brick veneer - this is a facade with ventilation which has behind it has a sealed framed wall? so outer leaf is sealed. then you build an inner room which is also sealed. the outer brick veneer while technically a 3rd leaf is ventilated and likely more massive than either of the two inner layers of mass, so unlikely to be problematic. so if you have: brick (vented) -> small air gap -> plywood sheath w/ moisture barrier -> frame + insulation -> 1" air gap -> frame + insulation -> inner mass (plywood + 2x gwb) my thought is you likely need to beef up that outer sheathing - install drywall or cement board between studs to increase the mass there.

gullfo wrote:

as John noted - the MAM works if there are two sealed rooms - in the case of the brick veneer - this is a facade with ventilation which has behind it has a sealed framed wall? so outer leaf is sealed. then you build an inner room which is also sealed. the outer brick veneer while technically a 3rd leaf is ventilated and likely more massive than either of the two inner layers of mass, so unlikely to be problematic. so if you have: brick (vented) -> small air gap -> plywood sheath w/ moisture barrier -> frame + insulation -> 1" air gap -> frame + insulation -> inner mass (plywood + 2x gwb) my thought is you likely need to beef up that outer sheathing - install drywall or cement board between studs to increase the mass there.

Can you (generally) say that in 3-leaf design you should beef up inner/outer/midle leaf, or is there some generic guidelines for this? ie. what has the greates effect or what is the best place to add mass (apart from tearing the wall and making a 2-leaf design :D )