David Hafler
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David Hafler (1919 - 2003) was an American electronics engineer. He was best known for his work on an improved version of the Williamson amplifier using the 'ultra-linear' theories of Alan Blumlein.
In 1950, he founded Acrosound with his colleague Herbert Keroes. This company was primarily in the business of designing and manufacturing transformers for tube amplifiers. The partnership did not last, however.
In 1955 he founded Dynaco with Ed Laurent. He was instrumental in bringing affordable, high-quality audio kits to hobbyists, and his name was a household word in the international audio community for many years. He died May 25, 2003 in Philadelphia, Pennsylvania, USA.
In the 1970's he promoted "Passive Pseudo Quadraphonics", an inexpensive method of recreating ambient sound at the rear from ordinary stereophonic recordings. Known as the "Hafler Hookup", this consisted of two similar additional rear speakers, connected in series (typically 8+8=16 ohms) between the live feeds to the front speakers. The "crosstalk" or loss of stereo separation in the front speakers is less than 2dB while the rear sound level in a typical stereo-recorded live performance is about 7dB below the front, but clearly audible. This "passive" method is arguably as good as any of the expensive "active matrix" electronic decoders which attempt to reconstruct ambient sound from a stereo recording. It has been observed that ambient sounds in a concert, such as applause or even coughs from the audience, are generally received in "opposite phase" by the stereophonic microphones, while sound from the musicians is generally in "syncronous phase". Thus, if rear speakers are fed with the difference between the stereo channels, audience noises and echoes from the auditorium can be heard from behind the listener.
External links
- [Stereophile Magazine biography and obituary of David Hafler]
- [Greg Dunn's Dynaco page containing Hafler newspaper obituary]
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