by
Rick Beveridge
My
father, Harold Beveridge, was a highly skilled engineer with a deep love
for music. He studied electrical engineering at McGill University in
Canada. From 1947 to 1954, he worked at Raytheon, in Waltham,
Massachusetts. He was involved with designing vacuum tubes and the early
commercial development of Radar.
During those years, he always bought season tickets for himself and my
mother to the Boston Philharmonic and often attended the Boston Pops. He
almost never missed a concert of either. When I was old enough, about six,
he would take me when my mother couldn't join him. I enjoyed many concerts
with him. He enjoyed them so much that it became his passion to reproduce
that sound at home.
By 1951, he had already decided that the inherent limitations of a dynamic
speaker were so severe that, even with tremendous gains in technology,
they would never produce a satisfactory transient response. Several people
had been experimenting with electrostatic designs and had written about
their work. My Father read their reports and decided to look into the
potential he saw in electrostatic devices.
His first effort was a single-sided electrostatic transducer, or panel. It
was made from a rectangular piece of 1/4 inch gray slate. The plate, which
was 12 inches by 16 inches in size, had over one thousand 3/16 inch holes
drilled through it. The side away from the Mylar membrane was painted with
a conductive silver paint, spreading the charge over the entire surface.
My Father would put the transducer on a table with the membrane side up,
sprinkle table salt on it and photograph the patterns which would form at
different frequencies, amplitudes, and membrane tensions. He would also
put a piece of white paper on top of the membrane and sprinkle it with
iron filings so that he could observe the electro-magnetic field patterns.
I was often invited to watch. It was fascinating and good fun for both of
us. My Father spent quite a bit of time explaining to me how different
wave forms behaved and interacted. By then, I was probably seven or eight
years old. He explained concepts such as sine waves, resonant oscillations
and nulls, and intermodulation distortion. He studied every detail of
these fledgling transducers, and through watching him I too learned a
great deal both about sound and about experimental methodology.
By 1953, we were listening to music on this electrostatic transducer. It
was placed vertically in a frame and sounded pretty good. We heard highs
that regular speakers couldn't come close to producing. In fact, that was
part of the problem. Many speakers of this era sounded like the public
address system in the movie version of M.A.S.H. My Father's
"speaker", in contrast, accentuated the highs and diminished the
lows. So, compared to the standards of the day, it sounded far too
"bright" or "tinny".
Also, the back wave interfered, producing peaks and nulls at certain
frequencies. At least a half-dozen different forms of baffles and
reflectors were tried in an effort to diminish these effects and, if
possible, use the back wave to augment the sound. None were very
successful.
Another problem arose when the speaker was driven at too high an
amplitude; the membrane would get too close to the electrode and stick to
it, stopping the sound. At that point, we would have to turn off the power
and wait ten or twenty seconds until the polarizing voltage had dropped
enough to let the membrane "peel" itself away from the
electrode. Then we could turn the equipment back on again, this time being
careful not to drive it quite so hard.
Reflective Dispersal
By 1957, stereo was coming out, and my father decided to build two new
speakers. He had also decided to move to a two-sided transducer,
increasing both accuracy and sound pressure level (SPL). This meant,
however, that he would now need four electrodes instead of just the one.
Drilling all those holes in a sheet of slate was definitely out of the
question. In an attempt to replicate certain electrical properties of the
slate, he experimented with mixing several types of carbon powder and
barium titanate into Epoxy resin. After some experimentation, he came up
with a working mixture and we cast four electrodes.
By 1958, I was thirteen and helping to make these new electrodes. While my
father was back east on a business trip, I followed his recipe and cast
four new electrodes. There were many factors we hadn't learned about yet,
and for reasons we learned about much later, these electrodes were much
more conductive than the ones my father had made before. He did, however,
make them into transducers and found that they had some very interesting
properties. The "sticking" of the membrane to the electrode no
longer occurred and we could drive each transducer much harder than
before.
We used a pair of 1/4 inch glass plates to mold these electrodes. Each
plate was a little over one by two feet. We put a thin coating of grease
onto one side of each plate, then spread a sheet of aluminum foil onto one
of the plates. The plates were placed with their greased sides (one with
aluminum foil) facing each other. The plates were held 1/4 inch apart by
three lightly-greased wooden sticks. This was all clamped together and
stood upright with the open side up. The epoxy mix was poured into the
cavity, then allowed to cure.
This produced a one by two foot, 1/4 inch slab of epoxy composite with
aluminum foil on one side and a very flat surface on the other. Using the
table saw, we cut a large number of parallel 1/8 inch slots, leaving about
3/16 inch of material between adjacent slots. We then poured a
non-conductive epoxy rim around the entire border, finishing the
electrode. These electrodes made fairly good transducers.
To build the new speakers, My Father made two cabinets. Each one measured
about 36 inches wide by 24 inches deep by 30 inches tall and had a
rectangular opening in the top. A transducer measuring 12 by 24 inches was
placed horizontally below this opening, with a grill cloth above it.
To disperse the higher frequencies into the room, my father created a pair
of acoustic "reflectors". He made a wooden bowl, about one foot
tall and eighteen inches in diameter. The sides dropped, following a
parabolic curve, to a 6 inch diameter base. The bowl was then cut in half
vertically, forming a pair of half-bowl reflectors. The reflectors were
fastened in place on the top of the cabinets, at the back side of the
transducer openings, with their curved sides facing towards the room.
The reflectors protruded out and over part of the transducer, causing some
of the high frequency sound beaming up from the transducers to be
reflected out into the room. This brought the ratio between the highs and
lows to a more acceptable level and did, in fact, sound excellent.
The back (bottom) wave from the transducer, or at least the lower
frequencies from it, came out the bottom of the cabinet, which was open.
By going to larger transducers, of a design which produced better bass,
and by only reflecting part of the highs into the room, my father had
greatly improved the frequency balance. The "tinny" sound, or
"over-brightness", was mostly gone.
Two of these speakers were built by 1959, giving us a very good sounding
stereo sound system. The cabinets looked good, but took up a substantial
amount of floor space. Also, the artificial flowers my mother had put in
each "bowl" for decoration had to be removed after the first
time that a cleaning lady watered them, drowning the transducers!
The Acoustic Lens
In
1965, my father was more excited than I have ever seen him about anything,
before or since. He had conceived of the acoustic lens and the full-range
cylindrical wave front. These innovations were, and continue to be, the
unique hallmark of Beveridge systems. Providing comfortable levels of
crystal-clear sound throughout the room, they offer a unique audio
experience for the listener.
The acoustic lens solved several problems and solved them beautifully.
Because the entire lens is driven by a single, continuous driver, the
sound retains complete phase coherency. All frequencies of interest,
including the "beamy" upper frequency ranges, are formed into a
six foot tall, 180 degree, vertical, cylindrical wavefront. Everywhere the
lows go, the highs go, too. He had achieved truly uniform dispersion over
the entire frequency range!
In addition, my father made an important decision about cabinet design. He
could find no way to allow the back wave into the room without seriously
adulterating the sound in one way or another. So, from then on, he never
allowed it into the room at all.
My Father's lens and cabinet combination accomplishes a tremendous amount.
The lens throat, combined with the "empty" space in the cabinet,
creates a Helmholtz resonator in the 40 to 50 Hertz range. This works very
well, extending the bass capability of the speaker.
So, we built two cabinets, each three feet wide, two feet deep, and six
feet tall. Each cabinet held a continuous six-foot lens and transducer
combination. We had also managed to cast twelve new electrodes in a new
mold that my father had made. Those made six new transducers, enough for
the first pair.
We later called this pair our model 1's. Only one pair was ever made.
Eight years later, when we decided to go into production with this
concept, we honored this first pair by calling our first production
speakers our model 2's. The pair of 1's was sold to a friend in Santa
Barbara who had a huge house overlooking the ocean. The pictures taken of
our first model 2's (the white lacquered ones shown in our first brochure)
were taken at his house.
What my father had created was truly novel: a high performance, phase
coherent, full range, full height, full width, cylindrical wave front,
line source speaker with incredible transient response. A series of
patents attests to the novelty of his designs.
The new design had the added benefit that it was a true line source, as
opposed to a point source. Consequently, sound pressure level drops off as
one over the distance from the speaker to the listener. In contrast, a
conventional cone speaker is a point source and the sound pressure level
drops off as 1 over the distance squared.
Because these new speakers were true line sources with a 180 degree
dispersion patterns, their placement in our home was novel. Our living
room at that time was about twenty feet wide by fifty feet long. There was
a large circular fireplace on the centerline and about twenty feet from
one end. Each speaker was placed with its back to a long wall, facing the
fireplace and the other speaker. The highs, mid-range, and lows were
dispersed uniformly throughout the entire room. There were no more
"bright" and "dull" spots.
They manner in which these new speaker introduced sound into the room was
astonishing. As one moved about the room, the relative change in the
volume from each speaker was minor. We found that we could set the volume
for an acceptable listening level, go right up to either speaker, put one
ear right up against it, and still hear the other speaker with the other
ear.
Commercial Development
In
1972, Akio Morita, the founder of Sony, spent several days at our house in
Santa Barbara. He was very impressed with the sound made by my father's
speakers. He wanted to purchase all of the rights to build them and made
my father an offer to do so. Unfortunately, this offer precluded any
further involvement by my father and was unacceptable to him because of
that. My father had some other ideas and wanted to remain involved with
development.
I suggested to my father that I could help and that we could build
speakers ourselves. He was retired by then and really didn't want to start
a manufacturing company, but my offer of a year's free labor was an
significant enticement and we got started.
During that year, Don McFarland, a close friend and talented designer,
helped us reshape the cabinet. Because the cabinets were so large, we
couldn't employ the usual brute-force, high density particle-board style
of cabinet design: the result would be impossibly heavy.
So we tested a thin-walled cabinet at every possible frequency, making
notes of all the resonant locations. These places were strategically
reinforced, adding little to the overall weight. The result was a
remarkably light cabinet which was remarkably sound-dead. It was, however,
not completely sound dead; some listeners believe that the speakers sound
better because of this fact.
My Father and I spent an intense five weeks brain-storming and developing
the tooling to manufacture the lenses. Several modifications were made in
the electrode molding and coating and transducer assembly processes. A new
amplifier was also designed, using conventional tubes instead of the radio
transmitter tubes used in the model 1's. The result of this effort was the
Model 2.
The systems performed beautifully, as far as acoustic accuracy. The major
thrust in those days, however, was for the highest possible sound
pressure, with real fidelity taking a back seat. Consequently, some
speaker designs were beginning to reach some pretty amazing sound pressure
levels. One very highly respected reviewer even refused to audition ours
until we made them louder! Hence the birth of the model 2SW.
The addition of a subwoofer allowed us to redesign the lens and open up
somewhat the throat of the lens: a more constricted throat reinforces the
bass response. With the line source pumping out a few more decibels, and
the subwoofer pumping out more, we actually did get higher total sound
pressure level. The model 2SW then enjoyed some very favorable reviews. It
was even called, by one of the most critical reviewers, "a prime
candidate for the world's best speaker." One reviewer kept the
speakers, using them as the standard against which he measured all other
speakers for nearly ten years.
They were, however, expensive to build. We had been selling the Model 2's
for $2,000, wholesale to dealers, for about two years before we found out
that they were actually costing us about $2,500 a pair to build! So, we
simply doubled our price and kept on going.
For the Model 2SW's, we were paying a little over $500 per pair just to
have the cabinets built. The Model 2's used three two foot transducers,
and also three two-foot-tall lenses per speaker. Both systems were very
labor intensive to produce.
The Model 3 was my Father's answer to trying to cut the cost of
production. The two-foot diameter cylindrical cabinets were intended to be
much less expensive to build. It was also hoped that by building three
foot long transducers and lenses, we could seriously reduce the production
costs. Eliminating a built-in amplifier also reduced costs and increased
our customer base.
Unfortunately, it turned out that the costs did not actually go down. The
increased transducer length meant that everything in the tooling had to be
that much bigger. With the increased difficulty in handling, it actually
took about twice as much labor to build a three-foot transducer as a
two-foot one. The same was true of the lenses.
In addition, the round tubes we used to build the cabinets took up a
tremendous of space to store and were in many ways more time-consuming to
build than we had thought they would be. I personally believe that we
didn't save a dime on any of those round cabinets.
It was in 1980, during the development of the Model 3's, that I left the
company. I was never again involved in any of the companies that followed.
What I know from there on, I have gotten second hand.
After I left, my father designed an all-new type of transducer. The
electrodes were made from circuit-board material. They measured one foot
by three feet and performed very well. They required less labor to make,
but they didn't hold up very well over time. They would burn up the Mylar
much more readily because they lacked some of the electrical
characteristics of the cast epoxy-composite type of electrodes. These
circuit board type transducers were used in Models 5's, and 6's, which
also had cylindrical cabinets, but smaller diameter, about eighteen
inches, and were sold without their own integral power amplifiers.
The Model 5 was five feet tall, with a single three-foot transducer and
lens above. It only had about a 130-degree dispersion angle, and had a
subwoofer in the base. Model 6 was a return to the full-height, six-foot
line source, although not with a full width 180-degree dispersion, but
again more like 130 degrees, and with a separate subwoofer cabinet about
eighteen inches tall underneath it.
The Model 2 was the last speaker my father engineered solely to satisfy
his own personal criteria. That is:
- It was a full range electrostatic system: no crossovers,
- It was full height: at least 3/4 of the distance from floor to ceiling,
- It was full Width: 180 degree dispersion starting essentially at the wall,
For
its simplicity of concept and clarity of sound, it is the personal
favorite of some, including my younger brother Ross. The step from the
Model 2 to 2SW exchanged the simplicity of a single source for increased
volume and bass presence. While the Model 2 is perhaps the finest for solo
guitar music, the Model 2SW is better for demanding pieces such as pipe
organ music. The models following the 2 and 2SW, while excellent,
represented compromises that met with varying degrees of acceptance in the
world.