Does this count as a 'leaf'

Please note - I started 4 separate threads at the outset of this adventure. This one - which has become the main ongoing discussion.... And then, viewtopic.php?f=2&t=17302 - Should I use (denser) 13ml soundchek or 16mm fyrcheck? viewtopic.php?f=2&t=17296 - Triple leaf viewtopic.php?f=2&t=17294 - Please help with options for room within room - Hi again. My question is now more simple - would the floor of the level above (where I want my rehearsal room) - which is a hardwood floor nailed/glued to tongue-groove chipboard flooring count as a 'leaf' - when a) it is so heavy b) it is 10" away from the draywall leaf below it (the current ceiling downstairs) c) the airspace between the ceilling drywall and this wooden floor is broken up by the joists and cross-pieces. Thank you Peter

Hi Pete, The simple explanation of what a leaf is is this. It is one heavy piece of mass. Now that can be attached to framing or it could be a free standing block wall...it could be horizontal as in an overhead ceiling or floor system or it could be vertical as in an exterior/interior wall. The determination comes in many answers as to what is a leaf. In the strictest of sense, a leaf is determined by the enclosed air around it. In other words, If you have a heavy mass that you are thinking it is a leaf...but it is without sides, no hard boundaries to contain the air...guess what...still a leaf :) Sorry about eveyone's luck that thinks otherwise:) The mass of the leaf is almost as much at fault as the enclosed air. Once the frequencies, or rather if the frequencies make it thru the one boundary...and then hit this other hard boundary that has no enclosed air space...the mass still moves the vibrations and dilutes the isolation...in the strictest sense. Your floor is mass. And the 10 inch air space is good. The biggest issue is that you HAVE to decouple a two leaf system, or any attempt at mass/spring/mass to get the absolute highest degree of isolation available to you from your efforts. The framing is basically a coupling of the floor...your walls are constructed the same way. The coupling of this type of construction, while required to keep the shear of the structure as high as possible, is not aimed at acoustics in the strictest sense of the word. You have to look into several things. One is to decouple the ceiling with clips and hat track...and the other...the MAIN thing you should do, is to get your build on the ground...out of an upper floor area...it is just consumed with issues that cannot be overcome by talking about it on a forum, although some might have you believe otherwise.

Thank you so much for the clarity in your reply. I can see what I need to do now. (Though any other comments would be greatly appreciated!) Take off all the plasterboard that was used to create this room as it creates 2 leaves on 3 sides and the roof....and is coupled...so will never be great at reducing sound levels out of the room. This will leave me with wall 1 - brick (outside of house) wall 2 - wooden frame with plasterboard on far side (another room) wall 3 - like wall 2 wall 4 - concrete retaining wall (in fact I might leave this plasterboard sheet in place as it is attached direct to the retaining wall with no battens/air gaps - so is still a single leaf Plus ceiling - joists with wood floor above And then build a freestanding wooden frame inside the space (and plasterboard one side - the inside - of this frame - walls and ceiling) This wooden frame will ONLY connect with the walls mentioned above via the floor. (Which is a concrete slab under the whole house) Unless someone tells me otherwise - in which case, if you think it's better, I could leave a gap in the flooring I am using (a polystyrene underlay, under a regular timber floating floor) so that the flooring ends at the perimiter of the outer walls...and restarts at the perimeter of the inner walls. I guess I might as well use all the plasterboard I am taking off to add mass to the existing single leaves left behind? And I assume I am right that the gap between the INNER and OUTER rooms should be an AIR gap, not filled with insulating wool? Thanks again for all your help! Green Glue at the ready!

General questions, How thick is the plasterboard used? How thick is the concrete wall? Any idea of the type of concrete?

wall 4 - concrete retaining wall (in fact I might leave this plasterboard sheet in place as it is attached direct to the retaining wall with no battens/air gaps - so is still a single leaf

This may constitute a single leaf, however the plaster may not be adding anything in terms of mass, any may in fact degrade the isolating properties of the concrete wall alone - but I'll leave that for someone more knowlegeable to answer.

I guess I might as well use all the plasterboard I am taking off to add mass to the existing single leaves left behind?

Depending on it's thickness, perhaps, perhaps not - if it's less than 15/16mm it's not much use.

And I assume I am right that the gap between the INNER and OUTER rooms should be an AIR gap, not filled with insulating wool?

No, that assumption would be wrong. Light insulation in the airgap has the beneficial effect of increasing the apparent gap from an acoustic perpective.

The current plasterboard I'm taking off is 2 layers of 13mm on each of the walls and the ceilling

The general recommendation here is to use 16mm drywall. Thinner is less effective.

It is 13mmx2....if I add it to the back of the plasterboard (that's making walls in the next door rooms - that's walls 2 and 3) - then as this is only 10mm plasterboard....I imagine it will help with adding mass

10 mm is way too thin. Even 13mm is "iffy". It's not just adding mass that matters: there are other factors involved too, such as rigidity, flexibility, resonant frequency, etc. Using several thin panels is not a good idea, as the panels still act individually, as well as collectively. Just go with thick layers.

VERY interesting - I thought there couldn't be ANYTHING connecting the inner leaf to the outer - THANK YOU!.

The insulation does not connect the inner leaf and outer leaf mechanically. It isn't solid, and isn't very massive. It only creates a flanking path if you jam it in, compressing it a bit. If you just lay it in, with no compression, then there won't be any flanking. In fact, filling the air gap with insulation does not eliminate the air gap. The air gap is still there. Insulation is mostly air anyway. And as Brian pointed out, adding insulation increase the effective mean path that sound waves must travel, by roughly 140%, so the air gap actually appears BIGGER to the sound waves. Not intuitive! If you compare two identical MSM walls, one with insulation and one without, the one without insulation will perform between about 5 and 16 db WORSE for isolation, than the one with insulation: That's huge! You definitely need it. - Stuart -

Thanks Stuart - clear as a bell. I will fill the space with insulation. May I ask one final question as there seem to be some different POVs on this. The floor on which I am building the room within the room is a concrete slab (holding the house upright on the hill!)..... The existing framing (walls 1,2,3) and the brick outerwall all physically touch this concrete slab. When I build my room within the room - do I put my inner-room framing straight onto the slab....or use rubber strips to separate the framing from the concrete? Thanks so much. Peter

When I build my room within the room - do I put my inner-room framing straight onto the slab....or use rubber strips to separate the framing from the concrete?

My standard answer applies here too: "It depends."! :) It depends on your reasoning. If you just want to use the rubber (usually neoprene) to seal the gap under the frame, due your concrete being very uneven, for example, then that will work. But if you plan to use it to try to decouple the frame from the slab, well, that won't be very effective. It won't decouple very well, since you still have to attach the frame to the concrete with bolts or nails! And the bolts or nails create direct flanking paths right through the rubber, mechanically linking the two. If it were possible to just let the wall rest on the rubber, with no bolts / nails, then that could work to "float" your wall, but of course you can't do that in reality, as the wall has to be firmly attached to the floor. However, it IS possible to float walls, floors and even entire rooms, but the cost and complexity are both very high. - Stuart -

Hi Stuart and thank you again! I was actually not planning on using nails to attach the inner room to the concrete slab - but instead - was planning on using a glue that's for sale over here in OZ which is supposed to be good for the purpose. So I could glue the frame to the rubber and the rubber to the concrete....if the consensus is that this will help reduce sound escaping.... I'm assuming too that my rubber strips have to be wide enough to ensure that (if I'm going down this route) my drywall sheets on the inner room don't touch the concrete either! All the best P

Glue? For attaching the wall to the floor? :shock: Personally, I would never do that, and the building code where I live absolutely does not permit that.

So I could glue the frame to the rubber and the rubber to the concrete....if the consensus is that this will help reduce sound escaping....

It's not about sound escaping: it's about floating your wall, which is different. Like I said: there are two reasons you might want to put rubber under the wall. 1) Seal the gap airtight. 2) Float the entire wall (to fully decouple it from the floor). You seem to be talking about #2 here, which is NOT about stopping sound from getting out: it is about decoupling and isolating the wall, to prevent flanking between wall and floor. That's not the same at all.

I'm assuming too that my rubber strips have to be wide enough to ensure that (if I'm going down this route) my drywall sheets on the inner room don't touch the concrete either!

No, the rubber needs to be the correct width to give you the correct calculated deflection of the correct type of rubber under the real load conditions of the wall, for each section of each wall! A rubber strip under the floor is great for sealing where there is major unevenness in the floor slab, but that's not what you are talking about, it seems. Rubber can also be used to float a wall, but like I said before, that is NOT easy to do correctly. You need to calculate the total weight (mass) of the wall and of everything that will be attached to it, such as doors, windows, the ceiling, HVAC, electrical, lighting, treatment, decorations, etc. You need to know all of that in advance, because you MUST have the entire total weight correct in order to know what kind of rubber you need, and how wide to cut it. The rubber MUST be compressed to the exact correct working range when the room is finished. If you calculate wrong (or don't bother calculating at all) then there are two possibilities: A) The rubber will not be compressed enough, the wall will not float, and it will be nothing but a very expensive flanking path around the entire room: You will have wasted a lot of time and money for zero effect. B) The rubber will be over-compressed, the wall will not float, and it will be nothing but a very expensive flanking path around the entire room: You will have wasted a lot of time and money for zero effect. Your chances of everything working out by pure chance or sheer luck are practically nil. For most types of rubber, it must be compressed sufficiently to deflect around 10% to 20% under full load (depends on the type of rubber) in order to float and isolate the wall. Any more or less and it does not work. So you need to know the exact load (kg/cm2) on the sole plates, and use the right type / thickness / width of rubber to get the right deflection. The trouble is, the weight is not constant around the wall: Some places will have higher weight (EG, under windows, under door frames, etc.) and some will have lower (EG. long stretch of blank wall with minimal treatment. So you need to calculate the correct loading for each PART of each wall, and use the right type/dimensions of rubber for each section. Like I said, that isn't easy to get right. If you are up to the challenge, then go for it! But you also then need to spend much more money to get it right, as you then need to isolate your wall anchors... Floating works great when done right, but "done right" is not easy... However, in none of your multiple threads do see the most basic information that you need in order to decide on things like floating walls, air gaps, mass and such like: I don't see your numbers! I don't see how loud you are, how quite you need to be, your TL goal, your MSM tuning frequency, or any of the other basic data that is essential for determining the details of how to build. Maybe I missed that, and if so then please point me at it, but if not then I'd suggest that, before you start chasing after construction techniques that might or might not be useful/doable, you should first get those numbers in place, and define your goals for this build. If you have no goals, then it is guaranteed that you will fail to meet them! :) If you DO have goals, then you can have a plan, and the chances are much better that you will meet the goals. - Stuart -

Stuart - once again a HUGE thank you for taking your valuable time helping me. My primary goal is to create a space in my house where I can play my trombone without disturbing the baby or the neighbours - please see attached picture. range - 82 Hz to 520 Hz volume 85 - 114dB The room I have selected is on the ground floor on the concrete slab. The house is 2.5 levels. Level 1 (where the music room is). Level 2 directly above it (our living spaces) and Level 2.5 is offset - like a mezanine from level 2 - as the house is on a steep slope. The ground floor has a 1.5 m high retaining wall along the side of the hill and then an air gap under the rest of the house. So the easiest way for sound to travel from the music room, to the baby's room, is over the top of the retaining wall...under the house....and in through the floor of the baby's room. The original attempt at soundproofing this music room - done simply by using 2 layers of 13ml plasterboard was pretty effective in keeping noise levels to an acceptable level in the baby's room. However - the noise transference up to the living spaces was unacceptable. And, the noise transference through the one external wall of the music room to the nieghbour's childrens' rooms was also a bit high. I am looking for a 50-60% reduction in noise through to our living rooms. And a 20%-30% reduction in noise to the neighbours And a 15-20% reduction on noise to the baby's room. The music room as it stands is 2.3m x 1.9m x 2.6m (high) My room within the room is probably going to be around 2.1m x 1.7m x 2.4 (high) Peter

Great! So we have some numbers. :)

range - 82 Hz to 520 Hz

That's the fundamental frequencies, not considering harmonics, but that's good enough as we are only interested in the lowest note. So if the lowest tone you need to isolate is 82 Hz, general rule of thumbs says your wall should be tuned below 41 Hz. Call it 40 Hz.

volume 85 - 114dB

Once again, that's a theoretical range, but once again, it's good enough for your purposes, since it is the maximum level that counts: Call it 115 dB. So you've answered the question "how loud are you?" and "what frequencies do you need to isolate?". Now we need to nail down "how quiet do you need to be?".

I am looking for a 50-60% reduction in noise through to our living rooms. And a 20%-30% reduction in noise to the neighbours And a 15-20% reduction on noise to the baby's room.

Unfortunately, percentages aren't much use in acoustics, since sound is perceived logarithmically, and percentages are linear. A subjective reduction of 15-20% is less than 1 dB, and not even audible. Barely even measurable. A subjective reduction of 50% is roughly 10 dB: hardly worth doing! That would still leave the levels outside your room at 105 dB, which is way loud. There are two ways to move forward here and define the level that you need to hit. For the neighbors, it is easy: call your local municipality and ask for a copy of the noise regulations governing your neighborhood. That will define the legal limit that you must comply with. Regulations usually state that the level must be measured at the property line, so that's what you'll need to do. Get a sound level meter, and get someone to measure, at the property line, the actual level or your very best efforts to blow the roof off with your trombone. Measure during a quite time of day, such as late at night when there are no other loud noises going on in the neighborhood that could skew the reading (traffic, lawnmowers, radios, TVs, etc.). Measure both the ambient level (with no trombone) and the peak level during your playing. Now do the same for the baby's room, living room, and other locations around the house. This will give you objective numbers, regarding the amount of isolation that you need, and the amount that you already have. You also mention different levels of isolation in different directions, but isolation is an "all or nothing" proposition. You'll get roughly the same in all directions, especially with low frequencies, since low frequency sound is not directional: once it is out, then it is out and will wrap around objects whose dimensions are smaller than the wavelength. So all sides of the room need to be done to the same level. It is no use designing one wall for 50 dB of isolation and another for 30 dB. If you do that, you get 30dB all around. So EVERYTHING must be designed for the same level: walls, ceiling, doors, window, HVAC and electrical.

The music room as it stands is 2.3m x 1.9m x 2.6m (high) My room within the room is probably going to be around 2.1m x 1.7m x 2.4 (high)

You probably don't need to lose that much height. It should be doable with 2.45, maybe even a bit less if your existing joist layout permits interleaving. However, you'll lose a bit more on the length and width, since you have to allow for the depth of the left wall PLUS the depth of the right wall, (ditto front and back). So I'd guess at final room dimensions (not considering acoustic treatment: just isolation) of around 2.0m x 1.6m x 2.45m. Your plan to strip the room down to bare studs / concrete, then beef up the walls and ceiling is good! That's the way to go. Once you have it down to that, post some photos so we can get a better idea of what you are dealing with. If it isn't already sealed, then start by sealing the surface of that concrete retaining wall: concrete is porous, and needs to be sealed. Also, seal all joints and gaps in the other walls around the room, and in the floor above you. That outer leaf must be totally airtight. Even tiny gaps will seriously compromise your isolation. If you even vaguely suspect that what you are looking at might be a crack, seal it. And even if you are absolutely certain that it isn't a crack, then seal it anyway, just in case! :) One thing I didn't see in your plan, is HVAC: That room will be sealed totally airtight, twice over, so you won't be able to stay alive in there for very long if you don't have HVAC! You need both fresh air and cooling. Fresh air to stay alive, and cooling to stay comfortable. You can't play your trombone well if you are too hot, and breathing stuffy, stale air. And it's even harder to play if you are dead from suffocation! :) So you need to consider how to get air in and out, through silencers (to retain the isolation), and you need to consider how to keep the room cool. If your current house HVAC system has the capacity, you can just hook into that. If not, you can do a separate vent system for bringing fresh air in and exhausting stale air, plus maybe a small mini-split air conditioner to keep it cool and dehumidified. But overall, it sounds like you have a good plan! - Stuart -

Thanks again Stuart - all excellent and encouraging! I'll post photos when it's stripped....and put a link to the dead vent I found that looks achievable... I do have a ducted heating system which has a fan setting that could force air into the room...but by connecting into this I am connecting the music room to every other room in the house..which makes me nervous. I think (presme??) it would be safer to have a dead vent between the music room and the adjacent (rarely used) room on the ground floor - so if there is any sound leakage via the vent it will be to a space further away from the children's bedrooms/neighbours....understanding what you said about having to think of insulating in EVERY direction! I must confess I am still puzzled about how an air vent can be 'dead' but I'll read more before I post!! There are lots of good examples on this site I know. Just on those percentages - sorry if I wasn't clear...the numbers I gave relate to the INCREASE in isolation I would like relative to how things are now...(and I'll stop using percentages!!) Overall I want to get the noise in the children's bedrooms and in the neighbours' bedrooms to be no more than an adult whisper - 30 db...that's 85db reduction from 115db.... I will try and get a proper reading on what things are now - but my wife says that the noise in the baby's bedroom was half way between talking and a whisper - so say 50db?? So my hope is that by doing a proper soundproof room rather than just the current double plasterboard setup, I will get an improvement from 50db in the bedroom to 30db or less. (i.e. an improvement in db-reduction from -65db to -85db) In terms of the livingrooms - my wife says it sounds like the trombone is in the room - so if I can get a reduction down to something less than normal talking - say 40-50db (i.e. -65 to -75db) that would be great! Of course, if I can get it down to whisper quiet I will! NB re your comment on tuning the wall below 40 Hz....I'll read some more about what this means in terms design etc! Thanks again - your help is FAB! Peter PS My house is very very quiet....no road noise etc...birdsong and the wind in the trees is pretty much all we hear unless the neighbours are on the deck (and tonight's thunder of course!)

A few more questions - please if you have the time to help me out further! Beefing up I"ve had a good look through the posts and haven't managed to find a pic of a cleat - am I right in thinking that a cleat, in this context, is simply a piece of timber nailed into place holding up the drywall in between the joists? (Just like the pieces - mostly 2x6 or 2x8 I think) that are there now - stopping the joists from moving/rotating? It is my intention to use green glue on the drywall being fitted up between the joists - and am wondering - given that GG needs to be 'compressed' to be effective - whether drywall with GG on it, when being put in between the joists, should be screwed to the subfloor (to get the compression) rather than just 'held in place' prior to the caulking/ fitting of additional sheets and ultimately the cleat? Throughout the cleat/beefing posts there is mention of 'backing rods' - are these just there to reduce the amount of caulk used - or do they play an active role in damping etc? Ventilation There are lots of different ventilation options on this site - dealing with lots of very different sized rooms. Given my room (within a room) is comparatively small - 2x1.6x2.45....does anyone have a suggestion for the best way to go? I like the dead vent that has an inlet and outlet with a small fan. And I assume that having a room within a room makes it a little easier (I assume the vent lies in the gap between the two rooms - but I'm not too clear!) Thank you as ever P

A cleat is basically anything that holds the drywall in place! strictly speaking it is a small strip of wood, maybe 3/4" square (9mm or so), nailed sideways into the stud or joist. It holds the drywall in place without needing any nails or screws to actually go through the drywall.

given that GG needs to be 'compressed' to be effective - whether drywall with GG on it, when being put in between the joists, should be screwed to the subfloor (to get the compression) rather than just 'held in place' prior to the caulking/

It doesn't need to be compressed to extremes. The GG instructions just say to "press the board against the wall or ceiling". They do also say "screws assist with the compression of the Green Glue layer into a thin film", but that's more for full sheets of drywall attached over the studs, not so much for small "between the studs" strips like you are doing. You can use screws if you want to, but that could decrease the performance slightly, and you also run the risk of damaging your floor above if the screws are too long. The cleats will hold it in place firmly enough, but it you are really concerned about this, you could build "T" shaped bars to hold each strip in place while the GG sets. Just cut a 1x3 a bit longer than the distance from floor to underside of drywall, nail a "T" piece across one end, and jam it in place. Make a few of those, so you can carry on working while the GG sets.

Throughout the cleat/beefing posts there is mention of 'backing rods' - are these just there to reduce the amount of caulk used - or do they play an active role in damping etc?

Both! :) Backer rod is just a flexible foam "tube" that you press into the joint before caulking. It creates an extra seal that you wouldn't have if you only used caulk, and also reduces the amount of caulk you need.

There are lots of different ventilation options on this site - dealing with lots of very different sized rooms. Given my room (within a room) is comparatively small - 2x1.6x2.45....does anyone have a suggestion for the best way to go? I like the dead vent that has an inlet and outlet with a small fan. And I assume that having a room within a room makes it a little easier (I assume the vent lies in the gap between the two rooms - but I'm not too clear!)

The best method is to instal silencer boxes in-line with your air ducts. Think along these lines: viewtopic.php?f=2&t=1929&hilit=silencer&start=74 viewtopic.php?t=8425&start=2 viewtopic.php?f=1&t=11542&start=5 viewtopic.php?f=2&t=9761&start=0 viewtopic.php?f=2&t=11485&p=89855&hilit=silencer#p89855 viewtopic.php?f=2&t=11508&p=96578&hilit=silencer#p96578 viewtopic.php?f=2&t=13821&p=97928&hilit=+silencer+ducts+might+look+#p97928 viewtopic.php?f=1&t=15378&p=110641&hilit=+duct+silencer+#p110641 The silencers can go any place they will fit. But bear in mind that you might need access to them one day, to clean/replace the lining, fix blockages, or do other maintenance, so it would be good to put them some place where you can get at them without destroying your isolation wall! :) - Stuart -

Overall I want to get the noise in the children's bedrooms and in the neighbours' bedrooms to be no more than an adult whisper - 30 db...that's 85db reduction from 115db....

:shock: Just to put that in perspective, the very best, top, multi-million dollar studios in the world aim for that type of isolation. That's really hard to do for a small facility on a limited budget. 85 dB is a LOT if isolation. Most folks here are happy to get 50-something, really happy to get low 60's, and wildly, ecstatically, dizzily happy if they even get close to 70. An average house wall of 2x4 studs with drywall on both sides will get you around 30. To increase that to 50, you need to absorb 100 times as much energy. To get 60, you need to absorb one thousand times the amount of energy. 70 means ten thousand times the energy, and 80 means that your walls floor and ceiling will need to stop one hundred thousand times more energy than a normal house wall. That's a LOT of energy that you need to stop! It can't be done with simple, low-cost methods, and requires some construction materials and techniques that are beyond the ability of the average DIY studio builder. So I'd shoot for something more reasonable, such as maybe 60-something. That is doable on a reasonable budget with common techniques and materials. It is an attainable goal. Yes, 30 dB is the equivalent of a soft whisper a few feet away, but you'd need to be in an extremely quiet environment to even hear something so quiet! Such as maybe the middle of a windless desert, or inside an anechoic chamber... Ambient noise is way higher than that in most towns and cities, even late at night. With a TL of 65, for example, your PEAK level will be down to 50 dB, and your AVERAGE level down to around 40, which should be plenty good enough, even for stringent noise restrictions. To get a better idea of what you are dealing with, I'd really suggest that you get a sound level meter and do some real-world tests. A decent meter is not expensive, and goes for about US$ 50 to US$ 100 on e-bay, Amazon, etc. It's also a useful tool to have around anyway, for any sound guy or musician. - Stuart -

Thank you Stuart - for the clarification on cleats...GG....and the links on ventilation. Thank you too for the db info...I will certainly get a monitor...that's clearly the way to go. Alas, I have also realised a significant problem in the meantime. Running between the joists that are above the music room is an aircon (heating) duct that starts under the middle of the house (where the heating system is) and runs to a vent at the front in the floor of the living area by the windows at the front. If I remove this duct, my ability to keep the living room warm will be significantly reduced...I can do it...but I'm not going to be liked for it! But if I leave it in place....at worst, Scenario 1: I won't be able to get any beefing up between those two joists - which going by the principal that one 'gap' in the isolation system negates all the rest...is a tragedy and effectively means there's no point beefing up any of the space between the ceiling/floor joists.... Plus that aircon duct is going to faciliate noise transfer into the living space above...just what I'm trying to avoid! Scenario 2...there may just be enough space to beef up the gap between the joists and let the duct run in the air-gap/insulated gap between the inner room and the outer room...but I assume that if I do that, then I am still going to get significant noise transfer, along the duct, into the living room...again negating the benefit of the 'beefing'. Both these scenarios basically make the Inner room isolation pretty much the only isolation against noise travelling into the living room. What are your thoughts? Do I just HAVE to remove the air duct and live with the heating problem? Or can I do something with it (it's a 10" flexible duct) to minimise the noise transfer along it - NB it is a heating duct not an aircon duct - this means it has to be wider as the airflow is slower than in an A/C system. If I leave it in place, is it still worth doing the beefing up between the other joists... OR do I just go mad with the inner room and do three or even four layers etc? What a shame! Thank you as ever. P

The normal method for dealing with problematic ducts like that is to build a "soffit" around it, that remains part of the outer leaf. That basically means boxing it in with drywall that is attached only to the floor above. Fill the gap between the duct and the drywall with insulation. Yes, it will compromise your isolation a bit, but it doesn't have to be a big deal, if you box it in well. You won't lose that much. - Stuart -

So not so much of a disaster! I get it - with this box construction around the duct I will effectivley have a mini 3 leaf system - inner room (leaf) - airgap - box (leaf) - duct - floorboard (leaf) - but because it is just a small part of the overall structure - not too much of a problem. Thanks Stuart. As a matter of interest - when I do the beefing up - do I try and get the extra drywall BEHIND the duct and onto the floorboards above - so that the joist/drywall mass is even all the way across the ceilling..... (and then put a bit extra in to box the duct) - image 1 on attached jpg... or Do I beef to the floorboards between all the other (non duct carrying) joists...and box in the duct with the equivalent 2-3 sheets attached to the joist image 2 on attached?. Thank you (I presume it's 1. recognising that this will lower my headroom probably - but that's ok!) P

I'd go with 2. Perhaps you could also add a bit of light loose insulation around the duct.

Yup, I'd go with #2 as well. And also with plenty of insulation in the gap. - Stuart -

You still attempting to make this build in an elevated wood structure Peter? Because if you are, I have a few documents you want to look into. As stated before, there are far too many issues in this type of build that a ground level build does not have. And the issues are not going to be what you "google" or what even some of the most well intentioned might say on the Internet. In my on-going attempt at writing a book on construction for audio purposes, your room, a room in an elevated wooden structure that is part of the residence...on a scale of 1 to 10, 10 being the least desirable choice, this one is at number 8, right after a wooden framed floor structure at ground level in a typical residence/home and right before a thin metal sheathed shed with a concrete floor but minimum floor space. I'm just saying, this is not something that will transfer if you look at the numbers that might be given for a supported wall assembly on concrete damped by Earth transposed to an upper level wooden structure. You have to, simply have to get educated or your about to blow a wad of cash on something that may or may not give you anything. We have seen it before recently. Good luck.

You still attempting to make this build in an elevated wood structure Peter?

No, he's building it in his basement, on a slab, but with a wood framed floor above him. The problem is that he has about three or four threads going at once, in different areas of the forum, with different questions in each one. So it's a bit hard to follow and keep track of all the parts of the basic plan! That's probably why you thought it was an upstairs build, Brien. But fortunately, it's a basement build, and the issue he's talking about here is a problematic HVAC duct up between two joists in the floor above where the room is going to be. - Stuart -

Thanks for the clarification - and appologies once again for my having started separate threads with separate questions earlier. Is it possible for you to simply delete the threads other than this one - for clarity? I am so grateful for the help - I don't want to be making things difficult for those people who are trying so hard to help me! P PS Thank you for the comments re boxing in the duct (and for putting up with my hand/mouse drawn pics!). When you talk about putting insulation in with the duct - are you talking glasswool/batt style insulation or a more solid foam kind of product?

Naah, not a good idea to delete the threads: they are good questions, and might be useful for others, years from now. But maybe you could choose one of your threads to be your main one from now on, then edit your very first post there to add links to these other threads (and on each of the others add a link back to your main thread): That will help to keep things neatly tied together. Don't sweat it! :)

When you talk about putting insulation in with the duct - are you talking glasswool/batt style insulation or a more solid foam kind of product?

Ordinary pink fluffy fiberglass is fine. So is mineral wool. The purpose is just to provide a bit of damping on possible resonance in the cavity, and also to reduce the levels a bit. Solid foam doesn't have much use in acoustics: most types are closed cell (you need open cell for acoustics), and the more solid it is, the more it conducts sound. So pretty much all references to "insulation" on the forum are about plain old fiberglass or mineral wool. - Stuart -