Hello!
This is my first post, hope I don’t screw up =)
I’m from Sweden so if some sentences seems like they are written by a five-year old, it’s because of that.
Like the title suggest I’d like some advice regarding sound isolation for a tracking-room/vocal booth. I’m planning to build a room-within-a-room in my hallway. At this stage it’s not about how much material I need for a specific STC-rating or so. I'm wondering which method’s the best.
My wish is to be able to do vocal (scream as loud as I can :wink: ) and acoustic guitar at any hour of the day, including night, without bothering the neighbors (see attached file for an overview of the hallway and adjoining rooms that also show where I plan to build my booth).
Adjoining wall to neighbor is concrete (don’t know how thick, say 7-8’’), ceiling/floor is concrete and bedroom wall is drywall-frame-drywall (don’t know whether that’s relevant).
If I have got it right, instruments such as vocals and acoustic guitar is more airborn-sounds than impact-sounds. If that’s correct, does it minimize the need of decoupling? How should I think here? Is it always a matter of compromise or should I head straight for mass-mass and again mass if that’s what would gain me the most?
Another thing I was wondering about was how crucial it is to keep a distance from the original wall when building a RWAR, and in this case when the walls are made of concrete. Ideally I want to build as close as possible without connecting, but if every inch improves sound isolation I of course have to take that into consideration.
So to summarize:
1. What option should I go with when building a vocal booth intended for vocals and acoustic guitar?
2. What do I gain from maintaining a distance from original walls of concrete when building a room-within-a-room?
To be clear, I'm not asking for specifics (that would be hard to give with the information I provided), but rather what I should take in priority.
Thanks in advance
Peter
EDIT: Hope I explained myself clearly, or at least understandable. I forgot to mention a budget. I would hope I could get away with 2000$, seing as it's only a vocalbooth. That budget doesn't include acoustic treatment, and considering the approximate room ratio, I guess I'll need some...or lots.
Sound isolation for tracking-room/vocal booth
Originally posted at johnlsayers.com, topic 18115.
I would really appreciate some help here :)
" but if every inch improves sound isolation I of course have to take that into consideration."
In this specific instance what you are doing is building a single booth inside of an existing room, correct?
You would want to have at least 12 inches of clearance between the new booth and the existing walls to get a better transmission loss.
Since you are not building a room in a room.
If you ARE building a room in a room, then everything changes, the distance of 12 inches increases to about 3 feet and you have to give us more details about what you are in and what you want to construct.
Make sense?
Thank you for the response! I think I’ll need a little explanation of some physical laws though =)
By the way, I’ve noticed that the wall between my hallway and bedroom wasn’t drywall-frame-drywall. It is solid, some sort of light weight concrete I guess.
When you say “12 inches”, do you mean a 12 inch gap and then framing-drywall or do you mean 12 inches from existing wall to new walls end (i.e. last layer of drywall)?
This is probably totally wrong, but when I’m thinking room in a room, I’m thinking drywall>framing>airgap>framing>drywall, not regarding any existing walls or ceiling; Outer ceiling rest on outer walls and inner ceiling rest on inner walls. I’m trying to understand why there’s a problem having such a construction standing with just a couple of centimeters from existing walls and ceiling.
If the alternative is to build a single wall apart from the existing walls (i.e. existing wall>airgap>framing>drywall, is there really a purpose in letting the other two walls, those two not directing existing walls, be constructed in any other way? I Mean, wouldn’t the sound transmission loss be the same everywhere at the moment the sound reached through the new construction?
Not so easy to explain, but I hope it went through.
A couple of years ago I built a wall to reduce sounds coming from my living room to my bedroom. The existing wall is made of 7 cm light weight concrete (again, not 100% sure about the material. Whatever it is, it’s solid anyway). I left an airgap of 2,5 cm followed by light gauge steel framing filled with insulation, and double drywall on top of that. I had borrowed a Sound Level Meter from my local authorities. Initially, before any changes were made the sound coming through the wall registered at 55 Db. After the steel framing and insulation were installed it registered at 35 db and the drywall (+ caulk) added an additional 7 db reduction.
This experience left me with the notion that it shouldn’t be impossible to reduce sounds from singing and acoustic guitar to the level that it wouldn’t reach neighbors, seeing as the present sound isolation in this house is already pretty decent. What I wonder is what role decoupling plays when it comes to reducing sounds of that character; If it’s important or if it’s just a waste of space and what I really should do is to add like five layers of drywall all around me and I’ll be safe.
I don’t know what information I should add regarding dimensions, surrounding and so on. As I said, neighboring walls are 20 cm concrete, same with the floors and ceiling (see original attached picture). Let’s play with the idea that the STC-rating between me and my neighbors lands on 50. With my goals, as mentioned above, what method should be the most successful for reducing sound transmission? I can’t build a room with a 3 feet gap from the original walls. I would have no hallway left and I wouldn’t fit in the vocal booth I built anyway. Aren’t there a couple of alternatives here?
Thanks
Peter
Hi Peter, and welcome! :)
Just adding to what Brien said:
The best method at the lowest cost is the famous fully-decoupled 2-leaf MSM "room in a room" system. See below...What option should I go with when building a vocal booth intended for vocals and acoustic guitar?
More isolation. :) The basic principle of a 2-leaf MSM system is that it is tuned. The wall consists of an outer leaf, an air gap, and an inner leaf. In terms of the laws of physics, that constitutes a "Mass-Spring-Mass" system, where the air is the "spring". Air is resilient, as far as sound waves are concerned. So the system will resonate naturally at a certain frequency, and it will NOT want to resonate at all other frequencies. In other words, it acts like a notch filter, or a bandpass filter on your console's EQ. At the resonant frequency, it is a really lousy isolator, and lets sound straight through. But at higher frequencies, it is a darn good isolator. So the trick is to tune it low enough that the resonant frequency is way below the frequencies you need to isolate. You "tune" the wall in one of two ways: you change the mass on each leaf (make it heavier or lighter). Or you change the air gap (make it bigger or smaller). High mass and big air gaps get you the best isolation. So you have two possibilities, as Brien explained. If you are going to build your booth close to existing walls, then those walls will act as one leaf of your MSM system, and you therefore only need one extra leaf for your booth. But if the booth is going in a corner, then you have a problem: you only have existing walls on two sides of the booth, so you need to extend those around the other two sides, to finish off your outer leaf. In other words, you need to build the four walls of the booth as single-leaf, then build another two walls around the booth to finish enclosing it, also as single-leaf. On the other hand, if you have enough space in your hallway that you can have your booth a long way away from ALL the walls, then you can build it as a two-leafs system all by itself. So you would put up a stud frame put a layer or two of drywall on the outside, then put resilient channel across the studs on the inside to decouple, then attach drywall to the resilient channel. And of course, fill the gap between the leaves with insulation. Now, if you were to take that two-leaf booth and put it in the corner, you have a potential problem: those two walls in the corner can, potentially, act as a third leaf, which could REDUCE your isolation in low frequencies, believe it or no. This is due to some complicated mathematically reasons, and does not seem intuitive, but it is true. All other factors being equal a three-leaf wall will give you worse isolation that a two-leaf wall in low frequencies. It will be better at isolating high frequencies, but worse for low. But if the booth is far enough away from the existing walls, then the three-leaf effect becomes negligible again. It is all related to that critical air gap between the booth and the walls. So in theory, you could have the situation where the booth isolates great 3 feet way from the wall, but if you push it up to just one inch away from the wall then your neighbor starts yelling at you to turn your darn music down, even though you are playing at the same volume. And one more issue here: if the existing wall is already a 2-leaf by itself, such as drywall on each side of 2x4 studs, then you have a FOUR-leaf system, which is even worse still at isolating the low end...What do I gain from maintaining a distance from original walls of concrete when building a room-within-a-room?
That's correct. That's the normal way of doing a "room in a room" WHEN THERE IS NOTHING ELSE AROUND. Ie, no existing walls or ceiling. That is not your situation, since you do have walls and a ceiling.This is probably totally wrong, but when I’m thinking room in a room, I’m thinking drywall>framing>airgap>framing>drywall, not regarding any existing walls or ceiling; Outer ceiling rest on outer walls and inner ceiling rest on inner walls.
Because you change the rules of the game. Mathematically, a different set of equations apply to that wall, since it is 3-leaf (or 4-leaf). Let me explain: Any time you have a large, solid, massive surface next to an air gap, next to something else, then you have a tuned circuit. If you add another leaf to that, also large massive surface with an air gap, then you have added ANOTHER circuit. You now have two circuits, and the affect each other. They do not act as separate systems any more, but as a single whole, where there are multiple interactions going on between the various leaves and air gaps. A normal 2-leaf wall has one single fundamental resonant frequency, generally called "f0" in the equations. A 3-leaf wall has at least TWO fundamental resonant frequencies, called f+ and f-, and they are BOTH higher than the "f0" would have been if the wall were built as 2-leaf with the same total mass and air gap. So basically adding the extra leaf, re-tunes the entire system, and a new set of equations come in to play.I’m trying to understand why there’s a problem having such a construction standing with just a couple of centimeters from existing walls and ceiling.
How did you managed to measure 28 dB? :shock: Not many meters are capable of measuring such low levels! They must have lent you a really nice one! Also, how did you measure that? What was your noise source? (speech, music, impact, white nose, pink noise, brown noise, etc.) And did you measure that with "A" weighting or "C" weighting, and fast or slow response? There's a world of difference between measuring a level of 55 dB with rock music on the "C" setting with fast response, and measuring 55 dB with white nose on the "A" setting with slow response. In any event, you got a 27 dB reduction in level by adding two layers of drywall (I'm assuming 5/8"), decoupled, with an air gap of just 2.5 cm, and insulation. Theoretically, the resonant frequency of that wall is 55.51 Hz, so it does not isolate below 78.5 Hz, isolates reasonably at 110.03 Hz, and isolates well above 166.54 Hz. So I'm pretty sure you didn't measure those levels with heavy rock music, with a deep, pounding kick-drum beat and lots of bass. That wall would have been about 10dB worse isolating at 55 Hz than the original single-leaf concrete wall... :) On the other hand, that wall will isolate quite well for speech and higher frequencies. I'm guessing again, but I reckon you probably measured with "A" weighting, and maybe white noise or perhaps just a radio or TV playing. Anyway, that worked because you followed the rules and built a proper two-leaf MSM wall. The original wall was already a single-leaf and reasonably massive. If that original wall would have been a typical 2x4 wall with 10mm drywall on each side, your solution would not have worked nearly as well, since you would have created a 3-leaf system like that. The resonant frequencies would have been 68.15 and 48.19, and it would not have isolated decently until over 204 Hz.A couple of years ago I built a wall to reduce sounds coming from my living room to my bedroom. The existing wall is made of 7 cm light weight concrete (again, not 100% sure about the material. Whatever it is, it’s solid anyway). I left an airgap of 2,5 cm followed by light gauge steel framing filled with insulation, and double drywall on top of that. I had borrowed a Sound Level Meter from my local authorities. Initially, before any changes were made the sound coming through the wall registered at 55 Db. After the steel framing and insulation were installed it registered at 35 db and the drywall (+ caulk) added an additional 7 db reduction.
Decoupling is major, big-time important! If you do not decouple, then you only have one leaf, and that's yet another ball game. Single-leaf walls are governed by yet another equation, commonly called "mass law", which is not your friend.What I wonder is what role decoupling plays when it comes to reducing sounds of that character; If it’s important or if it’s just a waste of space
Five layers of 5/8" fire-rated drywall has a surface density of roughly 60 kg/m2, so your isolation according to mass law would be 38.8 decibels (TL). :shock: Like I said: mass law is NOT your friend! That's barely better than a normal house wall with just 1 layer of 1/2" drywall on each side of the studs.... Four times the mass for just a slight 8 dB increase in isolation...what I really should do is to add like five layers of drywall all around me and I’ll be safe.
Actually, STC is not a good method for measuring the isolation of music. It was never intended for that, and does not take into account low-frequencies, which are the hardest to isolate. It is better to think in terms of TL (Transmission Loss) If your booth is ONLY for vocals, then STC is fine, but if you might use it to isolate an instrument or an amplifier, then STC doesn't tell you all you need to know.Let’s play with the idea that the STC-rating between me and my neighbors lands on 50.
OK, with a 20cm reinforced concrete wall, you should be getting about 50 dB of TL. At 50 Hz that would be down to 37 dB. So the question is, how much isolation do you need? You say that your goal is to not be heard when you "scream as loud as I can", but that's not a number! Some people have supposedly been clocked screaming at 128 dB! :shock: An average scream is maybe 110-115. OK, so maybe you weren't actually saying that you want to scream in there literally, just sing very loud. So call it 105 dB, at a rough guess, but you really should measure your own level. So, assuming you need to isolate 105 dB. The question is, how quiet do you need to go? That's the question you need to answer here: how quiet does your scream need to be on your neighbors side of the wall. Let's assume that he thinks 35 dB is about right. Dropping from 105 dB to 35 dB is a 70 dB reduction, which is pretty major! Fortunately, if we are only talking about voice frequencies here, then that is do-able, since the average human voice doesn't put out much energy in low frequencies, below about 150 Hz. But if you wanted to get 70 dB isolation for a bass guitar or drum kit, that's a different story. You would probably find that your iso booth would need a single layer of 5/8" drywall on ONLY THE OUTSIDE of 2x4 studs, with a gap between that and the concrete wall of about 6 inches (15cm), filled with insulation. Since we are talking about putting your booth in the corner, then you will also need to build the "other two sides" of the outer leaf around it. To do that, you need a second stud frame for ONLY those two sides, with an air gap of about 8 inches (25cm), and two layers of 5/8" drywall on ONLY THE OUTSIDE of those studs. That would theoretically get you where you want to go, assuming that you seal everything perfectly, and have suitable silencers in the ducts for your HVAC system for the booth. That also assumes a pair of doors, back-to-back, with double seals on each. It also assumes there are no flanking paths between your hall and your neighbors room. But the big question here is if my guesstimates are correct. You need a sound level meter to determine that. Find out how loud you REALLY scream, and find out how quiet your neighbor REALLY thinks is acceptable. - Stuart -With my goals, as mentioned above, what method should be the most successful for reducing sound transmission? I can’t build a room with a 3 feet gap from the original walls. I would have no hallway left and I wouldn’t fit in the vocal booth I built anyway. Aren’t there a couple of alternatives here?
Thank you Stuart for a very thorough answer! It’s a lot to take in and I feel what’s best now is to read up on what you’ve mentioned before posting a reply.
One thing I would like to ask at once though is about your example on how I could build a booth. I think I only partially got it, so I made a picture of how I’m interpreting it, more or less. Don’t look at it as an exact sketch; it’s just there to illustrate my questions.
The things I don’t get:
1. Are we talking 15 cm gap and THEN framing or is it 15 cm gap from drywall to existing wall?
2. On condition that there’s a 15 cm gap from frame to existing wall, am I supposed to fill that void with insulation as well? I’m thinking insulation inside of the frame and then a 15 cm airgap of… well, nothingness.
3. It seems odd to let the outer walls that have a double layer of drywall end without anything connecting to it. I guess I don’t want them to connect to the existing walls.
In my illustration there’s a staggered stud wall but that wouldn’t change the principle I suppose?
Even though you narrowed it down pretty well, I have the ability to completely misunderstand instructions. I would be more than thankful if you’d have the time to explain what I didn’t seem to get.
Thanks
Peter
In acoustics, "air gap" always refers to the distance between the actual hard, massive surfaces on each side, not considering insulation or anything else. It is the direct distance from the surface of the inner-leaf drywall to the surface of the outer-leaf concrete (or drywall, as the case may be). In fact the studs can actually go on either side of the drywall: it makes no difference to toe isolation if you put the studs in the cavity ("normal" or "conventional" construction) or in the booth ("inside-out" construction).1. Are we talking 15 cm gap and THEN framing or is it 15 cm gap from drywall to existing wall?
Filling the entire cavity is good, if you can afford to, and if your building code allows you to. It might not. Studs measure about 10 cm (depending on where you live), so with a 15cm air gap and conventional construction, you will still have a 5cm gap of "nothingness" ( :) ). If you can, filling that space too, as well as the stud bays, will add a bit of extra isolation: it drives down the resonant frequency even lower, improves damping, and adds more mass.On condition that there’s a 15 cm gap from frame to existing wall, am I supposed to fill that void with insulation as well? I’m thinking insulation inside of the frame and then a 15 cm airgap of… well, nothingness
It seems odd, because in reality they do have to connect! The outer-leaf must be a complete envelope, a full "shell" around the inner leaf, and it must be sealed air-tight, just like the inner leaf.3. It seems odd to let the outer walls that have a double layer of drywall end without anything connecting to it. I guess I don’t want them to connect to the existing walls.
It would not be easy to do that with staggered studs. It would be better to have separate stud frames for each leaf: that also increases isolation. Even the the studs are isolated with the staggered system, the sole plate and top plates are not, so there is still some flanking going on there. Staggered studs is much better than single studs, but double studs is the best of all.In my illustration there’s a staggered stud wall but that wouldn’t change the principle I suppose?
The other item is the way you drew the doors: For maximum isolation, each leaf has its own door frame and door. One opens outwards, the other opens inwards. The two frames do not touch.I would be more than thankful if you’d have the time to explain what I didn’t seem to get.
Yeah, this acoustic stuff can be pretty hard to grasp at first! Some of it does not seem intuitive at all, so it is much better to do what you are doing: draw diagrams and ask questions! :) - Stuart -Even though you narrowed it down pretty well, I have the ability to completely misunderstand instructions.
Hi again! Thanks for the input! This would be next to impossible without the help I’ve already gotten so far.
I’ve made another drawing, this time everything’s in scale. It’s still at a conceptual stage so studs placement and c/c distance are just crazy for now. I’m thinking 45 cm c/c for some reason, don’t know if that’s overkill and I should stick with 60 cm.
However, please take a look at the studs connected to the exterior wall. Is that the way the drywall is supposed to connect to be a full shell around the inner leaf?
For the double stud frame wall I’m thinking about using 45x70 studs (millimeters, translates 2 x 3’’). Though I’m not a building engineer, I’m assuming they could take the weight of the drywalls, even if I do double layers. The reason for that is just to save some space. As of now, I would still have 90 cm left of my hallway (to the left of the booth) and that’s pretty decent. I will have to check what load those studs can carry though.
I’m guessing that the ceiling should rest on the inner walls? That would make the space between the inner ceiling and exterior ceiling identical to the inner walls and exterior walls. Once again, I’m thinking about using 45x70 joists, and I’ll have to check if the studs can carry that weight.
I have drawn double layers of drywall also on the inner walls. What do you think, Unnecessary or not? I don’t think I’ll have the budget to buy Green Glue. Here in Sweden I can only buy a 19 litre (5 gallons) pail for 475 $ that would cover 33m2 (365 sq ft) and I would at the most need to cover 20m2. Anyway, that was just a footnote. Back to the question, double drywall everywhere, do or don’t?
The room dimensions aren’t exactly optimal, but I’ve expected that from the start. I’ll have to think about acoustic treatment later, or else my head will explode. I guess I will have some trouble in the 220hz region or something, but what the hell, at least I have a little room for some traps and stuff... like egg cartons…kidding =)
I haven’t mentioned the floor yet, but I want to get this part a hundred percent before I move on. HVAC and electrical will have to come later as well.
As I’ve said before, and I’m starting to repeat myself, this would be next to impossible without the help I’ve got and I’m really thankful!
EDIT: Just a footnote: I know the drywalls aren't suppose to overlap each other at the connection point as the illustration shows. I was just lazy when I drew it.
Hi again!
I still don’t know if I understood everything correctly about how the inner- and outer leaf are supposed to be built. I tried to draw how I interpreted your explanation. Don’t know if I got it all wrong or not.
Anyway, now I have a question about the floor as well =)
I haven’t touched that subject yet, because I wanted to get the rest first, but what the hell, let’s go!
I have got the impression that building a wooden deck isn’t always the way to go. But if I consider my concrete floor one leaf, wouldn’t I want to decouple the floor in my vocal booth from the existing floor to imitate the rest of the construction as far as possible? I don’t know if gravitational law makes the floor harder to decouple than the rest. I made a sketch of…well something (see attached image).
I’m thinking the inner walls should rest on the floor to avoid flanking. Don’t know if that’s really stupid or not.
Please feel free to question both this post and the last one! There must be a lot of things I’m missing here.
Thanks
Peter
Yup, that's it. You got it right. :)I still don’t know if I understood everything correctly about how the inner- and outer leaf are supposed to be built. I tried to draw how I interpreted your explanation. Don’t know if I got it all wrong or not.
True!I have got the impression that building a wooden deck isn’t always the way to go.
You can if you want, but you have a concrete floor that is resting directly on Planet Earth. It's hard to beat that for mass! :shock: There's an awful lot of planet down there, under your floor... Seriously, the concrete is way massively already, and the earth under the concrete acts as a damper, so you really don't need to do anything to that floor. There are two reasons why you see floated floors in studios: #1) The studio really does need it, because it is on the second floor of a building, or next to a railway line or major road that makes the ground vibrate, so they had to do it, and spent a fortune to get it done right. #2) The studio does not need it, but the people who build it didn't have a clue, and weren't smart enough to ask, so they did it anyway and it didn't work. Fortunately, you re not in the second group! :) And hopefully you won't need to be in the first group either... :) This might help to explain the issues about floating a floor: viewtopic.php?f=2&t=8173But if I consider my concrete floor one leaf, wouldn’t I want to decouple the floor in my vocal booth from the existing floor to imitate the rest of the construction as far as possible?
Yes it does, because gravity forces the inner-leaf to be in direct contact with the outer leaf if you try to float it. That's why most people don't even try. De-coupling a floor is not easy (see above thread), needs a lot of mass, and a lot of money. This is not a problem with walls, since they stand up vertically and gravity is not forcing the leaves together, but it sure is a problem with floors.I don’t know if gravitational law makes the floor harder to decouple than the rest. (see attached image).
Not stupid at all! If you really do need to float your room, that would be the way to do it for maximum isolation. However, that also brings in a whole bunch of other issues: the wall has to be attached to the sub-floor (and though that to foundations), so you then need isolation mounts and/or isolation anchors, and maybe seismic snubbers, sway braces and other expensive things to do that correctly, adding more cost and more complexity. So your idea is correct, but the implementation is not as simple as you might hope. And it is most unlikely that you need to do that anyway. Plain old concrete is actually a really good floor for acoustics, too. So just leave it as plain old concrete, or you could polish it, stain it or do other decorative things to it. Or if you don't like the look of concrete, then you could lay laminate flooring, or ceramic floor tiles, or lino, or something like that. - Stuart -I’m thinking the inner walls should rest on the floor to avoid flanking. Don’t know if that’s really stupid or not.