Resonance of case affected audio

[Marco]

It's because I'm typing on my phone and I can't properly see the predictive text doing it's annoying thing - happy?

Are you getting stroppy, sweetheart? If so, I'll spank yer botty...!

I'm (well) aware of acrylics properties - it a reasonably good insulator (both of electricity and of heat) but that isn't the reason DNM used (may still use) it for their cases - I've already alluded to that - eddy currents - induced magnetic fields in non ferrous materials. This phenomena definitely exists but whether it is generated in an amplifier and whether it is relevant in this context are different issues.

Indeed... I'm sure that all those factors are relevant, but hey, if it sounds better, then worry not about why and just enjoy the music

Marco.

[brucew268]

Acrylic would have been a good idea for the CD transport. Don't know why I didn't think of that. My pre, however, has the top and sides molded as a single piece (bent steel), so I'd have to do some bonding. Best to try the no cover first to see if there is enough benefit to warrant the effort. I hadn't thought of the earthing issue (see braininjuryhelp.com ), but certainly could attach a section of earth wire if the mechanically isolated lid 'sounds' as good as lid removed. I'll have to see if I've got time for the initial experiment this weekend.

[YNWaN]

You can do sides and top as one piece in acrylic, no need to bond it (in this case ) I've done the top, sides and bottom all in one piece.

[Marco]

Looks fantastic, Mark... Top job, as usual!

Marco.

[YNWaN]

Thanks, they were a bit of a PITA to get right - the dark grey tint acrylic isn't sold by my usual supplier either so I had to but it from elsewhere (more expensive). I only made them because I thought it would be cool to be able to see the internal LED's and circuit board.

I also made a small equipment rack to hold the two boxes apart - to aid cooling. You can just see it in my rather poor iphone pictures.

[Sovereign]

Nice one mark, I think most of us want to see inside our kit, I've often thought of a clear lid. Looks great.

[Jimbo]

Hi Bruce,

your post got me thinking as I am aware valve amps do benefit from vibration Isolation. This morning I started playing some music and held my hand on top of both my pre and power amp casework which I believe are made out of steel. The Crofts use a top steel cover which is bolted to the chassis.

The amount of vibration my cases were picking up was unbelievable, they felt like a massive tuning fork. So what does that imply for the rest of the components and obviously the valves in the case?

I did a bit of research into valve amp Isolation some time back and found various forms from removing the casework to placing massive weighted metal objects on top of the casing to reduce vibration, bit strange However not sure if any of these stopped the valves themselves vibrating?

The only total solution as far as i can think would be to have the amps in another room, but this would be a bit impractical. Not sure if vibration platforms /racks would stop this either as the casework as you have found can ring like a bell!

Difficult one this.

I did take the case off and listened and there was a definite improvement especially in overall clarity but this may be peculiar to valve amps in that there can be some electrical magnetic interaction between the valves and the casework, so I believe? Does anyone ( Anthony TD) know if this can be the case?

[Marco]

I've no doubt whatsoever that acrylic, in terms of amplifier design, has a valid role to play - for all the reasons previously discussed by Mark.

However, I'm not sure, in that respect, that simply removing the lid from a valve amplifier is going to be universally beneficial, as much will depend on the material the lid in question is made from... I've done this numerous times with the (non-magnetic stainless steel) lid on my Croft preamp - in fact it lives most of the time with its lid off, in order to facilitate speedy tube-rolling, etc - and there is never any difference in the sound of the amp, whether the lid is on or off.

Reducing microphony, however, in any area of a system, by whatever method is genuinely effective, is an entirely different matter - and if successfully achieved can produce significant sonic benefits.

Marco.

[brucew268]

Those one-piece top and sides looks pretty slick, Mark! Don't think I've got the kit in my garage to do that though!

James, nearly 20 years ago I experimented with weights and also Dynamat (soft bitumen sheets with aluminum backing and adhesive). The weights worked to good effect and the Dynamat seemed pretty similar in the results, though far better for aesthetics and practicality. However, 20 years on, and the bitumen has hardened up mostly. So I imagine it is doing far less for my hifi than it once did... and that is with a solid state preamp which can't be putting out a whole lot of heat.

I did find that the greatest result was on my CD transport, and the least result was on my power amp. The SS preamp did benefit, though I'm sure that anything with valves would notice the change far more. Whether with dampening sheets or weights on tops, I found it important not to over dampen. Too much Dynamat or too much weight and the energy started to get sucked out. Too little and you got no appreciable result. And with the weight, it seemed better to use material that doesn't ring in and of itself, so no steel or glass, but sand or lead shot both worked well.

(... this keyboard seems to be slowly going south. I can't seem to type a single sentence without letters getting dropped and having to go back and correct!)

[brucew268]

...but removing the case sides and top altogether was a whole different level, which the dampening efforts were merely striving towards.