Drum rehearsal/recording basement studio in Madrid

[vdegou]

In the MSM equation, there are 2 variables. Mass and Spring. The sheathing we use is the mass. Surface density is what matters here. Whether you use lead or glass or wood or drywall, it doesn't matter. Drywall is recommended all the time because it is fairly easy to work with, it's cheap, and it looks great when painted.

Got it, that's good to know. This is fairly in line with the little knowledge I've obtained from researching into this topic.

Often is is recommended to use a layer of OSB behind your drywall so that you can easily mount treatment devices anywhere without having to find a wall stud.

Also makes sense! I'll have to compare prices around here to see how I can work around the structural integrity of the drywall. I think I'm not going to be going to deep into wall construction yet though.

A little update and a short-term plan for now:

1. Definitely the first thing to do will be to seal that giant, perfectly square hole in the wall (hole_in_wall_.jpg in the first post). I'm thinking of just brick and mortar to cover it up, and then maybe apply a thin layer of cement on top of that so the brick isn't visible. I'll do some tests when I have the brick and mortar set in, as the cement layer might not even be a good idea (a thin layer might not add too much mass comparatively to the rest of the wall). What do you guys think? Also, I think it will be very interesting to procedurally repeat the SLM tests I took as we add to the studio, in order to see how the changes improve one at a time.

2. After the hole in the wall, the next step is to address the water pipes. I need a little bit of guidance on this matter. Does it make sense to wall the pipes in a 2-leaf walls system, following MAM principles, knowing that later when I build the inner shell of the room these pipes will be between the two leaves of the room studio? It's kind of hard to explain, but if we take a look at the image studio_layout_top_down_constraints.png from the first post, it's easier to visualize. The water pipes are in the yellow section of the studio, and this yellow section, at least in my mind, is a good candidate for being the airspace between the external concrete walls and the internal studio shell/walls, which is it's own 2-leaf MAM system. So, we will have a MAM within a MAM, which will create, at best, a 3rd leaf if the external leaf of the water pipe is the concrete wall, and a 4th leaf if it is not. Both of these situations are undesirable as they decrease the overall absorption levels of the studio. So does anybody have any advice on how to approach the water pipe situation? I can make a Sketchup model of this to clarify if needed.

3. I'm starting to dive deeper into the HVAC matter. This topic is greatly explained in Gervais' book, and now I'm just looking into what system I should go after. Ideally, to avoid complicating the build with duct work which I have absolutely no experience in, I'd like to go for a mini-split system. Problem here is, of course, not all are designed for bringing fresh air into the room. I did run into this model (Daikin Ururu Sarara) from another post in the forum. It claims it can fill a 26m^2 room in 2h. This is a bit sketchy to me because... well, how can you claim to fill a 26m^2 room when that is a measure of area and with air and other fluids we are concerned about filling a volume? To be fair, I haven't gotten around to reading its specs. Also its pricepoint is kind of steep at 1500 euros... Anyways, the thing is there might be new mini-split or other systems nowadays that provide easy access to fresh air and I would really appreciate you guys' input on that.

4. Regarding the ceiling of the studio, I have more info. Although I haven't been able to obtain how thick the concrete is, it must be thick enough to support the weight of a car. I hadn't mentioned this before, but the roof of the studio is actually the floor of the garage right above! So this must mean it has to be at least somewhat thick. Also, I went ahead and took some more SLM measurements to see what we're dealing with. The new measurements are:

Studio baseline levels (same as before, just for reference): 31.7 LAeq, 68.7 LCpeak, 47.5 Max level
Garage baseline levels: 32.7 LAeq, 62.1 LCpeak, 42.4 Max level
Studio levels while drumming (same as before, just for reference): 102.2 LAeq, 127 LCpeak, 108.8 Max level
Garage levels while drumming: 59.8 LAeq, 84.5 LCpeak, 65.8 Max level
Garage levels while drumming near the water pipes (pipes in the studio lead to garage): 61.1 LAeq, 87.6 LCpeak, 68.1 Max level

The updated graphs are here:

laeq.PNG

lcpeak.PNG

max_level.PNG

I know the measurements are not 100% accurate, especially them being taken from an iPhone app... but does it make sense to say that our concrete studio ceiling is giving us 102.2dB - 59.8dB approx 40dB of attenuation? That seems a bit high, but I'll take it if it's true!

Having these values, does it make sense to put in an inner ceiling in the studio to decouple the structure from the concrete ceiling? If we manage to do that properly, how much of an increase can we expect to obtain keeping in mind our space restriction (1.95m height)?

5. Lastly, I'm a bit confused as to how to leverage the MSM equation -->

In the MSM equation, there are 2 variables. Mass and Spring. The sheathing we use is the mass. Surface density is what matters here.

According to the formulas that Gervais' presents, a doubling in the mass of the walls represents an increase of 6dB in STC (if I understood this, the sound will be "half as loud"). So my question is, in my current context, a doubling of the mass implies the mass present in both leaves? Or overall? Am I supposed to have an inner, drywall/wood leaf of the same mass as the concrete wall (impossible, I know) so I can get an extra 6dB reduction? What if I can't calculate the weight of the concrete walls? How can I know the STC increase? Does the weight discrepancy between inner and outer leaves matter? How does airspace fit into this? ... Sorry for all the questions. I guess I just need a kick in the right direction here on how thick / dense these walls should be.

As a closing statement, I think I'm going to redo the baseline values I took in the basement. Like I said in a previous post, I had a 3d printer do some work in the background and this was affecting the readings. Will update with new charts once I get those new values.

Apologies for the huge read everyone, but thank you all so much for the input!

[Soundman2020]

Ideally, to avoid complicating the build with duct work which I have absolutely no experience in, I'd like to go for a mini-split system. Problem here is, of course, not all are designed for bringing fresh air into the room.

Very, very few of them do that, and NONE of them do so at a rate that makes sense, or is even legal (in the sense that it meets code)...

Not to mention that the very, very few mini-splits that do bring in fresh air, do NOT also ventilate the stale air! In a typical house or office, that isn't too much of a problem, since those are very "leaky" rooms, with lots of gaps, cracks, and holes for the air to escape through. But with a studio, there are zero holes, zero gaps, and zero cracks... the studio must be completely air-tight in order to isolate.... so where is the stale air supposed to go? You can't pump air into a room and not also have a path for the excess air to get out again...

Short summary: there's no way of avoiding having ducts in your studio.

It claims it can fill a 26m^2 room in 2h. This is a bit sketchy to me because... well, how can you claim to fill a 26m^2 room when that is a measure of area and with air and other fluids we are concerned about filling a volume?

Exactly! Beware of HVAC specs that only mention floor area, without considering anything else.

Not to mention that the ASHRAE specs, and therefore most building codes, specify that studios need at least six full room changes per hour, not one change every two hours! So that unit falls short by a factor of 1200%... Assume that the hypothetical 26m2 room has the height of a typical house room, at 2.4m: That implies a room volume of about 62m3. The unit in question takes two hours to change that much air, so it therefore can move air at the rate of 31m3 per hour. What you would actually need, according to ASHRAE, building code, and plain old common sense, is 372 m3 per hour (six changes per hour....). So you need 372, and this unit gives you 31... Hmmm: You are totally right... it does seem to fall a little short!

Then there's the issue of speed... If it takes two hours to move all the air through the room, then that means that any buildup of CO2, stale air, or bad odors, will take at least 2 hours to clear.... Do you really want to be stuck with the smell of the drummer who hasn't showered in a month, or the guitarist who ate garlic bread for lunch, or the singer with a bowel problem.... even two hours after they already left, and the next band arrived? On the other hand, if you go with the correct ventilation rate, all of that nasty stuff will be gone in six minutes, not two hours....

To be fair, some fresh air is better than no fresh air, but the tiny little bit that comes in through such units is way, way short of what you need.

Anyways, the thing is there might be new mini-split or other systems nowadays that provide easy access to fresh air and I would really appreciate you guys' input on that.

Simple answer: Nope! No such thing exists. If it DID exist, it would need normal large diameter air ducts, many inches in diameter, in order to provide the right amount of fresh air.

Sorry. There's no short-cuts here...

I know the measurements are not 100% accurate, especially them being taken from an iPhone app...

Yup! Considering that a typical drum kit played normally produces around 115 dBC, and you are only showing around 100, I'd say that it is WAY off! You also show a peak of 127 dBC, which is equally unlikely.... Unless maybe you took the measurement INSIDE the kick drum!.... To be honest, I doubt that the tiny little voice-oriented mic on an iPhone would be able to measure 127 dB... It is design to capture typical spoken word frequencies, at typical speaking SPL levels, from a distance of a few inches, not massively deep pounding very low frequencies, at very high SPL levels, such as kicks and toms... way lower and way louder than any human voice can go.

So I'd take those numbers with a pinch of salt. When you can, beg, borrow or buy a real hand-held sound level meter, and use that to repeat your measurements. Maybe your meter really is accurate.... but maybe it isn't, and the only way to find out is to check it against one that IS accurate, measuring the exact same thing at the exact same time.

[quote...]approx 40dB of attenuation? That seems a bit high, but I'll take it if it's true! [/quote]It's possible for a thick reinforced concrete slab, capable of carrying the weight of cars..... However! You have CARS driving over your studio? Ummm.... I would expect some rather deep low-frequency rumbling from that ceiling, from engines idling and heavy weights rolling across it... not to mention doors slamming, radios playing, and just plain old footsteps. Lots of impact noise going on there.

Having these values, does it make sense to put in an inner ceiling in the studio to decouple the structure from the concrete ceiling?

Yes, definitely. Given that you have cars driving over your studio... see above.

If we manage to do that properly, how much of an increase can we expect to obtain keeping in mind our space restriction (1.95m height)?

195??? Wow! You are going to loose at least 10cm of acoustic height (assuming that you do your ceiling inside-out, which is basically the only option here) plus whatever is needed for the framing, which will set your visual ceiling height. Assuming that you can get by with only 2x6 joists, that implies losing another 15cm (If you need 2x8 joists, then it would be 20cm). So allow for losing 25 to 30 cm, meaning your final visual ceiling height will be around 170 or as low as 165. This does not seem viable to me, unless you and your musicians are not very tall. Even if you skimp on isolation, and use very high density materials for your mass, your final visible ceiling height is never going to be more than about 175cm. Even if you don't install any isolation at all, and simply treat the existing concrete roof with suitable acoustic treatment, your visual ceiling height is still not going to be more than 180cm...

a doubling in the mass of the walls represents an increase of 6dB in STC

Forget STC. It's not a valid method for measuring studio isolation. Here's why: STC was never meant to measure such things. Here's an excerpt from the actual ASTM test procedure (E413) that explains the use of STC.

“These single-number ratings correlate in a general way with subjective impressions of sound transmission for speech, radio, television and similar sources of noise in offices and buildings. This classification method is not appropriate for sound sources with spectra significantly different from those sources listed above. Such sources include machinery, industrial processes, bowling alleys, power transformers, musical instruments, many music systems and transportation noises such as motor vehicles, aircraft and trains. For these sources, accurate assessment of sound transmission requires a detailed analysis in frequency bands.”

It's a common misconception that you can use STC ratings to decide if a particular ceiling, wall, window, door, or building material will be of any use in a studio. As you can see above, in the statement from the people who designed the STC rating system and the method for calculating it, STC is simply not applicable.

Here's how it works:

To determine the STC rating for a ceiling, wall, door, window, or whatever, you start by measuring the actual transmission loss at 16 specific frequency bands between 125 Hz and 4kHz. You do not measure anything above or below that range, and you do not measure anything in between those 16 points. Just those 16 small bands, and nothing else. Then you plot those 16 points on a graph, and do some fudging and nudging with the numbers and the curve, until it fits in below one of the standard STC curves. Then you read off the number of that specific curve, and that number is your STC rating. That's it. There is no true relationship to real-world decibels: it is just the index number of the reference curve that is closest to your curve. To clarify: the STC number is NOT how much isolation you will get in a studio: it is just the number that somebody once assigned to a curve on a graph. So for the STC-70 curve, they could have called it "STC-GGFQRT" or "STC-Delta-RED" or "STC-Elephant-seven" or anything else, and it would tell you just as much about isolation as "STC-70" does: ie, nothing. It's a REFERENCE number, not an actual isolation number. For speech conditions, yes, STC-70 might actually be close to 70 dB of isolation, but not for music.

When you measure the isolation of a studio ceiling, wall, door, etc., you want to be sure that it is isolating ALL frequencies, across the entire spectrum from 20 Hz up to 20,000 Hz, not just 16 specific points that somebody chose 50 years ago, because he thought they were a good representation of human speech. STC does not take into account the bottom two and a half octaves of the musical spectrum (nothing below 125Hz), nor does it take into account the top two and a quarter octaves (nothing above 4k). Of the ten octaves that our hearing range covers, STC ignores five of them (or nearly five). So STC tells you nothing useful about how well a wall, door or window will work in a studio. The ONLY way to determine that, is by look at the Transmission Loss curve for it, or by estimating with a sound level meter set to "C" weighting (or even "Z"), and slow response, then measuring the levels on each side. That will give you a true indication of the number of decibels that the wall/door/window is blocking, across the full audible range.

Consider this: It is quite possible to have a door rated at STC-30 that does not provide even 20 decibels of actual isolation, and I can build you a wall rated at STC-20 that provides much better than 30 dB of isolation. There simply is no direct relationship between STC rating and the ability of a barrier to stop full-spectrum sound, such as music. STC was never designed for that, and cannot be used for that. It was meant for describing isolation of speech, not music. It's reasonably useful for what it was designed for, but not very useful for music.

Then there's the issue of installation. You can buy a door that really does provide 40 dB of isolation, but unless you install it correctly, it will not provide that level! If you install it in a wall that provides only 20 dB, then the total isolation of that "wall+door" combination is about 20 dB: isolation is only as good as the worst part. Even if you put a door rated at 90 dB in that wall, it would STILL only give you 20 dB. The total is only as good as the weakest part of the system.

So forget STC as a useful indicator, and just use the actual TL graphs to judge if a wall, door, window, floor, roof, or whatever will meet your needs.

(if I understood this, the sound will be "half as loud").

Not really, no. You need a change of 10 dB to judge that a sound is half as loud (or twice as loud). 6 dB is not a big change.

As a closing statement, I think I'm going to redo the baseline values I took in the basement.

Great! But it would be best to do those with a proper meter, not an app on an iPhone. Apps are fine for getting a rough idea of typical situations, but they can't handle extremes. And to start with, the mic on an iPhone is not omnidirectional... real acoustic measurement mics are: they have to be. But phone mics are specifically designed to be very directional, and even to cancel out noise coming from other directions.... Food for thought...


- Stuart -

[vdegou]

Very, very few of them do that, and NONE of them do so at a rate that makes sense, or is even legal (in the sense that it meets code)...

Not to mention that the very, very few mini-splits that do bring in fresh air, do NOT also ventilate the stale air! In a typical house or office, that isn't too much of a problem, since those are very "leaky" rooms, with lots of gaps, cracks, and holes for the air to escape through. But with a studio, there are zero holes, zero gaps, and zero cracks... the studio must be completely air-tight in order to isolate.... so where is the stale air supposed to go? You can't pump air into a room and not also have a path for the excess air to get out again...

Short summary: there's no way of avoiding having ducts in your studio.

This actually makes a lot of sense the way you put it. Of course, we can't NOT have ducts and expect stale air to go out and fresh air to go in. I need to do some more thinking regarding this area then, because I cannot seal the hole in the wall knowing that it might actually come in handy for the duct work.

Regarding this, I saw some posts where people have had luck using another room adjacent to the studio as a "fresh air chamber". They'll pull the air in through ducts and ventilators from that room which already has AC installed. This seems like it would be the simplest solution in my case, since I have two adjacent rooms to my studio, and both with windows, and also one of those rooms I can reach via the gaping hole in my wall! I guess I could go for something like this mentioned in Gervais' book:

rsz_ac_design_exchange_chamber.jpg

I'll have to do some calculations to see how much air I'll actually need in order to get equipment that best fits the job, but I'm open to any pointers anybody has regarding this.

If it takes two hours to move all the air through the room, then that means that any buildup of CO2, stale air, or bad odors, will take at least 2 hours to clear.... Do you really want to be stuck with the smell of the drummer who hasn't showered in a month, or the guitarist who ate garlic bread for lunch, or the singer with a bowel problem.... even two hours after they already left, and the next band arrived? On the other hand, if you go with the correct ventilation rate, all of that nasty stuff will be gone in six minutes, not two hours....

The good thing is, for the time being I'll be the only drummer who hasn't showered playing in my room!

So I'd take those numbers with a pinch of salt. When you can, beg, borrow or buy a real hand-held sound level meter, and use that to repeat your measurements. Maybe your meter really is accurate.... but maybe it isn't, and the only way to find out is to check it against one that IS accurate, measuring the exact same thing at the exact same time.

Yeah, I totally agree. It would definitely be a good idea to shell out some money on a proper mic for testing, but at least we have some very rough values we can use as guidance for now.

You have CARS driving over your studio? Ummm.... I would expect some rather deep low-frequency rumbling from that ceiling, from engines idling and heavy weights rolling across it... not to mention doors slamming, radios playing, and just plain old footsteps. Lots of impact noise going on there.

I think I might not have fully explained myself! The garage is my own, 1-car garage that's sitting on top of the studio area. There will be absolutely no issue of noise from cars driving above as it will only ever be my car parked there With this in mind, taking height limitations into account, and knowing there will be no noise from cars coming from the ceiling, does it still make sense to have the decoupled inner ceiling?

195??? Wow! You are going to loose at least 10cm of acoustic height (assuming that you do your ceiling inside-out, which is basically the only option here) plus whatever is needed for the framing, which will set your visual ceiling height. Assuming that you can get by with only 2x6 joists, that implies losing another 15cm (If you need 2x8 joists, then it would be 20cm). So allow for losing 25 to 30 cm, meaning your final visual ceiling height will be around 170 or as low as 165. This does not seem viable to me, unless you and your musicians are not very tall. Even if you skimp on isolation, and use very high density materials for your mass, your final visible ceiling height is never going to be more than about 175cm. Even if you don't install any isolation at all, and simply treat the existing concrete roof with suitable acoustic treatment, your visual ceiling height is still not going to be more than 180cm...

Unfortunately, we are working with a very small ceiling height... Which is why I'd like to minimize losing headspace in the studio and leverage the powers of our concrete slab ceiling! Ok but on a more serious note, I have no issue at all putting in place an interior ceiling, I just want to make sure it's absolutely worth it and we can make something that truly works with the ceiling already in place. As long as I can get 175cm height in the room after treatment is in place, I'll be fine. In this case, how much airspace should there be between external concrete ceiling and the internal ceiling we are to build?

Forget STC. It's not a valid method for measuring studio isolation. Here's why: STC was never meant to measure such things. Here's an excerpt from the actual ASTM test procedure (E413) that explains the use of STC.

Explained beautifully, Stuart. Thank you

Stuart, do you think my plan of action going forward makes sense?

1. Design HVAC system with priority on getting fresh air in and stale air out
2. Fill gaping hole in the wall
3. Start diving into the specifics of the inner assembly: wall thickness, material, airspace and distance away from exterior walls, insulation
4. Electrics shouldn't be a problem here, I've got good access in the studio.

Would love some more pointers!

Thank you all!

[Soundman2020]

I need to do some more thinking regarding this area then, because I cannot seal the hole in the wall knowing that it might actually come in handy for the duct work.

Right! so first figure out what your needs are in terms of how much air volume you need to move, and what the velocity of that air will be inside the ducts: that allows you to calculate the size of ducts that you will need, and the size of the of the silencer boxes.

The "silencer boxes" are the "thingies" (very technical term that! ) which you need to use to allow the air to go through the wall but block the sound.

Think of it this way: the duct is basically just a huge, enormous, gaping hole in your wall. If you just put in a typical flex duct, or thin sheet metal duct, the sound will go right through that hole and out the other side, practically attenuated. And vice-versa: sound outside will get in through that hole. In other words, the simple act of installing HVAC ducts totally trashes your isolation. The solution is "silencer boxes". Sometimes also called "baffle boxes". Each one is just a large wooden box with a few baffles inside, and lined on the inside with "duct liner". The air can flow around the baffles easily, but the sound cannot. Here's a few examples that forum members have built:

http://www.johnlsayers.com/phpBB2/viewt ... 0&start=45
http://www.johnlsayers.com/phpBB2/viewt ... 9&start=74
http://www.johnlsayers.com/phpBB2/viewt ... 42&start=5
http://www.johnlsayers.com/phpBB2/viewt ... 61&start=0
http://www.johnlsayers.com/phpBB2/viewt ... 5&start=98
http://www.johnlsayers.com/phpBB2/viewt ... &start=157
http://www.johnlsayers.com/phpBB2/viewt ... =2&t=13821
http://www.johnlsayers.com/phpBB2/viewt ... 8&start=44
http://www.johnlsayers.com/phpBB2/viewt ... 2&start=16

Not all of those are good designs, but you get the idea. You need one such box at ever pint where a duct goes through a wall "leaf".

Regarding this, I saw some posts where people have had luck using another room adjacent to the studio as a "fresh air chamber".

That's the "exchange chamber" concept, and you can do that if you want.... but the "other room" cannot be a habitable space: most building codes do not allow you to dump stale air from one habitable space into another. You can only do that if the "other room" will not be used by people (or pets).

Also, the "exchange chamber" does not negate the need for silencer boxes, ducts, or the mini-split itself. You still need all of those. It's only really useful if you have a very noise mini-split and don't want it in the studio with you. In which case, you bought the wrong mini-split! You can accomplish the same result by using a ducted mini-split located outside of your studio, instead of a non-ducted ("unducted" or "ductless") unit inside the room. Here's what the two different types look like:

HVAC--mini-split-ahu-and-typical-indoor-unit-ducted-and-unducted-non-ducted-compare-NOLBL.jpg

The one on the left is the typical non-ducted unit that you see in homes, shops and offices all over the place. The one on the right is a similar "ducted" model. It's basically the same thing as the one on the left, without the pretty plastic casing around it, and with duct flanges attached on each side. That's it. They both do the same job.

So, instead of having a ductless unit inside your room plus separate ducts for supplying the fresh air circulation, you can combine both systems into one by installing a ducted unit in one of your "extra" rooms. You simply run the supply and return ducts through the wall and hook them up to the ducted unit, which then circulates the air through the room while also treating it (cooling / heating / dehumidifying ). You then add a much smaller extension duct to dump a small percentage of the return air to the outside world, and another similar small duct to bring in fresh air from the outside world. Done!

In other words, the unit itself circulates the required "six room changes per hour" through the room, while also adding in some amount of fresh air to that, and dumping the same amount of stale air. Usually, you want to have about 20-40% of your recirculating air replaced by fresh air, to keep things happy and healthy. Figure roughly 30% initially, then refine that if need by.

And that's it! It's not a complicated solution, and it works very well. That's the way I do most studios these days.

I'll have to do some calculations to see how much air I'll actually need in order to get equipment that best fits the job, but I'm open to any pointers anybody has regarding this.

Calculate the total volume of air in your room (length times width times height). Multiply that by 6 (because you want six room changes per hour). That tells you how much air you need to move per hour. Must fans and HVAC systems specify the air flow rate in cubic feet (or cubic meters) per minute, not per hour, so you need to divide by 60 to get that. Some metric systems specify in "liters per minute" or "liter per hour", so you'd need to do the relevant conversion there. But the basic concept is that you need to replace the entire air volume of your room, six times per hour at least. Better is eight times per hour, or more, but at least six.

Yeah, I totally agree. It would definitely be a good idea to shell out some money on a proper mic for testing,

Don't get confused here! An acoustic measurement mic is one thing, but a sound level meter is another! You might need both.... The sound level meter is a calibrated device that should give you an accurate reading of how loud things are. The acoustic measurement mic is for testing the actual acoustic response of the room, using something like REW to do that.

I think I might not have fully explained myself! The garage is my own, 1-car garage that's sitting on top of the studio area. There will be absolutely no issue of noise from cars driving above as it will only ever be my car parked there

There are no other similar garages on either side of yours? Yours is the one and only parking spot in the building?

With this in mind, taking height limitations into account, and knowing there will be no noise from cars coming from the ceiling, does it still make sense to have the decoupled inner ceiling?

If you are certain that there won't be any structure-borne impact or flanking noise in that slab above you, then you might be OK. But if that slab extends beyond just your parking garage to other places where there might be noisy things happening, then it would be wise to isolate. However, if you have structure-borne noise in your ceiling, then it is also in your walls... You might need to isolate your walls too.

In this case, how much airspace should there be between external concrete ceiling and the internal ceiling we are to build?

This all a "juggling game", where there are many parameters to take into account, but basically you have to tune the resonant frequency of that ceiling to be at least one octave below the lowest tone that you need to isolate. That's what the MSM equation is all about: it teaches you how to juggle. The resonant frequency depends on basically two factors: the mass of each leaf, and the distance between them. If you have very high mass on both, then you can get away with less distance and still get the same result. Conversely, if you have plenty of space, then you can get way with less mass. In your case, you do have good mass on one leaf (the existing concrete slab), so you might be able to get away with less gap. The normal recommendation is a minimum gap of 4" (10cm). That's the distance across the cavity from the surface of the outer leaf mass to the surface of the inner leaf mass. The location of the supporting framing for your inner-leaf mass is irrelevant here: the joists could go inside the cavity (above the drywall), or they could go inside the room (below the drywall). If you need a thinner cavity, then you probably do need to get the joists out of it, as they take up a lot of space, so building your ceiling "inside out" would be the best option. If you use something that has a much higher density than drywall (eg, fiber-cement board), then you can save another few mm of height.

In other words, you need to do some math here, to figure this out. But count on a gap of at least 2" (5cm): I can't see it being possible go with less than that. And fill that cavity with suitable insulation, of course!

So, assuming 7cm of air gap, and 3cm of sheathing (drywall/fiber-cement/MDF/etc), you have 10cm for the actual isolation part. Then below that you need some type of framing to support it. The dimensions of that framing lumber depends on the total weight that you need to support (the isolation stuff, plus the framing itself, plus the insulation, plus any treatment that will be hung from the ceiling, plus lights, wiring, etc.), and the distance that they have to span. That is likely to be at least 2x6 joists, which measure 14cm deep. Thus, the total lost height is 14cm + 10 cm = 24 cm. If the distance to be spanned is short enough, and / or the weight is low enough, you MIGHT be able to get away with 2x4 joists spaced closer together (eg, 12" OC, instead of 16" OC), which would be great because those are only 9cm deep. So you would lose just 9cm + 10cm = 19cm in that case. I can't see it being possible to get less than that, though.

- Stuart -

[vdegou]

Right! so first figure out what your needs are in terms of how much air volume you need to move, and what the velocity of that air will be inside the ducts: that allows you to calculate the size of ducts that you will need, and the size of the of the silencer boxes.

That should be straight forward enough. So I decided to do the math taking into account the external walls of the studio and not the inner shell itself. The difference isn't that big anyways, but when talking about air I guess it's better to overestimate than underestimate. This puts us at 40.04m^3. Taking into account we want 6 room changes per hour, we're looking to move 240.24m^3 of air per hour.

Now, from what I've gathered, lower velocity air in the ducts should be quieter, correct? In fact this is why we can compensate the slower speeds with larger ducts because we can move the same amount of air at a lower velocity and thus less noise. Anyways, putting that as an aside, I still have to take a look at HVAC systems specs because I'm not exactly where the "speed" comes from in this system. Does the speed of the air depend on the ventilator unit placed outdoors? Do I have to put fans inside the vents? I'd appreciate some pointers here and if you know of any good brands of system, I'd be more than glad to hear it.

You need one such box at ever pint where a duct goes through a wall "leaf".

Got it. I have a feeling we'll be making a couple of these baffle boxes then. Not a problem!

...if you have a very noise mini-split and don't want it in the studio with you. In which case, you bought the wrong mini-split!

I'm hoping the specs regarding DB's on these units are easily provided by manufacturers! I think it's about time to go HVAC hunting.

Usually, you want to have about 20-40% of your recirculating air replaced by fresh air, to keep things happy and healthy. Figure roughly 30% initially, then refine that if need by.

Thank you for that. I love working with concrete numbers, makes everything much less of a guessing game! Given your explanation, I think I will take a look at ducted mini-split systems and see if I can find something that suits my room requirements.

Don't get confused here! An acoustic measurement mic is one thing, but a sound level meter is another! You might need both.... The sound level meter is a calibrated device that should give you an accurate reading of how loud things are. The acoustic measurement mic is for testing the actual acoustic response of the room, using something like REW to do that.

Aah got it. Didn't know that. I think for sure the acoustic measurement mic will come in handy. Even though we know it's a small room and we will have modal issues with lower frequencies, it will be best if we can have some accurate REW values to optimize the treatment.

There are no other similar garages on either side of yours? Yours is the one and only parking spot in the building?

Nope. The studio is in a house / townhouse kind of situation. My parking spot is situated in the only garage in my house, only fits my car, and will have virtually no movement while I am in the studio, not from myself or neighbors, so we are kind of lucky that this is the ceiling we have above the studio. The only inconvenience with the studio walls is that I share one wall (however, it is concrete) with my neighbor's basement. I think he has a gym in there, so I don't think he'll mind much

If you are certain that there won't be any structure-borne impact or flanking noise in that slab above you, then you might be OK. But if that slab extends beyond just your parking garage to other places where there might be noisy things happening, then it would be wise to isolate. However, if you have structure-borne noise in your ceiling, then it is also in your walls... You might need to isolate your walls too.

I am not exactly sure if the concrete slab itself which supports the roof of my studio (and the floor of my garage) extends to my neighbor's house. To me, it doesn't make much sense for it to be a shared concrete slab, although I have no idea how these houses are built. Technically, the houses are side by side and touching each other, but other than the shared wall mentioned in the paragraph above, we shouldn't have too much of a problem with them. The neighbors aren't too noisy, and if anything the slab will support their living room floor and wouldn't even be directly on top of my studio.

I don't have a problem at all isolating and decoupling the walls. In fact I was expecting to do so, more so to prevent noise in my studio from going to other places in my house and disturbing the people living here than anything else.

Regarding the ceiling. I read your explanation and I appreciate the time you have taken to go into detail. It definitely looks like height will be an issue. However, I have a question that will probably have people call me lazy/crazy. Here goes:

I get a slight feeling that doing all that work on the ceiling will be a lot of effort for slight reward. If we take a look at the measurements I have taken (I know, an iPhone app isn't very reliable but it's something!) We can see that from ~100dB in the studio while playing, directly above in the garage we observe around ~60dB. In my noob opinion, this isolation doesn't look that bad for having absolutely no treatment; it seems that the cement structure is pretty sturdy. Given this, does it make sense to leave the ceiling treatment as a last resort? So what I propose is, let's focus on the very weak points first, which there are plenty (hole in the wall and very thin doors) and then move on to making the decoupled walls. I'll do another sound test, and if everything is within acceptable levels, we can call it and maintain that precious ceiling space.

Now, I know this has risks. If it turns out that after that treatment our weakest point is the ceiling and the sound attenuation is not enough, I know I will have to backtrack, modify the walls and possibly other things, and put the ceiling in place. What I want to avoid is losing ~15-20cm of ceiling space when we might end up with another weak point that will make all that lost space and effort basically useless. If we can make that concrete ceiling the weakest point in our assembly, I think that is some really good news!

However, if this is a stupid idea as it may very well be, I will trash this and revisit the ceiling treatment. So, does this approach make any sense at all? Hope it's not asking for too much!

Thank you all for your help!

[Gregwor]

In my noob opinion, this isolation doesn't look that bad for having absolutely no treatment

Acoustic treatment has next to no affect on isolation. Treatment and isolation are two completely different things.

So what I propose is, let's focus on the very weak points first, which there are plenty (hole in the wall and very thin doors) and then move on to making the decoupled walls. I'll do another sound test, and if everything is within acceptable levels, we can call it and maintain that precious ceiling space.

Totally. You would have to build your inner leaf room after the outer leaf is completely sealed anyway. So yeah, complete your outer leaf and hopefully it is good enough isolation for your needs.

Greg

[vdegou]

Acoustic treatment has next to no affect on isolation. Treatment and isolation are two completely different things.

I am aware of this. That was poor wording on my part, what I meant was that the isolation provided by the concrete slab ceiling by itself, without any further work on seems to do a pretty good job (approx 40dB reduction... disclaimer, measurements taken with iPhone app).

Totally. You would have to build your inner leaf room after the outer leaf is completely sealed anyway. So yeah, complete your outer leaf and hopefully it is good enough isolation for your needs.

Sounds like a plan. Looks like I'll be doing the inner leaf without the decoupled ceiling then to save that space. That should be enough for my needs hopefully.

Going to post a follow-up question in a couple of minutes. Drawing up the diagrams in the meanwhile.

[vdegou]

Hello again!

Another question regarding the wall assembly, especially regarding the MAM model. Greg already mentioned something regarding this issue in the first couple of posts, but I'd like to dive a bit deeper.

The issue surrounds the existing wall used to hold wines that is present in the studio. I can't take this wall down. It is made of what seems to be some kind of red ceramic and full of holes (pictures in the first and second posts). I've taken more measurements. It measures 23.5cm deep and it's outer face is 7cm from the exterior concrete foundation wall. Diagram to clarify:

inner_leaf_parallel_wine_wall.png

So, going over the basics. 3 Leaf systems are bad. 2 Leaf systems are much better. So the question is *what* to do with that wine wall. Should we treat that as our inner leaf? It's surface density can't be too good given that it is full of holes, and unfortunately I don't see any possible way of getting the insulation into the 7cm cavity behind it. Maybe we can reinforce this wine wall by putting another wall directly on its inner face, thus achieving the 2 leaf system and covering up the holes. However this still leaves us without a way of putting the insulation in the 7cm cavity.

Another way would be to go for the 3 leaf system. Put up an inner leaf parallel to the wine wall, enough airspace between the two to fill with insulation, and have that there, but of course this will probably not be as good as a well-designed 2 leaf system.

In this case, what's better, the 2 leaf system with no insulation? Or a 3 leaf system with proper insulation? Is there any other option I may be missing?

Thanks everyone for the help!

[vdegou]

Update for those following this thread: just found a good deal on moisture resistant MDF. It's a 3cm thick board, with a density of about 730kg/m^3 which translates to roughly 21.9kg/m^2. This is based off values found on the internet for moisture resistant MDF; I'm still waiting on the supplier for the datasheet to get the actual numbers.

Pros of going moisture resistant MDF:
1. Well, it's moisture resistant and I'm in a basement surrounded by water pipes. Could prove useful.
2. It's very sturdy material at 3cm thickness. Walls will not be as easy to break and I can hang acoustic treatment on it without necessarily having to find a joist for support.
3. Since it's already 3cm thick, I will not have to stack sheets of drywall to achieve the same thickness

Cons:
1. More expensive than gypsum board
2. Could possibly be a bit more difficult to install than gypsum board

The price I'm getting on the MDF is 55 Euros per 244cmx122cmx3cm board, which comes to about 18 Euros per m^2. Having around 36 m^2 of walls to put up, the price of the inner layer comes out to be around 650 Euros. That's not too shabby at all!!

This seems like a great deal for the density and benefits I am getting over the drywall, even taking into account drywall might come out to around 300-500 for the room. If we put price aside, are there any blatant reasons why I should not put up the inner studio shell with this type of material?

Thanks!

[Soundman2020]

That sounds like a pretty good deal!

If we put price aside, are there any blatant reasons why I should not put up the inner studio shell with this type of material?

Nope! No problem. It's high density, thick, strong, has a good nailing surface, reasonably priced, etc.

Depending on what your isolation needs are, you could probably get by with just that as the base layer on your framing, then a single layer of 16mm drywall on top. Likely, that will be enough.

By the way, I did answer your PM: Not sure if you saw that?


- Stuart -

[vdegou]

That sounds like a pretty good deal!

Yeah! I'm actually quite surprised. Based on my window (or wood) shopping I've done these days, typical price seems to be around 80Eur for that material in that thickness.

Depending on what your isolation needs are, you could probably get by with just that as the base layer on your framing, then a single layer of 16mm drywall on top. Likely, that will be enough.

That's also very good news. I'm hoping that even without any drywall on top we could get good results, and just put the MDF up over some framing. Depending on how I go about it, the MDF might be thick enough to stand without needing studs. Guess I'll have to give it a go and see!

Also, today I had an HVAC tech come take a look at the space and see what he recommends. I don't think he's worked with airtight rooms before, as he looked kind of confused with the whole idea and he kept mentioning what sounded to me like a lot of unnecessary equipment to get a proper result. Either that or probably I wasn't making myself clear haha.

For those following this thread: the plan is to start putting up the walls in early August. Will keep you all posted!

[Waka]

That sounds like a pretty good deal!

Yeah! I'm actually quite surprised. Based on my window (or wood) shopping I've done these days, typical price seems to be around 80Eur for that material in that thickness.

Depending on what your isolation needs are, you could probably get by with just that as the base layer on your framing, then a single layer of 16mm drywall on top. Likely, that will be enough.

That's also very good news. I'm hoping that even without any drywall on top we could get good results, and just put the MDF up over some framing. Depending on how I go about it, the MDF might be thick enough to stand without needing studs. Guess I'll have to give it a go and see!

Also, today I had an HVAC tech come take a look at the space and see what he recommends. I don't think he's worked with airtight rooms before, as he looked kind of confused with the whole idea and he kept mentioning what sounded to me like a lot of unnecessary equipment to get a proper result. Either that or probably I wasn't making myself clear haha.

For those following this thread: the plan is to start putting up the walls in early August. Will keep you all posted!

Hi there!

Just a quick note. Mdf is not structural board. So you can't support a ceiling or door frame etc on it. You will still need your timber framing . You will notice that Mdf is very easy to bend compared to structural board like OSB and plywood. Also mdf becomes like cardboard when wet.

It will be a good material for beefing up your walls though!

Dan

[vdegou]

Just a quick note. Mdf is not structural board. So you can't support a ceiling or door frame etc on it. You will still need your timber framing . You will notice that Mdf is very easy to bend compared to structural board like OSB and plywood. Also mdf becomes like cardboard when wet.

Hey! Thanks for the input

Yeah, in the end the timber framing will be necessary. I'm actually designing for it right now taking into account the dimensions of studs that I can find in my local hardware store.

I'm not sure how easily this MDF will bend though, noting that it's quite thick at 3cm and won't stand too tall (about 190cm tall). But yes! For sure these will have to be supported on the studs.

I'll put up some Sketchup models of the framing design soon once I've completed it. Thanks for checking in!

[lolomopa]

but I've got some studio monitors that I can borrow. Probably not ideal, but it's something for a first iteration

If they can put out somewhere around 115 dBC, and they have reasonably good bass extension (to about 35 Hz or so), then that should work fine.

PS: Also picked up Rod Gervais' Studio Construction book. Gotta get educated too if we're going to do this right!

Also get "Master Handbook of Acoustics" by F. Alton Everest. Very useful.

- Stuart -

What is your ceiling made of? Concrete? If it is sheet rock, I'd suggest removing the sheet rock so that your ceiling is taller (acoustically). You'd then just have to add mass to the underside of the subfloor. If it's concrete, that sucks in terms of acoustic height, but it's good for surface density!

[PROBABLE SPAMMER ALERT - TYPICAL BEHAVIOUR.... - MODERATOR]

[vdegou]

Just a quick note. Mdf is not structural board. So you can't support a ceiling or door frame etc on it. You will still need your timber framing . You will notice that Mdf is very easy to bend compared to structural board like OSB and plywood. Also mdf becomes like cardboard when wet.

You're right! I found that out after trying to find a way to support the MDF without any additional supports, which was a very silly idea. So I have framing in my mind now and the design is almost in place.

I apologize for the disappearance, but I am back! The MDF has finally arrived, and now I must wait for the framing material as well as make up my mind on what product to go for with regards to sheathing.

This is where my next question stems. Regarding the material to sheath the walls, the most widely available one in my country is rockwool, however I can't seem to find a consensus on what's better: higher density or higher GFR. Apparently there is a slight correlation between density and GFR, although not strictly linear, and a high GFR is desirable. But even then, I've read some posts stating that it's best to stick with 50kg/m3 for rockwool (or along those lines) even though there is rockwool with higher densities and higher GFR. That part is a bit confusing.

So, my question is, should I strictly go for the highest GFR rockwool? Will this help to absorb both low and high frequencies?

I've compiled some of the materials that are available to me in a table to easily compare their densities, GFR, and total price, but as I'm not 100% sure whether highest GFR should be the goal, I'm a bit stuck. Hopefully someone can chime in here!

Screen Shot 2019-07-30 at 16.49.43.png

If I were to choose based only on GFR, I would go for the Alpharock 225 product with a density of 70kg/m^3 and a GFR of >20. I've also read it is good to vary the densities of the sheathing as it might better absorb a different range of frequencies. I've got two leaves to put sheathing on top of here, so it could be possible to do this. Is it a good idea though?

As always, I appreciate any help!