Soundproofing rooms in my flat

doveman · Post by **doveman** » Sun Apr 30, 2017 8:20 am

Hi,

I had to take an enforced break from making music for a while due to poor health but I'm keen to get back into it again. Unfortunately the flat I'm living in has pretty poor soundproofing and I won't be able to move in the near future.

This is going to be quite a long post I'm afraid but hopefully I've included sufficient detail for you to be able to give me some advice. Apologies for the external links to photos but my Internet seems a bit flaky at the moment and I kept timing out and having to start my post from scratch when posting them to the forum. I'll edit this post to add internal links once I've successfully created it.

Details of property as it currently is

This is a photo from outside my block.

Outside block (750).png

I'm on the first floor on the left, in the orange box with the living room on the left and the bedroom and balcony on the right. To the right of that is the adjacent flat. The flat on the ground floor below is the same layout as mine, whilst above me the 2-bedroom flat is split over two levels, with the living room/kitchen/bathroom on the second floor and the bedrooms on the third floor. I'm not certain but I imagine the concrete slab between the floors spans across the width of the building, as indicated by the red line.

This is a sketch showing where the other flats/rooms are in relation to mine.

Block Layout.png

The vertical orange line indicates the party wall. In terms of noise, in my bedroom I hear the neighbour in the flat next to my bedroom shouting and slamming doors (previously I had a neighbour who didn't shout but who had a very deep voice, which carried right through the wall), not just in the party wall but in the other three walls of the bedroom and to a lesser extent in the living room. I don't hear much airborne noise from the flat above me but there's a fair bit of impact noise (which may be coming directly through the ceiling or transmitting via the walls) and squeaking floorboards are very loud/intrusive. I hear more airborne noise from below me, just normal daytime conversation level and sometimes loud TV (which again may be coming directly up through the concrete ceiling or via the walls). Most bizarrely I hear a lot of airborne noise (loud talking/shouting) from the flat adjacent to and above me (indicated by the green lines), which I hear both in the bedroom and on the living room side of the wall.

So clearly there's a flanking problem!

In terms of construction, the wall between my living room and bedroom appears to be cinderblock with about 25mm of plaster on top, in two layers, as can be seen here.

Corner of wall (750).png

Having found some blown plaster in the main window wall as well (in the upper right corner of this photo), that appears to be the same but maybe there's also brick beyond that, being as it's an external wall.

Main Window (750).jpg

Certainly there's brick on the outside of the side wall, as can be seen in the photo of the exterior at the start of this post. The living room section of that wall just has one small window in it although it's much deeper than the main window, at around 18cm instead of 9cm.

Small Window (750).jpg

I had a look at the wall between the hall and the kitchen and that also seems to have about 25cm of plaster over cinderblock.

Hall wall - old socket (750).jpg

Looking at the corner of that wall there appears to be a layer of plaster (orange line) over cinderblock (red line), then maybe some limestone on top of brick. Perhaps brick has been used here to provide adequate fire protection between the kitchen and hall.

Wall cross-section (Hall) (marked) (750).png

I've lifted a couple of floorboards to confirm that there's a concrete slab under my joists, with a shabby looking thin layer of insulation between the joists and under them. They don't appear to be joined to the wall, which I found surprising as I'd imagine they'd be rather unstable and liable to shift whilst trying to fix the floorboards to them but I've never built a floor, so what do I know!

Wall-board lifted wide (750).jpg

Wall--board lifted left joist (750).jpg

The joists are only about 35mm high. The cinderblock seems to be thicker with less plaster covering it in places, like to the right of these two conduits and where this joist is.

Wall-board lifted conduit (750).jpg

Wall-board lifted centre joist (750).jpg

This is the wall with the doors to the hall and the kitchen. The area in between the two doors is probably plaster attached to the end of the wall dividing the hall and kitchen but the rest of the wall above the kitchen door and below the kitchen window may just be plasterboard as the noise doesn't seem to flank along it much.

Hall-Kitchen Wall (750).jpg

This shows the corner of the wall by the balcony door, where there's about 50mm clearance between the wall and the actual door. There's also about 50mm between the main window wall and the hinges on the other edge of the door.
See post 5, picture 13: http://www.johnlsayers.com/phpBB2/viewt ... 20#p142120

This shows the corner by the door to the hall, where there's about 35mm clearance between the wall and the hinges.
See post 5, picture 14: http://www.johnlsayers.com/phpBB2/viewt ... 20#p142120

The bedroom sketch shows the radiator pipes (in brown) coming from the Water Tank on the right and running round most of three of the walls before going through the wall into the living room to feed the radiator in there, as shown in this photo.
See post, picture 15: http://www.johnlsayers.com/phpBB2/viewt ... 20#p142120

I've knocked up a couple of sketches of the Living Room and bedroom as well.
[Low-res pictures replaced with higher-res ones in post 3]

The two pipes (stacked one above the other) are approx. 17mm from the wall and 20mm in diameter. I don't think I'll be able to build a stud frame in the bedroom because these pipes will be right where the footer needs to be and whilst I could move the pipes inwards so that they sit inside the inner room, this may leave too little clearance around the edge of the room, although as they don't run along the dividing wall between the bedroom and living room it may be possible.

My plans and questions

My budget is quite limited, around £2000 tops but obviously I'd rather spend less if possible as there's plenty of other things I'd like to spend it on! My plan is to have the bedroom double up as a vocal room, so the soundproofing needs to stop neighbour noise getting in (which will also help me sleep) and voice frequency/amplitude noise leaking out. I'll have the PC, speakers, etc. in the living room, so the soundproofing will need to be a bit better in there but it's also further away from the party wall.

For the living room, I don't really have the room for a 10mm gap, 50mm stud frame, clips and hat channel and two layers of 15mm acoustic plasterboard. What I was thinking of doing is stripping off the plaster, giving me an extra 25mm or so, then screwing IB-1 isoclips and hat channel, which totals about 28.5mm, to the cinderblock, fitting 25mm insulation in the gap and then screwing two layers of 15mm plasterboard to the hat channel, for a total of 58.5mm. I currently have 35mm clearance by the hall door, so with an extra 25mm I'd have 60mm and at the balcony door I currently have 50mm, so with the extra 20mm I'd be fine there as well. Having found that the plaster appears to be less thick in places however, I can't be certain that I'm going to release an extra 25mm everywhere by stripping off the plaster and whilst it only really matters near the doors, so I could in theory have the middle of the wall slightly further in the room than it is near the doors, I don't know if the plasterboard wall can work if it deviates from a straight line and I can't even be certain there's going to be 25mm of plaster by the doors. I guess I could strip the plaster off just in the vicinity of the doors to check though.

I'm rather nervous about stripping off the plaster myself anyway, as I'd be worried about damaging the cinderblock walls, which may be load-bearing, so I'll probably have to get someone in to do that. I guess I need to get a structural engineer to confirm that it's safe to add the weight of two layers of plasterboard to the walls, or in the case of the wall between my living room and bedroom four layers, as I'll have two on each side, and they can also advise whether it's safe to strip the plaster off (which will remove some weight before I add the plasterboard).

If I don't strip the plaster off, then I only have 35mm to play with near the hall door, so I couldn't even fit one layer of 12.5mm plasterboard on clips and hat channel (total 41mm). The best I could do would be to add two layers of 15mm plasterboard screwed directly to the wall (through the plaster into the cinderblock) which means the inner wall won't be decoupled at all. What would you suggest I do with the walls? Whether I use clips+hat channel or not, is it worth trying just one layer of plasterboard first to see if that's sufficient? Is replacing plaster with the same thickness of acoustic plasterboard likely to significantly improve things? I'm thinking I might need one layer of plywood and a top layer of plasterboard so that the wall can support stuff, certainly on the window wall where it will need to support the radiator and curtain rail but it would be useful to be able to hang stuff from the other walls as well.

Once I've done the walls, I was thinking of using IB-1 clips, hat channel and plasterboard on the ceiling as well. I guess being concrete slab it should be able to support the weight but that's another thing I'll need to get checked. Assuming it can support the weight, would this be sufficient to block noise travelling through the ceiling to/from above? It's probably mostly impact noise coming down through the ceiling, with airborne noise travelling via the walls but I can't be certain of that.

I plan to do the floor last, as once I've done the walls and ceiling I'll be able to see if any noise is travelling via the floor. I can only increase the hall floor height by 20mm without blocking the front door, so I can't really increase the living room or bedroom floor height by any more than this or I'll have wierd variations between the rooms. I was planning on laying 4.7mm (or maybe 6mm) cork tiles as they're cushioning and noise absorbing but my floorboards are too uneven to just lay 6mm ply/OSB to stick the tiles to. 12mm ply/OSB might be enough to smooth out the deviations in the subfloor but I'm not even sure about that, so I may have to consider sanding down the floor or replacing the 18mm floorboards with 18mm OSB. I suppose in theory I could remove the floorboards and joists and just build my subfloor on the concrete slab using felt or rubber mat as the first layer to reduce impact noise, which would eliminate the gap under the subfloor and avoid the "drum" effect but that's not really practical as there needs to be a space for the electric cables under the subfloor. What would you suggest I do with the floor, bearing in mind I can't really increase the height from the subfloor more than 20mm?

For the bedroom I was thinking of doing the same as the living room, stripping off the existing plaster to free up some space, then attaching clips and hat channel on the walls and ceiling with plasterboard on top, then seeing what treatment the floor might need. I could possibly build a decoupled stud wall off the party wall if that would be significantly better and possibly do that for the whole room but it might be a tight squeeze. On the right-hand wall next to the door there's only about 50mm clearance between the wall and the hinges, so even if I can strip 20mm of plaster off that wall I'd still have to move the whole door and frame to the left to be able to fit a stud wall there.

For the windows, in the living room I only need to be able to open the pane on the right (the windows have been replaced since that exterior photo was taken, so I'll take a new photo of them and upload it) but I want to be able to uncover the whole window every day to let light in, so I can't screw plywood over it. I was thinking maybe I could make some kind of hinged wooden shutter than would fold back, perhaps with insulation stuck to the back which would sit in the reveal when closed, or else I could fit a sliding polycarbonate secondary glazing system like this https://www.secondarydiyglazing.com/sec ... trackglaze They recommend a max. height of 1m for the poly glazing to prevent it bowing and the inside of my reveal is 1.12m but I could reduce this a bit by screwing a thick piece of wood to the sill, which I might need to do to level it out anyway as certainly the living room sill slopes up to the left.

For the balcony door I was thinking of making a hinged wooden door, as I don't need light through there and don't often use the balcony, so that could stay shut most of the time. I could permanently block up the small window with wood as well, although it would be better to use plastic secondary glazing to let some light in but I won't need to access the window to open it. I was thinking of covering the large glazed area between the living room and kitchen with ply and fitting plastic secondary glazing to the glazed panels in the kitchen and hall door.

I look forward to reading your advice. In the meantime, in case it's useful to anyone else these Nor810 automatic door seals are currently available on sale (I snapped up three of them for my living room->kitchen, living room->hall and bedroom->hall doors). I understand these tend to cost a lot more in the US, although shipping costs may make it uneconomical to import from outside the UK. https://firesealshop.com/collections/ac ... -drop-seal

Soundman2020 · Post by **Soundman2020** » Sun Apr 30, 2017 2:07 pm

Hi there "doveman", and Welcome!

Congratulations on a very complete first post. It covers most things, but there's still a few missing...

1) How much isolation do you need? That's the key to all of this. You should put a number to that, in terms of decibels.

2) Are you allowed to do any/all of what you are planning? If you own the flat, then I guess that's fine, but if you are only renting it, then making major modifications to it is likely not an option.

3) Do you need some kind of planning permission from the local authorities to do this? Or maybe from the building administrator? Home-owners association (or whatever the equivalent is in the USA)

4) What are the dimensions of your rooms? I see numbers on your sketches, but I can't make them out. You also don't seem to mention height....

Now for some general comments:

I'm on the first floor...

That's a problem. Isolating a studio in the ground floor is already hard, but isolating something on an upper floor is harder. Your options and your "achievable" are probably not very high.

I hear the neighbour in the flat next to my bedroom shouting and slamming doors (previously I had a neighbour who didn't shout but who had a very deep voice, which carried right through the wall),

I'm guessing that this is a fairly old building? Clearly there are flanking paths that are bringing those delightful sounds to you. They are not getting to you through the walls, as a concrete block wall should have enough mass in it to keep voices out. Perhaps not slamming doors, though, since that is structure-borne, not airborne.

not just in the party wall but in the other three walls of the bedroom and to a lesser extent in the living room.

Confirmed. Something is flanking.

there's a fair bit of impact noise (which may be coming directly through the ceiling or transmitting via the walls) and squeaking floorboards are very loud/intrusive.

Yup. Re-confirmed. The building itself is not your friend, acoustically.

I hear more airborne noise from below me, just normal daytime conversation level and sometimes loud TV

My guess would be that most of what you are hearing is coming through poorly done doors, windows, ventilation ducts, electrical system, poorly sealed floors, gaps, cracks, holes, etc.

the wall between my living room and bedroom appears to be cinderblock with about 25mm of plaster on top,

That plaster is in pretty bad state. It is cracked clean through, and appears to be weak and flaking. It might need taking off and re-doing, in the rooms where you need isolation.

I've lifted a couple of floorboards to confirm that there's a concrete slab under my joists,

Is there a good slab under there? If so, how thick is it? Can you find out how it was built, and what the load-bearing capacity is?

They don't appear to be joined to the wall, which I found surprising

Are they attached to the slab underneath? If they are not attached to the walls, then I assume the walls are resting directly on the slab?

My budget is quite limited, around £2000 tops

I have bad news for you. That's not going to ge far enough to do all that you want to do. I'd suggest you talk a walk around your local hardware stores, and price the materials you will be needing, in the quantities that you will be needing them... do some math, start adding up....

the soundproofing needs to stop neighbour noise getting in (which will also help me sleep) and voice frequency/amplitude noise leaking out.

Numbers! You need a number here: How many decibels of isolation? For what frequency range?

I don't really have the room for a 10mm gap, 50mm stud frame, clips and hat channel and two layers of 15mm acoustic plasterboard....

You don't need it....

If you have a decoupled frame, then why would you also need isolation clips? When you swim in the ocean, do you also take a hosepipe down to the ocean floor with you, so you can get even wetter?

then screwing IB-1 isoclips and hat channel, which totals about 28.5mm, to the cinderblock,

... which would make your isolation in low frequencies even worse than it is now, because the MSM resonance of such a system would be very high, thus implying that it would actively amplify low frequency sounds, rather than attenuating them....

Take a look here:

resilient-channel-reduces-isolation--01.jpg

That comes from the excellent research paper on the subject, put out by the Canadian NRC. The document number is IR-586. You might be able to search for it on-line. Well worth looking at!

That shows how the isolation changes when adding drywall to a concrete block wall, using resilient channel. The light grey line is how well the wall isolates all by itself, the line with open circels shows how that changes if you screw resilient channel to it, and add drywall, but without putting insulation in the cavity. The line with solid black circles is the same, but with insulation in the cavity. And you think: "Wonderful! My isolation went up from STC-50 to STC-54! Well, yes and no. Yes it went up, but no it did not. Look at the left hand end of that graph, below about 200 Hz. In both cases, the isolation is far worse than for the bare wall by itself! So why did hte STC go up? Well, that would be because STC is a lousy system for measuring full-spectrum isolation. It was never designed for that. When calculating STC, the procedure does not even consider the bottom two and a half octaves of the musical spectrum, nor does it consider the top two and a half octaves. And since all of that reduced isolation lies in the area that it does not consider, the numbers went up, when in reality they should have gone down. In other words: STC lies. Don't use it to figure isolation. And don't use resilient mounts over thin air gaps: it will trash your low-frequency isolation.

I currently have 35mm clearance by the hall door, so with an extra 25mm I'd have 60mm and at the balcony door I currently have 50mm, so with the extra 20mm I'd be fine there as well.

You seem to be missing out on a key point about isolation: It is "all or nothing". Meaning that you have to do the same to the entire room: walls, ceiling, doors, windows... everything. You are trying to create a two-leaf wall system, whcih is good and the correct basic approach, so you MUST do the same for the doors, and the windows. In other words, you will need a second door for your new "inner-leaf" wall, just a short distance away from the existing door in the outer-leaf. The same applies to your windows: for every location where there is a window in your exiting outer-leaf, you will need to install a new window in the inner-leaf.

That's the way it works.

In order to isolate well at low cost, you need to create two independent "leaves" for your wall. A "box inside a box", sometimes called "room in a room". You already have the outer-room. Now what you need to do is to construct another complete "room" inside that, just a bit smaller than the existing one, but not touching it. There can be no mechanical connection between the existing outer leaf and the new inner leaf. Not even a single nail. The two leaves must create two compete "shells", or "envelopes" that are not connected in any way.

So it does not matter how much clearance you have around the existing door frame. That is irrelevant to your inner-leaf, which will have it's own door in it, exactly opposite the existing door, but opening the other way. Both doors will open away from the cavity between them. You could even have two different sized dors, or two different types of doors if you wanted, because they are entirely independent of each other. As long as each door is fully sealed into its own leaf, and has enough mass to create good surface density continuity around the entire leaf, then you are fine.

I can't be certain that I'm going to release an extra 25mm everywhere by stripping off the plaster and whilst it only really matters near the doors,

Not true. If you did that, it would not matter at all if there were variations in plaster thickness. You would merely compensate for that when you build the new inner-leaf, by locating it at a great enough distance such that the minimum gap is still large enough to get the MSM resonant frequency that you need, and the isolation that you need.

I guess I need to get a structural engineer to confirm that it's safe to add the weight of two layers of plasterboard to the walls,

You will need a structural engineer, yes, but not to look at your walls: You'll need him to look at your floor loading. Your new walls will not be attached to your existing walls: they cannot be! If you did, they would not isolate. Rather, your new inner-leaf walls will rest on your existing concrete slab floor, so your engineer will have to check that you are able to place many hundreds of kilograms of extra weight on thin linear loading around the edge of the existing rooms.

What would you suggest I do with the walls?

Build a simple stud frame all around your room, on your slab, leaving a gap of maybe 10mm between the new sole plate and the existing block wall, then put two layers of 15mm fire-rated drywall (plasterboard) on only ONE side of that frame, making sure that you fill the cavity completely with fiberglass insulation that has a density of roughly 30 kg/m3. Then build your new inner-leaf ceiling in the same way across the top of the new inner-leaf walls, making sure that the new ceiling does not touch the old walls or ceiling at all. Now install your new doors and windows in that new inner-leaf, seal it all up, and you are done.

I'm thinking I might need one layer of plywood and a top layer of plasterboard

Yes, but I would suggest using OSB instead of plywood. It is cheaper, denser, and therefore more effective acoustically, and better value for money.

so that the wall can support stuff,

The wall will support itself just fine without any plywood (or OSB). The plywood/OSB provides sheer strength, yes, but it does not support the wall.

once I've done the walls and ceiling I'll be able to see if any noise is travelling via the floor.

There will be. You don't' need to wait to test that. It's just a concrete slab on an upper floor, so it will be doing a fantastic job of transmitting sound to/from the room below. You do not have the budget to do a properly floated floor, so your only other option is to do an "isolated deck" approach, much like drum risers are built.

I can only increase the hall floor height by 20mm without blocking the front door,

Irrelevant. That door will not open into the room: the new inner-leaf door will open into the room, and it can be be placed on the new floor, even if it ends up higher than the external floor. That probably is not an issue, though: It should be possible to get the new floor at the same level as the old one was, if you design carefully.

12mm ply/OSB might be enough to smooth out the deviations in the subfloor but I'm not even sure about that,

I'm not sure why you are concerned about the existing sub-floor: that's the very first thing you will remove and throw away! It won't even be there at the time you start building, so it is not even an issue.

I could remove the floorboards and joists and just build my subfloor on the concrete slab

Bingo!

using felt or rubber mat as the first layer

Nope! Bad idea... you can't float a floor like that. Waste of time, money, effort, and with saddening results.

For the windows, in the living room I only need to be able to open the pane on the right

Sorry, but you won't be able to open any windows at all! Operable windows in a studio are a big no-no. Plus, you won't even be able to get to that window any more, since it will be located on the other side of your new inner-leaf window, which will certainly not be operable: it will be fixed and sealed firmly in place.

in case it's useful to anyone else these Nor810 automatic door seals are currently available on sale

That's an excellent price! You might want to buy several of those to put on your doors, when you eventually get to the point of making them. Thanks for the tip!

- Stuart -

doveman · Post by **doveman** » Mon May 01, 2017 11:37 am

Soundman2020 wrote:Hi there "doveman", and Welcome!

Congratulations on a very complete first post. It covers most things, but there's still a few missing...

1) How much isolation do you need? That's the key to all of this. You should put a number to that, in terms of decibels.

2) Are you allowed to do any/all of what you are planning? If you own the flat, then I guess that's fine, but if you are only renting it, then making major modifications to it is likely not an option.

3) Do you need some kind of planning permission from the local authorities to do this? Or maybe from the building administrator? Home-owners association (or whatever the equivalent is in the USA)

4) What are the dimensions of your rooms? I see numbers on your sketches, but I can't make them out. You also don't seem to mention height....

Hi Stuart, thanks for the welcome and the very prompt and comprehensive reply!

I tried to replace the photos with internal links but I ran into the 12 file limit, so I've had to leave them for now. I've also had to use external links for the pictures attached to this post as I needed to maintain the resolution/size to keep the details visible, so I hope that's OK.

1) It's probably quite hard to put a number to it. Having considered your reply, I think the living room is going to be impractical to soundproof adequately. In the bedroom which I want to use as a vocal room there won't be any amplfication so it's just a matter of keeping vocals in and neighbour noise out. The impact noise from the adjacent neighbour banging doors or the one above me walking across their wooden floor occurs less often and is generally less of a problem than the airborne noise which will probably be hard to measure as it's probably not loud in db terms but is nonetheless intrusive as it radiates from all four walls. I guess I need something that will show the db levels and frequency of the noise but I'm not sure what I could use for that. Are there any USB microphones that can be used with software on a PC for this purpose, that are reasonably affordable? Although PC soundcards/on-board soundchips are quite good quality now, the mic inputs still tend to be quite noisy, so a USB mic with a built in ADC would probably be the best way to measure this sort of thing.

2) I'm renting (if I owned I'd sell and buy somewhere easier to modify!) but I've got a secure lifetime tenacy and the landlord has said he's OK with me making modifications (within reason), as long as I run them by him first and I've had them OK'd by an engineer.

3) I don't think I need any other permissions, as long as I'm not modifying the party wall, in which case the Party Wall Act might apply but I wouldn't have thought that would apply if I'm just stripping the plaster off of my side. https://www.gov.uk/guidance/party-wall- ... 6-guidance

I'm guessing that this is a fairly old building? Clearly there are flanking paths that are bringing those delightful sounds to you. They are not getting to you through the walls, as a concrete block wall should have enough mass in it to keep voices out. Perhaps not slamming doors, though, since that is structure-borne, not airborne.

My guess would be that most of what you are hearing is coming through poorly done doors, windows, ventilation ducts, electrical system, poorly sealed floors, gaps, cracks, holes, etc.

I believe it was built in the late 1970's. When I hear airborne noise in the bedroom it can clearly be heard in all four walls by putting my ear against them (likewise with the noise I hear in the living room), so it's definitely emanating from the walls (although it may also be emanating from the ceiling and floor of course). As the flats are separated by concrete vertically and horizontally, it seems that somehow the noise is getting through the concrete.

Sorry about the unreadable floor plans. Here's some higher resolution copies.

Living Room with windows and doors (1200).png

High-res external link: https://ibb.co/j9ONvk

Bedroom with Pipes (1200).png

High-res external link https://ibb.co/kZSbMQ

The living room is approx. 4.4m x 3m x 2.3m (LxWxH) and the bedroom is 4.6m x 2.6m x 2.3m.

I tried to draw a sketch showing the possible flanking paths that I suspect but I found that a bit beyond me! I've drawn a sketch showing the flats relative to mine in more detail though. I haven't drawn the other half of neighbours 2, 3 and 5's flats to the right, or the third floor with neighbours 4 and 5's bedrooms. Although I don't know the exact thickness of them yet, I've drawn 6"/150mm concrete slabs above/below each flat and for the walls (grey, with the party wall in orange), with 35mm joists and floorboard on top (brown and black) and 25mm plaster on the walls and ceiling (yellow).

Flanking paths (1200).png

High-res external link: https://ibb.co/bWwpQk

The noise from neighbour 3 could be a) travelling directly through the party wall between his bedroom and mine, or b) going down through his floor into the concrete slab, travelling under the party wall and then up from the slab into my walls (either the plaster or the concrete, although the plaster isn't directly connected to the slab, only via the joists and floorboards), or c) going up through his ceiling into the concrete slab, travelling above the party wall and then down from the slab into my walls (either the plaster or the concrete, the plaster on the walls is directly connected to my ceiling).

The noise from neighbour 1 could be travelling a) directly up through his ceiling, the concrete slab and my floor, or b) into his walls and then up into the concrete slab and from there into my walls (either the concrete or the plaster), or c) down through his floor into the concrete slab, then into his walls and from there up into my room as per b.

Similar noise paths could be carrying the noise from neighbours 4 and 5. As shouting from neighbour 5 can be heard in my living room, I suspect it's travelling down from their flat into the concrete slab which runs above my bedroom and living room and then down into the walls.

Is there a good slab under there? If so, how thick is it? Can you find out how it was built, and what the load-bearing capacity is?

Unfortunately the local authority don't have any building records for these flats but hopefully an engineer will be able to answer these questions.

Are they attached to the slab underneath? If they are not attached to the walls, then I assume the walls are resting directly on the slab?

It's possible the joists are attached to the slab at some point under the floorboards where I can't see at the moment. Yes, the walls appear to be built directly on top of the slab.

]I have bad news for you. That's not going to ge far enough to do all that you want to do. I'd suggest you talk a walk around your local hardware stores, and price the materials you will be needing, in the quantities that you will be needing them... do some math, start adding up....

I feared as much but hopefully by concentrating on the bedroom I can do something useful. I worked out that there's about 44.2m2 to cover in the bedroom (walls and ceiling) although I'm overestimating as I based this on two 4.6m*2.3m long walls, two 2.41m*2.3m end walls and the 4.6m*2.6m ceiling. So using 2.4m*1.2m acoustic plasterboard panels like this I'd need 15.35 of them to cover the room https://www.roofingsuperstore.co.uk/pro ... GwodO34IlQ
and at £9.35 per board and using two layers this works out around £293.

The living room is roughly 47.24m2 and would cost about £312.90.

That's for 12.5mm board but 15mm board is about the same price or even cheaper http://www.wickes.co.uk/Knauf-Plasterbo ... m/p/138950?

I know you haven't recommended them but just for costs sake, if I were to use IB-1 clips on the walls and ceiling in both rooms, spaced at 16" on the horizontal and 24" on the vertical, as shown here http://www.soundproofingcompany.com/ins ... -overview/ then I'd need around 265 of them. I believe they cost about $1.50 each which would come to just under $400 but I can't seem to find anyone selling them over here and I don't know how much it would cost to import them. IB-2 clips are probably better with their rubber isolators but they obviously cost more. All that seems to be available over here are Genie clips http://www.soundstop.co.uk/ZGENIECLIP.php which cost over £3. IB-1 and hat channel is about 28.5mm deep, IB-2 and channel is 47.6mm and Genie clips and channel is about 44mm I think, so I'd lose more space using the more expensive clips as well.

Numbers! You need a number here: How many decibels of isolation? For what frequency range?

In terms of airborne noise, it's mostly going to be vocal range I need to block in both directions so around 80hz-10khz (but probably not much above 6khz). There are water pumps which come on whenever someone turns on a tap though, so I'll need to find a way to measure their frequency/amplitude.

You don't need it.... If you have a decoupled frame, then why would you also need isolation clips? When you swim in the ocean, do you also take a hosepipe down to the ocean floor with you, so you can get even wetter?

Lol

Whilst the stud frame will be decoupled from the wall, if it's attached to the ceiling and floor I'd think any noise travelling via the concrete slabs above and below my flat will then travel down the stud frame and into the plasterboard unless I use clips and hat channel to isolate the plasterboard from the frame.

which would make your isolation in low frequencies even worse than it is now, because the MSM resonance of such a system would be very high, thus implying that it would actively amplify low frequency sounds, rather than attenuating them....

Take a look here:

resilient-channel-reduces-isolation--01.jpg
That comes from the excellent research paper on the subject, put out by the Canadian NRC. The document number is IR-586. You might be able to search for it on-line. Well worth looking at!

That shows how the isolation changes when adding drywall to a concrete block wall, using resilient channel. The light grey line is how well the wall isolates all by itself, the line with open circels shows how that changes if you screw resilient channel to it, and add drywall, but without putting insulation in the cavity. The line with solid black circles is the same, but with insulation in the cavity. And you think: "Wonderful! My isolation went up from STC-50 to STC-54! Well, yes and no. Yes it went up, but no it did not. Look at the left hand end of that graph, below about 200 Hz. In both cases, the isolation is far worse than for the bare wall by itself! So why did hte STC go up? Well, that would be because STC is a lousy system for measuring full-spectrum isolation. It was never designed for that. When calculating STC, the procedure does not even consider the bottom two and a half octaves of the musical spectrum, nor does it consider the top two and a half octaves. And since all of that reduced isolation lies in the area that it does not consider, the numbers went up, when in reality they should have gone down. In other words: STC lies. Don't use it to figure isolation. And don't use resilient mounts over thin air gaps: it will trash your low-frequency isolation.

I've been reading about the "triple-leaf effect" here http://www.soundproofingcompany.com/sou ... af-effect/ which I think shows much the same thing, i.e with a small airgap the resonant frequency is relatively high, around 80hz and with a larger airgap it drops to around 50hz, where it's less of an issue. Their examples are a bit confusing though, as with Assembly 2 where drywall is attached directly to the concrete, creating a very small airgap, the low frequency response is better than with Assembly 3 where furring channel is used to create a larger airgap. With Assembly 4, with furring strip and drywall on both sides of the wall they say it has a larger airgap but it seems to me that there's separate airgaps either side of the wall, thus creating a triple-leaf and low frequency isolation is much worse. With Assembly 5 they've gone back to treating only one side like in Assembly 3 but added insulation in the gap, which acts to make the gap act is if it's bigger than it actually is, but still the low frequency isolation is worse with just the bare concrete wall.

So it certainly does seem like a bad idea from a low frequency POV to do anything that creates a small airgap. The wall that divides my living room and bedroom is problematic as ideally I need to treat both sides but that means creating a gap on both sides and thus creating a triple-leaf. I guess with the party wall, although I'll only be treating my side, in the (unlikely) event that the neighbour decided to treat his similarly, that would then create a triple-leaf as well.

You seem to be missing out on a key point about isolation: It is "all or nothing". Meaning that you have to do the same to the entire room: walls, ceiling, doors, windows... everything. You are trying to create a two-leaf wall system, whcih is good and the correct basic approach, so you MUST do the same for the doors, and the windows. In other words, you will need a second door for your new "inner-leaf" wall, just a short distance away from the existing door in the outer-leaf. The same applies to your windows: for every location where there is a window in your exiting outer-leaf, you will need to install a new window in the inner-leaf.

That's the way it works.

In order to isolate well at low cost, you need to create two independent "leaves" for your wall. A "box inside a box", sometimes called "room in a room". You already have the outer-room. Now what you need to do is to construct another complete "room" inside that, just a bit smaller than the existing one, but not touching it. There can be no mechanical connection between the existing outer leaf and the new inner leaf. Not even a single nail. The two leaves must create two compete "shells", or "envelopes" that are not connected in any way.

So it does not matter how much clearance you have around the existing door frame. That is irrelevant to your inner-leaf, which will have it's own door in it, exactly opposite the existing door, but opening the other way. Both doors will open away from the cavity between them. You could even have two different sized dors, or two different types of doors if you wanted, because they are entirely independent of each other. As long as each door is fully sealed into its own leaf, and has enough mass to create good surface density continuity around the entire leaf, then you are fine.

I guess I was thinking that as the noise is very bad in the walls and not in the doors or windows (as far as I've noticed anyway), then treating the walls and ceiling and floor would be enough. I think I'll have to concentrate on making the bedroom good enough for recording vocals then and just keep the volume low in the living room when monitoring, composing, etc.. I don't really need to turn it loud most of the time anyway as I'll be using nearfield monitors and I'll have to go elsewhere to properly mix and master tracks anyway.

In the bedroom I think I could manage to fit a double door, although it may be overkill just for recording vocals. In this sketch, I've added a 100mm inner wall (black), which seems about right for a 10mm airgap, 50mm stud frame and two layers of 15mm plasterboard+10mm plaster skim, and shown the outer door (red) and the inner door (green). Currently the door opens inwards, so I'll have to rehang that to open the other way and because of the depth of the inner wall on the right, the inner door won't be directly in line with the outer door (unless I alter the outer wall to shift the outer door to the left as well) which might cause problems getting furniture through the doors.

Bedroom with double-door (1200).png

High-res external link: https://ibb.co/iVMaWQ

Maybe another option would be to do it like this, with the outer door (light blue) in the hall and the inner/bedroom door (green) fixed to the inner walls and not touching the outer walls. This would still leave part of the outer wall on the left of the opening sitting in front of the new bedroom door but it might be easier to carry stuff through with only one door there instead of two close together. Otherwise I would have to cut away a bit of the wall on the left. I'd obviously have to soundproof the area between the hallway door and the living room and bedroom doors but it's quite a small area to treat (1.25m*1.06m)

Bedroom with double-door 2 (1200).png

High-res external link: https://ibb.co/fwJay5

If you did that, it would not matter at all if there were variations in plaster thickness. You would merely compensate for that when you build the new inner-leaf, by locating it at a great enough distance such that the minimum gap is still large enough to get the MSM resonant frequency that you need, and the isolation that you need.

Sure but it may affect the practicality of doing it, as the stud frame will have to be spaced 10mm from the most forward part of the cinderblock, which could just be a small area at one point leaving the frame perhaps 25mm from the majority of the wall, which could end up making the room too small.

You will need a structural engineer, yes, but not to look at your walls: You'll need him to look at your floor loading. Your new walls will not be attached to your existing walls: they cannot be! If you did, they would not isolate. Rather, your new inner-leaf walls will rest on your existing concrete slab floor, so your engineer will have to check that you are able to place many hundreds of kilograms of extra weight on thin linear loading around the edge of the existing rooms.

OK but I don't think having the inner walls secured to the concrete slabs top and bottom will isolate them either if noise is travelling via the slabs. I think some people secure the stud frame footer to the joists or even the new subfloor to help isolate it from the structure under the subfloor but obviously whatever it is attached to needs to be very steady to keep the frame secure, so whether I could do this will depend on how my new floor is constructed.

Build a simple stud frame all around your room, on your slab, leaving a gap of maybe 10mm between the new sole plate and the existing block wall, then put two layers of 15mm fire-rated drywall (plasterboard) on only ONE side of that frame, making sure that you fill the cavity completely with fiberglass insulation that has a density of roughly 30 kg/m3. Then build your new inner-leaf ceiling in the same way across the top of the new inner-leaf walls, making sure that the new ceiling does not touch the old walls or ceiling at all. Now install your new doors and windows in that new inner-leaf, seal it all up, and you are done.

Presumably I'll need a header plate secured to the ceiling as well as a footer plate secured to the concrete slab under the floor to support my stud frame?

Yes, but I would suggest using OSB instead of plywood. It is cheaper, denser, and therefore more effective acoustically, and better value for money.

Ah yes, good point. I was looking at OSB for the sub-floor as it's cheaper and it makes sense to use it for the first wall layer as well, where it won't be visible.

You do not have the budget to do a properly floated floor, so your only other option is to do an "isolated deck" approach, much like drum risers are built.

How would I make this? Even if I can't fully treat the living room, I'll probably need to replace the wonky floorboards anyway so I might as well look at isolating it whilst I'm at it.

Sorry, but you won't be able to open any windows at all! Operable windows in a studio are a big no-no. Plus, you won't even be able to get to that window any more, since it will be located on the other side of your new inner-leaf window, which will certainly not be operable: it will be fixed and sealed firmly in place.

That's another reason I can't do the living room then, as I will need to be able to open the main window and the balcony door. I'll need to open the bedroom window as well but as I'll only be recording vocals in there I won't need the same level of soundproofing as I would in a room with amplified and bassy music. I've been to houses which are right next to busy roads where their secondary glazing blocks the noise out almost completely, so I'm hoping I can get sufficient isolation for my purposes using that. I may be able to fit this secondary glazing frame http://www.diysecondaryglazingkit.co.uk ... er-kit.htm into my inner leaf stud wall but if that won't be strong enough to support it, if I strip the existing plaster off the reveal back to the concrete then I can either replace the plaster with acoustic plasterboard, or plasterboard on clips/channel to help isolate it from the concrete and then fit the secondary glazing frame within the reveal, which will partly be supported by the concrete wall underneath.

- Derek

Soundman2020 · Post by **Soundman2020** » Mon May 01, 2017 3:38 pm

I tried to replace the photos with internal links but I ran into the 12 file limit, so I've had to leave them for now.

Do as many as you can, then do the rest later.

Off-site photo links are a problem. Right now, yours go to a server at ibb.co, but what happens of that place goes out of business, gets bought, changes their domain name, or a dozen other things that would kill your photos.

Here's what would happen:

http://www.johnlsayers.com/phpBB2/viewt ... 11&t=13069

For people who want to learn from your thread in the future, it would be just as useless as that thread is now. Zero use. That defeats the entire purpose of the forum: to be a resource for others in the future.

I guess I need something that will show the db levels and frequency of the noise but I'm not sure what I could use for that.

You'll need a hand-held sound level meter. Something of decent quality that has both "A" and "C" weighting, as well as both "fast" and "slow" response, will cost around US$ 100.

Are there any USB microphones that can be used with software on a PC for this purpose,

Maybe, but I would certainly not go that route. How would you calibrate that?

Although PC soundcards/on-board soundchips are quite good quality now, the mic inputs still tend to be quite noisy, so a USB mic with a built in ADC would probably be the best way to measure this sort of thing.

Not unless you have some way of calibrating it accurately! Your best bet is a simple sound level meter. Get an Extech or a Galaxy, not some useless cheap Chinese junk toy.

When I hear airborne noise in the bedroom it can clearly be heard in all four walls by putting my ear against them

That does not mean that the sound is coming through the walls: it just means that the sound is IN the walls. It might have got there by any number of paths.

The noise from neighbour 3 could be a) travelling directly through the party wall between his bedroom and mine, or b) going down through his floor into the concrete slab, travelling under the party wall and then up from the slab into my walls (either the plaster or the concrete, although the plaster isn't directly connected to the slab, only via the joists and floorboards), or c) going up through his ceiling into the concrete slab, travelling above the party wall and then down from the slab into my walls (either the plaster or the concrete, the plaster on the walls is directly connected to my ceiling).

The noise from neighbour 1 could be travelling a) directly up through his ceiling, the concrete slab and my floor, or b) into his walls and then up into the concrete slab and from there into my walls (either the concrete or the plaster), or c) down through his floor into the concrete slab, then into his walls and from there up into my room as per b.

Similar noise paths could be carrying the noise from neighbours 4 and 5. As shouting from neighbour 5 can be heard in my living room, I suspect it's travelling down from their flat into the concrete slab which runs above my bedroom and living room and then down into the walls.

You are overthinking this, and not usefully. There's no point in trying to identify all of the possible paths that sound could take to get into your walls, since there is not a single thing you can do about that! The problem is not where the sound came from: the problem is that the sound is in your walls, period. How it got there does not matter. Since it is impossible to do anything about all of those paths, there's no point wasting time on them. The point is to create an isolation system to deal with the problem.

I worked out that there's about 44.2m2 ...

You forget about the studs. They don't give them away for free! And the nails. And the caulk. And the OSB, and the tools. And the insulation. And the mud/tape. And the paint. And the acoustic treatment that you will need inside the room once it is isolated. And the HVAC system that you will need to keep you alive. And the widows. And the doors. And the seals. And the electrical system....

But don't feel bad about that: most first time studio builders neglect to consider all of those things, just like you have. It's normal. The problem is, sound does not actually behave the way most people think it behaves. Acoustics is not very intuitive, sound does strange, unexpected things, and most people aren't aware of that until they start studying it.

All that seems to be available over here are Genie clip

Those are the good ones. That's why they cost more! As the saying goes: You get what you pay for." If you buy cheap clips, you will get cheap results. If you buy god quality clips, you will get good quality results.

Whilst the stud frame will be decoupled from the wall, if it's attached to the ceiling and floor I'd think ... ....

It will not be attached to the ceiling! As I said in my previous post, the inner room is a "box" that sites inside the outer room, just a a matchbox might sit inside a shoe-box. It sits on the floor, and that's it. There CANNOT be any physical contact between the inner-leaf and the outer-leaf, except for where the walls meet the floor. That's it. Nothing else.

I'd think any noise travelling via the concrete slabs above and below my flat will then travel down the stud frame and into the plasterboard unless I use clips and hat channel to isolate the plasterboard from the frame.

And your thinking would be wrong.

Firstly, the only point of contact is into the floor: there's no connection to the outer-leaf ceiling. Assuming you don't need very high isolation, that provides enough decoupling. The inner-leaf frame is free-standing. It consists of four walls and a ceiling, plus doors, windows, etc., but the ONLY point of contact is the floor.

Their examples are a bit confusing though...,

Right. The information in that page is not well presented, in a logical, progressive manner. Plus, across all of it they talk about isolation in terms of STC, which is a totally useless measurement for studio isolation, as I already mentioned. STC is no use at all for telling you how well your studio will be isolated. STC was never meant to measure such things. Here's an excerpt from the actual ASTM test procedure (E413) that explains the use of STC.

“These single-number ratings correlate in a general way with subjective impressions of sound transmission for speech, radio, television and similar sources of noise in offices and buildings. This classification method is not appropriate for sound sources with spectra significantly different from those sources listed above. Such sources include machinery, industrial processes, bowling alleys, power transformers, musical instruments, many music systems and transportation noises such as motor vehicles, aircraft and trains. For these sources, accurate assessment of sound transmission requires a detailed analysis in frequency bands.”

It's a common misconception that you can use STC ratings to decide if a particular wall, window, door, or building material will be of any use in a studio. As you can see above, in the statement from the people who designed the STC rating system and the method for calculating it, STC is simply not applicable.

Here's how it works:

To determine the STC rating for a wall, door, window, or whatever, you start by measuring the actual transmission loss at 16 specific frequencies between 125 Hz and 4kHz. You do not measure anything above or below that range, and you do not measure anything in between those 16 points. Just those 16, and nothing else. Then you plot those 16 points on a graph, and do some fudging and nudging with the numbers and the curve, until it fits in below one of the standard STC curves. Then you read off the number of that specific curve, and that number is your STC rating. There is no relationship to real-world decibels: it is just the index number of the reference curve that is closest to your curve.

When you measure the isolation of a studio wall, you want to be sure that it is isolating ALL frequencies, across the entire spectrum from 20 Hz up to 20,000 Hz, not just 16 specific points that somebody chose 50 years ago, because he thought they were a good representation of human speech. STC does not take into account the bottom two and a half octaves of the musical spectrum (nothing below 125Hz), nor does it take into account the top two and a quarter octaves (nothing above 4k). Of the ten octaves that our hearing range covers, STC ignores five of them (or nearly five). So STC tells you nothing useful about how well a wall, door or window will work in a studio. The ONLY way to determine that, is by look at the Transmission Loss curve for it, or by estimating with a sound level meter set to "C" weighting (or even "Z"), and slow response, then measuring the levels on each side. That will give you a true indication of the number of decibels that the wall/door/window is blocking, across the full audible range.

Consider this: It is quite possible to have a door rated at STC-30 that does not provide even 20 decibels of actual isolation, and I can build you a wall rated at STC-20 that provides much better than 30 dB of isolation. There simply is no relationship between STC rating and the ability of a barrier to stop full-spectrum sound, such as music. STC was never designed for that, and cannot be used for that.

Then there's the issue of installation. You can buy a door that really does provide 40 dB of isolation, but unless you install it correctly, it will not provide that level! If you install it in a wall that provides only 20 dB, then the total isolation of that wall+door is 20 dB: isolation is only as good as the worst part. Even if you put a door rated at 90 dB in that wall, it would STILL only give you 20 dB. The total is only as good as the weakest part of the system.

So forget STC as a useful indicator, and just use the actual TL graphs to judge if a wall, door, window, floor, roof, or whatever will meet your needs.

Sorry for the rant, but that's one of the many misleading things about acoustics, that confuse people, and point them in the wrong direction.

it certainly does seem like a bad idea from a low frequency POV to do anything that creates a small airgap.

Correct. Here's why:

Your wall will have a resonant frequency, because it is a "Mass-spring-mass" system. You have mass on your outer leaf (the concrete blocks) and mass on your inner-leaf (the OSB-plus-drywall), and a spring in between: the air in the cavity is the spring. So it is a resonant system: it want's to vibrate at a certain frequency, and does NOT want to vibrate at other frequencies. At that frequency, the wall will not just pass sound through, but can potentially amplify the sound. At all higher frequencies, the wall will isolate. So clearly, you want to get that frequency as low as possible. Well below the lowest frequency that you need to isolate.

That frequency is given by this equation:

MSM resonant frequency equation:

Fc=c[(m1+m2)/(m1 * m2 * d)]^.5

where:

Fc=resonance frequency (Hz)
c=constant (60 in this case)
m1=mass of first leaf (kg/m^2)
m2 mass of second leaf (kg/m^2)
d=distance between the leaves (m)

As you can see, for a small value of "d", the frequency will be high. Not good. In order to get the frequency low, you need a big gap. It's that simple.

The same applies to the two "masses". If one of those is low, then the frequency is high. So you need enough mass on each leaf, and a big enough air gap, to get the frequency down low enough. It's that simple.

Do the math for your self. Plug in some small numbers for "d", such as 10mm, or 25mm, or 35mm, and see what happens. Then plug in a much more reasonable value, such as 150mm, and see what happens.

It's that simple. The math does not lie. The equation is valid, and working through makes it a lot simpler to understand than looking at a bunch of pretty diagrams with nicely colored arrows on them.

The wall that divides my living room and bedroom is problematic as ideally I need to treat both sides but that means creating a gap on both sides and thus creating a triple-leaf.

Right. Sometimes there are no other options, and you have to do a three-leaf wall, in which case you just compensate for the lost isolation, by having larger air gaps on both sides, and higher mass.

I guess with the party wall, although I'll only be treating my side, in the (unlikely) event that the neighbour decided to treat his similarly, that would then create a triple-leaf as well.

Yep! It's not as unlikely as you think, actually. It does happen.

which seems about right for a 10mm airgap, 50mm stud frame

Careful! Don't confuse your terms! The "air gap" is the distance across the cavity from the face of the outer-leaf to the face of the inner-leaf. If you have a 10mm gap between the existing wall and the framing, and then you use 50mm studs, your air gap is 60mm... But 50mm studs are not going to cut it here: you will normal 3x4 studs, which commonly measure 38mm x 89mm. So your air gap will be 99mm, which is about right. You don't want to go less than that, for the same reason you see in the equation. If "d" is too small, then the frequency is too high. The minimum realistic air gap is about 100mm.

Sure but it may affect the practicality of doing it, as the stud frame will have to be spaced 10mm from the most forward part of the cinderblock, which could just be a small area at one point leaving the frame perhaps 25mm from the majority of the wall, which could end up making the room too small.

Then splay the wall! Angle it! There's no law that forces you to have walls that meet at 90° angles in the corners. You can build your wall at at small angle, such that it always remains the optimum distance from the existing wall.

OK but I don't think having the inner walls secured to the concrete slabs top and bottom will isolate them either if noise is travelling via the slabs.

It will...

And worst case, you can use proper isolation system for your walls, if you are really worried about that:

Isosil-anchor-bolt-decoupling-isolation-collar-and-pad.jpg

I think some people secure the stud frame footer to the joists or even the new subfloor

If they do, they they should be prosecuted for unsafe building practices! That's not only unsafe, it is also probably illegal. And if it isn't, then it should be...

Presumably I'll need a header plate secured to the ceiling

Nope! Because the inner-leaf wall is NOT attached to the outer-leaf ceiling. It cannot be. There can be no mechanical connection there. Not even a single nail. You will have a top plate, yes, but it will just be on top of the studs, and will not touch the outer-leaf at all. It will only support your inner-leaf ceiling. Actually, it will be a double-top plate, since the wall is load-bearing: it supports the ceiling.

as well as a footer plate secured to the concrete slab under the floor to support my stud frame?

Correct. All wall framing ALWAYS has a sole plate that the studs rest on, and a top plate (or more usually, a double top plate) at the other end of the studs. The sole plate must always be firmly attached to the slab, but the top plate must NOT be attached to anything.

How would I make this? Even if I can't fully treat the living room, I'll probably need to replace the wonky floorboards anyway so I might as well look at isolating it whilst I'm at it.

It's very simple: You put down a 2" layer of semi-rigid fiberglass insulation, such as OC-703 directly on the slab, then you put down two (or more) layers of of thick OSB on top of that (at least 19mm each layer), screwed together, but NOT touching your inner leaf walls. Leave a gap of a few mm all the way around, then fill that gap with flexible, non-hardening caulk. Then lay thick laminate flooring on top of that, using a suitable underlay. It is not a true floated floor (not even close), but it works wonders for reducing impact noise. It's the same principle as a drum riser.

I've been to houses which are right next to busy roads where their secondary glazing blocks the noise out almost completely,

... "almost" being the operative word! Try setting up your vocal mic in such a room, and record at the level you normally would, but with nobody speaking or singing. Now take a look at the spectrum if what you recorded... See the problem?

Compare that to my signature block, at the bottom of every single post I write here on the forum...

- Stuart -

doveman · Post by **doveman** » Mon May 01, 2017 11:21 pm

Picture 13:

Balcony Door corner 2 (750).jpg

Picture 14:

Living Room-Hall door (750).png

Picture 15:

Pipes rounds wall (750).jpg

Soundman2020 · Post by **Soundman2020** » Tue May 02, 2017 12:20 am

doveman · Post by **doveman** » Tue May 02, 2017 12:56 am

Soundman2020 wrote:Do as many as you can, then do the rest later.

Off-site photo links are a problem. Right now, yours go to a server at ibb.co, but what happens of that place goes out of business, gets bought, changes their domain name, or a dozen other things that would kill your photos.

Here's what would happen:

http://www.johnlsayers.com/phpBB2/viewt ... 11&t=13069

For people who want to learn from your thread in the future, it would be just as useless as that thread is now. Zero use. That defeats the entire purpose of the forum: to be a resource for others in the future.

OK, I've replaced the pictures in the first post, but because of the 12 attachment limit I had to relocate 3 of them to post 5. I'm not sure why but when I add the internal links it adds empty space to the right of each picture. I've added internal links for the pictures in post 3 but I've kept the higher-res external links as well, as the detail may not be readable on the internal copies.

You'll need a hand-held sound level meter. Something of decent quality that has both "A" and "C" weighting, as well as both "fast" and "slow" response, will cost around US$ 100.

That's fine for checking levels but it won't show me the frequency of the noise will it?

Maybe, but I would certainly not go that route. How would you calibrate that?

Hmm, good point!

That does not mean that the sound is coming through the walls: it just means that the sound is IN the walls. It might have got there by any number of paths.

I was just clarifying that the noise is definitely coming out of the walls and this may be the main path by which it's reaching me, so I may need to concentrate more on the walls than the floor or ceiling. Of course, once the walls are adequately treated I may then notice that there is significant noise coming through the concrete slabs above and below me.

You are overthinking this, and not usefully.

Yeah, I tend to do that

You forget about the studs. They don't give them away for free! And the nails. And the caulk. And the OSB, and the tools. And the insulation. And the mud/tape. And the paint. And the acoustic treatment that you will need inside the room once it is isolated. And the HVAC system that you will need to keep you alive. And the widows. And the doors. And the seals. And the electrical system....

But don't feel bad about that: most first time studio builders neglect to consider all of those things, just like you have. It's normal. The problem is, sound does not actually behave the way most people think it behaves. Acoustics is not very intuitive, sound does strange, unexpected things, and most people aren't aware of that until they start studying it.

I'm sure there's things I haven't thought of yet but I was just sketching out a rough figure for the main components (plasterboard and clips) that I can easily work out required quantities for. I'm pretty sure that the wood for studs will work out a lot cheaper than using clips. My calculation includes two layers of plasterboard, but OSB is cheaper so if I use one layer of that and one layer of plasterboard the cost will be less. Tools I already have or can borrow. The secondary glazing for the main window in each room will cost about £100 and I won't be using an HVAC system as I need to be able to open the window.

Those are the good ones. That's why they cost more! As the saying goes: You get what you pay for." If you buy cheap clips, you will get cheap results. If you buy god quality clips, you will get good quality results.

So what sort of results do you think I could achieve using Genie clips rather than a stud frame? I could just use them on the ceiling, which would mean the concrete slab rather than the walls would be supporting the weight. The concrete slab above me rests on the walls and in turn the concrete slab below me, so the walls and concrete slab below will still need to be able to support any extra weight I put on the ceiling, but it might make building the walls easier, whether I build a stud frame in front of them or use clips on the wall, if each wall only has to support the plasterboard in front of it.

It will not be attached to the ceiling! As I said in my previous post, the inner room is a "box" that sites inside the outer room, just a a matchbox might sit inside a shoe-box. It sits on the floor, and that's it. There CANNOT be any physical contact between the inner-leaf and the outer-leaf, except for where the walls meet the floor. That's it. Nothing else.

And your thinking would be wrong. Firstly, the only point of contact is into the floor: there's no connection to the outer-leaf ceiling. Assuming you don't need very high isolation, that provides enough decoupling. The inner-leaf frame is free-standing. It consists of four walls and a ceiling, plus doors, windows, etc., but the ONLY point of contact is the floor.

I just don't understand why, if noise may be travelling via/emanating from the concrete slabs, it's OK for the stud frame to be in contact with the lower concrete slab but not the upper one. I note what you've said about using isolating strip/bolt if I'm really concerned about it but if that adequately isolates the frame from the floor, why wouldn't it also be sufficient to isolate it from the ceiling? It just seems like the walls would be more rigid and secure if they're fixed top and bottom.

So forget STC as a useful indicator, and just use the actual TL graphs to judge if a wall, door, window, floor, roof, or whatever will meet your needs.

Sorry for the rant, but that's one of the many misleading things about acoustics, that confuse people, and point them in the wrong direction.

It's useful to have this explained, thanks.

Do the math for your self. Plug in some small numbers for "d", such as 10mm, or 25mm, or 35mm, and see what happens. Then plug in a much more reasonable value, such as 150mm, and see what happens.

It's that simple. The math does not lie. The equation is valid, and working through makes it a lot simpler to understand than looking at a bunch of pretty diagrams with nicely colored arrows on them.

Thanks, I'll experiment with that formula.

Careful! Don't confuse your terms! The "air gap" is the distance across the cavity from the face of the outer-leaf to the face of the inner-leaf. If you have a 10mm gap between the existing wall and the framing, and then you use 50mm studs, your air gap is 60mm... But 50mm studs are not going to cut it here: you will normal 3x4 studs, which commonly measure 38mm x 89mm. So your air gap will be 99mm, which is about right. You don't want to go less than that, for the same reason you see in the equation. If "d" is too small, then the frequency is too high. The minimum realistic air gap is about 100mm.

For the bedroom it may just about be manageable to reduce the room by 129mm on each wall (99mm airgap+30mm OSB/drywall) but it would be a stretch, especially with the radiator pipes at the bottom of the wall further intruding into the space, and may only work if I can strip the existing 20-25mm plaster off the walls first. Do you think this plaster (assuming it's in good condition and sealed) provides much benefit in terms of noise isolation, such that removing it would be a bad idea, or would replacing it with an insulated airgap of the same depth, or even plasterboard of the same depth directly attached to the wall, improve things, in a certain frequency range at least? If I did remove the plaster, I'd at least seal the concrete wall with something as I know cinderblock is very porous but the sealant should take up much less depth than the plaster does.

It's very simple: You put down a 2" layer of semi-rigid fiberglass insulation, such as OC-703 directly on the slab, then you put down two (or more) layers of of thick OSB on top of that (at least 19mm each layer), screwed together, but NOT touching your inner leaf walls. Leave a gap of a few mm all the way around, then fill that gap with flexible, non-hardening caulk. Then lay thick laminate flooring on top of that, using a suitable underlay. It is not a true floated floor (not even close), but it works wonders for reducing impact noise. It's the same principle as a drum riser.

OK, that is quite simple. The only problem is that 2"/50.8mm fibreglass + two layers of 19mm OSB = 88.8mm. Minus my 35mm joist height and 18mm floorboards leaves me with a height increase of 35.8mm before I've even added my 4.7mm cork tiles, which is 15.8mm higher than the hall floor can be, so that's not practical. I'd also be a bit concerned about the electrical cables (in conduit) being buried under the fibreglass and overheating, as I know that we're not meant to insulate around cables in wallboxes, etc. because of this risk.

"almost" being the operative word! Try setting up your vocal mic in such a room, and record at the level you normally would, but with nobody speaking or singing. Now take a look at the spectrum if what you recorded... See the problem? Compare that to my signature block, at the bottom of every single post I write here on the forum...

Believe me, I hate to compromise and would love to build an amazing recording space but I think "adequate" is the best I can hope to achieve here. If the secondary glazing doesn't block enough external noise, then I might be able to permanently stuff insulation in the 100mm gap between it and the primary glazing for two-thirds of the area and fill the remaining third (where the window that needs to open is) with insulation when I'm recording and need a lower noise-floor.

Soundman2020 · Post by **Soundman2020** » Tue May 02, 2017 10:36 am

I've replaced the pictures in the first post, but because of the 12 attachment limit I had to relocate 3 of them to post 5. I'm not sure why but when I add the internal links it adds empty space to the right of each picture. I've added internal links for the pictures in post 3 but I've kept the higher-res external links as well, as the detail may not be readable on the internal copies.

That's fine. No problem.

That's fine for checking levels but it won't show me the frequency of the noise will it?

There's many ways of determining the frequency spectrum of the sounds you need to isolate. I already gave you the easiest one: record the sound with your DAW, using a mic that has reasonably flat response, and take a look at the spectrum like that. Compare it to the "C" weighting curve, and you'll get a good idea of where your problems are.

so I may need to concentrate more on the walls than the floor or ceiling.

There's an analogy I often use to explain the shortsightedness of that approach: What you are saying is exactly equivalent to his scenario: You want to build an aquarium to put in your living room, but you notice that you only need to see the fish from the front, so you figure you'll only put glass on the front of the frame, and you'll use carpet for the back, since it is so much cheaper, and cardboard for the sides... How well do you think your fish tank will hold water? It will hold water about as well as your room will "hold" sound if you make some walls worse than others.

As I already mention, isolation is an "all or nothing" issue. Your isolation will only be as good as your weakest link. If you make fantastic walls, that isolate to 60 dB, but you only do the ceiling to 40 dB, then your total isolation is around 40 dB, and you wasted a hell of a lot of money on the walls. Sound is like water: it will take the simplest path out of the room (or fish tank), totally ignoring the strongest barrier. And once it is out, it is out all over. Just like your leaky fish tank will spill water all over your floor, in all directions, so too will your leaky room.

I'll repeat what I said before. ALL parts of your room must be isolated to the same level. That includes ceiling, walls, doors, windows, the HVAC system, the electrical system... If any part of that is not up to the same grade as the rest, then you wasted money on "the rest".

Here's a simple experiment: Go out in your car (or someone else's car), in heavy traffic, with all the windows closed, and listen carefully to the sounds that are coming in from outside. Now crack open one of the windows, just a tiny but, maybe a couple of millimeters.... What do you notice? Yep. A sudden large increase in the sound level inside the car. All of the rest of the glass, steel, and plastic around you is now irrelevant: what defines the noise level inside the car, is that tiny gap. The weakest link.

I'm sure there's things I haven't thought of yet but I was just sketching out a rough figure for the main components...

I'd suggest that you prepare what builders call a "bill of materials". It's basically a spreadsheet that lists all of the things you will need, with the unit price, quantity, and extended price of each, and adds up to a single total. Start filling that in with all the data you have so far regarding your materials and quantities, and see how it matches up to your budget. I always recommend that all of my paying customers should do this (some hire me to do it for them), so they are fully aware of what their studio build is going to cost, in terms of materials and services. It's usually an eye-opener.

Don't forget to include the cost of the electricians, since it's probably illegal (and unsafe) for you to try doing your own electrical work. Don't forget to include the cost of hiring the structural engineer, which is an unavoidable expense. You might also need to hire other skilled people, so make allowance for that. There might be inspection costs involved too, as well as possible costs of paperwork. They all add up.

and I won't be using an HVAC system as I need to be able to open the window.

If you "need" to open the window, then save yourself some money, and don't bother building a studio at all!

It's that simple. Operable windows are a major gash in your isolation shell, and trash your isolation. Trying to get a good seal on a window is a tough thing, and this graph shows what will happen if you don't achieve it:

loss-crack-reduction-effect-of-gaps-on-TL-GOOD!!!!.jpg

It's not very hi res, but basically it shows what happens to a wall, door, or window that is designed for "X" dB of isolation (horizontal axis), if there is a tiny crack (vertical axis). So for a barrier designed for 50 dB of isolation will end up having only 35 dB of isolation if there is a crack that takes up only 0.05% of the surface. Let's imagine that this a window that measures 50cm wide by 50cm tall (to make the math easy). That's 2500 cm2. 0.05% of that works out to 1.25 cm2. So if there's a gap just 0.25mm high along one edge of that glass (0.25mm * 50cm = 1.25cm2), your isolation is trashed. The reduction in isolation from 50 dB to 35 dB implies that your window is blocking 562% less sound than it would have. Yes, I did not skip a decimal point there: the 50 dB window does indeed block five hundred and sixty two percent more sound energy than the 35 dB window.

Yet another of the things that is not intuitive about acoustics. But the math does not lie.

So, if you "need" to have such a window in your room, then I hope you are OK with losing that 500%.

Here's another interesting, and far simpler statement, from a manufacturer of acoustic products: "Consider this, a 1/8” opening around all four sides of a door will reduce the effective rating of an STC 52 door down to an STC 21 – guaranteeing very poor acoustical performance". Yup.

I won't be using an HVAC system

That's yet another of those "rookie errors". Most people who want to build studios think the same as you, until they start investigating.

Think of it this way: If you had a plastic bag pulled over your head, would you prefer that it had a hole in it, close you your mouth and nose? Or would you prefer to brave it out with no hole?

That's the choice you have here, only it isn't quite as drastic (but still just as deadly). Your outer leaf will be sealed air-tight. Your inner-leaf will be sealed air-tight. I'm sure that you enjoy breathing, and that you like to do that several times per minute. So there's a question here: Where will the oxygen come from to keep you breathing happily, if you have two air-tight seals around you? And where with the deadly CO2 build-up go, if you are surrounded by what is effectively two very thick, very efficient plastic bags?

Most people think that it's the lack of oxygen that will kill them, if they are looked inside an air-tight container, but actually it isn't. You can die in air that has practically the right percentage of oxygen in it. What kills you is the CO2 build-up. With every single breath you exhale, a large percentage of that is CO2. Since it has no place to go (the room is doubly-hermetic), the level just carries on rising and rising and rising. It doesn't take long until it becomes unpleasant and stuffy, then the headaches start, then the vision loss and hearing loss, then the nausea, then unconsciousness, then eventually death. Of course, it's unlikely that would happen, since you'd run for the door as soon as the tunnel vision and nausea hits, but it doesn't seem like a good way to operate a studio, having everyone run for the bathroom to throw up every few hours.

You need HVAC.

So what sort of results do you think I could achieve using Genie clips rather than a stud frame?

I don't get why you are so obsessed with using things that you don't need, and that are very expensive! Here's a question: if you did not have stud frames, what would you attach the clips to? You already know that you cannot just attach them to the walls or ceiling, as the air gap would be way too small, just a tiny fraction of what it needs to be for good isolation. So what did you plan on attaching them to?

I could just use them on the ceiling, which would mean the concrete slab rather than the walls would be supporting the weight.

You could, indeed, support your inner-leaf ceiling from your outer-leaf ceiling, but not using clips. You would need isolation hangers, and you'd still need a frame of some type to support the drywall and OSB. I'd suggest that you look at the isolation hangers offered by Mason Industries: they have a pretty good range that would meet your needs. Not cheap, but really good.

the walls and concrete slab below will still need to be able to support any extra weight I put on the ceiling, but it might make building the walls easier,

Actually, not. It would make building the walls more complex, since you would then need to put sway braces on them, at the top, to provide the horizontal support that you'd be removing by NOT putting your inner-leaf ceiling framing on top of them. You can get those from Mason as well. Take a look in their catalogue.

I just don't understand why, if noise may be travelling via/emanating from the concrete slabs, it's OK for the stud frame to be in contact with the lower concrete slab but not the upper one.

Did you ever play the "string telephone" game as a kid? Taking a couple of coffee cans, punching a small hole in the middle of the bottom of each, and running a piece of string between them? When you stretch the string taught, you actually can have a reasonably good conversation like that, since the bottom of the can acts like a diaphragm, and the string is a pretty good conductor, when stretched taught between both cans. But if you cut off one can and take it away, how well does the other can and the floppy piece of string transmit sound now?

There's your answer.

It just seems like the walls would be more rigid and secure if they're fixed top and bottom.

I have a question for you: What holds up this structure? What keeps it rigid and secure? :

timber-shed-SML-ENH.jpg

After all, it is just four framed walls and a framed ceiling with sheathing on it! So it must just sort of flop around and fall over, right? Maybe the owner should build another, bigger, shed around that one, then attach the walls of this shed to the roof of that one, so that it does not fall down?

There's your answer.

The exact same thing that keeps that shed standing firmly, safely, solidly, and secure in place, without tipping over, is what will keep your inner-leaf room standing up just fine. If you can't figure out what it is that keeps the shed standing up, then I'm sure your structural engineer will be able to explain it to you.... (that's a big hint!).

Do you think this plaster (assuming it's in good condition and sealed) provides much benefit in terms of noise isolation, such that removing it would be a bad idea, or would replacing it with an insulated airgap of the same depth, or even plasterboard of the same depth directly attached to the wall,...

Plaster is basically just sand and cement, hydrated. The density of that is probably around 1900 to 2000 kg/m3. Taking off 25mm of that from your walls will reduce the mass by many hundreds of kilograms. You already know that mass is your friend (from the equation I gave you). You'd be replacing that with 19mm of drywall, which has a density of around 650 kg/m3, or roughly one third of the mass you would be removing. I think that's enough information for you to arrive at your answer!

leaves me with a height increase of 35.8mm before I've even added my 4.7mm cork tiles, which is 15.8mm higher than the hall floor can be, so that's not practical.

Why is it "not practical"? What would the problem be if your floor inside your room is 20mm higher than the floor outside of your room? Have you never seen steps before?

The jump in height will occur inside your air gap, only visible when both doors are open. So why is that a problem? You'll only ever notice when the doors are open.

I'd also be a bit concerned about the electrical cables (in conduit) being buried under the fibreglass and overheating, as I know that we're not meant to insulate around cables in wallboxes, etc. because of this risk.

The re-route the cables! You won't be able to keep the existing plugs, switches and light fittings anyway, as they will all be hidden behind the walls and ceiling, and you'll only have one single penetration for bringing the power feed into your room, so there's no big deal here. Just get your electrician to re-route any problematic cables, as part of the entire build. They can all go in the wall cavity.

I might be able to permanently stuff insulation in the 100mm gap between it and the primary glazing for two-thirds of the area and fill the remaining third (where the window that needs to open is) with insulation when I'm recording and need a lower noise-floor.

Yet another one of the common myths about acoustics, is that insulation blocks sound. It doesn't. If you don't believe me, run down to your local hardware store and pick up a small sample piece of thick fiberglass or mineral wool insulation, big enough to fit in front of your favorite full-range speaker. Play your favorite music on your speaker at around 85 dBC (standard calibration level for studios). Now put the insulation in front of the speaker, while you carry on listening.... What did you notice? Did it go silent? Nope. All you got was a slight reduction in the very high end, and maybe 1 or 2 dB overall reduction on your meter (tops). But you can still hear the music, loud and clear.

Insulation does not stop sound. It damps resonance, and changes the way air behaves (isothermal, instead of adiabatic), but it does not stop sound. You already know form the equations I gave you that what stops sound is mass, not insulation. So your plan of stuffing the window cavity with insulation won't work to stop sound getting in or out. It would be great for acoustics in side the room! Certainly! But that's a very different thing. That's treatment, not isolation. Those are the two sides of the acoustics coin, and they are totally different. Treatment is one thing, and isolation is something entirely different. Materials used to isolate a room are really lousy at treating it. And materials used to treat a room are really lousy at isolating it.

- Stuart -

doveman · Post by **doveman** » Fri May 05, 2017 9:24 am

Soundman2020 wrote:There's many ways of determining the frequency spectrum of the sounds you need to isolate. I already gave you the easiest one: record the sound with your DAW, using a mic that has reasonably flat response, and take a look at the spectrum like that. Compare it to the "C" weighting curve, and you'll get a good idea of where your problems are.

OK, thanks.

There's an analogy I often use to explain the shortsightedness of that approach: What you are saying is exactly equivalent to his scenario: You want to build an aquarium to put in your living room, but you notice that you only need to see the fish from the front, so you figure you'll only put glass on the front of the frame, and you'll use carpet for the back, since it is so much cheaper, and cardboard for the sides... How well do you think your fish tank will hold water? It will hold water about as well as your room will "hold" sound if you make some walls worse than others.

As I already mention, isolation is an "all or nothing" issue. Your isolation will only be as good as your weakest link. If you make fantastic walls, that isolate to 60 dB, but you only do the ceiling to 40 dB, then your total isolation is around 40 dB, and you wasted a hell of a lot of money on the walls. Sound is like water: it will take the simplest path out of the room (or fish tank), totally ignoring the strongest barrier. And once it is out, it is out all over. Just like your leaky fish tank will spill water all over your floor, in all directions, so too will your leaky room.

That all makes sense but it's possible that my ceiling is already better than my walls, so by focusing on the walls I'd be bringing them up to the same level as the ceiling. I may well end up making them better than the ceiling in the process but if the ceiling is already good enough for my purposes then I'd still end up with a room I could use. I must admit I find the water analogy a bit confusing, as if I have a door with a great big gap at the bottom, closing that door still significantly reduces the sound that reaches the other side of it and clearly the gap at the bottom isn't providing any isolation, so in theory even if the door provides 20 db isolation closing it shouldn't make any difference if there's a 0 db isolation path for the sound to escape by. With water, closing the door would slow the flow somewhat but over time the same amount of water would accumulate on the other side but with sound it doesn't accumulate in this way so that eventually it's just as loud as it would have been if the door had remained open.

I'd suggest that you prepare what builders call a "bill of materials". It's basically a spreadsheet that lists all of the things you will need, with the unit price, quantity, and extended price of each, and adds up to a single total. Start filling that in with all the data you have so far regarding your materials and quantities, and see how it matches up to your budget.

Don't forget to include the cost of the electricians, since it's probably illegal (and unsafe) for you to try doing your own electrical work. Don't forget to include the cost of hiring the structural engineer, which is an unavoidable expense. You might also need to hire other skilled people, so make allowance for that. There might be inspection costs involved too, as well as possible costs of paperwork. They all add up.

Yeah, that'd be a good idea. I was actually surprised to find that OSB costs more than Knauf Soundshield Plus acoustic plasterboard, about £15 compared to £9. Actually getting the boards is problematic as well, as most companies that deliver seem to expect me to offload them myself and then they need to be laid flat individually until used, which I'm not sure I'd have the space for. So if I were to use them I may have to look for a builder who can have them delivered to his premises (or collect them if they're available locally) and bring them to me as he fits them.

If you "need" to open the window, then save yourself some money, and don't bother building a studio at all! It's that simple. Operable windows are a major gash in your isolation shell, and trash your isolation. Trying to get a good seal on a window is a tough thing, and this graph shows what will happen if you don't achieve it:

I never really planned to build what anyone would call a "studio" as such in this flat. Originally I thought of making the bedroom suitable for use recording vocals and the living room suitable for composing/monitoring using nearfield speakers but after reading your first reply I pretty much gave up on the living room part of the plan (although I thought I still might be able to improve it somewhat, even if only to make it more pleasant to live in).

It's not very hi res, but basically it shows what happens to a wall, door, or window that is designed for "X" dB of isolation (horizontal axis), if there is a tiny crack (vertical axis). So for a barrier designed for 50 dB of isolation will end up having only 35 dB of isolation if there is a crack that takes up only 0.05% of the surface. Let's imagine that this a window that measures 50cm wide by 50cm tall (to make the math easy). That's 2500 cm2. 0.05% of that works out to 1.25 cm2. So if there's a gap just 0.25mm high along one edge of that glass (0.25mm * 50cm = 1.25cm2), your isolation is trashed. The reduction in isolation from 50 dB to 35 dB implies that your window is blocking 562% less sound than it would have. Yes, I did not skip a decimal point there: the 50 dB window does indeed block five hundred and sixty two percent more sound energy than the 35 dB window.

Yet another of the things that is not intuitive about acoustics. But the math does not lie.

So, if you "need" to have such a window in your room, then I hope you are OK with losing that 500%.

I'm not sure that I couldn't create an openable inner window/shutter that seals properly when closed though. Maybe the current double glazing has a tiny gap somewhere and loses 500% isolation but even if that is the case, it's still considerably quieter than with it open, so if I can add another panel (whether glass or wood) 100mm from the double glazing that seals at least as well as the original window I would think it would be quite beneficial. I might try and knock something up with some cheap wood though, to see how effective it actually is.

Your outer leaf will be sealed air-tight. Your inner-leaf will be sealed air-tight. I'm sure that you enjoy breathing, and that you like to do that several times per minute. So there's a question here: Where will the oxygen come from to keep you breathing happily, if you have two air-tight seals around you? And where with the deadly CO2 build-up go, if you are surrounded by what is effectively two very thick, very efficient plastic bags?

I think two air-tight sealed leafs is probably overkill for my vocal recording room and I know people manage to record vocals and acoustic guitar in rooms that haven't been fully soundproofed or sealed, although they probably don't start off as leaky as mine! If I can manage to stop mid->high range sound intruding in from, or leaking out to, my neighbours via the walls, ceiling or floor I think that will be sufficient and it probably won't matter so much if the window isn't fully sealed and provides a bit less isolation as there won't be anyone a couple of feet the other side of it as there is with the walls, so any noise would have to travel much further to reach anyone, or to travel from them to my window.

I don't get why you are so obsessed with using things that you don't need, and that are very expensive! Here's a question: if you did not have stud frames, what would you attach the clips to? You already know that you cannot just attach them to the walls or ceiling, as the air gap would be way too small, just a tiny fraction of what it needs to be for good isolation. So what did you plan on attaching them to?

I was thinking of attaching them directly to the wall as I simply may not have room to build a decoupled stud frame, particularly if I'm not stripping the existing plaster off. I appreciate that the air gap would be much smaller than it properly needs to be but my thinking was that putting any gap between the inner and outer walls and filling it with isolation would still be quite helpful in limiting the mid->high range sound travelling between the two walls, compared to just having plaster stuck directly on the wall as it currently is.

You could, indeed, support your inner-leaf ceiling from your outer-leaf ceiling, but not using clips. You would need isolation hangers, and you'd still need a frame of some type to support the drywall and OSB. I'd suggest that you look at the isolation hangers offered by Mason Industries: they have a pretty good range that would meet your needs. Not cheap, but really good.

I did look at those before but I believe they cost around $50 compared to $1.50 for IB-1 clips or even £3 for Genie clips, so I couldn't afford them. Several companies suggest using clips and hat channel on ceilings, http://www.soundstop.co.uk/solutions/ce ... tion_1.php http://www.soundproofingcompany.com/sou ... ceiling-2/ http://www.ikoustic.co.uk/page/soundproofceiling and their examples tend to refer to attaching them to a lathe and plaster ceiling or the joists underneath, so I'd think attaching them to my concrete ceiling with it's extra mass would perhaps provide even better results.

Did you ever play the "string telephone" game as a kid? Taking a couple of coffee cans, punching a small hole in the middle of the bottom of each, and running a piece of string between them? When you stretch the string taught, you actually can have a reasonably good conversation like that, since the bottom of the can acts like a diaphragm, and the string is a pretty good conductor, when stretched taught between both cans. But if you cut off one can and take it away, how well does the other can and the floppy piece of string transmit sound now?

I'm sure I'm displaying an embarrassing failure to grasp basic physics but I don't see how a floppy piece of string and a solid stud frame with plasterboard attached to it are comparable. Whilst not coupling it to the ceiling would obviously prevent noise travelling through it between the ceiling and floor, I'd still think that noise coming from the floor would transfer into the frame and plasterboard and if isolating strip would prevent that noise getting into the stud frame, I'd think that it would do the same for noise coming from the ceiling.

Plaster is basically just sand and cement, hydrated. The density of that is probably around 1900 to 2000 kg/m3. Taking off 25mm of that from your walls will reduce the mass by many hundreds of kilograms. You already know that mass is your friend (from the equation I gave you). You'd be replacing that with 19mm of drywall, which has a density of around 650 kg/m3, or roughly one third of the mass you would be removing. I think that's enough information for you to arrive at your answer!

Hmm, it doesn't sound like a very good idea then! I do wonder though whether the disadvantage from losing mass might be offset by the advantage of spacing the plasterboard away from the concrete wall and filling the gap with insulation, at least in terms of mid->high range? In most tests I've seen I think they measure how much sound travels from one side of the wall to the other, which is obviously important for my party wall but not so much with my internal dividing walls. What I'm concerned about is noise travelling up/down those to/from the neighbours but maybe the mass of the plaster is just as important for that as well, considering that sound doesn't just enter half way up the wall but also near the bottom and top where it doesn't have much wall to travel up/down to get to the concrete slabs and the neighbours.

Why is it "not practical"? What would the problem be if your floor inside your room is 20mm higher than the floor outside of your room? Have you never seen steps before? The jump in height will occur inside your air gap, only visible when both doors are open. So why is that a problem? You'll only ever notice when the doors are open.

It would simply be too much for my landlord. Anything I do that significantly impacts on the flat needs to be easily removable whenever I leave this place so that someone else can move in, so replacing the floor to the same height, fitting a lowered ceiling, replacing plaster with plasterboard of similar depth or fitting an extra door in the hall to isolate the hall from the living room/bedroom is fine but creating steps between the rooms isn't, as the landlord would have to remove the OSB and lay a new floor to make the rooms level with the hall again.

The re-route the cables! You won't be able to keep the existing plugs, switches and light fittings anyway, as they will all be hidden behind the walls and ceiling, and you'll only have one single penetration for bringing the power feed into your room, so there's no big deal here. Just get your electrician to re-route any problematic cables, as part of the entire build. They can all go in the wall cavity.

I did think I might be able to create a channel around the perimeter of the room to house the cables. At the moment they probably cut across diagonally, so the electrician would have to be able to extend the cables to run around the perimeter but hopefully this is possible, as he won't be able to run new cables from the fuse box. This sketch shows what I was thinking of, with clip/channel spacing the plasterboard off the concrete wall creating a space for the cables to run underneath.

Conduit channel.png

As the top of my floor can only be a max. of 73mm above the concrete slab, I've drawn a 25mm layer of rigid insulation (yellow), with 30mm (2*15) of OSB on top (orange) and a top 11mm layer consisting of 6mm plywood with 4.7mm cork tiles stuck to it, which comes to 65mm. So I could increase it slightly, by using 2*18mm OSB or 9mm plywood and 6mm tiles. I thought I'd also need a baton (brown) to stop the insulation/boards moving into the conduit channel and then I'd need to decouple that baton from the flooring and wall above with rubber strip (black).

I don't know if 25mm insulation would be strong enough but I found these:

https://www.insulationsuperstore.co.uk/ ... -pack.html
https://www.insulationsuperstore.co.uk/ ... -pack.html
https://www.insulationsuperstore.co.uk/ ... -25mm.html
https://www.alsfordtimber.com/building- ... eco25.html

Would any of those be suitable?

That would be for the bedroom, where I'd also hope to improve the walls and ceiling. For the living room I need to fix up the floor anyway so even if I don't do anything else in there I might still do this, as it would reduce the impact noise travelling downstairs but it will depend on whether I find a cheaper and easier way to fix the uneven floor. It might also be tricky to create a conduit channel if I'm not building the wall out to create a gap for it, as the boards would have to extend further towards the wall than the insulation, with the conduit encased in a wooden block, as shown here.

Conduit channel no extruded wall.png

Yet another one of the common myths about acoustics, is that insulation blocks sound. It doesn't. If you don't believe me, run down to your local hardware store and pick up a small sample piece of thick fiberglass or mineral wool insulation, big enough to fit in front of your favorite full-range speaker. Play your favorite music on your speaker at around 85 dBC (standard calibration level for studios). Now put the insulation in front of the speaker, while you carry on listening.... What did you notice? Did it go silent? Nope. All you got was a slight reduction in the very high end, and maybe 1 or 2 dB overall reduction on your meter (tops). But you can still hear the music, loud and clear.

Insulation does not stop sound. It damps resonance, and changes the way air behaves (isothermal, instead of adiabatic), but it does not stop sound. You already know form the equations I gave you that what stops sound is mass, not insulation. So your plan of stuffing the window cavity with insulation won't work to stop sound getting in or out. It would be great for acoustics in side the room! Certainly! But that's a very different thing. That's treatment, not isolation. Those are the two sides of the acoustics coin, and they are totally different. Treatment is one thing, and isolation is something entirely different. Materials used to isolate a room are really lousy at treating it. And materials used to treat a room are really lousy at isolating it.

That's useful to know, thanks. I had read that cheap low-density insulation is just as effective as the expensive high density stuff that soundproofing companies try and sell but wasn't aware that none of them are much use for blocking sound.

doveman · Post by **doveman** » Wed May 17, 2017 12:38 pm

I'd welcome your thoughts on whether the floor would be stable enough using OSB on 25mm rigid insulation and if any of those products I linked to would be suitable. I'm a bit concerned that the insulation, even if I was able to use 50mm, will compress somewhat under weight and as different parts of the room will have different weights on the floor, that this could create some unevenness as where there's weight on one end of a board then the other end might lift up somewhat, like a see-saw!

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