Soundman2020 - Studio Design Forum

Hi Everyone

Nice site!

I am located just outside Orange. (Rural setting, 3 ½ hours from Sydney, Australia).

For the last 12 months, I’ve been refining the design for a two-room studio in a stand-alone building on my property. The studio will consist of a live room and a control room. It is a standard “room in a room” approach with an “inside out” approach to the inner leaves. In the meantime, I am building the outer shell of the building that will house the rooms and my workshop.

Those of you that are on JohnSayers site may have seen earlier versions of the design.

I’ve attached some sketchup concept drawings and other plans that depict the design. I have a reasonably developed plan for HVAC and electrical but will leave that detail for later.

I expect that this will cost me $60-65k outside the slab/external framing/cladding.

I think of the building as consisting of two sections:

• The outer shell - which has no bearing on isolation
• The studio - which is the “room in a room” part

Not all of the space within the outer shell is being used as a studio – about one quarter of the externally clad area will be set up as a workshop. This helps a bit in HVAC design - but more on that later.

The outer shell sits on a 10.2m x 12.6m x100mm concrete slab (with appropriately placed 300mm deep piers). The outer shell has been created by:

• First, erecting a 250mm C section steel frame with a corodek (galvanised iron sheet) roof*;

• framing the walls under that structure with treated pine; and
• fixing corodek to that frame to create the walls.

This part of the structure has been described elsewhere as a “rain screen to keep your two leaf system dry”.

* - directly under the roof sheets sits a layer of “anticon” insulation which is a layer of reflective foil laminate with a 60mm layer of insulation between it and the corodek. This is designed to both insulate the structure and address condensation issues.

Isolation wise, I expect inside measurements up to 115dB. My nearest neighbour’s house is 25-30m from my building and I’d like to be at 40dB by the time I hit his back wall. My inside measurements are based off my own band (drums, bass, guitars and vocals) using my omni and REW software in the garage of my previous home.

The studio section has two leaves.

• The outer leaf - which is formed on 3 sides by attaching 3 layers of 16mm plywood/frychek (16mm drywall) to the inside of the wood frame that holds the external cladding. The 4th wall of this leaf is created by constructing a wood stud wall across the space. I’ll attach 3 layers of 16mm frychek to that wall frame to match the isolation capacity of the other 3 walls. This wall divides the studio section from the workshop area. The outer leaf ceiling will be 3 layers of 16mm fyrchek attached to a set of rafters hung from the C-section metal frame. The rafter structure has engineering signoff.

• The inner leaf is actually two isolated rooms – a live room and control room. AT THIS STAGE they have the same internal dimensions - 6.2 x 4.3 x 2.9m (h) (but see below). There will be a window between the two rooms – though I’ve yet to draw that in. The walls of each room will be 3 layers of fyrchek and the ceiling, 2 layers of 16mm fyrchek and one of 16mm plywood. I’m using the “modular approach” for the inner leaf ceiling that has been described elsewhere by Soundman2020.

In relation to the room sizes, I understand the “ideal” is that the control room should be a significantly smaller volume than the live room, but am currently still playing around with how I can make this work in this space in the context of my middle C-section rafter/column structure. Maybe dividing the current control room into a control room and a drum iso booth.

The minimum air gap between the rooms and the inner & outer leaves is 150mm (but see below, as for 95% of the structure it is 300mm) and I intend to use Bradford Soundscreen insulation at 110mm and 24kg/m3 in the gap.

As indicated, I have the assistance of an engineer with respect to wall construction/ceiling loads/design.

Initially I was concerned about the impact the outer cladding and C-section steel frame may have on isolation. Trawling the various sites and getting specific feedback, I have arrived at the view that:

• I should ignore the outer shell corodek in my isolation calculations as it is of minimal mass and air flows freely between it and the true outer leaf; and
• To treat the C-section steel that sits adjacent to the ply/frychek in 5 places on the outer leaf like it is just an alternative leafing material - albeit with a much greater density than the ply or frychek sitting next to it. However, I am not totally sure about this 2nd point and have explored it further below.

My goals in posting now is to;

• Get any general feedback on my plans; and
• Specifically, to get some wiser counsel on how best to think about the C-section steel columns that cut into the air gap between the outer and inner leaves.

My view on the C-section steel columns

I’ve used the mullion column on the side wall as the example.

• From the pictures you can see that the outer layer of the outer leaf ply/fyrchek butts up against the flange side of the C-section steel column. (In practice, I will be running a layer of sealant between the two).
• I’ve then put a length of treated pine to seal up the inside the flange side of the C-section as treated pine is a much easier to shape around the flange than frychek or ply. The 2nd layer of fyrchek on the outer leaf butts up against the pine – again sealant to be applied;
• The 3rd layer of fyrchek on the flange side then runs across and butts up against the steel column (with sealant);
• All of the three layers of fyrchek on the web side of the C-section butt up against the column – sealant will be applied to that join.

My logic in designing the isolation this way is that steel is 10x denser than Fyrchek/ply and the density of the pine is similar to the fyrchek so that:

At “a” – the density would be 10x that of 3 layers of frychek
At “b” – the density would be less than at a but still higher than 3 layers of frychek – the 2.4mm of steel acts like 24mm of fyrchek
At “c” - the density would be higher than b but less than “a” and still greater than 3 layers of frychek
At “d” - the density would be close to that of the 3 layers of frychek

SO QUESTION 1 is - Does this hold up or am I smoking something?

QUESTION 2 - from the point of air gap, can I treat the part of the C-section that protrudes from the line of the outer leaf into the air gap like a wood stud ie ignore it when calculating the air gap? If so, I can widen my rooms a little as the C-section can run much closer to the inner leaf – currently the air gap between the column and the inner leaf is 150mm and away from the column is approx. 300mm.

Sorry this post is so long but the devil is in the detail here

Andrew

gearjunk1e wrote:Source of the postMy view on the C-section steel columns

Hello Andrew. I wanted the quote to include the two images that followed but have lost the knack. I am unsure but it looks to me as though everything has been really well planned out except for what looks to me like both the outer and inner walls of your room in a room construction touch the C--section steel columns. That would be a flanking path and negate the isolation of the inner room. I hope it is my error in understanding your diagrams as I doubt you would have made such an error, but it is better to check than to ignore a mistake, if it is.

I am unsure but it looks to me as though everything has been really well planned out except for what looks to me like both the outer and inner walls of your room in a room construction touch the C--section steel columns. That would be a flanking path and negate the isolation of the inner room.

Yes, I noticed the same thing.

All the best,

Paul

Thanks Starlight and Paul

A rain day today and I am still weather dependent on the build. so plenty of time so consider design issues
I will say that flanking has me spooked

To clear up the most fundamental issue - the pics may not be super clear but I can confirm that the inner room walls do not touch the C section columns anywhere. In the version of the design I posted the closest they get to the inner leaf is 150mm.

The C section columns do however form part of the outer leaf.

Given that the inner and outer walls are in no way connected - where do you see the flanking issue/issues?
The most obvious candidate (to me anyway) is the C-section columns that form part of the outer leaf but extend into the air gap and also extend above the outer ceiling line - there are two of these on each side and the double column at the back. The argument would be that sound getting through the inner wall can then hit those columns and run UP through the column to the outside world without having to negotiate my outer wall. Here's a sketchup shot of one of the C-section side mullion columns where it cuts through the ceiling line.
and a reminder of how it looks with ceiling and insulation removed
and of how the C-section column forms part of the outer wall

Q; Is this the concern on flanking or am I missing the mark?

Andrew

gearjunk1e wrote:Source of the postI can confirm that the inner room walls do not touch the C section columns anywhere.

Phew! It was my misunderstanding. I am so happy that I was wrong and not you!

Hi all

Time for a design update – I’ve been busy with build work on the external structure - although hampered by the wettest winter here for a decade. (My build post is at https://forum.digistar.cl/viewtopic.php?f=6&t=918)

LAYOUT and Ceiling/wall issues

Since last posting I’ve made a few changes;

I’ve changed the sizing of my rooms – the live room is now 6.64m x 5.34 x 3.1m (average height) and control room 3.21 x 5.1 x 3.1m (average height). The average height reflects the fact that part of each room ceiling is slightly raked. The reason for the change is that most of the activity will be in the live room. If my research is any good, while the control room treatment will be more intensive the room can still be made functional at this size. For sure, it would be better if it was larger but one thing I have learned so far is that building studios is a series of compromises!

I can’t get timber beams for my ceilings as I’d planned. There is a huge shortage of pine in OZ which is not going away anytime soon. This means I’m now considering using steel C section purlins for the long spans in both inner and outer ceilings. (My walls are OK as I bought up the required framing timber before the shortage hit full swing.) I’ll do a separate post on the revised design of this element so as to keep this post to a reasonable length.

I’ve decided to frame and wall around the steel columns in outer leaf of my build – whether it’s a more isolation friendly move or not, the columns aren’t perfectly square and framing and gyprocking around them will make the fixing of the larger areas of ply and gyprock a whole lot easier. The air gap does fall to 50mm where the side and back columns push into the air gap space but if my research is right I believe this should have minimal impact on isolation if the air gap does not fall below 2 inches/50mm. The length of the sections that have only a 50mm gap are 170mm = a bit over 6 ½ inches. You can see these sections in the image above.

My slab is not too bad for a “garage pour” of this size – a variation of 15mm in height over 120m2. That said, I will need to address unevenness at the base of my walls. For the outer walls I was thinking that I’d just run some 90 x 45mm treated pine around the base as follows:

The alternative would be to cut the sheets to address the 5mm of slope across each 3.0m run or to be sealing a gap running from 3-8mm across each sheet.

QUESTIONS on this section:

1. Can anyone clarify the impact of having only a 50mm gap for the 4 places where my isolation modeling requires 200mm. ( I picked this up off a post somewhere but I can’t for the life of me find it again);
2. Anyone got a smarter way to address the unevenness of the slab?

HVAC

To finalise my ceiling plans I’ve needed to drill down on HVAC. At this stage I still intend to use a ducted mini split; with the AHU located above my workshop/storage area which will feed my silencers.

What I’m trying to nail down right now is the size and mounting positions for the silencers. I have spent countless hours researching this and am grateful to those who have gone before – that said I’m still nervous about my calculations and logic– hence this post.

I’ve only focused on the live room here to keep it simple and ignored the AHU/fan for now.

The detailed calculations are in the image below but the logic is as follows:

In A, I looked at CFM from two perspectives - room volume and people – I’ve adopted the volume approach (114.9) here rather than the per person measure (90) as it’s more conservative.

B is the CSA calculation for the duct size. What I’m solving for AT THIS POINT is NOT the velocity when it hits the inner room - but the velocity at the point the air exits the duct that runs between the outer and inner silencers. What I did was to play around with various velocities to see what velocity was consistent with a CFM of 114.9 and a 10” (CSA of 0.55 ft2) duct because a 10” duct is the largest I could run into my space without more modifications. I knew that something close to 200 cu ft per minute at that point in the system would work for me because I planned to double the CSA in the final silencer thus halving the velocity coming into the room.

C calculates the Outer silencer external dimensions. It is based on the target CSA from B and wall thickness of 50mm/2”, baffle widths of 25mm/1” and 1”/25mm duct liner. It uses Gregwor’s Iso box calculator but I have generalized his formulas to cater for different wall and baffle widths.

D calculates the inner silencer box size on the same basis as C except that I’m after half the velocity so I double the box length and use the “Y” style silencer that splits the airflow into 2 outlets - this gets me down to 105 cu ft/min.

This might all sound very confident but I’m not 100% sure it’s right so I’d appreciate feedback.
So my QUESTIONS here are
1. Are these calculations correct?
2. Is it fair to say that the velocity reduction you get from a silencer that has an X and Z measure (using Gregwors Iso box) equal to the diameter of a circular duct should reduce velocity more than the duct as a 10” x 10” square has a greater CSA than a 10” diameter circle?

Thanks for ploughing through this if you got this far!

Andrew

a 12" diameter duct would be 113in2 versus a 10x10 duct 100in2. if you're using a concealed duct unit, they then to be wide and low height which means some duct adapters would be needed or perhaps a split - one to the CR and one to the live room.

Thanks Glenn
I also belatedly picked up a reply from Stuart on a post I'd done in the reference area which is causing a rethink on the AC source - mini splits in each room are looking more "the go" now. I'd previously been trying to avoid them so as to avoid the whole process of dealing with piping running through theses lovely sealed walls I'll be constructing - but to quote a somewhat infamous Australian - "such is life"
Andrew

I’ve changed the sizing of my rooms

OK, but I would suggest a couple of other changes:

First, try moving the doors out of the corners of the rooms. Corners are often very useful for acoustic treatment, especially bass traps, because you get more "bang for your buck" in corners. So I would suggest moving the control room door to the middle of that wall, where it won't be in the way of that treatment.

The same applies to the LR, to a lesser extent: Live rooms are not so critical about tight acoustic control, but its still useful to have the corners available in case you need them.

For the CR, maybe you could move the wall with the door in it, outwards a little until it lines up with the LR wall? At 16m2, the CR is a little small on floor area. The "recommended minimum" for critical listening rooms is around 20m2. That does NOT mean that your room will be a flop if it is smaller! People sometimes get confused here, and assume that if the minimum is 20m2, then 19.9m2 would be useless, and 16 would be laughable: that simply is not true. All it means is that, if it is smaller than 20m2, then the room will need more treatment, and it will be harder to get it to comply with specs, such as EBU Tech-3276, and ITU BS.1116-3. So basically, you will have a tougher time making it work right for a CR. If what you plan to do in there is mostly hobby mixing, nothing commercial, then that's probably not a big deal. But if you are aiming at high end commercial mixing, or mastering, then it is definitely worth thinking about.

Also for the CR: It seems that the window to the LR is going to be on your left as you mix, so it would probably be a good idea to fully plan out the entire CR before you decide on the exact position of that window. Otherwise, you might end up with strong first reflections from that glass.

The average height reflects the fact that part of each room ceiling is slightly raked.

That might be an issue in the CR, depending on how the ceiling slopes. Symmetry is rather important for control rooms, so you might need to do some stuff up there to get the ceiling symmetrical.

I can’t get timber beams for my ceilings as I’d planned. There is a huge shortage of pine in OZ which is not going away anytime soon.

Ouch! Have you considered engineered beams for that? They look something like this:
That would be a good option, and since they are made from "scraps" (well, sort of!), they might be more readily available.

The air gap does fall to 50mm where the side and back columns push into the air gap space but if my research is right I believe this should have minimal impact on isolation if the air gap does not fall below 2 inches/50mm.

4 inches (100mm) is the common minimum recommendation for that. With smaller gaps, you run the risk of having an MSM resonant frequency that is too high, thus reducing your isolation. If you are concerned, then you should do the math...

On the other hand, when talking about the "air gap", what that actually means is the distance across the interior wall cavity from the face of the drywall (or other sheathing) on the outer leaf, to the face of the drywall (or other sheathing) on the inner leaf, regardless of any structural members or insulation that might be in there. The vibrating surfaces in the MSM system are the sheathing sheets on the opposing leaves, that are working on the air "spring" trapped between them, which is the "cavity depth". That's what you use in the MSM equations: the surface density of each leaf, and the distance across the entire cavity, ignoring any framing or insulation. It seems to me that you should be well clear of 100mm there.

For the outer walls I was thinking that I’d just run some 90 x 45mm treated pine around the base as follows:

Probably OK if allowed by code, but do put abundant caulk under that sole plate before you bolt it in place! Don't be skimpy here... In fact, I normally run three beads under sole plates, rather than just the two you see here...

Also, if dampness is a problem, use only pressure-treated lumber (as in the photo above).

In A, I looked at CFM from two perspectives - room volume and people – I’ve adopted the volume approach (114.9) here rather than the per person measure (90) as it’s more conservative.

Careful! That's two different things! Frequently confused, even by some experts. Basically "per person" refers to the amount of air you should be moving to keep each person alive and healthy, and is mostly related to removing the CO2 build-up in the room. You often see that confused as well, with people saying it is all about supplying enough oxygen, but that's only partly true. You will pass out and die from too much CO2 in the air, long before you pass out and die from lack of O2... Strange but true. So the "per person" figure is really about getting rid of the CO2 that people exhale. Of course, if you remove one cubic foot of stale air from the room full of CO2, then you are also replacing it with one cubic foot of fresh air full of O2, so it is sort of the same thing... (Semantics!).

The other issue is "circulation", which is basically independent of the CO2 / O2 thing, and is all about making sure that you are moving enough air through the room to keep it cooled, dehumidified, and pleasant, regardless of what the balance of gasses is. You could do that independent of whether it is pure CO2, or pure O2... Or pure nitrogen... the HVAC system doesn't really care what the gas is that it is moving: it just moves gas (hopefully it will be air!), and needs to do so at a rate that is fast enough for comfort. Why? Think of the extreme case that you move air through the room at a velocity of just one meter per day: the air might have all the O2 you need in it, and be at a nice comfortable temperature, with a nice comfortable humidity level.... but as you sit at the mix position, you would not know about that until this time tomorrow! Because that's when the air would finally reach you, if you move it very slowly. More than likely, you'd prefer to have your air reach you before tomorrow. Probably having it arrive in no more than a few minutes would be good! Hence the measure of "room changes per hour". If you replace all of the air in the room six times per hour, then you will be replacing it once every ten minutes. So in theory, at the very worst it should only take 10 minutes before the cool, clean, fresh air reaches you, and probably less. If you do eight room changes per hour, it only takes about 7 minutes, ten changes per hour makes it happen in 6 minutes. Etc. And of course, if you do just one change per hour, then it takes an hour! (OK, it's not exactly like that in reality, but this is a good way to think of the concepts.)

So, two different concepts: firstly you want to move enough VOLUME of air through the room to make sure you don't have to wait until hell freezes over to get your air, and secondly you want to make sure that the air that DOES reach you (eventually), has the right amount of O2 in it (or more correctly: that the air leaving the room carries the right amount of excess CO2 with it).

So you need both concepts.

So, where do you start?: Room Changes Per Hour! That's the key... What is the volume of your room? Multiply length x width x height. Then multiply that by at least 6 (preferably 8 ) to get the amount of air that must flow through your room every hour (or divide that by 60, to get the amount of air that must flow through your room every minute). This is entirely independent of duct size, for now: Don't start with duct size: Start with air replacement rate. THEN work forward from there to see if the available duct sizes you have on hand are suitable. And if not, then just run two ducts next to each other! You can often get by with smaller ducts like that. Also, the air velocity in the ducts isn't really too much of a problem (as long as you stick to the normal max speeds for each duct diameter). What really matters is the velocity of the air as it goes through the register, where it enters or exits the room. You want to keep that as low as possible, at least below 300 fpm, and preferably below 200 fpm if possible. The reason being that fast-moving air makes a noise!

It uses Gregwor’s Iso box calculator

I would take that with a grain of salt! I'm not so confident that it takes things into account properly. I gave Greg the equations originally, but I'm not convinced that his calculator implements them properly. It is better to do the math by hand: it isn't complicated.

Is it fair to say that the velocity reduction you get from a silencer that has an X and Z measure (using Gregwors Iso box) equal to the diameter of a circular duct should reduce velocity more than the duct as a 10” x 10” square has a greater CSA than a 10” diameter circle?

This is all about cross-sectional areas. Figure out the cross-sectional area of the duct supplying the box, and the cross sectional area of the register on the other end of the box. Do that as a ratio. For example, if the duct has a cross section of 100 in2, and the register has a section of 200 in2, then you have a 2:1 ratio, or 50% reduction in velocity (with the corresponding increase in pressure!). So, now you figure out what the velocity of the air is in the duct (by dividing the volume per minute by the cross section in square feet, not square inches!: thus 200 CFM flowing through a duct with a 100 in2 cross section, which is 0.694 ft2, would be 288 fpm). So if you have a 2:1 ratio of cross sections, then your 288 fpm in the duct would be 144 fpm as it leaves the silencer. I'm just using arbitrary numbers here, to show how the math works, not your actual numbers.

Hope that gets you on the track!

- Stuart -

one or two other things on HVAC - properly moving enough volume also helps regulate the temperature and humidity better as well as filtering (note: poop odors are molecules...) for dust etc. so CO2 removal, O2 replacement, all of the aforementioned contribute to better operation of humans and equipment.

Stuart

Brilliant input Thanks!

Good point on the doors - they can just as easily be along the wall away from corners – rookie error - will adjust the plan.

Control Room
The window placement is fluid - yes I should map out the control room; based on your comments on minimum "desired" floor area I'll play with the plan a bit and squeeze it out to 20m2. Then I can turn to the design of the control room re reflections etc.
The rake looks as follows.
Of course it is possible to lower the ceiling to flat at 2.85m - I was just trying to squeeze out maximum room volume.
I don't expect to do serious commercial mixing but I do have a couple of mates who do material for public release who are keen to use the space so I need to keep one eye on this issue.

Outer wall base
Message received on the caulk/sealant
I have taken my engineers profile drawing of the damp proofing and wall structure and added the additional outer wall base plate I have proposed (lets call it base plate #2) - I hope its not too confusing

QUESTION: The reason for posting this is that he has specified an additional layer of damp proofing under this base - I'm thinking that the damp proof is on the slab, the sealant on the damp proof and then the base plate #2?

Ceiling Beams
My engineer originally specified LVL's for both inner and outer ceilings - I've been looking at alternatives and the e-beams you referred to might be the go although I suspect they make the flanges here the same way as LVL's - from sheets of thin "peeled" pine. If so they’ll suffer from the same supply issues - let's see.
I could work with steel beams on the outside ceiling as I'm fixing gyprock underneath (you can just see that in the control room shot above) but what I want to do with the inner ceilings is the "inside out" approach using a version of the modular approach I've seen you use elsewhere.
I'm scouring alternative suppliers to see what the supply pathway looks like for LVL or the e-beams you highlighted as I do have some time up my sleeve before I hit that stage of the build but I’m a bit restricted right now – COVID restrictions here mean I can travel around regional NSW to collect but can’t go into Sydney so I’ve got to find a supplier somewhere in western NSW or one that can/will deliver from Sydney. As mentioned, I’ll post separately on this in detail.

When I post again on the ceilings I'll also address the 100m minimum air gap issue.

On HVAC – I’ll take this in over the next few days when it’s supposed to rain which will restrict my build work

Thanks again for the quick reply

Andrew

gullfo wrote:Source of the post one or two other things on HVAC - properly moving enough volume also helps regulate the temperature and humidity better as well as filtering (note: poop odors are molecules...) for dust etc. so CO2 removal, O2 replacement, all of the aforementioned contribute to better operation of humans and equipment.

Glenn
Thanks - per my reply to Stuart I'll rethink the HVAC and repost
Andrew

gearjunk1e wrote:Source of the post The rake looks as follows.

So if I'm reading that right, the CR ceiling would be lower at the front of the room, where the speakers are, rising up a little to roughly over the mix position, then flat from there to the back wall? If so, that's great! The problem is when you have left/right differences, which can potentially mess with symmetry, but have lower front/higher back is not a problem at all. In fact, it works to your advantage.

I was just trying to squeeze out maximum room volume.

Yup! For a small room, that is indeed the priority!

I don't expect to do serious commercial mixing but I do have a couple of mates who do material for public release who are keen to use the space so I need to keep one eye on this issue.

OK, so accuracy is important, but not an absolute fundamental necessity as it would be for a mastering room. Got it!

QUESTION: The reason for posting this is that he has specified an additional layer of damp proofing under this base - I'm thinking that the damp proof is on the slab, the sealant on the damp proof and then the base plate #2?

Check what he has in mind for that DPC. As in what material he is planning to use, and how well it adapts to uneven surfaces.

... but what I want to do with the inner ceilings is the "inside out" approach using a version of the modular approach I've seen you use elsewhere

I'd have to think it through a little, but I reckon it should be possible to still do inside-out with steel I-beams. The issue would be achieving good seals and good mass continuity. Hmmmm....

On HVAC – I’ll take this in over the next few days when it’s supposed to rain which will restrict my build work

I've written a couple of articles on that: not sure if you have seen them?

- Stuart -

Soundman2020 wrote:Source of the post I've written a couple of articles on that: not sure if you have seen them?

Absolutely
I just need some head space to work through the math and logic
Andrew

OK - so I had 4 take-outs from earlier posts (setting aside my ceiling problems):

1. Floor plan issues - rejig my rooms so that I got the CR up to over 20m2, address the position of the doors and address the air gap issues where the outside structural columns get too close to the inner wall
2. Provide some more background on the extra base plates I'm going to use under my outer walls
3. Revise my HVAC plan
4. Map out the control room

This post deals with #1 - no point calculating HVAC or mapping out the CR until I get the spaces right and #2 needs a separate post

Below is the revised floor plan

a. CR is now 4.01 x 5.15 = ~20.65m2 (this is measuring leaf to leaf) - no material change to the ceiling rake profile that Stuart commented on
b. the doors are part way along the walls - room for bass traps
c. I've altered the walls of the live room so that the air gap is 200mm all round, introduced some "box columns" to assist in that and shifted the CR away from the column on the outside wall (referred to as a mullion) so that the gap is 200mm

Does this hit the mark?

This gap between the mullion and the control room annoys me - to get the 200mm gap I now have a 440mm gap along the rest of that wall (it may not look like it in the sketchup image above but that's the just the angle). It seems a waste of space. BTW Here's a shot of the mullion in the wildWhen I come up with a solution for this I’ll post it – I'm thinking that it can only come from either

i). making the mullion part of the outer leaf while keeping mass continuity. If I understand correctly the part of the mullion that is inside the outer wall can be ignored in measuring the air gap. I was thinking something like this



...I just need to do the maths
ii). I haven't done enough analysis on control room plans yet but am holding out some hope that I might be able to deploy the "box column" solution I used in the live room because any incursion into the current wall line would be after the 37% mark - but that is beyond my current level of expertise - for now .

Andrew