Question On Biamping

[mtrycrafts]

both authors stated the 'IM' is reduced, they didn't say it was totally eliminated. Just curious......
JK

No, Axiom speculated with 'may occur'
This could prevent intermodulation distortion that may occur using one big “fire hose” or single speaker cable.

not that IM does occur.

And saying that a 'potential' for it

by eliminating potential intermodulation distortion between the low- and high-frequency portions of the audio signal.

Nowhere do I read that IM exists in single run wires caused by differential frequency currents.

If IM is there, at what current levels are we worried about? Between which frequencies? There certainly will be current differentials in the mid and high driver cable

 

[mtrycrafts]

Running separate wires from the amplifier can have a profound impact on relieving the tweeter circuit from the back flush of EMF (elector-motive force) generated by the woofer. When the audio signal to the woofer ceases, such as when a loud bass note is finished, the woofer tries to stop moving. In trying to stop, it actually goes through a process of "settling" because it is too massive to just stop instantly. As it settles, it moves forward and backward repeatedly until it can completely come to rest. During this movement, as the voice coil is moving through the field of the magnet, it generates its own signal. That generated signal is sent backward up the woofer wires and into the crossover, where it corrupts the rest of the music signal.
Best wishes.... Jk

A few discussions on Back EMF. Steve Eddy is a sharp cookie:
http://www.audioasylum.com/audio/cables/messages/35525.html and
http://www.audioasylum.com/audio/cables/messages/35554.html

And Richard Pierce? You can take it to the bank. Worthwhile reading:

http://groups.google.com/group/rec.audio.high-end/msg/5ac53c1befc02746?q=author:DPierce@world.std.com+back+emf&hl=en&lr=&ie=UTF-8&rnum=5

http://groups.google.com/group/rec.audio.tech/msg/71ca95c6df065c24?q=author:DPierce@world.std.com+back+emf&hl=en&lr=&ie=UTF-8&rnum=1

http://groups.google.com/group/rec.audio.high-end/msg/df02658d8fed441f?q=author:DPierce@world.std.com+back+emf&hl=en&lr=&ie=UTF-8&rnum=2

http://groups.google.com/group/rec.audio.tech/msg/9febaf18ece9484b?q=author:DPierce@world.std.com+back+emf&hl=en&lr=&ie=UTF-8&rnum=4

http://groups.google.com/group/rec.audio.high-end/msg/9e25180f03c7f4f9?q=author:DPierce@world.std.com+back+emf&start=10&hl=en&lr=&ie=UTF-8&rnum=12

 

[mtrycrafts]

Ok, let's assume this back EMF does exist, and that it's of an audible magnitude.
?

Before we assume it, I posted a few interesting discussions about it to him. Especially interesting are the Richard Pierce links.

 

[rmongiovi]

Before we assume it, I posted a few interesting discussions about it to him. Especially interesting are the Richard Pierce links.

But I had to assume it. If there's no audible back EMF, there's nothing for bi-wiring to make a difference to. And then I wouldn't have been able to argue that bi-wiring doesn't make any difference for other reasons.

I'm certainly not saying I believe in it. Only that I wanted to assume it for sake of the argument.

I really miss the days when usenet was king. Observing Mr. Pierce shred people was such a delight....

 

[JKnPA]

Axiom article.........@ Alan Lofft

Mtrycrafts,

I believe you are quoting from Alan Lofft's article on 'Biwiring & Biamping', when you say "potential IM distortion may occur......".
http://www.axiomaudio.com/tips_biwiring_and_biamping.html

What you didn't include is this statement.................
" Using biwiring, this distortion would not occur because the low-frequency part of the speaker crossover would draw the current it needs for the woofers (and they need lots of current) through one speaker cable, while the midrange tweeter section would draw less current (it doesn't need as much) through its own speaker cable."
1. Why didn't you include that in your quote?
2. I don't believe Alan Lofft is an audio engineer, I think he has a background in Journalism.
http://www.axiomaudio.com/lofft.html
3. Since I have a background( education/military/20yrs. in industry) in electronics......... I am biased toward articles written by design engineers, than journalists writing 'audio reviews/articles'.
4. If companies like Axiom conclude they can't hear "distortions" readily, as concluded in their test......... why include the 4 terminal feature on their speakers so users can 'Bi-wire' or 'Biamp' ?

* These are just questions to stimulate the discussion, they are not meant to discredit you or anyone else.
** I don't bi-wire, although I might bi-amp in the future!....FWIW.
*** Im glad that we have 'intelligent posters' here that can stimulate
the 'thinking process'.
Best wishes.....
Jk

 

[PENG]

* These are just questions to stimulate the discussion, they are not meant to discredit you or anyone else.
** I don't bi-wire, although I might bi-amp in the future!....FWIW.
*** Im glad that we have 'intelligent posters' here that can stimulate
the 'thinking process'.
Best wishes.....
Jk

John, I went down that path before, not much fun when people assume things you said/meant that you didn't. mtry was right though, and I don't think he was arguing the point whether bi-wiring would reduce IMD or not. He was simply quoting Axiom. He left out a couple of lines but it wouldn't have changed the argument even if he had included those lines.

 

[mtrycrafts]

mtry was right though, and I don't think he was arguing the point whether bi-wiring would reduce IMD or not. He was simply quoting Axiom. He left out a couple of lines but it wouldn't have changed the argument even if he had included those lines.

Thank you You are correct in what I left out. I read it a couple of times to make sure and what I was posting was sufficient, imo and you also seem to agree.

 

[mtrycrafts]

Peng answered well but here I am;

Mtrycrafts,

I believe you are quoting from Alan Lofft's article on 'Biwiring & Biamping', when you say "potential IM distortion may occur......".
http://www.axiomaudio.com/tips_biwiring_and_biamping.html

Yes, it is at Axiom's web page.


What you didn't include is this statement.................
" Using biwiring, this distortion would not occur because the low-frequency part of the speaker crossover would draw the current it needs for the woofers (and they need lots of current) through one speaker cable, while the midrange tweeter section would draw less current (it doesn't need as much) through its own speaker cable."
1. Why didn't you include that in your quote?

Firstly,
biwiring could offer theoretical advantages, particularly to loudspeakers that are linear and smooth, like the Axiom M80ti and M60ti, by eliminating potential intermodulation distortion between the low- and high-frequency portions of the audio signal.

If you read this, it offers a theoretical advantage. Is the practice in fact more than a theoretical advantage? Does in fact IM occurs in a wire due to the wire itself? Nothing in the article indicates IM is in fact real. So, it is not relevant.

2. I don't believe Alan Lofft is an audio engineer, I think he has a background in Journalism.
http://www.axiomaudio.com/lofft.html

Yes, I just read his bio. This is at the Axiom website. I shouldn't have assumed that it was reviewed by an Axiom engineer. So, I sent an email to them to find out. Perhaps, he has been around audio engineers in his lifetime long enough to ask them about it?

3. Since I have a background( education/military/20yrs. in industry) in electronics......... I am biased toward articles written by design engineers, than journalists writing 'audio reviews/articles'.

Me too. We'll find out soon how accurate that article is.


4. If companies like Axiom conclude they can't hear "distortions" readily, as concluded in their test......... why include the 4 terminal feature on their speakers so users can 'Bi-wire' or 'Biamp' ?

I think you missed their reason:

Axiom includes the extra terminals as a nod to those enthusiasts who believe that biwiring results in audible benefits and for the bi-ampers.

Appeasing the customers who are gullible enough to want it. Simple marketing and business practice. I would do it to get the business of those audiophiles too.
Dunlavy did it, so do many other companies do it. I called Paradigm some time back to ask for evidence of audibility for them including it. No evidence available and that is from a company that does DBT as a rule.
Why exclude a portion of the buying marketplace?

*** Im glad that we have 'intelligent posters' here that can stimulate
the 'thinking process'.
Best wishes.....
Jk

One reason I am here

 

[mtrycrafts]

ps

When Klipsch first came out with dual binding posts the scuttle butt on the Klipsch forum was that it was a marketing decision not engineering one. I could be wrong, but my guess is that if true, they were not the only ones.

Nick

I remembered I had an audio folder on the hard drive. Looked through it but didn't find that message
I did find one from Bryston and their amp filtering capability of AC line noise

 

[JKnPA]

Final thoughts.......... Axiom article.

Mtrycrafts,
Well I think we worked this topic over pretty good!...
I mainly think we interpret Axiom's article differently. Several people can read articles and come to different conclusions, as we all know from taking some college courses...... even scientific courses.
When I read the statement ...........
"Using biwiring, this distortion would not occur because the low-frequency part of the speaker crossover would draw the current it needs for the woofers (and they need lots of current) through one speaker cable, while the midrange tweeter section would draw less current (it doesn't need as much) through its own speaker cable. "
I interpret this as a 'statement of fact'. I think that is where we differ. To me that says 'IMD' does exist in some speakers, maybe not in Axiom or B&W speakers, but in other 'poorly designed' speakers, namely in the Xover
filter circuits.
I was mainly interested in 'Xover filter design' not 'back emf', even though I cited both links. This link goes into detail on 'Xover filter' design' and how important it is to the overall freq, response of the speakers. See par.1.13
http://sound.westhost.com/bi-amp.htm
Ok......... you can have the last word.
Respectfully,
Jk

 

[mtrycrafts]

Mtrycrafts,
Well I think we worked this topic over pretty good!...

Not yet, it ain't a dead horse.

When I read the statement ...........
"Using biwiring, this distortion would not occur because the low-frequency part of the speaker crossover would draw the current it needs for the woofers (and they need lots of current) through one speaker cable, while the midrange tweeter section would draw less current (it doesn't need as much) through its own speaker cable. "
I interpret this as a 'statement of fact'.

Yes, that is a fact that subs can and do use more current depending on the signal and mix of course. But that fact doesn't confirm the implications below.


I think that is where we differ. To me that says 'IMD' does exist in some speakers, maybe not in Axiom or B&W speakers, but in other 'poorly designed' speakers, namely in the Xover
filter circuits.

Not at all. One doesn't follow the other, unless it is a fact that frequency dependent currents of different magnitudes in wire causes IM.
This is where the Axiom article is making implications and hypothetical. It may be correct, I am just not convinced about it t5hat such differential currents in wire causes IM. Then we are in trouble as that condition is everywhere.

And, the filters would not come into play, I just don't see it yet.


I was mainly interested in 'Xover filter design' not 'back emf', even though I cited both links. This link goes into detail on 'Xover filter' design' and how important it is to the overall freq, response of the speakers. See par.1.13
http://sound.westhost.com/bi-amp.htm
Ok......... you can have the last word.
Respectfully,
Jk


Of course filters are most important to the FR. One reason why active crossover, no passive and amp for each driver is the best way to go. Much simpler to improve the FR. I don't think I implied otherwise. IM in the wire due to differential currents is where we have the discussions.

 

[PENG]

Not yet, it ain't a dead horse.

Not at all. One doesn't follow the other, unless it is a fact that frequency dependent currents of different magnitudes in wire causes IM.
This is where the Axiom article is making implications and hypothetical. It may be correct, I am just not convinced about it t5hat such differential currents in wire causes IM. Then we are in trouble as that condition is everywhere.

Since it is not a dead horse, let's keep is alive a little longer.

mtry, let me try to convince you as follow:

1) Stop focussing on Axiom's IM distortion thing, they really did not explain how it occurs.

2) Take a look of B&W's, link:http://www.bwspeakers.com/index.cfm/fuseaction/local.faq/ObjectID/F5CA2E9F-3D20-11D4-A67F00D0B7473B37, please read it.

3) In case you are too busy to read the link, let me quote part of it. I have done this before but this time I would highlight the key words:

"Assume for the argument that the amplifier delivers a perfect voltage waveform to the cable and the cable itself adds no distortion. However, each driver has a non-linear impedance (for example, the inductance of the voice coil alters depending on its position in the magnet gap) that causes the current to be non-linear. This non-linear current through the impedance of the cable causes the voltage drop along the cable to be non-linear and thus the voltage across the speaker terminals is also non-linear, even though it is linear at the amplifier end.

If we were just concerned with one driver, things would not be too bad. But that non-linear voltage at the speaker terminals may contain harmonics within the frequency range of one of the other drivers and that driver will reproduce them, albeit at low level. If, however, you separate the inputs to each driver filter, each driver’s distortion is kept to itself and the total system distortion goes down. We are talking small changes here, but the resolution of some modern drivers is now so good that small improvements like this are readily detectable by keen listeners.
Many people ask us whether the load on the amplifier is different if you bi-wire. It is not. As far as the amplifier is concerned, it matters not one jot whether you parallel the inputs to the filter sections at the speaker end or the amplifier end of the speaker cable."


If you read the bolded, italic part you will understand why I previously quoted Faraday's Law, Ampere's Law, Ohm's Law, and I should add Lenz's Law, Gauss's Law, Maxewell's Equation, and Fourier's harmonic theories etc. All these electrical theories are related to electromagnetic effects (except Ohm's Law, but it is obviously relevant in this case) and that's why have all these goodies created by electricity and magnetism. I hope you are not doubting them, no?

Now, focus more on the underlined part, how do you argue the fact that the induced harmonic (what some might have called it back e.m.f. or counter e.m.f.) voltages would cause signals that are reproducible by the mid/high drivers? As B&W stated, and if I remember correctly, you did too, the effect is small.

B&W claims that their speakers are so good that keen listeners could hear it but I think the three of us have gone past that and we remain engaged in a purely technical discussion only.

mtry, you and I both know that such so called IM (there must be a better term) effects should be measurable. If you ever come across such measurements reported, please post the link.

Thanks!

P.S. John, I agree with mtry, the crossover's should not have much to do with the claimed effect other than the fact that they need to be separated (in biwire/biamp) in order to avoid the potentially adverse effect.

 

[mtrycrafts]

I just have a hard head at times trying to figure things out

Since it is not a dead horse, let's keep is alive a little longer.
mtry, let me try to convince you as follow:
1) Stop focussing on Axiom's IM distortion thing, they really did not explain how it occurs.

Perhaps they are assigning this IM distortion to the frequency dependent non-linear impedance caused distortion? It is a harmonic distortion, isn't it?

2) Take a look of B&W's, link:http://www.bwspeakers.com/index.cfm/fuseaction/local.faq/ObjectID/F5CA2E9F-3D20-11D4-A67F00D0B7473B37, please read it.

I did. Your quotes are the meat of it.

"Assume for the argument that the amplifier delivers a perfect voltage waveform to the cable and the cable itself adds no distortion. However, each driver has a non-linear impedance (for example, the inductance of the voice coil alters depending on its position in the magnet gap) that causes the current to be non-linear.

Yes, a constant voltage at different frequencies will cause different currents at those frequencies. But, how is that different from having different currents at different frequencies due to signal variations? Or, am I hopeless?


This non-linear current through the impedance of the cable causes the voltage drop along the cable to be non-linear and thus the voltage across the speaker terminals is also non-linear, even though it is linear at the amplifier end.

Yes, current flow in cable is the factor that determines voltage drop. The cable is a constant impedance at the low end that we are talking about to the low driver.

If we were just concerned with one driver, things would not be too bad. But that non-linear voltage at the speaker terminals may contain harmonics within the frequency range of one of the other drivers and that driver will reproduce them, albeit at low level.

Why is this a may contain and not a will contain?


If, however, you separate the inputs to each driver filter, each driver’s distortion is kept to itself and the total system distortion goes down.

Why wouldn't this higher frequency distortion find its way to the mid/high frequency drivers through the other cable or does it? After all, those drivers' filters will let the harmonics pass through. The only thing that changes is that current now has twice the cable length to pass through? Is halving the harmonic distortion signal by the time it reaches the mid/high is the reason?


We are talking small changes here, but the resolution of some modern drivers is now so good that small improvements like this are readily detectable by keen listeners.

Well, this is where I take exceptions. Axioms experimentation under controlled conditions did not find those keen listeners.
I doubt the B&W is that much more linear or resolving than the Axiom speakers. And, what do they really mean by resolution? Lower distortion? Respond to smaller voltage changes?


If you read the bolded, italic part you will understand why I previously quoted Faraday's Law, Ampere's Law, Ohm's Law, and I should add Lenz's Law, Gauss's Law, Maxewell's Equation, and Fourier's harmonic theories etc. All these electrical theories are related to electromagnetic effects (except Ohm's Law, but it is obviously relevant in this case) and that's why have all these goodies created by electricity and magnetism. I hope you are not doubting them, no?

No, I am not doubting any of those greats and their work, just trying to better understand them in this particular condition we are discussing.

Now, focus more on the underlined part, how do you argue the fact that the induced harmonic (what some might have called it back e.m.f. or counter e.m.f.) voltages would cause signals that are reproducible by the mid/high drivers?

I guess this is where my hangup is, trying to see it clearly to understand it how and why frequency dependent impedance differences causing different currents if the input voltages are the same at those frequencies and signal variation caused current differences at those frequencies would not?


mtry, you and I both know that such so called IM (there must be a better term) effects should be measurable. If you ever come across such measurements reported, please post the link.


No matter what you name this distortion, IM, THD, it must be measurable down to such a low level that it is well below audibility If wire noise can be measured down to -150bD or more, so can this.

Perhaps, if B&W or Axiom would show that numerical difference in harmonic distortion or whatever differences they are talking about, it might make more sense and more meaningful.

Thanks for all your help in trying me to understand.

ps:

I just had a thought after moving on.

Is B&W talking about non-linearity of current due to frequency caused impedance variations as that is mentioned, causing this harmonic, or the position of the voice coil in the gap? If I understand them correctly that impedance changes as the coil changes its position in the gap, then how would that be frequency dependent and not signal level dependent? As the voice coil moves further and further out, caused by greater signal voltage, that would mean from what they wrote, that the impedance changes as does the signal level changes at constant frequency? What am I not seeing clearly here?

 

[PENG]

mtrycrafts, you are killing me! I have to go somewhere so I speed read your response. My quick impression is that I would probably have to agree with you up to 95%, may be 100% as soon as I have a chance to read it again carefully.

Remember though, no one is talking about eliminating the claimed effect, just reducing it. As to the use of the word "may" as oppose to "will", we would have to ask B&W but I think you might agree that the woofer "will" in fact do that sort of things as B&W explained, and I suspect they must have done some measurements for them to be that serious (apparent in the way they describe it) about the claimed effect.

 

[nibhaz]

Remember though, no one is talking about eliminating the claimed effect, just reducing it. As to the use of the word "may" as oppose to "will", we would have to ask B&W but I think you might agree that the woofer "will" in fact do that sort of things as B&W explained, and I suspect they must have done some measurements for them to be that serious (apparent in the way they describe it) about the claimed effect.

Hey guys, I love reading this series of post. However I must warn you PENG that you may be giving B&W too much credibility. Personally, I'm a B&W fan boy, but after watching one of their marketing DVDs that you can get here I have some reservations about accepting everything they say as gospel. I specifically had a problem with their claim that those electrical components that have the same specifications electrically have different sonic characteristics that are audible.

 

[mtrycrafts]

Hey guys, I love reading this series of post. However I must warn you PENG that you may be giving B&W too much credibility. Personally, I'm a B&W fan boy, but after watching one of their marketing DVDs that you can get here I have some reservations about accepting everything they say as gospel. I specifically had a problem with their claim that those electrical components that have the same specifications electrically have different sonic characteristics that are audible.

We are here to please
Yes, no one is above marketing hype, unfortunately.
What components were they talking about?

 

[mtrycrafts]

mtrycrafts, you are killing me!

What can I say
Hope it is in a good way though. How else will I get this stuff? Small price to pay

I have to go somewhere so I speed read your response. My quick impression is that I would probably have to agree with you up to 95%, may be 100% as soon as I have a chance to read it again carefully.

Anxiously awaiting your return.

Remember though, no one is talking about eliminating the claimed effect, just reducing it. As to the use of the word "may" as oppose to "will", we would have to ask B&W but I think you might agree that the woofer "will" in fact do that sort of things as B&W explained, and I suspect they must have done some measurements for them to be that serious (apparent in the way they describe it) about the claimed effect.

I will have to see your response to my post.
Yes, any driver has nonlinear areas of operation, not limited to the woofer although that may have it much more.
Happy resurrection. Later

 

[mulester7]

Remember though, no one is talking about eliminating the claimed effect, just reducing it. As to the use of the word "may" as oppose to "will", we would have to ask B&W but I think you might agree that the woofer "will" in fact do that sort of things as B&W explained, and I suspect they must have done some measurements for them to be that serious (apparent in the way they describe it) about the claimed effect.

.....I think Peng has stated a great case for the theoretical effects of this application....and, has stated he heard no audible effects leaving the backdoor appropriately wide open....wire is cheap....trying things and listening for differences with a source you've listened to a bazillion times beats reading all the reviews in the World....

 

[PENG]

ps:

I just had a thought after moving on.

Is B&W talking about non-linearity of current due to frequency caused impedance variations as that is mentioned, causing this harmonic, or the position of the voice coil in the gap? If I understand them correctly that impedance changes as the coil changes its position in the gap, then how would that be frequency dependent and not signal level dependent? As the voice coil moves further and further out, caused by greater signal voltage, that would mean from what they wrote, that the impedance changes as does the signal level changes at constant frequency? What am I not seeing clearly here?

I guess that's the 5% I couldn't agree with your earlier argument. But your after thought might have nailed it.

I think you are right, they apparently were not talking about the non-linearity of current due to the frequency dependent part. In fact, impedance changes owing to frequency variations are still linear.

Impedance=Resistance+Inductive reactance+capacitive reactance

Inductive reactance=2¶fL

¶ is a constant=3.1416, L is the inductance so if the inductance is constant then the inductive reactance (part of the total impedance) is frequency dependent only, that is, linearly proportional to the frequency.

If the inductance varies depending on the moving coil's position as B&W was saying, then you end up with a non-linear inductive reactance that will no longer vary linearly with frequency (the signal). Ampere's law and lenz's law would apply here.

Another point, if this non-linear voltage (counter emf?) generated by the bass driver is very low compared to the signal voltage at the amp's output terminals, it cannot drive a current component along the cable back to the amp terminals then cross over to the other drivers via the other cable. In the single wire (instead of bi-wire) scenario, the loudspeaker's crossovers are externally linked so the "very low" harmonic voltages would be able to drive some harmonic current components into the mid/high drivers via the common terminals that are linked when not bi-wired or bi-amped. (Superposition Theorem).

 

[mtrycrafts]

If the inductance varies depending on the moving coil's position as B&W was saying, then you end up with a non-linear inductive reactance that will no longer vary linearly with frequency (the signal). Ampere's law and lenz's law would apply here.

Another point, if this non-linear voltage (counter emf?) generated by the bass driver is very low compared to the signal voltage at the amp's output terminals, it cannot drive a current component along the cable back to the amp terminals then cross over to the other drivers via the other cable.

But, B&W states a harmonic of the original is what would be affecting the other drivers. Certainly the non harmonic fundamental would not get through the other speaker's crossover filters no matter how it is wired up, right? So, it has to be the harmonics. Then, the amps voltage is not of the same frequency and would not affect this harmonic distortion signal and would get to the other drivers no matter what, no?

As to Back EMF, if that is what this is, then there are a few very good discussions by a most knowledgeable person, Richard Pierce on Back EMF. If I understand him correctly, this would happen only at the mechanical resonance frequency only:

http://groups.google.com/group/rec.audio.high-end/msg/5ac53c1befc02746?q=author:DPierce@world.std.com+back+emf&hl=en&lr=&ie=UTF-8&rnum=5

in the very first paragraph.

Further discussion:

http://groups.google.com/group/rec.audio.tech/msg/71ca95c6df065c24?q=author:DPierce@world.std.com+back+emf&hl=en&lr=&ie=UTF-8&rnum=1

http://groups.google.com/group/rec.audio.high-end/msg/df02658d8fed441f?q=author:DPierce@world.std.com+back+emf&hl=en&lr=&ie=UTF-8&rnum=2

http://groups.google.com/group/rec.audio.tech/msg/9febaf18ece9484b?q=author:DPierce@world.std.com+back+emf&hl=en&lr=&ie=UTF-8&rnum=4

http://groups.google.com/group/rec.audio.high-end/msg/9e25180f03c7f4f9?q=author:DPierce@world.std.com+back+emf&start=10&hl=en&lr=&ie=UTF-8&rnum=12

So, is B&W talking about a different harmonic distortion? In either case, it can be measured no matter how it is sliced and should be able to show the differences from bi-wiring. Now, numbers I would look better


In the single wire (instead of bi-wire) scenario, the loudspeaker's crossovers are externally linked so the "very low" harmonic voltages would be able to drive some harmonic current components into the mid/high drivers via the common terminals that are linked when not bi-wired or bi-amped. (Superposition Theorem).


This harmonic distortion would also manifest itself in the mid range driver to a lesser extent.

Are we getting closer to the truth?