Soundproof Building Advice needed*

Hi folks, after months of much research, head scratching, gasping in awe and general pre-senile confusion I am nearly ready financially and informationally to give my small studio build a go or should I say, 'the go'! With the ominous combination of being a novice and lacking the wealth I literally cannot afford to mess this up! Hence some questions The back-story: Here's what you missed on last weeks show! Predictably I'm planning to build a room within a room - despite my small dimensions (15*9 & 9 feet high). The walls will use a green glue sandwich of 16mm fire rated plasterboard and perhaps 12mm plasterboard (as I read it's good to mix thicknesses). The rockwool slabs inside the wall will be 100mm RWA45. The whole studwall will sit approx 5-10 cm away from original brick wall. Ceiling will be pretty much the same as the walls. Now onto the floor! I read some 'heavy hitters' say in another thread that a cheap compromise to floating the floor is to use 2 layers of plywood sandwiched with GG sitting on top of 2 inch OC 703. This would help my construction as though my floor is solid concrete, it is on the 2nd floor of an industrial type building where noise seems to resonate from everywhere - e.g. I can hear footsteps from nearly every floor Ok question time: 1) Is it right to assume the stud walls will be secured to the plywood and will it be stable since the whole thing is sitting on fibreglass which is not touching any of the room boundaries? 2) The threads mention using OC 703 which I'm considering making a mocumentary about the impossibility of finding this Holy Grail in the UK! Is RWA45 a viable like for like substitute for OC 703 or is it too floppy in comparison? 3) Slightly unrelated but I have several unfinished electrical outlets in the current wall and once the new one is built in front of it, how can I navigate the problem of extending them without puncturing the studwalls and obliterating all my soundproof hard work? same question goes for hanging traps too 4) Does anyone happen to have instructions for construction of this type of floor and studwalls too? I have a carpenter but he's not experienced in these types of build - better yet, anyone in London UK willing to come and help! Sorry for being longwinded but one thing I've learnt b4 building is you need to be thorough! Any advice appreciated Thanks Rob

Hi Rob, and welcome back! Haven't seen you around in a while...

The walls will use a green glue sandwich of 16mm fire rated plasterboard and perhaps 12mm plasterboard (as I read it's good to mix thicknesses).

Well, using two different thicknesses is good, yes, and does have a small benefit. But as you guys in the UK say: "What you gain on the roundabout you lose on the swings" (or some obscure saying like that). In other words, you are gaining that small benefit in a place where you don't really need it, at the loss of a larger benefit where you do need it. This is a bit of a myth that still seems to be circulating, apparently being endlessly repeated by some home theater and audiophile web sites. Let me explain: By using different thicknesses you have several small benefits. One of those is that the two panels have different self-resonant frequencies (the natural frequencies that they would "ring" at, if held up by the edges and struck with something). At those frequencies, each panel passes sound rather well, instead of blocking it. So you'd think that this must be great, since the wall as a whole would benefit: where one panel "rings" the other doesn't, so at least one of them is doing some blocking, right? Well, not really. Drywall doesn't "ring" that much anyway, and the two frequencies are not that far apart. Plus, it isn't a single tight, fixed frequency, but rather a range of frequencies, so the ranges overlap a lot anyway. Not much benefit there! The same thing happens at the coincidence dip for each panel: Since they are different, they supposedly don't fall at the same place on the spectrum, so that must be fantastic too! Right? Nope. Same reasons. Then there's the issue of impedance mismatch: as sound waves travel through the interface between two dissimilar materials, they are attenuated due to change in impedance, and also change direction slightly. Once again, this must be wonderful, according to the myth! Free soundproofing, right? Not. The effect is rather small.... Well then, maybe if you add up all of these small effects, the total must be large, right? Well, no. None of them are very big to start with, and since they all happen at different areas in the spectrum, they don't really "add up" much at all. And to put the cherry on the cake, they all happen in a part of the spectrum where a well built wall is already isolating pretty darn well, so the slight additional benefit is neither here nor there. Just a drop in the bucket, really. On the other side of the coin, in the part of the spectrum which DOES need help, the very low frequencies, you have robbed the wall of two things it needs: mass and rigidity. The thinner drywall is more flexible, and therefore performs worse for isolating very low frequencies. And using thinner drywall for one layer means that the wall has less mass than it could have had, and in isolation, mass is your friend. In real-world terms, if you compare what you gained in the mids and highs against what you lost in the lows, you lost a lot more than you gained. So it makes sense to just use two layers of 16mm drywall, instead of one of 16mm and the other one thinner. Here too the effects are not huge: Maybe a dB or two. But in the low end, I'll take an extra dB or two any time I can get it! I only have maybe 15 or 20 dB to start with, way down in the low end, so gaining 2 dB is a major improvement. And I really don't care if that means I lose 2 or 3 dB in the highs, or even 5. If I already have 65 or 70 dB isolation before the coincidence dip, and I lose 3 of those, well, I won't be crying about that! Hell, I'd even take a 10 dB loss at 8 Khz, if it will give me a half dB gain at 50 Hz. So overall, go with the wall "sandwich" that has the greatest mass and highest rigidity. Maybe one day this myth will die, but it shows no signs of doing so, to date... :(

The whole studwall will sit approx 5-10 cm away from original brick wall.

That will give you an air gap of about 15 to 20 cm, roughly: that's pretty good.

Now onto the floor! I read some 'heavy hitters' say in another thread that a cheap compromise to floating the floor is to use 2 layers of plywood sandwiched with GG sitting on top of 2 inch OC 703.

Well, yeah, that works OK for impact noise, and does something for air-born sound too, but it isn't a true floating floor, so don't expect major results out of it. But once again, most of what it does is in the low end, so that is A Good Thing, and certainly worthwhile.

1) Is it right to assume the stud walls will be secured to the plywood and will it be stable since the whole thing is sitting on fibreglass which is not touching any of the room boundaries?

Nope! You can't build a wall on top of that, since it is not a stable base. For example, if your front wall turned out to be a lot heavier than the back wall, you could end up with the entire room tilting forwards... not nice. And by the time you add the weight of the walls, ceiling, equipment, people and everything else, you have probably squashed the 703 down to pancake size anyway, so it isn't doing much. This concept of mildly decoupling a floor works on the same principle as a drum riser, and is NOT meant to be a substitute for a properly floated floor. So your inner-leaf walls would still be firmly attached to your concrete floor, and the "drum riser" floor just sites within that boundary, not touching it. The walls must be firmly anchored to the structural floor: there's no getting around that.

2) The threads mention using OC 703 which I'm considering making a mocumentary about the impossibility of finding this Holy Grail in the UK! Is RWA45 a viable like for like substitute for OC 703 or is it too floppy in comparison?

"Floppy" is not what matters. Gas flow resistivity is what matters. That's the parameter that affects the acoustic usefulness of insulation. Unfortunately, you'll find it rather hard to find that number on manufacturer's specs for most insulation products! They don't bother measuring it, as it has no meaning for the primary purpose of insulation: thermal. It only matters to a very small percentage of their customers: us folks wanting to use it for acoustic purposes. And we don't matter: we aren't even much of a blip on their radar, so they don't bother testing their products and publishing those number, just for us. Or at least, most of them don't. Some do! Fortunately, there is a loose relationship between "gas flow resistivity" and another number that they do publish: density. It's not a very good relationship, and not very linear, but it does work. So, if you are using a fiberglass insulation product, then you need to look for one that has a density of roughly 30 kg/m3, and if you are using a mineral wool based insulation product, you need to look for one that has a density of roughly 50 kg/m3. That will get you very close to where you need to be.

3) Slightly unrelated but I have several unfinished electrical outlets in the current wall and once the new one is built in front of it, how can I navigate the problem of extending them without puncturing the studwalls and obliterating all my soundproof hard work? same question goes for hanging traps too

Surface-mount. You have one single penetration to bring power into the room, and you decouple and seal that where it passes through the walls (use conduit). Then you distribute from there around the rest of the room using surface-mounted ducts, plugs, switches, lights, etc. This is not cheap, but it is the only way to ensure that you do not degrade your hard-won isolation. For that single penetration, you have a piece of conduit that runs across your air gap, between outer-leaf and inner-leaf, but it does not go straight across: rather, it bends 90° as soon as it gets inside the wall, runs parallel to the drywall surface for a distance, then bends 90° again to to through the inner leaf. If you want to go to extremes, You can also cut out a small section in the middle of that conduit run, a few cm long, and wrap that with rubber, for even better isolation. And where the conduit goes through each leaf, you drill the hole a bit larger than the diameter of the conduit, and seal all around with acoustic sealant, so that the conduit does not actually touch the drywall at all: there's a ring of sealant around it that partially decouples it. Finally, once you have the cables pulled through, you then plug the ends of that piece of conduit by forcing insulation down it for several cm, then putting a blob of acoustic sealant over the end. That keeps it fairly well isolated, and if you ever do need to replace the wiring, or add more, then you can peal off the sealant, fish out the insulation, and still be able to pull cables though the conduit, as usual. That's the best method: but you might not need to go to such extremes, depending on how much isolation you actually need.

4) Does anyone happen to have instructions for construction of this type of floor and studwalls too? I have a carpenter but he's not experienced in these types of build - better yet, anyone in London UK willing to come and help!

Walls are simple: 2x4 bottom plate, with three beads of acoustic sealant run along the length as it goes down on the floor (one bead down the middle, the others a couple of cm each side). Bolt or nail that down to the sub-floor in the manner specified by your local building code. Add your 2x4 studs, either 16"OC or 24"OC (preferably), double top plate. Brace it perfectly plumb and all 90° angles. Add your first layer of drywall by resting it on a shim that is just a bit thinner than the backer rod you plan to use. Nail or screw it it in place, using half of the normal nailing / screwing schedule. Seal all joints. Pull out the shim under it, put in the backer rod, then add a bead of acoustic sealant. Now do the second layer in the same way, but staggering the joints between panels, so that none of the joints on the first layer line up with joints on the second layer. Us the same procedure: shim, nail or screw with the other half of the nailing schedule, and using nails or screws that are 16mm longer than for the first layer, seal joints, pull the shim, but the backer rod in, then seal that gap with one final bead of acoustic sealant. Oh, and don't forget to put the insulation in the cavity BEFORE you put the first layer of drywall on! It's rather hard to put it in afterwards... :) And if this is an exterior wall, then you might also need a vapor barrier in there somewhere. Check your building code. Of course, the framing CAN NOT touch any part of the existing structure (except the floor). You cannot attach the framing to the walls or ceiling. Or rather you can, to brace it while you are building, until you have all the framing in place for all four walls and the ceiling, but once that is done all the bracing has to come out, and the remaining framing will be standing alone, all by itself, fully self-supporting. This is critical to isolation. If you even have one tiny mechanical connection across that gap to the outer leaf, then all you did is in vain. Just one nail is all it takes. So your carpenter needs to work carefully...

Sorry for being longwinded but one thing I've learnt b4 building is you need to be thorough!

Oh yeah! Very true. "long-winded" now is way better than "Damn it! I didn't know that!" after you already built something. - Stuart -

Hey Stuart how's it going! I fell off the radar for a while, researching and working hard to raise the cash for this dream of mine :) I Love the clarity and concise nature of your answers, you are indeed the man!!! I don't fully understand the electrical design as I tend to see in pictures (my left brain thought still confers with my creative side :lol:) I'm sure an electrician will comprehend better though. During many stages of my research I had to make the admission that I'm out of my depth in this field and after setting upon the journey with wild ambitions of grandeur I've realised I need to lower my expectations as my project is solely determined by budget. I don’t need ‘pro’ facilities as such and my work primarily involves recording vocals for artists and mixing compositions down so I can compromise in some areas, e.g. creating a plywood/fibreglass floor system is ideal but is it essential? Essentially I require good enough isolation from at least the low-mid frequencies and vocals spilling out of the room as I have a one room set up. I am also willing to partially tolerate footfall and other ‘out-to-in’ noise as this isn’t a constant occurrence though reducing these levels a little is desirable. It is worth noting that when completed the studio room door will not open to outside the facility as there is a 3 metre hallway type entrance before reaching the room. Also none of the walls are shared directly with neighbours though I have some in close proximity. There is a corridor on 2 sides and a utility room on the other whilst directly above is a cleaners cupboard and corridor with bathrooms/corridor beneath the room. With no current soundproofing or even a door to the main studio room fitted, the sound doesn’t seem wildly excessive from outside, though it is clearly audible, which is why I need to treat it. I mainly use active near fields and only use larger Hi-fi speakers intermittently for lower end reference. Although I appreciate the answer will be circumstantial my next question given all that has been discussed is: Would an inner 2 by 4 stud wall and ceiling of green glue sandwiched 16mm fire plasterboards with a 5-10cm gap and 100mm RWA45 make a worthwhile difference to transmission loss to justify the cost? As the floor is transmitting sound - and the walls are sitting on the floor - the sound will transmit directly through the walls. though I assume this would be mainly low end information? Either way, I realise I’m going to have to get professional quality help from somewhere to design/build it but I’m trying to simplify the process and get the best outcome that my money can buy rather than throwing my money away. It's gonna be a stage by stage thing I guess. My carpenter can build the framing fairly easily but I'm probably going to need help/advice on the green glue and plasterboard aspect. Another thing I wondered was how will the stud wall hold the insulation in place? Again much appreciation for your input, feels like I’m planning critical open heart surgery with no medical knowledge, I begin sweating just thinking of the pressure to get it right Thanks Rob

I Love the clarity and concise nature of your answers, you are indeed the man!!!

:oops: Thanks for the kind words! Much appreciated.

I don’t need ‘pro’ facilities as such and my work primarily involves recording vocals for artists and mixing compositions down so I can compromise in some areas, e.g. creating a plywood/fibreglass floor system is ideal but is it essential?

It is essential if you want to save money! That sounds like a contradiction in terms, but in reality the most economical way to isolate is with this method. Anything less is not going to be good isolation at all. To get to the same level of isolation using mass alone, is going to cost you a lot more. The only real way to determine that is with a sound level meter: measure real-world situations that meet your needs, and see how that translates to materials/methods, which in turn leads to budget. So, for example, measure the sound levels at a typical recording session that do today, to see how loud that is, in terms of decibels. Then measure other places that you think are quite enough for what you need for your recordings. The difference between those two readings is the amount of isolation that you need, realistically. Based on that number, we can look at laboratory tested methods that can give you that number, in terms of materials and methods. You can look at those, and see which one meets your budget and building skill level. To be honest, I would not skimp on isolation, since you can't fix that later. I would isolate well then treat minimally to start with, and add additional treatment as funds permit. But that's just me, with my priorities: others might not agree.

Essentially I require good enough isolation from at least the low-mid frequencies and vocals spilling out of the room as I have a one room set up. I am also willing to partially tolerate footfall and other ‘out-to-in’ noise as this isn’t a constant occurrence though reducing these levels a little is desirable.

You might be underestimating the importance of sound coming the other way: What if a phone rings in the middle of your best-ever take? Or a helicopter flies overhead? Or your neighbor decides to mow his lawn? Or...? Excellent takes can be totally ruined like that, and then the artist loses the "vibe", and you just can't get it again. Speaks the voice of experience.... been there, done that....

With no current soundproofing or even a door to the main studio room fitted, the sound doesn’t seem wildly excessive from outside, though it is clearly audible, which is why I need to treat it.

It would be really good to get a handle on that sound, both in terms of level (measure with a sound level meter) and spectrum (measure with a spectrum analyzer, or even your DAW). You isolation plan should be tailored to the conditions that YOU have, so measuring those goes a long way to helping decide how to build this.

Would an inner 2 by 4 stud wall and ceiling of green glue sandwiched 16mm fire plasterboards with a 5-10cm gap and 100mm RWA45 make a worthwhile difference to transmission loss to justify the cost?

Will it make a worthwhile difference? Absolutely! Will it justify the cost? That depends on what you hope to achieve. Think of it this way: typical house / office construction gives you maybe 30-something dB of isolation if you are lucky. That's probably what you are getting right now, or most likely a bit less: call it 25 dB, realistically. The very best isolated studio on the planet gets about 100 dB of isolation, and cost millions to build. The practical limit for reasonable construction methods, is about 70 dB, and even getting there is really hard, and really expensive. 60 is more realistic. The type of construction you describe will get you in the range of 50 to 60 dB, if done very carefully. Each time you increase the isolation by 10 dB, you drop the perceived level to about half of what it was. So going from, for example, 25 dB of isolation to 55 dB of isolation will decrease the perceived levels to about one eight of what they were, which is pretty darn good. In fact, that should take the type of noise you are experiencing well below the ambient sound level, which is all you can really ask for. For example, if those noises are currently at 65 dB inside your room (roughly the level of normal conversation), then an extra 30 dB of isolation would bring them down to 35 dB, which is actually too low for most low-cost sound level meters to even measure! Even one layer of 16mm drywall is going to get you close to those numbers, and would still be a major improvement. The simple fact of decoupling the inner-leaf on that second stud frame makes a big difference already.

As the floor is transmitting sound - and the walls are sitting on the floor - the sound will transmit directly through the walls.

You can reduce that too, by using the concept of the "drum riser" and applying it to your entire floor... :)

Either way, I realise I’m going to have to get professional quality help from somewhere to design/build it but I’m trying to simplify the process and get the best outcome that my money can buy rather than throwing my money away.

While that is certainly recommendable, you might find that you can actually do a lot of the construction yourself: it isn't hard, if you can swing a hammer.

It's gonna be a stage by stage thing I guess. My carpenter can build the framing fairly easily but I'm probably going to need help/advice on the green glue and plasterboard aspect.

Hanging drywall (pasterboard) is actually very easy: You cut it with an ordinary utility knife, then nail or screw it in place. No big deal at all! Actually, you don't really "cut" it with the knife: you just "score" it on the surface paper, then snap it it with your hands. It breaks cleanly along the line you scored. You can learn to do this part very easily. The only problem with that drywall is the weight: it is heavy! So you might need help to lift it into place, and hold it there while you screw it or nail it into place. Really, it is not hard. If I managed to learn how to do it with my five thumbs on each hand, then you sure can too!

Another thing I wondered was how will the stud wall hold the insulation in place?

If you by batts, they fit into the bays between the studs. If you buy panels of 703, you cut them to fit in the bays. If you buy it in rolls, then that's a bit more fiddly, but basically works the same way. That's for the walls: the ceiling is a bit harder, as it often does not want to stay up between the joists by itself, so you need to put something across the joists to keep it there. Bits of string, packing straps, plastic strips, even wire, stapled to the joists will do the trick.

Again much appreciation for your input, feels like I’m planning critical open heart surgery with no medical knowledge, I begin sweating just thinking of the pressure to get it right

Great! That's a good sign! You are now fully qualified as an official home studio builder... If you did not have those symptoms, I'd be worried... :) But seriously, I sure do understand what you are saying. This whole acoustics thing is rather overwhelming, and scary enough on its own when you first look at it, then add in the whole construction thing, and it's enough to send you to the mad house, twitching and drooling! But hang in there: as you start working through it, things really do start to fall into place, and sort of "click together" in your brain. It eventually gets a bit clearer, and you realize that there actually is some sense and logic to it all, and that ordinary humans can actually do this without needing to be bitten by radioactive spiders... :) But if you really do feel that you just can't handle the design aspect yourself, or that you don't have the time to learn it all, then there's a simple solution for that too: hire someone to design it for you. The money you spend on that will buy you peace of mind, and can actually save you money in the long run, in many ways. - Stuart -

Anything less is not going to be good isolation at all. To get to the same level of isolation using mass alone, is going to cost you a lot more

When you say I won’t get the same level of isolation by using mass alone, do you mean if I don’t float the floor? Or if I don’t build an inner leaf? or both! I pretty much have my mind made up about building the inner walls and ceiling. I’m just unsure about the ‘drum riser’ aspect, will the transmissions from the floor make a significant impact on the inner walls? I know budgets can shoot up and I don’t really want to spend the extra money for this element unless it will make a significant difference. I suppose I could do it after the room is built in any case. Another thing I wondered about was acoustic sealing, i.e. under the base plates of the stud walls the gaps between drywall-is it a case of literally sealing everywhere where air could pass through?, guessing that will take a lot of sealant! I think it will be beneficial to get a cheap sound level meter to test how much isolation I need and am currently getting. I’ll have a dig around for an assignment I did at university creating contours and measuring Sound transmission Loss. Vaguely recall pink noise, protective headphones and 5 measurement points in each room! If I use the spectrum analyser on my DAW, what would it involve, playing pink noise to determine the amplitude of each frequency? Without testing, if I aimed for approx 30db + of isolation via the inner leafs that should garner good results, though that maybe too presumptuous for the scientifically minded. At the moment I may even be getting more than the typical 25-30db as the brickwork is solid, about 2-3 bricks deep! though the industrial type building is cavernous so noise from other places in the building still resonate somewhat. Am I right in thinking that thhis 30db+ isolation would attenuate those 'out-to-in sounds too? I have some indentations that I need to fill in and can’t remember previous advice about how to fill it in. one indentation is a past doorway, the other a section of horrible breeze block, I recall you mentioning equalling the mass of the rest of the wall. Is brick covered with stucco plaster the way to go or layers of plasterboard with insulation? I have pics below to clarify I also have some thick multi-core electric cable at the top of the wall that would need to go through the plasterboard somehow. Am I right to assume that lowering my ceiling to bypass this is preferable to having the cables penetrate the plasterboard and seal the holes with grommets, acoustic sealant and those putty pads that block fire? Sorry for so many questions, just trying to make sense of everything, it's a steep learning curve. Thanks for the encouragement, you make it sound less daunting & like you, 'that’ll do wont do!' Rob

When you say I won’t get the same level of isolation by using mass alone, do you mean if I don’t float the floor? Or if I don’t build an inner leaf? or both!

If you don't build the inner leaf. Mathematically, if you only have one leaf, then the amount of isolation you get is defined by mass law, which basically says that each time you double the mass, you get an increase of 6 dB in isolation. That isn't very much! And in reality, it is more like 4 or 5 dB, since "real" mass doesn't act exactly like the "perfect" mass that is assumed by the equations. And since isolation also depends on frequency, the amount of isolation you get also increase by 6dB in each octave, as you go up. On the other hand, by using a two-leaf system, you switch to a whole different ball game: Mathematically, your isolation increases by 18 dB per octave! That's a major improvement. So mass is your friend in both cases, but it is an awful lot more "friendly" with two-leaf MSM construction! You can use a lot less mass and still get really good isolation.

I’m just unsure about the ‘drum riser’ aspect, will the transmissions from the floor make a significant impact on the inner walls?

If you don't isolate the floor from the walls, and if the floor is not damped, then yes. If the walls are firmly attached to the floor, and the floor is not a concrete slab sitting on the ground, then the floor is basically acting like a drum head, and will vibrate easily, thus transmitting the vibrations to the walls. But if the floor is damped, due to sitting on the ground, then that is greatly reduced. Or if vibration and impact cannot get into the floor in the first place, that's even better! And that's where the concept of the "drum riser" floor comes in, just as you explained above "Now onto the floor! I read some 'heavy hitters' say in another thread that a cheap compromise to floating the floor is to use 2 layers of plywood sandwiched with GG sitting on top of 2 inch OC 703."If you can afford the lost room height (nearly 4 inches), then this is a good alternative to floating a floor, as it keeps impact out, and reduces the amount of vibration that can get through. It even damps the floor a bit, too.

...budgets can shoot up and I don’t really want to spend the extra money for this element unless it will make a significant difference. I suppose I could do it after the room is built in any case.

That would be the smart way of doing it! First build the room, then see if you need it. Of course, the entire acoustics of the room will change if you build the "drum riser floor" later, since you'll be reducing the height by those aprox. 4 inches, but that might be a small price to pay for the added benefit.

Another thing I wondered about was acoustic sealing, i.e. under the base plates of the stud walls the gaps between drywall-is it a case of literally sealing everywhere where air could pass through?, guessing that will take a lot of sealant!

Yes, and yes! Most people don't realize how critically important it is to seal both leaves absolutely air-tight. If air can get through somewhere, then so can sound, even through a very tiny crack. So yes, you do need to seal everything, and especially the sole plates of the walls. You normally have at least 5 seals down there...

I think it will be beneficial to get a cheap sound level meter to test how much isolation I need and am currently getting.

Absolutely!

If I use the spectrum analyser on my DAW, what would it involve, playing pink noise to determine the amplitude of each frequency?

Exactly, that's one approach. But you also need to test with music, of the type you plan to play/record in your room! Pink noise is constant, but music is not: there's beat, rhythm, impact, etc., and you need to hear ans measure how that works too.

Without testing, if I aimed for approx 30db + of isolation via the inner leafs that should garner good results,

Well, you can't really consider "how much will the inner leaf add", since it doesn't work like that: Adding the inner leaf changes the entire ball game! It's like asking "I have a fish: how much better is a bicycle?". It's two totally different things, not really comparable. As soon as you add the second leaf, you are now using a very different principle of physics to block the sound. So saying "My existing wall gives me 20 dB, so adding another one the same will give me 40" simply is not correct. You can't add fishes and bicycles! :) Rather, you should be aiming for a final number, then looking at the type of construction you need to get there, based on the type you already have, but not considering the ISOLATION you already have. I guess that sounds rather confusing....

At the moment I may even be getting more than the typical 25-30db as the brickwork is solid, about 2-3 bricks deep!

Theoretically, you should be getting around 40 dB at 1 kHz, dropping by 6dB per octave at lower frequencies, and rising by 6dB per octave at higher frequencies.

Am I right in thinking that thhis 30db+ isolation would attenuate those 'out-to-in sounds too?

Yes, isolation works both ways.

I recall you mentioning equalling the mass of the rest of the wall. Is brick covered with stucco plaster the way to go

Yes, definitely!

I also have some thick multi-core electric cable at the top of the wall that would need to go through the plasterboard somehow. Am I right to assume that lowering my ceiling to bypass this is preferable to having the cables penetrate the plasterboard and seal the holes with grommets, acoustic sealant and those putty pads that block fire?

Yes! But you don't need to lower the entire ceiling: just the parts where the cables are. - Stuart -

Had to nip out to pay the bills again! :lol:

You can't add fishes and bicycles!

Lol Oh believe me, I’ve tried many times!

I guess that sounds rather confusing....

Does… but it makes perfect sense! Though I’m not quite there yet I guess this Mr Anderson is starting to get glimpses of the binary code! You've sold me on the drum riser- no point going half the way! Just curious as to how you'd go about constructing one, do you build the thing in pieces? will I have to make a frame or butt it against the inner walls, how does it sit stable?

So yes, you do need to seal everything, and especially the sole plates of the walls. You normally have at least 5 seals down there...

When you say 5 seals, how would you do that, you mean 1 bead of sealant along each edge and three in between? Also wondered what type of acoustic sealant is best for the job or will any do? Is there a calculator to determine how much I would need to order for the size of my room? I've been imparting your wisdom to other enthusiasts, they're amazed - I appreciate your time & patience Thanks Rob

I'm also interested in a calculator to help determine how much acoustic sealant to buy. Liquid Nails now has an acoustic sealant out and looks to be one of the more inexpensive options out now. Is there a good method of calculation available?