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From: jj@rabbit.UUCP
Newsgroups: net.audio
Subject: superstition--wishes were horses night.
Message-ID: <1761@rabbit.UUCP>
Date: Thu, 4-Aug-83 17:04:58 EDT
Article-I.D.: rabbit.1761
Posted: Thu Aug  4 17:04:58 1983
Date-Received: Sat, 6-Aug-83 17:35:24 EDT
Organization: Bell Labs, Murray Hill
Lines: 61

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>