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Old 20th August 2009, 03:25 PM   #1
TheGimp is offline TheGimp  United States
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Default Chassis material

Which is better steel or aluminium, and why?

Or maybe it is a question of what are the advantages / dissadvantages of each.

Al is easier to work with and does not rust, however the only tube guitar amps I've seen used steel for the chassis, as did all the tube receivers and amps I've seen.

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Old 20th August 2009, 04:58 PM   #2
ChrisA is offline ChrisA  United States
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Which is better steel or aluminium, and why?
Aluminum is MUCH easier to drill and cut. Ever try to cut a large square opening in steel? Aluminum can be cut with woodworking tools.

As for sound quality, some people can claim a theory where one is better. In in real life there is none

For some people it is easier to paint steel. To do a first class paint job on aluminum requires more care and good primer paint. But aluminum will not rust so it may not need paint.

There are other materials. Stainless steel and galvanized steel.

If you are building a hifi amp then you can assume it will be treated gently. Guitar amps are different. They get moved around, hauled up and down stairs on dollys and so on. Even so strength of the chassis is not an issue because the chassis is typically put inside a wood enclosure. Even if you had to mount 11 pound transformers on the chassis strength is not an issue because you can add reinforcement to the under side or (better) mount the transformer "laydown" style.

If yu are doing the cutiing and drilling buy aluminum

Last edited by ChrisA; 20th August 2009 at 05:00 PM.
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Old 20th August 2009, 05:05 PM   #3
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Currently I prefer perforated aluminium. Best for convectional cooling.
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Old 20th August 2009, 05:10 PM   #4
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Originally Posted by TheGimp View Post
Which is better steel or aluminium, and why?

Or maybe it is a question of what are the advantages / dissadvantages of each.

Al is easier to work with and does not rust, however the only tube guitar amps I've seen used steel for the chassis, as did all the tube receivers and amps I've seen.

tks.
As has been said, aluminum is so much easier for the hobbyist to machine than steel. Powder coating is a cost effect and very durable finish for aluminum too.
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Old 20th August 2009, 05:35 PM   #5
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As for sound quality, some people can claim a theory where one is better. In in real life there is none
Curious how you came to that conclusion. Steel, with inherently lower internal damping, is much more prone to ringing from mechanical excitation. Tubes span the range of microphonics. It makes no sense to flatly claim there's no difference between steel and aluminum in this application.
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Old 20th August 2009, 05:51 PM   #6
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Curious how you came to that conclusion. Steel, with inherently lower internal damping, is much more prone to ringing from mechanical excitation. Tubes span the range of microphonics. It makes no sense to flatly claim there's no difference between steel and aluminum in this application.
Steel is much stiffer though and will have a higher frequency resonance than aluminum, which will be much lower in frequency. Low frequencies are going to be more problematic than higher frequencies. Aluminum will also store more energy than steel due to its compliance and release said energy at a slower rate. If I had the money, i would use a heavy gauge steel for my chassis, but I don't so 1/4" aluminum is what I intend to use.
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Old 20th August 2009, 07:44 PM   #7
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Aluminum will also store more energy than steel due to its compliance and release said energy at a slower rate.
Why aren't bells made of aluminum? My suggestion comes from experimenting with both steel and aluminum speaker cabinets. The former (1/4" wall EMT rectangular tube) was impossible to damp. 3/16" aluminum bonded to linoleum floor tile and glued to the interior walls barely made a dent. In contrast two face-to-face 1/8" aluminum sheets makes for a highly damped 1/4" plate prior to the application of any constrained layer techniques. It's not a subtle difference.
If you haven't purchased the material yet I recommend trying the experiment above at the metal supplier.
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Old 20th August 2009, 08:52 PM   #8
ChrisA is offline ChrisA  United States
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Curious how you came to that conclusion. Steel, with inherently lower internal damping, is much more prone to ringing from mechanical excitation. Tubes span the range of microphonics. It makes no sense to flatly claim there's no difference between steel and aluminum in this application.
He is talking about buying a ready made Hammon style chassis. Not making a speaking enclosure.

Look at the worst possible case. A guitar combo amp. These amps will mount the chassis and tubes inside the speaker cabinet inches away from the driver. If you could hear steel chassis vibrations it would certainly show up in that application. For over 50 years now musicians who likely have some very good ears have not complained even when the steel chassis is mounted inside a speaker cabinet.

Hammon made many, many organs this way too. Steel chassis mounted directly inside the tone cabinet along with a number of 12 and 15 drivers. Again no reported problems with chassis vibrations in over 50 years of use. But they did use very heavy steel.

I do agree that in theory there could be a difference but audible differences are not widely reported

All that said. I'd go with aluminum simply because of how much easier it is to cut and drill.

Last edited by ChrisA; 20th August 2009 at 08:56 PM.
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Old 20th August 2009, 09:17 PM   #9
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Look at the worst possible case. A guitar combo amp. These amps will mount the chassis and tubes inside the speaker cabinet inches away from the driver.
One is a music producer, the other a reproducer. The impact and desirability of microphonic bleed through are hardly equivalent. In most cases the primary source of chassis excitation in a hifi amp is the power supply transformer, a noise completely uncorrelated with the audio amplified.
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Old 20th August 2009, 10:46 PM   #10
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Hi Gimp,

There is a very big thread on this topic here -

Aluminium vs steel chassis

Rob
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