Sufficient size iso room

[wearashirt]

I'm planning to take over a small area in our office. We've measured things out, and we can build a room measuring ~2.5m in length, width, and height. The room is nearly cube shaped except for an L-shaped wedge due to a structural column.

The interior walls will consist entirely of 60kg/m^3, 10-cm thick rockwool covered with a thin, breathable cloth. Floor will be carpeted. Ceiling will be plywood but with 5-cm panels to act as clouds, and probably the only source of reflection in case needed.

The outer wall will consist of two ply wood layers with void space in between.

Question is - do you guys think I will run into issues with the size of my isolation room?

I have had success with acoustic panel "huts" and a bit of close micing, and even distanced micing. Problem with this is the noise floor, hence the need to have an iso room. Also have trouble recoerding other things aside from vocals.

[Sam Inglis]

I think you would do well to take professional advice here. A cube is the worst possible shape from an acoustic point of view. If you enter the dimensions into this online calculator for instance you'll see there are strong room modes at 69Hz, 97Hz, 205Hz and 274Hz, plus plenty of smaller ones inbetween. 10cm of Rockwool on the walls isn't going to help much at those frequencies, but it will absorb tons of upper mid-range and treble, making the whole structure sound boxy and honky.

[Hugh Robjohns]

^ I was about to type pretty much the exact same comments. Is there any possibility of more favourable room dimensions?

[andy cross]

Is it feasible to accommodate the structural column with an angled wall rather than an L-shape?

[Wonks]

Or angle all the walls so you’ve no parallel surfaces, (a wonky trapezoid) and maybe even slope the ceiling?

I’ll ask a general question: Would denser rockwool on the outside (say 100kg/m3) do better for sound isolation purposes, and then have fewer 60kg/m3 panels inside for room treatment purposes to avoid it sounding too dead at high and upper-mid frequencies? Would 6cm of 100kg/m3 be as effective for isolation purposes as 10cm of 60kg/m3? Or maybe 7cm of it? Just trying to find ways of minimising the overall wall thickness to maximise interior space.

Any thoughts on ventilation for the room? If sealed, it will be very well insulated and heat will build up quickly. And people perform better if not made sleepy by high CO2 concentrations.

[James Perrett]

In my studio I have about 50% coverage of 60kg/m3 Earthwool on the walls in the main room and closer to 80% in the booth. I also have floor to ceiling bass traps in 2 corners of each room. I'm happy with the way the rooms sound but the side walls are also splayed so that only the front and back walls are parallel.

[wearashirt]

I think you would do well to take professional advice here. A cube is the worst possible shape from an acoustic point of view. If you enter the dimensions into this online calculator for instance you'll see there are strong room modes at 69Hz, 97Hz, 205Hz and 274Hz, plus plenty of smaller ones inbetween. 10cm of Rockwool on the walls isn't going to help much at those frequencies, but it will absorb tons of upper mid-range and treble, making the whole structure sound boxy and honky.

Thank you for pointing this out. I may as well go for a trapezoid box.

[wearashirt]

But do the room modes matter if I will be recording things that i will filter out the LF from anyway?

- vocals
- steel guitar
- classical guitar (very soft)
- guitar cab

what if I get around to recording a string quartet?

-Definitely not drums, I would NOT waste my time attempting to record drums.

[wearashirt]

The comment about the cube shape was greatly refreshing. So here, the room is no longer a cube, and some trapezoidal areas were inserted.

https://app.sketchup.com/share/tc/asia/ ... source=web

[Wonks]

They will matter in a cube, where the interference peaks and troughs will be multiplied by a factor of three, so +/- 18dB worst case.

It’s not just the fundamental note, it’s all the harmonics of that as well.

You’ve got the first eigenmodes at 68.6, 97.0, 111.8, 137.2, 153.4, 168 and 205.8Hz, with other strong nodes at 274.4Hz, 343Hz and 411.6Hz, plus all the further multiples of 68.6Hz, but still with lesser corner to corner mode effects in there as well (strongest modes shown in bold). Acoustic treatment should take care of the higher frequency nodes, but as the frequencies drop it becomes less effective.

On typical male vocals you can normally filter up to 100Hz without affecting the tone, but with some deep voices that may be lower. Normally tuned guitar (acoustic and electric) fundamentals start at 82Hz, but dropped tunings, e.g. DADGAD, can lower that a bit (73.4Hz).

Normal bass guitar is 41Hz but a 5-string’s low B is 30.8Hz.

Also remember that the high pass filter frequency is given at the -3dB point so you can’t set one at say 80Hz on a guitar without having some effect on the lowest notes; you have to set it lower.

A trapezoid design is better than a square one, but with a strict trapezoid you’ll still have two sets of parallel surfaces (one set of parallel walls + the floor to ceiling at 2.5m seapration), so you still get big dips and 12dB peaks before treatment.

A 2.5m room doesn’t give you a lot of play in where you position people inside, so it’s hard not to position either the performer or the mic somewhere near the centre (or 1/3 or 1/4 of the way between the walls). And positioning them at the peak node points is almost as bad as as the nulls.

[Wonks]

The comment about the cube shape was greatly refreshing. So here, the room is no longer a cube, and some trapezoidal areas were inserted.

https://app.sketchup.com/share/tc/asia/ ... source=web

Was that big square ‘notch’ in the room always there? I expected something much smaller. In which case the room was never really square to start with (though it will have issues).

[wearashirt]

Yes, the notch is from the cornermost column of the building, where the room is. Instead of meeting the notch at a right angle, I figured to create to obtuse angle from that notch. Hope it will suffice.

Then, the extra "L" space at the opposite corner, hopefully will.. what? Trap some LF?

[Sam Spoons]

Why not make the angled walls the full length/width of the room? Is the door area a vestibule? Could it be removed to make more usable space in the room?

[Drew Stephenson]

Then, the extra "L" space at the opposite corner, hopefully will.. what? Trap some LF?

Not without anything in it, but if you fill it with appropriate trapping it could make a noticeable difference.

[BWC]

Looking at the drawing from above, rotated so that the notch / column looks like a "W", if you then placed an angled wall across the top of the "W", you'd have something that looks kinda like an ice cream cone (with some small adjustments to the walls at the top of the cone). I might go for something like that, with the ceiling angled in the same direction (if possible).