From: jreiser@scott.skidmore.edu (Jason Reiser... Asleep)
Subject: Re: Dual Voice Coil Subwoofers
Organization: Skidmore College, Saratoga Springs NY
Date: Tue, 26 Jan 1993 18:56:22 GMT

ajones@dadd.ti.com (Alan Jones) writes:
> Can someone briefly explain to me when to choose a dual voice coil subwoofer
> versus a regular single coil?  It seems to me that they make these for folks
> who want to install only a single sub, correct?  And when you do this, you
> simply connect both left and right channels to the sub, right?

DVC subs are used as you described by connecting both the right and
left channel outputs to the sub (they have two sets of separate
terminals that are NOT paralleled to one another).  The sub is useful
if you have an amp that will not operate in a mixed mono (3-way)
configuration, or to add only one sub with a non-bridgable amp.

> I'm confused because I was shopping this past weekend for subs and found a
> place which is clearing out it's Earthquake subs.  They're selling the EQ-12
> for ~$60.  (Anyone out there have one of these??)  The salesman there said 
> that if I hooked up the left and right channels of my amp the sub would tear
> itself apart.  Instead, he said I need to add a gizmo to one of the channels
> which would change the phase by 180 degrees such that both channels are in
> phase.  Does this make sense?

Exactly what kind of "gizmo" is he refering to?  Indeed, you do have
to make sure that both the left and right channels are in phase with
each other, or as one side pushes the sub forward (away from magnet)
the other channel will send a signal to pull it back simultaniously.
Now, will that tear apart the sub?  I would doubt it.  The electronic
pulses which serve to electromagnetically polarize what is essensially
a moving magnet attached to the woofer cone would get equal
(basically) and opposite signals.  These, I would suspect, would
cancel each other out.  It's still something that you wouldn't want to
do though.  In our music, low notes that this woofer will be designed
to play are basically the same in both the left and right channels.
Yes, they can differ somewhat, but you will not get opposite pulses
(sounds) from the left and right sides.  So, the woofer will respond
normally to both channels at the same time, as the two incomming
signals do not conflict with each other significantly.

The only "gizmo" I could think might be necessary, besides terminal
clips or solder, might be a crossover.  This need for a crossover has
nothing to do with your decision of single or double voice coils
though. 

> BTW, the amp is a Hafler MSE80.  It is a 4 channel amp rated at 20x4 or 80x2
> bridged (into 4 ohms).  What I want to do is run it 80x2 into the 2 coils
> of a single dual voice coil sub.  The MSE80's owner's manual is somewhat 
> ambiguous about this, but I'm pretty sure that when the amp is bridged to 80x2
> the two channels are stereo, not mono.

Sounds like...
20x4 into 4 ohms
40x2 into 8 ohms
and they claim that the amp will double its rated output into 1/2 the
normal impedance... leading to an optimistic rating of
80x2 into 4 ohms (probably the minimum impedance)

This is actually mono... or rather dual mono.  Yes, as long as there
are left and right inputs to the amp, it will still be audible as stereo.

Since what you have is basically a two channel amp here (as it won't
bridge down to a single channel), the DVC sub is a good choice if you
want only one sub, as it will make use of all the power you have to
provide.  I'm not familiar with the particular amp, but you should get
excellent results.  Keep in mind that as you 1/2 the impedance as in
this situation of running a 40x2 (into 8 ohms) at half the normal
impedance (80x2 into 4 ohms) you also half the damping factor.
Depending on the specific amp, and your taste in music, this may be a
consideration to try to run the amp at a greater impedance.

				- Jason
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