jj@rabbit.UUCP (08/05/83)
Mr. K's analysis of speaker response is mostly correct, except for the assumtion that the drivers have both flat phase response (Not true, but somewhat compensatable) and flat (and resistive) impedences. IF one is using a bi-amped system, AND has an extremely good set of drivers that have their phase responses MATCHED over the crossover region, (note, matched, not flat) then the statements made about first order crossovers will hold. IF one is using passive crossovers, which was the case under discussion, then one must also take into account the impedence of the driver, typically nothing near either resistive nor of flat magnitude. Woofers tend to lag by 45-90 degrees near the top of their useful range, tweeters to lead by a similar amount (unless one is close to the tweeter resonance, in which case all bets are off), leading to a considerable difference from the expected response. This phase shift must be 1) Known in advance. 2) The crossover points must be offset to account for the diffence. and 3) The tweeter must (occasionally) be connected out of phase to allow even approximate matching. In the case of second order crossovers, several other effects happen, i.e. the q and frequency of the crossover point are severely affected by the driver impedence, thus leading to considerably more trouble, unless one makes the appropriate allowances. <Incidentally, in second order crossoves with the tweeter NOT out of phase, without the frequency offset Mr. K suggests, one finds that the sum of both transfer functions is exactly: (s**2+w**2)/(s**2+2bws+w**2) which has EXACTLY a zero in it's transfer function, not a 9 dB dip, or whatever. Of course, this comment only holds for ideal drivers, which does limit its use a bit. I don't have any interest in carrying this argument any farther over netnews, since it really isn't of interest to anyone except, apparently, Mr. K. As to the part about the phase curve of a tweeter out-of-phase matching the phase curve of a DAD, I can only comment that one effect is at 500-2000Hz or so, and the other effect is at 17000Hz upward, leading to quite different effects, even assuming that the tweeters in BOTH speakers are mis-connected, which was not the case being discussed at the beginning of this discussion. Enough of this, where can I get some decently miked Discs??? Analog or Digital? Hi, Dave! rabbit!jj <try through research, harpo, allegra, or mhux* for mail>