Resonance of case affected audio

[brucew268]

20 years ago I had a Theta transport which performed heads and tails above anything I could find in its price class... and then the laser went out and had sadly gone out of production, with lesser replacements on offer. Before the Theta betrayed me, whilst looking inside one day, I found something that caused the music to take on a much greater sense of natural, analog-like ease that I'd not heard out of a digital in the 90's, without giving up any detail or definition. The cause was removing the case top. I had previously applied bitumen damping to the cover, which reduced some ringing and increased the sound stage. But removing the cover altogether was a revelation. Unfortunately at the time I could not think of a good solution to keep dust et al away from the transport drive and electrics. And I was a little concerned about health and safety. So I reluctantly screwed the cover back on.

It could have been a resonant interaction with the mechanics of the transport, and/or it could have been an interaction with some of the components on the PCB.

Reminded of that today, I wonder if my preamp would also respond well to removing or isolating the cover from the rest of the case. So I may try putting a thin layer of rubber between the case top and the main structure, screwing down only lightly. Since the cover wraps around on the sides, that will mean the side screw holes will not likely line up and will need to leave those unfixed.

[walpurgis]

That's an odd story Bruce. I've never tried using gear with metal covers removed, but some manufacturers like NVA and DNM use non metal casings, so maybe there's something in it.

I wouldn't necessarily recommend completely isolating a metal cover. There may be an earthing issue and that could impact on safety.

[Jimbo]

20 years ago I had a Theta transport which performed heads and tails above anything I could find in its price class... and then the laser went out and had sadly gone out of production, with lesser replacements on offer. Before the Theta betrayed me, whilst looking inside one day, I found something that caused the music to take on a much greater sense of natural, analog-like ease that I'd not heard out of a digital in the 90's, without giving up any detail or definition. The cause was removing the case top. I had previously applied bitumen damping to the cover, which reduced some ringing and increased the sound stage. But removing the cover altogether was a revelation. Unfortunately at the time I could not think of a good solution to keep dust et al away from the transport drive and electrics. And I was a little concerned about health and safety. So I reluctantly screwed the cover back on.

It could have been a resonant interaction with the mechanics of the transport, and/or it could have been an interaction with some of the components on the PCB.

Reminded of that today, I wonder if my preamp would also respond well to removing or isolating the cover from the rest of the case. So I may try putting a thin layer of rubber between the case top and the main structure, screwing down only lightly. Since the cover wraps around on the sides, that will mean the side screw holes will not likely line up and will need to leave those unfixed.

Hi Bruce, I have heard that valve pre amps in particular do benefit from being used without casing. Not tried it myself as I don't want to accidentally go up in puff of smoke.:eek:

[YNWaN]

I've just replaced the cases housing my phonostage with acrylic and their seems to be a sonuc advantage over the previous aluminium - this may be a resonance issue, an eddy current issue, or just my fancy (not decided yet).

[YNWaN]

I'm having a nice listen now and it definitely sounds better - which is odd as all I have done is replace the aluminium sleeves of the cases with acrylic and moved the two halves (it's mono in two cases) 40mm further apart. This is just the main circuit - all the power supply is in two more cases and they are a metre away already!

Edit: or, as ventilation is better, the DC thermal drift is better controlled - could be that.

[The Grand Wazoo]

Despite being held down against almost spring-like tension with about 12 screws, my pre sounds better without it's lid on. I never tried it without the identical bottom cover removing though. The Radford is also improved by the lack of it's box-like transformer cover, but I don't have the recklessness to try to risk the potential consequences of doing either long term.

[YNWaN]

Why is there 'spring like tension', is the lid bowed?

[Marco]

I'm having a nice listen now and it definitely sounds better - which is odd as all I have done is replace the aluminium sleeves of the cases with acrylic and moved the two halves (it's mono in two cases) 40mm further apart. This is just the main circuit - all the power supply is in two more cases and they are a metre away already!

Edit: or, as ventilation is better, the DC thermal drift is better controlled - could be that.

I believe that Anthony TD, in a discussion elsewhere about acrylic casing, said something along the lines of acrylic making an excellent insulator, or something like that. I can quiz him again on it, if you like? There were certainly sonic reasons why he built his Soul amplifiers with acrylic cases.

Btw, what's with this 'effected' pish (not just you, incidentally)? It's affected!! Honestly, wot skoolz did yooz lot go to? ;)

Marco.

[The Grand Wazoo]

Why is there 'spring like tension', is the lid bowed?

Yes, it's a sheet of metal, perforated except for a solid border and with a very slight curve in it, only becoming apparent when you begin removing the fastening screws. The apex of the curve runs across the width of the unit and I fasten the front and back of it against the tension, rather than pulling the centre down, as it would be it it were flipped over (if you follow me).

http://img233.imageshack.us/img233/1900/imgp1754ikb.jpg

[YNWaN]

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

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.

[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 :cool:

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 :rolleyes:), 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.

http://i62.photobucket.com/albums/h90/markemark_2006/Hi-Fi/AC26F254-583C-46E0-B6C4-0CE63018C814_zpsihdfpmqy.jpg (http://s62.photobucket.com/user/markemark_2006/media/Hi-Fi/AC26F254-583C-46E0-B6C4-0CE63018C814_zpsihdfpmqy.jpg.html)

http://i62.photobucket.com/albums/h90/markemark_2006/Hi-Fi/E06E8945-B77D-4434-BB43-0E750B4A312D_zpsecbsdsf0.jpg (http://s62.photobucket.com/user/markemark_2006/media/Hi-Fi/E06E8945-B77D-4434-BB43-0E750B4A312D_zpsecbsdsf0.jpg.html)

http://i62.photobucket.com/albums/h90/markemark_2006/Hi-Fi/BB224209-D431-46E3-8915-56B383600118_zpsismrukdg.jpg (http://s62.photobucket.com/user/markemark_2006/media/Hi-Fi/BB224209-D431-46E3-8915-56B383600118_zpsismrukdg.jpg.html)

http://i62.photobucket.com/albums/h90/markemark_2006/Hi-Fi/8A4C9CA3-87C3-496E-B31B-A6A40B02085F_zpsaoeqtuxb.jpg (http://s62.photobucket.com/user/markemark_2006/media/Hi-Fi/8A4C9CA3-87C3-496E-B31B-A6A40B02085F_zpsaoeqtuxb.jpg.html)

[Marco]

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

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?:eek:

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:scratch: 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.

[Jimbo]

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!)

The chap who tried weights was using lead but as you say aesthetics may be compromised:lol:

[brucew268]

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?:eek:

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:scratch: 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?

If I recall theories on sources of vibration include:
Vibration from sound waves of speakers
Vibration transmitted through the floor from walking, trucks going by, etc.
Vibration transmitted through the suspended wood floors, just due to the resonant nature of such.
Vibration from mechanical movement of transports/turntables, which could affect the transport itself or anything else on the same equipment stand.
Vibration from electrical currents and fields operating within a specific piece of kit, exacerbated by physical and magnetic interaction with casework.
Vibration produced by the filaments of valves themselves.

It seems that solid state could be affected by any of the above, though in some cases imperceptibly, and valves being microphonic would likely to be more highly affected by all of the above.

[brucew268]

I only made them because I thought it would be cool to be able to see the internal LED's and circuit board.

In making my mains distribution hydra, I thought it would be cool to see inside the box, and also thought it an extra measure of safety to be able to see in the odd event that a live wire came loose before opening the lid. Some have noted that distribution boxes tend to sound better if not made with ferrous metal or even aluminum. The downside would be that they may be more susceptible to EM and RF fields. I have noticed significant results by addressing this just as strenuously as physical vibration. But then I have my telly and Sky box close by (at the top of the equipment stand).

[StanleyB]

One of the problems that has affected metal cases in the last twenty odd years is that they are being made thinner in order to save on shipping weight and material. The lighter cases vibrate a lot more, which affects CD and DVD players a lot more for some reason. Next comes the level of coating. A lot of metal cases tend to have just a coat of paint over them these days, and maybe a primer underneath. But it is again a cost cutting measure. I noticed this problem when I was in the repair business, but it is not the kind of thing you go shouting about. The exist door and loss of a job is never far away if you start saying things like that. Who wants to employ a nut case after all?
But I myself decided to try to find a solution when I started to look for a case maker for my first products. I settled on a far thicker metal sheet, which is 2mm instead of the almost universal 1.2mm. The 2mm is far more rigid. It is also made of a denser steel, instead of the softer steel alloy now coming out of China. I also electro plate the case before priming and praying it. But it is not the kind of stuff one mentions in the product description.