John Sayers' Recording Studio Design Forum Archive

Hello. I'm in the final stages of designing a studio at the bottom of my garden, I had originally intended to buy a large wooden shed, line the walls with some 'magic soundproofing materials' and have the job done over a weekend for around £2000. I then discovered this forum and realised I had a lot to learn! 6 months later I'm now going with concrete walls and roof, and had to increase my budget ten fold. Thanks a lot!

I have planning permission, the next step is to pass it over to a structural engineer to do calculations and drawings, but before I do I was hoping to get some feedback on my designs to make sure I haven't made any silly mistakes from a sound isolation or acoustic point of view. I haven't figured out every last detail yet, but before I do it would be good to check some of the basics.

Purpose
The studio is just for my own use, and needs to be a multi purpose room. The primary purpose is as a pleasant environment for composing as well as playing and recording piano and violin. The secondary purpose is as a control room for mixing. I appreciate that I will need to make some compromises as it can't really be a great live room and control room, but where those need to be made I would favour the live side of things. (I need enough floor space to be able to squeeze in a small drum kit and double bass now and then for a rehearsal so I don't want to split the space in to more than one room).

Budget
Around £20,000 (25,000 USD)

Location
I'm in the UK, the studio is at the bottom of my garden, around 25m from the nearest house.

Dimensions The image above shows the dimensions. The shape is a bit odd, but it maximises the full space available at the end of my garden, the height (3m) is the maximum I was allowed by the planning office, I was hoping for a bit more but hopefully it will be ok (will be around 2.6m acoustic height internally). I struggled to work out if the proportions would be good as all of the room calculators I've found assume you have a rectangular room. I'm hoping the one angled wall will act in my favour in terms of room modes?

Isolation requirements
The maximum noise allowed in the UK is 34dba.
If I say a typical level for piano and light drums might be around 100dba, I'm going to base my calculations on 110dba to allow for the odd evening when things get a bit carried away. (I'd rather have too much isolation!)
The nearest house is 25m away, so that should provide 28db reduction.
So I calculate that the reduction required by the building is 110 - 34 - 28 = 48db.
From what I've read I believe 48db reduction should be achievable with the materials / design I've chosen.

Base
Concrete

Outer leaf
The outer walls will be concrete blocks, the roof concrete beam and block.

100mm gap between outer and inner leaf filled with insulation.

Inner leaf
Timber frame -> 16mm OSB -> green glue -> 16mm plasterboard (drywall). Sitting on the same concrete base as outer leaf

Ceiling
Inside out design: 16mm plasterboard -> green glue -> 16mm OSB -> 150mm insulation -> fabric. Built in 2.4m x 0.6m modules.

Floor
Wooden

Window
One non-opening single glazed window in each leaf. 12mm acoustic laminated glass.

Door
Solid fire door in each leaf, with a door closer

HVAC
I haven't figured out exact specs yet, but I have planned for a mini split for AC, and an inlet and outlet vent for fresh air with a fan on the exhaust and a passive inlet. The silencer box for the inlet is in the bottom of the bass trap (between the inner leaf and the outer leaf), the silencer for the outlet is on the outside of the building as I didn't think there would be room between the leaves on the other side of the room. I did consider putting the outlet in the other bass trap but wasn't sure if that would really encourage much airflow as they would both be at the same end of the room.

Monitor positioning
I believe that flush mounted is the way to go, I've had to put them at 75 degrees instead of 60 otherwise the mixing position was too far back in the room. I'm going to have a sub on the floor somewhere so monitors won't have to reproduce too much bass. I need to do a bit more research on the exact flush mounting assembly, but think I have a basic idea.

Storage
I've created a small storage area, with a light weight sliding door to avoid creating a 3rd leaf.

Specific questions

I guess the main thing is I'd appreciate any feedback on the overall design, a general sense check on things that I might not have considered.

Is there any way of estimating if the room proportions are going to be reasonable given the angled wall?

Is it OK to have monitors at 75 degrees instead of 60?

Could I put the outlet vent in the other bass trap in the other corner? I'm guessing it probably wouldn't be changing the air at the other end of the room if I did that. But the silencer box stuck on the outside of the building seems a bit of a bodge.

Should I go for 10mm glass in one of the windows and 12mm on the other? I'm not sure whether the isolation would improve because of the different resonant frequencies or be less because of the reduction in mass of one of the panes?

I've attached a few more images below in case they're useful, I've also uploaded the Sketchup file here: https://drive.google.com/file/d/13yCZ5m ... sp=sharing

Any feedback at all would be greatly appreciated,
Simon

Hi there Simon, and Welcome to the forum!

I had originally intended to buy a large wooden shed, line the walls with some 'magic soundproofing materials' and have the job done over a weekend for around £2000. I then discovered this forum and realised I had a lot to learn!

Thankfully, you found us in time, and didn't make that huge mistake!

6 months later I'm now going with concrete walls and roof, and had to increase my budget ten fold. Thanks a lot!

Only ten-fold??? We must be doing something wrong, then...

The primary purpose is as a pleasant environment for composing as well as playing and recording piano and violin. The secondary purpose is as a control room for mixing. I appreciate that I will need to make some compromises as it can't really be a great live room and control room, but where those need to be made I would favour the live side of things. (I need enough floor space to be able to squeeze in a small drum kit and double bass now and then for a rehearsal so I don't want to split the space in to more than one room).

For such a broad and highly varied range of uses, I would strongly suggest that you consider doing variable acoustic treatment, so you can change the acoustic response of the room across a wide range, from "bright" to "dull", and "specular" to "diffusive". There's no way you are going to get one single set of treatment that works well for all of those. Rather, you'd get one single set of treatment that sounds lousy for all of them!

Around £20,000 (25,000 USD)

You have about 28m2 footprint, as near as I can tell, so you are planning on spending less than £ 1k per square meter. That's a little on the low side.... I have designed a few studios for the UK, some from the ground up (like yours), and the clients who have built their places have told me that the cost is generally around £ 1,000 to £ 1,500 /m2. You might want to increase your budget.

I'm in the UK, the studio is at the bottom of my garden, around 25m from the nearest house.

Given the dimensions, I'm assuming that this is with full planning permission, and not going to be done under "Permitted Development" rules?

Also, does the building HAVE to be that shape? It would be much better if it were just rectangular. Easier to build, faster, cheaper, better acoustics.... I'm assuming that it is that shape because of some type of restriction, or something on the land that can't be moved? I saw that you said " it maximises the full space available at the end of my garden", but I'm wondering of there might not be a better shape...

the height (3m) is the maximum I was allowed by the planning office, I was hoping for a bit more but hopefully it will be ok (will be around 2.6m acoustic height internally).

Height doesn't just go UP... it also goes DOWN. You can dig a deeper hole for your studio, go down some more, still have the roof peak at 3m, but have as much height as you want inside. Some of my clients in the UK have done exactly that... Of course, it does mean that you need steps down to get inside, and you have to deal with the draining the water tha runs down the stairs, but it's a really good option if you need the height. You show a baby grand, and you mention drums, so you most certainly DO need the height!

I struggled to work out if the proportions would be good as all of the room calculators I've found assume you have a rectangular room. I'm hoping the one angled wall will act in my favour in terms of room modes?

Calculators don't apply much in your case, because you have one steeply splayed wall, so you can't trust any number that is associated with that wall. The vertical and side-to-side axials will be fine, as will the tangentials that only involve the remaining five walls, but the obliques will all be wildly wrong, as will the length-wise axials, and any tangential that involves that rear wall. In other words, whatever ratio you came up with is not really valid.

And no, having splayed walls does not improve your modal situation: in fact, it usually makes it worse, because you lose support for one or more axial modes, and those are the ones at the lowest frequency.

However, don't despair! Room ratios and smooth modal response are nice if you can get them, but you have to treat them anyway, regardless, so it's probably not a big deal. As long as your modes are reasonably well spread out, not all bunched up around the same frequencies, then you are OK.

On the other hand, I don't see any provision at all for bass trapping in your studio, so it's going to be a modal mess! You should work on that...

The maximum noise allowed in the UK is 34dba.
If I say a typical level for piano and light drums might be around 100dba,

Careful there! You are comparing apples to bananas! Not valid! The "A" weighting scale of sound pressure measurements is meant for low level noises (quiet) and speech, typically. ... because the "A" curve is a fairly reasonable approximation of how the human ear perceives quite sounds. The "C" scale is much more accurate for loud sounds, and music especially. ... because the "C" curve is a fairly reasonable approximation of how the human ear perceives LOUD sounds. But you cannot easily convert between the two scales, unless you know the spectrum of the sound. So normal speech will show up on both scales pretty much the same, regardless of whether it is loud or soft, but music is very different: there can easily be a difference of 20 dB or even 30 dB between measuring the exact same contemporary pop or rock song on the "A" scale or on the "C" scale. Not all decibels are equal! Some are more equal than others... .

Fortunately, your regs measure in dBA, which does not take into account the low end. And you will be "playing music in dBC" inside, so you have a big advantage there. By "playing music in dBC" I mean that the music you play inside will be loud, and you will perceive it inside the studio similar to what the C scale measures: It will seem like dBC to you: loud bass notes will sound loud. But if the cops come along to measure, they will have their meter set to "A" weighting, so even if they can HEAR the low notes, that won't show up on their meter! Because "A" is less sensitive to lows. In other words, you could be bashing out a bass riff at 100 dB, with pretty much all the energy in the low end, and you would measure that as 100 dBC. But if they came into the room and measured with dBA, they would only "see" that as maybe 80 dBA.

OK, so this is getting a bit complex, but it's important to understand the difference, when designing the isolation for your studio. And since you cannot compare dBA to dBC directly, you cannot say that if you have 40 dB of isolation, then the piano played at 100 dBC inside is going to be measured at 60 dBA outside....

You can't compare dBA to dBC.... Either you use dBA (which is no use for loud sounds), or you use dBC (which is no use for quiet sounds...)

So, in other words, you will need to decide how to measure! Should you use "A" or "C"? You might think that it would be better to measure everything in dBA, because that's what the regs say, and that's how the cops will measure if your neighbors complain... but you would be wrong! What matters, is dBC. Because that's what YOU will be hearing inside the room, and all of the sounds you will be producing are full-spectrum, and loud. It also means that if the cops do turn up and measure the level, they will see a LOWER reading than what you have, which is good for you...

So, from now on, use only dBC. Forget dBA, unless the cops really do pitch up! Do all of your measuring with your meter set to "C" weighting, and "Slow" response.

The nearest house is 25m away, so that should provide 28db reduction.

Perhaps... depending on what other buildings are around, as well as the temperature, prevailing wind, etc.

So I calculate that the reduction required by the building is 110 - 34 - 28 = 48db.

Assuming dBA.... A drum kit can easily put out 115 dBC, and more when played hard....

From what I've read I believe 48db reduction should be achievable with the materials / design I've chosen.

It's always better to shoot high, rather than low, for your isolation. How did you arrive at the conclusion that you will get 48 dB isolation from your structure? What calculations did you do?

The outer walls will be concrete blocks, the roof concrete beam and block.

Good start! That alone will get you decent isolation. How thick will the walls and ceiling be?

Timber frame -> 16mm OSB -> green glue -> 16mm plasterboard (drywall). Sitting on the same concrete base as outer leaf

good inner leaf, too. What size framing?

Inside out design: 16mm plasterboard -> green glue -> 16mm OSB -> 150mm insulation -> fabric. Built in 2.4m x 0.6m modules.

Make your modules smaller than that. Those would be extremely heavy to lift: complicated, and dangerous. It's better to have a larger number of less heavy modules. Easier to manage.

Floor
Wooden

Why? If you have a perfectly good concrete slab, then why would you put a wooden floor on top of that? And what type of floor are you talking about? You are on a VERY tight budget, so I would leave the floor out, and just use the slab. Nothing better, acoustically.

Window
One non-opening single glazed window in each leaf. 12mm acoustic laminated glass.

I can't see you getting 50 dB of isolation with such thin glass. That will be your weak point. I would suggest putting thicker glass in the outer-leaf at least. 20mm would be good. And the same on the inner leaf if you can afford it, or at least 16 mm.

Solid fire door in each leaf, with a door closer

... and multiple full-perimeter seals including threshold....

The silencer box

"The"? As in singular? Only one? You are looking for high isolation, in the region of 50 dB, so you will need two silencers on each duct: one where the duct passes through the inner leaf, and the other where it passes through the outer leaf.

is in the bottom of the bass trap (between the inner leaf and the outer leaf),

Sorry, I don't get that: How can your bass trap be in between the inner leaf and outer leaf? The bass trap is inside the ROOM, not inside the wall. And if you put an HVAC duct through your bass trap, then you are reducing the effectiveness of the trap! It's a small room, so it is going to need extensive bass trapping. You can't afford to lose efficiency.

the silencer for the outlet is on the outside of the building as I didn't think there would be room between the leaves on the other side of the room.

Ditto. See above. You need two silencers on that one as well, if you want high isolation.

I did consider putting the outlet in the other bass trap but wasn't sure if that would really encourage much airflow as they would both be at the same end of the room.

Right. Generally, I put the supply register at the back of the room, and the return register at the front, as far apart as possible.

I believe that flush mounted is the way to go,

Yes! Undoubtedly. Good move.

I've had to put them at 75 degrees instead of 60 otherwise the mixing position was too far back in the room.

That's probably fine, but do check your angles, distances, and probable acoustic response carefully, taking into account the actual speakers you plan to use.

I'm going to have a sub on the floor somewhere so monitors won't have to reproduce too much bass. I need to do a bit more research on the exact flush mounting assembly, but think I have a basic idea.

Sort of but not really! For example, you have shelving at the point where the soffit meets the wall, with a huge reverse "kink" in the baffle. That is going to produce all kinds of messy stuff in your room, with major edge diffraction, reflections, delays, comb filtering, and other stuff. If you take a look around the forum at rooms with soffit-mounted speakers, you will see that it is NEVER done like that. For a good reason.... The speaker baffle needs to merge smoothly into the side wall, with as little disturbance as possible. I often put "wings" out to the sides of the soffit baffle itself for this very purpose. The wings help blend the soffit into the wall...

There's other issues too: your speakers appear to be in the middle of the baffle, which is not the best place. Offset to one side or the other, to reduce the "focusing" or "lobing" effect that you can potentially produce otherwise.

Storage
I've created a small storage area, with a light weight sliding door to avoid creating a 3rd leaf.

It's still a 3rd leaf, and the area is REALLY tiny! I don't see it being much use like that. It also takes up the exact location where you need massive bass trapping...

I guess the main thing is I'd appreciate any feedback on the overall design, a general sense check on things that I might not have considered.

Done! See above...

Is there any way of estimating if the room proportions are going to be reasonable given the angled wall?

As I mentioned above, you can estimate to a certain extent provided that you only consider the numbers associated with the other surfaces, ignoring everything associated with the rear wall. So you cannot trust any oblique, many tangentials will be off, and all of the axials associated with that wall.

Is it OK to have monitors at 75 degrees instead of 60?

Yes, provide that you understand what the consequences will be, in terms of sound stage, stereo image, and sweet spot. But it seems to be that if you re-design your soffits, you should be able to get a better layout.

Where is the intersection point for the axes of the speakers?

Could I put the outlet vent in the other bass trap in the other corner?

What size do your registers have to be? What is the flow rate that you calculated for your HVAC system? How much of that is recirculated air, and how much is fresh air make-up? What is the velocity that you are using at the registers? What duct size does that give you? How big do your silencer boxes therefore have to be? What is the total static pressure that this system creates? Is your fan able to handle that flow rate and that flow speed into that static pressure and with that duct size? What is the latent heat load of your room? What is the sensible heat load? What mini-split system have you found that has the correct capacity for dealing with that heat load, while also moving the correct amount of air at the correct speed?

Lots of questions you need to answer about your HVAC system! I get the impression that this is one area of your design where you haven't completed your research yet...

Also, your current plan has the air inlet down at the bottom front of your room, yet the mini-split is way up at the top rear of the room.... How do you plan to get the incoming untreated, moist, warm air, up to the mini-split so that it can be conditioned, cooled, and dehumidified? It somehow has to travel across the entire room, without mixing with any room air, to do that... Not gonna happen! Think about that...

Should I go for 10mm glass in one of the windows and 12mm on the other? I'm not sure whether the isolation would improve because of the different resonant frequencies or be less because of the reduction in mass of one of the panes?

A couple of days ago I wrote a brief explanation for one of my clients who was thinking about the same issue, so I'll copy-and-past that here. Some of it might not be relevant (we were discussing PVB interlayers), but most is:

----------------
OK, here's the "all you wanted to know about laminated glass" deal for today...

Acoustic PVB is a bit thicker than normal PVB, and with some manufacturers its also a special formulation. It greatly improves damping at the coincidence dip, and to a lesser extent, at other points. It also drives the dip UP the spectrum, since it makes the two layers of glass act more like individual layers, and less like a combined layer with higher mass.

Here's the difference:
That's for two different types of laminated glass made by the same company. Same thickness. You can see that most of the difference is at the coincidence dip, but there is also an improvement lower down, until you get to about 200 Hz... However, below about 200 Hz, you are into another area, where there's some other type of internal resonance going on between the panes, that is reducing isolation slightly. So there are pros and cons. But mostly "pros"!

Now, about thicknesses: consider that the location of the coincidence dip on the spectrum depends on the density, but also on the thickness. If you are interested, the lowest frequency where coincidence can occur is:

Fc = c² / (1.8 * h * vl * sin²(a))

where:
c = the speed of sound in air (m/s),
h = the glass thickness (m),
vl = the longitudinal velocity of sound in the glass (m/s), and
a = the angle of incidence.

And of course, the "longitudinal velocity of sound" is a function of density (sound travels faster in more dense materials). For glass, it is about 5600 m/s (depending on glass type).

Thus, if you have two identical panes of glass, the coincidence dips of both of them will fall at the same spot on the spectrum, and you will have less isolation in that frequency range. Any sound that gets through the dip in one pane will get through the dip in the other pane, because the dips line up.

By making one pane thicker than the other, you'd think that there must be an advantage, because the coincidence dip would also move, and therefore the curve would move. Yes it does! But not by enough to be hugely useful. Take a look at the curve again in the above graph for ordinary laminated glass: the dip is around 1700 Hz. Now, imagine if you could make the glass 10% thicker, in order to move the frequency down the scale a bit... Do the math: a 10% change in thickness produces only a small change in frequency (there's that nasty "c²" term on top....). It's a small change, but I'm too lazy to do the math right now, but lets' say, for argument sake, that you get a massive shift of 100 Hz by going from 12mm to 19mm glass. Imagine, if you will, that same curve above, and a copy of that curve moved over by 100 Hz to the left, so the dip is at 1600 Hz, instead of 1700 Hz. Compare the curve and it's copy. Look at the intersection of those two dips: Most of the dip is still in the same place! The majority of the "coincidence dip" still lines up between the two thicknesses of glass! You need a very large change in frequency to kill the overlap.

So, yes, there's an improvement, but it's not really worthwhile, because the dip is so wide anyway: you would need a very large change in frequency to get the situation where the dips no longer overlap at all, so you'd end up using one pane of glass that is really thin, and the other massively thick... The dip runs from maybe 1000 Hz to maybe 2200 Hz, so to get the dips to not align at all, you'd need to change the frequency of one dip by about 1000 Hz... good luck with that!

Plus we aren't even concerned too much about the coincidence dip anyway! It's way up near 2 kHz and even at the worst point, isolation is still over 30 dB! What is REALLY important, is how the glass behaves down in the low end of the spectrum. The lowest point on the dip is over 30 dB, and that lines up roughly where the rest of the curve hits about 500 hz. Thus, below 500 Hz (the entire low end, plus half of the mid range...), isolation is far worse then even the worst part of the coincidence dip: It's that bottom ends that matter most. So the coincidence effect isn't such a big deal, really.

Basically: more mass is better. Thicker glass is better. And acoustic PVB is better than standard PVB. (With acoustic PVB, the coincidence dip stops being an issue at all.)

Bottom line: get the thickest glass you can afford, with acoustic PVB if you can. You want at least the same surface density as the rest of the leaf (but preferably higher, by a factor of about 1.4... ), and get the glass that has the best PVB (some manufactures use different materials, other than PVB for their interlayers: check the actual tested specs).
-----------------------

Hopefully, there's enough in there to answer your question.

One other thing: your door doesn't seem big enough to be able to get a baby grand in and out of the room all the time... And also: where will you store the piano when you are using the room for other things? I can't see you getting a baby grand AND a large drum kit in there at once... plus, even if you could fit them physically, it would sound pretty bad...

- Stuart -

Hi Stuart. Thank you so much for taking the time to give me feedback on my design, you gave me a lot to think about!

For such a broad and highly varied range of uses, I would strongly suggest that you consider doing variable acoustic treatment

Yes nice idea, I've added a dado rail along the top of the walls so that I can hang a selection of variable acoustic treatments.

You might want to increase your budget.

You may well be right, once the outer leaf is up I'll be doing most of the rest of it myself so hopefully I'll be able to save a bit of money. Once the design is finalised I'll be able to get a better idea of costs.

Given the dimensions, I'm assuming that this is with full planning permission, and not going to be done under "Permitted Development" rules? Also, does the building HAVE to be that shape?

Yes I have full planning permission for that size and shape. My garden is that shape and can't be changed, so if I were to have a different shaped building it would still have to fit within that plot which would make it quite a bit smaller.

Height doesn't just go UP... it also goes DOWN. You can dig a deeper hole for your studio, go down some more, still have the roof peak at 3m, but have as much height as you want inside.

Nice idea, I will look in to that some more, although I fear it may add significantly to the budget.

How thick will the walls and ceiling be?

I imagine I'll use hollow concrete blocks for the walls (probably filled with sand) which would be 215mm thick, the ceiling would probably be 100mm thick concrete blocks. I appreciate that the outer walls may as well be 100mm thick to match the ceiling but they may need to be thicker for structural reasons (once I'm happy with the basic layout I'll be passing the design over to a structural engineer).

What size framing?

I would assume 2x4 framing and 2x8 for the ceiling joists, although my structural engineer may well have other ideas.

If you have a perfectly good concrete slab, then why would you put a wooden floor on top of that?

Fair point, I guess I was worried about cold feet!

I can't see you getting 50 dB of isolation with such thin glass. That will be your weak point. I would suggest putting thicker glass in the outer-leaf at least. 20mm would be good. And the same on the inner leaf if you can afford it, or at least 16 mm.

I read on here that a guide was to use 1/3 of the thickness of drywall, so that's how I got to 12mm (32 / 3). I will try and source some thicker glass, especially for the outer wall.

How can your bass trap be in between the inner leaf and outer leaf?

I was looking at various designs on here and got myself quite confused I think! I've redesigned the room so that the inner leaf has square corners, and then I have corner soffits for the monitors with a bass port at the bottom, air vent at the top, and some kind of bass hangers inside. I've also added superchunks at the other end of the room.


Storage

It's still a 3rd leaf, and the area is REALLY tiny! I don't see it being much use like that. It also takes up the exact location where you need massive bass trapping...

I don't need much storage, but it's proving really difficult to fit it in somewhere! I've now added a few cupboards along one side wall which should enable me to hide some of the duct work and the mini-split a bit. The doors will have a layer of absorption to match the other side helping with the RFZ.

How do you plan to get the incoming untreated, moist, warm air, up to the mini-split so that it can be conditioned, cooled, and dehumidified?

Good point! I've redesigned the room layout so that the incoming vent is right near the mini-split, with a silencer built in to the top of a cupboard, the outlet is on the other side of the room with a silencer at the top of the wall (and another on the outside of the building).

you have shelving at the point where the soffit meets the wall, with a huge reverse "kink" in the baffle. That is going to produce all kinds of messy stuff in your room, with major edge diffraction, reflections, delays, comb filtering, and other stuff. If you take a look around the forum at rooms with soffit-mounted speakers, you will see that it is NEVER done like that.

Ah yes, but they looked nice! Ha ha. Ok, I've hit the delete button on the shelves. I've got some cupboard doors there instead now, I guess it still might not be ideal, but I'm really struggling to find anywhere for some storage.

One other thing: your door doesn't seem big enough to be able to get a baby grand in and out of the room all the time

On its side, with the legs off it'll fit, but I might make the door a bit wider just so it's easier to get things in and out. I won't be moving it in and out regularly.

I can't see you getting a baby grand AND a large drum kit in there at once... plus, even if you could fit them physically, it would sound pretty bad...

Yeah it would be a tight fit, it's not something I'll do very often and if I did it wouldn't be for recording purposes, I'd go somewhere bigger for that.

Lots of questions you need to answer about your HVAC system! I get the impression that this is one area of your design where you haven't completed your research yet...

Ok, here's my attempt at the HVAC calculations
From what I understand, the mini-split is responsible for temperature and humidity control, and the vents are purely for fresh air needs. So...

Fresh Air
15 CFM per person
Max people in studio: 4
15 * 4 = 60cfm.

To play safe I'd like to aim for 150 FPM for the velocity through the registers.

Cross section area = 60CFM / 150 feet per minute = 0.4 square feet
0.4 sq ft x 144 = 58 square inches

So a 6" x 10" register? (150mm x 250mm)

So a silencer box with 50mm duct liner and 32mm OSB would be roughly: 414mm x 314mm x 1200mm

width: 250mm + (50mm * 2) + (32mm * 2) = 414mm
height: 150 + (50mm * 2) + (32mm * 2) = 314mm
length: with 4 baffles would be around 1.2m (similar to this: http://www.johnlsayers.com/phpBB2/downl ... =62743&t=1)

AC
area: 25 m² / 270sf
volume: 65 m³ / 2300cf
refresh rate/h 6

CFM = 6 * 2300 / 60
= 6.5m3/m / 230cfm

BTU calculation:

Equipment
computer & screens 200W
power amp 150W
electric piano 100W
lights 100W (LED)
Mackie 450s x 2 900W
Turntables etc 50W
Total: 1500W

People
160 * 4 = 640W

Total Watts: 2140W
2140 * 3.4129 = 7300 Btu's / h

So the mini-split needs to be able to handle 7300 Btu and 230CFM?
And the fan 60CFM?

I think...

Yes nice idea, I've added a dado rail along the top of the walls so that I can hang a selection of variable acoustic treatments.

The normal method for building variable-acoustic devices is that they are fixed to the wall or ceiling, and some aspect of the device itself can be moved in some way, to change the acoustic response.

For example, here's a device I designed for one of my clients a while back:
And the result:

I would assume 2x4 framing and 2x8 for the ceiling joists, although my structural engineer may well have other ideas.

Sounds about right, but to maximize acoustic ceiling height, do consider "inside-out" construction. It makes a BIG difference.

Fair point, I guess I was worried about cold feet!

Maybe just lay laminate flooring directly over a suitable underlay...

I read on here that a guide was to use 1/3 of the thickness of drywall, so that's how I got to 12mm (32 / 3). I will try and source some thicker glass, especially for the outer wall.

You really should do the math, to make SURE you are getting the right amount of isolation, and that it covers the frequency range where you need it. Guessing is not a good way to build a studio!

I've redesigned the room so that the inner leaf has square corners,

Right!

and then I have corner soffits for the monitors

Soffits should not go in the corners like that. Or rather, the soffit can certainly COVER the corner, but the speaker should not be set on the dividing like of the corner, no should it be in the geometric center of the soffit. There are many threads here on the forum about building soffits: You should probably study those carefully, to understand the principles.

I've also added superchunks at the other end of the room.

YEs, but you still do not have any treatment at all on your rear wall. The rear wall in any room is by far the biggest contributor to acoustic problems of all types. If you leave it untreated like that, you will never be able to get good acoustic response in there.

I've now added a few cupboards along one side wall

... which means that you hve destroyed the room symmetry! It is critical that the room MUST be symmetrical, at least the front half. If not, then your left ear does not hear the same acoustic response as your right ear, so your stereo image will not be balanced, and your sound-stage will be skew. You will subconsciously try to correct that in the mix, until it sounds good in the room, but then it won't sound good anywhere else... In other words, your mixes will not "translate". The room must be symmetrical. At the very least, the front half must be symmetrical.

The doors will have a layer of absorption to match the other side helping with the RFZ

Unfortunately, it is not possible to create an RFZ with absorption. Even the best porous absorbers do not absorb all frequencies evenly. The only way to create a proper RFZ is with angled hard, rigid, massive surfaces that reflect the sound at the correct angles.

Good point! I've redesigned the room layout so that the incoming vent is right near the mini-split, with a silencer built in to the top of a cupboard, the outlet is on the other side of the room with a silencer at the top of the wall (and another on the outside of the building).

That might work, but once again, it would be far better to make the room symmetrical: Put your mini-split in the middle of the rear wall, directl behind you, with the supply register right above it, and then have the return register at the front of the room, over the soffits. That way, you get balanced audio AND balanced HVAC.

So the mini-split needs to be able to handle 7300 Btu and 230CFM?
And the fan 60CFM?

Looks about right. I didn't check the math, but you seem to have included all the concepts correctly.... except for latent heat! The MiniSplit cannot start cooling any air until it first deals with the latent heat, so you need to take that into account.

- Stuart -

Mackie 450s x 2 900W

Mackie states that under "normal" operation, each speaker will consume ~120 watts. When the speaker is clipping, it will pull ~300 watts. In your small room, if you're at all responsible with your hearing, you'll never have them at clipping volume. Either way, I'm pointing out that your 900 watt assumption for two of the speakers is too high. 600 watts would be the max.

People
160 * 4 = 640W

Everywhere I've researched, they recommend 600 BTU per person. I you've calculated it in power, but maybe check that it works out close to the same BTU.

Greg