What does the crossover do differently when you bi-wire? - Page 33 - diyAudio
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Old 29th September 2013, 01:10 AM   #321
gootee is offline gootee  United States
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Quote:
Originally Posted by SY View Post
"Instrumentation amplifier"
Oh, duh!
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Old 29th September 2013, 05:15 AM   #322
gootee is offline gootee  United States
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Quote:
Originally Posted by gootee View Post
I can do that. But just FYI, what I have presented recently was all direct "ac analysis", with no time-domain simulation involved.

Wait. What is "IA"?
Not sure what I was thinking, when I wrote that. The THD analyses were performed with time-domain runs in LT-Spice.

Anyway, doing more of them, today, with instrumentation amps connected, I can get the THD trend to go in the opposite direction, i.e. the single cable model does better than the bi-wired model, and even better as cable length is increased. FFT confirms. And apparently it's mostly third harmonic, probably from the IAs. Will try a better IA circuit, and see if it changes.
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Old 29th September 2013, 05:44 AM   #323
jcx is online now jcx  United States
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Spice has a "perfect IA" - the "E" VCVS

you can also clean up comparison in AC analysis by dividing waveforms by each other, or a reference waveform - works fine with the complex values, stepped parameter analysis

just use waveform arithmetic – enter equation of values in the waveform viewer “add trace” dialog box




I can't tell if people are going off the rails again – there is no intermod in linear systems, superposition works, works for linear R, L, C, even skin/proximity magnetic fields

you need to introduce nonlinear component models into the situation for distortion/intermod products

some are very second order

typical cable R is Cu, with a large 0.4%/C tempco - with a severe low pass from thermal mass/heat capacity

insulation isn't perfectly rigid so magnetic and "electrostatic" forces exist which in principle physically move the pair of wires together, modulating cable L, C

Last edited by jcx; 29th September 2013 at 06:05 AM.
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Old 29th September 2013, 09:28 PM   #324
gootee is offline gootee  United States
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Thanks, jcx. I used the e-sources as perfect differential instrumentation amplifiers and got the attached.

I ran time-domain ("Transient") simulations for cables of 13 feet and 513 feet, and then did FFTs, which are attached.

So there appears to be a difference between bi-wired and single-cabled, which also becomes more apparent as the cable length increases, as would be expected.
Attached Images
File Type: jpg bw_diff_fft_13ft.jpg (399.9 KB, 95 views)
File Type: jpg bw_diff_fft_513ft.jpg (380.1 KB, 95 views)
File Type: jpg bw_diff_fft_schem.jpg (256.9 KB, 97 views)
Attached Files
File Type: txt BI-WIRING2f_no_amp.asc.txt (16.2 KB, 1 views)
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Last edited by gootee; 29th September 2013 at 09:32 PM.
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Old 29th September 2013, 11:18 PM   #325
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Quote:
Originally Posted by keantoken View Post
I'm not sure whether skin effect is relevant here. I don't know whether skin effect gets worse when conductors are paralleled (proximity effect) or whether it gets better. I think skin/proximity effect maybe significant in the treble, but I couldn't figure out how to calculate it. Note: I define significant as whether or not the skin effect is greater than the inductance and resistance at any point along the impedance curve of the cable.
The "skin effect" so beloved of cable snake oil salesmen, is directly related to the frequency of the signal on the cable. It only starts to become important at frequencies WAAAAYYYYYY beyond audio frequencies in the megahertz.

The only real reason why stranded cable is prefered in most audio applications is that it is more flexible and breaks less easily.
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Old 29th September 2013, 11:27 PM   #326
gootee is offline gootee  United States
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Quote:
Originally Posted by gootee View Post
Thanks, jcx. I used the e-sources as perfect differential instrumentation amplifiers and got the attached.

I ran time-domain ("Transient") simulations for cables of 13 feet and 513 feet, and then did FFTs, which are attached.

So there appears to be a difference between bi-wired and single-cabled, which also becomes more apparent as the cable length increases, as would be expected.
Erratum: In the second plot that I posted, the 80 Hz amplitude was 60 V, not 16 V.

Also, the series resistances in the cable models look shorted, in the schematic. But they had been included in the inductors, as the ESRs.
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Old 30th September 2013, 12:45 PM   #327
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Quote:
Originally Posted by gootee View Post
Thanks, jcx. I used the e-sources as perfect differential instrumentation amplifiers and got the attached.

I ran time-domain ("Transient") simulations for cables of 13 feet and 513 feet, and then did FFTs, which are attached.

So there appears to be a difference between bi-wired and single-cabled, which also becomes more apparent as the cable length increases, as would be expected.
Your plots are showing transmission line effects. The mono case has a significantly different termination impedance, so your seeing reflection stuff. My expectation is if you double the length, the spikes will drop in frequency.

Is the biwire "difference" voltage levels subtracted after level measurement, or did you use an ideal analog subtractor and then measure the difference? Your schematic appears to be measure first, then subtract.

Ah, endgame preview. Do you have the ability to provide scope photo's of the analog diff?

And how is the transient capability of the package?

Nice work however, I thank you for taking the time and the effort.

John
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Old 30th September 2013, 01:14 PM   #328
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I think the most advantage is that you can use multiple amps to drive the speaker
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Old 30th September 2013, 08:07 PM   #329
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Default Please consider the amplifier in your thoughts about bi-wiring

Dear all,

Sorry I skipped reading all this thread, (too much hot air in the middle of it) but my 2 cents hypothesis for my observed beliefs (And I thought it was snake oil until I listened and heard a difference):

My hypothesis to explain the effect is that by sending the drivers harmonic distortion (causing back EMF) through two series resistors (the speaker wires) and one parallel resistor (the amp) you get greater attenuation of driver harmonic distortion effecting the higher frequency driver. This would explain Bi-amping being better than bi-wiring and bi wiring being better than a single cable. The advantages of Bi-wiring would be dominated by the ratio of speaker connection and cable resistance to amplifier output resistance.

I suggest an experiment to measure this effect.

First test if you can see a difference in the signal sent to drivers with normal passive cross over and with Bi-amping. Since most people say bi-amping is better than bi-wiring and conventional amping. If no differences are observed, put 0.5 Ohm or greater resistors in series with the speakers cables and remeasure.

* If no difference can be measured it does not prove biamping does not improve things only that you cant measure it and no further experiments should be completed.
* If a difference can be measured

A two way speaker, driven by a solid state amplifier (with as low output impedance as possible so definitely not a valve/tube amp) with 0.5 Ohm resistor in series with the speaker cable. Measure the signal reaching the tweeter then bi-wire with a 0.5 Ohm resistor in series with each bi-wired speaker cable, and remeasure the signal reaching the tweeter.

* Again if no difference can be measured it proves nothing.

* If you measure a difference then bi-wiring has an effect even with the 0.5 Ohm resistor in series.

If a measured difference is observable, but is reduced or disappears if you remove the resistors / use a higher output impedance amplifier, it would contribute to the evidence for the hypothesis. (it is my subjective listening opinion 20 years ago that this occurs)

Sadly no measurements have been made by me in this area by me.

Best of luck

Owen
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Old 30th September 2013, 09:06 PM   #330
tinitus is offline tinitus  Europe
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What does the crossover do differently when you bi-wire?

I know what mine will do differently

building a PA top with doubled outputs for two setups
one 2way, and one 3way
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