New rehearsal room/studio Transylvania

[Soundman2020]

Reading one of Your threads where You are talking about the distance between the leafs, You say that 8" gap between two walls made of double drywall would take care of all instruments including bass guitar and drums, and also 12" gap would be OK for space ships and canon rumble.

Right, provided that you also have a decent amount of mass on each leaf. Total isolation is a combination of both mass and air cavity depth. So assuming you have at least a couple of layers of 16mm drywall on each leaf, then yes, a 12" gap would be good.

- Stuart -

[dimarzio999]

Thank You for the prompt answer. 12" it is, and I have a massive brick wall, and 2 layers of heavy acoustic gypsum board (13 kg/m2). Gap filled with the best absorbing wool I could find. It is a challenge to do the metal profile-structure, I guess Eiffel would hang himself if He should do this. I probably would need an engineer from ancient Rome, who designed those underground water tanks with hundreds of columns of which none is identical in height. But I have 3 walls done, on left and the ceiling.

Those foams of 23 kg/m3 which is found on our market seems to be done in some garage by some creeps. I've ordered some from a company, and paid for them 6 weeks ago, and still nothing. They do not have the specs for anything they sell, so they are of questionable quality at least. An also despicable service.
Here is the link:
http://www.materiale-izolatie-fonica.ro ... it-d20.htm

they say that this stuff absorbs in the 32-225 Hz range with an alpha coefficient of 0,85 on all the range.

http://www.materiale-izolatie-fonica.ro ... mm-d18.htm

here it says that this stuff absorbs all frequencies and diffuses also. the perfect fit . Well, I seriously doubt it.

Today's question: I am trying to understand the theory behind gluing the two gypsum board layers with green glue. We don't have green glue here, but we have tapegum which is a hydro-insulation material which never gets rigid, and is designed for gypsum boards gap treatment. So my understanding so far is as follows:
1. forbidden to use gypsum for the gaps between the panels, because the whole structure gets too rigid, which is bad for both insulation and acoustics - so here I definitely will use elastic tapegum
2. one suppose to put green glue between the sheets of gypsum board (here is the part I don't understand), because you need then not to be glued, but elastic. this means the following: a. you need a shitload of green glue b. instead of gluing together the boards, you keep them apart, and this is good for insulation (I imagine this is a sort of panel absorber analogy). But this does not mean that in fact you are creating a multi-leaf system, with its own internal frequency, which is actually bad? (because you add a layer and instead of 2 leaf you will have 3 or 4 considering the glue layer). Also if I understood correctly, if one screws the layers together, all the dumping is inactivated (theoretically by one screw - and in this case there will be more that 36 screws per panel?

So, is there any use to put green glue between the layers? Or I should caulk only the perimeter of each panel with it?

Thank You, I really appreciate You precious help.
I will add some photos later today. Here they are. You can see the gap between the windows, the airlock, the inner wool's first layer, the gypsum board arrived (4,1 tons that stack). and the metal framing as I started to build it.
Before I added the wool and the second windows and door, I measured the the attenuation using REW. Looks like the brick wall does attenuate 30 db at 100 Hz, and 45 db at 1000Hz. (C scale). The waterfalls looks exactly the same in all corners as in the center, and as far as I can hear, I have only one corner with a slight bass buildup (not seen by the microphone however). I have a 180Hz leak at the windows, corresponding to a minimum in the waterfall (if I am doing the correct reasoning - the leak leaves less energy in the room at that frequency).
Tibi

[Soundman2020]

Those foams of 23 kg/m3 which is found on our market seems to be done in some garage by some creeps. I've ordered some from a company, and paid for them 6 weeks ago, and still nothing. They do not have the specs for anything they sell, so they are of questionable quality at least. An also despicable service.

Ahh yes! That reminds me a lot of the famous "foam by mail" people... Just one word here: As Dr Who would say: "RUN! Basically, just RUN!". Scary stuff, that. Stay away...

they say that this stuff absorbs in the 32-225 Hz range with an alpha coefficient of 0,85 on all the range.

Yep, for sure... And by the way, if anyone buys that, then I own nice bridge in New York that I can sell real cheap!

If people really understood just how difficult it is to trap 32 Hz, they would NEVER make claims like that...

here it says that this stuff absorbs all frequencies and diffuses also. the perfect fit . Well, I seriously doubt it.

You got that right! It probably also washes the windows and makes the coffee...

Today's question: I am trying to understand the theory behind gluing the two gypsum board layers with green glue.

Green Glue actually is NOT glue at all! I wish they would have used a different name for it, because it's confusing. It is not adhesive, and cannot be used to stick things together. In fact, it does the opposite! It keeps things apart. It is designed to decouple the two sheets of drywall, NOT to hold them together.

We don't have green glue here, but we have tapegum which is a hydro-insulation material which never gets rigid, and is designed for gypsum boards gap treatment.

Sorry, but that won't work. Or rather, it might work a little bit to some extent, but unless it is a proper visco-leastic polymer compound that is specifically designed to act as acoustic constrained layer damping (CLD), then it will not do what Green Glue does. There is no substitute for Green Glue that has been tested in independent laboratories to the same extent, and proven to work exactly as advertised. Green Glue Company has done extensive testing in their own labs and more importantly in independent labs, and they publish all the technical reports. Nobody else does that. So nobody else has a comparable product. (as far as I'm aware, anyway).

2. one suppose to put green glue between the sheets of gypsum board (here is the part I don't understand), because you need then not to be glued, but elastic. this means the following: a. you need a shitload of green glue b. instead of gluing together the boards, you keep them apart, and this is good for insulation (I imagine this is a sort of panel absorber analogy). But this does not mean that in fact you are creating a multi-leaf system, with its own internal frequency, which is actually bad? (because you add a layer and instead of 2 leaf you will have 3 or 4 considering the glue layer). Also if I understood correctly, if one screws the layers together, all the dumping is inactivated (theoretically by one screw - and in this case there will be more that 36 screws per panel?

Green Glue works like this: it damps sheer waves (bending waves that run along the surface of the panels). Those occur at all sorts of frequencies, but are most prominent in low frequencies. It damps the flexing, bending motion of the panels as they vibrate. Yes, the screws or nails do "short circuit" the panels to a certain extent, but GG is acting in the sheer plane mostly (not so much on normally incident sound), so the effect of green glue is much larger than the nails can counteract: it works, and it works very well.

Yes, you need lots of it (two to three tubes per panel of drywall), and yes it is expensive. But yes it does work. And no, there is no substitute. If you can't afford it, then do not try to substitute something else: it won't work. If you don't use GG, then just put your two layers of drywall right on top of each other, with nothing in between: no air, no glue, no MLV, no nothing. If you need more isolation, then use thicker drywall, or an extra layer of drywall. Don't ever glue your panels together, or leave small air gaps in them, for the exact reasons you mention.


- Stuart -

[dimarzio999]

Here are the photos. I guess meanwhile the last time You answered to me I was editing the message.

I am blocked by the asshole from proaudiostore.ro who non only did not delivered my ceiling hangers, but also kept my money which I paid 2 months ago. So I ordered them directly from his supplier from Greece, who is a really nice guy, and the shipment is on the road. Damned bank asked me 40 euro fee to transfer 160 euros to pay for it. No wonder banks rule the world.

You can see the gap between the windows, the future airlock, the inner wool's first layer, the gypsum board arrived (4,1 tons that stack). and the metal framing as I started to build it.
Before I added the wool and the second round of windows and door, I measured the the attenuation using REW. Looks like the brick wall alone does attenuate 30 db at 100 Hz, and 45 db at 1000Hz. (C scale). The waterfalls looks exactly the same in all corners as in the center, and as far as I can hear, I have only one corner with a slight bass buildup (not seen by the microphone however). I have a 180Hz leak at the windows, corresponding to a minimum in the waterfall (if I am doing the correct reasoning - the leak leaves less energy in the room at that frequency). Now, with the first layer of wool on the walls, and the second round of windows and door in place (as in the photos) I did a sound-check with my electric guitar and also with an active monitor (for drum-machine). The room is almost anechoic, and although one can hear it from outside, it is well attenuated. And I have no inner wall yet, and another layer of wool is to be added, and also a vapor barrier, which I bought one with small air bubbles and aluminum layer which according to the manufacturer will add some sound insulation too to the thermal one. The ventilation is fully functional, and changes the air in the room in 4 minutes. The sound boxes I made for both vent circuits work well, Thank You Stuart for the advice. I overdid them, but I am not sorry. Due to the fact, that the air input tube is the main wind direction, I have a slow convection of air input even if the fan is not functioning, and no sound escapes through the tube. So far I am pleased with the result.

4Stuart.pdf

I won't use anything between the layers of drywall, but I will use the mapegum to caulk and cover the gaps between the drywall pieces within a layer. I guess that is a better idea than using gypsum, and rigidize the whole structure. If I'm wrong, please tell me.
Thank You again
Tibi

[Soundman2020]

Damned bank asked me 40 euro fee to transfer 160 euros to pay for it. No wonder banks rule the world.

Ouch! That's expensive! Have you tried using PayPal? It is all electronic between you and the seller (or buyer), no banks involved, and the fees are a lot more reasonable.

Here are the photos

Please post those on the forum itself, so they can be seen more easily, instead of in the PDF attachment.

You can see the gap between the windows, the future airlock, the inner wool's first layer,

On page 3, I see the outer wall (brick?), then a thin layer of insulation, then metal framing, then more insulation, an air gap, and another frame, also with insulation on it. So I'm not really sure what I'm seeing there! Why do you need TWO frames? Only one extra frame is necessary, for your inner-leaf wall. If you add two walls there, then you will have a 3-leaf system, which means that your isolation will be WORSE in low frequencies than for the same 2-leaf system.

Before I added the wool and the second round of windows and door, I measured the the attenuation using REW.

I think you are trying to use REW for something that it was not intended to be used for. REW is meant for analyzing the acoustic response inside a room, not for measuring isolation between one room and another. To measure isolation (Transmission Loss) just use a hand-held sound level meter.

Looks like the brick wall alone does attenuate 30 db at 100 Hz, and 45 db at 1000Hz. (C scale).

That sounds about right for thick brick.

And I have no inner wall yet, and another layer of wool is to be added, and also a vapor barrier, which I bought one with small air bubbles and aluminum layer which according to the manufacturer will add some sound insulation too to the thermal one.

Ummmm... that isn't a vapor barrier. Vapor barrier does not provide thermal insulation, nor sound isolation: it is normally just a sheet of polyethylene plastic attached to the framing right before you put the drywall on. It's only purpose is to retard the movement of water vapor through the wall, in order to prevent water condensing on the structural surfaces inside the wall.

The ventilation is fully functional, and changes the air in the room in 4 minutes. The sound boxes I made for both vent circuits work well, Thank You Stuart for the advice. I overdid them, but I am not sorry.

Excellent! It is MUCH better to overdo things, than to "under-do" them in studios! One room change in 4 minutes is more than you need, but that's good. One change every 6 minutes would be fine.

and no sound escapes through the tube. So far I am pleased with the result.

Then you did it right!

I won't use anything between the layers of drywall, but I will use the tapegum to caulk and cover the gaps between the drywall pieces within a layer.

I'm not sure what "tapegum" is, but you can either "tape and mud" the joints between drywall panels, or you can leave a slight gap between the panels as you put them up, then fill the gap with backer rod and acoustic caulk, if you want really good seals.

- Stuart -

[dimarzio999]

Ouch! That's expensive! Have you tried using PayPal

Of course, I am using paypal, but unfortunately the company only accepts bank transfer. Another fee is 50 for TNT "economy" shipment, which takes a week. Slowly it is more convenient to go by car and retrieve the hangers myself. Or, swim. Which is yet cheaper

post those on the forum itself,

OK I will do so starting the next time. I have no novelties to show now. In fact I am amazed of those quick responses. Thank You a million times.

On page 3, I see the outer wall (brick?), then a thin layer of insulation, then metal framing, then more insulation, an air gap, and another frame, also with insulation on it

The additional frame is present only in the gap between the windows, and will sustain the drywall I will use to seal inner space between the windows from the gap between the walls. So it will sustain 2 vertical and 2 horizontal pieces of drywall, perpendicularly to the wall. There will be no 3 leaf system.

I think you are trying to use REW for something that it was not intended to be used for.

I used REW's sound generator through an active monitor, and measured the sound level inside and outside the studio with a professional handheld decibel-meter.

Ummmm... that isn't a vapor barrier

It is a multilayer membrane, which does the vapor stuff, and also has an aluminum layer to shield heat, and air bubbles for both sound and heat. Remember, here in winter there are sometimes -40 C and I will have electric heating...and since I will tape it hermetically together, I am sure there is no air-driven sound leak anywhere.

I'm not sure what "tapegum" is,

Tapegum [=mapegum] is a dedicated paste consistency stuff to caulk between drywall gaps, and it is very elastic, in fact it never becomes solid, and also hydro-insulator.

I had surprising answers from two sound treatment companies ( I am not sure if I can write the names so I won't) - using their free room evaluation: they both said, that I almost do not need basstraps in my room, because I got the measurements right, and have no parallel surfaces nor 90 degree corners. In fact one of them said that I don't have any axial mode problem, and the tangential ones are 2-6dB only, so I will probably get away with some mid/high absorption and a certain degree of diffusion. Kind of flattering, but we will see after I will be ready. I guess, I will need yet some help. I will try not to bother You too much. ANYWAY, WITHOUT YOUR HELP MY STUDIO WOULD'T BE HALF AS GOOD SO FAR AS IT IS. I am just an MD, PhD and DIY. No idea of acoustics. As a read more, I am more and more convinced that I do not know jack about it.
Tibi

[Soundman2020]

Tapegum is a dedicated paste consistency stuff to caulk between drywall gaps, and it is very elastic, in fact it never becomes solid, and also hydro-insulator.

Sounds perfect! That should work well. Just leave a slight gap between the drywall panels as you put them up, maybe 2 or 3 mm or so, and force that tapegum stuff well down into the gap, to make sure you get a good seal. If you have long walls, you might need to adjust the framing so that the drywall is still centered on the studs: EG. 6 panels of drywall next to each other with an extra 4mm gap for each is 24mm, so that's off the edge of the stud!

The additional frame is present only in the gap between the windows, and will sustain the drywall I will use to seal inner space between the windows from the gap between the walls.

Don't seal that with drywall! That will connect your inner leaf to your outer leaf, defeating the decoupling. Just use Homasote board, add a piece of OC-703 insulation on top, then wrap that all in black fabric. Glue that to ONE side of the gap (probably the brick wall side), and let it float just a bit above the other side, without touching (or touching only very lightly).

I used REW's sound generator through an active monitor, and measured the sound level inside and outside the studio with a professional handheld decibel-meter.

Ahhhh! OK, then that's fine: You were just using it as a tone generator. When you mentioned waterfall plots, I though you were trying to measure the transmission loss through the walls with waterfall plots!

I had surprising answers from two sound treatment companies ( I am not sure if I can write the names so I won't) - using their free room evaluation:

They went there to your place for FREE, and evaluated your room with proper test equipment? At not cost? If not, then I would not trust their assessment very much! If this is one of those services where they say "E-mail us your room dimensions and we will tell you which of you wonderful kits you need to buy", then be VERY aware... that's not a good way of determining what treatment your room needs.

This is something that you CAN measure yourself with REW, then post the data files here.

because I got the measurements right, and have no parallel surfaces nor 90 degree corners.

Ummmm... well..... I would not trust what they said at all then! Good room measurement do NOT make room modes go away: they just spread the room modes a bit more evenly. Making the walls non-parallel does NOT eliminate modes: In fact, it multiplies them. Sure, the axial modes might get a bit weaker, but you have to angle the walls quite a bit before they disappear.... and at the same time, you are creating many new tangential and oblique modes, which replace the axial modes....

Also, by angling your walls you make it impossible to predict the modal behavior using simple room-mode calculators, and then the only method for doing that is by using expensive FEM/FEA software, and paying a good operator who knows what he is doing to set up the boundary conditions that simulate your room, and then interpret the results for you... I guarantee that the "free analysis" people did NOT do that, because it costs money. So if they knew that your room has no parallel walls, and they still told you that you have good modal response, and they did not actually go to your room and measure it acoustically, then sorry, but they were rather less than honest with you.

Here's what you should do to find out for sure what the modal response of your room is, using REW:

Place your speaker down on the floor in one corner of the room, right in the corner where the two walls meet the floor, with the speaker facing down the length of the room (the longest distance, not the shortest distance). Now place your measurement mic up in the exact opposite corner of the room, where the other two walls meet the ceiling. Point the mic right into the corner, as close as you can get it without it touching the walls or the ceiling. In other words, you have the mic and the speaker as far apart as it is physically possible to place them in that room, in digonally opposite corners.

Now run REW, and post the resulting MDAT file here on the forum. It might be too big to post here, and in that case use a file sharing service such as Dropbox, and post the link here.

Then I'll download that and analyze it for you.

This is what REW is designed for: to measure room response. It is very good at doing this, and will certainly show the real modal behavior of your room. The reason for putting the mic and speaker in the corners, is because all room modes terminate in the corners, so by using the "tri-corners" of the room, you are triggering all possible modes, even down to the lowest frequencies, and also measuring them at the best point.

In fact one of them said that I don't have any axial mode problem,

We'll see if that is true or not... REW doesn't lie, and REW doesn't want to sell you a kit made up of pieces of foam....

and the tangential ones are 2-6dB only,

That makes no sense: 2-6 dB ... with respect to WHAT? Theory says that tangential modes will be 3 dB lower than axial modes, and oblique modes will be 3 dB lower than tangentials. But that doesn't mean much: that is only the maximum INTENSITY of the mode. What is important about modes is not so much the maximum intensity but rather the decay: How long do they carry on ringing? Do they decay at the same frequency, or do the change to other frequencies? Does the decay rate change, or is it constant? That's what matters.

but we will see after I will be ready.

It's better to see now, so you can be prepared for the treatment in advance...

I guess, I will need yet some help.

No problem! That's what the forum is here for.... To help.

No idea of acoustics. As a read more, I am more and more convinced that I do not know jack about it.

Well, for somebody who doesn't know much, you seem to be doing a lot of things RIGHT! And it seems to be working out pretty well, so far!!!


- Stuart -

[dimarzio999]

Thank You for Your kind words. I have to do yet a lot of work. The hangers arrived from Greece. Now I wanted to jump and continue the profile mounting on the ceiling, but it turns out to be rather difficult due to the measurements of the room. Nothing is horizontal nor equal or parallel And a lot of thinking ahead (something like Karpov vs. Kasparov 20 moves ahead).

Don't seal that with drywall! That will connect your inner leaf to your outer leaf, defeating the decoupling. Just use Homasote board, add a piece of OC-703 insulation on top, then wrap that all in black fabric

I won't seal it. The extra framing You have seen on the photo will hold it in a way that it will have physical contact only with the inner window, and all the structure lays on the floating floor. With the external leaf will not touch, only through a layer of wool. I was thinking to seal the small gap with elastomer, or tapegum, but Your idea with the cloth is excellent. So I will use cloth.

Here's what you should do to find out for sure what the modal response of your room is, using REW:

I have measured the room with REW as You told me to. Here is

May 30 15_49_15 4STUART.rar

the file.
Hopefully it is ok. Somehow I couldn't inactivate completely the internal microphone of the laptop. I also had to "rar" it because the site did not accept the extension of the file. Hopefully it is no problem that the allover volume of the studio will be less than it is now, and the wool is on the wall...and the framing stands, there is a stack of drywall and some wool packages laying around.
Thank You for everything, and now I go back to the drawing board and figure out the position of the hangers and the framing of the ceiling, which I am sure Eiffel would hang himself if he suppose to do it. Compared to my ceiling, the tower is simple
Tibi

[Soundman2020]

Nothing is horizontal nor equal or parallel

Yup, that's normally the way things are...

And a lot of thinking ahead (something like Karpov vs. Kasparov 20 moves ahead).

Only 20??? Why so few?

Seriously, yes, that's a very smart way of approaching studio design: Design the whole thing on paper or electronically first, then build it once you have thought of everything you possibly can.

I won't seal it. The extra framing You have seen on the photo will hold it in a way that it will have physical contact only with the inner window, and all the structure lays on the floating floor. With the external leaf will not touch, only through a layer of wool. I was thinking to seal the small gap with elastomer, or tapegum, but Your idea with the cloth is excellent. So I will use cloth

. Excellent. That will work fine.

I have measured the room with REW as You told me to.

The data looks OK, but you only measured up to 200 Hz! You need to measure the entire spectrum, from 20 Hz to 20,000 Hz. There are some modal issues apparent on that file, but I'd need to see the complete analysis. In the "measure" settings, make sure that you have "start" set to 20 hz (or lower) and "end" to 20,000 Hz.

- Stuart -

[dimarzio999]

Dear Stuart, I am really flattered by those fast responses. Seems like instead of working alone, I am working with You, which is excellent
I remeasured 0-24000 Hz. Looks like if I set different intensities on the monitor, the graph looks different. So I attach both files.

https://www.dropbox.com/s/0buf4l2jkdirh ... ements.rar

You were right, it doesn't fit into 500 kb.
Thank You
Tibi

[Soundman2020]

Seems like instead of working alone, I am working with You,

Thanks! But honestly, you just got lucky today, as I'm waiting for information from a couple of clients before I can proceed with their studio designs, so I happened to notice your posts and be able to check them quickly. I can't promise it will always be this fast! But I'll do my best....

Looks like if I set different intensities on the monitor, the graph looks different.

Right: And that shouldn't happen! In fact, there's something wrong with the way you are doing those measurements: your files are basically just low-level noise, with no actual signals in them at all. The first file you sent originally (up to 200 Hz) seemed to be OK, but the other two new ones have invalid data in them.

For example, here's the spectrogram from the original file:

tibi--sg--200hz.jpg

That's all good data, valid and makes sense.

Here's the spectrogram from one of the files you sent this time:

tibi--sg--full.jpg

That's basically just garbage, noise. Nothing there.

So please check your procedure, and follow the full calibration procedure in the REW manual, then try again.

- Stuart -

[dimarzio999]

Hi Stuart,

I am perfectly aware, that "not every day is Sunday" as they say around here. I am grateful for my luck though.

Here is the new measurement. This time it does not depend on the volume.

https://www.dropbox.com/s/80z2qayfw4u22 ... again.mdat

Thank You kindly for everything,
PS. I won't bother You too much, since now I have no acoustic dilemmas until I build the ceiling and the walls, which given the fact that I am working alone, it will take weeks.

[Soundman2020]

The level was a bit low, (you should do the test at around 80 - 85 dB) but it's OK for seeing the basic issues: There seem to be some modal problems in the low end. specifically, it looks like there are issues at 32 Hz, 41 Hz, 54 Hz, 76 Hz, 91 Hz, 102 Hz, 127 Hz, 150 Hz, and 199 Hz. The mid range and the highs seem to be OK, except for something very strange at around 10 kHz, but I suspect that might be noise in the room: your computer fan, maybe? Or something the ballast in some type of light fitting? It might even be something strange going on with your speakers: What speakers are you using? But I don't think it is a room acoustic problem.

What are the interior dimensions of the room, and what treatment do you already have in there?


- Stuart -

[dimarzio999]

I think we still should wait until I am ready with the interior walls. I am building the framing right now, and the wall is not there yet. I have almost all (exterior) walls covered with wool, the framing of the roof and of the interior leaf is there, a big stack of drywall and various cubic meters of wool is laying around. I don't think the reading is accurate, since I am measuring the brick wall instead of the inner shell. I've used a Laney active monitor CXP-110 (in mono). Inner measurement (will) be: 9,89x3,94x9,08x5,78 meters, the height is 3,2 m at the walls and rising to 3,54(at the shortest wall) and to 3,71 m (at the "5,78 m" wall)

Krausz Tibor studio folded.jpg

Please ignore the wall treatments and speaker position etc. This is a drawing I've got from a free room analysis and erased the company's name etc. There is no wall yet

[Soundman2020]

The rear end of that room is OK, but the front is not. The front wall needs to be angled so it is perpendicular to the side walls.

- Stuart -