John Sayers' Recording Studio Design Forum

Hello everybody. I'd be grateful for a bit of advice on a new studio I want to build in my first floor flat. I'm located in the UK and the aim is to have a high quality project studio where I can record live instruments such as amplified guitars and drum kits. In other words it's going to be very loud. The studio will be located in one room only and currently no work has been done or any equipment purchased.

The flat is brick built and sits above another identical flat below. There is no other accommodation above my flat. All external and internal walls are cavity walls ie. two layers of brick with a gap in between. The floors are steel reinforced concrete about six inches thick and the roof is a standard construction with outer tiles on a wooden frame and inner ceilings of plasterboard mounted on wooden beams. The nearest neighboring houses are about 10 meters away. The flat layout and studio dimensions are shown below:





My biggest worry is obviously the flat below. Will it be possible to achieve sufficient isolation so as not to disturb people below. At the moment it is possible to hear people in the lower flat if they speak loudly but it is muffled and individual words cannot be heard. Would a false floor be sufficient or would an isolation booth be required for instruments.

Are the walls sufficiently thick to contain this level of noise and would noise travel down the gap in the cavity walls to the flat below?

Can the window be sealed sufficiently without bricking it up.

And finally is the roof sufficient to contain the noise produced.

If it turns out to be impractical to play drums and use amplified instruments I would be satisfied to be able to mix at moderate volumes and record vocals without disturbing people below or in the surrounding area. In addition to advice on the soundproofing problems I would appreciate some ideas for the design of the studio itself given the dimensions and layout of the room. A design incorporating a vocal/instrument booth would be very interesting. My budget for the studio excluding equipment will be about £600.

Thank you in advance for your time

Andrew

Hi Andrew, and welcome to the forum!

You sure know hot to pick 'em, don't ya! Drums are the absolute loudest instruments out there, and the most difficult to isolate. They put out a lot of energy in low frequencies, which is the hardest part of the spectrum to isolate. And they inject impact noise into the building structure itself, which is even harder to isolate. And building on the second floor of a building (what you call the "first" floor in the UK, but meaning "the floor above the one that sits on the ground") introduces issues of its own, making it even harder to isolate.

OK, so before you throw up your hands in despair and decide to switch careers to become a beach bum, let me say this: It can be done. It is possible to build a well isolated drum booth on the second ("first") floor of a building. Like most things in life, it can be accomplished if you throw enough time, effort and especially money into it, which leads to the issue of budget.

Let me explain how you would go about it, and how to figure out your budget, to see if you want to do this.

But before going into that: your second option, of just having a mix room at moderate volume, is most certainly doable, and on a much smaller budget.

OK, so to isolate loud sounds you need a few basic things: mass, decoupling, and damping. "Mass", as in very heavy, dense materials, such as gypsum board (a.k.a. "drywall", brick, concrete, glass, etc.) "Decoupling" as in separating "you" from "them" mechanically, such that there is no direct path for sound to take. And "damping" as in things that stop resonance. The good news is that you already have some of that, just incomplete.

You have mass, in your brick walls and concrete floor. That's good. The bad thing is that you are sharing your mass with others: your floor is your neighbor's ceiling, etc. So anything that makes your floor vibrate also makes their ceiling vibrate, thus transmitting sound: There are two ways that such "vibration" could happen: airborne noise, and impact noise (structure-borne). Airborne noise means that sound waves are emitted by your drums into the air of your room, and the vibrations in the air cause the floor itself to vibrate. Impact noise means things like, for example, foot pedal impacts causing the floor to vibrate directly, or transmission of vibration through the legs of the drum kit into the floor, or through the guitar cab into the floor.

To deal with both of these, you have to "decouple" the sound source form the floor. In other words, you have to create a second barrier that is not in physical contact with the floor: it is "decoupled". So, for example, you set up a second massive platform a few inches above your existing floor, with an air gap between. That is called a "floated floor", and works extremely well. But it is not easy to do right, and is expensive. The problem is that when you have two massive surfaces with an air gap in between, you have created an acoustically resonant system: it will resonate really well at one specific frequency, and will therefore pass sound excellently at that frequency, while isolating all higher frequencies increasingly well. Technically, it is a "Mass-Spring-Mass" system where the air trapped between the two is the spring, and like all Mass-Spring-Mass ("MSM") systems, it rings loud and clear at its natural resonant frequency.

So you have to "tune" that resonance such that it is much lower than all of the frequencies you need to isolate. You tune it by using the right amount of mass on each side, and the right size of air gap between.

Finally, you also need to "damp" that resonance by putting something in between the two "masses" (also called "leaves"), such as mineral wool or fibergalss insulation, which helps to absorb the resonance, kind of like the shock absorber works on your car suspension. In fact, your car suspension is also an MSM system: the car body is one "mass" the wheel and axle is the other "mass", there is a spring that ties them together, and there is a shock absorber to damp resonance.

OK, so now you have the basis for isolation: If you want to isolate something loud (such as drums, for example), then you enclose it in a fully decoupled two-leaf MSM system. This concept is often referred to as "room-in-a-room", since you basically take your existing room and build another one inside it, a little smaller. The air gap all around the room is what does the trick: that is your "spring" that makes the whole isolation system work.

OK, so that's the theory; You float a new floor on top of your existing floor, then build some new walls on top of that floor, then build a new ceiling on top of those new walls. And NONE of that can touch the existing room AT ALL! Not even a single nail: the entire thing "floats".

If you were building on the ground floor (the one where the floor actually physically rests on mother earth), then you would no need to float your floor, since a thick concrete slab has lots of mass, and is directly damped by the entire planet (!), so that's hard to beat for isolation. In that case, you would only need MSM walls and ceiling.

But since you are on the second (first) floor, that changes things: the room below you is also an MSM system! It has a mass above (their ceiling = your floor), it has mass below (their own floor), and it has air in between. So it too can resonate, and you can bet Murphy's law will kick you really hard here, since Murphy guarantees that their room will be tuned to the note that you play most frequently and most loudly in your room!...

OK, so the ideal situation would be for you to float your room. But that is darn expensive, and hard to do. The best way to do it is to use proper isolation springs (instead of just air), set those on your existing floor, build a plywood deck on top of them, pour a layer of concrete on the deck, jack up the springs, then build your walls and ceiling on that. As you fall out of your chair, you'll realize that this is probably not what you had in mind for your room!

Fortunately, there's a second option: don't actually float it, just decouple it a bit. You can lay some panels of semi-rigid fiberglass insulation on the existing floor, put a couple of layers of thick plywood on top of that, and you are done. That will isolate your floor quite well for both impact noise and airborne noise. However, you can't build walls on top of that. So you build your new walls and ceiling on the existing concrete floor before you do that, then add the isolated floor at the end.

The new walls will just be simple 2x4 studs with two layers of 16mm drywall on only ONE side of the studs. The new ceiling is the same: wooden joists (correctly dimensioned for your span) supporting two layers of 16mm drywall. The drywall plus the air gap plus the existing walls is also an MSM system, so it is tuned to a frequency below what you need to isolate.

For your your window, there are two options: Leave it as-is (just seal up the edges air-tight) and add a second window in your new "inner-leaf" wall, so that you still get natural light and the view, if that's what you want. Or you can build a "window plug" to seal it off. Basically, that's just thick plywood on a frame with rubber and insulation.

That implies isolation in the region of 30-something decibels. (Loud speech is around 75 dB, and you seem to be describing what you are hearing as around 40 dB.) So clearly, there are flanking paths here that are bypassing your floor. A 6" concrete floor should do better than that. My guess is ventilation ducts, electrical conduit, poor sealing, or simply out through their window and in through yours.

To put that in perspective, a drum kit puts out about 115 dB, so getting that down to the same "muffled, indistinct" sound that you are getting from their voices right now, implies isolation on the order of around 70 dB. In other words, you need to stop about ten thousand times more energy than your home is stopping at present. Literally, ten thousand times. A change of 40 dB (increasing isolation from 30 dB to 70 dB) is an increase of 10,000 times in energy. that gives you an idea of how hard it is to isolate loud sounds, and why this is not an easy task.

If you wanted to just make this into a mix room, then "standard" monitoring level is 85 dB, with maybe occasionally peaks of 95, so you'd only need about ten to one hundred times more isolation than what you have now.

So that's should give you a rough idea of what can be done, and how to go about it. Either way, there's a huge amount of info on the forum about how to do it. So you are in the right place, for sure!


- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

Thank you very much for your reply Stuart, this is very helpful.

I think I may have to abandon the idea of recording drums in that room as I don't think my flat would structurally support a floated floor with an additional concrete layer. It may do but I think I would have to consult a surveyor to be sure. I'm also worried that I could do all that work and find the isolation still wasn't sufficient.

How good is the method of using a fibreglass layer with boards on top compared to a floated floor? If that was pretty good I might just go for a mix room using that method. If I did that would it be necessary to build a vocal/instrument booth or would there be sufficient isolation to be able to sing and play electric guitar without being heard downstairs.Also do any additional stud walls need insulation on the back of them or could I get away with not using it due to the solid brick walls?

Finally,there's the possibility of using a space in the loft for the studio instead. Would a room within a room structure built in my loft provide sufficient isolation both for the ground floor flat and neighboring properties. The advantage is the large air gap between the loft floor and the floor of my flat (2.4m). The disadvantage is that the roof is very porous to the outside world and traffic noise from the road outside is quite loud. However I have a feeling this may be a better solution. If so would amplified guitars and perhaps even drums be possible in this space. What kind of floor and walls would be best. Would a two layer plywood floor mounted on rubber strips be sufficient? And would it need a single or double stud wall structure?

Thanks again for your help Stuart, much appreciated.

Looks like I left you with more questions than answers! That's normally what happens: acoustics isn't all that intuitive, and does get to be rather confusing!

I'm glad you thought of that! I should have mentioned it. Yes, that is the other big issue with building on upper floors (ones that do not rest directly on the ground). Isolation implies mass, and the more isolation you want, the more mass you need to get there, so regardless of which plan you choose, you'll still need to get a structural engineer involved to confirm that your building can handle the extra mass. With existing brick and concrete structure you should be OK, but don't take my word for that! I'm not a structural engineer and have no idea about your building or about your local codes anyway, so getting a qualified engineer involved is very necessary. Once you have your room designed, call him in and show him the plans, and the existing place, then get him to put his stamp and signature on that.

If you did it all correctly, then you would get the level of isolation you want. But the issue is the precision of the workmanship (and of course the money!). Building this type of decoupled, isolated structure is not something that most contractors do every day, so they are not aware of the pitfalls and care that is needed. It just takes one stray nail or blob of mortar that happens to bridge your air gap, and that can severely degrade your isolation. Ditto the careless workman who forgot to seal up a gap somewhere, or a careless electrician that knocked a hole in your brand new isolation shell so he could install a light switch... This is not like building a normal house, office or shop, so the builders and tradesmen all need to be aware of what they are doing, and supervised like a hawk!

The concept of "massive plywood deck on fiberglass insulation" is actually the same concept as used in drum risers. A "drum riser" is just a platform, built exactly like that, just big enough for the drum kit to sit on, in an ordinary studio. They are commonly used to isolate the drum kit from the floor, and they work very well.

so, to answer your question: for impact noise it is fantastic, and works pretty well for airborne noise too, but not as well as a proper floated floor. I guess that perhaps the best option here is to build the room so it can be used either way: build it and see if it is good enough for drums, and if not then it will still be darn good for your control room (mix room).

You'd be fine for vocals, acoustic guitar, and similar things, and probably also fine for electric guitar, provided that you don't crank it up to eleven! Keep it to reasonable levels, and isolate the amp/cab from the floor, and you should be OK.

The insulation in the stud wall is the damping on the MSM system: it greatly increases the isolation, at low cost. It's probably the cheapest way of increasing isolation in an MSM system. The difference is somewhere in the range of 5 to 16 decibels. 5 decibels if you just put a thin layer in the gap (say 2" in a 4" gap), and up to 16 dB if you entirely fill a 6" inch gap. So probably around 10 dB is what you'd get in most cases. And ten dB is huge! That implies that you are blocking ten times more energy, thus reducing the subjective sound level by a factor of two: You'll be cutting the sound level in half by putting the insulation in the gap. That's worthwhile!

However, don't get me wrong: the insulation by itself is useless! If you just put a 4" layer of insulation on the existing walls WITHOUT building the second leaf, then you get zero isolation from that. Nothing at all. Insulation by itself does not stop sound: it merely attenuates it slightly. But when it is part of an MSM system, then it works wonders. The whole is greater than the sum of its parts.

It works like this: as I mentioned my previous post, the wall is an MSM system (MSM="Mass-Spring-Mass"). All the parts work together to do something that none of them can do alone. It is a tuned system, and is tuned to a frequency set by the amount of mass on each leaf (how many kilograms per square meter of wall) and the depth of the gap between the leaves. More gap=lower frequency=better isolation. More mass=lower frequency=better isolation. So either increasing the mass or increasing the air gap (or both), reduces the resonant frequency (F0), wich implies better isolation.

For tones that have the same frequency as F0, the wall is transparent: those tones go right through as though it wasn't even there. In fact, the wall can actually amplify those tones, making them louder on the other side! But for all higher frequencies, the wall isolates: it acts like a tuned electronic circuit, a bandpass filter (think of it like a parametric equalizer set to boos a certain range of frequencies). So there is a range where it boosts, but outside that range it isolates. At 1.4 x F0 it stops being transparent and starts isolating. at 2 x F0 it isolates reasonably. At 3 x F0 it isolates well, and it just keeps getting better and better the higher you go. In fact, theoretically the isolation improves by 18 dB per octave, all the way up the scale. So high frequencies are isolated really, really well, but low frequencies not so well.

So obviously, the idea is to "tune" the wall to a frequency of not more than half of the lowest frequency you need to isolate. For the kick drum, the fundamental tone is probably around 80 Hz. or so (depending on how you tune it), so tuning the wall to 40 or lower would be good. But bass guitars easily go down to 35 Hz, so that would need a wall tuned to 18 Hz. Normal hearing range is considered to be 20Hz to 20 kHz, but other things can go even lower than that. For example, if you are doing effects work for major movies, then there could even by sub-sonic stuff going on in your mix (earthquakes, explosions, deep rumbling machinery, etc.), so you'd need the isolation tuned way low for that. So your first order of business should be to determine what frequencies you need to isolate, and how much isolation you need at the lowest frequency.

On the positive side, human hearing is less sensitive to low frequencies than it is to mids and highs, so you don't need as much isolation (in terms of decibels) to make low rumbles inaudible. There's a set of graphs, called the Fletcher-Munsen curves, that show how sensitive average human hearing is at different frequencies, so you can also take those into account with your estimate of levels and frequencies.

But of course Murphy is in this too, and he gets you on the other side of things: Even though we don't hear low frequencies that well, it turns out that low frequencies are the hardest to isolate, and they also carry over larger distances. In order to stop very low frequencies, you need huge amounts of mass. Have you ever walked past a disco, bar or night club where they are playing loud music? What do you hear from far away? "Thump-thump-thump". All you hear is the kick, snare and bass, not the vocals, keyboards, guitars or cymbals. You hear the lows, since they are the hardest to stop, and their sound carries further.

Maybe, maybe not. It's hard to say, since so much depends on the actual structure, how it is built, where the flanking paths are, etc.

Yes, but that's on only one side of the room: what about the other five sides?

I often use this analogy: your room is like an aquarium: it needs to be isolated to the same level on all sides to stop the sound "leaking out", just like an aquarium needs glass on all sides to stop the water "leaking out". You can't say "Well, I only want to look at my fish from the front, so I'll only put glass there, and I'll just put cardboard on the other sides"... Clearly, that won't work. You need the same level on all sides to keep the water in, because once it gets out, then it is out and will splash around all over. Same with sound: you can't isolate in only one direction, as the sound will simply take all the other non-isolated paths, and go around the isolation. So regardless of where you build your room, you still need to isolate to the same level in all directions.

For example, if you build a floor, ceiling and three walls that get you 50 dB of isolation, but you only built the fourth wall for 30 dB because "nobody lives on that side", well then your entire isolation is 30 dB, not 50 dB, in all directions. The weakest link rules.

can yo beef that up somehow? Can you add a whole lot of mass to the roof, and seal it air-tight? If so, then it is an option. If not, then you are probably better off with the original plan.

Walls, floor and ceiling! Don't forget the ceiling: It is just as important as the walls and floor.

The basic plan that most people here use for their rooms is this: 2x4 stud framing for the new walls, resting directly on the existing floor, not touching the existing ceiling or the exiusting walls at all: this is a free-standing structure, that touches the floor only. Now put one or two layers of 16mm drywall on those studs. Both layers go on the same side of the studs! Very important. (If you put one layer on each side, then you have created a 3-leaf system, which will give you WORSE isolation for low frequencies, believe it or not). Then put joists across the top of those new walls, touching only the walls (not the existing walls or ceiling), and hang one or two layers of 16mm drywall form those. (The joists have to be dimensioned correctly for the span and weight, of course.) Fill all the gaps between the new drywall and the original walls with insulation (either mineral wool or fiberglass, of the correct density, but not spray-foam, polystyrene, or other similar things). Seal everything air-tight. Done!

Two layer plywood deck? Yes. Rubber strips? No. Well, OK, it could be "yes" if calculated correctly and built right, but the issue is this; rubber is a spring. So now, instead of using air as the spring in your MSM system, you are using rubber. The resilience of rubber ("springiness" if you prefer) is very different from the resilience of air, and it depends on the type of rubber, the thickness, and the surface area. You have to do the calculations to make sure that the floor actually does float. In other words, you have to figure out the total mass on the floor, including the weight of people, equipment, instruments, the floor itself, and anything else that might rest on it. Then based on that weight, and on the characteristics of the type of rubber you are using (for example, EPDM, neoprene, sorbothan, etc.) you will have to figure out how much total surface area and thickness of that rubber you need in order that it is compressed to the right percentage deflection in order to float. If you overload the rubber (too much mass) then it "bottoms out" and does not isolate. If you "underload" it (not enough mass to compress it correctly) then it "tops out" and does not isolate. For any give type of rubber there is a range of deflection where it isolates well, and you have to to the math to make sure that you have the right amount of rubber in the right places under your floor to ensure that it is, in fact, compressed correctly for the amount of mass on the floor.

Let's go back to the shock-absorber example, since that is easier to understand. Your car has a suspension system, consisting of springs and shock absorbers for each wheel, and that is what gives you a smooth ride, since the spring and shocks are "tuned" to the mass of the car and the wheels. If you take the springs and shocks from your car and install them on a bicycle, they wont work at all: the bicycle simply does not have enough weight to compress the spring to the point where it can "float" the bike: basically, the spring acts like a solid steel rod, and there is no "bounce" in it at all. On the other hand, if you take those same car springs and shocks and install them on a heavy truck, they also don't work. Now, the spring is completely squashed down, totally flat: once again, it acts like a solid steel rod, with no bounce. Your springs and shocks only work on YOUR car, since they were carefully designed to support the range of weights that your car can handle, neither more nor less.

Same applies to your plywood deck floor floated on rubber strips: Yes, that can work, provided that you do the math and build it right for THAT exact type of rubber, and with THAT exact load on the floor. If not, then it ends up being even worse than no deck at all, since there is still an air gap underneath (between the rubber strips), which is a resonant cavity...

Murphy's law is a bitch! It gets you no matter what you do, ... unless you do it right.

Double. Always double, never single, never triple.

For a single wall, or "single leaf" in acoustic parlance, the amount of isolation is determined by a principle of physics called "mass law". Mass law says that each time you double the total mass of a single-leaf wall, you get an increase of only 6 decibels in isolation. That isn't much to get enthusiastic about.

For example, consider a brick wall, such as your existing brick wall: even though it is a cavity brick wall, the two layers of brick are still tied to together internally, so it acts as more like a single leaf than a double leaf. Let's say that it is getting you 40 dB of isolation at present (for example), and you need to get to 70 dB of isolation (for example). If you just try to get there by adding mass, this is how it would work: to double the mass, you add another two layers of brick, so you go from 40 dB to 46 db of isolation. Double the mass again by adding FOUR new layers of brick, gets you 52 dB. Double the mass again, (add eight more layers of brick! (!) )and you get to 58 dB... Double the mass again (add 16 new layers of brick) gets you to 64 dB ... I think you see where this is going! It ain't going no place useful!

Clearly, mass law from a single leaf wall is not something to get all jumping-up-and-down excited about!

On the other hand, a two leaf MSM wall will get you an increase of 18 dB per mass doubling. That's a lot more to be excited about!

So if two leaves is good, then three leaves must be better, and four leaves must be fantastic, right? Well, yes but no. A 3 leaf wall will indeed get you 24 dB increase in isolation per mass doubling, but Murphy gets you here too! A 3 leaf wall does not have just one resonant frequency: it has two resonant frequencies, called F+ and F-, and they are BOTH much higher than the F0 frequency of a 2-leaf wall. So even though you get much better isolation for high frequencies with a 3-leaf wall, you get much WORSE isolation for low frequencies: You can compensate by using larger air gaps and more mass on your wall, but by the time you did that the wall is now thicker and heaver than it would have been if you would have used only two leaves.

Sigh! Damn Murphy!

So the rule is this: 2-leaf, only 2-leaf, nothing but 2-leaf. Never one leaf, never three leaf, or any other number of leaves. The only thing that makes sense is two-leaf. (Having said that, sometimes you have no choice but to build a 3-leaf wall: in that case, you can compensate with more mass and bigger air gaps, but it is better to avoid that where you can).

- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

Thanks again Stuart.

Lots of very useful information there. The stuff about mass doubling and multiple leafs is particularly interesting. Glad you told me that as I was thinking at one point of just adding lots of plasterboard to the walls but I can see now it would not be very effective.

I think I'll go for the fibreglass and plywood solution. It sounds like it will be quite good enough for a control room and for recording vocals etc. I've abandoned the loft idea as its too much work and cost as the floor would have to be strengthened and there are pipes and electricity cables everywhere.

Just a couple more questions for now. What grade of fibreglass is required and how thick would you make it? Also I have been reading Johns recording manual and he says putting a layer of fibreboard between the plywood boards improves isolation. Do you think that is worth doing?

All the best

Andrew