For Knightfly: Partition wall advice?

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First time poster here. Great forum!

I will have to work in a very small control room for a year or two, while my studio is being built.

I will use this space just for composing and mixing. I mainly do electronic music so live recording is not very much needed and I can do that in another studio anyway.

The room is 4.85m long, 2.41m wide and 2.2m high.

It is a basement, so all walls are 24cm thick concrete. There are two doors, as shown in the picture.

The bad part is that half of this room occupies a house heating system, large boiler and a gas stove, so I have to separate this room in half with a partition wall.

I have no idea how much isolation I need with this partition wall.

The whole room will not have any additional sound isolation, no floating floor, just concrete so no decoupling with the rest of the house. This is just a temporary place for a year or two so no complicated/expensive construction wanted.

Also, I'm not listening very loud for a longer periods of time, and I only have small nearfield monitors (genelec 1030a).

I got some great advices from guys at studiotips.com about acoustical treatment. As this is bare concrete, heavy absorption will be needed to prevent nasty comb filtering and room modes anomalities.
The rear and sidewalls will be "dead" (20cm thick rockwool sides + two giant removable cornertraps at the rear), front wall and floor will be reflective, and ceiling will be dead (20cm rockwool + corner absorbers in sidewall/ceiling corners).


The problem:

With so much absorption in the room, I'm afraid that I will not get enough bass response from my nearfields. I like bass, and I find that my mixes translate better if I have a little bit more bass while working, rather that linear response.

As a solution, I wanted to flush mount my genelecs in this barrier wall to get more bass and boost speaker output (+6 db), but after consulting with genelec, I am not so sure anymore. While they recommend flush mounting as the best option, they also say that with nearfield monitors the benefits are so small that it is not worth the hassle. They recommended freestanding nearfields directly against the front wall and playing with basstilt switch untill I get the response that I like.

I have to agree that it makes perfect sense beacuse it moves the SBIR dip up to 300Hz where speaker radiation is not omnidirectional anymore.

As my goal for this partition wall is to help my monitors with bass response, I guess that it has to be pretty massive, to reflect the bass in the control room and prevent leaking in the rest of the house.

What construction do you recommend that will do this job nicely and also be in harmony with my other isolation standards in the room? As this is just a temporary room, I do not want to make an overkill.

If I make decoupled double frame (8x5cm wood studs) with two 15mm layers in each leaf and 17cm airgap filled with insulation, do you think it would be an overkill? Considering that the rest of the walls are not so soundproof (no decoupling, no floating floor etc.)

I will also have 2 water pipes from heating system going thru this wall near the ceiling, so this is probably also bad for isolation? Weakest link?

Is it much more reasonable to make simple single frame (8x5cm wood studs) with 2x 15mm plasterboard leaf at studio side and 12.5mm + 15mm leaf at heating system side of room and stuff the cavity with 50kg/m3 rockwool?

I guess that I will have no big problems with higher frequencies as noone is living in the basement and also, there are door between the heating system room and stairway.

For dealing with low frequencies isolation, I guess that wood studs are prefereable to steel, and it is better to have the wall massive, without RC channel?

Alternative...

Do you think that it will be better if I make the studio side leaf very thin (one layer of 12.5mm) to help with bass traping inside control room and to make other leaf very massive (2-3 layers of 15mm) to help with sound isolation? If I go that way, do you think that I will still get enough bass response support for my monitors that way?

Sorry for the long post and bad english,

Best regards,
SF
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bump allowed?

[knightfly]

A double framed wall with 2 layers 15mm gypsum on the outside of each frame, 200mm from gypsum to gypsum, insulated with any fiberglass product up to maybe 48 kG/m^3, will be nearly identical to your 240mm concrete.

The pipes WILL be a weak link, you'd need to caulk them and very likely insulate and box them in with 2 layers same as the partition wall or they will flank sound in/out of the studio.

And your English is better than most americans I talk to; if you were "fishing for compliments", you got 'em

You may find that your "jennies" will sound better with several inches of absorption BEHIND the speakers; but it's gonna be a "cut and try" approach like a lot of acoustic things... Steve

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Knightfly,

thanks for reply and compliments about my english!

Unfortunately, I did some measurements in this room lately and I have some bad news...

1. The partition wall cannot be thicker than 12-13cm.

I have a sink right where the wall should be and, obviously, I cannot build a wall over it. It has to be there in case of emergency if water is leaking from the heating system boiler. On the studio side, I also have some permanent instalations so that leaves me with 12cm barrier wall.

2. I have been playing loud music lately in this room and realised that sound isolation is not that good. Concrete is doing GREAT with bass frequencies but not with mids and highs I can recognize songs and even lyrics in the next room (garage) without problem. Floor above, situation is better but still not very good.


Question:

Which wall construction do you recommend in 12cm thickness that provides best isolation for music (MTC)?

Do you think that staggered stud wall construction with 1 layer of 12.5mm plasterboard on one side and 2 layers of 15mm plasterboard on other (studs 5x3cm 8cm common base) is a good option? One 12.5mm layer would be on studio side for bass traping (60cm centers) and two 15mm layers on the other side for isolation (40cm centers). Cavity filled with 30kg/m3 or 50kg/m3 rockwool?

Best regards
SF

[knightfly]

In theory, using thinner wallboard on studio side will help bass trapping; but also, anything that makes it easier for the wall to absorb will ALSO make it have less isolation; and isolation is NOT a one-way street, so any low rumble from the furnace would be more likely to get into the studio.

Concrete passes sound as a shear wave really easy, so just having a single mass of concrete that's shared by the rest of the building will NOT (as you found) give good isolation. IN order for it to work, it needs to become part of a mass-air-mass wall by framing out separately and adding a couple layers of gypsum, with insulation between. This m-a-m construction needs to be EVERYWHERE, but especially in walls and ceiling. You can lessen the amount of sound that's flanking through the floor with a fairly simple floated riser if there's no room or budget for a full floated floor - something like

http://www.johnlsayers.com/phpBB2/viewtopic.php?t=4013

With your thickness limitations, either a staggered frame as shown or a straight frame with resilient mounts one side is all you can do - but I'd try for 2 layers of 15mm both sides if you can... Steve