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PostPosted: Thu Mar 14, 2019 4:23 am 
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Location: Hastings, East Sussex, United Kingdom
Hello & howdo’?

This is my first post to John Sayer’s Recording Studio Design Forum and I would like to begin with a word of praise for John, the administrators and moderators for the excellent resource that they have built. It truly is “A World Of Experience” as the 'strap - line’ says and all the more remarkable for being independent, free to use and based on trust; there are precious few things in the world (never mind on the internet) that can claim that!
My name is John and I’m developing a design to convert a double garage into a music practise room which can also be used to track instruments including drums and electric guitars.
The building is in East Sussex, in the South East of England which has a temperate climate, situated in a residential area, on a hill, amongst woodland and is detached from our house. The garage is at the edge of a levelled area cut into the side of the hill, so the South-Eastern aspect of the building is built into the earth to a height of 131cm (4’4”).

Attachment:
Garage Complete~4.jpg


It sits on a 4” (10cm) concrete base and internal dimensions are 4.85m x 4.98m (15’11” x 16’04”) - almost square! There is a half-hipped roof which is 4.46m (14’7”) at the highest internal point. The walls consist of a single tier of brick and are buttressed on 3 sides with breeze block columns, roughly at the centre point of each wall. There is a structural beam which runs from from the North-West wall to the South-East wall at a height of 2.24 M (7’4”). The North-West wall has an outward opening door and window and the South-West aspect has two large openings for the garage doors. I have attempted to model the room as accurately as possible using Sketchup.

Attachment:
Garage Walls + Joists6.jpg


Although I have learned a great deal of very useful information from Rod Gervais and F. Alton Everest’s excellent books (as well as this forum) I won’t pretend that I don’t have a great deal more to learn and I’m fully prepared to do this. Here is a brief outline of what I think I know about achieving my aim - I would be very grateful for any comments, criticism or suggestions if any of you have the (precious) time and inclination.
I have measured the ambient sound level in the area surrounding the garage at 35dB on a windless day and up to 68dB when to wind shakes nearby trees. Passing traffic sometimes elevates the level to 70dB and the occasional light aircraft passing nearby will give a reading of 55dB.
The loudest instruments I am going to record are drums (I tend to DI bass when recording) which I have measured peaking at up to 116 dB. Local noise regulations are non-specific when it comes to defining an actual level at which sound becomes a nuisance, but as we have neighbours at both sides (6m and 12 metres) I am aiming for a sound transmission reduction of 55dB or greater and while this is ambitious, the handy transmission loss calculator suggests that it’s possible, so I’m optimistic that it can be achieved. I have a budget of £15,000 - £18,000 and intend to undertake as much of the work as I practically can (although I will not attempt any electrical work, fitting the HVAC system or acoustic windows or doors - I would rather pay experienced professionals to do those parts of the job).
I plan to build a single room within a room consisting of two leaves (where possible*). The outer leaf will consist of the existing single tier, solid brick wall which will be sealed, up to a height of 221cm, then a combination of 18mm OSB and 2x 19mm gypsum board to meet a ceiling of similar construction, supported by the existing and some additional ceiling chords (I have consulted a structural engineer who tells me that with the correct reinforcement to the chords and lowest beam, this is both possible and safe).

Attachment:
Joist and Chord Reinforcement~.jpg

Attachment:
Chord Reinforcement.jpg

Attachment:
Cross Section.jpg


The South-West aspect of the building has two large “up and over” garage doors which will need immobilising, sealing and damping with mass loaded vinyl (or similar) before a 18mm OSB and 2x 19mm gypsum board wall (supported by 2x4 stud) is built in each gap. I realise that this in effect creates a 3 leaf system*, but I don’t see a way around this other than simply bricking up the gap which is unfortunately not an option in this case.

Attachment:
Door Block Cross Section.jpg


The inner leaf will be 2x19mm gypsum board with green ’glue’ in between, attached to a stud frame anchored to the concrete floor with an air gap of at least 30 centimetres between the leaves, which will be loosely filled with rock wool. The inner leaf frame will support a ceiling of similar construction at a height of 233cm (7’7”) which will be lowered in the middle of the room in order to avoid the structural beam which runs from the centre of the the North-Eastern Wall to the South-Western Wall.
Attachment:
Stud Frame & Plasterboard Cross Section.jpg


The existing window will be replaced on the outer leaf with a fixed one, glazed with 21mm laminated glass and one on the inner leaf using 12mm glass, conforming to the design in chapter 5 of the second edition of Rod Gervais’s book. The existing door will be removed and two, triple sealed doors (as similar to Rod’s “super door” as possible) will be installed with closers. I would ideally like to add laminated glass windows to the doors (I have spent far too many hours working in dark rooms)
but my calculations suggest that it would cause them to be very heavy!

Attachment:
Window & Doors CS.jpg


I have (so far) been unable to calculate the ventilation load for this room, so I intend to talk to a professional air conditioning engineer about local humidity and other requirements for AC** (luckily, I know one locally who has installed AC in studios before). It will need fresh air for up to 5 people (75 cubic feet per minute) which will be pulled though the room by an inline fan, although more often there will be only one or two people occupying the room. I will build 4 baffles, one for each time the ventilation system penetrates a leaf and I will need an appropriately sized mini - split system for temperature and humidity control **.

Attachment:
AC CS.jpg


I know that the limited space will make acoustic treatment more difficult - I intend to put bass traps in the two windowless corners and attempt to create a variable acoustic using dual purpose absorber / reflectors which can be moved along wall mounted rails or used as free-standing units on the floor, depending on the desired environment.
I’m sure there is much I have overlooked in this and other areas, but before I go into detail I’m curious to know if this idea is at all viable or could, at least, form the basis of a better design.

I would also like to ask a couple of questions. The concrete floor is not exactly level - it has been poured in two halves and at the North-East end of the room, one is roughly 1cm (less than half an inch) higher than the other. Is this difference tolerable or should I level the floor? I would also like to know what the most effective material for sealing the brick wall: damp seal, masonry paint or is there a better compound?

Thank you for reading my ramble and best wishes. John.


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PostPosted: Thu Mar 14, 2019 5:44 am 
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Wow!

Hi John, and welcome to the forum! :)

But WOW! Again! That has to be one of the best-ever first posts! I think you covered absolutely everything in there!

:thu:

Quote:
I have attempted to model the room as accurately as possible using Sketchup.
:shock: Right down to the individual nuts and bolts, too! Excellent.

Quote:
I am aiming for a sound transmission reduction of 55dB or greater and while this is ambitious, the handy transmission loss calculator suggests that it’s possible, so I’m optimistic that it can be achieved.
It's do-able, yes. Getting toward the limit of what can be achieved for most home studios, but achievable.

Quote:
I have a budget of £15,000 - £18,000
For the UK, for a 25m2 studio, that's probably about right. In the ball-park, for sure.

Quote:
The South-West aspect of the building has two large “up and over” garage doors which will need immobilising, sealing and damping with mass loaded vinyl (or similar) before a 18mm OSB and 2x 19mm gypsum board wall
You can probably save a bit of money there (on the MLV, which is very expensive), by just building a frame over the doors, and putting your sheathing directly on that. MLV has only a very few valid uses in acoustics, in my opinion. The largest use appears to be lining the pockets of the folks who sell it! But that's not a valid use, IMHO.

Quote:
I realise that this in effect creates a 3 leaf system*, but I don’t see a way around this
Right. Sometimes you just have to go 3-leaf. In which case you need more mass on the middle leaf, but you seem to be taking care of that with 18mm OSB + 2 x 19mm drywall, and good air gaps on each side, filled with insulation.

I would put the framing up tight against the existing wall, then put the sheathing on the other side of the studs, facing the room.

Like this:

Attachment:
PKNCUS-Garage-Door-Isolation-Plan-04.png


Attachment:
PKNCUS-Garage-Door-Isolation-Plan-05.png


Attachment:
PKNCUS-Garage-Door-Isolation-Plan-06.png


Attachment:
PKNCUS-Garage-Door-Isolation-Plan-07.png


That's the plan: here's the actual implementation from a client in the USA:

Attachment:
PKNCUS--garage-door-cover-01--locked-down-and-blocked.jpg


Attachment:
PKNCUS--garage-door-cover-02--locked-down-and-blocked--side-view.jpg


Attachment:
PKNCUS--garage-door-cover-03--framed-with-tyvek.jpg


Attachment:
PKNCUS--garage-door-cover-04--OSB-up.jpg



Quote:
The inner leaf will be 2x19mm gypsum board with green ’glue’ in between,
You might want to consider doing that with a layer of OSB on the studs, then a layer of drywall over that. It gives you a nailing surface around the entire room (through the drywall into the OSB), which can be very useful. It allows you to hand treatment, lights, or decorations any place you want them, without needing to hunt for a stud.

Quote:
The inner leaf frame will support a ceiling of similar construction at a height of 233cm
Have you considered doing an "Inside-out" ceiling, to maximize your acoustic ceiling height? It would probably make a lot of sense in your case.

Quote:
I would ideally like to add laminated glass windows to the doors (I have spent far too many hours working in dark rooms) ... but my calculations suggest that it would cause them to be very heavy!
Not a problem! Here's a series of photos from a studio in Australia, showing how one of my clients built the doors for his drum room (he teaches drums, so he often has TWO drum kits going at once in there! :shock: :) ) :

Attachment:
Site-built-door--BRAUS--102+--door-blank-cut.jpg


Attachment:
Site-built-door--BRAUS--106+--all-layers.jpg


Attachment:
Site-built-door--BRAUS--109+--frames-shimmed-and-squared-2.JPG


Attachment:
Site-built-door--BRAUS--112+--inner-door-hung.jpg


Attachment:
Site-built-door--BRAUS--114+--both-open-seals-and-gap.JPG


Attachment:
Site-built-door--BRAUS--115+--Finished-Entry-door-from-outside.jpg


Attachment:
Site-built-door--BRAUS--117+--both-open-from-outside.JPG


The sequence is fairly self explanatory, but let me know if you have questions. He built those doors on-site, and they work great. He gets about the level of isolation you are looking for.

Yes, they are heavy, but look at the hinges...

Quote:
The concrete floor is not exactly level - it has been poured in two halves and at the North-East end of the room, one is roughly 1cm ... higher than the other.Is this difference tolerable or should I level the floor?
If that were my room, I would level it. 1cm is enough that it would be annoying. You don't want musicians tripping over your floor all the time...

Quote:
I would also like to know what the most effective material for sealing the brick wall:
Any good quality masonry sealant will do the job. Do two coats, just to be certain that you covered it all.

Quote:
Thank you for reading my ramble and best wishes. John.
I'm looking forward to following your thread, John! It seems like you've taken the tie to do this properly: researching everything, doing a very complete, detailed design, dotting all the "i"s and crossing all the "t"s.... So I'm making this thread a sticky for now, as a shining example of how people should do their first post!

:thu:


- Stuart -


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PostPosted: Thu Mar 14, 2019 7:56 am 
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You have done great work, and I'm jealous of such Sketchup skills.

I'll take on the role of Oblique Strategies and Devil's Advocate here.

Your SPL numbers suggest that this is a quiet area. Drums are the loudest and perhaps most annoying instrument.

As a Recording Engineer and Producer I have found that overdubbing Drums late to last in the proceedings has quite a few advantages.
e.g. Recording them at a time when the Neighbours won't mind. Or in a bigger space which would likely deliver a better result.
Scratch drums can be done electronically, played or programmed.

I think rendering the brick wall should add about 6dB of TL, but I am not sure about the spectrum of that. Kick Drum can find it's way......

Perhaps replacing the metal doors with a brick wall would be more effective.

What is the ceiling plan?
Recording wise no ceiling would be just great, but you would lose isolation. Perhaps there is some in-between design possible.
Is rain on the roof audible in there?

DD


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PostPosted: Thu Mar 14, 2019 8:06 pm 
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Location: Hastings, East Sussex, United Kingdom
Thank you for your helpful, detailed and amazingly prompt reply Stuart - I know you have a great deal of other things to consider.
Thanks also for the kind words; it’s gratifying to know I haven’t been completely wasting my time!
Framing the garage doors in the way you indicated makes much more sense and should be easier to build I think. I’m going to draw a similar solution into my plan. I’m also delighted to hear that it is practical to fit windows of appropriate mass in the triple seal doors as I’m determined for the finished room not to be a gloomy, dismal space - your Australian client’s doors are magnificent by the way!
I have also noted your advice regarding sealing the brick work and levelling the floor - my initial idea was to use a vinyl floor covering over the concrete which I figured would mitigate the unevenness, but as you say "That'll do" doesn't amaze people!
The challenge for me will be understanding the “inside out" ceiling concept. It’s a great shout Stuart and I hadn’t considered it before now, so I’ll do some more research and revise the plan. Thanks again for your interest and time. John.


Hello & howdo’ DanDan?
Thank you for your interest in my design and sharing your thoughts on it. I have noted your comments regarding day time use and this is really how I intend to use the room as it will primarily be a practise space and secondarily a recording space. I will never do any serious mixing in there as, well, mixing is not one of my skills and I would always prefer to take my recordings to someone like yourself who is experienced, professional (and doesn’t have two kinds of tinnitus)!
Great shout regarding rendering - this hadn’t occurred to me, thanks. I know that bricking up the garage door gaps would be the best (and simplest) solution in terms of transmission loss, but I have to build in a way that is reversible, so I’ll have to opt for the framing instead. As far as the ceiling goes, I have some homework to do! Stuart suggested an “inside-out” design which I don’t properly understand - so I’ll have to get back to you on that.
Thanks also for your kind words on my Sketchup drawings - I employ the “stab-wildly-at-all-the-buttons-until-one-of-them-works” method! I should probably get out more. Best wishes, John.


Last edited by John Steel on Sun Mar 17, 2019 9:39 pm, edited 3 times in total.

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PostPosted: Thu Mar 14, 2019 10:44 pm 
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Location: Cork Ireland
I installed a Pergo hospital grade slate look vinyl floor recently. Cork comes from the Irish word Corcach, meaning Bog! So my 25 year old floor was quite uneven and sloping.
A large amount of levelling compound fixed this.
A fully absorbent area overhead is a great start. Stuart's inside- out technique delivers absorption, but with a blocking layer above it.
Just think of a normal plasterboard ceiling with a thick layer of fibre laid over it. Now invert that.
The fibre will of course have to be contained. This can be done with fabric and slats. Or using absorbent ceiling tiles in some sort of frame.
Polyester has become available and I highly recommend it as a surface/containment layer pretty much anywhere. http://www.autexacoustics.co.uk have been very helpful, including cutting double sized panels with no extra cost. Caruso Isobond is also a great performer and is now available in retail quantities. https://www.don-audio.com/CARUSO-ISO-BO ... -bond-30mm

In a way, it seems a waste to obscure that high vaulted area. There are other ways to achieve isolation and absorption up there. More expensive though.

DD


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PostPosted: Fri Mar 15, 2019 12:21 am 
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Quote:
The challenge for me will be understanding the “inside out’ ceiling concept. It’s a great shout Stuart and I hadn’t considered it before now, so I’ll do some more research and revise the plan. Thanks again for your interest and time. John.
The "inside-out" concept was originated by John Sayers, as far as I know. The basic idea is simple: You put the drywall on the OTHER side of the studs (in the case of a wall) or joists (in the case of a ceiling). So for a ceiling, instead of putting the drywall below the joists, you put it above the joists. Thus, the joists are still in the same place as they would have been (usually.. some exceptions), so the acoustic height of the ceiling (the height that the low frequency sound waves "see") is much higher, by the depth of the joists. The room volume is also greater, which is another advantage and you also have the entire depth of the joists available for acoustic treatment (usually thick insulation), so you end up with less treatment hanging down below your ceiling surface: the visual ceiling can be the bottom edge of the joists, if you want. It's a win-win-win situation.

The only down side to it, is that you normally can't get up there into the ceiling cavity to nail on the drywall from above, because there's no space at all to do that. So, the construction becomes more complex: you build a "backbone" of large dimension joists that can be spaced further apart than normal, leaving large gaps between them, then you build a number of "modules" down on the floor of the room, made up of a simple 2x4 frame with the OSB/drywall nailed on, and raise those modules into the gaps between the joists, one by one. It's more work, yes, but the outcome is certainly worth it!

Here's an example, from that same client in Australia, who his inner-leaf "inside out":

CONCEPT:

"Backbone" of oversized-doubled-up joits:
Attachment:
Modular-inside-out-ceiling-000.jpg


A couple of modules shown in place, without the "backbone", for clarity:
Attachment:
Modular-inside-out-ceiling-002++.jpg


Close up of one module, without the backbone:
Attachment:
Modular-inside-out-ceiling-003++.jpg


Completed ceiling, with all modules and backbone in place.
Attachment:
Modular-inside-out-ceiling-004++.jpg



IMPLEMENTATION:

The actual "backbone". You can see the outer-leaf ceiling directly above the backbone here, and the gap is minimal between the bottom of the outer-leaf joists and the top of the inner-leaf joists. In this photo it even looks like they are touching, but they aren't: there's a small gap there: no contact at all between outer-leaf and inner-leaf.
Attachment:
Inside-out-ceiling-01.jpg



Raising one module up, in between the joists of the "backbone". The modules are made just a little smaller than the hole they will fill, to leave a gap of a few mm around the sides. That gap is completely filled with good quality flexible caulk, that is smeared on thickly to the sides of the module just before the final raise, then more caulk is forced into the gap from below, once the module is nailed/screwed/bolted in place.
Attachment:
Inside-out-ceiling-02.jpg



One module in place already. You can also see the "lip" that they made around the top of the hole next to this one, which is also caulked just before the module is raised, to get an even better seal.
Attachment:
Inside-out-ceiling-03.jpg



All of the modules in place, except for the very last one, which is just going up in this photo.
Attachment:
Inside-out-ceiling-04.jpg



The modules being filled with insulation, held in place with package strapping, then the layers of fabric going on:
Attachment:
Inside-out-ceiling-05.jpg



Ceiling half covered with fabric.
Attachment:
Inside-out-ceiling-06.jpg



Final stretch of fabric over the last section of the ceiling:
Attachment:
Inside-out-ceiling-07.jpg



Thin trim going on, to cover the staples and the joints in the finish fabric:
Attachment:
Inside-out-ceiling-08.jpg



Another view of the nearly compete ceiling with trim:
Attachment:
Inside-out-ceiling-09.jpg



Lights installed:
Attachment:
Inside-out-ceiling-10.jpg



Complete ceiling:
Attachment:
Inside-out-ceiling-11.jpg


Another view of the completed ceiling.
Attachment:
Inside-out-ceiling-12.jpg



It's an excellent method, and I use it for most of the studios I do, especially when ceiling height or room volume are lacking.

One caveat! You do need to get this approved by a structural engineer before you start building it!! Never do any structural work unless the design has been checked by a qualified, certified structural engineer. Hanging thousands of kg of building materials over your head is a dangerous thing: get it approved for safety, and for compliance with code, then build it safely, with precautions to prevent accidents during construction! Even though the modules are relatively small they are still heavy, ... you do not want any of that falling on you while you are raising it! So take care with that...

- Stuart -


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PostPosted: Fri Mar 15, 2019 1:31 am 
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Hello again Stuart,
I like this idea a lot (notwithstanding the added difficulty building it), because it also offsets the lack of acoustic treatment on the wall in which the window and doors are set - as you say, it's a win-win. The thing I can't wrap my head around is this; by inverting the ceiling, this will surely reduce the air gap between the inner and outer leaf (by 10cm in my design), so it must reduce the overall transmission loss and alter the resonant frequency of the whole structure. Or is the difference this causes negligible and not worth worrying about?

Thanks for your recommendations DanDan (filed for future reference) and I hear you loud and clear when you say that the roof space is wasted. The problem here is the low structural beam which spans the room NE to SW. I couldn't figure out a way of building the inner leaf around this and through the ceiling chords on top of it without forming a flanking path to the outer leaf (believe me I tried). The no-expense-spared solution would be to replace the existing structure with RSJs but this would have been ruinously expensive and involve removing and rebuilding the roof, so I think this design is 'right-sized' for me.
Attachment:
Garage Walls + Joists(planed)1.jpg


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PostPosted: Fri Mar 15, 2019 2:35 am 
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Quote:
The thing I can't wrap my head around is this; by inverting the ceiling, this will surely reduce the air gap between the inner and outer leaf (by 10cm in my design), so it must reduce the overall transmission loss and alter the resonant frequency of the whole structure. Or is the difference this causes negligible and not worth worrying about?
You do still need to tune the ceiling, of course, but you can easily compensate for the reduced air gap by increasing the mass of the leaves. In the example I gave you, the sheathing on the inner leaf is a layer of 18mm plywood on top of the framing, then two layers of 12mm fiber-cement board with Green Glue. At least, that was the design, but in the end we went with just one layer of 18mm fiber-cement on top of the 18mm plywood, for cost reasons. You can see that in photo number 2 of the actual build. Fiber-cement board ("FC") is two-and-a-third times the density of drywall, so that layer of 18mm board has the same mass as about 39mm of drywall would have (eg, two layers of 15mm plus one layer of 10mm). FC is also more rigid than drywall, and the coincidence dip is also higher up the scale, since the speed of sound is greater in the FC than in the drywall.

Now, here's the interesting thing: the owner of that room TEACHES drums! So he often has two drum kits going full-bore in there, plus music and a bass amp.... and yet he gets very good isolation. His neighbor's front door is just a couple of meters away, and his own bedroom is right above the studio... his wife says the sound is practically inaudible up there, and his neighbor can't hear a thing inside his house.

So, as long as you compensate in the design for the reduced air gap by increasing the mass and damping, there's no problem. As the strange saying goes: "there's more than one way of skinning a cat...."


- Stuart -

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PostPosted: Fri Mar 15, 2019 6:20 am 
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Now there's a plan! I can't believe I have never heard of fiber-cement board until now (duh). I'm excited by this to the point where I'm wondering if I should incorporate it elsewhere? Excuse me while I do some catching up! :yahoo:


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PostPosted: Fri Mar 15, 2019 9:55 am 
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Quote:
Now there's a plan! I can't believe I have never heard of fiber-cement board until now (duh). I'm excited by this to the point where I'm wondering if I should incorporate it elsewhere? Excuse me while I do some catching up!
There's no need to stop with just fiber-cement board: there are several materials that are even higher density... the problem isn't so much the density as it is the cost.

For example, if you wanted to move up another notch, you could go with aluminium plate (or "aluminum", as some places spell it, that didn't get the memo... :) ). That's almost twice as dense as fiber-cement (about 1.8 times, to be more precise), coming in at about 2800 kg/m3 (vs. about 1550 for FB, and about 650 for drywall). So if you had a lot of spare money, you could buy some 9mm thick aluminium plate, and that would be the same mass (surface density) as those 39mm of drywall.

Next step up could be steel plate, which is nearly three times as dense as aluminium, coming in at rough 7850 kg/m3. So a 3mm steel plate (1/8") would be roughly the same mass as the 39mm of drywall.

And if you wante to get even more exotic, then nothing beats lead sheeting: at 12,500 kg/m3, it's about 1.6 times the density of steel, so with lead foil a bit less than 2mm thick you could get the same mass as those 39mm of drywall. Plus, lead has the advantage that it is considered somewhat to be "limp mass", since it is very soft and pliable, and also self-damping, so you could probably safely reduce the air gap by maybe 3 or 4 mm... thus, you would lose no thickness at all! The amount you lost from the 2mm of lead thickness, you could more than make up for due to the favorable characteristics of the lead allowing a slightly smaller air gap...

So, in theory you could save about 4cm up there, by using 2mm of lead foil instead of 39mm of drywall... But I think you'll find that 2mm lead foil is just a tad more expensive than three sheets of drywall... :)

However, of course, if you used lead foil on BOTH leaves, instead of drywall, you could save 8cm of space... and probably blow your budget too, in the process! :)

There's other materials too that I didn't mention, for various reasons. For example glass is around 2500 kg/m3, which is a bit more dense than concrete, but there's more reasons than the feminist issue of having a "glass ceiling" in your control room.... :) Or MLV which is about the same density as fiber-cement board, but likely a lot more expensive... on the other hand, like lead, it is limp mass, so there's that....

Anyway, my point is that there' a cost/benefit consideration here: there are very high density materials that could be used, and would give great results: high mass in thin package. But can you justify the elevated cost of such materials, just to save a few cm? For FC, the answer is probably "yes", but for steel plate or lead sheet, it's more likely to be "no".

By the way, what is your actual goal here, in terms of MSM resonant frequency (Hz), and overall isolation (dB)?

Quote:
I hear you loud and clear when you say that the roof space is wasted.
It doesn't have to be wasted: You can still use that for your HVAC ducts and silencers...

- Stuart -

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PostPosted: Fri Mar 15, 2019 11:53 pm 
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Quote:
By the way, what is your actual goal here, in terms of MSM resonant frequency (Hz), and overall isolation (dB)?



If I understand the question correctly, I’m aiming for overall isolation of at least 55dB. The materials I intend to use and the method of construction employed would (theoretically) result in a resonant frequency of around 20 Hz (I think). To add more detail - my selection of materials was based on the following thinking.
The building has an existing single tier brick wall up to a height of 221cm (the NE & SE sides are slightly higher) which is a good dense barrier (surface density of approx 174 m2) and properly treated will give good isolation. However, in order to form a complete outer leaf including the ceiling and framing the garage door gaps, I will have to use other materials, which will mean that the overall transmission loss (for the outer leaf) will only be as good as those parts of the structure allow. I reasoned that, although not as dense as brick, a combination of two layers of 19mm Gyproc (SD=15Kg/M2) and 18mm OSB (similar density to Gyproc) would be sufficiently dense (in combination with the inner leaf) to produce the TL needed. I ran the numbers through the excel TL calculator (which assumes that both leaves are formed of stud walls, so is not ideal for this calculation) but this indicated that with an inner leaf formed of two layers of Gyproc*, a gap of 30cm and the inner studs on 24 inch centres, that the T/L for the outer leaf would be around 37dB and 34dB for the inner leaf - in theory! This combination would notionally produce a resonant frequency of 18.5 Hz (with cavity insulation) and a constant of 183 Hz. (* I now realise that your suggestion of a combination of 18mm OSB and one layer of 19mm Gyproc is much more practical for the reasons stated earlier in the thread, but for the purposes of this calculation does not make a huge difference).
I checked the numbers using Gregwor’s calculator which is much more flexible and that gave slightly different results:

Leaf 1 T/L = 36.37 dB
Leaf 2 T/L = 33.47 dB
Res. F = 17.36 Hz (insulated)
Constant = 141.42 Hz

I think that this is probably more realistic but I’m also aware that this is not a ‘real world’ value - more of a guide that will be effected by all sorts of factors (not least of all the tolerances and accuracy of the build and materials). Much obliged for your thoughts on the cost benefits of various materials - I’m still researching fiber-cement board (the cost, how easy it is to work, special tools needed etc) and I’ll update my drawing to include an "inside-out” ceiling on the inner leaf.

Quote:
It doesn't have to be wasted: You can still use that for your HVAC ducts and silencers...

I do intend to put the outer leaf ventilation supply baffle in the roof space (it’s not clear from the jpegs that I posted) but I pictured it sitting like this:
[img]
Attachment:
OL%20Input%20Baffle%20location.jpg
[/img]


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PostPosted: Sat Mar 16, 2019 6:32 am 
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Quote:
I do intend to put the outer leaf ventilation supply baffle in the roof space (it’s not clear from the jpegs that I posted) but I pictured it sitting like this:

The penetrations for the silencer boxes through your leaves in your picture show flex duct. The penetrations need to be the same material as the silencers themselves. Basically just build a square or rectangular "sleeve" that sticks out of the box. That sleeve will penetrate the sheathing. The inner and outer silencer box sleeves can be joined using any air tight flexible material (neoprene, flex duct, canvas, etc).

Greg

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PostPosted: Sat Mar 16, 2019 9:09 am 
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Hello & howdo' Greg?
Thank you for your interest and advice - I'm getting there - one short step after the last! Best wishes, John.


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PostPosted: Tue Sep 17, 2019 11:04 pm 
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Location: Hastings, East Sussex, United Kingdom
Hello again to all,

I’ve spent a few month’s considering the suggestions made by Stuart, Dan Dan
and Gregwor in response to my first post - thank you for your help, it’s very much appreciated.


My revised plan looks like this:

The concrete floor of the garage will be levelled where necessary.

The upper outer leaf will incorporate a layer of 12.5mm cement board and 18mm OSB with green ‘glue’ in between.
Attachment:
Upper Outer Leaf 1.jpg

Attachment:
Upper Outer Leaf 2.jpg


The inner leaf structure will incorporate walls made up of a layer of 19mm plasterboard and 18mm OSB with green ‘glue’ in between.

The gaps for the two garage doors will be framed with timber, insulated with rock wool and an inner wall of one layer of 12.5mm cement board and one layer of 18mm OSB with green ‘glue’ in between will be added.
Attachment:
garage door gap.jpg


The inner leaf ceiling will be built using an ‘inside - out” design, detailed by Stuart earlier in this thread. The ‘backbone’ will support timber framed modules which will be capped with one layer of 12.5mm cement board and one layer of 18mm OSB with green ‘glue’ in between.*
Attachment:
Upside-Down Ceiling 1.jpg

Attachment:
Upside-Down Ceiling 3.jpg


Because of the extra weight of the new materials in the design, I thought it would be a good idea to re-check the loads and spans with a structural engineer (new to my project) and I’m very glad that I did (for a number of reasons)! His recommendations were that the main supporting beam be either replaced with a steel I-beam or modified to form a ‘flitch beam' (i.e. reinforced by a 10mm steel plate with two staggered rows of bolt holes, sandwiched between another identical beam and held together with M12 bolts). I think the latter option is the more practical as it will avoid the need to place support jacks while a steel beam is put in place.
Attachment:
Flitch_Beam_4.jpg


He also advised that reinforcing the ceiling chords could be achieved by bolting them to the joists with M12 bolts, rather than ‘collaring’ them as previously suggested, and this will be both simpler and cheaper.
Attachment:
Chord_Reinforcement_1.jpg

Attachment:
Chord_Reinforcement_2.jpg


*The inner leaf stud frame will need to be reinforced on either side of the main beam with two steel 152x89x16mm universal beams in order to support the inner ceiling in a single span. These will need to be pre-drilled in order to attach the connecting timbers.
Attachment:
Upside-Down Ceiling V.5 Flitch Beam.jpg




I've also been taking some time to consider the ventilation requirements of the design (I think I may be suffering brain damage as a consequence)! As many of you already know, it’s laborious and fiendishly interactive with other aspects of the design - I have lost count of the times I have started, checked, junked and re-started.

Anyway - here goes:

The interior size of my new room will be 38.42m3 or 1356.79 ft3. Six changes of air per hour will require an airflow rate of 8140.74 ft3 or 135.67 cu feet per minute. So the minimum cross sectional area of the ducting, while maintaining a velocity of less than 300 feet per min at the register, needs to be no less than 5.42 inches (CSA = CFM/300 or 135.67 divided by 300 = 0.452 ft (5.42 inches). To be safe, let’s call the pipe diameter 6” (152mm).
So for the supply ventilation path, I think I’ll need an 200mm x 200mm outer louvre (radius of minimum CSA multiplied by itself 76mm x 76mm = 5776mm² then multiplied by 3.142 = 18148.192mm² and doubled to allow for the 50% ‘free’ area of the louvre design = 36296.384mm². The square root of this last number gives the height & width - both 190.5160mm, let's round that up to 200mm).
Attachment:
Ventilation 1.jpg


The louvre will be fixed to a plenum box and then approximately 75cm of 6”diameter round duct which will be connected (via a 6” sleeve) to an outer leaf silencer box made of 25mm MDF, lined with 25mm of duct liner, with a CSA of 100 in² (645.16 cm²) throughout and incorporating 8 x 90 degree turns. This will penetrate the outer leaf and feed into another run of 6” round duct (approx 100cm) which will connect to a larger, inner leaf silencer, similar to the outer leaf silencer, but increased in size to allow a CSA of 144 in² (929 cm²). This will penetrate the inner leaf at head height, adjacent to the mini-split inner unit, via a deflection grill.
Attachment:
Ventilation 2.jpg


The exhaust ventilation path will be similar only in reverse, with the important difference that it will include an inline fan sized to provide the correct airflow pressure and velocity and powerful enough to cope with the static pressure in the ducts and silencers*.
Attachment:
Ventilation 3.jpg


Which brings me to the thorny subject of static pressure!


To calculate this I used the equivalent length method as this seemed the least complicated to comprehend.



Equivalent length method indicates 2 x small silencers = 240 meters of straight duct.

Silencer box flow calculations using the equivalent duct length method:

10” Equivalent diameter round duct area = 10.9” (small silencers)

12” Equivalent diameter round duct area = 13.1” (large silencers)

Equation for converting a sharp 90 degree bend into an equivalent length of straight duct is:

Duct Diameter x 60

10” x 60 = 600” or 50’ for each 90 degree turn

x 8 for each silencer = 400 feet of straight duct for each outer leaf silencer

and

480 feet of straight duct for each inner leaf silencer.

Using the engineeringtoolbox.com friction or head loss calculator this results in


"Friction Loss (inH2O): 0.0474
Friction Loss (inH2O/100 ft): 0.0119
Air velocity (ft/min): 252
Air velocity (ft/sec): 4.1899999999999995"
(Outer leaf silencer)

and

"Friction Loss (inH2O): 0.00809
Friction Loss (inH2O/100 ft): 0.00809
Air velocity (ft/min): 216
Air velocity (ft/sec): 3.6"
(Inner leaf silencer)

Giving a combined loss for all 4 silencers of 0.11098 (inH2O) or 27.643887046833 pascals and apparently achieving an air velocity of 216 ft/min at the point it enters the inner leaf.
Adding in the losses for 2 outer louvres with insect screen [2x 0.05 in.wg], 2 plenums[2 x 0.01] and 4 metres of additional 6” ducting[0.08 in.wg] (with 2 x 90 degree turns[2 x 0.04] and 4x 45 degree turns[4 x 0.03]).
Total = .71098 in.wg or 177.09 pascals.

So I reckon a fan with a similar spec to this ought to do the trick*
https://www.ductstore.co.uk/acatalog/info-TDSIL-500-150-160-T.html
Attachment:
fan.png


If I am at error on any point here and you have the energy and time to indicate where, I'd love to hear from you. I'd also like to hear any suggestions or tools that would assist with calculating latent and sensible heat loads if you have them.
Thanks and best wishes, John.


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