John Sayers' Recording Studio Design Forum Archive

Hi everyone,

it's been a couple of months since I started gathering all the information to be able to build my personal space for creating music. This forum along with Rod Gervais book provided invaluable information and it's finally time to start things up - I would really appreciate if you could give me some feeback regarding my design options.

I'm an amateur musician/songwriter and I want to create a "music room" - a place to practice and to record and mix guitar/piano/vocal demos. The place I have available is rectangular room 5.5m long x 3m wide x 2.7m high with one door, one window and one heating element under the window (see empty_room.skp):

I measured sound levels in and outside of the room. Outside of the house I measured 70dB on a busy Saturday morning (my neighbour was sawing bricks). Inside the house I measured 80dB in the living room when kids got really crazy and about the same 80dB in the bathroom with washer going at 1200rpm. Measured myself playing/singing etc and I never went over 100dB, even playing electric guitar through a small tube amp. Ideally I think 60dB isolation would be enough for all my needs.

The room has brick walls (outside wall has additional rockwool insulation, 3 inside walls don't), concrete floor and drywall/rockwool ceiling, see the picture:
My brick walls have catalogue STC number 46, I expect the real world number will be a little lower (around 40dB hopefully?). The door and window are the real weak links at the moment and need to be addressed in some way.

I see 3 possible scenarios to treat the room:

1. quick and noisy (aka "Only record at night or beg the kids to keep it down") version:
I'll install drop down seal into existing door, caulk where necessary, add another STC40 door on the inner side. I'll replace existing window with STC50 type, add a layer of insulation to the front and back of the room and then I'll shamelessly copy John's design from the "Small studio in 3D" thread, because the dimensions of my room are the same. The ceiling will be addresed in some way - probably V shaped ceiling (left to right, the highest part being in the middle of the room, lowest parts on left and right). Then I'll pray that final isolation will be at least 40dB and I will use portable panels when recording to tame the volume.
It will look like this:
Pros:
least expensive
most free space
can do it myself
best acoustics

Cons:
worst sound isolation


2. Proper isolation (aka "Close myself in a small closet with a bunch of bass modes") scenario:
I'll contract help to build a proper inner leaf (brick wall - air gap 10cm - rockwool insulation 10cm - 2layers of gypsum boards). This should (if done properly) bring me over 60dB sound isolation, but I'll loose 0.5m from both the length and width of the room and 0.25m from the height. The inner room dimensions will become 5 x 2.5 x 2.5m and I'll need heavy acoustic treatment for the room to make it usable. Another thing is that because the existing doors are very near to the back wall the inner leaf will have to be slanted in the door region, eating even more space, like this (only frame is shown, no insulation or gypsum boards attached):
Pros:
best sound isolation

Cons:
most expensive
have to hire help
worst acoustics
least free space



3. Compromise scenario:
Same as above, but I'll keep the inner leaf thickness to the minimum: air gap 1cm -> rockwool insulation 4cm -> single layer gypsum board "acoustic" type. The company behind this new product claims this can add up to 28dB isolation (depending on the original outer leaf). When confronted with my real world scenario they expected 10-15db isolation increase based on their previous experience. This solution would eat less of the room space, provide acceptable isolation(probably) and the insulation behind softer wall would probably help with bass traping? Also if the leaf would be less than 6cm thick I think I could do without slanting the inner doors and so save space within the room. This is my preferred scenario at the moment, because I think I can always add another layer of gypsum boards in case the sound isolation won't be sufficient? If my reasoning is flawed in some way, please let me know.


Prices in our country (as 1US$ ~ 1 Eur at the moment):
50mm x 100mm wood framing $1.5/m (200m needed)
CW/UW aluminium framing $1/m (200m needed)
12.5mm thick drywall $0.8/m2 (80m2 needed for 1 layer)
15mm thick drywall $2.4/m2
12.5mm thick high density "acoustic" drywall $3.2/m2
Rockwool rockton (50kg/m3) 40mm thick $3/m2 (80m2 needed for 1 layer)
Rockwool rockton (50kg/m3) 100mm thick $7/m2


I would like to keep the costs under $3000 - can go up to $5000 but that has to include all the acoustic treatment of the room (and preferably a pair of nice monitors )

Can you provide some insights regarding my proposed scenarios? Or please suggest some other inner leaf structure/dimensions if you think it will suit my needs better.
Thanks a lot!

Martin


Sketchup models:

Hey guys,

I have a feeling that my questions weren't specific enough, so I'll try to make them more to the point:

1. After some additional studying I found out that scenario 3 (5cm air gap + single layer drywall) probably isn't the smartest idea, as thin air gap together with low mass leaf will result in high resonance frequency of the MSM system and in the end I could get even less isolation from 2 leaf system than my current single leaf brick wall. Is this correct?

2. What is the minimum air gap useable for home studio use - 10cm?
Is 10cm air gap filled with insulation together with 2 layers of 12.5mm gypsum board going to work if I need isolation above 80Hz(guitar low E string)?
Is it for the better if the 2 gypsum board layers have different density?
How much of the air gap thickness should be filled with insulation? Can insulation touch the outer wall?
I've found information, that it's best to fill the whole cavity and insulation can touch both leafs but it can't be compressed too much?

3. Is there any way to bring a pair of 1/2 inch plastic pipes for heater (radiator) through the inner leaf and not compromise sound isolation? Or shall I just ditch the water filled heating element and use electrical heater instead?

4. As room ratios go, is the 525x275x255cm isolated room much worse than my current 550x300x270cm room? If isolation is going to make the room acoustically unusable I could probably live with single leaf system given my walls have enough mass (30cm brick) and I'd just need to add some mass to the ceiling and change door and window for "sound-locking" types (aiming for >40dB isolation at >80Hz) ?


Any answer would help me a lot because in my current state every next thread I read seems to generate more questions than answers...

Thanks a lot guys,

Martin

Hello,
it's been a couple of months but I'd like to report a success: my 2 leaf structure isolates well! I measured between 50-55db drop in sound pressure (C weighed, slow response) - subjectively even washing machine going at 1200rpm and 84db, standing right next to the brick wall, is not noticeable within my room. Of course some of the sound of my guitar amp (>100db) aimed right at the door gets in
After reading a LOT of threads on this great forum, I utimately went with these layers:

brick wall -> 10cm rockwool, 50kg/m3 density -> 2 layers of different density drywall sheets

Total costs were close to $4000 - a little more than I expected, but well worth it from my perspective.


Now I'd like to ask you for a little help regarding acoustic treatment - here's how the inner room looks like:
Dimensions:
5.2m long x 2.7m wide x 2.5m high (I realize not optimal, but I have to live with that)

Important details:
- angled door
- window on the left wall; dimensions 1.25m wide x 0.7m high; positioned 1.6m above floor (i.e. above listening level)


Here's my starting point for acoustic treatment:

I followed John's modular design from this thread, as the dimensions are similar:
http://johnlsayers.com/phpBB2/viewtopic.php?f=1&t=5457

Wall absorbers will be modeled after John's design:
http://www.johnlsayers.com/HR/index1.htm


Most of the ceiling(70%) will be covered with a cloud (10cm thick rockwool insulation, 30kg/m3 density), bass trap in the rear corner will be of "superchunk" variety.

Questions:
- should I put a wall absorber above the piano to maintain as much of the room symmetry as possible or is it not that critical?
- I'm not quite sure how to make the upper part of the left wall absorber moveable, so that I could move it in front of the window when mixing and pus it away when trying to open the window.
- I really like the look of perforated drywall and I'd like to use if for the overhead cloud. Is it a good idea? If yes, how big should the holes be and what portion of the whole cloud area should the holes cover? I think something like this, but with holes of random diameter and random position:
- I made the front absorber thicker than neccessary (>30cm) to move the listening position closer to 38% of the room length. This could theoretically help with the bass frequencies, too - is it so or is it not such a good idea?
- finally, am I on the right track or completely off?

Thanks a lot!
Martin

Looks like you're on the right track. Just a couple of thoughts...

It might be time to do some REW measurements of the room as it is - empty, to get an idea of what is actually going on. And move from there. Being a small room you are going to need to treat the hell out of it.

The second absorber you've got on the left wall seems unnecessary - probably flat panels from that point back will suffice...?. The 38% mark is theoretical...so measurements of the room will help to determine the best placement for the mix position.

Post some pics of the room - we all love pics!

Cheers,

Scott

Thanks for your comments, Scott!
Here are pictures of the room (stiched from about 30 pictures, that's why the weird black cut-outs)
Front: Back: I ordered a measurement mic, should be here within a week, I'll post some REW measurements then. I planned to measure the room once the first round of treatment will be finished (corner bass traps + first reflection points absorbers), but I see the reason behind measuring the room as it is now.

Any tips as to where to put the mic and the speaker(s)? Should the room be absolutely empty (no table, not even me standing there)?

Thanks a lot!

Martin

my 2 leaf structure isolates well! I measured between 50-55db drop in sound pressure (C weighed, slow response) - subjectively even washing machine going at 1200rpm and 84db, standing right next to the brick wall, is not noticeable within my room.

That's a pretty good achievement! 55 dB TL is excellent.

Of course some of the sound of my guitar amp (>100db) aimed right at the door gets in

That is one of two things: either the door is not massive enough, or the seals are not good. However, I also noticed that you said "door" not "doors", making wonder if you really do have a pair of back-to-back doors, with one in each leaf?

Dimensions: 5.2m long x 2.7m wide x 2.5m high (I realize not optimal, but I have to live with that)

That's just a slight understatement! "not optimal"... hmmmm.... One well-respected room mode calculator classifies it as "A worst case scenario". Was there no way at all to increase the width? I played around with some numbers, and it turns out the width is the limiting factor in this case.

Well, it's too late now... you'll just have to live with it, but that room is going to need some MAJOR treatment!

I agree with Rockindad: I too would suggest that the very first thing you should do, with the room still empty, is to run a test using REW. Set up your speakers where they will be in the end, and set up your measurement mic where the mix position will be, calibrate REW (set it for 85 dB(C) with both speakers on, using the pink noise generated by REW). Run three tests: one with just the left speaker, one with just the right speaker, and one with both speakers. upload your MDAT file to a file sharing service (such as DropBox), and post a link here so we can downlod that and analyze it.

- I'm not quite sure how to make the upper part of the left wall absorber moveable, so that I could move it in front of the window when mixing and pus it away when trying to open the window.

Open the window???? Why on earth would you want to open the window???? If you did that, you would destroy your isolation. The window must remain closed, permanently, and be sealed shut.

I agree with Rockindad here too: the rear angled absorber is not necessary.

- I really like the look of perforated drywall and I'd like to use if for the overhead cloud. Is it a good idea?

Depends on how you use it! If not used correctly, it could end up as a tuned device, and it would be numerically-based, with all the negative aspects that such devices produce, close to your head. Maybe not a good idea for your control room, but it could be good in the live room.

If yes, how big should the holes be and what portion of the whole cloud area should the holes cover?

There should be NO hard cover under the cloud! (Perhaps on top, but not under). The purpose of the cloud is to control first reflections coming back from the ceiling. The cloud is supposed to absorb those. If you make it reflective by putting a hard surface under it, then you are just replacing one reflector with another reflector, so you are not solving the problem at all! Clouds sometimes have a hard back on top, but thick absorption below, and in that case they should be angled.

- I made the front absorber thicker than neccessary (>30cm) to move the listening position closer to 38% of the room length.

Changing the thickness of the absorption does not affect the location of the mix position at all. It still remains exactly where it was, in relation to the original hard, solid, massive boundary walls of the room. The absorption does not change that: You still measure the position of the desk, chair and everything else with respect to the actual real wall, NOT with respect to the absorber.

Here are pictures of the room:

Great! It is now clear that you don't have a problem with the side absorber on the left hand first reflection point: It does not need to cover the window. That one only needs to go up to the bottom of the window. In fact, I would skip the entire side absorber unit, and just hang a large, thick absorbent panel on the wall just below the window. Much simpler, and just as effective.

Any tips as to where to put the mic and the speaker(s)? Should the room be absolutely empty (no table, not even me standing there)?

You can have a table in there, roughly the same size as the desk you will have there finally, and a chair as well, similar to what the final chair will be, but apart from that, level the room empty. And yes, you should also not be in the room when the tests run: Use the start-delay feature in REW to do that.

- Stuart -

Hi Stuart, thanks a lot for your comments. I delayed my reply a little thinking the measurement mic would come before weekend and I'll post the measurements, but it's still on it's way, so until then I'll try to explain the missing bits a little better:

Of course some of the sound of my guitar amp (>100db) aimed right at the door gets in

That is one of two things: either the door is not massive enough, or the seals are not good. However, I also noticed that you said "door" not "doors", making wonder if you really do have a pair of back-to-back doors, with one in each leaf?

Yes, there are 2 back-to-back doors, each in one leaf. By the comment I merely meant, that although the structure isolates well, if the sound is loud enough, it will get in...

Open the window???? Why on earth would you want to open the window???? If you did that, you would destroy your isolation. The window must remain closed, permanently, and be sealed shut.

I'd like to leave the windows operable (actualy 2 back to back windows, one in each leaf) to, well, let some fresh air in. I didn't put HVAC in as it's almost never needed in our climate. After researching the thing quite a bit it seemed to me that 2 quality windows would provide good enough isolation.
But your comment have made me anxious so I tested the isolation today - with circular saw running right outside the window (measured 95dB C weighed) the sound level in the room raised from 32dB to 38dB, all C weighed. It was less than a whisper, I wouldn't hesitate to record guitar/vocal demo in similar conditions. It may be that the windows would loose some of their isolation properties over time - is that why they should be avoided? 57dB isolation I measured looks fine to me...
Bear in mind that there's 30cm gap between the windows and those are acoustic grade windows - thick glass plates, different thicknesses and different gaps inside each of the window.

There should be NO hard cover under the cloud! (Perhaps on top, but not under). The purpose of the cloud is to control first reflections coming back from the ceiling.

Understood. I really liked the look of the perforated drywall but I'll make my peace with fabrics covered rockwool

I made the front absorber thicker than neccessary (>30cm) to move the listening position closer to 38% of the room length.

Changing the thickness of the absorption does not affect the location of the mix position at all. It still remains exactly where it was, in relation to the original hard, solid, massive boundary walls of the room. The absorption does not change that: You still measure the position of the desk, chair and everything else with respect to the actual real wall, NOT with respect to the absorber.

Understood - I didn't explain my point precisely enough: the listening position is 38% of the room length in relation to the hard walls. I meant that by making the front absorber thicker I moved the speakers closer to the 38% mark, thus making it easier to maintain the equilateral triangle. I hope it's clearer now...

One question about measuring the room - I now have Alesis M1 MKII passive speakers that can't be easily soffit mounted due to the back port and I'll be using them mounted on stands until I buy better speakers, those will go into soffit. Will the now measured values still be valid with those new, soffit mounted speakers or should I expect need for changes in room treatment when changing speakers?

Thanks once again for your help!
Martin

After some delay the mic finally arrived and I took some measurements of the empty room. I placed the mic at the listening position (38% of the room length) and placed monitors on towers made from hollow concrete blocks, situated like this: The height of both the mic and the speaker's axis was 1.2m.

Here are REW mdat files (left speaker(L), right speaker(R) and both(LR)):
https://dl.dropboxusercontent.com/u/920 ... 5B1%5D.rar

For a quick glance here's a slightly smoothed frequency response of the room (both speakers on, measured at 75dB level):
I'm no expert but those hills and valleys between 60 and 200 Hz would need some treatment in my opinion . Any ideas? For starters I'm thinking as much bass trapping as possible, but that was predictable even without measurements... Would the room benefit from some tuned elements?

Thanks in advance!
Martin

By the comment I merely meant, that although the structure isolates well, if the sound is loud enough, it will get in...

... which goes back to what I said: The doors are not isolating to the same level as the walls. There's only three possible reasons for that:

1) Insufficient mass on the doors (perhaps they are hollow, not solid, or solid but not thick enough / dense enough)
2) Incorrect seals: The seals on each door do not run around the full perimeter of the door unbroken on all four edges or there's only one seal when there should be at least two. Or the seals are not properly compressed (over-deflected or under-deflected are just as bad).
3) The space between the doors is not deep enough (distance across the gap from door face to door face) or there is no insulation / wrong insulation around the edges in the gap between the two door frames.

Those are the only three possibilities. If you want to fix the problem, then those are the places you should be looking.

I'd like to leave the windows operable (actualy 2 back to back windows, one in each leaf)

Then you won't be able to get good isolation! Operable windows are really hard to seal properly. Without good seals, you don't get good isolation.

to, well, let some fresh air in.

How would that work? In order for air to move from one place to another, there has to be a pressure difference and two paths. Your room is doubly sealed air-tight, twice over hermetic. There is no pressure difference and there is no other path. Air will not move. It's not like a typical room in a house where there are numerous small air leaks all over the place, and opening the window provides both the pressure difference and the additional path. That simply does not happen with a studio.

I didn't put HVAC in as it's almost never needed in our climate.

Sorry, but yes you DO need it. Not because you live in Slovakia, but because it is a studio. It is SEALED! Air tight. Hermetic. Highly insulated. There is no way for air to get in or out, and no way for heat to get out, and no way for humidity to get out. As I explained above, opening the window won't to any of that, no matter how nice your climate is.

If you park your car on a flat street, and then release the handbrake: it will just sit there, not moving. It would only roll away if the street sloped down in one direction. The same with your studio: There is no pressure "slope" that would cause air to move, even when you "release the hand brake" by opening the window. The air will just sit there, doing nothing, not moving in or out.

You seem to be entirely misunderstanding the purpose of HVAC in a studio: it is NOT there to keep you warm or keep you cool. It is there to keep you alive by supplying fresh air (oxygen) and removing the deadly gasses (CO2, etc.) that build up without it, as well as to control the humidity inside the room, and to remove the excess heat from your body, your equipment, your lights, other musicians, their equipment, etc. Without a properly designed HVAC system, your room interior will get warm, the humidity will rise, the oxygen levels will drop, and the CO2 levels will rise. Initially that is unpleasant, then it makes you unconscious, then eventually it kills you. The humidity changes also cause problems for acoustic instruments and condenser mics, and excessive heat and humidity causes damage to your equipment.

So if you want to stay alive in your studio, with instruments that stay in tune and equipment that does not burn out, then you need HVAC. If you don't mind fainting, dying, destroying your equipment, and re-tuning your instruments ever few minutes, then fine, leave out the HVAC....

with circular saw running right outside the window (measured 95dB C weighed)

A circular saw does not produce much sound in the low frequency region of the spectrum. Practically none, in fact. Most of the energy is in the mids and highs. Instead, set up full-range speakers out side and play typical contemporary rock music, then measure like that: That will tell you how well your studio is isolating.

different thicknesses and different gaps inside each of the window.

I'm not understanding you: How can there be "different thicknesses and different gaps inside each window"? That's only possible if you did something wrong, such as using double-glazed units for EACH window... Please tell me you did not do that!? Studio windows are made from SOLID laminated glass, very thick, with NO air gaps inside.... In a correctly built studio window, there is only ONE air gap, and it is very large: it is the distance between the leaves of the wall, at least, and hopefully more. If you have more than one air gap, then you have more than one MSM resonant frequency, and the final isolation characteristics of the window in the low frequency end of the spectrum will be poor.

If you used two double-glazed units, then you have a 4-leaf window... That won't perform very well at all...

by making the front absorber thicker I moved the speakers closer to the 38% mark, thus making it easier to maintain the equilateral triangle.

That's another myth, actually. Yes, there needs to be a triangle, and yes the two sides of that triangle need to be the same length (same distance from speaker to ear on both sides), but the base of the triangle (distance between speakers) does NOT need to be the same as the distance from speaker to ear. In fact, the best sweet spot is achieved with an angle of slightly less than 30°, and a listening position slightly forward of the "traditional" equilateral triangle. The reason is simple to understand: the "traditional" equilateral triangle, where the acoustic axes of the speakers intersect inside your head, would work perfectly for people who have ears inside their eyeballs , but for the rest of us, who have ears on the SIDES of our heads, and sticking out, the acoustic axes need to be spread apart a bit more, and the listening position needs to be further forwards than the intersection.

Also, 38% is not a rule: it is just a guideline. In reality, around 34-36% turns out to be better for most people in most rooms.

So if you have your room set up with the famous-but-wrong equilateral triangle, then you should modify it so that the speakers are about 28% of the room width away from the side walls, tight up against the front wall and angled so that the acoustic axes intersect about 20 to 30 cm behind the back of your head when you are seated with your ears at about 36% of the room depth: Whatever angle and distances that gives you, is roughly correct. You will find that it gives you a broader sweet spot, better stereo imaging, clearer sound stage, and good bass response (assuming the room is treated correctly).

I now have Alesis M1 MKII passive speakers that can't be easily soffit mounted due to the back port

Actually, they can be soffit mounted. I used to think that it was impossible to soffit mount rear-ported speakers, then I though it was just very hard to do... but now I have come to realize that it can be done, with just a little extra care and planning, as compared to front ported or un-ported speakers, in most cases. The only speakers that really cannot be soffit mounted are true dipoles and cabinets that have extra drivers firing out the sides, top, or bottom. Apart from those, most speakers can be soffit mounted (with the possible exception of those that have highly curved or highly angled front baffles, simply due to the practical complexity of cutting the soffit baffle to match that, but not for any real acoustical reasons).

Will the now measured values still be valid with those new, soffit mounted speakers or should I expect need for changes in room treatment when changing speakers?

There will be changes, yes. The speakers will not be in the same location, and when you put the new soffit-mounted ones in, all of the room-related artifacts will disappear. There will be no SBIR, edge diffraction, or comb-filtering related to having the speakers in the room, and the bass response will be smoother and extend lower, among other things. You might need to adjust some of the treatment at that point, but the change will be for the better, mostly.


- Stuart -

Hi Stuart, wow, what a detailed answer. I really, really appreciate your direct and to the point words.

... which goes back to what I said: The doors are not isolating to the same level as the walls.

You're right, the doors' isolation is not quite the same as the walls. Thanks for the points to check - I already found out there's only one seal in one of the doors. If that doesn't help would attaching 10cm thick dampening material(rockwol or foam) to one of the door help? The airgap between the doors is 30cm wide.

RE: HVAC vs operable windows
This one hurts - I feel kind of stupid right now, especially after re-reading Rod Gervais' chapter on HVAC - I really missed the whole point, I really thought the windows would work. I'll replace the windows with solid walls, then calculate my hvac needs and contact local professionals (I can use those windows elsewhere so the financial loss is not that big). Any tips as how to do the HVAC most efficiently in my situation? Where to put the duct silencers, how to go about it so that I won't need to make more holes than necessary into the existing MSM system?

Will the room acoustics change much when I replace the windows with solid wall, or is it still worthwile to do REW measurements and continue acoustic treatment design while waiting for HVAC? If it makes sense to continue, then I have a couple of questions about speaker placement:

So if you have your room set up with the famous-but-wrong equilateral triangle, then you should modify it so that the speakers are about 28% of the room width away from the side walls, tight up against the front wall

I suppose this is true when you have already treated room, so you place the speakers tight up against absorptive panels on front wall? In another words: where should I put my Alesis monitors for doing REW measurements of bare empty untreated room, keeping in mind that I plan to soffit mount them? Btw thanks for good news about the possibility of soffit mounting rear ported speakers, I definitely plan to do so!
Thanks once again for your time and effort, Stuart!

I already found out there's only one seal in one of the doors.

That sounds like it might be the problem, or part of the problem. Does that one go all the way around, top, bottom and both sides? Many people forget about the gap UNDER the door, and neglect to put a good seal in there....

Your best bet here is to add an extra layer of wood to the door, a little smaller than the existing leaf (or get a router on the edge of the leaf), and buy some commercial seals, such as those made by Zero International. Get the adjustable type, so you can tweak them later, as it sags, settles or warps slightly over time (most do...)

If that doesn't help would attaching 10cm thick dampening material(rockwol or foam) to one of the door help?

That will help too, yes. It will help to damp all the resonances going on in the gap, which is a good thing.

RE: HVAC vs operable windows
This one hurts - I feel kind of stupid right now, especially after re-reading Rod Gervais' chapter on HVAC - I really missed the whole point,

Well, everyone makes mistakes, and you are still at a stage where it can be fixed without too much hassle.

I'll replace the windows with solid walls,

You can keep windows there if you want... many people like to have natural light in there studios. So considering that you already have the place to put them cut into your walls, it would simply be a matter of taking those ones out and putting in fixed windows that have thick laminated glass in them. (You do also need desiccant in the air gap, to adsorb the moisture trapped between the two panes, so it does not condense on the glass surfaces...).

then calculate my hvac needs and contact local professionals

Hopefully you will be able to find HAVC installers who have done studios before... it's a bit different from doing a normal house or office....

Any tips as how to do the HVAC most efficiently in my situation?

I think Rod mentions this in his book: trying to explain how to do HVAC for a studio is a pretty big subject! You could write a large book just about that alone!

Where to put the duct silencers,

Let's start from the beginning: How much isolation are you aiming for? Based on that, you decide if you need silencers on only ONE leaf of each duct, or on BOTH leaves for each duct. For high isolation, you need it one silencer box on each leaf for each duct. I suspect that is your case. Also, the more isolation you need, the thicker the wood needs to be for making the boxes.

Now for size: first you need to figure out how much air you need to move (volume, or flow rate: how many cubic meters per minute or hour). That is based on the size of your room (cubic meters) and the exchange rate you need for your room (room changes per hour). Once you know that, you can calculate how big your ducts need to be in order to move that volume of air slow enough that it does not cause any air noise by itself: Based on that, you can figure out the size of your silencer boxes, such that the internal cross section is about twice the cross section of the duct.

Now that you know how big your boxes need to be, only now can you look for places to put them: Obviously, the only place they can go is places where there is enough space...

Also, you need to plan this so that the air comes in at one end of your room, and goes out at the other, such that there is a general movement of air across the room, from inlet to outlet.

how to go about it so that I won't need to make more holes than necessary into the existing MSM system?

You will need two large holes in the wall: one for the supply duct, and one for the exhaust duct, plus another, smaller hole, for the bundle of pipes that links the two halves of your mini-split air conditioner (assuming that you are going to do it that way).

Will the room acoustics change much when I replace the windows with solid wall,

Not really. There's isn't a lot of difference between glass and drywall. There will be some change, probably but nothing important.

I suppose this is true when you have already treated room, so you place the speakers tight up against absorptive panels on front wall?

Right.

where should I put my Alesis monitors for doing REW measurements of bare empty untreated room, keeping in mind that I plan to soffit mount them?

Put them roughly where they will be in the final position once the soffits are built, AND ALSO put them up against the front wall. In other words, do two sets of tests, one against the wall, one in the final location.

Thanks once again for your time and effort, Stuart!

- Stuart -

Thank you for your answer, Stuart, I started with my HVAC research

While calculating my HVAC requirements and studying more about the topic I spent some time measuring the room and altering the design for acoustic treatment. Here are 2 sets of measurements (speakers up against the front wall + speakers at future soffit position):
https://dl.dropboxusercontent.com/u/920 ... ments2.rar

Here's a new sketch of acoustic treatment plan: I replaced the angled slot resonators on side walls with thick absorbers, as per Stuart's recommendation (also, I figured the angle wasn't steep enough to create RFZ). The whole ceiling is covered with 10cm thick insulation, also I plan to put superchunk style bass traps in the upper corners where left and right wall meet the ceiling.

Thicknesses of absorbers:
front wall - 40cm
back wall - 20cm
side wall - 20cm front part, 10cm back part

Roughly 75% of the room area is covered with absorbing material - is this roughly correct number for my room?
I realize this would make a really dead sounding room so I'd like to put plastic foil on top of rockwool to get some of the highs back into the room. How much of the absorbing area should be covered with plastic?

Regarding mids/Highs in the room - I like the look of long wooden slats on the walls as seen here:
http://www.weslachot.com/project38.html
I realize it wouldn't work as Helmholtz resonator, but would it help me get some of the highs/mids back into the room? If yes, how much of the absorbent area can be covered with wooden slats to not alter the bass response?

One more thing - how deep should the superchunk bass traps be to help tame those deep spikes between 80 and 200Hz?

Thanks a lot!

Martin

Hello guys,
I spent some time studying HVAC designs and needs for my studio and I've come up with some calculations - I would really appreciate if you'd take a quick look to see whether there are some fundamental flaws or not.

Fresh air needs:
Usually I'll be all by myself in the room, ocassionaly recording another artist. Let's say up to 4 people (that means my family watching movie there).
Our local code requires at least 20m3/h of fresh air per person, Rod Gervais states 15cfm, which is about 25m3/h, so I'll go with that. Included are values in imperial units in the brackets:

Number of people:4
Air volume exchange: 4 x 25 = 100m3/h (60cfm)
Duct diameter(round): 0,15m (6 inches)
Duct cross-section: 0,018m2 (0,2 sq ft)
Air velocity: 100m3/h : 0,018m2 = 5,6km/h (305 fpm)

I think this will get me close to the air velocity in the duct that Rod Gervais recommends in his book (<300fpm). Given that mostly I'll be there alone I'd like to have a HVAC system that can regulate the airflow betwen 25 and 100m3/h, giving me air velocity in the duct below 100fpm most of the time.

I'd like to maintain my >50db isolation so I guess I'll need duct silencers on both leaves of my MSM system.
Here's my first draft - silencers have various dimensions to accomodate available space, but clear inner cross sections are the same, about 0,034m2(close to 2x the cross section of the duct). Is it possible to have a duct silencer built "into the wall" on the outer leaf like shown in the picture? This way I could use the cavity that was occupied by 2 windows:



Now for the "AC" part of the HVAC...

Cooling needs:
Sensible loads:
Audio processing devices: 1400W
PC, TV, lightning: 500W
4 people: 600W

Total:2500W

I'm still a little lost at the whole latent loads concept. Let's say I know that average relative humidity in my town in July (when AC will be used the most) is about 70%, average highest daily temperature being about 30°C (absolute highest temperatures close to 40°C). How much additional load does this represent (given I aim for 22°C, 45%rh condtitions)?

Thanks a lot!
Martin

Construction phase is documented here:
http://www.johnlsayers.com/phpBB2/viewt ... 10&t=21539