Beveridge's slate and mylar electrotats

[diamondsouled]

Hello all,

Came across this interesting story about Harold Beveridge's first attempts at making an electrostatic speaker. His son Rick recalls:

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.

http://www.bevaudio.com/Beveridge_History.htm

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Talk about ingenuity! Must have been heavy brutes those first slate panels.

Lar

[arend-jan]

Nice story. And although a fun read, judging by the story, he was not quite the genius Walker (Quad) or Baxandall were, them being way ahead of him in those days and had advanced electrostatic speakers to a whole new level. As wel in practice as in theory.

[EdwinR3]

I can say that the Model 2SW is still the most impressive
speaker I ever heard (it must have been around '75, i'm getting old).

It was also the first ESL I heard.

No quad ESL has ever made the same overwelming impression.

Edwin.

[diamondsouled]

Hi Edwin,

I've heard the same thing about the early Beveridge speakers from some other people in the States: that they are some of the most impressive speakers they ever heard.

Although his speakers weren't as successful commercially as the Quads they are are considered by some to be quite collectible not only for their rarity but for their sound.

Reading some of the testimonials of Beveridge speaker owners is interesting:

http://www.bevaudio.com/t/Testimonials.htm

Lar

[Calvin]

Hi,

them being way ahead of him in those days and had advanced electrostatic speakers to a whole new level. As wel in practice as in theory.

One should just add, that neither the concept of segmentation, nor the concept of delay was new. In fact both concepts were known for app. 30 years before Quad! The genius can imho be seen in the profound knowledge of the persons involved and the clever way how they constructed a marketable product.
To my ears the result of that really smart and clever work is still rather unimpressing sonically.
Technically there are no real advantages in the delay-concept that a much simpler segmentation couldn´t do equally well, but there are serious disadvantages, as for example the need for ridiculously high transformation factors. Ask a transformer winder to wind a tranny with 1:260 (!) And wide bandwidth And dynamics And good sound and he´ll probabely breaks into laughter.
The result is sonically and measurable: very restricted dynamics.

Beveridge on the other hand thought of and researched constructional and material basics like insulator materials for stators, or electronic feedback and designed a new direct drive amplifier (later refined by Mr. Strickland) that still pepresents one of the most efficient ways to generate a HV-Audio-signal and which was a basis for Stricklands refined Version (which was then ´copied´by AudioExklusiv)

I think, there is no reason at all to judge one of them higher than the other. They invented or created milestones. They were working on the same field, but dealing with different aspects of the theme.

jauu
Calvin

[diamondsouled]

Thanks for the imput Calvin.

You're right of course that it isn't a contest but an art form where sound is the palate.

There are some interesting pics in the technology section at the Beveridge Audio site:

http://www.bevaudio.com/Technology.htm

The process doesn't look at all high tech but what was achieved speaks volumes about human ingenuity.

What pioneers such as Peter Walker, Harold Beveridge, and Oskar Heil, etc. achieved is remarkable, especially considering the limitation of materials being used at the time. That their designs still endure is a testimony to their innovation.

Lar

[arend-jan]

Wow guys, I did not intend to start a ******* contest and sure don't want to be in one.

It just struck me as odd that they would be experimenting with single-plate elements and metalised diaphragms and having problems with sticktion etc, while at the same time in England those men were designing the original Quad ESL and backing it up with the math too. Things like that were already known back then for a long time.

From that I concluded that the guys from Quad were way ahead at that time. Perhaps I spoke to early.

Note that I never said anything about Beveridge speakers or their quality.

Sorry if I offended anyone.

[bear]

Peter Walker's Quad company, research and speakers pre-dates the appearance of Beveridge's products by nearly 20 years... fwiw.

The main improvement in the Beveridge speaker, imho, was/is the "lens" that permits them to produce a very wide dispersion, permitting the speakers to be faced AT each other from opposite sides of the room rather than the typical "left & right" stereo configuration...

_-_-bear

[diamondsouled]

Hi bear,

Having never had the opportunity to hear a pair of the Beveridge speakers I was wondering about the effect of the lens.

Lar

[bear]

The lens is more or less a standard sort of diffracion lens/waveguide - not a horn type waveguide.

The general idea is to create uniform dispersion (polar response) in the horizontal plane, as frequency increases.

The usual pattern for large surface radiators is to narrow the dispersion (horizontal) as frequency increases to the point where the pattern is extremely narrow.

You'd have to listen to the Beveridge yourself to decide how sucessful or not the implementation is. Also you'll have to decide for yourself how they keep the overall freq response "flat" if the polar response is maintained as flat off axis. There are issues with that vs. power response and "sensitivity" & output levels...

_-_-bear