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Old 12th July 2003, 08:27 PM   #1
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Default Suggestions for lid material

Not being much of a handyman it took me a while before i built a reasonable enclosure for my clone. For a long while it merrily buzzed enclosure-free on my rack. The case looks a bit like Peter's, only it's a lot larger (ps inside), not very well made and far from cute. It's made out of 10mm alu but the base is wood. The chips are mounted on 20mm copper blocks to reduce the length of wiring between chip and binding post.
Now for the problem. I had some doubts that such an expanse of alu will aid the sound much, but seemingly all was well before i bolted the lid. With the top in place the sound took a major turn for the worse: an obvious midbass resonance and worse - an unpleasant grind on voices. The alu itself doesn't seem to be culprit, with the cover resting diagonally on top the sound is fine; it only gets screwed with the cover firmly in place. I briefly tried different materials like 10mm acrylic and PVC and the acrylic sounded quite unobtrusive. Unfortunately the only type i can get in 10mm is clear which i would rather avoid. The best solution is probably a cover with multiple large holes which won't allow the forming of a resonant cavity. Any suggestions not too difficult to implement are very welcome.

peter
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Old 12th July 2003, 08:46 PM   #2
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try some foam tape on your lid around the mating surface.
It would be ashame to waist it
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Old 12th July 2003, 08:52 PM   #3
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What about wood? I also have plenty of tinted (black) acrylic. If you interested I could send you some

You migh talso try to attach something to the bottom of top alu panel. Don't tight the screws or use additional tension rod through the center of the box (from the bottom).

What are those small holes in top panel?
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Old 12th July 2003, 09:16 PM   #4
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Quote:
try some foam tape on your lid around the mating surface.
Good point. I tried several layers of cork in all corners to no effect. Foam tape will probably be similar.

Quote:
What are those small holes in top panel?
Peter, you really don't want to know Did them by mistake. I mostly do programming and mistakes there are quite a bit easier to fix than holes in metal. Dunno if damping the lid will help; the main resonances will certainly remain. If i could i would drill giant holes in it and combine that with damping. Wood, i still haven't tried. It will probably sound ok but may look quite out of place. It's very amusing how terrible the cover sounds; i would put up with almost anything just to avoid extra work, but this is just too much.
Oh, and thanks for the acrylic offer. As much as i like shopping for parts from Canada, shipping a hulk of plastic half way (or is it full way?) accross the world exceeds even my madness.

thanks guys
peter
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Old 12th July 2003, 09:28 PM   #5
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On my monoblocks I used 1/4" aluminum plates as bottom covers. One cover is under electronics section, the other, bigger under transformers. I didn't like the sound of those amps in the beginning, the sound was muffled and colored. Out of curiosity I removed the smaller cover and used a piece of solid maple wood, 3/4" thick, no spike, block of wood acts as footing.

The change in sound was tremendous, no more colorations, more space and detail. I like to use maple and I think that wood sounds better than acrylic. If you finish it nicely, top cover out of wood might look really good.
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Old 12th July 2003, 09:51 PM   #6
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I think that an all metal box - even aluminium - causes some kind of magnetic restriction that trashes the openness of the sound.

I think that denis moorcroft developed this theory and consequenly uses acrylic for his enclosures and avoids metal of any kind as much as possible. He puts his O/P devices on quite thick ceramic heat tranfer washers to keep them away from the heatsink.

perhaps at least one non-metalic surface in an enclosure is essential ?

mike
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Old 12th July 2003, 10:05 PM   #7
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Quote:
Originally posted by mikelm
I think that an all metal box - even aluminium - causes some kind of magnetic restriction that trashes the openness of the sound.

I think that denis moorcroft developed this theory and consequenly uses acrylic for his enclosures and avoids metal of any kind as much as possible.
I wouldn't count that out. Did you try those stones immersed in reisn in your monoblocks yet Mike?
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Old 13th July 2003, 12:07 AM   #8
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Default acrylic

if you can only get clear acrylic
you could always spray the inside w colour/black/logo?
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Old 13th July 2003, 08:00 AM   #9
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Quote:
Originally posted by Peter Daniel


I wouldn't count that out. Did you try those stones immersed in reisn in your monoblocks yet Mike?
not yet, you mentioned somewhere recently about simple crossovers sounding best and I'm reaping rich sonic rewards on that front at present.

Thanks for the idea.

When I've finnished I'll post my results in loudspeakers and get back to GC monoblocks.

cheers

mike

p.s. good luck with your commercial venture, the amp looks great ( I hope the wingers have not put you off the idea )
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Old 13th July 2003, 08:45 AM   #10
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Quote:
I think that an all metal box - even aluminium - causes some kind of magnetic restriction that trashes the openness of the sound.
This was my first thought. Interestingly, when the cover sits on top askew, electrically touching the sides, the sound is fine. Alu should have no magnetic effect, other than that of eddy currents. I somehow feel that the audible effect is mostly the result of acoustical resonances. Peter Daniel's enclosure is much smaller which means higher resonant frequencies which are apparently less damaging and easier to control. Oh, and the cover adds another 3kg to the mass, probably not a good thing as well.
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