It's a new build so i was thinking of using dense concrete blocks for the exterior walls, and 2x4 stud timber with 2 layers of 15mm soundbloc plasterboard hung with resilient channels and auralex sheetblok in between the layers.
If you build your inner-leaf like that, with a separate stud frame isolated from the concrete blocks, then you do not need the resilient channel. The separate frame already decouples the inner-leaf, so there is no need to decouple it again.
You also do not need expensive, proprietary drywall: Plain old ordinary 15mm fire-rated drywall will do the job just fine, and is much cheaper. Sound waves can't read price tags, and do not care how much you paid for your mass: All they see is mass, and the react to the amount of mass in front of them, regardless of how much it cost.
The same applies to MLV (Mass Loaded Vinyl) and similar products: there's no demonstrable advantage to that: It is simply mass, and very, very expensive mass at that! And when you see claims like "
6dB more effective than solid lead at stopping the transmission of sound", you really have to wonder!
You might want to ask them for proof of that claim, as shown by a full set of tests in a recognized, independent acoustic laboratory. In other words, two identical walls, one with 1/8" of their product, and the other with 1/8" of lead sheeting. You can imagine which of the two tests I'd put my money on...
also the floor will be concrete slab and ceiling same as walls.
Excellent! You should be able to get pretty good isolation with that.
I have taken your suggestions on board and have been playing around with room ratios, the best i've come up with is 6x4x3 which is a ratio of 1:1.33:2.00
Did you test that in a ratio calculator, such as this one?
http://www.bobgolds.com/Mode/RoomModes.htm
Take a close look at those numbers: Not very good. The length is exactly twice the height, which means that the odd harmonics of the modes for one line up exactly with the even harmonics of the modes for the other. Perfect overlap. Bad. Not only that, but four times the height is three times the width and also twice the length. Very bad. There should be no simple integer mathematical relationship between dimensions.
i originally wanted a vocal booth but don't think this is possible with the space?
I agree: it is probably a bit too small for that. You could fit one in, but then both rooms would be very small.
Please can you advise on soffit mounting my speakers (Adam a7x) and angling the walls?
You only need to angle part of the side walls, at the front of the room. Normally about one third of the wall is enough. The exact angle is different for every room, based on the dimensions, geometry, speakers, and things inside the room, and the only way to figure it correctly, is by "ray-tracing".
Do it like this:
http://www.johnlsayers.com/Studio/Pages/Somewhere.htm
(Those are P22's, not A7X's, but the concept is identical)
- Stuart -
also the floor will be concrete slab and ceiling same as walls.