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From: steve@ncsc.navy.mil (Mahan)
Newsgroups: rec.audio.high-end
Subject: Unconventional Speakers
Message-ID: <2781@uwm.edu>
Date: 6 Mar 90 13:58:07 GMT
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Approved: tjk@csd4.csd.uwm.edu


 
In issue 15 John Allen expands on the unconventional speaker question with
the following list:
 
>I am curious too, but if we could go a step further:
>
I can't answer for all of them, but will try for those I know about.

>Speaker Builder		Technology type		
>
>1) Magniplaners 	(dipole?/electromagnetic?)
   (Magneplanars)        electromagnetic/electrodynamic

These speakers including Magnepans use linear magnet strips on a
supporting framework to provide the field.  The diaphram is imprinted with
conducting ribbons of some metal.  The metal strips are aligned with the
magnetic strips on the framework.  The magnetic field runs in opposite
directions for each adjacent conductor and the conductors zigzag so that
current is in opposite directions for each adjacent conductor.  This provides a
fairly uniform drive over the entire surface of the membrane.  The opposing
directions of current flow result in a fairly low reactive component in the
speaker resistance and an easy load for an amplifier.  The tympani 1D was 8
ohms and sounded best biamplified (poor internal crossover) and with a
subwoofer.  Positioning was extremely important as the membrane radiated sound
in both directions.  

>2) Quads 		(?)

The Quads along with the Infinity Servo-Stats, the Dayton Wright Mk 8, the
Martin Logan, and a few others are electrostatic types.  The operating
principal is electrostatic attraction/repulsion.  In general a charged diaphram
is positioned between two conducting grids.  The output voltage from the power
amplifier is applied to the two grids thereby providing a fairly uniform
electrostatic field.  The electrostatic force applies a uniform acceleration to
the diaphram and thereby moves air.  Most speakers of this type have relatively
poor bass response, the exception being the Dayton Wrights.  Martin Logan uses
a crossover to an air suspension woofer in the Monolith.  These speakers
typically have a relatively poor efficiency and present a difficult load to an
amplifier.  Dayton Wrights need at least 300 W/channel and start sounding good
with 1Kw/channel. 
>
>3) Apogies		(ribbon?)
>
I thing the speaker is similar in design to the Magneplanar.  Heard them a few
weeks ago.  Beautiful highs but cannot match the bass of my Kef 107's.

>4) Accustats		(electrostatics)
>
See under 2 above.

>5) Magnet		(plasma flame)
>
>6) ??			(asetolene flame )
>
There was a speaker about 10 years ago that used a plasma driver.  You needed a
tank of helium to provide the plasma.  The speaker applied a magnetic field to
the ionized gas to move it directly.  It was an ultimate low mass diaphram.
Supposedly it had fabulous high frequency response but had serious usability
flaws.  It required 500 w/channel tube amplifiers (supplied with speaker) that
made great space heaters, needed a helium tank and regulator, was very large,
and had an annoying hiss from the helium feed.

[This is the Hill Plasmatronic I mentioned earlier. It ionized the jet and
the AC signal was applied across the bias supply to provide the modulation.
The biggest problem with the sound was the regular cone drivers weren't as
fast as the modulated helium jet.		- tjk]

Other interesting varients include ESS with the Heil Air-Motion Transformer.
This was a small frame with plastic encased ribbon conductor folded into a
zigzag so that the conductor ran parallel to the fold directions.  When
suspended in a magnetic field the conductors would squeeze together on one side
and spread apart on the other and thereby move air.  Not particularly
impressive.

The only other one I can recall at the moment is the Walsh driver from Ohm
Acoustics.  This is a conventional cone mounted face down.  The cone is fairly
flexible and supposedly the ripples propagating down the cone create a
cylindrical sound wave moving outward.  The inside of the cone is filled with
damping material.

Stephen Mahan
steve@ncsc.navy.mil