Electret vs. Electrostatic

[Carl]

Quote:

Originally Posted by wualta As you yourself know, there are a very few exceptions to this; the Toshiba/Aurex HR series comes to mind. The only electret 'phone I know that's comparable to the SR-X.

I know. The Final Sound electrostatic speakers are also like that. There are also some like the Beverage stats which send the signal to both the diaphragm and the electrodes and use no direct charging.

But for simplicity sakes, I decided to talk just about the "normal" implementation of the technology.


Quote:

Whoa, you lost me on that one, pardner. I'm doubly stumped now.

The diaphragm isn't the only thing being fed high voltage, right? So isn't the only thing storing a capacitive charge, right?

It's the reason why electrostatics can sound better after a couple of songs, even if you've left them to charge overnight.

 

[stewtheking]

Quote:

Originally Posted by wualta You really got me there, STK. A "normal" 'stat needs to charge up its diaphragms through a very high resistance after long storage, so it does take awhile in that specific case-- think of an old-fashioned under-the-tongue thermometer-- but I wouldn't expect a 'tret to have that problem, since its diaphragm isn't connected to anything and is fully charged 24/7/365. If there were electrolytic capacitors somewhere in the signal path, they'd need re-forming after long storage, but other than that... I'm stumped.

My only other guess was dust on the membrane that gradually fell off as the diaphragm was pushed into service again... or as i say, burn in, as the driver creaked out of it's re-"settled" position.

 

[wualta]

Quote:

Originally Posted by Carl The diaphragm isn't the only thing being fed high voltage, right? So isn't the only thing storing a capacitive charge, right?

We-e-e-ellllllll...no! Because if the stators were storing anything, it would sound like the Reverb From Hell. The stators are supposed to let go of any voltage that's on them the instant it's removed. Otherwise we'd be calling electrostats "slow" and "ain't got rhythm".

Now-- does any capacitorlike setup like a 'stat 'phone have little parasitic charge nonlinearities distributed here and there? Could very well be. Are they audible? I think they'd be swamped by all the other problems of a mass-produced practical transducer. And this just could be something unique to STK's ATH-7..

Maybe a high-pass filter in there that uses electrolytics, or possibly the LED level meter circuit. I've never busted my ATH-8 transformer box apart to look; maybe I should. I've never noticed the effect with any of my ancient ECR-500s, which have a dead simple box. Dunnaow, mate. Or, as we say here in the States, I got nuthin'.
.

 

[mirumu]

Quote:

Originally Posted by Carl The diaphragm isn't the only thing being fed high voltage, right? So isn't the only thing storing a capacitive charge, right? It's the reason why electrostatics can sound better after a couple of songs, even if you've left them to charge overnight.

The actual "capacitor" in such a circuit is the two plates with the air between them acting as the dielectric. This means that it is actually the air holding the charge, not the plates. The bias applied to the diaphragm determines how large a force is applied to it by the charged electric field in the air. Potentially you could use any dielectric instead of air but that would only restrict the movement of the diaphragm. It has made me wonder though if cotton might be a great material for making the spacers.

 

[wualta]

Quote:

Originally Posted by mirumu The actual "capacitor" in such a circuit is the two plates with the air between them acting as the dielectric. This means that it is actually the air holding the charge, not the plates.

But wouldn't a total vacuum work just as well as a dielectric? Can a vacuum hold a charge?



Quote:

It has made me wonder though if cotton might be a great material for making the spacers.

You bring up a very intriguing point. Back in 1956 a company called Pickering sold an add-on electrostatic tweeter called the Isophase. Most 'stats have tensioned diaphragms. Most condenser mics likewise. But that always creates problems. What if you could have a non-tensioned diaphragm? That might solve a lot of.. oh, no, wait, wait, you'd need something to suspend the diaphragm. How about a zillion little springs? Or, how about something like tiny curls of fiber? How about something like the nap of a carpet? You could mass-produce the thing at any disused carpet mill. You could breed special electrostatic sheep for special curly wool... Anyway, that's what motivated the Pickering engineers and that's what they built. I think it's time to bring back the nontensioned electrostatic diaphragm.

 

[nikongod]

Quote:

Originally Posted by wualta Anyway, that's what motivated the Pickering engineers and that's what they built. I think it's time to bring back the nontensioned electrostatic diaphragm.

did it sound like poo?
it is not dificult to build a LOW tension electrostatic headphone.

 

[wualta]

Quote:

Originally Posted by nikongod did it sound like poo?

Dunno. Me mum told me never to listen to what poo has to say.

Of course, in NYC they have highly trained talking poo..

(An old radio colleague of mine ended up working for Grey.)


Quote:

it is not dificult to build a LOW tension electrostatic headphone.

Build, no. Use, yes.

 

[mirumu]

Quote:

Originally Posted by wualta But wouldn't a total vacuum work just as well as a dielectric? Can a vacuum hold a charge?

Well when a system like this is operating in a vacuum without dielectric, what you have is essentially electrons that are moving from one plate to the other through the vacuum unhindered. No charge is stored on the way as it would be with dielectric. The diaphragm could move even more freely in the electric field without all that air in the way. The only problem is that we couldn't hear anything without having some material such as air for the diaphragm to push against.

Quote:

You bring up a very intriguing point. Back in 1956 a company called Pickering sold an add-on electrostatic tweeter called the Isophase. Most 'stats have tensioned diaphragms. Most condenser mics likewise. But that always creates problems. What if you could have a non-tensioned diaphragm? That might solve a lot of.. oh, no, wait, wait, you'd need something to suspend the diaphragm. How about a zillion little springs? Or, how about something like tiny curls of fiber? How about something like the nap of a carpet? You could mass-produce the thing at any disused carpet mill. You could breed special electrostatic sheep for special curly wool... Anyway, that's what motivated the Pickering engineers and that's what they built. I think it's time to bring back the nontensioned electrostatic diaphragm.

I'd be keen to see some more research down this path. It also poses the question, "Do audiophiles dream of electrostatic sheep?".

 

[wualta]

Quote:

Originally Posted by mirumu "Do audiophiles dream of electrostatic sheep?".

I know I do, mate.

But seriously..

As you probably know, wool has unique acoustic properties and has long had a role in the design of speakers, especially British transmission line speakers. Breeding a sheep whose hairs are like little coil springs might not be possible, but we can dream, eh? Alternatively, it might be possible to make a suspension from silicone rubber drawn into short "fibers" of carefully randomized lengths.

Basically, I simply wanted to point out that the tensioned diaphragm is not the only way to go.

 

[SoundGoon]

Quote:

Originally Posted by wualta I know I do, mate.

x2

 

[wualta]

Quote:

Originally Posted by mirumu ...in a vacuum without dielectric...

I know we're mostly funning about here, but the serious point I wanted to make was that a vacuum is a dielectric, in fact an ideal dielectric (dielectric constant = 1.000), and so it's clearly not on or in a dielectric but rather on a capacitor's plates that the charge voltage appears. And disappears. To be replaced right smartish by a different charge. In accordance with the audio signal; ie, no charge storage in the stators of a properly operating 'stat, ie, no warmup due to such a thing is possible or desirable. Don't. Even. Thinkaboudit.

That's all I got. Back to the fun.

EDIT: Oh, and the Pickering electrostatic mid-tweet model 581 was well-regarded at the time. The Audio Circuit site has a little information and a modest chunk of the history. They were apparently working on a two-way full-range model when someone pulled the Pickering plug.

 

[PalJoey]

Recently launched (and rather pricey), the ENIGMAcoustics supertweeters are electrets. This review mentions a couple of other manufacturers:
http://www.theabsolutesound.com/articles/enigmacoustics-sopranino-super-tweeter/


 

 

[Linn9000]

Hey guys, 
 
Coming in late on this one...
 
I have a new (old) pair of SR80s with the imbalance problem. It's not bad bu when first used the balance is 60 - 40 this improves to about 55 - 45. Not perfect but perfectly livable. Could this indeed be a charging issue? Or maybe debris on the membrane which is loosened? 

 

[mindblownDt48]

im a big noob on this subject, so if anyone can give a straight short comment... Do electret hp stop working at some point (discharge or whatever) ? are they worth it sound wise?

 

[nick n]

Only if they have been overdriven, or stored in poor conditions generally speaking. Theoretically they should last 10,000years
I have had my share of lower volume ones, but also ones that were fine like the new in box 40+years old set and worked/still works perfectly.
So it is a gamble, and always best to ask a seller if there are ANY imbalances between sides as that is permanent and will never recharge, ever.
Buying one where they cannot or will not test them, you simply take your chances.

Soundwise there's so many variations, as well as personal preferences involved.
I've yet to try the later "Back Electret" style.