AES Section Meeting Reports

San Francisco - March 19, 2009

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Wes Dooley spoke at AES San Francisco's March meeting. Forty people attended.

Dooley is president of Audio Engineering Associates, in Pasadena, California. AEA manufactures and services ribbon microphones, and preamplifiers.

Ribbon mikes use a strip of corrugated metal a few microns thick, mounted in a strong magnetic field. The ribbon acts like a coil, of just one turn. It generates a voltage which is proportional to the velocity of the ribbon.

Ribbon mikes naturally have a figure-of-eight pattern. They are equally sensitive to sound from the front and the back.

Ribbon mikes have a number of unique qualities. Their polar response pattern is broad, in the horizontal plane. This is useful, as most performers don't move up and down much, but often move from side to side. Ribbon mikes' on and off axis frequency response is remarkably similar, providing a natural sound quality. They can make rooms sound bigger. Reflected sound from the back of the room is canceled, as the front and rear lobes are out of phase.

A ribbon mike can be used as a tweeter, by driving it with an amplifier, also creating a broad, even pattern in the horizontal plane.

Ribbon mikes have no internal components to degrade with age. Bing Crosby's personal RCA 44BX sounds as good today as it did in the 1940s. Few condenser mikes sound good after forty years.

RCA stopped servicing ribbon mikes in 1976.

Ribbon mikes are especially sensitive to wind blast, as they respond to pressure gradients. Blowing on a ribbon mike may cause permanent damage, as can slamming the lid shut on a microphone case. Ribbons have to move twice as far for each octave reduction in frequency. Wind blasts are nearly the same as direct current. Blast protection, such as a 'popper stopper' is recommended.

The meeting was held at Dolby Laboratory's screening room, at its headquarters in San Francisco.

- Paul Howard

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AES - Audio Engineering Society