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Old 25th February 2005, 11:43 PM   #11
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I have a pair of Beveridge model 3's recently rebuilt by Rick Beveridge (who is now in Forestville in the North CA wine country) and they sound gorgeous. My pair (I am the 3rd owner) was built in the 70's and over time and having been abused, the coating on the mylar had vaporized in places, and carbon buildup had caused arcing. Even with that they played amazingly well.

Rich rebuilt them for a very reasonable price, and I had the bass drivers reconed and they now play like new. An option for those not having an extra $65K burning a hole in their pockets might look for a used pair of 2's or 3's in disrepair and have Rick rebuild them. Shipping costs and logistics if you don't live within driving distance would be the biggest problem.

As to metallized diaphragms, Rick could explain why they work so well in his implementation. I have built Roger Sanders/Barry Waldron flavor electrostats with the high resistance graphite coatings and they work well, but they don't do what the Bev with the "acoustic lens" can do.
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Old 11th August 2005, 07:55 PM   #12
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I have a pair of 2SWs I purchased at an estate sale in 1985. I have used them on and off over the past 20 years. I have 5 of the 6 panels. I have replaced leaky caps and 1 Pacific Electric transformer over that time.

They now hiss some -- and really need faster woofers than the RH Labs behemoths I got with them (the owner had traded the original mediocre subs for these.

Rick B. can make them new again. I don't want them any longer the way they are, and don't really want to invest to make them new. Good opportunity to buy cheap, and then overhaul for much less than new.
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Old 14th August 2005, 03:08 AM   #13
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Sgabbard, please email me off list...

bear at bearlabs dot com

As far as the present panels in the Beveridges - I'd bet they no longer use metallized diaphragms. At least a little bird told me so...

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Old 19th August 2005, 06:42 AM   #14
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Default Beveridge diaphrams

The panels in the Beveridges do use a mirror coated mylar which is much lower resistance than the graphite impregnated mylar I have used for DIY panels. The design of the Beveridge is quite different from your typical stat, however. The cast carbon stators are very different from the perforated metal or wire stators used in others.

By the way, Rick Beveridge recently moved back to Santa Barbara, CA. He hopes to set up a shop there where he can work on building new units as well as providing repair service for older models. Some models (newer than the III's) used perforated phenolic boards for the stators and they did not age well at all and are probably not reasonably repaired.

sgabbard, the IIs are the best Beveridge made and when working properly are spectacular. The hissing is most likely the same problem I had with my III's, which was arching from stator to mylar due to rough spots on the stator. Rick repaired those and replaced the mylar, as the arching had destroyed the coating in large areas of my diaphrams. Now they are louder and no hissing! You said you have 5 of 6 panels? Didn't they originally have 3 panels to the side? What happened to the 6th? Rick could probably help you there as well if you want to get them working.
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Old 8th September 2005, 09:39 PM   #15
rbev is offline rbev  United States
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Default aluminized Mylar

I want to make it perfectly clear that all Beveridge transducers
were, and still are, made with fully conductive aluminized Mylar.

Your observations regarding the pros and cons of differing membrane
conductivities fail to consider the impact of differing "stator"
designs. Most stators use metal as a conductor, protected by an
an insulating coating. This design causes problems that our Epoxy
composite stators do not experience.

In some stators, like the Accoustat, the metal is in the form of an
insulated copper wire. Other designs use a copper layer on a circuit
board and are insulated either by another circuit board or by a layer
of insulating material which is applied by silk-screening or spraying.
The most common method uses perforated metal (usually steel), coated
with an insulating coating.

Since he decided to build an electrostatic driver in the early
1950's, my father chose to use Aluminized Mylar. In order to do so,
it was necessary for him to develop an ingenious design for what is
now commonly called a stator. He never referred to them as "stators".
He preferred to call them "electrodes" because he felt that the term
was more precise. He also never referred to the drivers he made as
"panels", but called them "transducers".

He developed an electrode with very unique properties. It was made
from a highly resistive material. It had a highly conductive coating on
the side away from the Mylar membrane. This electrode material also
has a very high dielectric constant. It is this resistive-capacitive
material which carries the full force of the field to the air gap
without threatening to burn the Mylar, even if it is fully conductive
aluminized Mylar. Specifically, the resistive component handles the
DC polarizing component, while the RC "mesh" handles the AC component.

One benefit of the capacitive property of this electrode material is
that it doesn't lose its punch when a heavy demand is temporarily
made upon the transducer. This is not true of resistive membranes.
With medium- to high-resistance membranes, a heavy demand will
severely reduce the charge stored in the membrane. Under the best of
circumstances, after a high voltage demand, a high-resistance
membrane will take several minutes to restore the membrane to its
full operating voltage.

If the circumstances are not so ideal, like when humidity is high,
this can take hours to restore. If the humidity is very high, and the
membrane resistance is also very high, the membrane will never
achieve its full charge. The loss of charge to the humid air exceeds
the charging capability of the membrane. This is not a problem with
fully conductive aluminized Mylar membranes.

Several popular electrostatic speakers on the market today, which use
high resistance membranes, can only maintain half of their normal
membrane charge on humid days. This causes the electrostatic driver
to lose half of its power. To make matters worse, these speakers
usually have the bass produced by standard dynamic cones; having the
electrostatic element varying its output against a constant bass
output throws off the balance between them.

Besides humidity, another problem encountered with conventional
membranes is that they collect dust. This is because they are given a
positive or negative charge which is maintained at a constant level
(if humidity doesn't interfere). The membrane then attracts any
particles with an opposing charge. Electrostatic air filters are very
effective. This attraction of dust is a common cause of arcing and
failure of convention systems.

A fully conductive membrane is driven like the electrode. Both the
voltage and the polarity change with every half cycle. The only dust
that collects in a Beveridge transducer is dust that has no charge
and does not settle onto the membrane because the membrane is moving.
Neutrally charged particles are shaken off and charged particles are
not attracted.

Another nasty problem solved with fully conductive membranes is that
of total voltage. In conventional electrostatic panels, the membrane
is passive. It takes on a charge, but that charge remains at a
constant, or is at least supposed to do so. The membrane is moved by
applying a high voltage charge to one or more electrodes near the
membrane. All electrostatic speakers commercially made today are
made with one electrode on either side of the membrane.

With a fully conductive membrane, it can, and is, driven along with
the electrodes. It is not passive, but is a working member of the
unit. The same total sound pressure level can be achieved with half
the total voltage. This ability to produce the same SPL at half the
voltage of conventional designs has many benefits.

As you say, fully conductive membranes can not be used with normal
stators. However, using a design such as ours is not an easy "fix".
Making the electrodes the way we do is difficult, requiring skill,
knowledge, and experience.

As a result, our transducers are neither easy or cheap to produce.
Despite this method's obvious benefits, no other electrostatic
speaker company has yet tried to accomplish it. It certainly does
not lend itself to the low cost and ease of production required by
the DIY market.

In an effort to reduce the cost and difficulty of production, my
father sought to produce a more conventional electrode. These were
his circuit-board electrodes. They were a total disaster. They would
have worked with more conventional membranes, but they did not work
well with the aluminized Mylar. This was especially true when used
in conjunction with step-up transformers and conventional amplifiers.
Although the circuit-board electrodes would have worked with more
conventional membranes, they would have gained all of the problems
of conventional transducers.

As far as low frequency capability is concerned, in the model 2SW,
the single electrostatic transducer plays from 100 cycles on up.
There is no need for a "woofer panel". Of the 30 plus pair of model 2
SW's sold by our Singapore dealer, all were made prior to 1980. Most
or all of them are working in a very humid environment, but not one
pair of them has yet had a reported transducer failure.

It is the combination of my father's original electrode, working with
highly conductive aluminized Mylar, that produced a truly superior
electrostatic speaker. This is borne out by the fact that there are
presently about 175 pair of Beveridge speakers still playing in at
least 17 countries around the world. The last ones made are at least
20 years old, with the largest majority of them being between 25 and
30 years old and using our unique electrodes and aluminized Mylar.
After more than a quarter century, less than 15 percent of the speakers
which use our Epoxy composite electrodes and fully conductive
aluminized Mylar have needed work on their transducers.

I have decided to continue to produce them, with their aluminized
Mylar membranes, in spite of the difficulty and cost. As Harry Pearson put
it so prophetically, "They are not for everyone".

After 30 years, I would add that, for some, they are perfect.

I hope that this will clear the air about aluminized Mylar membranes.

Rick Beveridge
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Old 8th September 2005, 10:38 PM   #16
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Thanx Rick... that was very interesting.

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Old 9th September 2005, 07:17 AM   #17
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Is the beveridge a 'reverse' ESL? (audiovoltage on the membrane). In that case the use of low resistive membranes is logical. The new Final speakers are also reverse esls.

In normal ESLs aluminized membranes only causes a lot of trouble since it tends to leave the membrane. The exact mechanism is not clear to me, but the high charge density might be one of the things. Many DIY ESLs in holland have suffered from metalized membranes developing holes. Not to mention the charge migration and associated distortion.

A well designed esl (good isolation parts) combined with a stable high voltage power supply and an EC-coating will show minor variations upon humidity. Unfortunately this is not always the case.
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Old 9th September 2005, 07:14 PM   #18
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That's a good question about a reverse esl. I would propose that the first thing to do is to define what constitutes an esl.

The common use and widespread acceptance of the high resistance, constant charge membrane working between two stators is what most people think of as an esl. In these systems the membrane is passive and the stators do all of the work.

If we accept that definition, then a reverse esl would be to have a constant charge on each of the stators and the membrane carrying the audio. This would make the stators passive and the membrane would do all of the work. In that case, the amount of voltage necessary would not change.

In a Beveridge system, there is no passive component. Both the stators and the membrane are active. All three carry the audio. The benefit of this is that it reduces by half the amount of voltage necessary for the same amount of sound pressure. I think that this is still an esl, but certainly is not what most people think of as an esl.

As far as having the aluminum evaporate from the Mylar when used with conventional electrodes, I may be able to shed some light on that.

I have studied the loss of aluminum I found in the transducers my father made with the more conventional circuit board electrodes. I believe you are correct regarding the high charge density, and specifically that it is caused by corona.

Corona is formed at the surface of a conductor carrying high voltage. It still forms even if the conductor is well insulated. On my father's circuit board electrodes, the edge of the thin copper sheet around each hole is like a knife blade. Even where the insulation did not break down, corona forms quickly at the edges around these holes.

In studying the Mylar from at least 50 of these transducers, I have found that the aluminum coating started evaporating in small circles around each hole. In more severe cases, these circles had grown to the point of overlapping each other. In the most severe cases, virtually all of the aluminum coating was completely gone from the entire surface.

I have a highly polished copper pipe which is about one inch in diameter. It has a long wooden handle. I use it in conjunction with a Variac and a neon light transformer to check my electrodes for arcing. This set-up can produce up to 9,000 volts. I place plastic spacers along the sides of an electrode and then I slide this copper pipe back and forth along the spacers. When I do this in a darkened room, I can see the blue light of the corona forming between the electrode and the copper pipe. The more voltage I apply, the brighter the corona.

With the circuit board electrodes, the corona first forms as circles around the holes and other places where there is an edge of the copper sheet underneath the insulation. The corona forms at relatively low voltages at these edges. At higher voltages, this blue circle gets very bright and even develops into a white ring surrounded by blue corona.

When I do the same thing with the Epoxy composite electrodes which we made in the '70's, this corona forms a uniform blue light along the whole surface of the copper pipe. At higher voltages, the blue light is brighter and some white "sparkles" appear as well. With my new electrodes, these "sparkles" still appear, but at much high voltages. With them at extremely high voltages, the lovely blue corona just gets thicker and a brighter blue and is still perfectly uniform.

I have been told that corona is mostly empty space with a few highly charged particles moving very fast. I know that the aluminum coating on the Mylar is only a few atoms thick. It is my guess that every once in a while, one of these high energy particles hits the Mylar and knocks off one or two atoms of aluminum and that this can eventually remove the whole coating. That is what it looks like to me.

Rick Beveridge
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Old 10th September 2005, 09:18 AM   #19
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Hello Rick,

Apparently, the beveridge is quite unique the way it works. Maybe a schematic picture of the principle might make things more clearly, since I still don't get the point of the membrane and the stators being 'active' the same time.

I have studied electroconductive nanolayers at the university of utrecht. One of the things I saw with vaporised gold on glass, that it went completely off with increased current. Since voltages were very low, it was not likely to be caused by corona. That's why I introduced the 'current density'. Apparently corona discharge has a similar effect.

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Old 26th September 2005, 07:29 PM   #20
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The way we drive our ESL's is quite unique in several ways. I have asked some very knowledgeable friends to help me draw a diagram to post here and it has turned out to be the start of a complete white paper on the subject. One associate is even making an animated drawing.

When it is ready, I will put it up on my website and post it to this thread as well. It should be done in the next two to four weeks. In the meantime, you can look through the patents on my website and get some understanding from them. I am glad that all this has come up. While the pros and cons of all of these differences can, and should, be debated, at least my father's work will no longer be thought of as just like all other ESL's.

I am also glad that you brought up this "current density". I am very interested in this and want to know a lot more about it. I may have been wrong to blame the loss of aluminum all on corona as I have done.

For the time being, I have packed up all my tools and equipment and put them into storage. I have moved back to Santa Barbara and will be setting up my shop here. When I get my shop set up, I want to do some experiments which will explore the effects of current density, and corona, on these thin metallic films. I would very much appreciate any suggestions you might have for such experiments.
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