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PostPosted: Thu Dec 14, 2017 12:51 pm 
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I live in Mexico. The room was just completed: 20’ x 18’ x 21’ high. It is quite echo-y in there! All walls are concrete, floor is tile over concrete, ceiling is tongue-and-groove wood topped by 3” of concrete, with 3” x 8” beams every two feet and a skylight 4’ x 16’. First floor level has glass patio doors on three sides (one side with 4-foot-wide fireplace jut-out from floor to ceiling (see pic); fourth side has an 8’ x 12’ wide variegated stone facing, with jagged stones facing all different angles.

Second story level has windows on three sides, flat concrete on the fourth side.

The room will be used for band rehearsals, house concerts, and tracking/recording live musicians. (I have a separate, well-damped much smaller control room on the second floor where I do my mixing, etc.) Styles I intend to record vary from acoustic folk to jazz groups to occasional rock bands.

I am not concerned about sound isolation; neighbors on one side are insulated from me by my great room, second side by about 10 feet of air space, third side by about 30 feet, and fourth side faces the street with an empty lot.

I am planning to construct multiple 2’ x 4’ x 2” acoustic (rockwool) panels myself, with a budget of up to $2,000.

1. How many 2x4x2” panels (with a space between them and the wall) will I likely need and where would be the best places to install them?
2. Will I need to install such panels between the joists in the ceiling?

Thanks.


--Gabriel Heiser


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PostPosted: Tue Jan 02, 2018 2:32 pm 
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Hmmm, 95 views but no comments, yet. Is my room that weird? Thanks.


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PostPosted: Tue Jan 02, 2018 3:31 pm 
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Joined: Thu Aug 21, 2008 10:17 am
Posts: 10398
Location: Santiago, Chile
Hola Gabriel, y muy bienvenido! :)

I'm glad you posted that second message: I actually had completely missed the first one!

Quote:
20’ x 18’ x 21’
Unfortunate dimensions: It's practically a cube! And certainly having the width and height so close is going to be an issue: Expect problems at around 27 Hz (likely won't be a problem, unless you have a pipe organ in there!), 41 Hz (bass, keyboards, electric guitar), 55 Hz (ditto), 62 Hz, 68 Hz, and a few others. This is one of those rare cases where I might even consider tuned bass trapping for a couple of those. Perhaps membrane traps. I'm normally not a big fan of tuned devices, but this might be a situation where I'd consider it. Tuning them that low, and that accurately will be a bit of a challenge, though!

Quote:
fourth side has an 8’ x 12’ wide variegated stone facing, with jagged stones facing all different angles.
:thu: Excellent! That helps to some extent, but the variations in stone depth are not that great, so it's only going to be effective mostly for the mids and highs. The lows are still going to be an issue.

Quote:
I am planning to construct multiple 2’ x 4’ x 2” acoustic (rockwool) panels myself,
If you make them all the same size, then they will all treat the same frequency range, and you'll end up with a room that is not balanced. 2" of rockwool is going to be killing the highs mostly: it peaks around 2.5 kHz. You'd still get a bit of absorption lower down, to maybe 800 Hz or so, but not much at all in the low end, where the big issues are going to be. I'd suggest that you need a more balanced approach to the treatment, with some general broadband absorption, and also a few other devices targeting specific issues, in addition to the tuned bass trapping.

Quote:
1. How many 2x4x2” panels (with a space between them and the wall)
That depends on what you want the room to sound like! It's a live room, so it does need some type of character, "color", "vibe" or whatever you want to call it: it has to sound like something, but YOU Have to define what that "something" should be. You might want it to be "warm" or "bright" or "cozy", or "open" or "subdued"... that's up to you: it's your room, so you should define it. Based on that definition, you can then get a decent idea of how much treatment you'd need, what frequencies to target, and where to put each type of treatment. You could also define it as a set of decay curves for different frequency bands, if you wanted to be more technical and precise. Or perhaps just as an overall RT60 time, if you just wanted a general, broad guideline.

For example, if you wanted to aim for a typical "music studio" type sound, such as you'd find in a university practice room maybe, for things like vocals, acoustic guitars, and such like, then you'd probably be shooting for around 400 ms decay time, so you'd need roughly a thousand sabins of absorption with an average coefficient of maybe 0.4 to 0.5, and that would need to be spread around the room fairly evenly, and well balanced across the spectrum. If you wanted it more live than that, such as you'd find for a grand piano tracking room, then you'd probably go with something more like 1000ms decay time, so you'd need only around 350 sabins, with a somewhat lower coefficient of absorption: maybe only 0.15 or 0.2, but more titled towards the bass end of the spectrum to control the "boominess", and NOT so balanced: More treatment on one wall, less on another, so you can have different response by placing instruments at different places in the room. Brighter closer to the less treated walls, drier closer to the more treated walls.

Or you could take a more "middle of the road" approach, such as you'd find in a typical general-purpose rehearsal room, for orchestral instruments, and maybe go with 600 ms reverb time, then you'd need around 550 sabins averaging more like 0.25 coefficient, tilted towards the high and low ends, but less in the middle of the spectrum, where you might even want some diffusion. (Actually, for that room you'd probably want some diffusion anyway, for all situations).

If you ask 20 people what's the best way to tune your room, you'll probably get 30 different answers! All of them conflicting with each other. So it's something you have to decide, then design the treatment accordingly. Decide what you want the room to sound like, translate that into the spectrum and decay times you'd need, then design the treatment that will accomplish that.

What I would NOT do, is just hang a few dozen panels that all have the same dimensions and absorption spectrum, since that would skew the tuning into one single band.


- Stuart -

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PostPosted: Wed Jan 03, 2018 2:17 am 
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Joined: Sun Sep 17, 2017 9:26 am
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Stuart,

Thanks! I hadn't thought about the same-size panel problem, before.
Very helpful!

Gabriel


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