Electrostatic headphones

[johnuk]

Just wondering...

I've been having a read about electrostatics and noticed a lot of them use two stators to push/pull the diaphragm.

That's not strictly necessary right? The speaker would also work with just one stator in single ended mode?

Same pros & cons as push/pull vs. single ended amp construction I imagine... push/pull has better control of distortive, excursions due to actuator mass, but also relies on two bodies acting against each other, which increases the possibility of subtle sounds being distorted. Single ended, better chance of actuator overshooting (distortion) but only one drive point means less chance of subtle sounds being missed.

Thanks,
John

 

[labrat]

Deleted.

 

[JaZZ]

IIRC there were some speaker drivers working with just one (rear) stator. If it's designed for this kind of operation, it should work fairly well, but as the OP stated, there's the disadvantage of an inhomogeneous electrostatic field and thus driving force during membrane movement. The advantage is indeed that there's no stator grid between the membrane and the listener which could corrupt the sound waves by compression and reflection effects -- although I suspect there was some kind of protection grid instead anyway, and the rear stator has its adverse effects nonetheless. I've never heard such a design myself.

 

[johnuk]

Indeedo,

I didn't mean there are phones like this or that you could just unplug two of the stators in a normal pair and run them in single ended mode, I meant... you could design a pair like that.

The normal layout is push pull, like you say. But the only thing moving the diaphragm is the strength of the electrostatic field between it and the stators; it doesn't need to have positive one side and negative the other.

You could have a single drive stator on one side only, provided it swung negative and positive compared to it's resting field it would produce a symmetrical movement on the diaphragm.

I'm only really thinking about this because I was having a read on the net earlier and found a site I'd read before, as well as another I haven't, about DIY'ing electrostatic drivers.

Provided you're patient and careful, it doesn't actually look too far beyond a DIY'er. Removing one of the stators would be a good way to make building the driver even easier; just the stator, spacer and mylar. But, as it's already been pointed out, it wouldn't run from a normal electrostatic amp configuration.

Think about the Gold leaf charge detectors used in Physics. You have two very thin pieces of Gold leaf suspended, together at one end with the remainder of their lengths loose, in a jar, to keep them safe from damage and drafts, with a contact in the lid. If you put some static on the needle, the leaves separate. Discharge the contact and the leaves fall back together.

Now fit the same thing to a pair of phones, one per ear, but make one of the leaves a fixed, rigid stator.

 

[trbl]

Quote:

Originally Posted by johnuk I'm only really thinking about this because I was having a read on the net earlier and found a site I'd read before, as well as another I haven't, about DIY'ing electrostatic drivers.

I mentioned this in a diferent thread some weeks ago, but you might find it useful, as not everyone has spent time reading 1950's issues of "Wireless World."

For electrostatic theory, including the explanation of why the diaphragm is constructed and biased as it is (to try to put a constant charge and not a constant voltage on it) a seminal reference is Walker's "Wide Range Electrostatic Loudspeakers" From Wireless World in May 1955.

One version of this can be found here:

<http://www.onethingaudio.com/FOR/QUA/GEN/PDF/9512-QUA-GEN-HIS-WW-PW1-WL.pdf>

 

[johnuk]

Quote:

Originally Posted by trbl I mentioned this in a diferent thread some weeks ago, but you might find it useful, as not everyone has spent time reading 1950's issues of "Wireless World." For electrostatic theory, including the explanation of why the diaphragm is constructed and biased as it is (to try to put a constant charge and not a constant voltage on it) a seminal reference is Walker's "Wide Range Electrostatic Loudspeakers" From Wireless World in May 1955. One version of this can be found here: <http://www.onethingaudio.com/FOR/QUA/GEN/PDF/9512-QUA-GEN-HIS-WW-PW1-WL.pdf>

Excellent article! Definitly useful!

It'll take me a few days to read through and fully understand I expect.

I noticed the explaination for having two stators, I also like the discussion of diaphragm dimensioning ratios for better reproduction.

I'm impressed more audiophiles haven't tried making their own pair given the simplicity of the end result compared to a normal moving coil speaker.

I must admit, the idea of strapping 500V+ to my temporal lobes kind of bothered me at first as well.

Seem like a definite situation where using monoblocks for each channel is the best idea, even if the audio is mono, since it'll lower the possibility of setting your brain up as a short.

 

[trbl]

Quote:

Originally Posted by johnuk I'm impressed more audiophiles haven't tried making their own pair given the simplicity of the end result compared to a normal moving coil speaker.

There were quite a number of articles by David Hermeyer and others from the 1970's Audio Amateur magazine (available on CD) on building your own electrostatic speakers and matching direct-drive amplifiers. The discussions were interesting, as was the evolution of the various designs over time.

<http://www.audioxpress.com/magsdirx/audelex/aabilist.htm>

Electrostatic loudspeakers are big, so making the stators and diaphragm would be time consuming (have to get the resistivity of the diaphragm uniform and in the correct range so it operates in constant charge mode, the requirement for linearity discussed in the Wireless World articles by Walker). With headphones the difficulty probably comes in getting the stators made and positioned well. The loudspeakers used stators made of metal bar, or thin metal rod, or perforated metal depending on the builder and version of the speakers. With a headphone, where you're listening to the near field, the acoustic effects of the stators will be much more pronounced. So finding a proper design (and one that can be made with limited facilities) can be tricky. The Stax Lambda, Stax Omega, and Sennheiser Orpheus are all different, presumably in an effort to find the stator that's the least resonant and most acoustically transparent, and which provides the most uniform electric field to drive the diaphragm.

 

[DanT]

Quote:

Originally Posted by johnuk I'm impressed more audiophiles haven't tried making their own pair given the simplicity of the end result compared to a normal moving coil speaker. I must admit, the idea of strapping 500V+ to my temporal lobes kind of bothered me at first as well.

Here a very nice attempt by hozo

http://www6.head-fi.org/forums/showthread.php?t=143031