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Aluminium sub enclosure


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17 replies to this topic

#1 of 18 Stephen Dodds

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Posted June 11 2001 - 05:48 PM

This came up at AVS in the big Stryke thread, but without much response, so I thought I'd try here.

A guy asked about having an aluminium enclosure built, and this intrigued me enough to get the details of where it could be done. It is not too far from me.

John Janowitz couldn't think of any real positives to doing this, but I'm interested in any negatives anyone can think of.

I'm looking at the 22 inch cube 15.2 design. I like the thought of aluminium because it would fit in with my decor (ultramodern). I would also imagine it would be lighter than the MDF enclosure.

The main negative I can think of is that unless the Al is very thick, it would be difficult to countersink the drivers.

Anyone have any thoughts or suggestions?

Thanks

Steve

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#2 of 18 Julian Data

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Posted June 11 2001 - 06:01 PM

Hmm, I don't think the thickness would be an issue since AL is stronger the MDF, I would do at least 0.500" thickness though. I do worry about resonance issues with AL and that you will have to deaden the enclosure.

I think AL enclosure would look killer polished. I use to have AL sheetmetal manifolds ($1500/pop) on my racecar and when I got done polishing it I had a local company asking me to work for them as they did polishing and plating etc.. Posted Image

You want to be even more exotic? Build a mock up and use carbon fiber. Although, the budget goes way out of hand. I recall seeing some carbon fiber laminates though.




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#3 of 18 Hank Frankenberg

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Posted June 11 2001 - 11:54 PM

First, I would be greatly concerned about cabinet resonance/ringing with the aluminum. I believe you would have to line the interior with the best (expensive) multi-layer energy absorbing/dampening liner you could buy.

Julian: good idea about carbon fiber - that would look awesome in the right decor. I bet either Wilson Art or Formica has a carbon fiber-look laminate. They must - they have made laminates that imitate just about every surface imaginable.

#4 of 18 Dustin Haug

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Posted June 12 2001 - 02:48 AM

I posted a while ago about making an aluminum keg into a sub. I have seen a car audio system (damn good one) use an aluminum sub enclosure. If memory serves me right the guys name was Chad Klodner. He was one of the top competitors on the IASCA circuit a few years back. He lined his enclosure with dynamat and modeling clay to deaden it. I'll see if I can find anything else out about it.

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#5 of 18 John_Lee

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Posted June 12 2001 - 02:52 AM

Krell seems convinced.

http://www.krellonli...series.html#MRS

#6 of 18 Dustin Haug

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Posted June 12 2001 - 03:06 AM

Found this on caraudioforum.com, this is the guy I was talking about. Haven't been able to find any pics or anything yet.

"I don't know if any of you guys remember or not but back in '93 & '94 Chad Klodner won the Pro class at the IASCA Finals with a Mustang that used a STEEL subwoofer enclosure and STEEL kickpanel enclosures, so I guess metal enclosures CAN sound good. What's most important is a good seal and rigidity. CA$E and Car Stereo Review both did features on Chad's car if I remember correctly. Definitely worth a look; lots o' cool tricks on this ride!"

Here's a link for another guy with small steel enclosures lined with noisekiller.
http://www.sounddoma....d=30434&page=4

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#7 of 18 Mark Seaton

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Posted June 12 2001 - 03:51 AM

Hey guys,

There is no reason an awesome aluminum enclosure couldn't be constructed and be perfect for the use. As others have noted, Krell has done this in the extreme case. I must say that their MRS subwoofer does have the most inert cabinet of any subwoofer I have ever experienced. It should considering there is over 200lbs of machined aluminum there. Remember, Krell has been doing metalwork for years, so it came as a natural progression for them to make their killer sub out of 1" thick aluminum. SITTING on top of the sub while it's going full-tilt, I wouldn't have known the sub was on if my pant legs weren't flapping. NOW, I want to also note that there are 2 reasons for the MRS's inert operation. First and quite important, the drivers being mounted on opposing sides of the enclosure create a "balanced-force configuration" to steal a phrase from Martin Logan. This was also my goal when I decided to go with a configuration like the 15.6. By balancing all the forces of the drivers' motion, weight of the enclosure is no longer an issue. Now we only need be concerned with the rigidity of the enclosure and make sure we are not exciting panel resonances.

I think the first issue to address is resonance. As we well know, Aluminum will resonate with a very high Q, or very peaky in nature. Fortunately, since it is relatively rigid and light for a given thickness, this resonance will be relatively high in frequency. The concern is to keep this resonance from being excited. Now, for a given thickness of material, as the unbraced panel area is made smaller, the first resonance moves higher in frequency.

My first suggestion would be to determine how thick the Aluminum needs to be for both mounting purposes and strength issues. I agree that 0.5" would be a minimum, and 1" probably be the ideal. There are others on the forum who have a much better knowledge of materials than I, and here I deffer to them.

What I'm not certain of is how the enclosure will be assembled? Krell uses precision machining and screws the beast together, and I've heard others talk about welding. With so many large holes in the box for active drivers and PRs, there's really no need for removeable panels, so that one is up to you, yet I don't know how issues of strength and air-tight sealing might affect this decision.

One interesting benefit is that the enclosure will be smaller in external dimensions since panel thickness will only be 0.5"-1" rather than 1.5". Before jumping into this, I would consider what sort of cosmetic you are after. I'm sure the HE15 would look fine surface mounted, and the PRs would have a nice contrast with the black on aluminum, but this is a very subjective thing.

Fortunately the actual surface area on these box designs are rather small since most of the enclosure is driver and PR, and this allows 1.5" thick MDF to work quite well. You might be better off just going with an aluminum surfacing on the MDF like John mentioned he will be offering on his finished subwoofers. I believe he had mentioned NuMetal as an option.

Mark Seaton
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#8 of 18 Greg Monfort

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Posted June 12 2001 - 04:06 AM

For max electro-acoustic efficiency, a cab must be extremely rigid. One way to do this is to use a rigid material such as metal, which has a high resonance. Since a sub's BW is well below aluminum's Fs it's a suitable cab material. For you welders, steel is even better.

Another plus for high 'speed' materials is that it takes less to damp out any unwanted resonances if used in wide BW speakers due to energy density falling at 3dB/octave with increasing frequency. I used to make speakers from the better quality electrical component boxes that the plant I worked at threw away. A little bit of fiberglass and modeling clay was all that was necessary to quell any unwanted resonances.

The downside is that metal is highly reflective, so a large metal cab can wreak havoc with the in-room response of a nearby speaker.

GM

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#9 of 18 Julian Data

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Posted June 12 2001 - 07:36 AM

Hank,

I know Select Products has some carbon fiber laminate although in very small sheets.

I have been to WilsonArt and other laminate companies in the past and they didn't have any carbon fiber laminates.



#10 of 18 DanWiggins

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Posted June 12 2001 - 08:36 AM

For carbon fiber, kevlar, and a bunch of other cool fabrics, check out http://www.fiberlay.com located right here in Seattle. I really like the woven carbon fiber/kevlar blended fabric... Posted Image

Dan Wiggins
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#11 of 18 Julian Data

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Posted June 12 2001 - 10:04 AM

Woo..

Dan, that's a nice site! Posted Image

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#12 of 18 DanWiggins

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Posted June 13 2001 - 05:02 AM

Even nicer store to walk in to and browse around... Posted Image

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#13 of 18 Parker Clack

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Posted June 13 2001 - 10:42 AM

Stephen:

Another thing to think of to use in your ultramodern decor would be a combination of wood and aluminum. Build the frame and bracing out of wood/MDF and use aluminum side panels for the look you want.

Just an idea.

Parker

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#14 of 18 Julian Data

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Posted June 13 2001 - 12:12 PM

Actually Parker's idea is a good one, it would keep your wallet heavy.




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#15 of 18 ChrisA

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Posted June 13 2001 - 05:26 PM

For purposes of practicality, I decided against Aluminum.
I remember when I was bringing this topic up around 10 months ago. After working with 1.25 inch thick marine ply, I think I've found a keeper. It's around $160 for a 4x8 sheet. I remeber they also could have ordered 1.5 inch thick marine ply, but 1.25 inch was plenty rigid!
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#16 of 18 Dustin Haug

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Posted June 14 2001 - 02:14 AM

$160/sheet is practical? Wow, I'm really poor. Posted Image

Just kidding ChrisA, your subs absolutely kick ass.

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#17 of 18 Stephen Dodds

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Posted June 14 2001 - 08:04 AM

Packer,
That's probably the most sensible option, but I'll continue to ponder options. That's half the fun.

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#18 of 18 Jeff Rosz

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Posted June 15 2001 - 11:00 AM

hello stephen,

i am finishing my baffles in brushed stainless with deep red cherry trim and top to match my B&W 805's. $120 for a 4x10 sheet. yep i know its expensive but what the hell. if you do decide to go with aluminum, get a shop that has a plasma cutter to cut the holes. it makes a VERY neat cut. ask them to do some practice runs on some scrap to get the setting on the plasma just right.
why have one when you can have two for twice the price?