Plasma Tweeters
lee_dormon
Could any one give me some info on these so called plasma tweeters.
The book I'm reading doesn't go into to much detail, apart from they cost mega
bucks, I'd just like to know how they work and things. Are plasma woofers a
physical possiblity ?
Cheers alot
Lee
Ps How much is mega bucks
wm.keith.brummett
In article <1992Jun24.1...@oracle.us.oracle.com>, Lee Dormon
writes:
> Could any one give me some info on these so called plasma tweeters.
> The book I'm reading doesn't go into to much detail, apart from they
> cost mega bucks, I'd just like to know how they work and things.
Hmmm. I recall hearing of a plasma-tweeter loudspeaker many moons ago,
like the late 70's or early 80's. I believe it was just one company
(or maybe even one individual) that was constructing the things, so it
really wasn't a generic technology. I doubt if more than handful were
ever made.
Anyway, the picture I saw showed a truly massive box that appeared to
house a somewhat normal (though large) woofer and maybe a midrange.
The tweeter was a pair of high-voltage electrodes that conducted an
electric arc ("plasma") between themselves. The tweeter signal was
imposed upon the arc such that the arc's diameter expanded and
contracted, thus setting up pressure waves in the surrounding air.
It sounded to me like a rather dubious technology -- creating micro-
thunderclaps by modulating a welding set. :-)
A major drawback was the fact that the electrodes would quickly burn
themselves up unless they were constantly bathed in helium gas. So,
part of the humongous enclosure was used to store a large tank of
helium (which had to be refilled fairly often) and the attendant
delivery plumbing. A minor annoyance was the system's tendency to
replace your home's nitrogen/oxygen atmosphere with one of ozone and
helium. In fact, I believe that the combination of high voltages and
gaseous pollutants made it questionable as to whether or not the things
would ever be made available for home use.
> Are plasma woofers a physical possibility ?
Under the system described above, no. You just couldn't move enough
air without crisping the enclosure, you, your cat, your couch, the room,
and everything else for yards in all directions.
> Ps How much is mega bucks
Tens of thousands of dollars, as I recall; but, the system itself
made such matters rather moot.
-- Keith
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`----------------------------------------------------------------------'
Norman P. Tracy
[Lee at ldo...@uk.oracle.com asked about Plasma tweeters.
Keith at w...@cblph.att.com replied describing a large speaker system using a
plasma tweeter. ]
Ah yes, the plasma loudspeaker, like gas turbine cars a popular subject for
magazine articles but in reality something few of us have ever driven (or heard).
Being a fan of esoteric technologies and a saver of old magazines I was able to
pull out a couple of old articles on plasma (a.k.a. ion) speakers.
The huge speaker Keith described was the Plasmatronics Speaker System
designed and marked by Dr. Alan Hill, a laser physicist/audio casualty.
A review of this system appears in 'the abso!ute sound' vol. 5 no. 19 Sept. 1980.
I also have the July 1984 issue of Hi-Fi Answers which has an article detailing
the history of ion speakers as a preface to reviewing one. From the Hi-Fi
Answers article:
In the 1930s William Duddell reproduced sound by modulating a carbon arc
with signal currents. In 1951 a Frenchman, Siegfried Klein, patented the
Ionophone (or Ionovac in the US), British patent 756,546. The Ionophone
is made up of an electrode connected to a high voltage RF generator which
can be modulated by the audio signal. From Klein's British patent comes
this description of the devices operation: 'Power is applied to the oscillator
and within less than 5 seconds the tip of the electrode becomes incandescent.
The corona discharge is evidenced by a light blue "flame" which projects from
the tip....the corona discharge quickly heats the tip to such temperatures
(1000 degrees C or more) that electrons are given off by thermionic emission.'
Klein then goes on to propose two theories as to how the ion cloud
produces sound waves. 1.That the number of ions impinging upon air molecules
is a function of the modulated audio wave. 2.That the amplitude of the
ions vibration (and thus its kinetic energy) varies with the signal and the greater
the ions kinetic energy the greater the air pressure causing the air pressure
to vary in accordance with the modulation. He then states 'While the above is
believed to be the mechanism by which the elastic wave is created, it is not
known to definitely to be so.' I have also read that a process like that used in
electrodynamic rail guns is at work. I am not a physicist so will refrain from
commenting, any qualified netters care to speculate?
Production ion speakers:
Fane Acoustics' Ionofane 601 circa 1965. Horn loaded, good from 3.5kHz up to at
least 50kHz. The electrode and its quartz cell required replacement periodically.
I think this must of been the Ionovac in the USA, I recall these could be seen
for sale in the Audio classified ads in the 1970s when I first got into audio, like
direct heated triode amps a hard core under ground thing.
Plasmatronics Speaker System early 1980s. Horn loaded ion driver could be used
from 700 Hz up, driven by direct coupled tube amp which was part of the system.
Midrange was a 6 inch cone, bass a 14 inch cone; both driven by user supplied
amp. Cost was $8,000 in 1980. As Keith described a tank of helium supplied gas
to the ion chamber to stablize the corona and prevent O3 production. It must
of been successful at this, the TAS reviewer never mentions O3. The review
is a bit of a slam, state of the art highs at moderate levels, honking midrange
and slow bass is the TAS verdict. This starts a flame war between Dr. Hill &
TAS that would do this net proud. He claims the reviewers room was the worst
he had ever heard, bar none. TAS counters, why didn't you complain when you
set up the system? In his reply to the review Dr. Hill claims the Plasmatronics
can output 108 db at 1 meter from one driver and a pair will drive a 4200 cubic
ft. room to 125-130 db.
Magnat Plasma MP-02 mid 1980s. Omnidirectional tweeter, no specs given in Hi-Fi
Answers. Unlike the above systems its not horn loaded, the MP-02 looked like the
finned case from a car amp with a wire ball (like a Shure '58) from a microphone
stuck on top. The case contained the electronics with the electrode and its ion
cloud in the wire ball which kept fingers out and RF in. The article I have is a
history/teaser for the review which appeared in the next issue. I left England before
getting that issue, sigh. Anybody in netland have a review of this system?
Vaporware ion speakers:
In the 1980s Nelson Pass, then partner and chief designer for Threshold, showed
up at a CES with a full range ion speaker prototype. It looked like a six ft. tall
electrostatic speaker they forgot to install the plastic diaphragm in. Reports on
the sound were good, low distortion, very low sensitivity. What got the most
attention was how sick the ozone it produced made Pass, talk about audio
casualty!
A year or two ago a French built full range ion speaker was shown at CES, no
details on its technology were given at the time. I do not have the name, it has
not been heard from except at that one show. European netters, any details?
Norman Tracy (znp...@trc.amoco.com)
CCE...@utxvm.cc.utexas.edu
w...@cbnews.cb.att.com (wm.keith.brummett) describes plasma tweeters. I do
not recall the features he mentioned but I do recall reading of one
additional feature. The spark made the standard crackling sound that
sparks make. Since it was in the throat of a horn, it was quite audible.
I recall no comments on whether the noise was euphonic.
WATERS,CLYDE GORDON
>Hello all
> Could any one give me some info on these so called plasma tweeters.
>The book I'm reading doesn't go into to much detail, apart from they cost mega
>bucks, I'd just like to know how they work and things. Are plasma woofers a
>physical possiblity ?
>
Not very handy on the modus operandi, but they apparently work by manipulating
the spatial characteristics (size, location, etc) of a self-generated
plasma field ("ion mass" for lack of a better description).
Heil, I believe, manufactured these (or was he the designer?), under the
name of "the Air Motion Transformer", back in the late-70's - early 80's.
They were, in short, pretty ugly to look at; I have never been able to
encounter one in working condition to listen to, alas.
Regards,
Gordon.
--
WATERS,CLYDE GORDON-Georgia Institute of Technology Atlanta Ga 30332
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Richard d Pierce
>Not very handy on the modus operandi, but they apparently work by manipulating
>the spatial characteristics (size, location, etc) of a self-generated
>plasma field ("ion mass" for lack of a better description).
>
>Heil, I believe, manufactured these (or was he the designer?), under the
>name of "the Air Motion Transformer", back in the late-70's - early 80's.
>They were, in short, pretty ugly to look at; I have never been able to
>encounter one in working condition to listen to, alas.
>
Not correct: the Heil Air-Motion Transformer was (despite the furious
protestations of the the promoters) nothing more than a fairly conventional
horn-loaded ribbon tweeter (with something of a twist, or should I say a
wrinkle or two). Those who remember it might find my description of "horn
loaded" a bit odd. But the only way the makers could get the efficiency they
claimed was by constructing the magnet in such a way that they got about a
6 dB boost from essentially conical horn that resulted from the magnet yoke.
Similar prototypes could not deliver on the supposed output if they did not
have the horn loading even though they were able to deliver as much if not
greater flux density at the diaphragm.
I am sure this will generate a flame or two from the remaining Heil proponent
out there, but, what the hell, the newsgroup is getting pretty boring lately,
what with all the controversy about record clubs and all that :-)
.
--
| Dick Pierce |
| Loudspeaker and Software Consulting |
| 17 Sartelle Street Pepperell, MA 01463 |
| (508) 433-9183 (Voice and FAX) |
Rick Karlquist
in a different class? I didn't see it mentioned in your
very complete sounding history.
Rick Karlquist
rka...@scd.hp.com