First, some historical context... I live and record in a small terraced house with neighbours on both sides. For the past 3 years or so, I've been doing all my guitar recording by plugging my amp into an isolation cabinet (built by Paul Cornford). I've been satisfied with the sounds I've been getting, using the Celestion Vintage 30 and either an Oktava MK012 or an SM57.

However, it's now time to take things a little further.

I want to record my Fender Champ, but the design of my iso box doesn't really allow for the addition of another speaker (the Champ is 4 ohm, whereas the existing speaker is 8 ohm). I'm sure the box could be modified by a half-decent joiner, but I've come to consider selling it and designing THE BEST COMPACT ISOLATION CABINET EVER!

So... I'd appreciate any advice or suggestions on perfecting my design, in terms of soundproofing and acoustics-related internal dimensions.

The first criterion is that it has to be reasonably compact. The current box is 36" (L) x 24" (W) x 20" (H), and I wouldn't really want to go any bigger than that. It also has its single speaker mounted on a plywood baffle half-way down the length of the box, although I'm not sure why (perhaps to simulate the sound of an open-back cabinet?). I'd like to have a baffle at each end, one for the 8" speaker, one for the 12" speaker, allowing plenty of distance in between for experimenting with mic placement.

Then, what about the soundproofing? The current box is constructed from 18mm MDF, lined with strips of the standard grey foam you get from Studiospares (probably about 20mm). Would a box-within-a-box be a better idea? Perhaps a layer of thin MDF or plywood within the layer of foam?

Enough of my waffle... all suggestions gratefully received!


Adrian

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Quote Adrian Clark:

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..... Would a box-within-a-box be a better idea?

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A box within a box would certainly give great isolation if done properly.

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Perhaps a layer of thin MDF or plywood within the layer of foam?

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This isnt' such a good idea. I would hazard a guess the resonant freqeuncy ofthat contruction would lie in the midrange. Which would mean you'll get no isolation ( and perhaps worse amplification ) at that frequency range.

I would do it like this. Build your outer box out of 18mm MDF,and screw a layer of 1/2" plasterboard to the inside. Make it so there's a 2" gap between it and the inner box ( all the way around, including the floor ), and partially fill the air gap with rockwool.

The inner box should sit on some kind of decoupling blocks. Elastomers like rubber, neoprene etc are good, and so is foam. but you must make sure the decoupling blocks compress at least 15% to 20% or it won't work properly.


This will mean TWO access doors, and making sure all cable entrances are airtight, but it'll be damn soundproof!

I'm doing exactly that for my cabinet to silence my DAW computers and the EXTREMELY NOISY cooling fan!


Paul

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Pauls Studio Build Diary at http://forum.studiotips.com/viewforum.php?f=1

Quote Paul Woodlock:

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I would do it like this. Build your outer box out of 18mm MDF,and screw a layer of 1/2" plasterboard to the inside. Make it so there's a 2" gap between it and the inner box ( all the way around, including the floor ), and partially fill the air gap with rockwool.

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How crucial is the plasterboard? I'm reasonably satisfied with the amount of isolation I'm currently getting (Cornford Harlequin at 50-60% master volume) so if just the rockwool, air gap and double box would be a good improvement on that, I'd be very satisfied.

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The inner box should sit on some kind of decoupling blocks. Elastomers like rubber, neoprene etc are good, and so is foam. but you must make sure the decoupling blocks compress at least 15% to 20% or it won't work properly.

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Thanks for the help, Paul... that sounds like a plan!


Adrian

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GReetings


The platerboard ain't critical, but it will give you extra isolation. So think if it as optional

Paul

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Pauls Studio Build Diary at http://forum.studiotips.com/viewforum.php?f=1

Quote Paul Woodlock:

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The platerboard ain't critical, but it will give you extra isolation. So think if it as optional

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Gotcha.

I also started thinking about the issue of the internal dimensions. Seeing that the microphones will probably never be more than 9 inches or so from the speakers, how much would size be an issue, regarding resonances and so on? Also, the reflectiveness of the inner surfaces... since I'm close-miking, should I aim to make the box as acoustically dead as possible?


Adrian

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Have you read this review that Paul White did on a commercial unit that sounds like it does what you want? I think he was sufficiently impressed that he acquired the review model. The review gives some detail on its construction that might be helpful.

Hugh

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Technical Editor, Sound On Sound

Quote Hugh Robjohns:

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Have you read this review that Paul White did on a commercial unit that sounds like it does what you want? I think he was sufficiently impressed that he acquired the review model. The review gives some detail on its construction that might be helpful.

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Ooh... nice one, Hugh! I knew there had been a commercial version, but wasn't looking far enough back in my back issues (and couldn't remember the name).

"A slot-shaped port in the baffle helps avoid the boxiness that often results from putting a speaker in a smaller-than-optimum enclosure, and contoured acoustic foam is used inside the inner enclosure to attenuate standing waves."

More things to look into!


adrian

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see also

http://www.soundonsound.com/forum/showflat.php?Cat=&Board=GTR&Number=68656 &Searchpage=1&Main=68184&Words=hermit&topic=&Search=true#Post68656

a forum member who bought the hermit cab

Mmm... it's been very informative reading about the Hermit. I'm just *so* close to being able to use one of those, but the sticking point is the Fender Champ and its 4-ohm speaker. Or rather, the need to be able to use both 8-ohm and 4-ohm speakers without having 2 boxes!


Adrian

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