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In Reply to: Re: I have no anti-utilitarian bias posted by stuck.wilson@gmail.com on February 23, 2007 at 12:39:11:
"good home and good PA drivers ARE capable of good performance USED PROPERLY, entirely dependant on the application and the driver. either can be great or horrid depending on the design of the system they're in. period. every venue, system, and/or listening room is different"
I agree.....but the thread is about time coherence and NO high power handling PA system is time/phase coherent. Zero. Zilch. Notta one. Not even close.
Follow Ups:
"and NO high power handling PA system is time/phase coherent. Zero. Zilch. Notta one. Not even close."Not so fast. Tom Danley makes phase coherent PA gear. Many PAs use time coherent digital crossovers that also feature time alingnment. And of course PA speaker makers have been aware of time alingment and featured it in their designs ever since the Eleanor Powell "double tap" incident at MGM in the 1930s.
Tom,
From reading their design paper reprinted in the AES Anthology, John Hilliard and his engineers reduced the interdriver time delay to just a little less than one millisecond, whereupon the double-tap of the tap dancer went away. Since 1933, the transient distortions of the entire recording and reproduction chain have been vastly reduced, so even that much time delay today is considered audible, especially when that inter-driver time delay is also constantly changing at different frequencies, via high-order crossovers in the case of speakers. While no amplifier, cable, CD player or recording machine has this problem of varying the time delay with frequency, two examples of varying time delay exist in the musical-instrument world: in the flanger effect box for guitars, and in the controls of a synthesizer. One can sweep a time delay through the frequency range, purposely changing the time-relationships between a fundamental and all of its harmonics, and between the harmonics themselves. The change in sound is plainly audible. It's called 'phasey.'
Phase/time coherent and PA systems do not go together, for true time/phase alignment can come only by using a 1st order crossover. I know of no PA speaker systems that utilize 1st oder crossovers. It would be counterproductive to do so, as PA speaker systems need to be designed for very high power handling capacities, and generally use high order filters to achive this. Can you show me a 1st order crossover PA system? Give me a link.
"Phase/time coherent and PA systems do not go together, for true time/phase alignment can come only by using a 1st order crossover."
A false premise. The use of digital crossovers allows the use of high order crossovers without the phase problems of high order analog crossovers.Ed Long and Doug Stax claimed phase coherency, or at least time alingment, with Long's Urei monitors and Stax's Mastering Lab crossovers for the Altec 604 coax, this was the setup in the Big Reds.
Tom Danley makes phase coherent PA gear and understands this issue on a level far over my head. There is some info from Tom over on the HE asylum right now about his take on this. If you want to go over there and question him, he can explain it far better than I.
Steep slope filters are what cause the majority of phase shift in loudspeakers, be it digital or analog filters.
The Dolby Lake processor has linear phase filters. Linear phase digital filters is probably what Tom is referring to with digital filters.
To utilize a horn enclosure containing all of the drivers in the same "mouth" intended to address the usual challenges of dissimilar radiation patterns and incoherency. And clever guy that he is, fashion the enclosure in a trapezoidal shape to easily accommodate multiple bins for large arrays.
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