#1
Hi UG,

I'm currently building a closed back 2x12 oversized cabinet and i have some questions.

-If i understand well, its crucial to have it air tight. I have big metal handles to install on both sides (as in most 2x12s). Won't this cause any bleed? as it takes away wood and the metal seems to resonate?

-To seal it off perfectly, is it smart to use silicone?

thanks in advance!
#2
What about putting some sort of foam on the inside to dampen them?

Do some research and check out which metals resonate less than others. But still, if it's fastened securely, it shouldn't be noticeable. So silicone would work good enough, along with screws of course.
#3
Thanks for the reply,
I was thinking about making wodden caps to put ofer them, so the cab stays closed airtight.
The material seems to be exactly the same as most cabs.
#4
if you're going to have a lot of dead space, have you thought about porting? There's not a ton of places for the sound waves to go so it's not going to take an acoustic engineering degree to do. If you build everything to come apart relatively quickly, you can dampen some areas and let others resonate and pretty much "test and tune". A less dense wood will require very little baffling/dampening. I just got done building mine, played everything open back vs closed, chambered and ported. There was an amazing difference in the tone of the cabinets. Don't worry much about small spaced that aren't 100% sealed... it won't be as crucial as the building material for resonance/dampening.
#5
Quote by AEnesidem
Hi UG,

I'm currently building a closed back 2x12 oversized cabinet and i have some questions.

-If i understand well, its crucial to have it air tight. I have big metal handles to install on both sides (as in most 2x12s). Won't this cause any bleed? as it takes away wood and the metal seems to resonate?

-To seal it off perfectly, is it smart to use silicone?




It's not a bad idea, and certainly won't hurt anything.

The point of building 1) "oversize" and 2) closed back is to maximize low mids and power usage. If you have a lot of air wheezing around the edges, you may as well not bother with the weight and just build an open-back cabinet.

If you have speakers that *have* good low end response (such as the Eminence Delta ProA's or EV-L's), it's an even better idea to check with build recommendations for optimal internal volume. For the ProA's, for example, a sealed cabinet of 1.00 - 1.25 cubic feet is recommended (double that for a pair of speakers).
#6
Quote by Beakeroyeast
if you're going to have a lot of dead space, have you thought about porting? There's not a ton of places for the sound waves to go so it's not going to take an acoustic engineering degree to do. If you build everything to come apart relatively quickly, you can dampen some areas and let others resonate and pretty much "test and tune".


There are sites on the web that will let you plug in the TS parameters for a given speaker that will give you the correct port sizes (rather than simply cutting a random hole) if that's what you're going to do. Here are sample parameters for the Delta ProA from Eminence: http://www.eminence.com/pdf/Delta_Pro_12A.pdf

You should pretty much never "let others resonate." That was the "we don't know what we're doing" practice in the '60's, but some 50 years on there are smarter ways. You can get some nasty random resonances that way.

The 4x12 cabinet was pretty much drawn in chalk on a factory floor around four 25W Greenbacks. That was the Marshall design process. When they built the things, they realized that the big back panel was resonating at a frequency corresponding to a wavelength multiple of the diagonal of the panel, and it was nasty. It was also "oil-canning" and losing some of the power Marshall had designed into the amp. In order to get rid of it, they put in the chunk of wood that extends from the middle of the baffle to the center of the back panel in order to change the frequency of the resonance and reduce its volume.

These days it's possible to reduce the thickness of the material you use (and the resulting weight) while preserving impact resistance and eliminating stray annoying resonances by using some smart bracing on the panels themselves:

#7
Well currently my cabinet is 18mm russian birch ply, baffle from the same material. There's a centre pilar from front to back, and bracing all around the cab. So it shouldn't resonate too
much. Everything is fitted to the maximum and eventual small holes are being filled up. The bracing inside also ensures any openings are sealed.

I was just concerned that the holes for the iron handles on the side would ruin this, since they basicly are big resonating chunks of metal.
Last edited by AEnesidem at Oct 7, 2015,
#8
Quote by dspellman
You should pretty much never "let others resonate." That was the "we don't know what we're doing" practice in the '60's, but some 50 years on there are smarter ways. You can get some nasty random resonances that way.

poor choice of words... meant more along the lines of deflection and directing/allowing sound wave travel. That is a very cool reference for figuring our the porting the first time. I used a lot of carpet padding to deaden most of the surfaces. I don't have an acoustic engineering degree and I don't pretend to know the nuances of full porting... I have always been under the impression that a smaller area cabinet benefits from allowing the internal pressures to be diverted outwardadding to the SPL. All of my knowledge is in the form of what I've found on the interwebs and what other musicians have told me paired with how it sounds to me. Mine went together and apart a handful of times, sounded like I was playing through a tin can or a dozen pillows before it sounded the way I wanted it to. And I have no idea if what I have for chambering inside the cabinet actually does any good or not. Just sounds good to me.
#9
Porting is science. It's actually tuning. You don't just guess when you're tuning an instrument, right? Same with cabinet tuning. As it turns out, cabs actually need to be (in general) a bit bigger when they're ported than when they're sealed. The TS parameters of the speaker will determine 1) how well a speaker will work for a sealed or ported cab; sometimes mutually exclusive 2) the internal volume needed for optimal performance 3) what frequency range the cabinet tuning should be. Also, sealed cabs like to be stuffed, but ported cabs prefer to be lined.

RE: OP
Foam gasketing will be fine, just be sure the handles are snug and screws are tight.
#11
Quote by AEnesidem
so i should put foam on the inside everywhere?


Won't matter. Not for what you're building.