[Vintage-Audio] Dual Voice Coil For Woofer?

[Matt Johnson]

> I spoke with Judith Fulkerson, Oxford, Michigan
> today. She has been
> rebuilding speakers professionally since 1976. The
> only brand she knew of
> that were set up like this one was made by Infinity.

Curious, as many manufacturers have made dual voice
coil drivers over the years. I don't know this person
and I wouldn't wish to question their knowledge but
how they couldn't know of dual voice coil drives makes
me wonder. They must not deal with car audio much I
suppose. Still there were a number of home system subs
that used dual voice coil drivers to make integration
easier. Cerwin Vega was a common dual coil system in
the 80's.

Here is a link on the Crutchfield site describing dual
voice coil drivers and their use in car audio.

http://www.crutchfieldadvisor.com/ISEO-rgbtcspd/learningcenter/car/subwoofers_dual.html
 	
> I believe the phasing is not as simple as you
> assert. A speaker cone can
> not travel in two different directions at the same
> time. How is this
> compensated for?

It is as simple as I described. At worst if the two
channels were driven with equal amplitudes 180 degrees
out of phase there would be zero net motion. Drive
both channels with an equal amplitude signal in phase
and the excursion would double. Its simple magnetic
summing. Of course since most low bass information is
equal in phase most of the summing results in
increased drive not decreased.
	
> 	
> You make reference to more than one amplifier, this
> involves only one.

Kind of, but we are dealing with two amplifiers, one
for the right channel and one for the left. I also
made reference to a true biamplified system that is
dividing frequency ranges before the amplifiers as
opposed to using a passive high level crossover after
them. This is the only way I care to run a sub for
numerous reasons. Apart from my perviously mentioned
impact to the damping factor the high level crossover
creates, the other thing that bothers me is that its
is very difficult to create a passive crossover under
100 cycles. The inductors are simply too large is they
are able to handle any power without saturating. A low
level active crossover is much better at these low
frequencies. As you can surmise I feel that a sub
crossover point of 250 hz is too high. My JBL sub only
handles 70 cycles and below.	
> 	
> Keep in mind this was when the so called "sub"
> woofer was a new concept.
> Much has changed since this was developed.
> Personally, I would call this a
> woofer being shared by two channels, as you can not
> have a sub-woofer
> without a woofer, right?
	
The term Subwoofer is one of those terms that attempts
to be descriptive although it isn't really all that
accurate. Of course it could just be refered to as
being a woofer. It seems that it generally is applied
to a woofer that is added to a existing system to
augment bass extension/output. It also seems to apply
when a single driver is used on both channels of a
stereo playback system.

Regards,

Matt



		
__________________________________________ 
Yahoo! DSL – Something to write home about. 
Just $16.99/mo. or less. 
dsl.yahoo.com