Electrostatic Loudspeaker Bret Spencer ECE Mechatronics

History – Early Patents In 1929, E.W. Kellogg filed for a patent for an early magnetically driven electrostatic speaker In 1953, Arthur Janszen was granted a patent for a high-frequency electrostatic speaker

History – On the Market In 1957, first full-range electrostatic speaker put on market by Quad ESL based on Kellogg’s patent design In the early 1960’s, Arthur Janszen, with KLH loudspeakers, introduced a rival electrostatic loudspeaker to Quad ESL

Vs. Janszen Electrostatic SpeakerQuad ESL Design Photos courtesy of

Electrostatic Speakers Today electrostatic-speaker-subwoofer-audiophile-audio.jpg Electrostatic technology has steadily increased New materials and new techniques have improved electrostatic loudspeakers

Types of Electrostatic Speakers 1.Static film charge 2.Dynamic film current

Center film has a very high, constant charge Outer plates are driven with input signal Front and back plates are driven in anti-phase Static Film Charge Electric Field

Diagram courtesy of Wikimedia Commons Static Film Charge Changing electric field causes inner film to move Rapid changes cause vibrations and sound is produced

Outer plates have a very high, constant voltage Current is driven through center film Dynamic Film Current

Illustration courtesy of Dynamic Film Current

A constant electric field is generated by the outer plates The change in charge on the diaphragm causes it to move and vibrate within the electric field

Diaphragm Construction A very early design used pig intestine with gold leaf coating as the diaphragm Plastics coated in conductive substance were a standard diaphragm material Polyester films, such as Mylar, are commonly used today

Speaker Construction

Advantages Very low sound distortion levels Excellent frequency response due to low diaphragm mass Sound carries further because of increased sound producing surface area

Linear Sound Emitter Electrostatic Speaker is a linear sound emitter Sound is produced along the whole length of the diaphragm Sound carries longer distances

Top View Electrostatic speaker Conventional Speaker Linear Sound Emitter Conventional speakers have greater spread Electrostatic speakers are concentrated in a single direction

Disadvantages Poor low frequency response Thin diaphragms are very fragile Highly directional Much more expensive than conventional speakers High impedance input Requires use of amplifier

Low Frequency Response The poor low frequency response can be countered with adding a conventional magnetically driven cone loudspeaker, a woofer

Alternative: Magnetic Coil Most common type of loudspeaker today Uses electromagnetics to drive a conical diaphragm Size can be altered for a wide array of frequencies Durable Low impedance input Photo courtesy of Wikimedia Commons

Alternative: Magnetic Coil

Alternative: Ribbon Magnetic Very similar to electrostatic loudspeakers Uses an electrically charged metallic ribbon placed in a strong magnetic field Can be more fragile than electrostatic diaphragms

Cost & Availability From $500 to over $6000 Several companies available worldwide produce electrostatic speakers A variety of designs Floor standing Wall mount Wide or narrow dispersion

High End Electrostatic Speaker 20%20%20BLKBLKhttp:// 20%20%20BLKBLK Frequency Response 24 – 23,000Hz 30° Horizontal Dispersion 400 Watts total power Just over 5 feet tall $7,000

Low End Electrostatic Speaker ontentID=218663http:// ontentID= Frequency Response 41 – 23,000Hz 200 Watts total power $539

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