Electrostatic Loudspeaker Bret Spencer ECE 5320 - Mechatronics .
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Transcript of Electrostatic Loudspeaker Bret Spencer ECE 5320 - Mechatronics .
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
http://www.virtualdj.com/image/oldblog/95/23138/image.jpg
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
• 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
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
http://free-hosting.infodiv.com/geocities-quad_esl63/images/home/esl63exposed.jpg
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
http://gizmodo.com/assets/resources/2007/10/martinlogan_speaks.jpg
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: 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