Why?
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Bi-Wiring without Bi-Amping
- Thread starter MediumRare
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Why?
A technical tear-down of the concept (in french) :
OP
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- #23
My understanding is a subwoofer may have much lower sensitivity and impedance and therefore require copious amounts of power, especially current. Mine, for example, has a 1,250 watt class D amp. My tweeters, OTOH, are 8 Ohms and sing loudly on 20 watts. So, at these extremes, does it not make engineering sense to separate those two jobs? (This is my understanding of bi-amping, not only bi-wiring.)
OP
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- #24
Auriez-vous l'amabilité de nous faire un bref résumé en anglais?
Yes, sure, but power requirement is pretty much the only difference. That is why active speakers tend to have lower-powered amps for mids and treble, but usually same technology and design.
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You're talking about bi-amplification. Different thing than the bi-wire cult. Or McIntosh tri-wiring (which was what I was specifically ridiculing). Biamplification (or other multi-amplification schemes) allows one to concentrate on specific power and bandwidth requirements of a specific driver inside a specific enclosure. So sure, that is an option if it's done right. Simply adding more hook up wire from an amp to a full range speaker in order to increase the soundstage and front to back depth, which as near as I can tell is what proponents of the practice claim? Idiotic.
Avec plaisir, cher ami, as soon as I find time to write a quick and dirty condensed transcript
Here you go, 1st half (I'll go through the 2nd if kindly enough asked to ) :
(Feynman intro)
The audio world is rotten with pseudo science.
Bi wiring myth, two kinds of it ; are they up to something else than marketing blurb ?
There are 2 manners to see it, an electrical one and an anthropomorphic one with no physical reality, which is pure nonsense : if the hypothesis that low and high frequencies pollute each other when transmitted together thru some cable was true, there would be no spectrum analyzer etc possible, which is not verified ; or take an LF signal generator, make it spit a square wave which is a mix of one sine and an infinity of harmonics with specific amplitude and phase, if they were interacting and interfering with each other there would be no square wave at the end of a cable but an uncontrolled, noisy mix of them, or whatever.
So the idea that different frequencies might influence each other in cables is wiped out by facts – and yet it exists, but only in audio world and notably in speaker cables, hence bi-wiring – with no evidence whatsoever.
Now let’s look at the electrical aspect of it :
(6 :00) Here is a mono wiring sketch : we have an amp, a cable with given impedance, a 2-way speaker with high pass and low pass filter. The connection between them is short enough to be negligible.
There are 2 topologies wrt bi wiring : speakers with 2 pairs of connectors, and a different cable from amp to each set of connectors – not necessarily the same, audiophiles like a fat cable for the bass and a thin silver one for the highs (8 :10) go figure. In this version of things, cables sit between amps and speaker crossover.
8 :24 Another topology involves putting the crossover at the output of the amp, from which each cable, not necessarily the same, goes to its driver of destination.
Which is the difference, electrically speaking, between single and bi-wiring ?
First, there’s a difference : by doubling the amount of cable you put more copper into the system, which should result in something observable.
(10 :00) Let’s study the single wiring case and then the bi wiring one, the one with dual speaker connectors preceding the crossover ; the other one won’t be specifically studied but we’ll simulate it later.
10 :30 let’s compare single wiring (left part of the board) and bi wiring (right)
What does the amp see with single wiring ? Cable impedance, Zc, and then two impedance components Z1 and Z2. What’s that ? These are impedances of each crossover section as seeen by the amp. Z1 is the combined impedance of the 1st filter and 1st driver, Z2 the same for the other one.
11 :48 With bi wiring it’s not the same : Z1 and Z2 are the same but the amp doesn’t see xactly the same thing since each cable adds its own impedance (Zc and Z’c) to the mix, before Z1 and Z2 respectively.
12 :10 U0 being the voltage at the output of the amp, same in the 2 cases, with single wiring we have U1 the voltage across Z1 and U2 across Z2, the voltage at the speaker input.
12 :33 with bi wiring we also have U1 and U2, in both cases with intensity I1 and I2 respectively
13 :22 Without getting into the math, there is a basic difference which makes the behaviour of one not exactly the same as the other : first case (single wiring), the voltage across each crossover section is the same, U1 = U2 ; second case (bi wirng) it’s not guaranteed. U1 and U2 will be different inasmuch as the cables behave differently. At frequencies which don’t involve one section or the other, the case is equivalent to single wiring. But when both drivers are operating, notably at crossover frequency, it behaves differently 14 :19 since we have different voltages arriving at the speaker inputs, as much as the cables differ.
This is the basic difference. Problem is, this is a flaw of bi wiring. Why ?
14 :50 Because when the speaker mgfr designs some speaker and Xovers, computing speaker sensitivity, speaker impedance and crossover frequency, they intend that both filter sections face the same conditions in order for them to work predictably and correctly.
They don’t have an idea of which Zc and Z’c some given audiophile will introduce in the system, so they absolutely can’t set the Xover according to one bi-wiring setup or another. The Xovers are thought of as receiving the same thing, as they do with single wiring, there’s no other way to do it. Or they’d have to provide the cables themselves, so cable and Xover properties would be designed to match together. Even so, they can’t know which length of cable is required…
16 :30 Of course if cables are near perfect and their impedances close to zero, there will be no difference at all between the two topologies (single and bi-wiring). But with different cables we have two different situations, of which one doesn't fit the way the Xovers are designed.
So bi-wiring doesn’t solve anything, rather it’s a problem !
) :(Feynman intro)
The audio world is rotten with pseudo science.
Bi wiring myth, two kinds of it ; are they up to something else than marketing blurb ?
There are 2 manners to see it, an electrical one and an anthropomorphic one with no physical reality, which is pure nonsense : if the hypothesis that low and high frequencies pollute each other when transmitted together thru some cable was true, there would be no spectrum analyzer etc possible, which is not verified ; or take an LF signal generator, make it spit a square wave which is a mix of one sine and an infinity of harmonics with specific amplitude and phase, if they were interacting and interfering with each other there would be no square wave at the end of a cable but an uncontrolled, noisy mix of them, or whatever.
So the idea that different frequencies might influence each other in cables is wiped out by facts – and yet it exists, but only in audio world and notably in speaker cables, hence bi-wiring – with no evidence whatsoever.
Now let’s look at the electrical aspect of it :
(6 :00) Here is a mono wiring sketch : we have an amp, a cable with given impedance, a 2-way speaker with high pass and low pass filter. The connection between them is short enough to be negligible.
There are 2 topologies wrt bi wiring : speakers with 2 pairs of connectors, and a different cable from amp to each set of connectors – not necessarily the same, audiophiles like a fat cable for the bass and a thin silver one for the highs (8 :10) go figure. In this version of things, cables sit between amps and speaker crossover.
8 :24 Another topology involves putting the crossover at the output of the amp, from which each cable, not necessarily the same, goes to its driver of destination.
Which is the difference, electrically speaking, between single and bi-wiring ?
First, there’s a difference : by doubling the amount of cable you put more copper into the system, which should result in something observable.
(10 :00) Let’s study the single wiring case and then the bi wiring one, the one with dual speaker connectors preceding the crossover ; the other one won’t be specifically studied but we’ll simulate it later.
10 :30 let’s compare single wiring (left part of the board) and bi wiring (right)
What does the amp see with single wiring ? Cable impedance, Zc, and then two impedance components Z1 and Z2. What’s that ? These are impedances of each crossover section as seeen by the amp. Z1 is the combined impedance of the 1st filter and 1st driver, Z2 the same for the other one.
11 :48 With bi wiring it’s not the same : Z1 and Z2 are the same but the amp doesn’t see xactly the same thing since each cable adds its own impedance (Zc and Z’c) to the mix, before Z1 and Z2 respectively.
12 :10 U0 being the voltage at the output of the amp, same in the 2 cases, with single wiring we have U1 the voltage across Z1 and U2 across Z2, the voltage at the speaker input.
12 :33 with bi wiring we also have U1 and U2, in both cases with intensity I1 and I2 respectively
13 :22 Without getting into the math, there is a basic difference which makes the behaviour of one not exactly the same as the other : first case (single wiring), the voltage across each crossover section is the same, U1 = U2 ; second case (bi wirng) it’s not guaranteed. U1 and U2 will be different inasmuch as the cables behave differently. At frequencies which don’t involve one section or the other, the case is equivalent to single wiring. But when both drivers are operating, notably at crossover frequency, it behaves differently 14 :19 since we have different voltages arriving at the speaker inputs, as much as the cables differ.
This is the basic difference. Problem is, this is a flaw of bi wiring. Why ?
14 :50 Because when the speaker mgfr designs some speaker and Xovers, computing speaker sensitivity, speaker impedance and crossover frequency, they intend that both filter sections face the same conditions in order for them to work predictably and correctly.
They don’t have an idea of which Zc and Z’c some given audiophile will introduce in the system, so they absolutely can’t set the Xover according to one bi-wiring setup or another. The Xovers are thought of as receiving the same thing, as they do with single wiring, there’s no other way to do it. Or they’d have to provide the cables themselves, so cable and Xover properties would be designed to match together. Even so, they can’t know which length of cable is required…
16 :30 Of course if cables are near perfect and their impedances close to zero, there will be no difference at all between the two topologies (single and bi-wiring). But with different cables we have two different situations, of which one doesn't fit the way the Xovers are designed.
So bi-wiring doesn’t solve anything, rather it’s a problem !
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