MartinLogan CLS IIz Specifications download pdf (Page 17)

Electrostatic Loudspeaker History 17

In 1947, Arthur Janszen, a young Naval engineer, took part

in a research project for the Navy. The Navy was interested

in developing a better instrument for testing microphone

arrays. The test instrument needed an extremely accurate

speaker, but Janszen found that the cone speakers of the

period were too nonlinear in phase and amplitude response

to meet his criteria. Janszen believed that electrostats

were inherently more linear than cones, so he built a

model

using a thin plastic diaphragm treated with a conductive

coating. This model confirmed Janszen’s

beliefs, for it exhibited remarkable phase

and amplitude linearity.

Janszen was so excited with the results

that he continued research on the

electrostatic speaker on his own time.

He soon thought of insulating the stators to

prevent the destructive effects of arcing. By 1952, he had

an electrostatic tweeter element ready for commercial

production. This new tweeter soon created a sensation

among American audio hobbyists. Since Janszen’s tweeter

element was limited to high frequency reproduction, it

often found itself used in conjunction with woofers, most

notably, woofers from Acoustic Research. These systems

were highly regarded by all audio enthusiasts.

As good as these systems were, they would soon be

surpassed by another electrostatic speaker.

In 1955, Peter Walker published three articles on electrostatic

loudspeaker design in Wireless World, a British electronics

magazine. In these articles, Walker demonstrated the benefits

of the electrostatic loudspeaker. He explained that electrostatics

permit the use of diaphragms that are low in mass, large in

area and uniformly driven over their surfaces by electrostatic

forces. Due to these characteristics, electrostats have the

inherent ability to produce a wide bandwidth, flat frequency

response with distortion products being no greater than the

electronics driving them.

By 1956, Walker backed up his articles by introducing a

consumer product, the now famous Quad ESL. This speaker

immediately set a standard of performance for the audio

industry due to its incredible accuracy. However, in actual

use, the Quad had a few problems. It could not be played

very loud, it had poor bass performance, it presented a

difficult load that some amplifiers did not like, its dispersion

was very directional and its power handling was limited to

around 70 watts. As a result, many people continued to

use box speakers with cones.

In the early 1960s Arthur Janszen joined forces with the

KLH loudspeaker company, and together they introduced

the KLH 9. Due to the large size of the KLH 9, it did not

have as many limitations as the Quad. The KLH 9 could

play markedly louder and lower in frequency than the

Quad ESL. Thus a rivalry was born.

Janszen continued to develop electro-

static designs. He was instrumental

in the design of the Koss Model One,

the Acoustech and the Dennesen

speakers. Roger West, the chief

designer of the JansZen Corporation,

became the president of Sound Lab.

When JansZen Corporation was

sold, the RTR loudspeaker

company bought half of the production tooling. This tooling

was used to make the

electrostatic panels for the Servostatic, a

hybrid electrostatic

system that was Infinity’s first speaker

product. Other companies soon followed; each with their

own unique applications of the technology. These include

Acoustat, Audiostatic, Beverage, Dayton Wright, Sound

Lab and Stax, to name a few.

Electrostatic speakers have progressed and prospered

because they actually do what Peter Walker claimed they

would. The limitations and problems experienced in the

past were not inherent to the electrostatic concept. They

were related to the applications of these concepts.

Today, these limitations have been addressed. Advancements

in materials due to the U.S. space program give designers

the ability to harness the superiority of the electrostatic

principle. Today’s electrostats use advanced insulation

techniques or provide protection circuitry. The poor dispersion

properties of early models have been addressed by using

delay lines, acoustical lenses, multiple panel arrays or, as in

our own products, by curving the diaphragm. Power handling

and sensitivity have also been increased.

These developments allow the consumer the opportunity to

own the highest performance loudspeaker products ever

built. It’s too bad Rice and Kellogg were never able

to see just how far the technology would be taken.

These developments allow

the consumer to own the

highest performance loud-

speaker products ever built.

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MartinLogan CLS IIz Specifications Page 17

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