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Question about Ceilings & Acoustics... large air gap vs extra height...
Old 4 days ago
  #1
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Question about Ceilings & Acoustics... large air gap vs extra height...

Hi, so my room is approx 6.8m x 3.8m x 2.6m high

I recently got approval to remove a false ceiling of drywall to discover an additional 1.1m of height available.

the original design was to have 3" of OC 703 floating on 1x4 slats, which rest across 2x4 sidewalls, which are approx 2.6m high...

so now that I have extra space up top, I'm considering adding approx 1m of 2x4 framing to the existing 2x4 wall construction... then having a much higher ceiling with the same idea... cloud of 3" OC 703 on 1x4 slats...

however, there are numerous difficulties (large, deep structural concrete beam running the length of the room on one side, AC/ducting to work around, maybe reposition)...

so i had the idea: what if I just keep the original plan, with the 2.6m high ceilings and a cloud of OC 703, but now I have a 1m+ air gap...

would the acoustics greatly benefit from the added wall height i'm thinking of adding, or was removing that drywall to open up the air gap enough?

of course there is the aesthetic of a nice high ceiling, the spiritual/psychological aspect... but from the point of view of the sound... is there that much of a difference?

it will really be a much more complex task to frame that extra meter of wall height... & the ceiling framing, i don't even wanna think about that!

FWIW the entire room will basically be covered with 3" OC 703, and there are pretty sizeable chunk bass traps in the front corners... the back wall will be 6" of material...

also, I am privileged to not have to worry about isolation at all, so room acoustics are my only consideration :D
Old 4 days ago
  #2
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Jason Foi's Avatar
 

Yes to gaining the extra height, but no to the 703 unless you cover the entire ceiling with a large airgap above the 703, but you might save a bit of money and get better results by filling the entire cavity with cheap fluffy fiber insulation with low GFR. Keep the faux ceiling height roughly the same, but the volume will help acoustically
Old 4 days ago
  #3
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Quote:
Originally Posted by Jason Foi View Post
Yes to gaining the extra height, but no to the 703 unless you cover the entire ceiling with a large airgap above the 703, but you might save a bit of money and get better results by filling the entire cavity with cheap fluffy fiber insulation with low GFR. Keep the faux ceiling height roughly the same, but the volume will help acoustically
thanks for the reply.

so it seems that 703 over the whole faux ceiling with a large air gap would be pretty effective... i feel it would be much easier to install rigid panels than that much pink fluffy... fabric-wise and covering it and all... I dunno... pink fluffy is cheaper, but how would i cover the ceiling slats with fabric?? just long fabric runs?? I dunno it's hard to imagine it... are there pix of anyone whose done this? i'd be interested to see how others solved this problem

what is GFR?
Old 4 days ago
  #4
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Well, using 703 you will get a boost in LF absorbtion due to a membrane effect if the entire ceiling is covered. Drop ceiling grids work great for this. With a gap of 400mm or more i believe you should be able to get absorbtion down to around 50hz more or less. With fluffy fiber around 1 meter thick and a GFR (gas flow resistivity) of around 3000-5000 you would get absorbtion as low as 20hz. You can use some sort of netting to hold everything in place and then do a cloth front.

Alternatively, a drop ceiling with acoustic tiles and the void above filled with fluffy fiber works great too.

More on GFR..
Should i Look for Density or GFR when deciding material for acoustic panels?

For more on GFR and calculating absorbtion use the forums search feature.
Old 4 days ago
  #5
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Quote:
Originally Posted by Jason Foi View Post
Well, using 703 you will get a boost in LF absorbtion due to a membrane effect if the entire ceiling is covered. Drop ceiling grids work great for this. With a gap of 400mm or more i believe you should be able to get absorbtion down to around 50hz more or less. With fluffy fiber around 1 meter thick and a GFR (gas flow resistivity) of around 3000-5000 you would get absorbtion as low as 20hz. You can use some sort of netting to hold everything in place and then do a cloth front.

Alternatively, a drop ceiling with acoustic tiles and the void above filled with fluffy fiber works great too.

More on GFR..
Should i Look for Density or GFR when deciding material for acoustic panels?

For more on GFR and calculating absorbtion use the forums search feature.
so we're talking realistically about a difference between 20hz & 50hz... but i'm pretty sure my genelecs only work down to around 40 hz anyways lol... so the difference between the two approaches seems negligible in my case

i just wish i could see pix or videos of someone doing one or both of these construction methods... i've never installed a drop ceiling before, or acoustic tiles lol

i'm in asia, where i can't just go tell them 'drop ceiling grid' or 'acoustic tiles' - i have to kinda know my stuff before i head to the industrial area to scrounge around hahaha
Old 4 days ago
  #6
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Quote:
Originally Posted by studiobuild View Post
so we're talking realistically about a difference between 20hz & 50hz... but i'm pretty sure my genelecs only work down to around 40 hz anyways lol... so the difference between the two approaches seems negligible in my case

i just wish i could see pix or videos of someone doing one or both of these construction methods... i've never installed a drop ceiling before, or acoustic tiles lol

i'm in asia, where i can't just go tell them 'drop ceiling grid' or 'acoustic tiles' - i have to kinda know my stuff before i head to the industrial area to scrounge around hahaha
Ok, pics of drop ceiling grid with acoustic tiles or 703 instead of tiles (fill void above with fluffy fiberglass/mineral wool) OR fluffy fiber with a cloth front
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Question about Ceilings & Acoustics... large air gap vs extra height...-images-2-.jpg   Question about Ceilings & Acoustics... large air gap vs extra height...-images-3-.jpg   Question about Ceilings & Acoustics... large air gap vs extra height...-inside-out-ceiling-04.jpg   Question about Ceilings & Acoustics... large air gap vs extra height...-inside-out-ceiling-06.jpg   Question about Ceilings & Acoustics... large air gap vs extra height...-inside-out-ceiling-03.jpg  

Old 4 days ago
  #7
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Quote:
so we're talking realistically about a difference between 20hz & 50hz... but i'm pretty sure my genelecs only work down to around 40 hz anyways lol... so the difference between the two approaches seems negligible in my case
Not really! The low frequency limit for your Genelecs might well be listed as 40 Hz, but that doesn't mean that they put out nothing at all from 39 Hz down. When a manufacturer states that his speakers have a range of Eg 40Hz - 25 kHz, those two numbers refer to the point where the intensity has rolled of by 3 dB, that's all. From there on down, the intensity will fall at a fixed rate that depends on the speaker design, but is commonly 12 db/octave (for ported boxes). So, if the speaker was producing, say, 75 dBC at 40 Hz, that will have reduced to 63 dBC an octave lower... which is 20 Hz! That's right: it will still be able to put out over 60 dB, way down low. If your speaker is NOT ported (sealed box), then it rolls off even slower, at 6 dB/Octave. There might also be a low shelving filter circuit built in, which can roll of faster, but even then it's unlikely to be more than 24 dB/octave

Either way, there's still plenty of energy coming out of your speaker, well below the "cut-off" frequency.

Thus, it's not negligible by any means! Take it all into account.


- Stuart -
Old 3 days ago
  #8
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Quote:
Originally Posted by Soundman2020 View Post
Not really! The low frequency limit for your Genelecs might well be listed as 40 Hz, but that doesn't mean that they put out nothing at all from 39 Hz down. When a manufacturer states that his speakers have a range of Eg 40Hz - 25 kHz, those two numbers refer to the point where the intensity has rolled of by 3 dB, that's all. From there on down, the intensity will fall at a fixed rate that depends on the speaker design, but is commonly 12 db/octave (for ported boxes). So, if the speaker was producing, say, 75 dBC at 40 Hz, that will have reduced to 63 dBC an octave lower... which is 20 Hz! That's right: it will still be able to put out over 60 dB, way down low. If your speaker is NOT ported (sealed box), then it rolls off even slower, at 6 dB/Octave. There might also be a low shelving filter circuit built in, which can roll of faster, but even then it's unlikely to be more than 24 dB/octave

Either way, there's still plenty of energy coming out of your speaker, well below the "cut-off" frequency.

Thus, it's not negligible by any means! Take it all into account.


- Stuart -

so it sounds like 1+ meters of pink fluffy stuffed above my 2.6m framing is the way to go...?

it's just hard for me to believe that extra room volume is not as effective as, or less preferable than, extra fluffy above... but if that's what the science says i'll have to believe it...

any difference between fabric vs acoustic tiles as a covering?

should there be a layer of 703 (how thick?) then the pink fluffy? or just the pink fluffy...?
Old 3 days ago
  #9
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Quote:
Originally Posted by Jason Foi View Post
Ok, pics of drop ceiling grid with acoustic tiles or 703 instead of tiles (fill void above with fluffy fiberglass/mineral wool) OR fluffy fiber with a cloth front
thanks!! now... can you come build it for me?? hahahaha :D
Old 3 days ago
  #10
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Quote:
Originally Posted by studiobuild View Post
thanks!! now... can you come build it for me?? hahahaha :D
Sure, i've always wanted to visit asia! Where do i send the invoice?
Old 3 days ago
  #11
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Also, if it were my room, i would do just a full fluffy fiber fill. I dont really see a bennifit to the extra layer

Blue line is full fluffy fiber, green is with 703 on the front. This calculator doesnt account for the membrane effect, so green should be a little better in reality, but i dont think it will be substantial enough to justify the cost.
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Old 3 days ago
  #12
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Quote:
Originally Posted by Jason Foi View Post
Also, if it were my room, i would do just a full fluffy fiber fill. I dont really see a bennifit to the extra layer

Blue line is full fluffy fiber, green is with 703 on the front. This calculator doesnt account for the membrane effect, so green should be a little better in reality, but i dont think it will be substantial enough to justify the cost.
a meter of pink fluffy it is lol

if it were your room, what would you go with in terms of acoustical tile? i'm worried about reflections, etc

or would you just do fabric?


also: since i can't just say 'pink fluffy' here, how should i look/shop for that over here? when i was searching for equivalent of OC703 I told them 48kg/m^3, etc... any kind of equivalent generic term i might use to describe pink fluffy to someone who doesn't speak much english? lol. does it have to be fluffy or can it be batts? i'm new to all this... i've only ever used rigid fiberglass treatment
Old 3 days ago
  #13
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Quote:
Originally Posted by studiobuild View Post
a meter of pink fluffy it is lol

if it were your room, what would you go with in terms of acoustical tile? i'm worried about reflections, etc

or would you just do fabric?


also: since i can't just say 'pink fluffy' here, how should i look/shop for that over here? when i was searching for equivalent of OC703 I told them 48kg/m^3, etc... any kind of equivalent generic term i might use to describe pink fluffy to someone who doesn't speak much english? lol. does it have to be fluffy or can it be batts? i'm new to all this... i've only ever used rigid fiberglass treatment
I would just do a fabric front. No need for a higher impediance layer.

This is what i mean by fluffy fiber

https://www.homedepot.com/p/Owens-Co...RU71/202689769
Old 3 days ago
  #14
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Quote:
Originally Posted by Jason Foi View Post
I would just do a fabric front. No need for a higher impediance layer.

This is what i mean by fluffy fiber

https://www.homedepot.com/p/Owens-Co...RU71/202689769
that stuff is 9" thick... so for an ~43" cavity, that would be roughly 4-5 layers of R-30?!? that seems like overkill....?

i'm still not understanding why it's not better to raise the actual height of the room... sorry if i'm being thick... (ha! pun)

edit: so at four layers, ~280 sq ft, 48 sq ft coverage per roll, then it would take approx. 20-24 rolls of this stuff... am I missing something??
Old 3 days ago
  #15
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Quote:
Originally Posted by studiobuild View Post
that stuff is 9" thick... so for an ~43" cavity, that would be roughly 4-5 layers of R-30?!? that seems like overkill....?

i'm still not understanding why it's not better to raise the actual height of the room... sorry if i'm being thick... (ha! pun)

edit: so at four layers, ~280 sq ft, 48 sq ft coverage per roll, then it would take approx. 20-24 rolls of this stuff... am I missing something??
9 inches thick, yes, 4 layers is 36 inches. Perfect, and it is not over kill if you want decent absorbtion down to 20hz. (I would also do the same for the back wall).

By removing the sheetrock you ARE raising the height of the ceiling acoustically. Your height axial mode is still going to need treating, and sound waves dont see the cloth front, they see rigid boundaries.

If thats the math that's the math.
Old 3 days ago
  #16
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Quote:
Originally Posted by studiobuild View Post
... am I missing something?
Possibly. When I made my superchunk traps with similarly light fluffy mineral wool, I was using 15cm (6") thick wool and calculated how many layers I would need to fill the neight. To my dismay, light fluffy piled on light fluffy piled on light fluffy, and so on, meant that the whole pile squidged down to approximately 3/4 of the height it should have been. Let Jason and the others advise you properly but to avoid compacted light fluffy, creating a frame to provide fresh, solid support at half height might help.
Old 3 days ago
  #17
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Quote:
i'm still not understanding why it's not better to raise the actual height of the room... sorry if i'm being thick... (ha! pun)
The acoustic response of your room is mostly related to the volume of air inside it. The more volume you have, the better response you can expect. With caveats, of course. There is still a need for a reasonable relationship between the three dimensions (L, W, H). So a concrete pipe 65m long and 1m in diameter is going to have terrible acoustics, while a room measuring 6m x 3.5m x 2.6m is going to have decent acoustics, even tough they both have the same volume of air! But in your case, the extra air volume is very useful.

- Stuart -
Old 3 days ago
  #18
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Quote:
Originally Posted by Starlight View Post
Possibly. When I made my superchunk traps with similarly light fluffy mineral wool, I was using 15cm (6") thick wool and calculated how many layers I would need to fill the neight. To my dismay, light fluffy piled on light fluffy piled on light fluffy, and so on, meant that the whole pile squidged down to approximately 3/4 of the height it should have been. Let Jason and the others advise you properly but to avoid compacted light fluffy, creating a frame to provide fresh, solid support at half height might help.
Right! 3 or 4 small shelves part way up the height of the unit can help with that. If the fiber is down to 3/4 of it's nominal thickness, that also means that it is compressed considerably, so the density has changed! And therefor also the GFR. The average compression is 25%, yes, but it's far more compressed at the bottom than the top. Maybe 50% (guessing... too lazy to do the math...) So the acoustic properties have also changed. Using shelves minimizes the compression.

This is why semi-rigid insulation is better, if you can get it where you live, since it won't compress in the same way as light fluffy insulation does.

- Stuart -
Old 3 days ago
  #19
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Quote:
Originally Posted by Starlight View Post
Possibly. When I made my superchunk traps with similarly light fluffy mineral wool, I was using 15cm (6") thick wool and calculated how many layers I would need to fill the neight. To my dismay, light fluffy piled on light fluffy piled on light fluffy, and so on, meant that the whole pile squidged down to approximately 3/4 of the height it should have been. Let Jason and the others advise you properly but to avoid compacted light fluffy, creating a frame to provide fresh, solid support at half height might help.
Yes, or roll it out on it’s edge/side. It’s surprisingly strong as long as it’s supported or squeezed in sufficiently!
Old 2 days ago
  #20
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Quote:
...or squeezed in sufficiently!
As long as you don't squeeze it too much: compressing insulation changes the density, and also the GFR, which affects the acoustic performance. A little "squeeze" doesn't do much harm, but over-compressing it can do things you were not expecting...

- Stuart -
Old 2 days ago
  #21
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Quote:
Originally Posted by Soundman2020 View Post
The acoustic response of your room is mostly related to the volume of air inside it. The more volume you have, the better response you can expect. With caveats, of course. There is still a need for a reasonable relationship between the three dimensions (L, W, H). So a concrete pipe 65m long and 1m in diameter is going to have terrible acoustics, while a room measuring 6m x 3.5m x 2.6m is going to have decent acoustics, even tough they both have the same volume of air! But in your case, the extra air volume is very useful.

- Stuart -
Yes, I understand that extra volume is better acoustically. What I'm having trouble wrapping my head around is (keeping the numbers simple) that I'm being told an 8 ft ceiling height with 4 ft of insulation is better than, say, a 10 ft ceiling height with 2 ft of insulation, or 11 ft with 1 ft of insulation.... sure, that's less insulation to absorb low frequencies, but it's also a larger room dimension, so there are not as many room mode problems since the very long low frequency waves have more space to travel before reflecting back, right?

at some point, doesn't the height of the actual room trump the amount insulation up top? for example if I had a 20 ft clearance i don't think an 8 ft ceiling with 12 ft of insulation above it would be as effective as a 16 ft ceiling with 4 ft of insulation above it... or maybe it would? you see what i mean? i'm sure it's a trade-off of ceiling height vs. insulation depth, but how and why and where that point is, where the optimal trade-off point is, is what's confusing me lol

PS at this point this is purely a theoretical concern for me, i'm most likely gonna take the advice here and do 8 ft ceilings with 3-ish ft of insulation above- just trying to understand WHY i'm doing that lol thanks so far everyone i'm learning a lot in this discussion
Old 2 days ago
  #22
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Quote:
Originally Posted by studiobuild View Post
What I'm having trouble wrapping my head around is ... but it's also a larger room dimension
It is quite simple, really, as the room's dimensions are to the hard surface, not to the start of the insulation. How much or little insulation you install does not change the hard boundaries and therefore the room's dimensions.
Old 2 days ago
  #23
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Quote:
Originally Posted by Starlight View Post
It is quite simple, really, as the room's dimensions are to the hard surface, not to the start of the insulation. How much or little insulation you install does not change the hard boundaries and therefore the room's dimensions.
Ah, ok, so the room modes are the same regardless of insulation depth, they're defined by hard surfaces only, that makes sense... acoustically, an 8 ft ceiling with 4 ft of insulation will behave like a 12 ft ceiling... so might as well put the insulation in to get extra absorption... I think I get it now. In school I was great at math but horrible at physics lol
Old 2 days ago
  #24
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Room modes are caused by a wavelength not fitting within a boundary. 45hz for example is over 24 feet long, so unless your room is BIG you are going to deal with room modes, and there will never be a point where you dont need acoustic treatment in a control room. In order to absorb low frequencies it takes low density/GFR insulation and lots of depth. In theory, you have 100% absorbtion at 1/4 wavelength from the boundary, but in reality, you still see fantastic results at 1/8 wavelength. Ok, so knowing this you could see that it would take a bass trap over 12 feet thick to completely absorb 20hz. Now nobodys saying to make your traps 12 feet thick, and luckily 2 to 4 feet thick over a large area does a pretty good job. If budget won't allow for a full fiber fill (which is better), then leaving an airgap behind the fiber is advised. So full 36 inches of fiber or 9 inches of fiber with 27 inches of air behind it, the important thing is depth. Most people treating their rooms ignore that and use thin fiber with little to no airgap. This results in full absorbtion from mids up and little effect to the low end (where ALL the problems are). Its a waste of time and money.

And just for fun... on your statement of a 8 foot ceiling with 4 feet of insulation acts like 12. A cloth front is not the ceiling. A rigid boundary is. If the actual ceiling is 12 feet and you place 4 feet of insulation on the ceiling, acoustically, your ceiling is higher than 12 feet. The speed of sound is slower in insulation so acoustically speaking, the wavelengths "see" a larger room.
Old 2 days ago
  #25
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Quote:
Originally Posted by Jason Foi View Post
If the actual ceiling is 12 feet and you place 4 feet of insulation on the ceiling, acoustically, your ceiling is higher than 12 feet. The speed of sound is slower in insulation so acoustically speaking, the wavelengths "see" a larger room.
mind, blown. hahaha
Old 2 days ago
  #26
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Quote:
8 ft ceiling height with 4 ft of insulation is better than, say, a 10 ft ceiling height with 2 ft of insulation, or 11 ft with 1 ft of insulation.... sure, that's less insulation to absorb low frequencies, but it's also a larger room dimension,
All three of your examples refer to the exact same size room. In all three cases, the room is 12 feet high. There's no difference there.

- Stuart -
Old 2 days ago
  #27
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Quote:
In theory, you have 100% absorbtion at 1/4 wavelength from the boundary, but in reality, you still see fantastic results at 1/8 wavelength.
... There's also usable absorption down to 1/16 wavelength for normally-incident sound, and 1/32 wavelength for randomly-incident sound...


Quote:
The speed of sound is slower in insulation so acoustically speaking, the wavelengths "see" a larger room.
Right! Putting very thick absorption in a room usually does bring down the modal frequency slightly, in addition to damping the ringing and smoothing out the level. It's exactly the same as putting absorption inside a resonant device: it damps the resonance, lowering the Q and the effective F0. Because, when you think about it, a mode in a room is really just resonance inside a resonant system... ... and a bass trap is just damping inside that resonant system.

- Stuart -
Old 2 days ago
  #28
Gear Maniac
 

I like the idea of a drop ceiling grid. There are a number of products for those. Some are basically 703 with a fabric face. You can intersperse with grid diffusion panels. Add extra fluffy above where you want. Change acoustics, have a diffused live area etc just by moving the panels Also gives easy access to anything up there that might need maintenance or repair at some point. Plumbing, HVAC, electrical etc. Nothing worse than having to tear up a finished ceiling to fix a drip or add a circuit or audio line.
Old 2 days ago
  #29
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Quote:
Originally Posted by tymish View Post
I like the idea of a drop ceiling grid. There are a number of products for those. Some are basically 703 with a fabric face. You can intersperse with grid diffusion panels. Add extra fluffy above where you want. Change acoustics, have a diffused live area etc just by moving the panels Also gives easy access to anything up there that might need maintenance or repair at some point. Plumbing, HVAC, electrical etc. Nothing worse than having to tear up a finished ceiling to fix a drip or add a circuit or audio line.
What are grid diffusion panels and are there any design specifications for building them? I think I have an idea of what you're referring to but I have no experience with those..

diffused live area just by moving the panels? you mean the grid diffusers right? i can see how a modular type of set-up would be convenient, although more work upfront to install for sure

I read somewhere on here that drop ceiling systems can tend to rattle like hell, maybe I misunderstood

I ought to mention this room will be a combo room. Will be for mixing on the speakers but also for headphone overdubs (vocals, acoustic guitars, percussion, potentially a full band DI'd and on headphones, but for the drums)
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