Bi-wiring?
On Mar 5, 10:24*am, ST wrote:
I am music lover and would like to share observation.
I can't tell any difference whatsoever nor any of my
so called audiophile friends. Of course I didn't tell
them I am doing any blind test. The only aspect
of bi-wiring that I hope someone can reply is:-
1) When the woofer moves the coils suppose to
generate electricity and it suppose reverse to
the amplifier or get filtered or something like
that.
Yeah, or something like that, but not.
So when we connect the tweeter and subwoofer or woofer won't
this little current affect the tweeter?
No. Why would it There are a several reasons why it
won't:
1. Let's take your little voltage "generator" model:
That voltage generated by the voice coil is isolated
from the rest of the system FIRST by the series
DC resistance of the voice coil. In the non-biwiring
case, it's a short hop over to the tweeter, where
there's already a pretty hefty filter to prevent this
stuff from getting through. But, as importantly,
there's also a near dead short to ground: the
output impedance of the amplifier.
Let's follow the tortured path of the signal. Assume
speaker leads are 10 feet of 16 gauge standard
copper zip cord. That's 0.08 ohms resistance. Now
assume the amplifier has a modest, but not atypical
output impedance at low frequencies of, oh, 0.16
ohms (a "damping factor" of 50). And lastly, assume
a 7 ohm resistance in the woofer voice coil.
IN the non-biwrired case, the "generator voltage"
you hypothesize will be attenuated by the series
attenuator formed by the DC resistance and the
combination of the speaker lead and amplifier
resistance, e.g.:
G = (0.08+0.16)/(0.08+0.16+7)
Which works out to 30 dB.
And THAT voltage is further attenuated by the
tweeter crossover. Assume the tweeter crosses
over at 2000 Hz with a 12 dB/octave slope, and
the woofer system resonance (the point at which
your "generator voltage" is at its max) is 50 Hz.
That tweeter crossover then further attenuates
you "little generator voltage by a further 70 dB,
for a total attenuation of about 100 dB by the
time it reaches the tweeter.
So let's bi-wire using the same wire. Now, the
attenuation at the point where the tweeter and
woofer can talk to each other has merely been
moved from the speaker to the amplifer: the
connection is still there, just with the resistances
in a slightly different position.
In the bi-wire case, the attenuation is now:
G = (0.16)/(0.16+0.24+7)
or 33 dB. Add to that the same 70 dB of crossover
attenuation, and you now get 103 dB.
Can you show that the level difference at the tweeter
of a 50 Hz signal that's 100 dB vs 103 dB down is
discernable?
2. GO bone up on the good Mr. Thevenin. When you've
done that, you can show that, at resonance, the point
where the back EMF voltage is at its maximum, the
load presented to the amplifier looks like a pure
resistor: Thevenin's theorem states, in such a case
that there is no difference between an 8 ohm voice
coil with a back-EMF behind it equal to 3/4 of the
impressed amplifier voltage, and a 32 ohm resistor
with no generator (a very typical impedance of a
woofer at resonance).
Unless you are ready to prove Mr. Thevenin wrong,
why would you expec a 32 ohm load to benefit from
bi-wiring (hint: it doesn't).
3. Take the example worked on in point #1: replace
the 16 gauge wire in the non bi-wired case with
12 gauge wire. Just that alone will give you 102
dB of total attenuation.
2) *By bi-wiring there's no "disturbance" in current to tweeter.
Is this possible?
It can be shown that it does not have the effect
claimed by the proponents of biwiring.
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