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PostPosted: Sat Aug 25, 2018 5:43 am 
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Location: Paris, France
Hello everyone,

I'm a thirty year old from Paris, France, part-time musician, part-time sound engineer with a very serious hobby in electronics (at least the audio stuff) planning on getting able to finally get rid of my part time day job :D

I'm moving my home studio (which wasn't in my actual home but that's what it felt like :wink: ) and I'm taking the opportunity to upgrade to a more professional setup. Maybe this should go into the Studio design forum since the room is already existing and I'm not planning on making a lot of construction work but my first questions (which are quite specific to the room btw) seem to belong here...

Anyways, the room is just under 15m2, dimensions are roughly 4.3 x 3.4 x 2.3 meters (the walls are not exactly straight so you'll have to check out the drawing I made for exact dimensions). It's small but actually, for Parisian standards, it's not bad, real estate is so darn expensive here. The ratios seems pretty nice, according to Mr Bolt at least.

My primary use would be mixing - analog (tape and all) and digital - but I will also be doing recording and some rehearsals. If I can manage to get enough isolation for drums it would be great but it's not the biggest deal if I can't acheive that.

Neighborhood is quiet (for a big city that is). Sorry no measurements yet, I lent my SPL meter to a friend who's currently away from town, hoping to get it back next week. But I reckon that keeping noise out shouldn't be too much of a problem. It's still noisy enough that I can get away without total isolation (when it comes to sound coming out).

Directly above the studio is the courtyard for the building. The building is on one side only of the courtyard. On the other sides we have walls between 2m and 3m high (depending on the wall) and then a very big open space. Many courtyards in Paris are small enclosed spaces that go all the way to the rooftops. Here the sound won't reflect too much before going out in the open. I'm pretty fortunate :)

The ground floor of the building is occupied by a stuctural engineering company. They're the ones letting me use their basement, are fully aware of what it entails and shouldn't be bothered by some noise. They don't make too much noise either. The rest of the building are residential flats with double glazed windows and I definitely don't want to bother them (especially the owner of the building who lives on the third floor (that would be the fourth floor if you consider the ground floor to be the first).

I think it's time for a few pictures. Will write a second post later tonight, maybe tomorrow, with more details (about the existing walls and ceilings, my budget, compromises I'm ready to make and others that I want to avoid) and actual questions :yahoo: but right now it's dinner time :D


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PostPosted: Sat Aug 25, 2018 10:45 am 
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Hi there, Arthur, and Welcome to the forum! :)

This looks interesting! I'll check back later to see if the rest of the comments and the questions are up.

- Stuart -

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PostPosted: Tue Aug 28, 2018 12:15 am 
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Location: Paris, France
Hello Stuart, I'd like to take the opportunity to thank you (and the others) for contributing so much to this forum, I have learnt a lot so far and looking forward to learning a lot more :)

I realize that a full floor plan for the basement and the ground floor would probably be very useful (my comments for the pictures must have been a little confusing) and so I've attached the one I currently have to this post. However the dimensions are completely off (when it comes to the basement, it's not too bad concerning the ground floor). I will get around to doing a proper one at some point, but in the meanwhile it should clear some things up.

--

Back to the point, the walls of the studio are composed as such :

Ceiling: 36cm thick (give or take 1 cm, it's hard to measure pretty reliably) including the courtyard tiles (1cm), so that gives us 35cm of poured concrete (most likely with those metal rods inside, how do you call that ?).
I found the following (apparently approximate) formula to calculate transmission loss in a single leaf wall: TL = 20 * log10 (ms * f) - 48, where ms is the mass per unit area and f is the frequency. Graph is attached to this post but I calculated 47dB attenuation at 63Hz.

Back wall: 70cm thick. I'm guessing it's a massive block of poured concrete (building foundations) but maybe concrete blocks or bricks. The actual building wall doesn't start right above it but about halfway in (speaking from inside the studio perspective). That's probably not very clear... to put it another way: the first half on the wall is underneath the courtyard, the second half underneath the actual building structure. I don't know if this fact could actually help when it comes to sound transmission through wall up to the building but I'm guessing it can't hurt.

Right wall: 11cm thick, hollow concrete blocks, supposedly 10cm with mortar finish. The section right above the door is 7cm thick, made of hollow bricks with the same mortar finish. The glass areas are 4mm thick, mounted on metal frame with joints that look like plaster but I think it's not exactly that. The door is full wood and glass. Glass is probably 4mm, wood 45mm excluding a section underneath the glass that's more like 20mm.

Left and front wall: The two other walls would also be concrete, maybe brick, no clue as to what's on the other side. Well there's only two possibilities, the basement of adjoining buildings (likely for the left wall, as well as for the wall that's after the corridor with the stairs right outside the studio) or earth, which I'm quite sure is the case for the front wall as there's a big house on that side with a large garden around it. If they are basements on the other side, they would be used as storage units for the residential housings.

Floor: Underneath the studio is solid ground. As you probably have guessed from the pictures, the floor is made up of ceramic tiles.


So when it comes to isolation, I reckon that the biggest issues (aside, obviously from the various openings inside the room) are the right wall, and the ceiling, since the latter is the only thing standing between the studio and the neighbors (aside from a little distance and their double glazed PVC windows.)

Although I might be wrong in thinking so, the back wall and the left wall wouldn't need extra isolation.

I'm not too sure what to make of the backwall. Airborne sound through the wall shouldn't really be a problem but I'm slightly worried about structure-borne noise. Since the floor is on solid ground and the wall really massive I'm guessing that vibrations from the floor won't really transmit upwards. (At least up to the first floor, as I said in my first post isolation requirements to the ground floor are not that high). But still, could it be an issue to be taken seriously? Or could airborne sound in the studio hitting that wall transmit itself through the structure right up to the first floor and above? What about flanking effects out into the courtyard?

I have to admit that I really don't know how much I should worry about structure-borne noise in my situation.

--

I definitely don't have a huge budget but it's flexible. If I can stay under 3000€ it would be great but I could go up to 5000€. I could find a some extra cash but it would have to really be worth it. It all really depends how much I gain versus cost - I'm not going to spend an extra 1000€ to increase isolation by 3dB :) Said budget is for isolation and also sound treatment (at least enough sound treatment to get a usable studio, I suppose can always spend more as time goes by to improve the sound inside the studio, plus I already got some treatment from my old studio.

I hopefully will have to spend peanuts when it comes to electrics, there is plenty of sockets in the room on a total of 4 different circuits, including 2 which are spread out throughout the whole studio. I have a separate budget for gear in which I will include expenditures for cabling and patching throughout the studio. Oh, and ventilation is under works, I already got the fans and the ducts, will just need to build silencer boxes to put inside the studio.

So basically it's all to be spent in isolation and treatment. (And maybe lighting, but I can keep spending for that to a bare minimum for starters).

I'm planning on doing as much as I can myself, I have a decent amount of tools and I have friends willing to help, including an architect, structural engineers and one who has done a lot of construction work in the past. That does not mean I will not feel obliged to pay them as best as I can if they put in a big amount of work but it does mean that most of my expenses should probably be in actual construction materials.

--

Now, I really want to keep as much space as possible. I'm a big fan of live tracking so I really want to be able to have enough space to record more than one person at a time while keeping things spacious enough. That would be with 2-4 people recording, obviously, things are going to get cramped in there if I get a full cumbia band :). Basically I would love to have 9m2 of free space inside the room. I pretty sure I can keep front wall treatment and console desk to 3.5m2. So that would leave around 2m2 for isolation and the rest of the treatment which I fully realize is far from ideal and probably not enough.

Of course, compromises can and will probably have to be made but I really want to avoid doubling up all the walls with 300mm wool and adding 1m of bass trapping on the back wall. I do realize that I will probably need quite a lot of treatment for bass due to the thick walls. I'll certainly have to find the right balance between the space I want to keep and the amount of treatment I want to put up.

Other than that, I really want to keep the opening in the ceiling that lets the daylight in (I even get quite a bit of sunshine in the afternoon :) ) as well as keeping a glass bay between the corridor and the studio since the corridor will be the engineer's place for tracking.

--

So anyways, what I will be definitely be doing in terms of construction work is doubling up the right wall since that is most likely the weakest spot in terms of sound spillage (again, setting aside the various openings, which I'll have to take care of too). I'm planning on keeping the existing door (adding mass to it of course) and add another heavy door in front of it (there should be just enough space between the existing and the staircase for it to fit). I will also add a door between the corridor right outside the studio (labelled 11 on the map) and the workshop (labelled 17) and could maybe add a third door on the other side of the workshop.

I will in all likelihood double up the ceiling too, if only to avoid impact noises in the courtyard ruining takes. However since it is already quite low and since there is anyways only 10cm between the top of the door and the ceiling, I'll have to keep that pretty thin (and will probably implement something along the lines of John Sayers' "inside out" ceiling arrangement).

I'm having trouble figuring out if I can achieve enough isolation for drums. Although, like I said in my first post, drums are not an absolute requirement, what I'm willing to spend actually depends on this. Tracking drums (and loud guitars and bass) would bring me more business and if it's not possible I would really like to keep spending to a minimum. So I'd rather not go through this blindly, get as much isolation as my budget and space constraints allow to then find out that high levels still spill to an unacceptable level.

Like I mentioned, the goal is not to have complete silence right on the other side of the studio walls but to avoid bothering the neighbors living in the building which are two floors up - are more exactly, 35cm of concrete, 3 meters of air (for the closest ones) and a double-glazed window away (which, the weather being what it is in Paris - cold and damp - would be closed most of the time).

So I'd like to evaluate how much isolation I'd need for drums (let's say 115dB SPL). I'm supposing that there's only three significant ways the sound could travel up to the neighbors.
a) Either directly through the ceiling, into the courtyard and through their windows 3m up.
b) Through the right wall, into the corridor (11) and then either up the stairs into the shed and then out into the courtyard or through the two ventilation conduits in the corridor and go up in the courtyard.
c) Up through the building, that is either through the right wall or the back wall, into the workshop and then up.

So, from here, I suppose I need to make the following measurements.
- Sound spillage from the workshop (17) to the ground floor
- Sound spillage from the corridor (11) to the courtyard. (With the conduits isolated as best as I can, since right now, one of them is a straight path from the corridor to the courtyard, and the other one is a PVC tube going from the storage room (14), through the corridor and then through the courtyard.)
- Noise levels in the courtyard.

For the ceiling, I don't think I could currently make any meaningful measurements. Well there is one, how much sound leaks out of the opening for daylight in the ceiling. From there I could figure how much isolation I would need from the glass I install there to get approximately as much isolation as I would get from the rest of the ceiling (the original cement pour and whatever I add underneath it).
I need to figure out how much isolation could I achieve with something 25mm gypsum board and a thin gap, maybe 4cm, filled with fiber wool insulation... I tried to looking for data concerning similar structural arrangements to this but didn't manage to find anything meaningful. Does anyone have a clue as too how much increase in isolation I could gain ?

I also tried looking for data concerning double glazed windows (something along the likes of 4mm glass / 6mm air / 4mm glass) which is the standard thing you'd find here. I only found STC curves, indicating a worst case of 20dB insulation but I'd love to get a figure around 60Hz.

--

Anyways, I'd love to get general feedback about the whole thing. I think I gave about as much details as I can currently but if there's something important missing let me know. I suppose I can always dig a little deeper for certain things or ask more knowledgeable people about the building's structure. I can also post more pictures or try to explain better things that are not clear.

And, to sum up, my specific questions at this stage are:
1 - Should I worry about flanking issues and structure borne transmissions from the walls? - By the way, the actual floor of the building is made up of bricks on a metal frame (on the basement side) and tiles on the ground floor. No idea what's in between, maybe some sort of concrete, maybe some sort of gap with a timber frame... I'll try to ask knowledgeable people what building practices where for buildings of that era but we won't get anything better than an educated guess.
2 - Does anyone have better isolation data for double glazed windows than STC curves?
3 - How much increase in isolation could I gain by doubling up the 35cm concrete ceiling with something like 25mm gypsum boards and a few centimeters of fiber glass wool?


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PostPosted: Fri Nov 16, 2018 3:14 am 
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Quote:
I found the following (apparently approximate) formula to calculate transmission loss in a single leaf wall: TL = 20 * log10 (ms * f) - 48, where ms is the mass per unit area and f is the frequency. Graph is attached to this post but I calculated 47dB attenuation at 63Hz.

That's called the "mass law" equation, and is used for calculating the average isolation of the one-third octave band centered on the frequency given by "f". It is not used to calculated the isolation at a specific frequency. So you won't be getting "47 dB at 63 Hz." but rather "approximately 47 dB across the entire one-third octave band centered on 63 Hz, which extends from 44.7 Hz to 89.1 Hz".

There's a simplified version of the Mass Law equation that estimates the isolation across the entire spectrum:

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

Where: M = Surface Mass in kg/m2

According to that, you would be getting about 55 dB from that 35cm concrete slab.... assuming that that there are no windows, doors, holes, cracks, skylights, or walls that have lower isolation.


Quote:
Right wall: 11cm thick, hollow concrete blocks, supposedly 10cm with mortar finish. The section right above the door is 7cm thick, made of hollow bricks with the same mortar finish. The glass areas are 4mm thick, mounted on metal frame with joints that look like plaster but I think it's not exactly that. The door is full wood and glass. Glass is probably 4mm, wood 45mm excluding a section underneath the glass that's more like 20mm.
The weak spot there is obviously the glass, then the door itself, then the section above the door. The isolation of the room is only as good as the isolation at the weakest point, so basically all that concrete in the ceiling above doesn't really matter, until you take care of improving the isolation of the door, glass, and header. Mass law says that 4mm glass will give you about 37 dB, but for the 63 Hz band it would only be about 8 dB. So that's how much total isolation you'd be getting for your room: about 8 dB for the 63Hz band.

Quote:
So when it comes to isolation, I reckon that the biggest issues (aside, obviously from the various openings inside the room) are the right wall, and the ceiling, since the latter is the only thing standing between the studio and the neighbors (aside from a little distance and their double glazed PVC windows.)
Not really: Once again, the total isolation of the room is only as good as the weakest isolation. Once the sound gets out through the weakest part, it is free to expand outwards from that point, especially low frequency sounds, which are not very directional.

So your plan should be to work on those areas that are the weakest, and bring them up to the same isolation level as the rest of the room.

Quote:
I'm not too sure what to make of the backwall. Airborne sound through the wall shouldn't really be a problem
Why? Sound that gets through that wall has left your studio, and is now in the "outside world". ...

Quote:
Since the floor is on solid ground and the wall really massive I'm guessing that vibrations from the floor won't really transmit upwards.
It's never a good idea to guess with acoustics! Structure-borne impact noise will be audible throughout the entire structure. If you expect to be transmitting vibration or impact noise into the slab, then you should design something to prevent that: a simple drum riser would work.

Quote:
Or could airborne sound in the studio hitting that wall transmit itself through the structure right up to the first floor and above?
Yes. That wall is a flanking path from your studio to the outside world.

Quote:
I have to admit that I really don't know how much I should worry about structure-borne noise in my situation.
It can be a major problem, going in both directions. If you plan to play drums in your room, then you have a potential impact noise issue. Ditto if you plan to have a loud bass cab sitting on the floor, or anything else that directly touches the slab. Likewise, if you have noise sources outside the room but in contact with the building structure, such as pumps, fans, doors slamming, people walking on floors, water in pipes, washing machine, dryer, etc, then you have a potential problem.

Quote:
Basically I would love to have 9m2 of free space inside the room. I pretty sure I can keep front wall treatment and console desk to 3.5m2. So that would leave around 2m2 for isolation and the rest of the treatment which I fully realize is far from ideal and probably not enough.
It would ba a mistake to plan your acoustic treatment in terms of square meters of floor area. Rather, design the actually devices that you will need to attain ITU BS.1116-3 or EBU Tech.3276 specifications. Start with the simple, bulky options, and see how that works out. If you see that those will use up too much space, then you'll need to substitute for the more expensive, more complicated types that take up less space.

That said, a small room like that is going to need a LOT of treatment, especially for bass trapping.

You don't have many options for the location of your desk: your room is only 4.3 m long, so the mix position will have to be n the room center-line and about 160 cm from the front wall. That's it. Your speakers will have to go up tight against the front wall, with a 10cm gap for inserting a panel of OC-703. The speakers will be set up about 95cm from the side walls (putting them 150 cm apart, at a height of about 124 cm, roughly. They will be aimed at a spot about 40 cm behind the mix position, so roughly 200cm from the front wall, on the room center-line.

Quote:
I really want to avoid doubling up all the walls with 300mm wool
You would not need that much insulation. Typically, it would be about 100mm, and since that fits in the stud bays, you don't lose more than that plus the thickness of the sheathing, for the total wall thickness. Maybe 130mm or so, total.

Quote:
really want to avoid ... adding 1m of bass trapping on the back wall.
Most of the rooms I design have about 50cm or so of bass trapping across most of the rear wall, with a bit more in the corners.

Quote:
. I do realize that I will probably need quite a lot of treatment for bass due to the thick walls.
Not due to the thick walls, no. They are irrelevant here. The reason you need a lot of treatment is due to the size of the room. That's the main factor here: it is a very, very small room, so it will need a LOT of treatment. It's the SIZE of the room that mostly determines how much treatment it needs.

Quote:
I'll certainly have to find the right balance between the space I want to keep and the amount of treatment I want to put up.
Most people do things the other way around: they first determine what treatment will be NEEDED to get the room to produce the acoustic response they want, then try out different treatment options to see which ones are the best match for them, in terms of the space they take up, and their budget. Cheap treatment takes up lots of space. More complex treatment that takes up less space is more expensive. But there are limits: Even the most expensive, lowest profile bass traps still take up considerable space, especially in small rooms.

Quote:
I really want to keep the opening in the ceiling that lets the daylight in ... as well as keeping a glass bay between the corridor and the studio
So you really don't want good isolation for your studio? :)

Quote:
So anyways, what I will be definitely be doing in terms of construction work is doubling up the right wall since that is most likely the weakest spot in terms of sound spillage
That would be a waste of money. Seriously. As I said several times above, the isolation of your room is only as good as the weakest part. You already have the mass law equations, so now you need to sit down with pencil and paper, to calculate the isolation for each part of each wall, ceiling, window, door, etc. Find the lowest number: that's where you need to start, to improve your isolation. Work on the WEAKEST elements, as shown by the math, not by guessing. Once you have all the weak parts taken care of, then you can do the math all over again, and see if the new lowest number is higher than the amount of isolation that you need. If not, then keep on going!

Just building a wall on one side will NOT solve your isolation problems. If you don't isolate ALL sides of the room (including ceiling, walls, doors, windows, HVAC, electrical system, and possibly also the floor, under some conditions), then you won't have any isolation at all!

Think of this: Imagine there's a guy who wants to have an aquarium in his living room, because he likes to look at fish, so he goes to the store and buys a metal frame to make his aquarium. But then he thinks: "I only need to see them from the front, so I'll just buy one sheet of glass to put on that side, and leave the rest open". How well do you think that aquarium will hold water? :) Obviously, it won't hold water at all! But that is what you would be doing if you only isolate one wall...

In other words, if you do need to isolate your room from anything, then you need to isolate it from everything. You cannot isolate a room in only one direction, just like you cannot build an aquarium with glass on only one side. As soon as you put water in it, the water will simply gush out and splash all over, in ALL directions, even the direction where the glass is, since the water will go over, under, and around that glass. If you only isolate one side of your studio, then when you "pour" sound into it, the sound will gush out and splash all over, in all directions, including the direction where that one isolation wall was, because the sound will go under, over, and around that wall, as if it wasn't even there.

Therefore, if you do need isolation, then you need to build the same amount of isolation in all directions around your room, and in all aspects: every wall, ceiling, door, window, electrical conduit, HVAC duct, and everything else, must all be isolated to the same level. Acoustic isolation is only as good as the weakest point, so if you isolate your studio fantastically all around except for the window, then you might as well not isolate anything, because sound will take the "easy" path out through that window...

Quote:
I will in all likelihood double up the ceiling too,
See above: same reasoning. A waste of money if done on its own, without also doing the walls, windows, doors, HVAC and electrical.

Quote:
I'll have to keep that pretty thin (and will probably implement something along the lines of John Sayers' "inside out" ceiling arrangement).
When we build inside-out ceilings as part of the isolation system for a studio, that inside-out ceiling MUST rest on the new inner-leaf walls (which might also be inside out, to save space....). An inside-out ceiling that is attached to the outer-leaf walls, does not provide much isolation at all, due to flanking....


Quote:
I'm having trouble figuring out if I can achieve enough isolation for drums.
Drums played normally produce around 110 dBC to 115 dBC, and played hard can be twice as loud. Let's assume that you will only every play them normally, at 115 dBC. Your weakest weak point at present is the thin glass, apparently, which will get you around 30 dB of isolation (realistically, in real life): So your drums inside at 115 dBC will be producing about 85 dBC outside. To make that inaudible, you would need to get it down to about 35 dBC, so you would need another 50 dB of isolation, in addition to what you get from the glass.

If you decide that you will only mix in there, never track, then the "rule of thumb" is that most engineers mix at around 80-85 dBC, and occasionally turn it up to around 100 or 110 to "check the bass". So at normal levels of 85, your glass would be getting that down to about 55 dBC outside, and you'd need another 20 dB isolation to get that inaudible.

Quote:
the goal is not to have complete silence right on the other side of the studio walls but to avoid bothering the neighbors living in the building which are two floors up
So one of your priorities MUST be to prevent sound from getting into the building structure.

Quote:
two floors up - are more exactly, 35cm of concrete, 3 meters of air (for the closest ones) and a double-glazed window away
No. You said that you have a skylight in the ceiling that you want to keep, so that is the only thing separating you from the neighbors. Double-glazing is not much use for isolation low frequencies, such as drums, bass, keyboards, and electric guitar.

Quote:
I'm supposing that there's only three significant ways the sound could travel up to the neighbors.
... And also the "I really want to keep the opening in the ceiling that lets the daylight in ... "... :)

Quote:
So, from here, I suppose I need to make the following measurements.
What you need to do, is to get a decent quality sound level meter, then set up a full-range speaker in the room, and play bass-heavy contemporary music through it at 115 dBC, measured in the room about a meter away from the speaker. Now take your meter and go measure at many, many locations outside the studio, both inside the building and outside the building, including inside your neighbor's homes. Then turn off the sound system, and measure the ambient noise levels at the exact same locations. With that information, you can calculate how much isolation you have at present, and how much extra you need.

Don't guess! Do the actual measurements, with your meter set to "C" and "Slow", and make notes. Then do the math.

Quote:
For the ceiling, I don't think I could currently make any meaningful measurements.
I don't understand why not! In what way would the procedure that I just outlined, fail to take into account the ceiling? You cannot judge your total isolation by thinking about individual parts of the room: the room is a SYSTEM, not a bunch of separate paths. The entire room (including the ceiling) currently produces a certain level of isolation, which will be measured by the procedure above. That's what matters: the TOTAL isolation you are getting at present, as compared to how much isolation you NEED to get. Trying to measure the isolation of each part of the room by itself is pointless at this stage: All that matters is the TOTAL isolation. Once you have measured that, then you can try to figure out where your weak points are, and beef them up, then repeat the same procedure , to see if you have enough isolation yet.

Quote:
I need to figure out how much isolation could I achieve with something 25mm gypsum board and a thin gap, maybe 4cm, filled with fiber wool insulation... I tried to looking for data concerning similar structural arrangements to this but didn't manage to find anything meaningful.
You could not find anything meaningful to answer that question, because you are not asking the right question! :)

25mm of gypsum board with a thin gap of 4cm filled with insulation, up against a concrete wall, will give you an MSM resonant frequency of around 55 Hz, and therefore it would not isolate at all below 78 Hz. It would only isolate somewhat starting at around 112 Hz, and would isolate well starting at about 162 Hz. Total isolation at resonance would be around 10 dB, rising to 42 dB at 250 Hz, for a overall total isolation of around 60 dB.

Quote:
I also tried looking for data concerning double glazed windows (something along the likes of 4mm glass / 6mm air / 4mm glass) which is the standard thing you'd find here.
Based on standard MSM equations, that would give you an resonance frequency of around 340 Hz, very poor isolation below about 480, and decent isolation above about 690Hz. Total isolation around 36 dB, but really lousy in the low end (only 24 dB at 500 Hz) so STC-20 would be about right. Double-glazed units are not good for low frequencies: only useful for mids and highs. There's also the major issue of coincidence dip to consider, around 4k for typical glass.


Quote:
1 - Should I worry about flanking issues and structure borne transmissions from the walls?
Yes.

Quote:
2 - Does anyone have better isolation data for double glazed windows than STC curves?
See above. Also, these might be useful:

Attachment:
glass-isolation-for-typical-double-glazing.jpg


Attachment:
glass-isolation-for-typical-double-and-triple-glazing.jpg


As you can clearly see, isolation from double-glazed units is very lousy in the lows and low-mids No use at all for studios. You only get reasonable isolation above about 1 KHz, but then coincidence kills that again at around 4 kHz.

Quote:
3 - How much increase in isolation could I gain by doubling up the 35cm concrete ceiling with something like 25mm gypsum boards and a few centimeters of fiber glass wool?
As above: about 60 dB, which is getting close to your flanking limit.

Quote:
To make up for the fact that it doesn't give as much isolation in the low frequencies as I was hoping, I compared it with our hearing threshold per frequency
I don't understand why you used the threshold of hearing. That makes no sense. You should have used the curve that describes the EXPECTED level at the receiver, probably the 50 phon curve in your case, or maybe the 60 phon. You seem to be misunderstanding what those graphs are showing you...


- Stuart -


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