sony MDR V6 headphones

[Bob Carlyon <bob.carlyon@xxxxxxxxxxxxxxxxx>]

=46ollowing Brian Karlsen's request on the list for recommended headphones,
and chris mandra's recommendation of the sony MDR V6, I recalled talking to
soren buus about some problems with crosstalk on these headphones. I
reproduce soren's comments below:

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Many Hi-Fi earphones are prone to crosstalk between the two
earpieces.  The problem is notable in the Sony MDR-V6
earphones, which otherwise are excellent earphones.  The
problem results from a shared ground wire for the
two earphones.  If you feed one earphone a signal while
the other is connected to the output of a driver amplifier
(which may or may not be producing a signal--it doesn't
matter), the current fed in to the first earphone will divide
between the shared ground and the other earphone in
proportion to the impedances to ground at the point where
the two earphones are connected to the common ground.
This results in some of the current from the first earphone
taking a return path through the other earphone, such that
cross talk (in antiphase) occurs.  Our experience is that this
cross talk is roughly 30 dB below the signal in the earphone
that is used.  The cross talk can be eliminated by not
connecting the unused earpiece, but of course that is only a
workable solution for monaural experiments.

The cause (and amount) of cross talk can be visualized as
follows:
                                                 (Amp output=3D
(Signal)                                    virtual ground)
   Left                 Ground                   Right
     |                           |                             |
    >                         >                             >
    >                         >                             >
    >        Wire         >                             >
    >    resistance  >   (about 1 ohm)>
    >                         >                             >
     |                          |                               |
     |                          |                               |
     --VVVVVVVV----|----VVVVVVVV-----|
          Left                          Right
        Earpiece                Earpiece
     (63 ohm)                  (63 ohm)

When the left earphone is fed a signal of, say, 64 mV the
1-mA current, which must return after passing through the
left earpiece, divides between the shared ground and the
right earpiece, whose "hot" end is connected to a virtual
ground (as far as the left earphone signal is concerned).
Thus, slightly less than 1 mA returns through the shared
ground (doing no harm) and slightly less than 1/64 mA
returns through the right earpiece and the right "hot" wire
(making an antiphase cross talk with an amplitude of about
1/64th of that in the left earpiece).

  This problem of cross talk surely is not unique to the Sony
MDR-V6, but applies to any (usually, Hi-Fi) earphone, which
uses a shared ground wire.  Because it is a question of
relative impedances, the problem is usually greater the lower
the impedance of the earphone is.  Certainly, the 63-ohm
nominal impedance of the Sony MDR-V6 makes it a
significant problem.

S=F8ren Buus
ECE Dept.
Northeastern University
Boston, MA 02115

E-mail: buus@neu.edu
___________________________________________

I hope these are of some help


bob

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--
Bob Carlyon
MRC Applied Psychology Unit
15 Chaucer Rd.
CAMBRIDGE CB2 2EF
England

Phone: (44) 1223 355294 ext 720
=46AX:   (44) 1223 359062

email: bob.carlyon@mrc-apu.cam.ac.uk
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