Hi Mike, and I'll add my welcome to Steve's.
A couple of additional comments, extra to what Steve already said...
I’ve measured the level of my band rehearsing and we got up to 115db, although we were generally around 105db. So if we call an average of 110db in one room, I would like this cut down to 40db in the neighbouring room. I don’t know if 70db of TL is too ambitious with the designs below, but that’s why I’m here talking to you guys.
Your measured levels sound very typical of rock bands, and your goal is reasonable. But also it is ambitious. As Steve said, you can get 70 dB of isolation if you want, but it does mean fairly massive walls with large air gaps, and lots of careful attention to detail during the build.
Originally I had drawn up a plan using timber stud walls with acoustic plasterboard, but after discussions with an acquaintance in the audio industry who has built studios before, we decided there was not enough mass in my design and the level of isolation would not meet my requirements
Actually, it can be achieved with drywall (plasterboard), but it does need several layers and reasonably large air gaps. By the time you get to that type of complexity, it probably is just as easy to switch to block walls, even though that introduces another set of issues and caveats.
My plan is to build individual room within rooms, utilising the MSM principal. 100mm concrete block wall – 100mm air gap – 100mm concrete block wall. Both walls will have a 100mm block and beam roof.
Whoaaa! Your diagram shows THREE-leaf walls!
That will REDUCE your isolation for low frequencies. It is better to go with only 2-leaf walls (plus they are cheaper and easier to build!). You really should get rid of those extra "webs" that are not supposed to be there.
Also, don't forget that block-and-beam ceilings require that you have access from above, in order to set the beams and the blocks in place, then put the final surface over it. You do seem to have enough room up there, but there will be costs associated with scaffolding as well as hoisting and lifting gear, to get the materials up there.
The internal dimensions of the block rooms will be 4m x 6m x 2.6 metres,
Can you adjust those? They aren't too bad for modal response, but it could probably be better if you were to play around using a room mode calculator, and see if you could get a smoother spread.
but will be slightly trapezoid in shape in an attempt to combat standing waves between parallel walls.
That's actually a myth, and it is not necessary to angle the walls. It only complicates construction, and then makes it difficult to fit things in the corners of the room, because the are not right angles. And it has next to no effect on the acoustics.
Let me explain, because this is one of those myths that refuses to die...
"Standing waves" are also known as "room modes". They occur any time that there is a path that a wave of a specific frequency can take around the room, and arrive back at its starting point, in phase with itself. You do NOT need parallel walls for that to happen! Standing waves will occur inside ANY shape room: rectangular, triangular, hexagonal, octagonal, dodecahedron, cylindrical, spherical... any shape you can think of for a room will ALWAYS have paths that a wave can take around the room, get back to where it started, and still be in phase. You cannot get rid of modes ("standing waves") by changing the shape of a room. All that you accomplish it to change the mode from one type to another, or move it from one frequency to another.
Yes, it is true that the modes that occur between parallel walls are the most prominent, and they are called "axial modes" because the occur along the 3 major axes of a rectangular room (length, width, height). Axial modes involve only two walls of the room. But there are also tangential modes, which involve 4 walls, and oblique modes, which involve all six walls. If you change the angle of one of the walls in a parallel pair by a large enough amount, then yes it is true that the axial mode disappears.... only to be replaced by a set of tangential and obliques! (which will be at higher frequencies). And you have now removed one of the most useful capabilities of the room: it's ability to support low-frequency modes. The goal with modal response is to have a large number of possible modes that are even spaced across the low-frequency end of the spectrum, so that no frequency tends to excite more or fewer modes than any other frequency. So the response of the room becomes smoother. If you get rid of low frequency modes and change them into high frequency modes, then you now have fewer modes down low, and they are spaced more unevenly, and further apart!
So it's not a good idea to even try to get rid of low frequency modes. Instead, it is a good idea to treat them, so that they are not overwhelming, and are fully under control.
Then there's the issue of how much you would need to angle the wall in the first place, to "get rid" of an axial mode. The angle is much larger than you'd think. You only need to consider the very large wavelengths that we are talking about, in order to understand this. A tone at 35 Hz is 9.8 meters long: it won't even fit in your entire room! Sound waves pretty much ignore objects and room features that are smaller than their own wavelength. Let's say you were to angle one of your 4m walls by 5°. To do that, you'd need to have one end of the wall 35cm out of line with the other end. So we are talking about a difference of 0.35m for a wave that is 9.8 m long... Not exactly an earth shattering difference! The wave will hardly notice that, and will still act mostly like an axial mode, but probably with a phase shift of frequency shift in the decay. You'd have to angle your wall by something like 30° (a 2m difference between ends) in order to have a large effect on a 35 Hz mode.... Actually, you don't have any modes at 35 Hz in your room, but you do have one at 43 Hz, where the wavelength is "only" 8 m...
So unless you are able to angle your walls by very large angles, you won't have any useful effect on the modal response, and even if you could angle them that much, the effect would be detrimental to the room acoustics, not beneficial.
But your diagram shows a difference of just 200mm! That's a bit less than 2°. The effect of doing that is basically nothing at all.
But what about flutter echo? Well, yes that is form of reverberance that can benefit from splayed walls. True. However, you need a difference in angle between the two parallel walls of a
t least 12° to accomplish that. It could be 6° on each side, or 9° on one plus 3° on the other, or all 12° on just one wall... it doesn't matter, as long as it is 12° or more. On the other hand, you could hang a single simple porous absorber on one of the walls at the critical location, and solve the problem much more simply! And for just a few pounds, vs. hundreds of pounds on trying to build non-perpendicular walls using building materials that are design to make perpendicular walls: rectangular blocks....
Then there's the issue of the ceiling: If the walls are not parallel, then you can't just order all the same size beams and blocks for your beam-and-block ceiling! You'll need a different length beam for each position on the wall, and some of those will have to be custom made, since they won't correspond to standard lengths... and you'll need to cut an awful lot of blocks at some strange angles... and all of that trouble, expense and time to "fix" a problem that doesn't even need fixing, and where the "fix" will actually make it worse, not better!
Sorry about the rant, but this is one of my pet peeves! Just build rectangular rooms that have a good ratio, so that the modal response will be decent to start with, then treat the rooms suitably. Period. End of story. Save yourself time, money, frustration, and end up with a better room.
Inside, the walls and ceiling will have acoustic plasterboard decoupled from the wall using timber batten and glued with acoustic mastic
Why? That would create a 3-leaf wall around most of the room, and a 4-leaf wall in places! In fact, at some points you'd have an amazing five-leaf wall! That would really trash the low frequency response. In fact, I can't think of a better way to transmit the low frequencies between adjacent rooms using sympathetic resonance! You would basically have a matched pair of resonators in adjacent rooms, and with a 5-leaf wall you'd have a really good chance that you could accomplish some interesting things... Assuming 2x4 battens, the resonators would be tuned to about 63 Hz, so if you play a an open "C" on a bass guitar in one room, there's a really good likelihood that the resonator in the wall in the next room would pick that up and start humming the same tune!
I think that's probably not what you are trying to achieve here...
This may assist in improving the acoustics inside the room,
Actually, no, it would not. It would create a tuned resonator around the entire room, which would not only play havoc with the acoustics inside the room, it would also potentially provide a tuned system for passing certain low frequencies between rooms, due to the 5-leaf walls (which isolate very poorly at low frequencies anyway) and the identically tuned structures on both sides.
but mainly it gives cabling space for power / lights etc.
Just use plain old ordinary surface-mounted structured cabling systems, such as those made by Legrand, Kalop, WireTrack, and others. Much simpler, much cheaper, much more elegant, and no issues with trashed acoustics or sympathetic resonance....
http://www.calcentron.com/Pages/fram-tr ... aceway.htm
http://www.export.legrand.com/EN/dlp-wa ... ng_95.html
But that same image shows something very sinister: "Carpet with underlay":
Carpet? Inside an acoustic space? Ummm .... NO! The answer is just that: NO!!
Carpet is a really, really bad idea for any type of acoustic space, because it does the exact opposite of what the room needs. Carpet absorbs high frequencies very well, some mids, and no lows at all. That is the exact inverse of what is needed! Rooms this size need huge amounts of low frequency absorption, a fair bunch of mid absorption, but no extra high absorption at all.
If you want to make your rooms sound, dull, honky, boomy, hollow, and rumbly, where bands wont be interested in coming back, then by all means carpet the floor. But if you want a room where bands will fight to come back and rent more time, because the room sounds harmonious, pleasant, lively, warm, and with a great vibe, then forget the carpet.
The block ceiling will have a small service hole in one of the blocks to run power, Ethernet and aircon into the room
Ummm, well it COULD, but not if you want the very high level of isolation you are aiming for! There are very specific methods for bringing the power feed, Ethernet, phone, audio, and HVAC into the room, but "chopping a hole in the ceiling" is not the way to do it. For the electrical power feed, that needs to come in through a suitable conduit that is decoupled in the middle, mid way between the two leaves, where the gap is wrapped and sealed with suitable resilient material, both ends are plugged with suitable insulation, and then caulked correctly with proper acoustic sealant. For the HVAC piping to the mini-split systems, you need to either leave a large coil of pipe in side the cavity, or you need to stagger the holes in the leaves buy a very large distance, and the the pipe needs to be curved suitably in the wall, with the pass-through holes suitably sealed with Sorbothane gaskets and abundant caulk. The actual HVAC ducts must have silencer boxes on them, and since you need such a high level of isolation, those silencers will be very big, and very heavy. You'll still have to do all the calculations for the HVAC systems of course (static pressure, flow volumes, flow rates, flow velocities, sensible heat, latent heat, etc.), but that's the basics.
The plasterboard lining the celling will contain the light fixings.
plasterboard lining? Where did that come from? That converts your 2-leaf ceiling into a 3-leaf ceiling, and once again introduces those fun issues of resonances...
Do yourself a favor, and just some concealed lighting in the acoustic treatment on the ceiling (which you will need anyway), and a few fixed spots here and there, perhaps on adjustable stalks. That's all you need. And feed it all with the same Legrand structured surface-mount system.
The ceiling plasterboard will be angled slightly from one end of the room to the other, creating a ceiling height of 2.3m at one end to 2.5 at the other in an attempt to break up the parallel surfaces of the floor and ceiling.
Same issue as for the angled walls: a lot of effort that accomplishes nothing. Just render the bottom of the block-and-beam surface to get a good seal and provide a nice flat surface, then hang suitable acoustic treatment from it. A hard-backed cloud here and there, hung at a steep angle, would do wonders for vertical axial modal issues, as well as flutter echo, and can also look very neat.
The floor will be thick carpet, laid on acoustic carpet underlay on top of the existing concrete floor.
See comments above on this. Very bad idea. Either leave the plain concrete, or stain and polish it, or lay laminate flooring. But not carpet. NEVER carpet.
Think of this: how many professional studios do you see with wall-to-wall carpeting in their live rooms? I'll tell you: zero. There's a reason for that...
The walls will have hanging acoustic panels – 2 on each 6m wall and 1 on each which will be constructed using the following method, or similar:
Well, some of the treatment could be done like that, yes, but you'll need much more than just a couple of porous absorbers on the walls.
The corners of each room will have a ceiling height bass trap. These will be constructed using the following method, or similar
... commonly know as "superchunks". Yes definitely.
The studio will have a ductless mini-split air conditioning system, with an external condenser and an evaporating unit in each room to cool and ventilate. These systems require smaller piping than traditional AC units.
Well, yes, that takes care of the cooling and humidity issues, but you are forgetting a rather important aspect of HVAC: the "V" part of it! People have this annoying habit: they need to breath in order to survive. You probably wont have too many repeat customers if they keep on passing out and dying on you, inside the rooms...
OK, so I exaggerate a little, but it got your attention! You absolutely do need ventilation in your rooms. You need one set of ducts to bring fresh air into the room, and another set of ducts to remove stale air. Imagine what your rooms will smell like after half a dozen hot sweat musicians have been jamming away in there for a couple of hours, with no fresh air coming in, and no stale air exhaust... Once again, your chances of high repeat clientele is not too god....
Yes that does mean you need to bash a couple of huge holes in each room, to bring the ducts in, which obviously trashes your isolation, but that's what your silencer boxes are for: they allow the air to flow through but prevent the sound from getting through.
You need this.
- Doors. My original plan was for doors to consist of a double door entry system - two heavy fire doors fitted so that one opens outwards and the other opens inwards. Both fitted so as to be acoustically sealed when closed using acoustic door seal kits
Correct, except that you show both doors attached to the same leaf. In reality, you put one door in each leaf. One door goes in the outer leaf, the other goes in the inner leaf. And you need at least two full-perimeter seals on each door for the level of isolation you want. I'd go for 3 full seals, for that scenario.
However, with a two-leaf wall I cannot see how to put this in place. Having one door on the inner wall and one on the outer would presumable drastically compromise the sound reduction, as it would not produce an air-tight seal in the door way.
Why not? Each door is has two (or preferably three) complete seals all around the perimeter , including the threshold: why would that not be air-tight? The seals are slightly staggered, with the jambs being slightly offset, to ensure that each seal is perfectly hermetic. Three seals on each door will absolutely ensure that they are air-tight. I don't understand why you think they won't work.
Would having 2 doors on the inner wall, and one on the outside be an option? This is the idea I feel is probably going to be most suitable.
Ummm... that's a 3-leaf system again: it REDUCES your low frequency isolation. It does not IMPROVE your low frequency isolation. The rule is: 2-leaf, only two leaf. Never one leaf, never 3 leaf, never 4 leaf, or another other number. Each time you add a leaf, you raise the lowest resonant frequency for the entire system, thus reducing isolation in the low end. Bad idea.
Or should I be bridging the gap between the walls at the point of the door?
Why would you want to do that? That provides a direct flanking path between the two leaves, basically trashing your isolation. Are you concerned about the ability of the wall to keep the door from sagging, twisting and warping as it opens and closes? that can be an issue for wood-framed walls, yes, but you are going with concrete block walls. As long as you have very hefty, solid door frames, well bolted and sealed to the concrete, and four heavy-duty hinges on each door, there should be no issues with that.
- Can you offer any advice on this? My budget will not stretch to cover 6 specialist heavy acoustics doors. I have looked through the FAQ stuff on doors on struggled to find a suitable answer.
You can build the doors yourself for a few hundred dollars (Euros) each: You build them up from several layers of MDF and/or plywood: Some people throw in a layer of MLV, others us Green Glue, others even suggest lead sheeting. Basically, the heavier you make it, the better it will perform. As long as it has roughly the same surface density as the wall it is in, and as long as the air gap between the doors is larger, you will be fine. The most critical issue with doors, is the seals. especially the threshold seals. Those you will have to buy, and the best place to get them is Zero International.
- Should I have the whole ceiling at an angle, to remove the parallel surfaces of the floor and ceiling?
No. Not necessary, and ineffective unless you have a huge angle.
- Do you think this design will provide the noise reduction I require?
If you fix the 3-, 4- and 5- leaf issues, and take into account the various other problems and solutions mentioned above, then yes, you really can get 70 dB of isolation. It will require vary careful design, and vary careful construction, with great attention to detail on sealing everything, multiple times. The simple truth is that if air can get through a tiny little gap, then so can sound. There cannot be any gaps, cracks, holes or other air paths. Not even a minute one.
But apart from that, what you are planning is feasible, and should work, once you iron all the bugs out of your design.
- Stuart -
