Studio build in Wales, UK...again!

I've been quiet lately but I do have some updates for you all. I finished the cable troughs and yesterday we finally poured the concrete down inside. I'll write a post with some pics tomorrow as today is our wedding anniversary. Paul

Hi guys, To all those of you who are more experienced, I have a question regarding the BBC R. Walker "No integer multiple within 5% rule" when it comes to vaulted ceilings. Does it still apply, or is it only for rectangular rooms? To remind you, my room is L 24' 1" x W 19' 9" with an average ceiling height of 10' 7.5" these dimensions all comply to the 5% rule. The ceiling is vaulted; 8' 9" at the lowest - 12' 6" at the peak. Between 8’ 9" - 9’ 4" it passes the 5% rule. Between 9’ 5" - 10’ 5" it fails the 5% rule. Between 10’ 6" - 11’ 5" it passes the 5% rule. Between 11’ 6" - 12’ 6" it fails the 5% rule. How much of an issue is this likely to be? I chose my dimensions based on the most amount of volume I was permitted, this meant that I needed to use a vaulted ceiling. I used the average height while inputting my dimensions into various room calculators to check and double check that my ratio would at least be decent enough, but I did not consider until now that due to the angles caused by the vaulted ceiling it would at certain heights fall below recommendations. For example, the actual height at the peak is just over half the length, which fails the rule, despite the average ceiling height being very good. Am I panicking about insignificance? I am planning to treat the peak like any other corner and fill it with a superchunk, below which I could put hangers etc. But I am worried I have not given myself the best start, acoustically, before treatment. I would even move a wall now rather than later if it's worth it. Any advice/reassurance appreciated. Paul

To all those of you who are more experienced, I have a question regarding the BBC R. Walker "No integer multiple within 5% rule" when it comes to vaulted ceilings. Does it still apply, or is it only for rectangular rooms?

Room ratios only apply to rectangular rooms. To a lesser extent, they can be useful in providing some info about rooms that are not quite rectangular, such as when a wall is angled slightly. But a vaulted ceiling is rather different: that's some pretty steep sloping, usually, and there are two surfaces up there, not just one.... so the room now has seven sides, instead of just six. That implies that ratios are not really valid measurements.

I chose my dimensions based on the most amount of volume I was permitted,

:thu:

this meant that I needed to use a vaulted ceiling. I used the average height while inputting my dimensions into various room calculators to check and double check that my ratio would at least be decent enough, but I did not consider until now that due to the angles caused by the vaulted ceiling it would at certain heights fall below recommendations.

Don't sweat it too much! You will need to put treatment on the ceiling in any case, so the only real difference is the type of treatment, and how much of it. In the worst case, you might need to cover a large portion if the ceiling with thick absorption. That's about the only consequence.

Am I panicking about insignificance?

:) You could say that! But it's always good to ask if you have any suspicions! NOT asking would be a big mistake.

the actual height at the peak is just over half the length, which fails the rule, despite the average ceiling height being very good.

Think of it this way: Most of your ceiling does not have that problem! It's only for one specific strip if ceiling (range of dimensions) that you "fail" the test.... so worst case, you are only "off" by a small fraction of the total ceiling area.... Plus, the ceiling is angled steeply in two different planes, so it is not even parallel to the floor! It's most unlikely that there will be any problem here. And if there IS an issue, then just put treatment on it! :)

Any advice/reassurance appreciated.

Reassurance! It's not a big issue. Don't sweat it. - Stuart -

Any advice/reassurance appreciated.

Reassurance! It's not a big issue. Don't sweat it. - Stuart - Thank you as always Stuart, now I can sleep at night :yahoo:

Hey guys, What do you guys think about turning my rear inside out wall into a massive membrane trap? I'd have to shoot the room and see if it's needed and at what frequency range, but as a potential idea for treatment it might work quite well. Porous absorption or hangers could also be placed in front of it, especially in the corners as well as a diffuser in the middle if desired. My vision is using the stud bays as the cavity with insulation, and then fixing the membrane to the studs. If a bigger cavity is needed then more studs can be placed in front of the wall studs to increase the cavity, and then the membrane could be either plywood, MLV or whatever is needed to target the desired frequency range. Has anyone ever tried this? Paul

Membrane devices can be very effective at target frequencies using minimal depth. The cons with them is that they continue to resonate after initial excitement and they can be difficult to tune. I've never seen or thought of placing a membrane behind a set of hangers but in theory it should work. Maybe John has some thoughts on this as he has developed some crazy rear wall devices and has probably thought of and/or tested something like this in the past! Greg

I've never used panel absorbers on a rear wall. cheers john

Thanks Greg for your words of optimism... it might be a fun experiment, or an expensive disaster!

John Sayers wrote:

I've never used panel absorbers on a rear wall. cheers john

Hey John, good to have you back 8) thanks for your words

Hi Paulus, Have you got a problem you're trying to treat with a membrane absorber, or is it hypothetical? The reason I'm asking is because, although you have an idea for a massive membrane, it would only be useful if there's a specific frequency you need to target that is high energy at that position. You might be able to use membrane absorbers back there, but it would be better to measure and create multiple smaller "modules" you could fit in an array in the wall tuned to specific frequencies and areas of high energy. **** Misremembered research: ignore this, see my next post for details **** Also you need to stand off any absorption / cloth or treatments at least 6cm from the membrane absorber for it to not negatively affect the device. *************************** Dan

Waka wrote:

Hi Paulus, Have you got a problem you're trying to treat with a membrane absorber, or is it hypothetical? The reason I'm asking is because, although you have an idea for a massive membrane, it would only be useful if there's a specific frequency you need to target that is high energy at that position. You might be able to use membrane absorbers back there, but it would be better to measure and create multiple smaller "modules" you could fit in an array in the wall tuned to specific frequencies and areas of high energy. Also you need to stand off any absorption / cloth or treatments at least 6cm from the membrane absorber for it to not negatively affect the device. Dan

Hey Dan, Purely hypothetical at this stage, until I measure I won't know if it's needed or not, but it's always good to make provisions for such things... not that I'm hoping to have major problems of course! Your room is looking great btw, thanks for all the updates Paul

Waka wrote:

Also you need to stand off any absorption / cloth or treatments at least 6cm from the membrane absorber for it to not negatively affect the device

Just to correct myself here! I misremembered what I read in a BBC paper. I have read you indeed need to "stand off" the fabric/absorption from a panel absorber to preserve it's effectiveness, but the 6 thing was to do with a different effect. The BBC paper was researching the effect of a fabric covering over different absorbers including wide band. They found there is a marked increase in high frequency absorption if fabric is OVER about 6mm (not cm :oops: ) of an absorber surface, if that absorber mainly reflects those high frequencies; they used a perforated panel absorber to illustrate this. So you have to be careful, if you intend to maintain high frequency energy in your room, by covering a panel/helmholtz/perforated panel absorber or reflective surface in fabric, you can unintentionally, add significant high frequency absorption. So, what I said in my last post about standing off at least 6cm wasn't correct. The BBC research didn't mention how far away a covering has to be before the additional high frequency absorption is mitigated, but they showed that having it very close to the surface is a good mitigation. All of which is unrelated to your hypothetical membrane absorber with absorption standing in front of it, apologies! :lol: as you have no intention of retaining high frequency energy and instead intend to fully absorb them. Good reading, that paper, though for those interested: https://www.bbc.co.uk/rd/publications/rdreport_1981_08

Just to add a little more here. I've found the BBC research that shows that putting a fabric covering over the face of a helmholtz absorber, significantly reduces the helmholtz performance. Here's the paper: https://www.bbc.co.uk/rd/publications/rdreport_1992_10 They put their fabric draped loosely in front of the helmholtz and it shows the peak absorption coefficient dropping from 0.95 to 0.7 with very little widening of the frequencies affected. And when they fixed some tissue paper over the face, the affect was severely worsened dropping to 0.4! So I think you could expect that putting anything that reduces velocity of the air directly infront of a helmholtz will degrade performance. This is also the paper that they design their great A10 general purpose very low frequency membrane absorber in. So for you Paul, this won't really affect your membrane wall idea, as long as the hangers are not touching the wall. But will probably affect if you put a slat wall behind your hangers. Dan

Waka wrote:

Just to add a little more here. I've found the BBC research that shows that putting a fabric covering over the face of a helmholtz absorber, significantly reduces the helmholtz performance. Here's the paper: https://www.bbc.co.uk/rd/publications/rdreport_1992_10 They put their fabric draped loosely in front of the helmholtz and it shows the peak absorption coefficient dropping from 0.95 to 0.7 with very little widening of the frequencies affected. And when they fixed some tissue paper over the face, the affect was severely worsened dropping to 0.4! So I think you could expect that putting anything that reduces velocity of the air directly infront of a helmholtz will degrade performance. This is also the paper that they design their great A10 general purpose very low frequency membrane absorber in. So for you Paul, this won't really affect your membrane wall idea, as long as the hangers are not touching the wall. But will probably affect if you put a slat wall behind your hangers. Dan

Thanks for the clarifications and information Dan

Hi Guys, I have a lot of pics of my progress but can't seem to upload them on here despite me trying for an hour or so! I just can't get the size and format right... Anyway for those of you that are interested I've uploaded them all in albums on my studio's facebook page: www.facebook.com/nightowlstudios.co.uk That'll have to do for now as I am too tired to keep trying to upload them here, I'll have to try again another time. Here's what I've done since my last major update: - Concrete is now poured into the compartments between the wiring conduits. This was such hard work as all the perimeter walls were already in place so tamping and levelling proved to be very fun. It was worth it though, the concrete is over kill at between 7" & 9" thick, but that's what it took to get the ground level and also provide enough depth for my wiring conduits. An 6mm underlay with DPM and laminate floor will go over this. - Finished off more framing by installing rafter and collar ties as well as some cross members between the studs as well as new door frames. The door frames are solid with 1 jack stud & 2 king studs per side plus an over sized header and horizontal supports. The incredibly heavy doors hang and swing nicely with a sub 2mm gap around the perimeter. Still need to install the seals and trim as well as the automatic door closers. - Sealed every single seam, gap, crack, hole and joint with acoustic caulk. This took hours and around 80 tubes of caulk, I really do not wish to see another tube of the stuff again though will have to when I start work on the other rooms. My wife helped out with this which cut the time in half, but still took ages. - Started insulating the stud bays/ceiling. I'm using Isover light fluffy as this is just to line the bays behind the rest of the treatment which will consist of mostly hangers and deep broadband traps on the side walls. Now I have a questions where I could use some advice: I will cover the insulation with Dacron and then some very cheap fabric and leave it as is for a while until I am ready to buy/build the majority of the acoustic treatment. I have some very breathable cotton dust sheets which I bought from new which have a thin plastic layer attached on the back (to waterproof it and stop paint dripping through when used to protect stuff while decorating) I would like to use this fabric just to cover the walls and the ceiling for now to make the space a little more presentable. I know the acoustic effects of thin plastic but how about the risk of condensation? Do you think it would be a bad idea to cover the entirety of the space with this plastic backed fabric? am I asking for condensation problems? Many thanks, Paul

I have a lot of pics of my progress but can't seem to upload them on here despite me trying for an hour or so! I just can't get the size and format right...

I can't advise how to resize on a windows computer as I'm an Apple user, however there is a super powerful free program called Gimp you could try to use to resize if you're on a windows computer. On an Apple computer, open the picture in Preview and then go to Tools --> Adjust Size and then whatever your largest dimension is (in pixels), type is 1200 and then resave the picture. If the file size is above 500KB, you will need to export it in a smaller file format. I've found that going File --> Export then choosing the file type as JPEG then moving the quality slider just a hair less than full will dramatically drop the file size. After that, hit save and you're ready to upload it to the forum!

Anyway for those of you that are interested I've uploaded them all in albums on my studio's facebook page:

It looks awesome. I haven't fully gone back through your thread to remember your entire design, but I see one of your FB friends brought up a rotting issue. I'm hoping you've considered and sorted that all out?

- Sealed every single seam, gap, crack, hole and joint with acoustic caulk. This took hours and around 80 tubes of caulk, I really do not wish to see another tube of the stuff again though will have to when I start work on the other rooms. My wife helped out with this which cut the time in half, but still took ages.

I quite literally have experienced the countless tubes of caulk pain. I eventually bought a cordless caulking gun to alleviate the pain. It also didn't help that I did it with a recently discovered dislocated wrist :roll:

I know the acoustic effects of thin plastic but how about the risk of condensation? Do you think it would be a bad idea to cover the entirety of the space with this plastic backed fabric? am I asking for condensation problems?

Again, I'm not entirely following where you'll be putting this (is this going to be on your final inner leaf insulation or our outer leaf temporarily before you put up your inner leaf? Any plastic needs to be on the cold side of your inner leaf sheathing. This would act the same as your vapour barrier in a regular basement. I hope I've explained that clearly. Greg

Gregwor wrote:

Again, I'm not entirely following where you'll be putting this (is this going to be on your final inner leaf insulation or our outer leaf temporarily before you put up your inner leaf? Any plastic needs to be on the cold side of your inner leaf sheathing. This would act the same as your vapour barrier in a regular basement. I hope I've explained that clearly

I'm not sure about this for the UK Greg. We tend to put vapour barriers on the warm side of the room (just beneath the internal plasterboard) and vapour permeable membranes on the cold side. This keeps warm vapour in the room and not meeting the cold damp exterior air to condense. Although with inside out designs this design goes all up in the air. The vapour control barrier should go directly against the plasterboard/osb3, without a cavity behind it. What kind of membrane are you putting on the OSB3? You could get problems with condensation with another impermeable barrier infront of the insulation. Dan

Dan, I think we are saying the same thing, just differently. It's 3:30am here right now and after tomorrow I leave on a holiday to Maui for a week :yahoo: otherwise I'd draw something up in SketchUp showing an inside out build to show what I mean. Basically, I'd just be drawing what you did with your personal build though. To try and reword what I meant, the "warm" side of the inner leaf drywall is what you'd paint or hang a picture on. The "cold" side of the inner leaf drywall would have the barrier and then insulation within the cavity of the inner and outer leaves. Does that make more sense? Granted, the barrier would be "warm" since it's on the warm side of the insulation. But I'm not sure how else to word it to say that he shouldn't put the barrier on the exposed side of the drywall :? A drawing is worth a million words. I'll ask Siri to remind me to draw it up when I get home from my holiday. Greg

Hi Greg & Dan, Thanks for your input guys, I appreciate that. So I am not intending to use plastic backed fabric to be a vapour retarder, more I am just worried it will act as one as a side effect of using the fabric for aesthetic reasons. Perhaps it would be better to just use different fabric and not risk it. Greg: regarding the ceiling rotting out, I do not think it will be a problem in my design. What you have seen in the pictures is the inner inside out leaf. As it stands, that's all I have constructed at the moment and I will be building the outer leaf around it at a later date. So not only have I built it inside out, but also in reverse, which is unusual. But the reason for doing so was because I need a functional space (even if it is temporarily not completely isolated) that I can use for mixing and teaching. I cannot currently afford to build all the other rooms of the studio and therefore the outer shell must also wait. By doing the inside first it enables me to get all my gear in and get use out of the space in the mean time. I also wanted my control room to have as much volume as possible which meant that I needed to do a dual pitched roof with no attic space, and permitted planning in the uk states that a dual pitch roof can be at a maximum height of 4m in stead of 3m with a single pitch roof. that leaves me with the dilemma of how to vent the roof space since both my internal leaf and outer leaf are both dual pitched. So I decided to build it with an unvented design with a warm roof. If the roof deck is insulated above, between and below the rafters then there is no need for it to be vented. It is a newer more efficient way of building, similar to how passive houses are constructed. From the pictures, can you see any potential problems with anything else or any other suggestions? Regarding the resizing of the pictures, I too am an Apple user and I did the procedure you described in your reply however I could not get some of them below 500kb which is why they were not uploading, so then I used the jpeg2000 format but that is not accepted on the forum. By that time I gave up as I had so many pictures to upload and it is very tedious uploading them on here one by one! I will get round to it one day, but hopefully most people use facebook and are able to see them on there. Have a great holiday Greg! Cheers for now, Paul

By doing the inside first it enables me to get all my gear in and get use out of the space in the mean time.

:thu:

From the pictures, can you see any potential problems with anything else or any other suggestions?

I totally get your idea and working with your limitations, I think you've utilized the space well.

I too am an Apple user and I did the procedure you described in your reply however I could not get some of them below 500kb

Either: - slide the quality slider lower until it goes below 500KB - if for some weird reason it is still above 500KB, save it with the quality as low as it will go and then open it again and try making the quality even less -- again. Basically "stack" the crappy quality haha - if you can't get decent enough results with the above method, try setting the pixel size to a smaller value such as 1000px, or even 600px. - if you can't get any of this to work for some bizarre reason, please upload the full resolution pictures to dropbox or something so that myself and/or other members can see if we have any luck.

Have a great holiday Greg!

I SHOULD be in bed right now as it's going to be a long trip with my little kids on the airplane and I didn't fall asleep last night until 7am :evil: But, of course I'm up getting in a last minute Sayer's forum sesh! hahaha Thank you though. I guess I'm leaving at the perfect time because the temperature here is supposed to get really cold this week: (note, I put this picture (730px X 788px)to the lowest quality setting making it ~38KB) Greg

Hi guys, The inside is really taking shape now, I've got the main window plus the two side window frames in plus the wall/ceiling corner soffit framing done. All the inside out walls have their bays filled with insulation and I'm ready to install the insulation and hangers in the ceiling. The challenge is knowing how best to arrange the hangers in a dual pitch ceiling. Here's a really quick diagram of my initial idea; Since I have some simple trusses up there I thought I'd take advantage of the cross members by using them to hang the hangers from as well as supporting some thick fluffy. So the ceiling bays between the rafters will be filled with fluffy, and then the peak in the middle of the ceiling can be filled with fluffy down to the collar tie line, then the large central hangers can be hung from those collar ties, angled towards the speakers. Since the hangers will be around 8' long and 2' wide that leaves some space around the edges. So I thought I could fill that space with some straight down vertical hangers which would fit between the central hangers and the ceiling corner traps, this is the part I'm not sure about since ideally these hangers would be angled towards the speakers as well but difficult to do so due to the angle of the pitched ceiling. Then finally there would be a layer of fluffy below the hangers down to the rafter tie line, which will be covered in fabric. Any suggestions? Paul

John is the wizard of hangers but I think it looks pretty good other than the tiny little hangers. I'm not sure those are doing any good. Greg

Gregwor wrote:

John is the wizard of hangers but I think it looks pretty good other than the tiny little hangers. I'm not sure those are doing any good. Greg

Hey thanks Greg, how was your vacation? yeah I agree with you - I won't be making hangers that are actually that small, I just did a quick sketch that's not to scale just to demonstrate a concept rather than an accurate design. So if you think the general idea is good then I'll go with that for now. Things are continuing to progress in the studio, we've started insulating the ceiling bays with the itchy stuff - not a very easy or pleasant job! But it'll be worth it. Since I'm installing the ceiling corner soffits and will soon construct the rear and front wall framing it's about time I build some silencer boxes, so I come seeking advice to help me make some decisions. I will have a simple passive inlet and an outlet with a fan, then a mini split for cooling/heating. I am lucky in that there really is no limit to the size that the silencer boxes can be (within reason) and I could install them either in the cavity between the leaves, or some inside the control room and some in the cavity. The cavity will be about 13" deep (8" between the framing + 5.5" thickness of the framing) so that would be the limiting factor if I put one or both inside the cavity. If I put them inside the rooms then they could be even larger since I'll have about 3' of "loft space" in my dual pitched ceiling where the acoustic hangers are hung, plus I'll have space above and behind the middle section of the speaker soffits, and a massive amount of space above the rear wall soffit (around 3' x 7' x 19'). Now here's something that makes this easier; I figured out that I can completely do away with any ducting inside the rooms as I can install the silencer boxes right where I need the in/out vents to be. So the silencer boxes can just have a register on the end and then to join the silencer boxes between leaves I can use either MDF sleeves with a rubber joint, or a little flex duct. So Greg (or anyone else reading this) you are a total whizz at HVAC now and I'm begging for your expertise. With the above info in mind, could we come up with a design for my silencer boxes together? bearing in mind these boxes are just for air exchange only, so no air con to link in with them. If you are willing to help, please let me know the info you need in order to make the calculations so that we can come up with the dimensions for the boxes plus the amount of baffles within the boxes and I'll draw out some designs. Here's some info I can give you straight away: The room volume is approx 5000 cubic feet, let's say they'll be 10 people max in the space at once and then we'll need 6 air changes per hour (I think that's the required amount?) we worked out in some previous posts that I need 154.48cfm, so now how to work out what size boxes I need? please let me know if there's any other info needed to work this out. Thanks so much, Paul

Hey thanks Greg, how was your vacation?

It was amazing. Crazy to have the cold streak at home with people living in between -45°C and -50°C and then me in Maui living in between 28°C and 30°C! That's literally 80°C difference. Hard to fathom.

I could install them either in the cavity between the leaves, or some inside the control room and some in the cavity.

I can help you for sure but I need you to decide where you want the boxes and then give me the dimensions we have to work in.

The cavity will be about 13" deep (8" between the framing + 5.5" thickness of the framing) so that would be the limiting factor if I put one or both inside the cavity.

This one concerns me because we have to stick to 24"OC which means the silencer can be a max of 22.5" wide and 13" deep (this is if you're willing to only have 1/2" for your MSM gap!). Punching those numbers into my basic silencer box equation: Y = width = 22.5" X = (Y-7)/2 X = (22.5-7)/2 X = 7.75" The length of your box with 3 baffles (I recommend more if you can handle the static pressure) would be: length = (4X) + 11.5 length = (4*7.75) + 11.5 length = 42.5" Now, if we did maximize your depth at 13", we will have 2" of MDF + 2" of ductliner eating up that available depth. So, our inner silencer dimension will be 13" - 2" - 2" = 9" So, that means our cross sectional area (CSA) within your silencer will be: CSA = X * inner silencer dimension CSA = 7.75" * 9" CSA = 69.75 sq in CSA = 69.75 sq in / 144 = 0.4844 sq ft 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 CFM (according to what you said was figured out previously) is 154.48cfm Now, to confirm, is this the CFM if you wanted 6 air changes per hour for the entire space or is this just the amount you need for fresh air? Note: Entire space CFM would be if we were using forced air and we were exchanging the entire space. Fresh air CFM would be 25-30% of the entire space CFM. This is the amount of fresh air your forced air system would exchange in it's design. If you're using a mini split for heating and cooling, your ventilation design would only have to exchange 25-30% of the air in the room with fresh air. For small spaces (and in the right climate) I will always recommend ductless mini splits for this reason alone. Simply put, the ventilation system (mainly the silencer boxes) take up way less space! So: v = 154.48cfm / 0.4844 sq ft v = 318.93 ft/min This is just slightly over to the recommended velocity. In a pinch it could work. Now, we need to ensure that we have the CSA change by at least a factor of two going into the silencer box. So, if our CSA in the box is 69.75 sq in, half of that is 34.88 sq in. Area of a circle = π r2 Radius = half of the diameter Using round duct, that means that the diameter of our inlet duct is: d = 2 √ (A/π) d = 2 √ (34.88/π) d = 6.66" So you could either use 5" or 6" round duct to feed to your first silencer and then use between the inner and outer silencers. As you said, you can just cut a big square hole in your box with a sleeve to have as your inlet/outlet to your room. If you were concerned with the air velocity you could modify the last little chunk of the silencer box to allow for a larger sleeve penetrating your room. Sorry if some or all of these calculations are wrong. I just pounded through it quick as my kids were disturbing me. Use these same steps to figure out the specifications for other potential locations. It all starts off of your available space. If you have unlimited space then of course you're not going to be building your silencers the size of an airplane but I do recommend making them as big as you can within reason. MDF sheets typically come in sheets that are only 4' wide so that's a good starting point for maximum size in both your width and depth. Also, consider how much they are going to cost to build and whether you're going to be able to physically move them into place. If the weight of the silencers is going to be hanging off of your inner leaf joists, make sure your joists can handle the weight as well. It's pretty simple to estimate the weight of the silencers knowing the density of the material you are building them with (MDF for example). I hope that helped some even though it was just an example for the MSM cavity location. Greg

Gregwor wrote:

Hey thanks Greg, how was your vacation?

It was amazing. Crazy to have the cold streak at home with people living in between -45°C and -50°C and then me in Maui living in between 28°C and 30°C! That's literally 80°C difference. Hard to fathom.

I could install them either in the cavity between the leaves, or some inside the control room and some in the cavity.

I can help you for sure but I need you to decide where you want the boxes and then give me the dimensions we have to work in.

The cavity will be about 13" deep (8" between the framing + 5.5" thickness of the framing) so that would be the limiting factor if I put one or both inside the cavity.

This one concerns me because we have to stick to 24"OC which means the silencer can be a max of 22.5" wide and 13" deep (this is if you're willing to only have 1/2" for your MSM gap!). Punching those numbers into my basic silencer box equation: Y = width = 22.5" X = (Y-7)/2 X = (22.5-7)/2 X = 7.75" The length of your box with 3 baffles (I recommend more if you can handle the static pressure) would be: length = (4X) + 11.5 length = (4*7.75) + 11.5 length = 42.5" Now, if we did maximize your depth at 13", we will have 2" of MDF + 2" of ductliner eating up that available depth. So, our inner silencer dimension will be 13" - 2" - 2" = 9" So, that means our cross sectional area (CSA) within your silencer will be: CSA = X * inner silencer dimension CSA = 7.75" * 9" CSA = 69.75 sq in CSA = 69.75 sq in / 144 = 0.4844 sq ft 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 CFM (according to what you said was figured out previously) is 154.48cfm Now, to confirm, is this the CFM if you wanted 6 air changes per hour for the entire space or is this just the amount you need for fresh air? Note: Entire space CFM would be if we were using forced air and we were exchanging the entire space. Fresh air CFM would be 25-30% of the entire space CFM. This is the amount of fresh air your forced air system would exchange in it's design. If you're using a mini split for heating and cooling, your ventilation design would only have to exchange 25-30% of the air in the room with fresh air. For small spaces (and in the right climate) I will always recommend ductless mini splits for this reason alone. Simply put, the ventilation system (mainly the silencer boxes) take up way less space! So: v = 154.48cfm / 0.4844 sq ft v = 318.93 ft/min This is just slightly over to the recommended velocity. In a pinch it could work. Now, we need to ensure that we have the CSA change by at least a factor of two going into the silencer box. So, if our CSA in the box is 69.75 sq in, half of that is 34.88 sq in. Area of a circle = π r2 Radius = half of the diameter Using round duct, that means that the diameter of our inlet duct is: d = 2 √ (A/π) d = 2 √ (34.88/π) d = 6.66" So you could either use 5" or 6" round duct to feed to your first silencer and then use between the inner and outer silencers. As you said, you can just cut a big square hole in your box with a sleeve to have as your inlet/outlet to your room. If you were concerned with the air velocity you could modify the last little chunk of the silencer box to allow for a larger sleeve penetrating your room. Sorry if some or all of these calculations are wrong. I just pounded through it quick as my kids were disturbing me. Use these same steps to figure out the specifications for other potential locations. It all starts off of your available space. If you have unlimited space then of course you're not going to be building your silencers the size of an airplane but I do recommend making them as big as you can within reason. MDF sheets typically come in sheets that are only 4' wide so that's a good starting point for maximum size in both your width and depth. Also, consider how much they are going to cost to build and whether you're going to be able to physically move them into place. If the weight of the silencers is going to be hanging off of your inner leaf joists, make sure your joists can handle the weight as well. It's pretty simple to estimate the weight of the silencers knowing the density of the material you are building them with (MDF for example). I hope that helped some even though it was just an example for the MSM cavity location. Greg

Thanks Greg, that's brilliant. So let's go with the silencers inside the room, I think it makes it a lot easier from both a design and installation standpoint. What I would like to do is install the inlet box and vent in a large soffit above my rear wall treatment, there is a massive amount of space there to do so. The outlet box and vent could go above the middle section of my front wall, it can either take up some space in the "loft" space or I was thinking it could be a very long but thin (1.5') Y box, of the same volume as the inlet box but with 2 vents on each end where the air will be sucked in by the fan on the other end. Do you think that could work? Then I could have the two vents above my speakers in the soffits. Perhaps the ventilation for the speakers could tie in to this box as well? To answer your question regarding the total CFM being for replacing the air in the entire room or just the 30% fresh air - in short I don't really know or understand or remember... But here's how the CFM figure was worked out which you said looked good previously: "If I worked it out using the amount of people then if I said there is going to be 10 people then it would be: 10 x 15cfm = 150cfm If I worked out using the 30% minium fresh for my room volume with 6 air changes per hour then it would be: 23.92 x 19.57 x 11 x 6 = 30,895.55 30,895.55 / 60 = 514.93 30% of 514.93 = 154.48cfm So, very similar numbers. I just want to check with you that I have done that all right, and therefore I need to spec a fan/HRV that can provide that amount of cfm? In the UK we use the metric system and I am only see specs in m3/h, things like this: Extract Air Performance: Boost – 100 m3/hour Trickle – 30 m3/hour Intake Air Performance: Boost – 100 m3/hour Trickle – 30 m3/hour which means I need to convert my cfm to m3/h: 154.48cfm x 60 = 9268.8 9268.8 = 262.46 m3/h Have I worked that out correctly?" In the above calculations my room volume is actually different to what I've ended up with due to me deciding to not beef up my walls internally but to instead clad them using cement board externally, and also the concrete slab taking up a little more space than previously thought. But, I do not know enough about this subject in order to know whether or not I need to replace the entire room volume's air or I only need to replace 30% of it, but I am confident with your help the boxes I build will work and create a safe environment for my space. Let me know the next step and info you need in order to help you help me! Paul

Paul, From what you've just shown me, the 154.48cfm looks correct for 30% fresh air. So that's what you should be basing your silencers off of.

Do you think that could work? Then I could have the two vents above my speakers in the soffits.

In theory, yes. You'll have to draw this plan up in SketchUp to see if it will fit in reality (assuming SketchUp's dimensions are accurate to your real life room).

Perhaps the ventilation for the speakers could tie in to this box as well?

Unnecessary. There will be enough air movement in the room to move that air into the return silencer. And really, it's going to be so minimal it's nothing to worry about.

Let me know the next step and info you need in order to help you help me!

I think you've nailed everything on the head with your plan. Go into SketchUp and draw up some silencers with the correct interior cross sectional areas and you're off to the races! Greg