SOUND ON SOUND

[Studio Support Gnome]

further points...

you can fit baffle boxes in the rear corner of corner mounted bass traps ...


airflow should cover as much of the room as possible, sop diametrically opposed corners, inlet at bottom, in say rear left corner, outlet at top at front right corner.... or inlet at bottom in both rear corners, outlets at top in both front corners.... , or single outlet front and centre at top.... but twice the flow rate than the two rear bottom mounted inlets...

easiest was to duct this in limited space is to use a semi-rigid duct type.... connected to a plenum to join low diameter pipes together for fan interface and room interface....


could do the same for using two inline fans, a small distribution box allowing you to connect multiple pipes to each fan....

[jmch]

Thanks SSG, I really appreciate the time you've taken.

I looked at the two fans you suggested and they look excellent. My builder has suggested 150mm ducting which seems like a good idea.

However, he has raised the issue that if I use one of these inline fans, it will be in the roof cavity and access to it will be impossible - something I am clearly not comfortable with.

I've read elsewhere that these exterior mounted fans are a good idea - this would mean I could access it. And as my studio room will have a decent sized awning, I could site it so it's protected from rain.

What's your view on this fan?

https://www.fastlec.co.uk/uec150-150mm- ... n-(600m3hr).html

Thanks

John

[jmch]

further points...

you can fit baffle boxes in the rear corner of corner mounted bass traps ...


airflow should cover as much of the room as possible, sop diametrically opposed corners, inlet at bottom, in say rear left corner, outlet at top at front right corner.... or inlet at bottom in both rear corners, outlets at top in both front corners.... , or single outlet front and centre at top.... but twice the flow rate than the two rear bottom mounted inlets...

easiest was to duct this in limited space is to use a semi-rigid duct type.... connected to a plenum to join low diameter pipes together for fan interface and room interface....


could do the same for using two inline fans, a small distribution box allowing you to connect multiple pipes to each fan....

I looked at the two fans you suggested and they look excellent. My builder has suggested 150mm ducting which seems like a good idea.

However, he has raised the issue that if I use one of these inline fans, it will be in the roof cavity and access to it will be impossible - something I am clearly not comfortable with.

I've read elsewhere that these exterior mounted fans are a good idea - this would mean I could access it. And as my studio room will have a decent sized awning, I could site it so it's protected from rain.

What's your view on this fan?

https://www.fastlec.co.uk/uec150-150mm- ... n-(600m3hr).html

Thanks

John

[jmch]

If you are planning on having any corner bass traps then the soft insulation would make a good filling for those behind the more dense Rockwool face.

I'd be a bit worried about blocking air circulation if you filled the wall cavities completely with it.

Again, thanks James.

Your post made sense to me, but my builder is saying he thinks we should put the soft insulation in the 75mm gap - based on the view that its lack of density won't inhibit air flow, will have dampening effect, and will help with insulation.

I have to make the decision today!

Do you think putting it in would definitely have an adverse effect? Is my builder not correct?

I've told him if we do it I don't want even thick fluffy insulation (which it is) compressed as I do feel that would be wrong.

Cheers
John

[James Perrett]

Do you think putting it in would definitely have an adverse effect? Is my builder not correct?

I'm not a general building expert so, if he is happy that it won't cause damp problems due to a lack of circulation, then it should be OK. I'd still keep some back to fill the bass traps though.

[Studio Support Gnome]

I would leave the cavity empty.



material infill will bridge the gap acoustically to some degree, and similarly the thermal gap will no longer work to allow the room to breathe .... moisture migrates through the materials used, and will condense out on the exterior cold layer. if you infill then that condense still happens, but the surface layer of the infill then gets exposed to pretty much permanent moisture to some degree. eventually this will cause problems

[jmch]

Again, thanks for all the comments. I will certainly update this post with the results once my build has finished.


Could I ask everyone's advice re the baffle boxes for my ventilation?

1. What's the best material to put in there to line them? I've read "acoustic foam" but I really need a more precise suggestion / product spec.


And I've read conflicting statements on the following two issues:

2. Does the ducting need to run through the box or does the ducting go to the box and just the air goes through?

3. Should I make them out of MDF / Plywood? Do they really need to have to same mass as my walls (OSB + 2 layers of fire board) as the interior boxes will be inside these same walls?


Finally, if anyone could tell me how big I should make these, given the dimensions of my room, that would help as I don't understand the calculations I've read on this.

Thanks

[blinddrew]

There's some good stuff on baffle boxes in this thread here: https://www.soundonsound.com/forum/view ... &start=100
In terms of your questions, I did scribble some thoughts but decided to limit my losses and just say, 'don't know'!

[Wonks]

2) The ducting goes to the baffle box. The air goes through the baffle box. There is ducting on the other side of the baffle box.

The ducting certainly doesn't run through the baffle box - or there would be no point in having the baffle box.

Ideally each section of the baffle box should have an internal CSA no less than the supplying duct. You don't want to speed that air up, you really want to slow it down and make it less turbulent. Slowing the air velocity down also increases the amount of time the air spends within the baffle box and so increases the noise absorption.

Commercial HVAC silencers are normally of steel sheet construction, with fibre-glass or rockwool absorption material held in place by perforated steel sheets. R

Home-made baffle boxes would be quite tricky to make like commercial units, especially regarding loose-fibre retention, so you can use acoustic foam, but use the solid sheet stuff, not the ridged foam stuff that you often get in tile form. And the thicker the better. At least 2" thick. However, I feel rockwool will provide better sound attenuation over a wider frequency range. You just need to find a mechanism to hold it in place whilst not letting it shed fibres into the airstream. Less of an issue on the extract, but you don't want the outside air supply into the studio full of rockwool fibres.

[jmch]

2) The ducting goes to the baffle box. The air goes through the baffle box. There is ducting on the other side of the baffle box.

The ducting certainly doesn't run through the baffle box - or there would be no point in having the baffle box.

Ideally each section of the baffle box should have an internal CSA no less than the supplying duct. You don't want to speed that air up, you really want to slow it down and make it less turbulent. Slowing the air velocity down also increases the amount of time the air spends within the baffle box and so increases the noise absorption.

Commercial HVAC silencers are normally of steel sheet construction, with fibre-glass or rockwool absorption material held in place by perforated steel sheets. R

Home-made baffle boxes would be quite tricky to make like commercial units, especially regarding loose-fibre retention, so you can use acoustic foam, but use the solid sheet stuff, not the ridged foam stuff that you often get in tile form. And the thicker the better. At least 2" thick. However, I feel rockwool will provide better sound attenuation over a wider frequency range. You just need to find a mechanism to hold it in place whilst not letting it shed fibres into the airstream. Less of an issue on the extract, but you don't want the outside air supply into the studio full of rockwool fibres.

Thanks for this Wonks.

I understand I need to make the inside of my baffle boxes wider than the ducting. But what does CSA mean?

Also, I'm tending towards acoustic foam (or duct liner) to line the insides, to remove the problem of having to seal the rockwool. But I can't find any on the web. Any suggestions?

Finally, thanks for confirming that the duct doesn't go through the box - makes sense. But how do I connect the end of the flexible duct that's coming through the ceiling to the box? Do I make the hole bigger and then use acoustic foam around the join? Or will acoustic caulk round this do?

Appreciate your advice.

John

[Wonks]

CSA = cross sectional area.

[Wonks]

You'd normally fit a flanged spigot to the inlet and outlet of the baffle box to match the duct diameter you're using. You can use some self-tapping screws to keep the duct and box joined together. Some form of mastic to help seal the joint and you can then use duct tape wound round the joint to make doubly sure.

This is just the first web source I found when searching: http://www.ductstore.co.uk/acatalog/Flanged_Spigots.html

[jmch]

You'd normally fit a flanged spigot to the inlet and outlet of the baffle box to match the duct diameter you're using. You can use some self-tapping screws to keep the duct and box joined together. Some form of mastic to help seal the joint and you can then use duct tape wound round the joint to make doubly sure.

This is just the first web source I found when searching: http://www.ductstore.co.uk/acatalog/Flanged_Spigots.html

Thanks Wonks

I wanted to attach a rough diagram of how I propose my silencer box to work. But I couldn't work out how to do it.

My plan is for the ducting to pass through my inner leaf ceiling close to the wall into the silencer box, that's fixed to the inner wall, and then at the other end I was intending it just to have a vent - or even just an open hole into the studio, no ducting.

There will be one of these on opposite walls, one connected to the exterior mounted extractor fan, and one connected to a passive air inlet.

Does this sound workable?

John

[blinddrew]

I wanted to attach a rough diagram of how I propose my silencer box to work. But I couldn't work out how to do it.

You'll need to host the image somewhere else (imgur is good) and then post the link here, the forum doesn't hold attachments.

[jmch]

I wanted to attach a rough diagram of how I propose my silencer box to work. But I couldn't work out how to do it.

You'll need to host the image somewhere else (imgur is good) and then post the link here, the forum doesn't hold attachments.

Thanks Blinddrew.

The drawing of my silencer box design is here.

https://imgur.com/4MJ9awN

Again, the ducting would pass through my inner leaf ceiling close to the wall, into the silencer box, that's fixed to the inner wall, and then at the other end I was intending it just to have a vent - or even just an open hole into the studio - no ducting here.

There will be one of these on opposite walls, one connected to the exterior mounted extractor fan, and one connected to a passive air inlet.

Does this work as a concept?

[Sam Spoons]

Why not mount the attenuators in the void between the inner and outer walls (or is it a case of "too late")?

[James Perrett]

In one studio I did something similar with the baffle boxes - they were just mounted on the inner leaf with a duct to the outside. They seemed to work well at attenuating the sound through the duct but they seemed to resonate a bit with the fan mounted behind them.

We just had slot in the bottom of the box as the air inlet.

[jmch]

Why not mount the attenuators in the void between the inner and outer walls (or is it a case of "too late")?

Sam, yeah it's too late for that and anyway the gap is nowhere near big enough.

Cheers, John

[jmch]

In one studio I did something similar with the baffle boxes - they were just mounted on the inner leaf with a duct to the outside. They seemed to work well at attenuating the sound through the duct but they seemed to resonate a bit with the fan mounted behind them.

We just had slot in the bottom of the box as the air inlet.

Thanks for that James. My extractor fan will be a fair distance away mounted on the outside block wall.

What's the best thing to use to seal around where the duct meets the box - foam or caulk?

John

[Sam Spoons]

Why not mount the attenuators in the void between the inner and outer walls (or is it a case of "too late")?

Sam, yeah it's too late for that and anyway the gap is nowhere near big enough.

Cheers, John

Oh well :(