New Studio Build

[Soundman2020]

doesn't this box made out of OSB hard bridge the two leafs together?

It sure does, if there's a hard mechanical connection on both sides! It would only be OK if there is some type of resilient decoupling on both leaves (oar at least one of them!)

At the moment I plan to mount both my intake and outlet baffle boxes on the inner leaf. I'm hoping to get enough isolation with this but I can always add baffles to the outer leaf if the isolation isn't sufficient.

Smart plan! As long as you have the ability to decouple the duct that passes through both leaves, that's fine.

it then needs to connect to flexible ducting which I assume needs to be wrapped in insulation to prevent condensation

Use insulated flexduct:

HVAC-flexduct-SML-ENH.jpg

the flexi duct has no mass so any sound waves that makes it through the inner baffle will then be in the cavity?

Right. Which is why you will probably need silencers on both sides, or a massive sleeve that goes through both leaves and is decoupled on both sides.

From what I'm reading the cross section of the baffle box should be at least double that of the ducting pipe I use going through the inner and outer leaf? If I used 110mm then 220mm? I assume that means the opening into the room too?

Yes, but it's more complicated than that! I'm real short on time to explain now, but I have written about that on several other threads. Hopefully you can find it! There's a whole process of calculation that you need to go through here...

Also should the extraction baffle have the same dimensions as the inlet so going from a 220mm vent in the room down to a 110mm duct through the inner leaf?

Yes, at least! Some HVAC people consider it good practice to make the return duct or exhaust duct a bit larger than the supply duct. But at the very least, both supply and return should be the same: return should never be smaller than supply.


- Stuart -

[rickybobby]

Hi Stuart,

Thanks for the fast response, especially as you're short on time.

Right. Which is why you will probably need silencers on both sides, or a massive sleeve that goes through both leaves and is decoupled on both sides.

If I was to build a massive sleeve to go through both leaves please can you point me to some other posts about how to decouple this (having trouble finding an example)? I'm guessing it needs decoupling before it goes through either leaf but then I'm thinking I'm back to the issue I'd have with flexi duct where there's a 'thin' point in the cavity for sound waves to penetrate easily? Possibly I'm best to just go with a baffle box on the outside of the building.

I've since had a long read around the forum since I first wrote the above paragraph. I'm confused! I see you saying to someone that

I NEVER pass a duct directly through a leaf. That would be rather silly! The hole and the duct would totally trash your isolation. Instead, I design a wood "sleeve" that passes through the leaf. The wood sleeve has the correct internal cross section, and the duct connects to the end of it, on the other side of the leaf.

I'm confused as to why making a sleeve that passes from the back of the silencer to go through the inner leaf is much different than a well sealed plastic pipe if the silencer box is tightly mount to the inner leaf with no gap behind it? This was what I planned to do. I will change it if it's key to isolation to have a sleeve though?

The other bit I'm stuck on is the calculation for cross section of the silencer. The easiest thing for me is to use 100mm plastic pipe through my outer leaf connected to insulated flexi ducting which then connects to another bit of plastic 100mm pipe through my inner leaf directly into the back of my inner leaf mounted silencer box, all leaf penetrations will be sealed with acoustic caulk. Is 100mm pipe for inlet and outlet from the outer leaf sufficient for the size of the room? I have a 100mm core drill bit already bit can rent a bigger one if needed.

I understand that the silencer or point where the pipe enters the baffle box should at least double in diameter. Is this true of the reduction on the baffle box for the air output?

My flow rate is:

h=2.380m x w = 3.545 x L = 6.685 volume = 56.4 m3

Flow rate 56.4 x 6 = 338.4 cubic meters per hour

I see from other posts that

speed of air should not exceed 300fps

or 91.44 m/s (not sure this conversion to metric is right though as my results seem crazy!

A = q / v

where
A = duct cross sectional area (m2)
q = air flow rate (m3/s)
v = air speed (m/s)

which would mean A = q / v

where
A = duct cross sectional area (m2)
q = air flow rate (m3/s)
v = air speed (m/s)

a = 339/91.44 = 3.7m ??!


where did I go wrong? This is something I need to work out urgently so I can give the carpenter the right information. The silencer boxes will be built out of 22mm OSB with a layer of 15mm around the outside to achieve the same thickness as the inner wall.

If I do put a baffle box outside the building what's the best thing to clad these in? I've got plenty of OSB to make them out of but we've just a very nice looking extension done and you would see the inlet baffle box from the front of the house, by the front door The wall is white rendered behind it so I'd want to make it blend in as much as possible.

Update
-------
So I'm having a few issues, I found this before - it's tricky getting trades to work at the level of detail required for a studio build. I've found various timbers touching the outer leaf I'm getting those taken out and redone, it's frustrating. Is there a minimum gap I must have between any point on the 2 leafs? 'm referring to where the inner leaf rafters have diagonally cut ends in order to avoid contact with the outer leaf (lower section of roof rafters that are covered with 22mm chipboard and 10mm OSB)? This gap is small but it is a clear gap and my understanding that any break should work? Or am I wrong and vibration will travel across a gap if it's too small? I'm not that happy with this design choice but it was the best we could come up with to maintain the height of the room. See the photo for the gap I'm referring to:

joistsInplace.jpeg

I've also noticed that, despite me saying it was key to not leave a big gap at the bottom of the layers, on the inner leaf there are points where it's up to 10mm! I have some backer rod and will get this filled with acoustic caulk but isn't better to to have these floor to ceiling? The floor is a screed with insulation and 2 DPMs so there should be no moisture penetration.

innerleafbottom1.jpg

I've already got the door design sorted with 2 rubber trunking seals (chrylser type recommended in Rod's book), both doors are oak FD30 with 3/4 " plywood on the back. Both doors also to have strong fire door closers. I may add the magnetic strips if the isolation isn't good enough to the adjoining room but budget is tight so I'll try without first. One thing I've notice is where the carpenter has installed the outer leaf door lining there are the usual gaps between it and the masonry wall. This obviously must be filled with some material with mass. What do you recommend? The gap above the head is quite large. I could have this filled with a concrete mix and the caulk any small gaps/cracks? the sides are a little more tricky and are still too big for caulk. Here's a couple of photos:

outerdoorframe2.jpg

outerdoorframe1.jpg

Separate point
---------------

An interesting issue came up with the inner leaf ceiling joists today. When I saw how much the ends needed to be cut on a diagonal to avoid touching the outer leaf (technically my middle leaf that I have because of the tiled roof) rafters that are OSB boarded out for my middle leaf I was concerned about strength to take the weight of my inner leaf ceiling.
Here's a photo of the cut joists on sitting on the wallplate. If highlighted the diagonally cut ends in red. Before you panic, I had my structural engineer work out if they could take the sheer load of 1 layer 22mm OSB board + 1 layer 15mm soundbloc plasterboard and it's easily ok with this reduction in timber thickness at the wallplate. I was surprised and asked about 4 times, until he was almost annoyed!

Here is the sketch we did for him and a photo of a cut 8x2 rafter held over a piece of CLS (same as used for the wallplate). One diagram shows a single wallplate and the other shows a double. He said either worked but the double plate was a better option so we've gone with that, even though it means the joists got cut thinner to get the diagonal.

joistendsketch.jpeg

here's the photo:

actualjoistendmeasurement.jpeg

I thought this was interesting as there's a lot of talk about how heavy these ceilings are, and they are! But I found it interesting that 8x2 rafters at 400mm centres can take this load so easily that cutting the bearing ends down like this is still ok. The structural engineer is highly respected in my area of the UK so I'm sure he's correct.

The other thing to factor in, that the structural engineer left out of his calculations but said would help some, is the walls are clad in 22mm OSB which butts right up under the joists providing more support for them as it kind of extends the wall plate inwards.

Thought I'd share that last bit as a point of interest.

This question is a bit late in the day as we've already started build the studwalls with a vapour barrier but I have been reading some conflicting opinions on vapour barriers. They seem like a good idea in the winter when the room is warm and it's cold outside. Check the vapour on the warmside of the insulation to provent interstitial condensation in the insulation or cavity. But when it's hot outside (not that hot in the English summer!) and cold in the room thanks to the AC then surely the reverse is true potentially leading to condesation on the outside of the vapour barrier leading to damp/wet timbers and insulation in the cavity and roof space? Maybe the AC and air inlet/outlet with fan is enough to control the vapour levels in the room but nothing is controlling them behind the studwalls in the Summer. Because I sealed my concrete bricks on the outer leaf they won't allow much if any vapour to evapourate which means it can only evapourate upwards towards the roof space. It would have to go through my middle leaf of 22mm chipboard + 10mm OSB first though. Maybe I'm overthinking this but I've seen how much water can appear from condesation in the roof of my house when we first bought it and it had no insulation, the rafters were literally dripping until we had the issue sorted and put some ventilation up there as well as insulation. Appreciate your thoughts on this, please keep in mind I live in the UK so that's the climate we're dealing with.

Thanks

Ricky

[Soundman2020]

I'm guessing it needs decoupling before it goes through either leaf but then I'm thinking I'm back to the issue I'd have with flexi duct where there's a 'thin' point in the cavity for sound waves to penetrate easily?

The way I normally do it is to have a short plywood / MDF / OSB sleeve on the end of the silencer, and that penetrates the leaf, a little way into the cavity. Then there's the flex duct that runs across the cavity and joins up with a similar sleeve on the silencer box on the other side. So the flex duct in the cavity does not matter if it is thick or thin: there's no issue at all if sound gets into it, as the silencer boxes on each side stop it the sound from going further.

I'm confused! I see you saying to someone that

I NEVER pass a duct directly through a leaf. That would be rather silly! The hole and the duct would totally trash your isolation. Instead, I design a wood "sleeve" that passes through the leaf. The wood sleeve has the correct internal cross section, and the duct connects to the end of it, on the other side of the leaf.

Right. The duct itself does not go through the leaf! The sleeve does. If you have a piece of duct going through a leaf, then it creates a huge path for sound to travel through. So the duct does not pass through the leaf: the sleeve does.

I'm confused as to why making a sleeve that passes from the back of the silencer to go through the inner leaf is much different than a well sealed plastic pipe

Because the mass of the leaf is way, way higher than the mass of a thin piece of plastic!

if the silencer box is tightly mount to the inner leaf with no gap behind it? This was what I planned to do. I will change it if it's key to isolation to have a sleeve though?

If you can actually do that without having any gap between the silencer and the wall, then that could work. But you'd have to pretty much glue and caulk the box directly onto the wall to do that. I'm not convinced it would work. However, for high isolation, I normally keep the silencer separate from the wall, resiliently mounted, such that any resonances in the silencer cannot be transferred to the wall, and vice versa.

The easiest thing for me is to use 100mm plastic pipe

I would suggest using proper flex duct or rigid duct. I'm not sure that I'd want to breathe air that passed through something not designed for breathable air... Also,a couple of millimeters of plastic has far, far less mass than the large thickness of wood that you use to make the silencer boxes... Just a small fraction. You might as well not bother building a thick wood silencer box if you are then going to trash all of what you gained, by using a thin walled, low mass pipe to connect it through the leaf...

all leaf penetrations will be sealed with acoustic caulk.

Is 100mm pipe for inlet and outlet from the outer leaf sufficient for the size of the room?

For the diameter of the duct that conducts the air outside the room, or between the leaves, that's fine. As long as you slow down the air enough inside the silencer and at the register, that's what matters. It needs to come out the register at slower than 300 FPM.

I have a 100mm core drill bit already bit can rent a bigger one if needed.

You have a 100mm drill bit? That's about 4"! Pretty big. But you don't need a bigger bit to drill a bigger hole. There are several techniques for drilling large holes without a large bit. I can drill a 100mm hole with an 8mm bit....

I understand that the silencer or point where the pipe enters the baffle box should at least double in diameter

Not diameter: cross sectional area. If you double the diameter, you do NOT get double the cross sectional area. For example, if you have a 4" (100mm) diameter duct, and you increase that to 8" (200mm) diameter duct, then you have increased the area from 50 in2 to 201 in2. That's about 4 times the area. Increasing from 4" duct to 6" duct would do it. That's going from 100mm to 150mm.

Also, if you have a 100mm round duct and you go to a 100mm square duct, you increase from about 7,800 cm2 area to 10,000 cm2, so without even going wider or higher than the round duct, you already get 25% more by going to square section. A square duct of 125 mm per side will get you 15,600 cm2, which is twice the area of your 100mm round duct.

Is this true of the reduction on the baffle box for the air output?

That depends. If the output goes directly to the register, then no. You need to keep the speed at the register below 300 FPM. So you could go to double the area again (in other words, four times the original area of the duct. But if there's another duct that the connects to the register down stream, you could go back to the same original diameter, then widen it out slowly just before the register. The length of the part that widens out should be at least 5 times the diameter of the duct. So if you have a 100mm duct, you need at least 500mm of wider duct just before the register.

speed of air should not exceed 300fps

That's a typo: it should be FPM: Feet per MINUTE, not feet per SECOND.

(not sure this conversion to metric is right though as my results seem crazy!

You did the conversion right, but the number was wrong. 300 FPM is about 1.5 m/s.

If I do put a baffle box outside the building what's the best thing to clad these in?

You could cover it with fiber-cement board. Something like 4mm or 6mm would be plenty. You can then paint that, render it, stucco it, or whatever you want.

I'll get back to you on the rest later.

- Stuart -

[Soundman2020]

... rest of reply:

it's tricky getting trades to work at the level of detail required for a studio build.

yup!

I've found various timbers touching the outer leaf

Is there a minimum gap I must have between any point on the 2 leafs?

I would aim for at least 1/2", and more if possible. I'm assuming we are talking about the gap between a joist or stud on one leaf, and the surface of the other leaf?

I've also noticed that, despite me saying it was key to not leave a big gap at the bottom of the layers, on the inner leaf there are points where it's up to 10mm!

That should be redone. There should be a small gap there, yes, to be caulked, but not more than about 1/4" or so (6mm, give or take). The fact that there's a large gap, which is also at an angle, tells me that the sheathing was not put up properly at all. The correct method is to place thin shims on the floor, about 1/4" thick, then rest the bottom edge of the sheathing in the shims. After the sheathing is nailed in place, pull out the shims and caulk the gap. If you do it like that, then there's a consist, non-varying 1/4" gap under each sheet, all around the room, and a consistent seal. Repeat that for the second (and additional) layer(s), shimming and caulking each one individually.

One thing I've notice is where the carpenter has installed the outer leaf door lining there are the usual gaps between it and the masonry wall. This obviously must be filled with some material with mass. What do you recommend?

Depends on the size of the gap: if it is something that can be filled with caulk, ten backer rod, then caulk, that's fine. But it if is too big for normal backer rod, then it would be better to use mortar, as you suggested, then caulk once the mortar is completely dry (several days).

I had my structural engineer work out if they could take the sheer load of 1 layer 22mm OSB board + 1 layer 15mm soundbloc plasterboard and it's easily ok with this reduction in timber thickness at the wallplate. I was surprised

I'm surprised too, I must admit. What did your building inspector say about that? Did it pass inspection like that? It seems to me there's not much material at the joist ends. I've heard the "rule of thumb" that taper cuts should never reduce the end thickness by more than half of the original joist height at the joist end, 1/4 height over the other edge of the bearing surface, and the taper should never extend back along the joist more than 3x the joist height. To me, it looks like you have a lot less than 1/2 of the joist height... You say you have 2x8 joists, so by that rule it should not taper down to less than about 90mm at the very tip of the joist, and the taper should not extend more than about 550mm back along the joist. It looks like yours do not meet that. I'd get a second opinion on that. I can't say how things are where you live, but that would not pass inspection where I live.

- Stuart -

[rickybobby]

Ok so if I make the corrections you suggest from my previous post:

My flow rate is:

h=2.380m x w = 3.545 x L = 6.685 volume = 56.4 m3

Flow rate 56.4 x 6 changes per hour = 338.4 cubic meters per hour

speed of air should not exceed 300fps
or 91.44 m/s (not sure this conversion to metric is right though as my results seem crazy!


A = q / v

where
A = duct cross sectional area (m2)
q = air flow rate (m3/s)
v = air speed (m/s)


which would mean A = q / v

where
A = duct cross sectional area (m2)
q = air flow rate (m3/s)
v = air speed (m/s)

a = 339/91.44 = 3.7m ??!

A = q / v

where
A = duct cross sectional area (m2)
q = air flow rate (m3/s)
v = air speed (m/s)

max air speed = 300 FPM is about 1.5 m/s

339 flow rate in cubic meters per hour so convert to m3/s

3600 seconds in an hour

flow rate =339/3600 = 0.0942m m3/s

A = 0.0942/1.5

area = 0.0628m2 or 62.8mm2 this stil seems odd, small?

You have a 100mm drill bit? That's about 4"! Pretty big. But you don't need a bigger bit to drill a bigger hole. There are several techniques for drilling large holes without a large bit. I can drill a 100mm hole with an 8mm bit....

Yup I've done this too in the past with lots of small holes that I then join together but I find it way easier to get a neat hole with a core drill the right size.

I've found various timbers touching the outer leaf

This has been remedied and there is now a good gap at all previous problem points.

I'm surprised too, I must admit. What did your building inspector say about that? Did it pass inspection like that? It seems to me there's not much material at the joist ends. I've heard the "rule of thumb" that taper cuts should never reduce the end thickness by more than half of the original joist height at the joist end, 1/4 height over the other edge of the bearing surface, and the taper should never extend back along the joist more than 3x the joist height. To me, it looks like you have a lot less than 1/2 of the joist height... You say you have 2x8 joists, so by that rule it should not taper down to less than about 90mm at the very tip of the joist, and the taper should not extend more than about 550mm back along the joist. It looks like yours do not meet that. I'd get a second opinion on that. I can't say how things are where you live, but that would not pass inspection where I live.

I''ve had these calulations double checked by my structural engineer (I've messaged you privately with these as I didn't think it was fair to him to share them publically). I've also had them checked by a structural engineer I used before when I lived in another town and he says they're fine. I've also sent them to Building Control and they are happy with them. Odd as it seems when you look at the load per joist it's not that much - 84lbs I think. I weigh double that and wouldn't expect the timber to break or even close if I hung off it. I've also since asked the engineer to add the 300m of 45kg/m3 rockwool in just so I have a legal calculation, there's plenty of headroom in the calc for this though. The key is there can never be any imposed load from above, live or otherwise because the structure is sealed. Noone can ever access the joists. All they will ever support is the inner leaf and rockwool and whatever lights I have. No chandeliers are planned!

[rickybobby]

Hi,

We’re just getting on to Building the linings for the internal windows.
Because I have to have a sliding internal window I’m having this made by a joinery off site.
It will have 10-15mm acoustic laminate glass (depending on price), the joiner understands the seals must be excellent and the frame will be thick pine, I don’t have dimensions yet.

That leaves the carpenter to make two linings like the photos you sent me. They will have a gap so they don’t connect the two leafs. I see you advise black cloth over this join, what type of cloth do you find lasts a long time? It would be hard to replace this if it would ever perish? I was wondering if a nylon weave type cloth might be best? Still flexible so doesnt bridge but durable?

Update: Having looked at this some more the best solution seems to be to dot n dab (but don't just do dots of bonding, cover the whole masonry cheek) and line it with 15mm soundbloc so it's perfectly level with the inner leaf frame. That way we can make up a double lining with fabric joiner the way you showed and just slide it with minimum gap around with can be sealed with acoustic caulk.

Also I don’t see any insulation going in around the frame pics you sent, because this is in the cavity behind the studwall it’s
A potential cold spot, what are your thoughts?

Talking to the carpenter he was talking about where he would need to use some packers to get the linings in, particularly on the outer leaf against the concrete brick work. What do you suggest filling these small gaps with around the lining? If we make both linings up together and put temporary blocks as show it would be impossible to get anything around the outer frame to seal it. The way you’ve shown is the only to install the fabric across the gap though. Keep in mind my outer layer has triple glazed upvc windows, not ideal but that’s what I have to work with, so the lining will fit up tight to them.

Thanks as always for any help

Ricky

[rickybobby]

Hi stuart,

Hope you’re well?

I was wondering if you could help me work out what thickness glass to have in my internal sliding windows?
I have a quote now to have these made up out of tulip wood with quality acoustic seals.
My inner leaf is 1x 22mm osb + 1 x 15mm soundbloc.
I want to get the Best isolation I can without overspending.
If you recall I have triple glazed upvc windows in the outer leaf which is not ideal but I have to live with it for now. It’s possible in the future I might be able to replace these with timber framed windows with a single pane of thick acoustic glass.
From what I’m reading i should have the inner windows install in a way to make the air gap between the windows as big as possible?
Should the glass panes be sealed in the frames with intumescent tape?

Thanks for any help, Merry christmas!

Ricky

[Soundman2020]

I was wondering if you could help me work out what thickness glass to have in my internal sliding windows?
I have a quote now to have these made up out of tulip wood with quality acoustic seals.
My inner leaf is 1x 22mm osb + 1 x 15mm soundbloc.

You need to get at least the same surface density in your glass as you have in the leaf, but in your case even more, due to the outer window problem. OSB is around 610 kg/m3, and drywall is around 690, so you have roughly 13 + 10 = 25 kg/m2 on your leaf. To get the same in laminated glass, it would need to be 10mm thick, but I'd go for much more than that: I'd shoot for 16mm at least, and maybe 18mm if you can get it. In other words, you'd need 8mm+PVB+8mm, minimum, or better would be 9mm+PVB+9mm. You could go with different thicknesses if your glazier offers that: eg, you could go with 10mm+PVB+8mm, or some such.

From what I’m reading i should have the inner windows install in a way to make the air gap between the windows as big as possible?

Right. Whatever the air gap is in your cavity right now (surface to surface, inside the wall, between the leaves), you should aim for at least 20% more, and hopefully 40% more if you can. So for example, of your gap at present is 100mm, then go for at least 120mm between the glass panes, and 140mm would be better.


- Stuart -

[rickybobby]

Hi Stuart,

Happy New Year!

I'm just working on the baffle boxes with my carpenter now. We've made 2 for the inside (inner leaf). We made them with the 30mm thick collar around the pipe that penetrates the wall and the plasterboard was cut as tight as possible to this. When we fitted the baffle boxes we put some acoustic silicone around the collar so it filled and sealed any gaps.

We haven't yet built the boxes for outside yet. I have 2 questions about these.

Because the front of the inner baffle box isn't on yet I can see into the pipe that penetrates the inner and outer leaf, the pipe is joined with insulated flexi duct across the cavity between the inner and outer leaves.
If you look at the photo you can see condensation in the pipe where it goes through the outer leaf. The outer leaf is made of 2 skins of concrete blocks with cellotex in the cavity. The pipe currently has tape over the outer end to prevent things getting in the pipe. This end will be cut off when the outer baffle box is fitted.

inletpipe.jpg

Is condensation an issue you see or will the outer baffle box help with this as the warm air from the room will gradually cool down as it snakes it's way through the outer baffle box? The picture is actually the air in so the air will be flowing inwards - cold to warm but the same is happening on the outlet baffle box and pipe.
The outer baffle box willl also be lined with AC ducting foam and I'm just concerned this is going to get damp in the water with this condensation and be a potential hazard?

The second question is relating to the outer baffle boxes. I assume the front panel needs to be removable so these can be cleaned every now and then? If so how do you make them water tight when covering them with cement board and rendering them?
I'm contemplating looking for a ready made box in plastic that coud fit over my baffle box. something like a gas meter box cover but bigger. It would probably be cheaper than making something and more weather tight.


In addition to those questions I'm working on the inner window design with my carpenter. I'm not sure if you recall but the inner window also had to open as a means of egress. I was looking at a sliding window design because I also use the 'studio' room for writing software in - my day job. In the Summer it would be good to have the windows open when I'm doing this work as I much prefer to work in fresh air than AC and the summers in the UK aren't very hot. A sliding design would've meant I wouldn't have to worry about what's put near the windows in terms of block it swinging inwards.

Anyway I've scrapped the sliding design because noone manufacters good acoustic seals for sliding windows. This is mainly because I think it's hard to do as you can't achieve compression on to the joins between the sashes and the dividing beads.

I'm now going for a design where the sashes open inward using parliment hinges which means they can open all the way back and out of the way. I'll be using 3 heavy duty hinges because the sash will weight between 25-30kg with 15mm acoustic laminate glass.

I plan to have a double seal the same as my doors.

doorseals.jpg

Unfortunately I've run out of the rubber seal which is the Chrysler weatherstripping Rod recommends in his book. I had to order this from the USA as no stocks it hear in the UK and it was expensive with customs tax.
I've been looking at other acoustic seals for the windows and wondered if a double seal like the photo of the door with one of these would be enough in terms of isolation. One layer of seal provides 48db of reduction, if I know acoustic laws 2 layers of seal won't be double that but it should be a fair bit better right?

https://www.norseal.co.uk/browse/acoust ... als/nor710

Lorient also do a similar seal but it doesn't perform as well.

If the chrysler rubber trunking is way better I will of course order some more? I plan to have a latch that pushes the window sash hard on to the seals.

Simo's post here is very useful in terms of constructing the windows, he obviously doesn't have an opener but the rest will be great for me.
http://johnlsayers.com/phpBB2/viewtopic ... al#p133093

Thanks for your help

Ricky

[Soundman2020]

we made them with the 30mm thick collar around the pipe that penetrates the wall and the plasterboard was cut as tight as possible to this.

It's usually better to leave a small gap all around, a few mm, and fill that with backer rod and caulk, to reduce mechanical transmission. Of course, that also assumes that you mounted your silencer boxes resiliently. But this is already done, and you don't seem to need extreme isolation, so it's probably OK.

Is condensation an issue you see or will the outer baffle box help with this as the warm air from the room will gradually cool down as it snakes it's way through the outer baffle box?

It shouldn't be a problem if you line all your ducts and silencer correctly, with proper duct liner. That's both thermal and acoustic insulation. So the air will not be in contact with cold surfaces until it exits the outside register: then it will dump it's humidity as it hits the cold air outside.

Is condensation an issue you see or will the outer baffle box help with this as the warm air from the room will gradually cool down as it snakes it's way through the outer baffle box?

Make sure that you use a waterproof duct liner!

If you are concerned about this, then you could install an HRV or ERV to recover the heat from the exhaust air and return it to the fresh air. And of course, once you have your actual air conditioner running, it will be controlling the humidity inside the room.

The second question is relating to the outer baffle boxes. I assume the front panel needs to be removable so these can be cleaned every now and then? If so how do you make them water tight when covering them with cement board and rendering them?

Your intake register must have air filters on it! To keep out the dust, pollen, particulates, as well as bugs and spiders, etc. Clean/replace the filters regularly. You could also put a filter on the return registers inside the room, for the same purpose: to keep the garbage out of the return ducts. That's less necessary, but still an idea. If you have filters installed properly, and cleaned regularly, then there should be no need to clean out the ducts or silencers.

Anyway I've scrapped the sliding design because noone manufacters good acoustic seals for sliding windows.

These guys do: https://www.schlegel.com/media/flipbook ... 1cb035.pdf

Or you could just buy a ready-made acoustic sliding window...

https://www.rylock.com/uploads/pdfs/Pro ... S_V171.pdf

https://bimobject.com/en/atrium/product/atrium-001

http://www.awsaustralia.com.au/vantage/noise-reduction

One layer of seal provides 48db of reduction,

I'd take that with a grain of salt! 48 dB TL on a single barrier requires a surface density of nearly 300 kg/m2! Assuming that the rubber is 1cm thick, it would have to weigh 3000 kg/m3 absolute density.... but normal runner is only about a third of that (around 1200 kg/m3). So either that seal is about 3cm thick at the THINNEST point, or the number is pure marketing hype.

48 dB TL is substantial. Even assuming that the seal is made from magical rubber sprinkled with pixie dust and extruded with purest unicorn hair, you would still only get 48 dB if the window itself can give you that much: Which would require glass that is nearly 20mm thick, in a frame of matching density.

Anyway, that stuff you link to MIGHT work, but I'd be skeptical of the high isolation claims. I'd expect something rather more modest than that: maybe 30-somethng dB, which is still pretty decent.

Have you looked at the Zero International catalogue? They have a rather decent selection of acoustic seals. There's an entire section of the catalogue devoted to purely acoustic applications, for both door and window seals.

- Stuart -

[rickybobby]

Hi Stuart,

So good news I've got all the secondary acoustic glazing in and the second door is on with seals and fire door closers that can apply enough latching force. I don't have a sound level meter to record the results but I have to say I'm extremely pleased with the results. With my 3 piece rock band playing flat out in the studio you can hardly hear a thing outside! The weakest point is leakage through the double doors to the breakfast room in the house. I've still got some sealing to do there and I'm going to get the carpenter to adjust one of the door jams where the seals aren't meeting the door.

Thanks for your help, it was never meant to be a high end studio on my budget but it is remarkably successful. I'm moving on to treating the room a bit next to improve monitoring.

Could you advise on what type of air/pollen filters are best for my intake and outakes? I've got an S&P TD 350/125 fan to install on the outlet and I know I need to fit these filters.

Thanks again

Ricky

[rickybobby]

Can anyone recommend air/pollen filters that I can fit over my inlet and outlet baffle boxes? The inlet baffle box filter would be underneath it outside. I'm guessing these are normally washable and need checking at regular intervals to prevent blocking?
The inlet and outlet pipes are 110mm diameter.

Thanks for any help, noone seems to be answering the post I put up ages ago and I'm really stuck on what to get.

Ricky

[Waka]

Hi Ricky,

My design uses a filter box with replaceable filters on the inlet:
http://www.ductstore.co.uk/acatalog/Duc ... Boxes.html

And the extract has a replaceable filter in the casing of the ceiling diffuser:
http://www.ductstore.co.uk/acatalog/Panel-Filters.html

I had to use different types for access reasons. My design has the inlet filter box between the exterior inlet grill and the silencer box (keeping exterior dust out of it), and the extract filter is inside the room above the ceiling diffuser, before the silencer box and extractor fan (keeping in-room dust out).

Here's a picture of my inlet filter box installed (extract filter isn't in yet)

filter box in roof void-888x522.jpg

And outside grill (I still have work to do on the fascia etc. here but it should give you an idea):

intake weather louvre from outside.jpg

I hope that helps!