Designing a mix room

Hello What a great find you folk are… I've been dipping in and out of this forum for about a year now. And early on, it led me to Rod Gervais's Book, 'Home Recording Studio', and to Sketchup, which has tested my resolve, but I think I'm getting the hang of it. I'm located in Warwickshire, England and I've been recording material here and there for the last 5 years. However, I've come to the point where I want to mix it properly- and therefore I need to hear what's actually going on. My aim is - if this does not sound too ambitious - to house a 48channel mostly-analogue setup in a small hut to mix in as near-acoustic perfection as is possible. The setup includes approximately 48u of rack gear and a mid-sized 32channel analogue desk, and I'd like to maintain enough space (and even better, if possible a big enough sweet spot) for two people to sit side by side during mixing. Therefore, I have the building attached (see Sketchup file), and a budget of £2000. I'll be doing most of the work myself, although I have a carpenter I can call on. The building is the last third of a wooden hut, located 50yds from the nearest house. The construction is entirely wooden, using 15mm wooden slats on a frame. The floor is concrete, and it has a corrugated roof that isn't metal (I'm not sure what it is made of). We've tried using it before for listening back to stuff over a pair of monitor speakers, but without any treatment. Unsurprisingly it sounded pretty dreadful, but I was able to establish that we aren't bothering anyone with noise. The other two thirds of the building are used by a company supplying vinyl via mail order- it is stacked floor to ceiling, but aside from 2 hours a weekend there is never anybody there. If they ever vacated, I'd want to use it myself (I have too many organs cluttering up my recording space). Therefore I don't need any extra isolation (which is probably a good thing with wooden construction). However, it does get very cold in the winter, so I will need some insulation to keep it warm! A few questions to start off with: 1 I have read a lot about acoustic treatments in an existing bricks-and-mortar (or stud frame) room- but I am left fairly clueless as to what to do with a 1-skin wooden frame. Should I just insulate it and plasterboard, or is there a way of taking advantage of the fact that they are thin and of relatively little mass? 2 The ceiling is just the bare inside of the corrugated roof at the moment. It did have a flat false ceiling, but this rattled and brought the level down to less that 2m, so I removed it. I will install a cloud above eventually, but does it matter how I insulate and finish the roof? I'd like to follow the apex if I can, to make the ceiling as high as possible. 3 Slightly ahead of myself at this point, but would a carpet or a hard floor be better? 4 The dimensions of the room at the moment (admittedly guestimating the ceiling measurement at 2.3m) are H:2.3 W:3.43 L:3.48. This gives me a ratio of 1:1.56:1.58. On page 29 of Rod's book, he refers to 'known good ratios' of room. If I've got my maths right, (kudos to my little brother who's doing an engineering degree for his help here), if I was to bring in the ceiling down a little and the left hand wall in (as per the Sketchup file), I could get very close to Sepmeyer's 2nd ratio of 1:1.28:1.54. It would also solve the symmetry problem, as one window would be covered up, and give me somewhere to recess all that bulky gear. Is this a good idea? 5 On a more general note, when calculating these things and the associated acoustics (and therefore when it comes to translating diagrams to reality) how accurate does one need to be? Millimetre accurate? Or is to the nearest 10-20mm ok? Any thoughts and expert wizardry greatly appreciated. :D P.s. I've put the roof, walls and roof beams on separate layers of the sketchup file to make it easier to work with.

welcome! and nice introduction! for a quick response: keep the hard floor. if you don't need a lot of isolation, then allowing sound to escape will help with the treatments but you have to consider outside noises interfering with your work... but isolation isn't a primary issue, then a single layer of drywall all around on the inside and proper insulation and moisture sealing should be a good start. i'd have someone verify the building integrity to ensure you can add all the necessary mass - drywall, absorbers, electric, etc. you will want to factor in ventilation if not heat/cooling. most times a isolating ventilation system and a split unit heat pump for heat/ac should do it. LED track (or equiv) lighting. electrical mounted on the inner wall surface. any windows or doors should be decent enough to meet your isolation needs and seal well. what type of monitors do you have? it would help to understand all the equipment in terms of model # s owe can determine an appropriate layout.

At the moment I'm using Mackie HR824's, which I'm hoping to soffit mount (I've been reading up on this elsewhere on this forum). I'm using hard disk recorders- Mackie HDR's- and a Soundtracs Solo Logic 32 desk. Here's a jpeg of my sketchup file, with the roof removed Is a wall where I've proposed a good idea? Or am I just wasting space? I'm working on a design which I'll post shortly, but I just need to know I'm not barking up the wrong tree!

Why do you want to put that wall there? It seems to me you are wasting a lot of space like that, unless there's a really good reason for doing so! - Stuart -

"W:3.43 L:3.48." Yes you should most likely look into installing an additional wall since your room is almost a square. The next issue that will arise is that the symmetry the roof once had, e.g. the center of the ridge was first directly over your head, it will now be offset over your right shoulder. Building an overhead cloud should help correct this sonic impediment. An alternative would be to construct a wall on either side to alter the shape and keep the center line o the roof directly overhead there by improving the isolation, at least in the areas where your ears are. And then an overhead cloud would be installed center on the room. The thing is, I think Glenn touched on this, is that the external environment, weather, rain, wind, etc. can beat on that roof and make noise on a regular basis. I assume there is no ventilation in this existing structure so the addition of insulation's can change the dynamic of how this room interacts with the existing climate since it is more than likely a very porous or air accessible structure which allows this movement of air/heat in and out. Once you close these small access areas up, the building will find other ways to convert the heat or cold and find ways to escape. Maybe insulating the roof, making certain you have roof venting for heat to escape and installing 16mm fire rated sheetrock would eliminate some of the heat exchange on the interior.

Many thanks for the replies so far- you've given me a lot to think about! I'll respond to your posts one at a time, to make sure I don't miss anything important. Gullfo- There isn't much isolation required. The windows are double-glazed sealed units with wooden frame, and the door appears to be solid wood, so I think I'm alright on that score. Ventillation and aircon/heating I'm quite concerned about- previous neglect of this in past venues (not necessarily by me) has resulted in horrors such as extreme humidity (not good for the gear) and mouldy walls. I'm keen to prevent this! Stuart- It's not entirely wasted space, as I would recess the equipment like this: (The big omission from this diagram is soffit mounting the monitors). The equipment racks are those I'm using already. If I can use them again- win! (Less cost and less work). I also have a 24u steel rack- but wherever you put it it's too tall and reflects high frequencies, so it's in storage at the moment. Unless anyone can see a genius way of using it that gets around this, I think it'll stay that way. Another advantage is that I would leave a gap in the left hand wall the exact height of the racks- then when it's time to wire it all up or change/maintain anything I can pull them forwards into the room and get in behind (I was thinking of having a door or removable panel in the false wall at the rear of the room). Also it would give me a space to store those extra flight cases, bass cabs, etc . xSpace- Would a false ceiling as I've demonstrated work? There is currently a supporting beam (shown in the sketchup file) in the way of this on one side- I'll ask the carpenter if this can be moved or removed entirely (the roof isn't attached to it). I will put a cloud in, but I need to maintain as much height as possible. While the idea of bringing both walls in an equal amount would be simpler for the ceiling, it does then render the reduced width as 'dead space'. External weather noise is, I think, pretty much unavoidable- but thankfully noisy weather (heavy rain/hail/strong winds) are relatively rare in these parts. Your last point, which ties in with Gullfo's, is what concerns me most- providing heating/cooling and ventilation, preventing inside getting excessively humid, hot or cold. After all, hopefully folk will be spending some serious lengths of time in there. I fear I'm lacking in enough basic builder knowledge to be confident in a solution on this point. Advice appreciated. One further related question- The previous tenant had got halfway through lining the walls between the wooden frame with polystyrene, then screwing 6mm ply in front of that. If I'm only aiming to keep the warmth in, and let the sound through, could I finish what he started (at least with the polystyrene)? Or am I better sticking with my original idea of removing it all and replacing it with rockwool? Thanks again in advance...

Would a false ceiling as I've demonstrated work? There is currently a supporting beam (shown in the sketchup file) in the way of this on one side- I'll ask the carpenter if this can be moved or removed entirely (the roof isn't attached to it).

Saw the sketchup , don't see enough to make a prediction on what may or may not happen. Obviously making a decoupled assembly in this roof is better than the single sided assembly it is now. But...we still have to address the hvac/air con/ extraction requirements and the placement of those might require a vaulted decoupled interior roof assembly.

I will put a cloud in, but I need to maintain as much height as possible. While the idea of bringing both walls in an equal amount would be simpler for the ceiling, it does then render the reduced width as 'dead space'. External weather noise is, I think, pretty much unavoidable- but thankfully noisy weather (heavy rain/hail/strong winds) are relatively rare in these parts.

Well, it renders some aspects of this build mass/air/mass, and that is a requirement for isolation, but you did already say it was not a requirement for you, isolation that is. But still the same, balance is an enviable thing, and you have opportunity to meet it up straight rather than learn the difference of how one cavity of some depth versus another cavity of marginal depth will compete for your ears in different frequencies.

Your last point, which ties in with Gullfo's, is what concerns me most- providing heating/cooling and ventilation, preventing inside getting excessively humid, hot or cold."

That requires mechanical heating and air guys that are informed of what you want...and that come to you from a trusted source.

Hi, Listen to Xspace! His advice is sound. Think about it this way. Right now you have the opportunity to build in a way that makes increasing your isolation at a future point possible if you want or need it. From the way your plans are taking shape you may as well build room inside room. If you frame strongly enough to support a second layer of drywall, frame for a second door, surface mount the electrical boxes etc.... You may never need the isolation, may never need a second layer of drywall, may never need a second door.... but if you decide it would be useful to track the odd overdub....if you find the sound of rain pattering against the roof distracting.... At this point the extra cost would be negligible, I would seal up the exterior walls at this point too. Also remember, as Xspace pointed out, that the biggest thing about good ratios is low end frequencies. Now low end frequencies are going to cut right through a thin wall, to a degree. To how much of a degree and what it will do to the freq graph of your thin walled well dimensioned room... I'll leave that to smarterer men than I, but it certainly will have an effect on the room. If you go with your original plan of putting a big hole in the wall to hold gear.... What is more important to you, good sound or storage? Steve

...balance is an enviable thing, and you have opportunity to meet it up straight rather than learn the difference of how one cavity of some depth versus another cavity of marginal depth will compete for your ears in different frequencies.

Good point number 1.

What is more important to you, good sound or storage?

Good point number 2. Definitely good sound. Rethinking my design here...

From the way your plans are taking shape you may as well build room inside room.

While I would love to do this, my constraint is the length of the room - the shorter it is, the lower the ceiling. I can't see how I would: A) build a room within a room without losing at least 20cm. This corresponds with a loss of 13cm in height. B) build said room without either blocking off the rear window (which I'd rather not do), or compromising the isolation around the window. Any thoughts on this? Meanwhile, here's some photos of the room at the moment: I'm just shrinking and tidying up my sketchup file, I'll post my new design tomorrow... thanks for the feedback so far folks :mrgreen:

Ok, first things first, I've attached a new sketchup file. I've removed the outside walls and the roof- which has made the file much smaller. I'm looking into aircon - hoping to get somes quotes and advice on the system John mentions in his thread here for starters http://www.johnlsayers.com/phpBB2/viewtopic.php?f=1&t=15724 Looks like it will do ventilation, dehumidifying, heating and cooling. So to my new design - I've started by lining the walls with gypsum (sheetrock? plasterboard? all the same thing I think, so I'll call it gypsum from now on). The back (internal) wall I think I'll have to put a layer of stud behind as the wood is fairly irregular. This does lose me a few vital centimetres length though! The windows have no sill, so I'll be able to board right over the one opposite the door. Next idea - build a stud wall frame inside that meets the end walls, but is independent of the side wall and ceiling, like this: I could do this with a flat roof like this (top view): or follow the apex of the ceiling like this: A flat ceiling would mean I can keep my proportions almost perfect, but would mean that by the time I've got a cloud in there, tall people are in danger of banging their head. An apex gives a little more headroom- but I don't know what effect this will have acoustically, or for that matter, how I would then calculate 'height'- the top of the apex? The average height? Or the lowest point? Half of me still thinks I'm missing something obvious and I'll have to start again... feel free to let me know what...!

you could (should) go with the apex approach. if the structure can handle it, maybe isolation clips and furring strips/hat channel will preserve more height with slightly less isolation.

Right. I've taken the plunge, and called in a professional builder. He's done in a week what would have taken me months - built me a ventilated room to my specifications to work in. HVAC is sadly outside of my budget, so I'm relying on his expertise and natural convection. Many thanks for the help so far, reading back through this thread I realise how far my design has come from where I started, even though it's relatively simple. Also, I feel I must reiterate at this point - I am not aiming for any soundproofing at all. It is simply not necessary or within my budget. The only requirement is for the acoustics to be as good as possible, and the room to be comfortable all year round. So here's what I have so far:I've brought both walls in the same amount each side, blocking off the side widow. This gives me a room that is almost perfect Sepmeyer 2 dimensions (see further up this thread). I've lined the roof following the apex, to maintain as much height as possible. The polystyrene has gone, and I've lined the three outside walls with Rockwool insulation for warmth (standard 150mm loft insulation reclaimed from my previous premises). The internal walls are then constructed of 9mm gypsum on a stud frame. I have one concern with what I've done so far - I have used 9mm gypsum as it was what the builders' merchant had on the day I had a van available, BUT I was reading the other day (although typically I can't find it now) that 9mm plasterboard is unsuitable due to its resonant frequency. Is this true? Am I doing ok so far? :roll:

I'm trying to understand here: Is isolation not important for this studio? Was the only purpose here to just get a "good ratio"? If isolation is important, then how come the new side walls are tightly coupled to the existing end walls? Major flanking going on there! And how come there are no new end walls? Without building those, the overall room isolation will not have changed much at all. Trying to isolate a room by only building two side walls is about as effective as trying to build an aquarium by only putting glass on two sides...

The internal walls are then constructed of 9mm gypsum on a stud frame.

:shock:

BUT I was reading the other day (although typically I can't find it now) that 9mm plasterboard is unsuitable due to its resonant frequency. Is this true?

Yes it certainly is true. 9mm is WAY too thin to be useful for isolation. Very flexible, very low mass, very high resonant frequency... They ONLY recommendation you'll see here is for 16mm drywall, since anything less isn't that useful, for isolation. But once again, looking at that SketchUp, it seems like isolation isn't important for this build. - Stuart -

Isolation is not important at all. I'm 30 yards from the nearest house, 30 yards from the nearest road, and the room will only be used to mix material that has been recorded elsewhere. I've just gone in there and done an iPhone-decibel measure (probably not that accurate, but good as a guide) - and the average reading is 45db. Being basically a control room without the adjoining studio, it will have plenty of gear in there as well, which means there is no point in making it any quieter - the recorders have cooling fans which will add a few db while we're working anyway. My only concern is if the resonant frequency of the gypsum will affect the acoustics of the finished room.

Thanks for your response Stuart - and sorry if my previous response was a little abrupt. You've got me thinking... Am I missing something here? When we use the term 'Isolation' are we just talking about what the layman (and me accidentally in previous posts) would refer to as 'soundproofing' - i.e preventing sound inside getting out, and vice versa? Or is there another aspect I'm missing? My room is to be used for mixing. I want sound reproduced as accurately as possible for this purpose. There's nothing loud outside to bother me, and nobody out there telling me to turn it down. Therefore, the room I have (so far) is designed with one priority in mind: acoustics. The fact that my walls have low mass was not a concern to me. Page 136 of Rod's book, the 1st page of chapter 8, states - "In fact, a lack of sound isolation will probably help you in this regard, because the more sound that escapes the room, the fewer problems you will have relating to modal issues." Please comment! I need to know if what I've done so far is going to cause any problems before I move on and do any more! If I've messed up, I'd rather put it right now... it's less expensive that way... :|

When we use the term 'Isolation' are we just talking about what the layman (and me accidentally in previous posts) would refer to as 'soundproofing' - i.e preventing sound inside getting out, and vice versa? Or is there another aspect I'm missing?

That's it! Just keeping sound in or out. That's all that isolation means.

There's nothing loud outside to bother me,

No wind? Rain? Cars arriving/leaving? Airplanes flying overhead? Trains? Radios playing? TV's? People talking? Dogs barking (or other animals)? No machinery? Nobody using water in the building? Flushing toilets? Microwave ovens? Vacuum cleaners? Telephones ringing? etc. Those are things that many people don't think about as being potential issues that could disturb their mixing sessions. Even out in the middle of nowhere, with no road in sight, you can still get noise from the weather, and from other things.

Page 136 of Rod's book, the 1st page of chapter 8, states - "In fact, a lack of sound isolation will probably help you in this regard, because the more sound that escapes the room, the fewer problems you will have relating to modal issues."

Yep. Very true. So we'll assume you are OK with all of the above, and are fine on isolation. I guess we just get hung up on isolation issues a lot here, since that's where most people run into problems with their designs.

I need to know if what I've done so far is going to cause any problems before I move on and do any more!

If isolation is not an issue, then you seem to be doing OK! :) The issue that I'm still concerned about is the thin drywall over those deep cavities. I haven't done the math yet to figure out what frequency that works out to, but you might have resonance issues there. Anyway, which way are you planning to orient your room? Are going to have the window at your back, or are you going to face the window? Orienting the room with the window behind you gives you better possibilities at the front of the room for doing proper soffits, and getting your geometry right, but leaves the rear hard and reflective. Doing it the other way around gives you a nice large rear wall for bass trapping, but makes it harder to do the front end. Maybe you can sketch out roughly what you have in mind, in terms of layout inside the room? Just mark in your proposed position of desk, chair, speakers and initial treatment, and we can comment on that. - Stuart -

Thanks for your quick reply. **Breaths sigh of relief I don't have to start again** :wink: The window will be behind me - I want to get the soffits right. I have a first draft design, which I'll tidy up and post later this week.

The issue that I'm still concerned about is the thin drywall over those deep cavities. I haven't done the math yet to figure out what frequency that works out to, but you might have resonance issues there.

How do you work this out? And if it is an issue, will increasing the mass of the side walls by adding another layer of gypsum help? Here's my first draft design for soffit mounting and arrangement. At this point I'm just aiming to get the layout right; details of construction I'll work out later. To summarise: The speakers are at a 75 degree angle, indicated by the red triangle. This is a compromise; 60 degrees left them either too close together or the sweet spot ending up in the centre of the room. 90 degrees left the sweet spot too small for two. As it is, the tip of the triangle is at 38%, with the other two points aligning with the inside edge of the speakers. The side walls are splayed at 6 degrees. The equipment racks are recessed into the walls (I'm not sure if this has any acoustic implications - discussion welcome). The screen is angled down by a few degrees, to ensure it isn't parallel with the window. I'm thinking of installing a big one as shown, because I think I'll probably end up editing video as well as audio in there. I will also add a cloud and at least some bass trapping, but I haven't got that far yet. Expert opinions, as always, welcome

Right, I've now got a much more detailed design, for the soffits at least. Things are really starting to move... I have my trusty builder free to resume work later this week, and I've been blessed with funds to double my budget :shock: However, this raises the stakes somewhat - I can't make a mess of it now! Here's a picture of where we are now Nice to have the desk and speakers back on the go, they've been stored for a while. I've just had the power supply for the desk reconditioned, and it sounds ace. Quieter (less noise), and crisper with a tighter low end. Can't wait to hear it in a finished room! Anyway, back to the task in hand...

The issue that I'm still concerned about is the thin drywall over those deep cavities. I haven't done the math yet to figure out what frequency that works out to, but you might have resonance issues there.

There's enough drywall left to add a second layer to the side walls - bonding them with something non-hardening. This should hopefully prevent any resonance issues. Is there any need to do the same to any of the other walls or the ceiling? If so, then now's the time to do it... I've borrowed most of the detail for my soffit design from Dynamike's project here http://www.johnlsayers.com/phpBB2/viewtopic.php?f=2&t=8205 - he has the same monitors as me and the room is a similar width. (Thanks Dynamike) Here's some detail The sketchup file is here I'm feel I'm going out on a bit of a limb having the speakers at 75 degrees, as I haven't found anyone else on here using that angle... but it is halfway between 60 and 90, and seemed a reasonable compromise given the limited length of the room, and wanting to retain a reasonably wide sweet spot (wide enough for two people if possible). 60 degrees would put me halfway back, pretty much sitting on the 50% line, and around 90 degrees would make for a very small sweet spot. Also, as the ceiling is quite low, the centre of the speakers is not far off 50% between floor and ceiling (although they are 30mm too high in the sketchup - I've not had time to correct that yet). It's not dead centre, and I'm hoping that as my ceiling is not parallel to the floor, it won't be too much of an issue... I'm still to design and add a cloud, and bass trapping to the rear wall, and I'm considering slot resonators above the equipment racks - though I need to do more research and learn a bit more about them before I can get any further with that. I'm also sorting out some pictures to begin a construction diary - it might take a me few weeks, but I want to get it up there, particularly as Dynamike's thread was so useful to me. Please comment! I'm on my own here, my builder is trustworthy and interested enough to do things the way I want, but I'm the one calling the shots - which is kinda scary as I've never done anything like this before! :mrgreen:

OK, now you REALLY got me confused! You seem to have THREE leaves in you wall! Either that, or I'm not understanding the photos and drawings. Just to clarify, in the photo of the room that you posted above, with the console and speakers in it, the side walls seem to be splayed. So what are we looking at there? Is it the RED wall in this diagram, or the BLUE wall? If we are looking at the red wall, then does the blue wall also exist behind it? That needs to be clarified before anything else... -----

The speakers are at a 75 degree angle, indicated by the red triangle. This is a compromise; 60 degrees left them either too close together or the sweet spot ending up in the centre of the room. 90 degrees left the sweet spot too small for two. As it is, the tip of the triangle is at 38%, with the other two points aligning with the inside edge of the speakers.

Just to clarify here too: the apex of the triangle should NOT be at 38% of the room depth! Your EARS should be at 38% of the room depth, and therefore the apex of the triangle will be several inches behind your ears, and therefore also several inches behind the 38% mark. In any case, 38% is just a guideline: it isn't a law!

The side walls are splayed at 6 degrees.

That's what I'm confused about. See above, on the red-wall/blue-wall question...

The equipment racks are recessed into the walls (I'm not sure if this has any acoustic implications - discussion welcome).

It probably does, yes, but since you didn't show those on the original plan, or in the photo, it is impossible to way what the effect will be.

There's enough drywall left to add a second layer to the side walls - bonding them with something non-hardening.

You cannot glue layers of drywall together! That isn't safe. Sooner or later it will star falling apart. Drywall has to be nailed or screwed to the studs, always, no exceptions. Glue is not an acceptable way of mounting drywall. If you want to add a second layer, then you have to use longer screws, to ensure that they actually do penetrate into the studs correctly. Which brings me to another point of confusion: In the photo of the room (above), it looks like we are seeing the bare, unpainted outer face of the drywall: I see what looks like the places where you caulked the seems, which is good... but I don't see the nail heads, or screw heads! How is that drywall attached to the studs? :idea: :shock: You DID nail it or screw it to the studs, didn't you? Also, why are we seeing text printed on the drywall? The text is normally printed on the REAR face of the drywall, so it should never be visible in the room: Did you put the drywall in backwards? :shock: Or is there another reason why that text is visible? Also, it's hard to be sure from the photo, but there seems to be a large gap under the drywall on the front of the room: Just behind the base of the left speaker stand, there seems to be a very big gap under the edge of the drywall. Is that correct, or is it just an optical illusion? - Stuart -

Phew! I've had a few days off to focus on this. Now I've stopped and re-read everything, I think I was panicking a bit. 'Headless chicken syndrome!'

So what are we looking at there? Is it the RED wall in this diagram, or the BLUE wall?

Ok, ignore the red wall. I've been reading (again) all about helmholtz resonators and reflection free zones - and I'm finally seeing first glimmers of how to apply them. The angled walls were just a draft version of me saying 'something other than a flat untreated wall here'. I had a vague notion of a 6 degree splayed surface, but nothing detailed. I've removed it from the SU for now. Incidentally - would a (theoretical) third leaf affect the way the wall behaved acoustically, inside the room? More leaves seem to be generally accepted as a bad thing, but from what I've read so far this is due to reduced isolation (generally speaking, the same materials arranged in such a way as to create less leaves = more effective isolation, more leaves = less effective isolation).

the apex of the triangle should NOT be at 38% of the room depth! Your EARS should be at 38% of the room depth, and therefore the apex of the triangle will be several inches behind your ears, and therefore also several inches behind the 38% mark.

I'm glad you said that. Actually, I've aligned the inside edge of the speakers with the triangle, not the centre - this means ears at about 38% (more by luck than judgement). I think I'm going to end up tweaking the angle anyway, so I'll bear that in mind. What I noticed was how close 38% and 50% are - only a little over 30cm. That's small enough to lean back in your chair and end up at 50%! :shock:

The equipment racks are recessed into the walls (I'm not sure if this has any acoustic implications - discussion welcome).

It probably does, yes, but since you didn't show those on the original plan, or in the photo, it is impossible to way what the effect will be.

That's because I don't know what I'm doing! Since I have so much gear in such a small space, I'm worried that if I don't recess it, the racks will be large, in the way, and spoiling the sound. As I've brought the walls in, I was hoping to utilise some of the 'lost' space. But I'm worried I'll be creating a cavity and wreaking acoustic havoc...

You cannot glue layers of drywall together!

Don't worry, the glue was only an attempt to get the two layer to act as one - it is nailed as well. We tried it, but nailing seems to be sufficient without glue. Three walls are now double-boarded (all except the window wall). Hopefully this is enough to stop any unwanted resonance, especially from the cavities behind the side walls.

You DID nail it or screw it to the studs, didn't you?

Yes, all nailed - just not the best photo.

Did you put the drywall in backwards? :shock: Or is there another reason why that text is visible? Also, it's hard to be sure from the photo, but there seems to be a large gap under the drywall on the front of the room: Just behind the base of the left speaker stand, there seems to be a very big gap under the edge of the drywall. Is that correct, or is it just an optical illusion?

The main problem we had to solve to begin with was to turn a single-skin wooden structure into a room that can be used all year round, without getting too hot, too cold, too damp or too humid. After reading Rod's book and my initial posts here, and taking into account my location, budget and limited length of the room, along with my initial aims (quoting myself here)...

My aim is - if this does not sound too ambitious - to house a 48channel mostly-analogue setup in a small hut to mix in as near-acoustic perfection as is possible. The setup includes approximately 48u of rack gear and a mid-sized 32channel analogue desk, and I'd like to maintain enough space (and even better, if possible a big enough sweet spot) for two people to sit side by side during mixing.

I eventually came to two conclusions. Firstly, I didn't need to build an isolated shell. It was not practical in the space and budget available, and I would have to make too many acoustic compromises to fit it in, probably lose all natural light, and then I would have major problems with ventilation, as HVAC was simply outside of my budget. As I am blessed with a location that is quiet and far enough from anyone else not to be an issue, I focussed on making a practical space, useable all year round. Secondly, I needed a builder for at least the first half of the project, as my builder-skills were simply not up to the task. This also means that he knows how to keep damp out, ventilate properly, and ensure I'm not making anything dangerously flammable! :mrgreen: As a result, the room was lined with the intention of being plastered. Because of this, nothing is caulked, and yes there is a gap at the bottom. BUT it's not plastered yet either. I did search the forum for plastering - but not a lot came up. The few mentions I found seemed to say 'plaster if you want to make it pretty'; i.e. if what's behind the plaster is right, it doesn't matter. Plastering also seemed a good option to tidy up and seal the ceiling around those beams. And I was presuming that if it was plastered, then there is no need to caulk... Am I heading for a metaphorical cliff edge here?!

Firstly, I didn't need to build an isolated shell. It was not practical in the space and budget available,

Then I guess I'm more confused than ever! If you didn't need to build those walls, then why did you build them? :shock: Why bother with the sound-lock double-doors? Sure, you had a small room ratio problem to start with, which could have been fixed by building one extra wall, but you seem to have gone to all the trouble of building an isolation shell that isn't actually an isolation shell, and doesn't seem to be necessary? I guess I'm just not getting the design criteria. If you wanted an RFZ (which you didn't mention originally: only now, in your last post), you could have splayed your side walls, or at least splay the front half of them, but it's too late now: they are already built.

I had a vague notion of a 6 degree splayed surface, but nothing detailed.

6° is the recommendation for flutter echo and the minimum for RFZ. Mostly it will need to be much greater, to get good-sized clearance around the mix position (unless the room is very wide).

Incidentally - would a (theoretical) third leaf affect the way the wall behaved acoustically, inside the room?

Most likely, yes. But that depends on what frequencies it is tuned to. If they are low enough, the effect would be minimal to non-existent. But if they turn out to be in a critical part of the spectrum for the work you do normally, then the effect could be significant. They would basically act as panel traps, absorbing one specific frequency range very efficiently.

More leaves seem to be generally accepted as a bad thing, but from what I've read so far this is due to reduced isolation (generally speaking, the same materials arranged in such a way as to create less leaves = more effective isolation, more leaves = less effective isolation).

Exactly, yes, but only with regard to the low end of the spectrum. More leaves improve isolation in the high end, and does so very, very well. But it messes up the low end. So, combining the two answers above: depending on how it is built and what frequencies it ends up tuned to, a third leaf could be detrimental to the isolation of the room, or the acoustics of the room, or both, or neither. Getting to the "or neither" configuration isn't easy...

What I noticed was how close 38% and 50% are - only a little over 30cm. That's small enough to lean back in your chair and end up at 50%!

Yup! Small room geometry is a bitch, for sure! Small changes can have big effects. And 38% is only a guideline, so don't sweat it too much! Get close, maybe a little further forward, and then tweak the actual location in reality, not in theory. Actually sit in the chair, and move things around a bit at a time to find the optimum layout.

Don't worry, the glue was only an attempt to get the two layer to act as one -

That would actually be a bad idea acoustically too! Glad you gave it up. Gluing only screws up everything, isolation wise! :)

Hopefully this is enough to stop any unwanted resonance, especially from the cavities behind the side walls.

It's not just the cavity: The resonant system is the drywall AND the cavity: they act together. Either one by itself is nothing. But put them together and they make a resonant system. The resonant frequency depends mainly on only two parameters: the surface density of the leaf (kg/m2), and the depth of the cavity. Adding an extra layer of drywall simply changes the frequency. That's all. So now it will resonate at a different frequency from what it did before...

...then I would have major problems with ventilation, as HVAC was simply outside of my budget.

Hang on a sec: You say you have 48 RU of gear, plus a large-format analogue console, and you say you don't need HVAC? :shock: How is all that equipment going to be cooled? Racks with no ventilation get hot. Equipment works best and lasts longer when it is NOT hot. Plus you also say you want to embed your racks into the wall, where they would have no ventilation at all? I'd say you might want to re-think that. Rackmountable equipment is designed to suck in cool air at the front and exhaust hot air out the back, where it is supposed to be routed upwards and out the top of the rack. The rack itself needs to suck in cool air at the bottom, and direct it vertically up the rear, for the same reason: keep the airflow going in the right direction. Seal a rack into the wall, and the hot air has no place to go. If there is no cool air inlet in the rack base, and no hot air exhaust in the rack roof, then you have a major overheating problem on your hands. Audio gear does not work well when overheated. There's a reason why rack manufacturers offer large fan modules as accessories for their racks: you need them! They come in all sorts of shapes and sizes: for the rack base, and the rack roof, and even in intermediate rack shelf format, as well as in modules for front panel blanks. The back of a rack is a hot place, and needs to have really good airflow to keep the equipment operating the way it was designed. Block the airflow at your own peril. But even if you do get the airflow going right, 48 RU of gear is a lot, and you still need supply COOL air at the front. Just recirculating the same old warm air over and over just makes the air warmer. When I design a machine room, I normally specify a temperature of around 19°C for the cooling air coming into the rack (maybe lower, depending), and that can easily hit 35°C by the time it gets to the top... Believe me, I've spent enough years designing machine rooms and rack layouts, both large and small, as well as designing, installing, troubleshooting and fixing racked equipment, to have a pretty good idea of how this whole scenario will play out if you don't correctly ventilate your rack... (It's not a pretty picture, and I don't think you want to hear about it. I could tell you some sad stories, but that would probably only leave you depressed....)

Plastering also seemed a good option to tidy up and seal the ceiling around those beams. And I was presuming that if it was plastered, then there is no need to caulk... Am I heading for a metaphorical cliff edge here?!

If you don't need isolation, then caulking isn't necessary, and plastering is purely aesthetic: Do it if you want it to look pretty, or not if you don't care. There's no acoustic benefit to either, if you don't need isolation. Personally, I'd plaster and paint. - Stuart -

Looong time away. Much more reading, studying, thinking... A few points to point out, to save anyone joining here from having to read back through the thread if they don't want to. My original aim was this:

...to house a 48channel mostly-analogue setup in a small hut to mix in as near-acoustic perfection as is possible. The setup includes approximately 48u of rack gear and a mid-sized 32channel analogue desk, and I'd like to maintain enough space (and even better, if possible a big enough sweet spot) for two people to sit side by side during mixing.

I have NOT built an isolation shell. (See earlier up the thread if you want details, but basically it was not necessary due to location; new windows/doors were impractical and I cannot afford HVAC). The room was almost square when I started - not good. Also I had to build SOMETHING to turn what was basically a garden shed into a habitable room, to keep out extremes of hot and (more frequently) cold, slugs, bugs, spiders, small rodents etc, and to allow all-year-round use. I brought the walls in on either side, building a plastered stud wall room which brought my dimensions close to Sepmeyer's 2nd ratio (although I had to fudge the ceiling a little, and followed the apex of the roof to maintain height). I am also hoping that the low mass of the timber walls outside (single layer, 1inch thick) will mean I need less low frequency treatments when I'm done. As most of the threads in this forum I have read start with a given room and look at ways of improving it, I guess in my initial ignorance I split my task in two - making a room, then treating it. However, as I've now learned, this isn't the way to build an effective RFZ. As I always intended to cut a hole in the wall each side to recess equipment, I'm just going to cut a bigger hole floor-to-ceiling and replace sections of the side walls. Not how I'd plan to do it if I knew what I was doing from the beginning, but no reason I can see it shouldn't work (and I have discussed it with the builder). The point was raised about heat buildup from the equipment - while I do have a lot of gear, most of it is quite modest, the majority runs from power adaptors. My whole idea is that it's there if I need it, if not it's left switched off and out of the signal chain. This design should enable the cooling of the equipment to happen behind the wall; extra ventilation (fans/vents) can be installed back there at a later date if we find it necessary, and hopefully the fan noise from the recorders will be reduced as well. I'll install a couple of temperature probes in the top of the racks so I can keep an eye on the situation as we begin to work in there. So, I've ray-traced and reworked the design until I ended up with this The three heads indicated would not be there all at once; it is just the positions of either one person, or of two people. The speakers are at 60 degrees to maintain as wide a sweet spot as possible. I couldn't work out how to ray trace in 3 dimensions in Sketchup, so instead I built a light wooden mockup of the soffits and got a reflective surface on a frame to represent the front of the racks, then sat in all 3 positions in the sweet spot. I moved the racks around until I couldn't see a reflection of either speaker. I've attached a stripped-down version of the sketchup file here Just noticed I haven't put the bottom of the soffit back in the sketchup yet. It's there in my head, I'll put it in over the weekend. Please comment... I'm still trying to understand Helmholtz resonators, and if they would be useful for my situation, but I'm not there yet... more reading I guess!