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From: alummus@airmail.net (J. Alan Lummus)
Newsgroups: rec.audio.marketplace
Subject: FS: Stereo pair "Hill Plasmatronic Speakers"
Date: Sat, 06 Apr 1996 12:58:09 GMT
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FS: Stereo pair "Hill Plasmatronic Speakers"

FOR SALE: One stereo pair of matched "Hill Type I
Plasmatronic Speakers", in good operational and cosmetic condition,
priced at $2,000 obo FOB Dallas, Texas, and offered by the original
owner/seller:

J. Alan Lummus
5629 Emrose Terrace
Dallas, Texas 75227 U.S.A.
Telephone: 214-388-7868
Facsimile: 214-388-5943
EMAIL: alummus@airmail.net,

These two units were purchased new from the Dallas area dealer in 1982
by the present owner/seller. In order to best describe these units,
all associated equipment, and operating characteristics, the following
quotation has been lifted directly from the owner's manual:

----------------------------------------

QUOTE:

FEATURES AND CHARACTERISTICS

A single massless plasma driver operated from
700 Hz to well above audibility. Since the air
molecules are excited directly by electric forces,
there is no electro-mechanical coupling. This
means that there are no resonances to "color" the
sound, no inertia to damp transient response, no
cone excursion limits to cause distortion or
clipping, and no Doppler shift or other
intermodulation distortion mechanisms to fragment
the sound (short of theoretical limits due to
properties of air itself). Its frequency response
is essentially flat and linear compared to any
mechanical transducer operating at comparable
amplitudes. It can produce single transient
pulses with no ring up or overshoot and its steady
state distortion level is comparable to good
amplifiers at normal listening levels. The plasma
background noise level is normally inaudible tin a
typical listening environment, even in the absence
of program material.

The plasma transducer radiates uniformly in
phase in all directions. there is no backgoing,
out of phase wave. Hence, neither an acoustical
enclosure nor horn loading is required as is the
case with conventional drivers. Consequently,
coloration normally associated with horns or
enclosures is absent. Since the wave front is
spherical (except for physical blockage toward the
rear), excellent stereo imaging qualities from a
pair of these units may be expected. Phase
coherence is almost "laserlike" owing to the small
physical size of the single mid and upper
frequency plasma transducer; its entire volume is
only several cubic centimeters. This aids
diffraction spreading around solid objects.

Size, cost and AC power considerations
preclude the use of plasma to reproduce the bass
and low midrange frequencies. Instead, we use an
extremely heavy duty 12" subwoofer which operates
from 10 to 100 Hz, combined with a highly accurate
conventional 5" low midrange driver which operates
from 100-700 Hz. The integrated system is
optimized to yield excellent transient response
and flat, smooth frequency response. We have
extended its response into the bass as far as
possible without compromising our primary
objectives. Tone burst ring-up time is, at worst,
1 cycle in the 30-100 Hz range and 3/4 cycle in
the 100 Hz - 1 KHz range. The system is nearly
flat over its operating range down to 40 Hz and
falls off 10 db at 10 Hz.

SUPPORTING AUDIO ELECTRONICS

Due to the nature of the plasma transducer,
the system must be bi-amped. We intend that the
user supply a conventional high quality power amp
which covers the bass frequencies only.
Interfacing to the user's equipment is
accomplished by a separate 4 1/8" x 19" panel
mount chassis intended to be placed next to the
user's amp and pre-amp. We supply an electronic
crossover, a LED display systems which allows
optimum choice of 700 Hz or 1000 Hz crossover
frequency depending on listening level, an
electronic balancing circuit which permits perfect
balance of upper and lower frequency units, and
all power amplification and plasma control
circuits for the upper frequency driver. Our
amplifier electronics are all vacuum tube, class
A, and are coupled directly to the plasma without
use of transformers. The waste power normally
associated with class A circuitry is salvaged to
create the plasma. Exceptionally heavy filtering
is used in our power supplies to maintain quiet
operation. A single cable connects each stereo
speaker unit to the chassis, which, in addition to
carrying the audio signals, provides high-low
frequency balancing and also on-off control. Care
has been taken to drive both high and low
frequencies into appropriately impedance matched
cables.

Each speaker unit contains independent power
supplies, plasma control circuits and power
amplifiers, and a 100 Hz passive crossover to
split the subwoofer and low midrange drivers.
Adjustments, warning lights, and appropriate
meters are housed on a panel hidden behind tinted
reflective plexiglas on each unit. No adjustment
is needed during normal operation or startup
unless signaled by lights which shine through the
glass.
...

SPECIFICATIONS:

Unfortunately, many of the specifications
which provide the unique performance
characteristics of these units are not
standardized. Some of the more readily
quantifiable "standard" specifications follow:

Frequency Response: less than 3 db variation
from 30 Hz to greater than 20,000 Hz (significant
acoustical power at greater than 100 KHz); down
only 10 db at 10 Hz.

Harmonic Distortion: less than 1% at 90 db
SPL at 10' (3.3 meters) from two units, as
measured in a room of average dimensions, 15' x
28'.

Maximum Steady State Acoustical Power
Available: 107 db at 1 meter SPL, single plasma
driver (or 107 db at 3.3 meters from two units) as
measured in a room 15' x 28'.

Cabinet Dimension: 57.5" high x 24.5" wide x
18.5" deep, with a separate rack-mount Interface
Unit measuring 4 1/8" high x 19" wide.

Required Accessories: high quality, full
range pre-amplifier, high quality stereo amplifier
for low frequency section (100-200 watts RMS per
channel suggested).

Helium Supply: Use standard 9" x 52" 1A gas
bottle, nominally 213 cu ft of helium at 70
degress F. Fresh bottle pressure should be
approximately 2000 psig.

UNQUOTE

----------------------------------------

Given the size of each cabinet, the large casters on
which each cabinet is placed, the tube amplifier built into
each plasma unit, and the full sized helium gas tank
required in each speaker, each unit is quite heavy,
necessitating at least two persons to safely handle each
unit. The helium bottles are usually available from any
welding supply house, and tubes are not too expensive and
still readily available from a number of sources. The two units
offered for sale are complete with owner's manual, schematics,
packing crate instructions, all interconnecting cables, and 2
crossover units (the use of two units allows for the avoidance
of crosstalk that was inherent in the crossover's original
design without modification). The new purchaser will have
to supply only the single stereo amplifier described in the manual
excerpt above for the low-mid and subwoofer drivers.

The plasma units should be packed separately from the
cabinets, and their dimensions are:

H=20.75"
W=23.25"
D=17.5"

Also, the cabinet dimensions given above are without
the large casters normally supplied, which increase the
overall height to 62.75". Also, the helium tanks are rented
from a local welder's supply and are not furnished with the
speakers.

In the owner/seller's opinion, these speakers still
represent the state of the art in the reproduction of the
upper-mid and high frequency areas; however, they no longer
incorporate leading edge technology in the lower-mid and
subwoofer areas, which is the reason they are presently for
sale. For the asking price, these are an incredible value and
easily best speakers costing 5 times as much.

For further information or to arrange an audition, please
contact the owner/seller.

J. Alan Lummus
-------------------------------------------------
P.O. Box 225419; Dallas, Texas 75222-5419 USA
Telephone: (214) 388-7868 FAX: (214) 388-5943
email:
-------------------------------------------------