Please help with acoustic baffle box...

Ah I see. Have your actually checked with the council that you can't put a ventilation grille in the garage door? You can get a white one and it would be barely noticeable. Just drill a big hole with a core drill bit in the garage door, and fit the grille plate in the hole. Like this one: https://www.ac-one.co.uk/outside-air-lo ... gKVRfD_BwE Definitely the simplest way of achieving fresh air. Dan

Waka wrote:

Ah I see. Have your actually checked with the council that you can't put a ventilation grille in the garage door? You can get a white one and it would be barely noticeable. Just drill a big hole with a core drill bit in the garage door, and fit the grille plate in the hole. Like this one: https://www.ac-one.co.uk/outside-air-lo ... gKVRfD_BwE Definitely the simplest way of achieving fresh air. Dan

It's something I could enquire about, but the problem then would be that I couldn't open the garage door, which was always the intention. Plus I don't know it would be possible to even construct this solution without then sealing yourself in the space lol!

atomicus wrote:

It's something I could enquire about, but the problem then would be that I couldn't open the garage door, which was always the intention. Plus I don't know it would be possible to even construct this solution without then sealing yourself in the space lol!

You could use flexible duct to connect the silencer to the grille in the garage door. And make it extra long so the garage door can still be opened. As long as you used insulated duct you shouldn't have problems with condensation in it. Each end would be attached with a hose clip and aluminium tape to keep it secure, and you should be able to open and close the garage door occasionally for replacing filters etc. Dan

I think Dan's idea would work great!

Gregwor wrote:

I think Dan's idea would work great!

It's a good idea, and I can enquire, but I know the rules are quite strict, so ultimately it may not be something that I'm allowed to do. For argument's sake though, if I were able to do this, this would then be the passive intake I presume? My query a few posts back might have got lost, but just to ask again as something is confusing me regards these sleeves between the silencer boxes. I will be going with the 4 boxes, so 2 on each side of the inner and outer leaf, but I'm not sure how I connect everything? From the picture you posted above, the sleeve is built into the box... so if I do this, and the box is up against the wall, how do I get to the gap around the sleeve to fill it with caulk? Is there a correct order to doing this? Should I have all my insulation/plasterboard up, then cut the holes in it for the sleeves, or have all the boxes and necessary sleeving in place, then build the walls around them? Regardless which way I do it, I'm having trouble imagining how I will seal ALL gaps with caulk, plus get access to that bridging point on the sleeves between the inner and out leaf box and deal with that properly.

atomicus wrote:

argument's sake though, if I were able to do this, this would then be the passive intake I presume?

You need an active intake, to make sure you get a good enough supply of oxygen and extraction of CO2. You could fit a inline fan between the silencer and the garage door. The extra long flexible duct would just be attached to the fan and the garage door grille.

atomicus wrote:

sleeve is built into the box... so if I do this, and the box is up against the wall, how do I get to the gap around the sleeve to fill it with caulk?

Are you fitting the silencers directly onto the wall, or decoupling them at all? If fitting directly on the wall: You just put lots of caulk all over the silencer box where it meets the wall, press it up right against the wall, fix it in place and caulk around the outside perimeter. The only bits you can't caulk, will be bits covered by the box, in which case the box will have had caulk on that face anyway and have been compressed against the wall, sealing the gaps.

atomicus wrote:

Regardless which way I do it, I'm having trouble imagining how I will seal ALL gaps with caulk, plus get access to that bridging point on the sleeves between the inner and out leaf box and deal with that properly.

Here's how I would do it: Build all your framing first, without any facing material (plasterboard etc). Then place a small piece of plasterboard/osb on the areas for each silencer. Make it small enough for your to be able to comfortably reach through to the sleeve in the cavity. Cut a hole for each silencer sleeve. Caulk up your silencer and fit it in place. Fit the matching silencer on the other side of the wall on its own piece of plasterboard. Now access the side of the cavity (remember your didn't plasterboard the whole wall yet) and join the sleeves. Repeat for the other pair of silencers. When you're all hooked up, it would be best to test your ventilation and ducts at this point, to look for leaks. Then you can go ahead and finish plasterboarding the rest of the wall. And move on to your second layer. Dan

Waka wrote:

You need an active intake, to make sure you get a good enough supply of oxygen and extraction of CO2. You could fit a inline fan between the silencer and the garage door. The extra long flexible duct would just be attached to the fan and the garage door grille.

Many thanks. Unless I interpreted it wrong, Gregwor previously said the opposite... quoted below... although exactly what "slight advantage" he's referrng to I'm not sure. I always understood that fresh air would be pulled into the room regardless, as I cannot create a vaccuum in a sealed space. And if the fan is on extract, there should be no issue with co2 build-up. I'm not married to either solution, I will just go with whatever is most optimal. I'll need to know beforehand though, as it will determine what side the fan is wired and mounted on. This doesn't stop me building the boxes however, which is my next step, so I have some time to decide this. If it ends up that I cannot cut a hole into the garage door, it seems the best solution will be to bring air IN from the behind the garage door (which gets decent air flow around the large gaps), and extract it in to the hallway. Dumping air into this space shouldn't be a problem, as it is well ventilated, not a living area and adjacent the front door. It's just a question of where the fan goes. I know this scenario isn't ideal, but if I am unable to cut a hole in the garage door, it is the only option I can see.

Gregwor wrote:

You could have the fan on the supply side if you want. Again, the difference is minimal, but from my studies, there is a slight advantage to pulling stale air out of the room. You should only have 1 fan. Since the room will be a completely sealed system, the fan pulling air out will ultimately pull fresh air in.

Waka wrote:

Are you fitting the silencers directly onto the wall, or decoupling them at all? If fitting directly on the wall: You just put lots of caulk all over the silencer box where it meets the wall, press it up right against the wall, fix it in place and caulk around the outside perimeter. The only bits you can't caulk, will be bits covered by the box, in which case the box will have had caulk on that face anyway and have been compressed against the wall, sealing the gaps.

Initially I was thinking it like this, but I then realised I'd be unable to caulk around the sleeve area given this would be entirely hidden by the box, and accessing the sleeve join would also be very hard. However, the idea you outline below seems like it would be easier and resolve these issues, avoiding any unwanted gaps. Thanks. :) How would you suggest I test for leaks accurately?

Waka wrote:

Here's how I would do it: Build all your framing first, without any facing material (plasterboard etc). Then place a small piece of plasterboard/osb on the areas for each silencer. Make it small enough for your to be able to comfortably reach through to the sleeve in the cavity. Cut a hole for each silencer sleeve. Caulk up your silencer and fit it in place. Fit the matching silencer on the other side of the wall on its own piece of plasterboard. Now access the side of the cavity (remember your didn't plasterboard the whole wall yet) and join the sleeves. Repeat for the other pair of silencers. When you're all hooked up, it would be best to test your ventilation and ducts at this point, to look for leaks. Then you can go ahead and finish plasterboarding the rest of the wall. And move on to your second layer.

atomicus wrote:

Many thanks. Unless I interpreted it wrong, Gregwor previously said the opposite... quoted below... although exactly what "slight advantage" he's referrng to I'm not sure. I always understood that fresh air would be pulled into the room regardless, as I cannot create a vaccuum in a sealed space. And if the fan is on extract, there should be no issue with co2 build-u

Sorry Atom, I misunderstood, I thought you were suggesting the entire system would be passive! It is personal preference whether you want your intake or extract to be the active side. A benefit of having an active intake, is a positive pressure in your room, which can improve the pressure on your door seals. But whatever works for you is fine.

atomicus wrote:

If it ends up that I cannot cut a hole into the garage door, it seems the best solution will be to bring air IN from the behind the garage door (which gets decent air flow around the large gaps), and extract it in to the hallway. Dumping air into this space shouldn't be a problem, as it is well ventilated, not a living area and adjacent the front door.

That could be a solution, it might put additional load on the fan though if it's difficult to draw enough air in from around the garage door gaps.

atomicus wrote:

How would you suggest I test for leaks accurately?

It doesn't have to be that accurate, just listen for escaping air and feel around the connections of the sleeve. If your feel/hear any air escaping just tape over the hole with aluminum tape. Your silencers should ofcourse be fully sealed as your walls are, but within the cavity at the bridge between the sleeves, it's less of an issue. Dan

Gregwor wrote:

Flow rate in CFM = ft3/min = [# of air changes per hour X cubic volume of room] / 60 min Air velocity in ft/min = CFM Flow rate in ( ft3/min) / CSA Cross sectional area in ft2 This is actually expressed as v=q/A Area of a circle = π r2 Radius = half of the diameter If you use flat oval duct anywhere: Area of flat oval = π (minor radius)2 + [(major diameter- minor diameter) x minor diameter)] OR [(π minor 2) / 4] + 3 (major - minor) BTU = British Thermal Units This is the quantity of heat required to raise the temperature of one pound of water one degree Fahrenheit Static pressure is in Pa Air Handler Unit must be able to handle more Pa than the system is

I have had some good news recently, having gone through the lengthy process of officially inquiring about cutting holes in my garage door, and have been told this is something I CAN do. Therefore I will now be able to have both supply and return going to the outside fresh air. :D However, now that I'm ready to build my boxes, I am really baffled (no pun intended), as to how big/small they should be? Your formula above has scrambled my brain somewhat, and my primary concern is that I will make them either too big or too small. I would just like to know roughly what size I should be looking at, given my room size, such that I don't end up with boxes that either don't work effectively, or are simply massive overkill. Taking into account the room size at 23 cubic meters, and what I envisage aesthetically, my plan was to build the boxes on the inside of the rear wall such that they look part of the room. This would put them, very approximately, at about 20-25cm deep, 65-70cm high and 40-45cm wide. There would be 4 of these, all the same size give or take, two on the inner leaf, two on the outer leaf (in the rear corners). Does this sound 'about' right? I don't expect to know the exact CFM setting on the fan from this just yet, but a ballpark would be useful, just so I know I'm on the right track.

I am willing to pay for someone to help me with this as I am totally unable to calculate the size my boxes should be and I am at the point of being unable to progress with my project. Can someone please help? :?

I am willing to pay for someone to help me with this as I am totally unable to calculate the size my boxes should be and I am at the point of being unable to progress with my project. Can someone please help?

You might get a bunch of private messages from people and I suggest ignoring them. You should message John Sayers and ask him if he will take on your project. He is the best and clearly this is his forum for a reason :) Greg

Gregwor wrote:

I am willing to pay for someone to help me with this as I am totally unable to calculate the size my boxes should be and I am at the point of being unable to progress with my project. Can someone please help?

You might get a bunch of private messages from people and I suggest ignoring them. You should message John Sayers and ask him if he will take on your project. He is the best and clearly this is his forum for a reason :) Greg

Thanks. I did that, but it's left me even more confused now really. He doesn't seem to want to take my money, but kindly suggested I should only go with two boxes, not the four. He also showed me a 3D model of a box, with only two baffles. Quite different from the one you showed yourself earlier. He hasn't answered my question on the fan. Your calculation would probably get me there, but I can't quite make head nor tail of it. So really, I'm not much further forward. I basically have two choices now. Give up entirely... or just wing it, build the boxes to some sort of approximation of what I think they should be, stick a fan on there and hope I don't die. :snack:

He doesn't seem to want to take my money, but kindly suggested I should only go with two boxes, not the four. He also showed me a 3D model of a box, with only two baffles.

You can totally get away with 1 box but for obvious reasons (structure-borne transmission) you're not going to get as much transmission loss as using 4 boxes. Lastly, from personal experience, the more baffles and the larger the cross sectional area inside, the more insertion loss you're going to get. 2 baffles would be fine if you weren't requiring a lot of isolation for your room. Maybe ask John if you could post the picture he sent you. I'd love to see it! Greg

Gregwor wrote:

He doesn't seem to want to take my money, but kindly suggested I should only go with two boxes, not the four. He also showed me a 3D model of a box, with only two baffles.

You can totally get away with 1 box but for obvious reasons (structure-borne transmission) you're not going to get as much transmission loss as using 4 boxes. Lastly, from personal experience, the more baffles and the larger the cross sectional area inside, the more insertion loss you're going to get. 2 baffles would be fine if you weren't requiring a lot of isolation for your room. Maybe ask John if you could post the picture he sent you. I'd love to see it! Greg

I already have the materials for the four boxes anyway, so that would be my intention. Sent you PM ref the box design. My issue comes back to box size and fan requirements... really not sure what to do at this point. Feel rather lost tbh.

My issue comes back to box size and fan requirements... really not sure what to do at this point. Feel rather lost tbh.

Preaching to the choir brother! Good luck.

Preaching to the choir brother! Good luck.

Dang guys, is there any specific thing you are confused about? Greg

I don't mean to hi-jack this thread - my difficulties will keep for another post!

Is there data available sustaining the suggestion these labyrinth boxes perform better then a box without these dividers?

Is there data available sustaining the suggestion these labyrinth boxes perform better then a box without these dividers?

I don't have any lab data, but basic acoustics theory applies here, and I can speak from personal experience saying that they work very well. Greg

https://www.gearslutz.com/board/studio- ... -look.html posts 17 18 19 might be of interest.

I designed/drew these up for him (John, don't worry, I didn't charge him but instead asked him to donate to the forum) :thu: Greg

Just a quick update on this... has taken me a while, mostly due to COVID related delays in getting supplies, but have finally got all my boxes built now. I went double layer, plywood and MDF, so they're pretty solid (and weight a tonne!) Next stage is getting the rest of the room finished, and then getting the boxes up and all connected etc, but I have a few more things to do before I'm at that stage. For now, I'm parking them out of harms way. A huge thanks to Gregwor, couldn't have done this without his help! :)

Just wanted to jump in and let you know that reading this single thread has increased my knowledge of HVAC ducting tenfold. Thank you!

Impressively neat job! Can I ask what you used to cut the foam with? Best wishes, John.

Update: Finally. Pretty much done now. Boxes are all hooked up and room is all but finished. Plasterer is due next week. Has been quite the journey to get to this point, and I'm just glad it's nearly complete! Many thanks again @Gregwor.