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Author Topic: Isocab build  (Read 2121 times)

JacksonRR

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Isocab build
« on: July 25, 2011, 10:07:13 PM »
So I ordered a Miracle Man bridge over the weekend(yes! finally had some play money!) and I had some money left over to play with so I'm doing an isocab, but I thought I'd go over the specs with the Bareknuckle braintrust before I start, just in case any of you have some good ideas or alterations I can incorporate BEFORE I start cutting wood and whatnot. What I'm going for is something smallish I can EASILY pick up take to the mountains or a buds house and not worry about the room I'm recording in. Something I can stick in a closet or under the desk or whatever.

So here's my basic brainstorm on it after looking at different isocabs like the Rivera Silent Sister, the Randall one, various homebuilts and so on:

I'm saying NO to any focus on volume reduction. I don't need that. It's the main downfall of all isocabs. The reflections inside a small box are undesirable. What I do need is let most of it out and have very little come back in. I feel strongly about impulse reverb as it can be excellent, but cabinet impulses are a no go. I might not want to record the room along with the speaker, but I will never want to remove the speaker/mic part of the recording chain. Rivera is sacrificing volume reduction for a natural interaction between the microphone and the speaker. I'm thinking a "cage" with one inch corners of ply. Expanded sheet metal will go on to increase rigidity(but still let the sound out) and Owens Corning or Rockwool on top of that(we're building these layers from the outside in).

Things I'm hung up on:
Will Owens Corning or rockwool be enough? Will the sound waves lose enough energy after going through that and bouncing around the room to not come back in?

Should these "semi open" sides have louvers instead of expanded sheet metal? I need it portable so is the sound wave redistribution/blockage worth the worry about durability?

Is a 16x16 box OK for a 12 inch speaker in this application?

Am I going to far with the "rockwool cage" idea and maybe I should just make the bottom of the mic part "open." This would have some reflections, but it would be firing all the waves at the floor instead of filling the room.

Should I port the speaker part and if I do, should I spend the money to make it so I can tune it on the fly with different lengths and widths of port material?

To Owens Corning 703 or Rockwool? Either will have a thin fabric between it and the expanded sheet metal(for looks and dust issues) and between it and the inside where the mic(s) will be.

What thickness I should use of either the Owens Corning or rockwool. If I use 2 inches for all sides, I'll have an 11.5"x11.5" space INSIDE where the mic is.

Black Tolex with red "grill cloth" or White Tolex with light brown "grill cloth."

Should I just enjoy jamming out to nature in those moments of amazing mental purity without thoughts of, "Man I wish I record this"?

Here is a pic I did in Paint to help illustrate. Yes, I know I should be using an SM57, but an SM58 was easier to draw.



So just to make it clear the 5 walls of the mic part, from the outside in are:

Expanded and pressed sheet metal
thin fabric
Owens Corning rigid fiberglass or Rockwool
thin fabric

I have the 3/4 Birch Ply and a few speakers. I'm ready to roll so any and all thoughts are certainly welcome! If it turns out to be good or great, I'll do a full set of instructions on a PDF for you guys.
« Last Edit: July 25, 2011, 10:11:06 PM by JacksonRR »

Deadstar

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Re: Isocab build
« Reply #1 on: July 26, 2011, 12:21:47 AM »
Depending on it's intended function there are a few different routes you could go down that I could advise.

What's the purpose of it if not to reduce volume: in a live environment to isolate from other instruments or
in multitrack recording to take out the room sound?

Personally if it's the latter I would use a higher density fibreglass (or alternative material there are a few that have the same properties but don't itch, or use gloves and long sleeves) in the region of RWA100 if you can get it, it makes the panel more rigid to begin with and is a greater isolator - also try for 4" thick. Then create a structurally stronger edge it can be easily coated in a liquid resin which will stiffen the edges. Then wrap the panels in a fabric to keep the fibres in.
This way you can create a little 'modular fort' that's still portable and another benefit is you can use them as bass traps when not assembled into the cab. You can also place the cab on one of the panels to prevent ground rumble which should help tighten up the sound. Ultimately it's a much easier build than you are suggesting but it might not suit your required task.
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JacksonRR

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Re: Isocab build
« Reply #2 on: July 27, 2011, 09:43:52 PM »
Bah. Redid some of the measurements to get more support in the "cage" part and to get rid of any perfect squares. Went to go cut cut plywood and it was cupped badly. About an inch in the middle over the length. I had it in my air conditioned basement for less than a week and it's already warping. I took it back for a refund so now I need to find a new board. I'm not in the mood to take another board from that store.

What do you guys think? Did I just get a weird one? It was 11ply Baltic Birch. I can drive an hour in both directions to my main specialty shop for a few different types of void free, but they're all 7 ply. I can get Hickory, N. American Birch, Cherry, Apple, Red or White Oak, Mahogany, Poplar or Walnut. These are all 100% 7 plys of whatever, no veneer with a weird core or anything.