Electrostatic LoudspeakerBret Spencer

ECE 5320 - Mechatronics

http://www.hometheaterhifi.com/images/stories/speaker_product_reviews/home_theater_speakers/2007-08-final-sound-1000i-speakers-90ht-system-product-reviews.jpg

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

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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 Speaker Quad ESL Design

Photos courtesy of http://www.martinlogan.com/learn/electrostatic-loudspeaker-history.php

Electrostatic Speakers Today

http://media.audiojunkies.com/martinlogan-spire-martin-logan-loudspeaker-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 charge2. 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 www.howstuffworks.com

Dynamic Film Current

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

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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 ViewElectrostatic 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

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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

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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 http://www.ariesmotor.com/products/neopro5i.jpg

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

• http://www.audioadvisor.com/prodinfo.asp?number=MLSUMX%20%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

• http://www.cowboom.com/store/productDetails.cfm?contentID=218663

• Frequency Response 41 – 23,000Hz

• 200 Watts total power

• $539

Sources

http://www.martinlogan.com/learn/electrostatic-loudspeaker-history.phphttp://history.sandiego.edu/GEN/recording/loudspeaker.htmlhttp://www.howstuffworks.com/speaker11.htmhttp://www.quadesl.org/History/Quad_History/quad_history.html