Acoustic Resonance in Cylindrical Capacitors

Acoustic resonace of a tube? In air? Open or closed end? If it's a narrow tube the end effects are less. It will change with the pressure. (and density of the gas.)

George H.

Do large cathedral pipe organs require re-tuning from season to season? Probably

I doubt it, they all stay in sync, but..

-Lasse

s

l

Plastic film capacitors also exhibit "charge soak" which I've always suspec ted to reflect mechanical movement within the capacitor - it's slower than the sort of acoustic resonance that's being talked about here, but relative ly easy to demonstrate in the right circuit - which in my case was a quad-r amp integrating A/D converter ...

--
Bill Sloman, Sydney

** The resonant frequency depends on the speed of sound which essentially only changes with the air's temperature.

The speed of sound decreases at high altitude because it gets very cold up there.

And as already stated, all the pipes of an organ are in the same boat or cathedral.

... Phil

ected to reflect mechanical movement within the capacitor - it's slower tha n the sort of acoustic resonance that's being talked about here, but relati vely easy to demonstrate in the right circuit - which in my case was a quad

-ramp integrating A/D converter ...

** Sure you are not thinking of DA or "dielectric absorption". You briefly short out a charged cap and 10 seconds later it has a small cha rge again. The effect is very obvious with polyester film and several other s but is largely absent with polypropylene film.

Kinda knocks your " movement" theory on the head.

BTW This is the stuff of audiophool dreams.

.... Phil

spected to reflect mechanical movement within the capacitor - it's slower t han the sort of acoustic resonance that's being talked about here, but rela tively easy to demonstrate in the right circuit - which in my case was a qu ad-ramp integrating A/D converter ...

Those are other names for the same effect.

harge again. The effect is very obvious with polyester film and several oth ers but is largely absent with polypropylene film.

People who have modelled the effect see a range of time constants.

Why? I was thinking of "blisters" in the metallised foil deforming under el ectrostatic stress. The time constant is going to depend on the shape and s ize of the blister - there won't just be one.

Polyester is worst, polycarbonate isn't much better, and polypropylene show s relatively little. Polystyrene is supposed to be good, but it isn't usefu l in applications where it matters.

Dielectric absorption is real enough. It's usually too slow to matter for a udio, which doesn't stop the crooks who exploit audiophools from selling ex pensive polypropylene capacitors that aren't appropriate for most audio app lications.

--
Bill Sloman, Sydney

Interesting idea, but I'd think that would exhibit hysteresis, 1/f noise and all other uglies of the worst sort. It would also suggest that shitty capacitors should have a lot more absorption and other bad effects than good, voidless ones, which... I don't know if that's the case, really. Most commercial parts I wouldn't think would exhibit those sorts of things any worse than any other example of the same dielectric. That is to say, they're all wound as tight as can be (and/or bonded), so it doesn't matter.

You can *hear* the crinkle of a hand wound high voltage capacitor, though...

Tim

--
Seven Transistor Labs 
Electrical Engineering Consultation 
Website: http://seventransistorlabs.com

I have heard that large cylindrical caps can have a self resonance at acoustic wavelengths.

Does anyone know how this is applied in practice?

In other words, if I wanted an acoustic resonance of 20KHz, how would I calculate the dimensions of the cap.

This is a ssuming it is comprised of a pair of nested thin wall tubes.

What part does the dielectric play in determining the resonance? For example air vs. Barium Titianate.

Note this relates to self-resonance, not part of a tuned circuit.

David King

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s

Charge soak/ dielectric absorbtion doesn't vary from capacitor to capcitor to capacitor or from manufacturer to manufacturer. Polyester dielectrics ar en't good, polycarbonate dielectrics aren't much better, polypropylene isn' t bad and teflon is reputed to be better.

Nobody has ever said what is actually going on. Mechanical displacement fit s the time constants, but it's a hypothesis that's never been formally test ed.

--
Bill Sloman, Sydney

I was actually referring to self-resonance at acoustic frequencies.

For example, the cylindrical peizo transducers of sonobouys are designed to ring at around 20KHz. The inner and out silver sintering are effectively capacitor plates.

Presumeably, air or mylar insulated cylindrical caps would have an analogous property.

How would their resonance be calculated?

I am thinking it is a function of the surface area, gap and dielectric constant.

David King

oops, sorry density is wrong. There is no temperature variation, but it does depend on the mass of the gas atoms/ molecules.

George h.

On $h!t, Scratch that,

Independent of pressure but NOT temperature. sorry,

George H.

A "cloud" of a given gas rests in a lattice where the spacing between the atoms depends on the absolute pressure of the cloud. This is why the air down here at sea level is a denser lattice than at 100,000 feet.

If the air at 100,000 feet were as dense as sea level air, all the spacecraft we ever sent up would have burned up on re-entry. (or bounced back out into space)

One reason why yhe projectile of a railgun is a wad of plasma by the time it reaches its target. 37,000 fps is pretty damned fast at sea level. Anything in that air at that speed is going to get very hot very fast.

A tank of the old, banned F-12 freon rests at an internal head pressure which nearly matches the outside ambient. So if the tank reads 72 psi, it is very likely 72 degrees where it was kept long enough to fully settle in at that ambient temp. That pressure is determined by how much of the liquid freon in the tank phases to gas in the 'head space' of the tank.

snip

Maybe you could first learn how to set the clock on your PC correctly.

On Sat, 24 Jan 2015 15:48:31 +0000 (UTC), DecadentLinuxUserNumeroUno

[...]

You don't think someone would have just added wings? Descent would take a bit longer, but the Shuttle wouldn't have had to land by "belly flopping" at, what, 25kmph?

Exiting the Earth might have been a bit trickier, unless there was a near-infinite pressure gradient ("barrier") at 100kft; if that were the case I think we could have flown prop aircraft to the barrier, then launched into vacuum with minimal fuel.

Or have I missed something?

Frank McKenney

--
    To learn is to change.  Learning allows an animal child to 
    finish the long, slow process of evolution by changing in its 
    own lifetime.  Tiger cubs, eaglets, or babies, nature brings 
    us all into existence with the ability to learn, and the rest 
    is up to us.             -- Susan McCarthy / Becoming a Tiger

A british company called Clarity Cap ran an extensive study a few years bac k to investigate acoustic resonance within a capacitor. That study can be f ound if you visit the Audio Engineering Society and do a search on capacito rs. The outcome was the development of the MR series cap. It's very expensi ve, but they claim that cap addresses mech. resonances. Here is a link to info on the MR cap

Reminds me of Druidia...

A shell would be pretty handy for mounting communications repeaters (they wouldn't be "satellites" anymore) and such.

Tim

--
Seven Transistor Labs 
Electrical Engineering Consultation 
Website: http://seventransistorlabs.com

That sounds like something we've answered, so you'll need to be more specific.

When you say "resonance", to what are you referring? The acoustic mode alone (Helmholtz resonator)? Electric mode alone (coaxial resonator)? Or the coupling between the two (which requires some motion mechanism)?

Tim

-- Seven Transistor Labs Electrical Eng>