From: brian@hopi.eel.ufl.edu (Brian Gentry)
Newsgroups: rec.audio.car
Subject: Re: Q: Tweeter wiring from CSR..
Date: 5 Oct 92 22:57:46 GMT
Organization: UF EE Department (student)

In article <1amv9iINN5o0@usenet.INS.CWRU.Edu>, kmr4@po.CWRU.Edu (Keith M. Ryan) writes:
|> 
|> In a previous article, brian@navaho.eel.ufl.edu (Brian Gentry) says:
|> 
|> >I got the impression from the original quote that the tweeters were 
|> >wired out of phase with each other--not with the mids.  Your 
|> >explaination seems a lot more logical, but I've seen weird things done 
|> >in cars before (like wiring tweeters out of phase with each other).  
|> >The only possible reason I can see for this is that the installer 
|> >*thought* he was time aligning the system or something along those 
|> >lines.  I would like to see/hear a system which has delay to the 
|> >passenger side speakers to make up for the arrival time difference
|> >between the driver's side and passenger side speakers.  Of course this
|> >would only sound right to the driver, but it would sound really good.
|> 
|> This may have been an attempt to time align the higher frequencies for
|> the driver. The time alignment of the speakers AT the speakers is not so
|> important. What is important is the time alignment at one's ears. 

Time alignment refers to drivers who's accoustical centers are in the
same plane; i.e. the arrival times of freqency x are the same for both
drivers.  I don't see how wiring one tweeter out of phase with the other
will time align midrange and tweeter drivers.  Furthermore the sound
from the tweeters will probably be reduced due to cancelation.  What we
are really concerned with is that the output of the tweeters and midranges
are not 180 degrees out of phase at any frequency.  With a 12dB/oct xover
this tends to happen at the xover frequency.  In home systems the tweeters
are simply wired out of phase with the midrange drivers to correct for
this cancelation problem.  In order for the tweeters out of phase with 
each other scenario to work, the path length difference between the left
tweeter and midrange (Ld) and the right tweeter and midrange (Rd) would have
to be exactly 1/2 wavelength at the xover frequency.  These path lengths
would be measured with respect to the driver's head.  This would justify
the 180 degree phase difference.

|So, in
|> reality, they may of been correct from the drivers seat. It could also
|> be correct for the passenger! Except, he may be 180 out of phase, referenced
|> to the driver's point of view.

In order for this to be true the same set of path length conditions I made
above must be true.  The only difference is that the path lengths would be
measured relative to the passenger's head.  I specify path lengths because
the sound may not travel along the same path to reach the passenger and
driver.  The driver may hear a reflected sound while the passenger hears
a direct sound or vise-versa.  Both people may hear two different reflected
sounds.

| There are some discussions of whether apso-
|> lute phase is audible, however, I doubt it'll be so subtle that in a car
|> enviroment, it will not be. [ do to all the reflections that abound in a 
|> car's interior ] 

I agree that this effect is probably totaly inaudible.  For absolute
phase arguments to be valid, the phase of the microphone/mixer interface
must be known anyway and this varies wildly from recording to recording.

|> >			Brian L. Gentry
|> >		   (brian@sioux.eel.ufl.edu)

|> -- 
|> 
|> 	" It's time for Congress to tell the president to shove his 
|> 	veto pen up his deficit! "  
|> 					- Rep. Jim Traficant.

As you can see the conditions above are extremely specific and very
unlikely IMHO.  I don't know what the original installer did, but it
doesn't seem like wiring the tweeters out of phase with each other could
be a good idea (although I wouldn't mind an A/B comparison).

			Brian L. Gentry
		    (brian@sioux.eel.ufl.edu)
Newsgroups: rec.audio.car