John Sayers' Recording Studio Design Forum Archive

Dear Gurus of studio design

I am planning to convert my detached single garage, which is currently a storage space for years of junk, into a simple one-room recording and rehearsal space. I would very much appreciate comments and suggestions on my questions, but also any other advice or observations - this is still in the planning phase and nothing has been decided or done yet (am still working on my Building Control application).

Inner dimensions of the existing structure, are 6.84m x 3.53m, with a height to the bottom of the existing horizontal joists of 2.4m. My son has an electronic drumset which he regularly bashes, and I do a fair bit of guitar and recording work. When the boy grows older, my luck would probably have it that he wants to jam with his heavy-death-trash metal band in here as well. For now, I also like to use the room to jam with friends (mostly folk and rock) from time to time or rehearse for the odd performance. Nearest neighbour has his bedroom window about 5 meters away, and our own bedroom windows are about 8 meters away. I also live on a fairly busy road (about 12 meters away). I have not measured myself in this space (too full of junk!), but am very keen to keep the neighbours (and wife who goes to bed early) sweet - hence I want to aim to get the maximum amount of sound isolation as I can reasonably achieve, on a budget of about £10,000 and using as many of the techniques I have learned from Rod’s book and these amazing forums.

Below is a sketch with dimensions and features.
The garage sits on a concrete slab about 45cm thick, which rests on concrete foundations along the perimeter, and presumably on compacted earth for the center. Walls are a single layer of concrete block construction (i.e. not hollow breezeblock, as far as I can tell, and not a double wall with insulation inside), plastered on the outside, with a tiled roof (uninsulated) that sits on timber A-frame joists. There is a good height loft space with a ply floor resting on top of the existing joists, which I intend to continue to use as a storage space - currently access to this is via a loft ladder from the inside of the garage, however I intend to replace this with a new hatch from the outside via the gable wall.

The current structure is not airtight or insulated at all. I realise I will have to do a lot of work to ensure all the gaps are filled, cracks are sealed etc. I intend to paint all surfaces as well to help with making it a bit more airtight. From the sketch you can see I will brick up behind the garage door, as well as brick up one of the windows (the one in the narrow, West facing wall). I am engaging a structural engineer to assist me in figuring out if my existing joists can support a dense new double mdf layer for the loft’s floor.
I plan to create a room within a room (MSM), with the inner leaf made of suitable timber studwork (I am asking the engineer about these as well to ensure my studwork will support the heavy inner ceiling and possible cloud) - with no part of the inner studwork touching the outer leaf or structure at any point (except for resting on the concrete slab of course). The new ceiling joists will sit in-between the existing, outer-leaf, ceiling joists (without touching), an inch below the existing joists. The dryboard will be a double layer of fireproof ⅝” plasterboard with a layer of Green-Glue in between - for both the walls and ceiling. I intend on using 100mm of 45kg/m3 Rockwool for insulation fitted in the stud-wall.

Ventilation will be using a supply or extract fan (still making my mind up). The fan, which will be in the loft space (hence outside the outer leaf), will be controlled with a variable speed panel from inside the studio, allowing me to up the speed if things get stuffy if there are many people rehearsing, and lower the speed when it is just me quietly mixing away. I have agonised over this for some time, and am leaning towards going without an air-conditioning unit - Oxfordshire's climate is mild all year round, and it is very rare that the outside temperature is higher than what you would want inside the room. Also, humidity is never an issue, and I believe I can control the humidity ad-hoc using a simple dehumidifier from time to time. On the sketch some of the ducts and the silencers are visible.

I have trawled this forum and Rod’s book, and think I have a reasonable idea of what to do, however will no doubt have loads of questions as construction begins and progresses. In the meantime I have a number of questions in this design/planning phase.

Ceiling:
I realise using the existing ceiling / loft floor will be the outer leaf, and the existing sloped, tiled roof is probably a third leaf. However, if I wanted to keep a freely ventilated loft storage space, this is the only way. How big a deal is this from a sound insulation point of view?

Window:
I have a south facing window which I would like to keep (obviously building it as in Rod’s book with a thick pane of laminated glass for both the inside and outside leaf). The other window visible in the plan will be bricked up as in the sketch. Given the south facing window’s position, is this asking for trouble from a symmetry point of view? I am thinking to hang an acoustic panel over the window when I am doing serious mixing if there is a large detrimental effect from reflections bouncing off the window. Am I asking for unnecessary trouble here, or is it a manageable issue? If this will be a disaster, I will consider bricking this window up as well (losing all natural light and inviting the ire of the wife into eternity).

Insulation:
I am placing slabs of 45kg/m3 100mm thick rockwool insulation in-between all studs and ceiling joists. However, from the shape of the room (you can see there are little buttresses sticking out of the wall), my total air cavity for much of the walls is going to be more like 22.5cm. Do I fill the rest of the cavity with the same 45kg/m3 insulation, or is it better to use standard fluffy loft-insulation (or nothing at all)? The same goes for the large cavities that will remain around the sides where the silencer boxes are placed (more on this below).

Ventilation:
I have done the calculations, and I understand that you want to keep the velocity of air moving through the ducts as slow as possible (and below 90 metres / minute). (Room internally is about 40m-cubed, so need to change 6 x 40 = 240m3 / hr, which is 4m3/min; if I want the speed under 90 m/min, the area of the duct needs to be bigger than 4/90=0.44m2, which equates to a diameter of at least 23.7cm). My first question is - is the velocity of air the most important at the point where the air exits through the vent into the studio, and is it ok to have the air moving faster in narrower ducting behind? For example, the fan I am thinking of getting (NuAire Dave Size 2) fits on a 20cm round duct. This will move the required amount of air too fast (around 127m/min), however when it hits the silencer its velocity will halve, and it should arrive at the vent at a decent speed of around 64 m/min.

Silencers / baffles:
Given I want as good as possible isolation, I have placed a pair of silencers (decoupled) for the inner and outer leaf holes, and each pair positioned in the cavity between the inner and outer leaf on the narrow sides of the room. I understand the concept that you want the surface of the duct in the baffle to double so it can act as a silencer. Hence, I have based my calcs on using 20cm diameter round ducting (see above), which then becomes 25cm/25cm square ducts inside the silencer (which is a doubling of the area if I am not mistaken and lowers the velocity of the air to acceptable levels).

I have drawn these silencers using 4 turns for now, making them around 1.65m tall - am I overdoing it here? Rod’s drawing in his book shows 2 turns. I reckoned given that I am using up the cavity space anyways, I may as well make these silencers as tall as possible, but please tell me if I am missing the point here or unnecessarily overdoing the size and number of the silencers.

Another question: Given that there is so much empty space on either side of the pair of silencers, can I put this space to good use? For example, can I use this as a “built-in bass trap” between the cavities. Or do I need to wrap the inner leaf around the silencers (as shown below) and do some treatment in these newly created spaces or use them as storage? Please tell me what you would do that would assist isolation, but also assist what the room will sound like eventually.
I very much appreciate any comments and time spent on this.


Francois

Hi there Francois, and WELCOME!!!

I totally missed your post, and I only found it now while looking for something else. I hope it's not too late!

The garage sits on a concrete slab about 45cm thick,

Concrete slab is excellent, but are you SURE it is 45cm thick? That's one hell of a slab.... Most are 10 to 15 cm thick.

Walls are a single layer of concrete block construction (i.e. not hollow breezeblock,

More good news!

currently access to this is via a loft ladder from the inside of the garage, however I intend to replace this with a new hatch from the outside via the gable wall.

For sure!

I plan to create a room within a room (MSM), with the inner leaf made of suitable timber studwork (I am asking the engineer about these as well to ensure my studwork will support the heavy inner ceiling and possible cloud)

You would probably be just fine with normal 2x4 stud farming, but it's always a good idea to listen to the structural engineer!

The new ceiling joists will sit in-between the existing, outer-leaf, ceiling joists (without touching), an inch below the existing joists.

You might want to consider flipping that upside-down, and do an "inside-out" ceiling. They work very well to minimize lost height and room volume. It's a bit harder to build, but the result is that your actual physical ceiling can be just an inch below the existing studs.

will be a double layer of fireproof ⅝” plasterboard with a layer of Green-Glue in between

Another option that works well and provides great structural integrity in sheer, is to use replace one of those with OSB. Put a layer of OSB as the first layer, directly on the studs, then put a layer of drywall over that, with Green Glue. Many advantages to doing it that way.

Ventilation will be using a supply or extract fan (still making my mind up).

... and also silencer boxes! You can't go without those. You will need one silencer box on each wall penetration. So at least two in total (one on your supply duct, the other on your exhaust duct), and perhaps four (two on each duct) depending in how you do it, and how much isolation you need.

and am leaning towards going without an air-conditioning unit - Oxfordshire's climate is mild all year round, and it is very rare that the outside temperature is higher than what you would want inside the room. Also, humidity is never an issue, and I believe I can control the humidity ad-hoc using a simple dehumidifier from time to time.

Hmmmm.... I'm not so sure about that! think of it this way: You plan to have a half dozen sweaty musicians in there, jamming away happily for hours while they guzzle down beer and pizza while playing loudly on half a dozen gazillion watt amps and cabs... and all of this is happening inside an extreme well sealed plastic bag that is wrapped in many inches of excellent thermal insulation, then sealed inside another perfectly hermetic plastic bag... Add to that that many musical instruments are sensitive to changes in humidity, as are some mics, and I think yo see where this is going...

HVAC is not an option for a studio. It it no luxury. It is a necessity. You need it just as much as you need electricity, and a door. And a small mini-split system isn't that much more expensive than a really good dehumidifier....

I realise using the existing ceiling / loft floor will be the outer leaf, and the existing sloped, tiled roof is probably a third leaf. However, if I wanted to keep a freely ventilated loft storage space, this is the only way. How big a deal is this from a sound insulation point of view?

It's fine. No problem. Yes, technically the roof is a third leaf, but It's so far away that it won't be an issue.

Given the south facing window’s position, is this asking for trouble from a symmetry point of view?

No problem. Glass and drywall are not all that different in acoustic reflectiveness.

If your building code allows it, fill the entire wall cavity: side to side, top to bottom, front to back: all of it. Don't jam it in, but do fill it as much as you can. You can use any type of insulation. If you use fiberglass insulation then use a density of 30 kg/m3 (roughly) and if you use mineral wool then around 50 kg/m3. You can also mix both if you want.

is the velocity of air the most important at the point where the air exits through the vent into the studio,

Yes, and also for a distance behind that: Try to have a straight run that has the same cross sectional area as the register itself, for many inches going back. A length of at least twice the diameter of the duct, and more if possible.

is it ok to have the air moving faster in narrower ducting behind?

On the OTHER side of the silencer box, yes, but not on the room side of the silencer box.

This will move the required amount of air too fast (around 127m/min), however when it hits the silencer its velocity will halve, and it should arrive at the vent at a decent speed of around 64 m/min.

That's fine.

I have drawn these silencers using 4 turns for now, making them around 1.65m tall - am I overdoing it here?

I don't see where you drew them! What you say sounds OK, but it would be good to see the diagrams.

I reckoned given that I am using up the cavity space anyways, I may as well make these silencers as tall as possible,

Given that there is so much empty space on either side of the pair of silencers, can I put this space to good use? For example, can I use this as a “built-in bass trap” between the cavities. Or do I need to wrap the inner leaf around the silencers (as shown below) and do some treatment in these newly created spaces or use them as storage?

On a limited budget, keep your inner-leaf construction as simple as possible: Make the entire room into a plain rectangle, even if it means wasting a bit of space (as long as it's not too much!). Doing all those extra corners and kinks takes up a lot of time, complicates things, increases waste, and increases costs. Keep it simple.

- Stuart -

Hi Stuart

Thanks for the reply! It is not too late, and I greatly appreciate the help. I have been tinkering with the design of this simple studio (its amazing how many little things you pick up as you read and re-read the forums - what a great resource you guys have created and maintain!!) and have sent off some initial paper-work to my local council planning department, but have not finalised the internal design yet and have not started building.

Here is a render of the revised design - I have re-positioned the ventilation and silencers, moving the outer leaf silencer into the loft space, and the inner leaf silencer becoming part of the inner wall and protruding into the cavity. This means less space is wasted in the wall cavity.
This does mean my supply and return grilles are on the same wall, about 2.2m apart - I suppose it would have been ideal to have the supply and return grille on opposite walls for airflow. Is this a serious issue?

While I am on HVAC - I have taken your point re AC and will be installing a mini-split for both heating and cooling purposes (as well as controlling humidity).

The new ceiling joists will sit in-between the existing, outer-leaf, ceiling joists (without touching), an inch below the existing joists.

You might want to consider flipping that upside-down, and do an "inside-out" ceiling. They work very well to minimise lost height and room volume. It's a bit harder to build, but the result is that your actual physical ceiling can be just an inch below the existing studs.

I am not sure what you mean here - I intend on placing the joist for the inner leaf ceiling on top of the inner wall head plate, in between the outer leaf ceiling joists, with a 2.5cm vertical gap between the head plate and the bottom of the outer-leaf ceiling joists. Then I intend on hanging the ceiling from under the inner-leaf joists. Here is an attempt on a zoomed in part of the render. Doing this means I only lose 2.5cm of height plus the thickness of the ceiling. Let me know if you think there is a better way, or if I am missing something about the inside-out ceiling.

will be a double layer of fireproof ⅝” plasterboard with a layer of Green-Glue in between

Another option that works well and provides great structural integrity in sheer, is to use replace one of those with OSB. Put a layer of OSB as the first layer, directly on the studs, then put a layer of drywall over that, with Green Glue. Many advantages to doing it that way.

I have read in some forums about this, however it seems the main advantage is that OSB takes screws better, so you can attach things anywhere to the wall whereas otherwise you may have been limited to only screwing into the timber framing. Are there any other advantages? Cost wise it seems OSB3 here in the UK is no cheaper (in fact often more expensive) that plasterboard, and with a lower density.

While on the topic of OSB. I intend on replacing the current outer-leaf ceiling / loft floor to try and match the density of the outer-leaf concrete block wall. So I hope to use 3 layers of 18mm OSB3, along with beefing up the outer ceiling from below in-between the joist with some plasterboard. This still does not match the density of the external wall, which is 10cm of concrete block, but does reduce the weakest point in my outer-leaf. Do you have any suggestions or comments on this?

Thanks again for the help. Any further comments appreciated.

Francois

Doing this means I only lose 2.5cm of height plus the thickness of the ceiling.

... plus another 5 to 10 cm, to fit in the insulation... you need at least 5cm of insulation across the entire ceiling, in between the leaves. And then you'll lose another 10 to 15 cm below the finished ceiling, for treatment

With an inside-out ceiling, you do it the other way up. The sheathing (drywall, OSB, etc.) sits on top of the inner-leaf ceiling framing, not under it, and therefore can be just under the outer-leaf joists. Yes, the inner-leaf joists are now projecting down into the room, which "apparently" causes you to lose some height, but in reality you would have lost the same height anyway to the treatment that you will need on the ceiling in any case, so you end up better off with an inside-out ceiling, since you don't need any additional treatment below it. The bottom of the joists is your final ceiling. Just put the fabric of your choice over it, and you are done. You lose no further height below that.

Like this:

Let me know if you think there is a better way, or if I am missing something about the inside-out ceiling.

however it seems the main advantage is that OSB takes screws better, so you can attach things anywhere to the wall whereas otherwise you may have been limited to only screwing into the timber framing.

... which is a major advantage! Not sure if you have ever gone hunting for studs behind drywall, so you can attach a heavy treatment device, or your electrical raceways... Good luck finding a stud through several layers of drywall and green glue!

But even so, that's not the biggest advantage: sheer strength is. A sheet of OSB provides all the sheer strength your walls will need. They are load-bearing walls, so they do need sheer. Your inspector will likely not approve structural walls that don't have sheer members...

and with a lower density.

Drywall is about 680 kg/m3. OSB is about 610 kg/m3. Not a huge difference.

try and match the density of the outer-leaf concrete block wall. So I hope to use 3 layers of 18mm OSB3

Ummm.... the absolute density of concrete is about 2300 kg/m3. The surface density of a concrete brick is roughly 175 kg/m2. The surface density of a sheet of 18mm OBS is around 11 kg/m2. You would need roughly sixteen layers of OSB to match the density of your concrete block wall. 3 layers falls far, far short. Even if you could do that, your joists would never support the weight.

Fortunately, you don't need to match the density! You just need to get enough mass in that leaf such that your MSM resonant frequency is at least one octave below the lowest frequency you need to isolate, and the total isolation from the ceiling matches the total isolation of the walls. It's not just the mass (surface density) that you use in setting the MSM frequency: the gap plays a major part too. It's the combination of air gap and surface density that defines the isolation. So if you can't get enough density, then increase the gap. And don't forget the insulation! Leaving out the insulation costs you 1.414 times the resonant frequency, and anywhere between about 6 and 16 dB in overall isolation.... That's a rather sever penalty! Fill the entire cavity with suitable insulation, and take that into account in your MSM calculations.


- Stuart -

Hi Stuart and everyone else

I have been quiet for some time as I waited for planning permission to be granted. After a few back and forths with the planning officer and Building Regs I am now clear to proceed! I will start a new thread in the "Studio Construction" area with photos of the prep I have done and post photos as I go along. However, I just have two (... and a half) more questions.

I have given the idea of inside out ceilings some thought. However, I am going to go with my original idea of interleaved joists, with the sheathing for the inner leaf on the side of the room. My outer leaf joists are going to be 15cm wide, plus a couple of cm gap to the inner ceiling sheath, so a total cavity of 17cm stuffed with insulation which will hopefully provide decent sound proofing.

Question one: I have read conflicting reports on the type of insulation to use between leaves - some people say the less dense "loft" insulation works fine and to use the Rockwool RWA45 or similar for your sound treatment panels inside the room. Others say use RWA45 in the cavity, as well as for sound treatment. Would love to find a definitive answer.

Re ventilation and HVAC, my second question. In the renders from previous post I have indicated the position of my in and out vents - these are on the same wall, about 2.2m apart. Intuitively I would have thought having one vent on the one short wall and the other on the opposite short wall would make for better circulation, however in the interest of maximising space I kept both vents on only one wall. Is this an acceptable position for the vents?

Last question relating to the 2nd: Where to put the internal radiator/fan of the split AC? I am thinking the neatest solution is high up against the short back wall between the two vents. Alternatively it could sit on the long side wall. Keen to hear suggestions on what would be best.

Thank you so much for this forum and all the help.

Francois

I have the same question re insulation. Its the 1 thing i have not ordered yet. Loft insulation 100mm is way cheaper than batt insulation what are the down falls

For walls i have seen figures of around 30kg/m3 most of what i can find in the uk does not state mass.

Earthwool loft 44 only shows thermal values. Of .44w/mk
https://www.roofingsuperstore.co.uk/pro ... -pack.html
Earthwool acoustic is 10kg/m3
http://www.knaufinsulation.co.uk/produc ... ustic-roll
Rwa is 45kg/m3

I can easily obtain the loft stuff locally

Is there any downfall to the roll vs the batts in walls?

Hi
As a fellow UK builder I had similar questions. I concluded from reading as many threads as I could that RWA45 would work fine for both within the walls and for acoustic treatment within the room.

I've been buying mine from Jewson, the 100mm thick sheets - they're not the cheapest but they're close to my work, and they do a discount when you buy more than 5 packs. They cut really easily with an ikea bread knife!

Hope this is helpful, hopefully Stuart or another more experienced builder won't correct me rendering my decision to use RWA45 incorrect!

Good luck with the build!

Gareth

hopefully Stuart or another more experienced builder won't correct me rendering my decision to use RWA45 incorrect!

It's the wrong color! Nooooo!!!!! Sound waves don't like that color!!!!



Naah, you should be fine with that. You don't need extreme isolation in your case, so there's no need to go for the more expensive stuff, like OC-703, just for the cavity fill. You might need something different for the acoustic treatment, for sure, but the cavity fill isn't so critical if you don't need extreme isolation.


- Stuart -

Thanks Stuart - RWA45 all the way then.

I am still unsure of the positioning of the ventilation vents, and not wanting to - is it ok to have both the supply and exhaust vent on the same wall (about 2.2m apart), or is it crucial to have the exhaust on the other side of the room in order to have a proper flow of fresh air in the room? I would prefer to have it on the one wall in order to lose less floor space.

is it ok to have both the supply and exhaust vent on the same wall (about 2.2m apart), or is it crucial to have the exhaust on the other side of the room in order to have a proper flow of fresh air in the room

Personally, I always try to have the vents on opposite ends of the room, to get good flow through the entire space. Studio HVAC is high volumes of air moving at low speeds, in order to keep air noise levels down. Therefore, you don't have the benefit of a fast-moving stream of air that can be "aimed" to blow across the entire room before it gets "sucked" back again by a deep low pressure in the return vent on the same wall it came out of.

In general, I try to have the supply registers at the rear of the room and the return registers at the front of the room, above the speakers, so there's a general slow movement of air from the rear of the room going forward, and those return registers are at the point where the warmest air is.

I would prefer to have it on the one wall in order to lose less floor space.

I normally have all of the HVAC either in the ceiling space (between the two leaves), above the top of the rear section of the room, or even inside the speaker soffits. Thus, there's no loss of floor area.

If you design it carefully, you can fit in the HVAC with minimal loss on room size and volume.


- Stuart -

garethmetcalf wrote:Hi
As a fellow UK builder I had similar questions. I concluded from reading as many threads as I could that RWA45 would work fine for both within the walls and for acoustic treatment within the room.

I've been buying mine from Jewson, the 100mm thick sheets - they're not the cheapest but they're close to my work, and they do a discount when you buy more than 5 packs. They cut really easily with an ikea bread knife!

Hope this is helpful, hopefully Stuart or another more experienced builder won't correct me rendering my decision to use RWA45 incorrect!

Good luck with the build!

Gareth

Thanks Gareth. Got a great deal at 11.89 per pack (13) and 28 sheets of 15mm board all for 383 so happy and its coming tuesday

I also looked at the NRC info as i will have a 50 mm air gap behind the insulation in my double stud walls but it looks valid so bring on delivery tuesday. Just hoping my green glue arrives before we start boarding tuesday