Jitter measurements

I wonder about the technical skills of any site that writes this about "Bi-wiring".

One cable carries only the low frequency currents, and the other only the high frequency currents. With this separation, the interaction between the low and high frequency currents are reduced, resulting in lower intermodulation distortion.

I have had to measure fs, no mean feat... One of the problems with measuring jitter is that its frequency response is also important, and in audio when used as a DAC clock the deterministic terms (clock or signal related jitter) are most important and take more time and effort to measure. The good news is that a good BERT (bit error rate tester) or serial analyzer (think $100k - $250k and up) will do it pretty much automatically. Catch is few places lay out for that kind of test equipment.

I wonder what the jitter is from the source material...

Technically, bi-wiring does that (separates the LF and HF currents), but they are the same at the amp so I find it hard to believe there would be audible differences. I am not sure how much IMD is changed by bi-wiring.

Nice article. Short and sweet.

Passive bi-amping retains the crossovers in the speakers and the AVR's amps still run full-range. At the amp outputs, no difference bi-wired or not (except for the extra capacitance etc. of the additional cable run). So, the voltage output is the same at the end of both wires.

Now, the bass section crossover does not pass HF, so the wires to the bass section do not have signfiicant (ideally no) HF current in them. That is, there's no HF load on the bass side. On the treble side, the crossover rejects low frequencies, so ideally no low-frequency current flows in the HF wires, again because there is no LF load. Voltage is the same, but current (and thus power) is a function of the load, which is indeed different for the two wires. Same voltage, different current, because the load is different. Does that help?

Since the load is essentially the same at the amp I don't really understand how it could reduce IMD (certainy not audibly). The arguments I have read discuss speaker (charge) kick-back into the amp, a real effect I agree, are better isolated by bi-wiring. This can be true if the wires provide enough impedance to provide some degree of isolation, but this seems somewhat unlikely, and perhaps even undesirable since that also implies higher impedance at the speaker. Usually the opposite of what we want in a wire, but certainly it could make some speakers sound "better" even if they are less accurate.

How wiring is done is done to the speakers is very important, but not for a lot of the nonsense reasons offered up by manufacturers. Objectivists say a piece of wire is a piece of wire; sorry, it's not, it's a combination of materials which have sorts of properties beyond purely reacting to Ohm's law. For a start, they may act as a beautiful aerial, injecting RF rubbish into the amp terminals. I don't have a full handle on it, but everything in this area matters if you have a high resolution setup.

Frank

Put more simply, the crossover ideally looks like an open circuit to out-of-band signals. So, the LPF to the woofer looks like an open circuit to higher-frequency signals, thus no current flows at HF in the woofer wire. Power is voltage times current. Similarly, the HPF to the tweeter looks like an open at LF, so no LF current flows in the tweeter wire. In effect the crossover removes the out-of-band load. In the real world, there may be shunt crossover components that draw out-of-band power but let's neglect those for now.

Using an example, say we have two light bulbs after a LPF (woofer) and HPF (tweeter) crossing over at 1 kHz. Apply a 10 kHz signal; the woofer does not light. No power is in the woofer light's cable because it does not "see" the woofer light bulb. Apply 100 Hz, and the tweeter bulb does not light; again, no power in the tweeter line. Apply 100 + 10,000 Hz and both bulbs light, but the woofer bulb only gets 100 Hz power and the tweeter bulb 10 kHz, so current only flows in the cable in relation to power drawn at the "proper" frequency.

Your 8-ohm woofer circuit looks like "infinity" to a high-frequency input and so does not load the amp. Same thing happens on the tweeter side for low frequencies. The voltage is still present, but no current flows and no power is drawn.

I'll have to think of another way to present it if this is not clear...

Hi Don. The company links to an AES paper by Jon Risch that showed intermodulation distortion that can be reduced using bi-wiring. I was surprised that such authoritative data may have been published. Alas, while I found various copies of the paper online, none are complete with pictures and all. The best copy I can find is in this link which seems to be a rather random combination of papers/docs written by the author is here: http://www.tmr-audio.de/pdf/jon_risch_biwiring.pdf

In there he talks a lot about IM distortion. He has created a complex composite signal he uses to excite the speaker/wire that he says is far more revealing of the true distortion in devices. He then plots the distortion. With the fragmented text/graphs, it is hard to follow what is what. He certainly seems to be convinced of this fact though. It is by far the strongest argument I have seen for bi-wiring. Wish I could find more data to dig in.

The crux of what he says is what you say. That the two pairs of wires carry different currents and hence don't modulate each other. Something to do with magnetic fields created differently than in a single wire but he does not dig into the reasons as to reduction in IM as best as I can.

I must say, I have never seen anyone have so much trouble just putting a darn document online! I mean how hard is it to save something to pdf with graphs intact???

This might be a little OT, but you might find it interesting.

I tried bi-wiring on my B&W N801 monitors a few months back. I used identical LF and HF runs. After letting the cables settle for a day or so I did some objective listening to music I was very familiar with. Initially my impression was 'WOW', what an improvement. Everything seemed more open and detailed... bigger. But after a few days I was noticing that everything I played had that same sound. Even tracks that previously were quite different from each other. Since the cables were identical, I just shorted LF to HF at each speaker, which essentially made it two parallel runs to each speaker, but at a thicker gauge (11 to 8). The sound promptly returned to normal. The characteristic of everything sounding the same was gone.

I started searching the net all over about bi-wiring. I found two articles that seemed to directly pertain to this behavior, especially the second one!

http://www.achievum.eu/bi-wiring.html
http://www.sonicdesign.se/biwire.html

Since reading the second article which so closely paralleled my experiences, I gave up on bi-wiring -- at least with these speakers.

--Bill

I'll have to read the articles, thanks.

Amir - I have tried to read various versions of that paper before and have never been able to follow exactly what and how they measure and conclude that the cables impact IMD. Of course the curents in the two cables differ, but I have not quite followed their rational for IMD reduction. I am not sure how they have isolated amp and crossover effects. Nor am I sure they ever measured the speaker (acoustic) output, etc. I admit I have not spent enough time wading through it -- it has never been a priority of mine and the paper was very hard to follow so I just gave up (i.e. found better things to spend time on).

Bill - Some of my earliest work with wires included a pair of original 801's as one of the speakers in the tests. They needed a good amp and very low-resistance cables to do well so I am not that surprised that doubling up on the cables helped. As to bi-wiring reducing IMD, the only way I can see that happening is if the wires isolate the amplifier by attenuating some charge kick from the speakers. That would seem to me to increase the actual acoustic distortion since the driver would be less well controlled by the amp. When I measured differences, they were generally negative, not positive. Listening tests were generally negative or inconclusive at best (no change), as I recall. Going from very small to very large wire gauge (or vice versa) was about the only repeatable statistically significant event. In any event, I have not done any significant research in many years.

Aside: In case this ventures off into passive bi-amping, I have no real input on that other than my previous thread in the tech area. I have not done it, or not enough to matter, as it was not really available back when I was in this biz, and I have had seen nothing in the past few years to convince me it is worthwhile.

bblue said:

Initially my impression was 'WOW', what an improvement. Everything seemed more open and detailed... bigger. But after a few days I was noticing that everything I played had that same sound. Even tracks that previously were quite different from each other. Since the cables were identical, I just shorted LF to HF at each speaker, which essentially made it two parallel runs to each speaker, but at a thicker gauge (11 to 8). The sound promptly returned to normal. The characteristic of everything sounding the same was gone.

I started searching the net all over about bi-wiring. I found two articles that seemed to directly pertain to this behavior, especially the second one!

http://www.achievum.eu/bi-wiring.html
http://www.sonicdesign.se/biwire.html

Since reading the second article which so closely paralleled my experiences, I gave up on bi-wiring -- at least with these speakers.

--Bill

Click to expand...

I'm intrigued, Bill. The second link you mention says the sound was "like a slime that pollutes every record you play. No wonder, since it is not a real, recorded quality but a "speaker characteristic" added to all reproduced material". Was this your feeling as well, that the sound had a type of distortion mixed in?

Frank

DonH50 said:

I'll have to read the articles, thanks.
...
Bill - Some of my earliest work with wires included a pair of original 801's as one of the speakers in the tests. They needed a good amp and very low-resistance cables to do well so I am not that surprised that doubling up on the cables helped. As to bi-wiring reducing IMD, the only way I can see that happening is if the wires isolate the amplifier by attenuating some charge kick from the speakers. That would seem to me to increase the actual acoustic distortion since the driver would be less well controlled by the amp. When I measured differences, they were generally negative, not positive. Listening tests were generally negative or inconclusive at best (no change), as I recall. Going from very small to very large wire gauge (or vice versa) was about the only repeatable statistically significant event. In any event, I have not done any significant research in many years.

Aside: In case this ventures off into passive bi-amping, I have no real input on that other than my previous thread in the tech area. I have not done it, or not enough to matter, as it was not really available back when I was in this biz, and I have had seen nothing in the past few years to convince me it is worthwhile.

Click to expand...

Hi Don,

I never made any claim that doubling the wire gauge improved the sound. It probably did improve the LF, but that wasn't the point. The point was that shorting the two bi-wire runs at the speaker eliminated the exaggerated sound that I was experiencing with bi-wiring, by simply removing the separation of crossover elements.

The theory is that remoting the junction of the LF and HF crossover elements, changes their characteristics, which produces a mid-range 'gap' at approximately the crossover point. I can't say that that was exactly or entirely the cause of what I was hearing, but I'm sure it has nothing to do with IMD. IF bi-wiring was lowering IMD it would not have been responsible for a sameness to the sound produced by different sources that I was hearing.

That said, I can't say that I agree with the lower IMD theory, either. There shouldn't be any IMD caused by wiring unless it was severely under-rated for the task. So far, with several different attempts to bi-wire (and despite the manufacturers recommendations to do so) I haven't heard a single improvement in doing so, that using a higher gauge single cable would not accomplish. My cabling is currently 7.5AWG in a fine-wire Litz configuration with 100's of individually insulated conductors, driven by a very low impedance and high damping Pass X250.5 power amp.

--Bill

fas42 said:

I'm intrigued, Bill. The second link you mention says the sound was "like a slime that pollutes every record you play. No wonder, since it is not a real, recorded quality but a "speaker characteristic" added to all reproduced material". Was this your feeling as well, that the sound had a type of distortion mixed in?

Click to expand...

Good question. It definitely was not a sound that you would characterize as traditional distortion, but it was a distortion of the original signal.

I guess you could call it a 'speaker characteristic' but it seemed like it was more an interaction between the cabling and the crossovers which I described in the last message. I don't think I would have ever come up with the term 'slime' as a descriptor, but once you realized it was there, and on every source, you realized how much the sound was being changed. It also remained that way even if you used dissimilar LF and HF cables for the bi-wiring, except that you would also hear the effects of the cabling mixed in with 'the slime'.

I'd imagine that the severity (hear-ability if there is such a word) of it would vary greatly from speaker system to speaker system depending on their impedance and type of crossovers being utilized.

--Bill