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Stereophile Tries To Come Clean About The DiAural Fiasco
http://www.stereophile.com/reference/1104red/ more specifically http://www.stereophile.com/reference...ed/index3.html "Although the initial fuss that accompanied Ray Kimber's 1999 launch of DiAural-the proprietary speaker-crossover technology developed by Eric Alexander-has died down, the fact remains that it was and still is promoted as a means of canceling the Doppler distortion introduced by microphones: "Doppler Decoding," in DiAuralspeak. To my knowledge, however, this claim has never been challenged in the audio press." "...for a microphone to introduce significant levels of Doppler distortion, its diaphragm would have to undergo large excursions-of the same order as the loudspeaker diaphragm, if cancellation is to be feasible. In fact, microphone diaphragm excursions are minuscule. I asked Stephan Peus, president of development at Georg Neumann GmbH, to provide me with some representative figures. He e-mailed back a document, "Some Amazing Facts with Condenser Microphone Capsules," which quotes the diaphragm excursion for Neumann's KM 184 microphone (a miniature cardioid) as being just 10 nanometers-that's four-tenths of a millionth of an inch, or about a 40th the wavelength of blue light-at an SPL of 94dB. Compare this with the 7.5mm peak excursion required to generate this SPL at 100Hz in free space and at 3m (10') listening distance, using a drive-unit of 200mm (8") effective diaphragm diameter. The two figures differ by a factor of 750,000! Depending on their mechanical characteristics, the diaphragms of other capacitor microphones may undergo larger excursions, but their displacements will still be orders of magnitude smaller than a loudspeaker cone's IOW, when Kimber snowed Stereophile about his abilities to correct Doppler Distortion in microphones, he was talking trash. I notice that the origional offending article has been expunged from the Stereophile web site. It used to be located at http://www.stereophile.com/shownews.cgi?416 . Here are quotes from the missing article and my comments about it that were posted here at that time: http://groups.google.com/groups?selm...u tput=gplain -------start long quote that embeds quotes from the Stereophile web article that now seems to have gone missing http://www.stereophile.com/shownews.cgi?416 says: "Five weeks ago we reported that Ray Kimber, of Kimber Kable fame, and his financial partner, Bruce Bastion, were in the process of bringing a new loudspeaker technology to market. DiAural, as they've named the technique, is claimed to eliminate what Kimber calls Doppler-encoding distortion---the modulation of high frequencies by low frequencies of higher amplitude." This roughly corresponds to the classic understanding of Doppler distortion. W/R/T classical understandings of how to reduce FM distortion in speakers, this article seems to make some false claims, such as "According to Kimber, this encoding takes place in the microphone, survives intact throughout the recording and playback chain, and, if left undecoded, seriously detracts from any audio system's verisimilitude." Actually, Doppler distortion is due to velocity and changes in velocity. Speakers like the Bose 901 are specially exposed to it because their woofers and tweeters are the same driver. When the speaker's cones travel at high velocities to produce bass, treble is FM modulated by the Doppler effect. If treble is reproduced by a different cone, or if the speaker cone is prevented from attaining a high velocity, then doppler is greatly reduced. Thus, the classic two-way speaker system has greater resistance to Doppler distortion than a single-way. Also, this means that one of the benefits of having a subwoofer is reduced Doppler distortion. As a rule, microphone diaphragms don't move fast enough to cause doppler distortion. Ever see a microphone diaphragm stroke like a small woofer being driven with heavy bass? Nope - most mics would be physically damaged if they tried to do that! Therefore, the "coding" mentioned here is unlikely to happen. "The DiAural technique, developed by designer Eric Alexander, performs decoding at the speakers themselves, using a couple of common parts configured in a novel way that enables a woofer and tweeter (or woofer, midrange, and tweeter) to "talk back" to each other, freeing them to jointly produce sounds more like those that originally impinged on the microphone." Sounds like low slope crossovers or some other technique that reduces the isolation betwen the drivers. This is old news, and generally found to be the exactly wrong thing to do if the goal is to minimize Doppler distortion. "The DiAural circuit replaces the traditional crossover network, which means the drivers are connected directly to the amplifier. All of which made for an interesting telephone discussion I had with Kimber before writing this story." If the speakers are "connected directly to the amplifier", then there is no crossover network. This is actually the worst case for creating Doppler distortion. -------end long quote that embeded quotes from the Stereophile web article that now seems to have gone missing |
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