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Dilemma: Should I not believe any reviewers who talk about cables or just ignore that section of... - Page 108

post #1606 of 1790

So what have fuses to do with your claim that the low pass filter function of a cable is level dependent?

 

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post #1607 of 1790

Yes the low pass filter function is level dependent -not just my opinion but many others if you read back issues of EE mag over the years. Fuses were brought up by a poster and I replied in mechanical terms to the comment They are an imperfect scientific invention a stop gap for something better and should be removed from  hardware like amps and replaced with electronic units which now have a fast response time and why not? $$$$$ thats the answer. Its the same with automobiles they can be made to run on hydrogen many people in the UK proved just that but what happened to their invention- You may well ask after the publicity talks in newspapers of  the public saving $1000s  and then silence. Bought off springs to mind. You know the reason why. So fuses will be with us as long as autos use gas.

post #1608 of 1790
Quote:
Originally Posted by duncan1 View Post

Yes the low pass filter function is level dependent -not just my opinion but many others if you read back issues of EE mag over the years. Fuses were brought up by a poster and I replied in mechanical terms to the comment They are an imperfect scientific invention a stop gap for something better and should be removed from  hardware like amps and replaced with electronic units which now have a fast response time and why not? $$$$$ thats the answer. Its the same with automobiles they can be made to run on hydrogen many people in the UK proved just that but what happened to their invention- You may well ask after the publicity talks in newspapers of  the public saving $1000s  and then silence. Bought off springs to mind. You know the reason why. So fuses will be with us as long as autos use gas.

 

I have read all the back issues of EE mag over the years and there are no such articles.

 

So there. I've just countered your claim.

 

Now if you'd care to cite a specific reference, I'd be happy to look into it.

 

In the meantime, I've designed and built a number of passive filters over the years, and I've never noticed their cutoff frequencies changing with signal level.

 

Quote:
Fuses were brought up by a poster and I replied in mechanical terms to the comment They are an imperfect scientific invention a stop gap for something better and should be removed from  hardware like amps and replaced with electronic units which now have a fast response time and why not? $$$$$ thats the answer.

 

And that was in a different thread on a different subject and I'm still left wondering what that has to do with what we are currently discussing in this thread.

 

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post #1609 of 1790

 So you don't believe me when I say that a very low level signal can be heavily influenced by induced /radiated noise/hum?? and is also affected by inductance/capacitance. Thats easy to prove wind two wires together get out your high grade LCR meter and it will measure at least a couple of PF and that the conditions for a tuned circuit cant happen to a length of wire with a lot of inductance/ capacitance RF design engineers would be interested in your reply. Ever worked on a vhf/uhf tuner I am talking of the old type before they made it easy by making it fully integrated.and digital. One quarter  inch of wire would change the set frequency. 

post #1610 of 1790
Quote:
Originally Posted by duncan1 View Post

 So you don't believe me when I say that a very low level signal can be heavily influenced by induced /radiated noise/hum??

 

You're bringing up a completely different issue. You said nothing about noise previously. You made specific reference to frequency response.

 

Let me refresh your memory:


I am not fully convinced about "the sound of cables" but what cant be argued against and doesn't seem to be mentioned is that any cable carrying a very low level signal that has has a high amount of inductance/capacitance  has  been proved scientifically to effect the frequency response of the signal .

 

To which I responded that the level of the signal is irrelevant. The cable's effect on the frequency response will be the same regardless of level. You apparently disagreed, but have yet to substantiate your claim with anything meaningful. And now you change the subject to something completely different.

 

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post #1611 of 1790
Quote:
Originally Posted by duncan1 View Post

 So you don't believe me when I say that a very low level signal can be heavily influenced by induced /radiated noise/hum?? and is also affected by inductance/capacitance. Thats easy to prove wind two wires together get out your high grade LCR meter and it will measure at least a couple of PF and that the conditions for a tuned circuit cant happen to a length of wire with a lot of inductance/ capacitance RF design engineers would be interested in your reply. 

The fact that a high level signal can, in some cases, be introduced into a cable carrying a low level signal via capacitive or inductive coupling is true, but to evaluate the effects of a specific set of conditions, you need to know a lot more about the circuit. It would not be correct to assume that any capacitive or inductive coupling always results in a problem with a low level circuit.  It's a question of degree of coupling, impedance of the circuit being coupled to at the frequency of the signal being coupled, and the ability of the next stage to reject the unwanted signal versus detect it or pass it.

 

 Your examples are irrelevant in the context of this particular thread, though might be relevant in some other.  Discussing cables here, not old radios. 

Quote:
Originally Posted by Steve Eddy View Post

 The cable's effect on the frequency response will be the same regardless of level.

 

+ > or =1  

 

Steve is dead on.  It's a passive low pass filter, it don't care about no signal level. Sort of the honey-badger of filters.  Same cutoff frequency, same attenuation regardless of signal level. A signal level modified filter would pretty much take an active and variable element, not simply cable LRC. 

 

And why are we talking about this?  Oh yeah.  We done? I'm buying you all a virtual round of beers, then the virtual designated driver can virtually drive us home. beerchug.gif

post #1612 of 1790

So I was just reading this thread because I have always wondered about the cable debate. You guys seem to be talking about capacitance and inductance, and whether that has any effect. I'm not sure about that, but it seems to be that impedance would effect frequency response anyway. I studied physics at uni but its been a while. I've been trying to remember what I used to know to think about how impedance would effect frequency response. Here is what I got:

 

So, when you are dealing with DC, you can characterise the response of a component like a cable in terms of a constant quantity - resistance. For a cable, resistance will be a function of area, length and material, but for a given cable it will be a constant. This would have no effect on the signal transmitted: you merely increase the power of whatever is driving current through this component to compensate for the added series resistance that it presents.

 

But with AC everything is different. There is no constant quantity that can characterise a given cable like resistance. The closest thing is impedance. Impedance, like resistance is a function of area, length and material, but importantly it is also a function of frequency. The same cable presents a different load to different parts of the frequency spectrum. If I remember right, the reason for this is that AC signals don't travel "through" the cable in the way DC ones do. AC signals actually propagate along the surface of a wire, only penetrating a small way into its interior. The amount they penetrate is called the skin depth. Now skin depth IS a function of frequency. The upshot of this is that because some frequencies penetrate deeper into the wire, they experience a greater effective cross sectional area, and so a decreased impedance. So different frequencies will be attenuated differently as they travel down the wire, and the wire will change the signal.

 

The skin depth varies a lot for different materials (I think it is much greater for silver, which might explain why silver cables don't attenuate highs so much), and I don't think there is any straight forward relationship between frequency and skin depth. It would be complicated and possibly vary greatly between different cables.

 

This all sounds very plausible to me, and makes me very open to the idea of different cables changing the sound quite a lot (especially in the high frequencies, where the skin depth is much less). Can anyone comment on this explanation - have I got the science right?

 

Interested in this debate... 

post #1613 of 1790

You left out proximity effect, which is arguably a "worse" offender than skin effect.

 

You have the basic physics right, but it's a matter of degree. And to date, no one has demonstrated that the effects of cable impedance, skin effect and proximity effect in a reasonably well designed cable rise to the level of audibility.

 

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post #1614 of 1790
Quote:
Originally Posted by Steve Eddy View Post

You left out proximity effect, which is arguably a "worse" offender than skin effect.

 

You have the basic physics right, but it's a matter of degree. And to date, no one has demonstrated that the effects of cable impedance, skin effect and proximity effect in a reasonably well designed cable rise to the level of audibility.

 

se

 

.... at audible frequencies with reasonable length cables.

post #1615 of 1790
Quote:
Originally Posted by BobJS View Post

 

.... at audible frequencies with reasonable length cables.

 

Well yes. Was hoping that didn't have to be said. biggrin.gif

 

se

post #1616 of 1790

It's also a question of what's driving the cable (is it a low Z amp, or a high Z output), what kind of load the cable feeds (is it a speaker with a complex impedance, or a high Z amp input) , and of course, how long it is (5 feet, 30 feet, 10,000 feet, 5 miles, etc.).  

post #1617 of 1790

Skin effect only enters the discussion with very large diameter wires or very high frequencies. For the cables involved in hi-fi it's not much of a factor.  The cables self inductance is a much larger factor at high audio frequencies.

post #1618 of 1790

Having a quick look here reveals that skin effect has a depth of about 0.5 mm at 20 kHz in a copper wire, or, in other words, it becomes an issue when the diameter of the wire is at least ~1 mm. So, it is obviously not relevant to anything other than speaker cables in audio. Even then, it only increases the impedance which may very well still not be high enough to have an audible effect anyway at usual lengths.


Edited by stv014 - 5/26/13 at 3:04am
post #1619 of 1790

Isn't it simpler just to try a particular cable and see if it makes a difference to an individual listener?

 

Regardless of the theoretical issues discussed previously, wouldn't the typical variances in audio perception be larger than any arguable effect?

 

Your ears = the truth for you.

post #1620 of 1790

I imagine that depends on how much it is going to cost to ignore the facts and trust my ears.

 

Human perception generally has fixed limits. It's possible that an individual will have impaired hearing, but it's highly unlikely that they are going to have superhuman hearing.


Edited by bigshot - 7/2/13 at 8:29pm
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