iso cab: 2" air space?

Hi, Just built the exterior shell for my isolation cabinet for recording guitars. Dimensions are 30" H x 36" W x 34.5" D 3/4" MDF. I'm planning to build a second box inside the first to further attenuate sound and I just wanted to be sure I'm on the right track. Is a 2" air gap on all sides, top and bottom betwwen the boxes a good choice? Also, for my cable connections I thought I'd just buy panel mount XLR connectors like this: http://www.redco.com/shopexd.asp?id=470 and mount them to the MDF and solder my cables to the other side. Need to find something similar for TS speaker cable. Is that a good plan or is there a better way to do it? Thanks! Seth[/url]

With the disclaimer that I don't have the experience with the material to back this up, I read earlier today on a speaker enclosure site that MDF is a fairly poor choice of construction material. The site was for building subwoofer enclosures for cars, and several of the members said that after a few months, the MDF starts to pull apart somewhat from the vibrations. The wiring is fine, but you could probably just get panel-mount XLRs and 1/4" and mount them directly in the box. XLR http://www.markertek.com/SearchProduct. ... &sort=prod 1/4" http://www.markertek.com/SearchProduct. ... &sort=prod There's no direct link to the one I'm trying to show you, but the NJ3FP6C is probably what you want. They're more difficult to work with, but the combo jacks (that have XLR and 1/4" in the same space) might be more flexible for you. MPEDrummer

Yeah I just went ahead and ordered the punched panel mount XLR and 1/4" jacks from redco. Will install those and wire them up. Anyone have comments on my plan of 2" air space between boxes? Really would love comments since I'm not sure that's te best way to do it; just making my best guess...

I think that in general, with any mass-air-mass system, the more air the merrier, up to about 12". After that is wasted space. What's the plan for decoupling the internal box from the external? It seems that any system would need to account for the weight of the amp inside, or the compression would go beyond the amount of spring in the decoupler and just bridge the two leaves, rendering the space useless. MPEDrummer

Good question; no definite plan yet but thought I'd try some sort of rubber mats (like the padded gym flooring stuf) or whatever. Perhaps it would be wise to buy the auralex amp isolation pad instead? Hate to spend to $50 but if the effectiveness of the box relies on it...

Would it be better just to go for mass and instead of building an inner box with a 2" air gap just add another layer to the box? In other words: 3/4 MDF --> 2" air --> 3/4 MDF vs 1.5" MDF ?

IT would certainly be less complex to build (which, in my experience, generally means better) - as for actual performance, I have no idea, that's beyond the limits of my understanding here. Hopefully, someone will be along shortly to answer. MPEDrummer

Or, carrying this one step further: would it be even better to have the two boxes with 2" air space but fill the air space with kiln dried sand? Certainly that would get me the greatest amount of mass... :P By the way I think I may buy the auralex ISO Producer pack. $130 and you get 1 gramma which I could use to decouple the inner box from the outer, 6 platfeet which I think I could use to decouple the 1x12 cab from the floor of the inner box, and the mopads which I've been meaning to try anyway.

I have the mopads and like them a lot, though I'm building massive speaker stands now that I'm moving to a more permanent place. I've never used the big one (Gramma? something like that) Sand in between would indeed provide the most mass, but it would also provide a bit of a problem - how do you expect to have the door working? Also, I wouldn't expect that you'd be able to move it once it's full, so be sure you like were you put it ;) MPEDrummer

mpedrummer wrote:

Sand in between would indeed provide the most mass, but it would also provide a bit of a problem - how do you expect to have the door working? Also, I wouldn't expect that you'd be able to move it once it's full, so be sure you like were you put it ;) MPEDrummer

Yeah this thing will stay where its put in my basement sitting on the concrete floor. The "door" is actually the lid (top) of each box so that's not a problem. I suppose instead of going with a box within a box if I went the sand route I could just add four new sheets of 3/4 to the walls spaced out by a 2x2 or whatever and pour the sand between the walls. I suppose one concern though might be that the glue, screws and l brackets holding the MDF walls together might fail with the weight of the sand pressing out on them? Here's a crude sktech demonstrating what I mean...

Well, I ordered the ISO pack. The current plan is to continue with the box within a box (mass-air-mass) by building a second box within the first and decoupling the inner box from the outer by placing it on an auralex Gramma. There will be 2" of air space between the boxes. If this doesn't do the job I'll try again using sand instead of an air gap. Any comments welcomed.

Wow this place is really dead. Anyway, finished my iso boxes with the exception of the cabling since the connectors and punched panel didn't arrive yet. Hoping to test the thing this week as soon as I can get the rest of the parts.

sethmeister wrote:

Wow this place is really dead. Anyway, finished my iso boxes with the exception of the cabling since the connectors and punched panel didn't arrive yet. Hoping to test the thing this week as soon as I can get the rest of the parts.

Did you finish it? If so, how did it work out?