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In Reply to: RE: Please explain bi-amp crossover to me posted by Raymond Leggs on February 21, 2017 at 14:57:12
This method of "bi-amping" is often called "fools bi-amping" in many audio circles. Google is your friend ;-)
In the name of being a career contrarian... ;)
There is potential merit to passive bi-amping because although each amp is applying a full-range signal to each network, the networks "complex impedance" is what will determine the current that flows in each amplifiers output stage.
Common wisedom says the voltage *AND* current will be the same in each branch, but this is not the case.
So, what you have is one amp "seeing" only woofer current and one amp "seeing" only tweeter current. Since bass is more current-intensive, it can drag down the DC rail voltage of the amp, especially if the damping factor is relatively low. So, this could potentially improve the situation for the "tweeter circuit amp". Also, too, you can mess with different speaker wires for each circuit. You can use a higher-power high-strand-count low impedance cable for bass, and then get away with a nice "fine wire" ribbon or silver-wire "guitar string" design for the tweeter (if your particular denomination of audio beliefs include room for 'time smear' in speaker cables!)
But, in agreement, you're not gaining anything power wise. Amp1 sees 'Current A' and Amp2 sees 'Current B' where a single amp simply sees "Current A+B".
The point of my post is to point out that although the voltage output of the amps will be full range, the currents will be different, and this can have a bearing on over-all amp performance. Amps store energy (large capacitors) so they provide some isolation from one another depending on the damping factor of the amp and the "stiffness" of the power source.
People have claimed they have had success by improving the branch circuit conductors from the panel to the audio room. Others have gone further and had the incoming cables to their home upgraded. With electrical sources, stiffer is better - especially when you start talking about current surges associated with higher-power bass applications. My friend's 2000W RMS sub amp likely dims house lights in a 1-block radius! ;)
I tried to follow your argument about current but Kirchoff keeps getting in the way. Assume the same complex signal is fed to both amps and the amps generate an augmented signal with current i and voltage v. The current returning to the amp will be -i (the sum of the currents at a node is zero) . This is true for both amps - the current flowing through the speakers will be the same (assuming the amps are identical).In the case of the low pass the voltage Vamp= Vind + Vwoof and for the high pass Vamp=Vcap + Vtweet. So while the voltage drop across the speakers is different the total voltage drop is the same for both circuits. And as you said, there is no power gain beyond the sum of the two amps.
With home electrical circuits, the advantage from isolated lines comes from 1) less interference from other elements in the home 2) less resistance in the circuit due to heating of the wires and less Johnson noise. However for the most part (ignoring the wire resistance issue), the current and voltage delivered is the same.
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