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Garden timber studio - walls

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Re: Garden timber studio - walls

Postby jmch » Wed Dec 05, 2018 4:05 pm

James Perrett wrote:More worrying is that your builder appears to be using standard plasterboard rather than acoustic plasterboard.

Hi James

Apparently he's using 12.5mm thick fire board (with green glue between).

I read in various places that this was as good as using 'acoustic board'.

John
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Re: Garden timber studio - walls

Postby jmch » Fri Dec 07, 2018 3:57 pm

Guys,

I am now trying to ensure my builder does exactly what I believe he should be doing. He's currently putting up the inner layer of fire board, green glued to the first layer.

The door (there's no window) and the ventilation are the next things which will be tackled. I would really appreciate all help and advice!

Regarding the door - or doors. The inner one is a heavy fire door. The frame has been built and is part of my inner leaf, decoupled from the outer. I've just ordered some rubber seal to go around the frame on all sides. It's 9mm x 5.5mm EPDM Rubber Draught Excluder which my builder has said will do the job - photo here:

https://imgur.com/Ag0QqdV

Image

There will be a heavy duty door closure to close the inner door back on itself. The door itself doesn't have a bolt or latch. I appreciate some people use pressure clasps to push the door tight to the seals, but I have also read that these aren't a good idea as it means that access from the outside could be a problem in the event of an emergency.

Can anyone recommend how I can push this door tight without obstructing emergency access from the outside?

Then there's the issue of covering gaps (sides, top and bottom) between this inner door and the solid composite door that's going on the outside leaf. This door comes with its own frame and airtight seals.

I have seen one method where a studio builder used expanding foam to hold strips of wood to the inner leaf only (with insulation behind) and then caulked the small gap from this piece of wood to the outer frame, so avoiding any direct contact from inner to outer leaf. I thought this would work for me so was going to order some of this foam.. Will this foam do the job at this point? (Everywhere else acoustic caulk has been used to fill joins and gaps.)

https://www.screwfix.com/p/soudal-geniu ... _container

Can anyone suggest any other method of closing these gaps?

Thanks all

John
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Ventilation advice please

Postby jmch » Sun Dec 09, 2018 10:36 am

Hi all

Further to my last post above asking for advice on my doors set up, I've put a link at the end of this post which shows (not to scale) the proposed design for my ventilation, as well as describing the make up of my inner and outer leafs.

One duct will lead to an exterior mounted variable speed extractor fan
https://imgur.com/a/jgNb2On
and the other to a passive inlet vent.

I'm concerned I might need to increase the isolation on this set up.

Do I need to construct my silencer boxes like my inner wall - i.e. MDF and two layers of fire board green glued together? Would that help?

Thanks

https://imgur.com/15b6yO2
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Re: Garden timber studio - walls

Postby Wonks » Sun Dec 09, 2018 11:57 am

With the silencer box in the space, then you'd certainly want as much sound-absorbing material around it as the rest of the wall. You don't want sound from the room to break into the silencer.
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Re: Garden timber studio - walls

Postby jmch » Sun Dec 09, 2018 12:23 pm

Wonks wrote:With the silencer box in the space, then you'd certainly want as much sound-absorbing material around it as the rest of the wall. You don't want sound from the room to break into the silencer.

Thanks Wonks. I understand what you're saying.

I was wondering how much impact that would have given that the box has an open hole at one end for the air to get in/out.

John
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Re: Garden timber studio - walls

Postby Wonks » Sun Dec 09, 2018 12:59 pm

It's only noisy at the open end (when playing loud instruments in the room) , and it can't be any noisier there than within the room. As the air moves through the silencer, the noise gets absorbed and it comes out a lot quieter than it goes in. What you don't want is noise leaking in through the sides to make the quietened air loud again. Obviously the ducted end of the extract air baffle box will have the quietest air so will be most prone to picking up noise.

If you are leaving the end of the box fully open, then I'd radius the exposed ends of the foam so that there are no sharp edges to cause more turbulence in the air, but so that they are nicely curved.
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Re: Garden timber studio - walls

Postby jmch » Sun Dec 09, 2018 2:25 pm

Wonks wrote:If you are leaving the end of the box fully open, then I'd radius the exposed ends of the foam so that there are no sharp edges to cause more turbulence in the air, but so that they are nicely curved.

Thanks Wonks.

By radius the exposed ends of the foam, do you mean as per the drawing here?

https://imgur.com/a/hKKn4aa

John
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Re: Garden timber studio - walls

Postby James Perrett » Sun Dec 09, 2018 2:27 pm

jmch wrote:Can anyone recommend how I can push this door tight without obstructing emergency access from the outside?

In my current studio I just rely on the pressure exerted by the door closers. However, in my last studio I had magnetic sealing strips all around the door (a bit like fridge seals).

jmch wrote:Then there's the issue of covering gaps (sides, top and bottom) between this inner door and the solid composite door that's going on the outside leaf. This door comes with its own frame and airtight seals.
...

Can anyone suggest any other method of closing these gaps?

As long as you don't couple the two leaves together you can use whatever you like. I've just wedged some spare acoustic foam in the gap between the control room and booth while I deliberately widened the gap between the outer and inner entrance doors to allow me to put a computer in there.
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Re: Garden timber studio - walls

Postby Wonks » Sun Dec 09, 2018 3:35 pm

Yes, rounded corners everywhere if you can, although the entrance to the baffle box should be arranged like this:

Image

Not as you had it in the diagram:

Image

...as that first inlet area would be practically useless and the baffle box would effectively start at the gap between the first baffle and the casing, so you'd be wasting space, wasting material and losing some attenuation.
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Re: Garden timber studio - walls

Postby jmch » Mon Dec 10, 2018 1:21 am

Wonks wrote:Yes, rounded corners everywhere if you can, although the entrance to the baffle box should be arranged like this:

Image

Not as you had it in the diagram:

Image

...as that first inlet area would be practically useless and the baffle box would effectively start at the gap between the first baffle and the casing, so you'd be wasting space, wasting material and losing some attenuation.

Thanks Wonks, makes sense. I'll also talk to my builder about getting two layers of fire board over the box as well as the MDF.

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Re: Garden timber studio - walls

Postby jmch » Mon Dec 10, 2018 1:24 am

James Perrett wrote:
jmch wrote:Can anyone recommend how I can push this door tight without obstructing emergency access from the outside?

In my current studio I just rely on the pressure exerted by the door closers. However, in my last studio I had magnetic sealing strips all around the door (a bit like fridge seals).

jmch wrote:Then there's the issue of covering gaps (sides, top and bottom) between this inner door and the solid composite door that's going on the outside leaf. This door comes with its own frame and airtight seals.
...

Can anyone suggest any other method of closing these gaps?

As long as you don't couple the two leaves together you can use whatever you like. I've just wedged some spare acoustic foam in the gap between the control room and booth while I deliberately widened the gap between the outer and inner entrance doors to allow me to put a computer in there.

Thanks for the suggestions James.

I've put a link to some photos of the inner door frame so far, that also show the gap I'm talking about.

https://imgur.com/a/oCpCRpw

John
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Re: Garden timber studio - walls

Postby jmch » Tue Dec 11, 2018 3:17 pm

Wonks wrote:Yes, rounded corners everywhere if you can, although the entrance to the baffle box should be arranged like this:

Image

Not as you had it in the diagram:

Image

...as that first inlet area would be practically useless and the baffle box would effectively start at the gap between the first baffle and the casing, so you'd be wasting space, wasting material and losing some attenuation.

Wonks, I've redesigned my silencer box as here:
https://imgur.com/vv95k5m

As I said before, I'm going with the two internal ones first (one for the exhaust and the other for the air in) on opposite sides of the room. There won't be space for any more inside the room. If necessary I can have another one outside for the passive inlet, but it'd be more problematic for the exhaust given the exterior fan I'm using :
https://imgur.com/ZgUG6gJ
This fan is recommended for studios where the aim is to keep fan noise outside.

The company who supplied the fan advised 8-10m ductwork max, so I'm a little concerned about adding too much extra 'length' in the silencer boxes. Currently there are two 10m ducts snaked in the now inaccessible roof cavity. I've told my builder he'll need to pull some ducting out through the exterior holes that will be bored, and shorten the length, to allow for the silencer boxes. Am I correct in viewing the area in the silencer boxes as extra length for the fan (and passive air in) to travel through?

Finally, I want to put some fine mesh in to prevent insects getting in. The fan company suggested this and said it shouldn't affect air flow significantly on this fan as long as this mesh is at the fan end:
https://imgur.com/JYYxvxB
My builder has suggested putting it inside the fan unit just behind the vents. And likewise on the passive inlet vent.
Any thoughts here?

Thanks

John
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Re: Garden timber studio - walls

Postby Wonks » Tue Dec 11, 2018 4:02 pm

That silencer design looks better. I don't know how close to ideal it, as until recently I designed HVAC controls systems and have picked up a lot of mechanical and electrical knowledge along the way. So I generally know what's wrong and right, and know some of the details but not all of them.

The maximum ducting length stated will be based on the pressure drop of the ducting at the nominal fan volume. The bigger the ductwork, the lower the pressure drop for the same flow rate. The baffle box has a larger cross-sectional area than the ducting from it (and so lowering the pressure drop), but it also has those 180° bends (increasing its pressure drop).

So you could probably allow its pressure drop across its length (not the total of the air path through it) to be that of the ducting.

The mesh should be OK. Ideally you'd fit it in an external grille that's bigger than the ducting to reduce the air velocity across it to both reduce the pressure drop across it and also reduce any noise it might generate.

Also note that if it does its job, the mesh will start to get blocked with insects, reducing airflow and slightly increasing any noise created by the mesh. So I'd make it easily removable for cleaning, and maybe have two meshes so that you can swap over and clean the dirty one at your leisure.
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Re: Garden timber studio - walls

Postby jmch » Tue Dec 11, 2018 4:58 pm

Wonks wrote:That silencer design looks better. I don't know how close to ideal it, as until recently I designed HVAC controls systems and have picked up a lot of mechanical and electrical knowledge along the way. So I generally know what's wrong and right, and know some of the details but not all of them.

The maximum ducting length stated will be based on the pressure drop of the ducting at the nominal fan volume. The bigger the ductwork, the lower the pressure drop for the same flow rate. The baffle box has a larger cross-sectional area than the ducting from it (and so lowering the pressure drop), but it also has those 180° bends (increasing its pressure drop).

So you could probably allow its pressure drop across its length (not the total of the air path through it) to be that of the ducting.

The mesh should be OK. Ideally you'd fit it in an external grille that's bigger than the ducting to reduce the air velocity across it to both reduce the pressure drop across it and also reduce any noise it might generate.

Also note that if it does its job, the mesh will start to get blocked with insects, reducing airflow and slightly increasing any noise created by the mesh. So I'd make it easily removable for cleaning, and maybe have two meshes so that you can swap over and clean the dirty one at your leisure.

Thanks again for your good points Wonks :thumbup:
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Baffle/silencer boxes

Postby jmch » Fri Dec 14, 2018 10:18 am

Guys

I've agreed with my builder that the top and one side of my boxes will be the inner ceiling and wall, which is made up of 2 layers of fire board with green glue between, a layer of 18mm OSB, and 100mm RW3 insulation behind.

So it will be the front side, bottom and end sides that are made and secured to the wall and ceiling, then caulked. These will be made of MDF with 2 layers of fire board green glued together.

See drawing here:

https://imgur.com/a/z5wUmzY

What's the view on doing this?

Thanks

John
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