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Electrostatic design - is a round design practical?
Electrostatic design - is a round design practical?
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Old 25th May 2004, 07:24 PM   #1
sashua is offline sashua  United States
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Default Electrostatic design - is a round design practical?

Hello all,
I am new to the forum here and I have my first question. I am curious as to if it would be possible to construct an ESL panel that is cylindrical. I have seen many designs for a curved panel but none that go the whole enchilada and curve into a cylinder. The major benefit, as I see it, would be an omnidirectional dispersion pattern. I am unaware, however, if this design is mechanically impossible or if there are any major negatives that would make it impractical to construct such a beast.

Can anyone chime in here with advice?

Thanks in advance!
Russ
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Old 25th May 2004, 08:08 PM   #2
SY is offline SY  United States
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One of the guys here did a cylindrical electromagnetic (Magneplaner-type) speaker- there was an article about it in Speaker Builder a few years back. IIRC, there were problems. Certainly, the acoustic transparency of an ESL panel will cause some interesting issues because of the backwave reflection and the interference between opposed sections.
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Old 25th May 2004, 08:21 PM   #3
sashua is offline sashua  United States
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Hello Sy,
Thanks for your reply. I would really like to read that article if you or anyone else reading this could offer me a link or info to hunt it down.

I have thought about the back wave issue and it seems that, given a large enough diameter, one could use a properly absorptive cylinder in the center (something looking like one of Michael Green's Tube Traps) to eat the reflections.

My goal here is not so much to marry myself to an EM or ESL design philosophy but, rather, to come up with a very low distortion, acoustically transparent midrange that is completely omnidirectional and covers a range of roughly 100 Hz to 1,000 Hz

Thanks,
Russ
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Old 25th May 2004, 08:37 PM   #4
sreten is offline sreten  United Kingdom
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Essentially you have to tension the diaphragm vertically.

As is done in Martin Logan panels. A full cylinder would
have problems with the back wave and IMO the dipole
nature of a panel isn't something you'd want to lose.

sreten.
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Old 25th May 2004, 08:46 PM   #5
Audiofanatic is offline Audiofanatic  Netherlands
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Default That's right!

Quote:
Originally posted by sreten
Essentially you have to tension the diaphragm vertically.

As is done in Martin Logan panels. A full cylinder would
have problems with the back wave and IMO the dipole
nature of a panel isn't something you'd want to lose.

sreten.

I did this ones, It didn't work.
You will loos your dipole effect and it'll be a great load to your amp if you make it with a diameter of 20cm or greater.

Cheers,

Audiofanatic
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Old 25th May 2004, 09:14 PM   #6
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by sashua
Hello Sy,
My goal here is not so much to marry myself to an EM or ESL design philosophy but, rather, to come up with a very low distortion, acoustically transparent midrange that is completely omnidirectional and covers a range of roughly 100 Hz to 1,000 Hz

Thanks,
Russ
For omni directional you will have to enclose the backwave.

As far as I know for electrostatics this simply doesn't work.

sreten.
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Old 25th May 2004, 09:27 PM   #7
sashua is offline sashua  United States
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O.K. then...lets stop thinking about electrostatics for the moment. Any other designs within the FR that I mentioned capable of a truly omnidirectional dispersion? By "truly", I mean 360 degrees on every axis...essentially spherical. The most promising existing design I have come upon thus far is the DDD bending wave converter offered by German Physiks loudspeakers. It is a capable design but it is not perfectly omnidirectional and it suffers from a slight "tizziness" in the upper register. there are plenty of other pretenders to the throne, such as Ohm, Mirage and Shahinian but none that even come close to the elusive ideal of the "pulsating sphere".

Russ
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Old 25th May 2004, 11:28 PM   #8
Timn8ter is offline Timn8ter  United States
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Are you looking for something like Steve Deckert's Radial Loudspeaker ?
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Old 25th May 2004, 11:28 PM   #9
sreten is offline sreten  United Kingdom
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For 100Hz to 1kHz its not difficult using dynamic drivers.

4 4" drivers, one on each horizontal face of a box would be very near.

sreten.
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Old 26th May 2004, 12:04 AM   #10
geolemon is offline geolemon  United States
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Quote:
there are plenty of other pretenders to the throne, such as Ohm, Mirage and Shahinian but none that even come close to the elusive ideal of the "pulsating sphere".
Not to nitpick, but I believe the inventor of the Walsh driver you speak of founded Ohm acoustics, making it the originator, not an imitator.

Also, you mention "pulsating sphere", and I've thought of this too.
I wonder - since it's not a stretch for anyone's imagination, who have pictured a "pulsating sphere" - why not mount a large driver, say, a 12" fullrange type driver inside a bandpass-like enclosure, so it's front-of-cone energy were directed through a tube... to the top of the tube, a balloon like orb.
Not a port, the tube's purpose would be to channel the air stimulations such that they stimulated the air inside the orb, causing the orb itself to be stimulated and emit sound.

Possibly the issue is, it would end up behaving essentially like a passive radiator... all the delays inherent in that.

But... maybe an experiment with a large compression driver.
Who knows. Just seems like something someone would have tried by now. Maybe they have.

Quote:
Originally posted by sashua
O.K. then...lets stop thinking about electrostatics for the moment. Any other designs within the FR that I mentioned capable of a truly omnidirectional dispersion?
The Decware Radial Loudspeaker is different too... as mentioned.
Simple, DIY-able, which makes it cool IMO - but it doesn't have the thing that makes the Walsh-driver (or DDD) a "wave-bending" driver -
The variable-thickness diaphragm that resonates differently at different locations on the diaphragm by frequency because of the tapering diaphragm thickness.

The original whitepaper is always a fun read. I've got it bookmarked, and every 6 months or so I stumble across it and it still evokes a smile. Creativity, beautiful.

But anyway...
When you start talking "wave bending", and variable-thickness diaphragms, one driver pops to my mind very quickly:
The Manger driver unit. Essentially, it's a flattened version of a Walsh driver, if you can pardon my oversimplification. It's got a variable thickness diaphragm that resonates in different zones at different frequencies. Because the diaphragm motion isn't really pistonic (even though the motor is), I'd expect it to behave more like a natural sound source, omnidirectional.
I wish I had the money to cough up for a pair of these... I'd love to try them in a car even!

And of course, if you aren't familiar with their work - another thing that could potentially be very DIY-able to mimick - NXT technology's DML technology.
I was fortunate enough to see some fabricated stimulator-based NXT prototypes at DLC labs, when I was fortunate enough to have received an invite to visit their Detroit facility for a little get-together.
By nature, these distributed mode loudspeakers simply make the diaphram they are mounted to resonate, in a non-pistonic way.
If you like, think of it as controlled 'cone breakup'.
And because of this, the sound from one of these is also not directional.

Have you played with dipoles? I'm working on my first dipole project... one reason is to obtain that room-filling, somewhat non directional sound - like the Martin Logans... and I am guessing most of that effect is due to the dipole nature of an ESL.
This may be what you desire...
Speaking of them... have you heard any Martin Logans? The Clarities (my personal favorites) are $2600... which is really a relative bargain, as high-end audio goes (of course, being a hard-core DIY guy, I'd never cough up for that personally).
In fact... one iteration of my dipole project is going to be for arrays of small fullrange drivers per side... 3x3 arrays, mounted on curved baffles, to try to really simulate some of that Martin Logan 'room filling' effect - but with traditional drivers.

Some things to ponder, anyway.
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