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Old 3rd October 2012, 01:00 PM   #41
DF96 is offline DF96  England
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Two ways to approach this issue, but Borbely confuses them.

1. Treat the interconnect as an audio transmission line. It will have a characteristic impedance which is high, reactive and frequency dependent over most of the audio range. Therefore you can't terminate it with a resistor as its characteristic impedance is not resistive. It will also have a frequency dependent propagation speed. Fortunately none of this matters because it is also very short in wavelength terms so you can just treat it as a low value resistor in series, with a low value capacitor to ground. The correct way to feed this network is from a low impedance, with a highish impedance load. Funnily enough, this is what sensible people have always done.

2. Treat the interconnect as an RF transmission line, and an audio signal as a sum of impulses. The usual terminations will then cause lots of signal reflections which will die away exponentially at a rate determined by the cable and terminations. However, the input signal is band-limited (all audio signals are band-limited) and the receiver has one or more low pass filters (all audio amps are low pass filters). Hence all the signal reflections will not be visible or audible; just compare the period of a 20kHz wave (50us) to the round trip delay on a 1m interconnect (around 10ns). Even 100's of reflections will do no harm, except to introduce a little delay - which can be calculated by using method 1 above.

If I were wiring a theatre or stadium I might start to think about this issue, and wonder whether I needed to add compensating inductors to the cables to reduce frequency dispersion - as used to be done on trunk telephone lines. For a short interconnect in my lounge I know that the quasi-static EM approximation is perfectly good enough so I can treat the cable as a resistor and a capacitor. This is first-year electromagnetism.
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Old 3rd October 2012, 02:31 PM   #42
marce is offline marce  United Kingdom
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Merlin give it a rest mate you are getting on my nerves, have a look at the use of numerous famous an infamous people whos names are used as a reference or an indication for other stuff. there is nothing contentious about it so go get a life and get of my back mate. OK GOT THAT

DF96 you forgot skin effect! tut tut

Oh I've also referenced Oliver Heaviside in my replys, I was also not being disrespectful to him, hough there have been numerous references to some of the seminal work he did on the problems (imagined for audio frequencies) we are discussing.
Now if I seem to be getting grumpy its cos I have a Pavlovian reaction to pathetic criticism.

Last edited by marce; 3rd October 2012 at 03:00 PM.
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Old 3rd October 2012, 02:56 PM   #43
SY is offline SY  United States
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Quote:
Originally Posted by DF96 View Post
When I want 'surreal' I think Monty Python rather than Dali.
Magritte.
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The more you pay for it, the less inclined you are to doubt it.- George Smiley
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Old 3rd October 2012, 03:03 PM   #44
marce is offline marce  United Kingdom
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Yes another excellent artist, who understood the human condition.
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Old 3rd October 2012, 04:28 PM   #45
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Quote:
Originally Posted by marce View Post
Merlin give it a rest mate you are getting on my nerves, have a look at the use of numerous famous an infamous people whos names are used as a reference or an indication for other stuff. there is nothing contentious about it so go get a life and get of my back mate. OK GOT THAT

DF96 you forgot skin effect! tut tut

Oh I've also referenced Oliver Heaviside in my replys, I was also not being disrespectful to him, hough there have been numerous references to some of the seminal work he did on the problems (imagined for audio frequencies) we are discussing.
Now if I seem to be getting grumpy its cos I have a Pavlovian reaction to pathetic criticism.
Forgive me cos Dali was Catalonian like I'm.
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Old 3rd October 2012, 04:29 PM   #46
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Quote:
Originally Posted by DF96 View Post
Two ways to approach this issue, but Borbely confuses them.

1. Treat the interconnect as an audio transmission line. It will have a characteristic impedance which is high, reactive and frequency dependent over most of the audio range. Therefore you can't terminate it with a resistor as its characteristic impedance is not resistive. It will also have a frequency dependent propagation speed. Fortunately none of this matters because it is also very short in wavelength terms so you can just treat it as a low value resistor in series, with a low value capacitor to ground. The correct way to feed this network is from a low impedance, with a highish impedance load. Funnily enough, this is what sensible people have always done.

2. Treat the interconnect as an RF transmission line, and an audio signal as a sum of impulses. The usual terminations will then cause lots of signal reflections which will die away exponentially at a rate determined by the cable and terminations. However, the input signal is band-limited (all audio signals are band-limited) and the receiver has one or more low pass filters (all audio amps are low pass filters). Hence all the signal reflections will not be visible or audible; just compare the period of a 20kHz wave (50us) to the round trip delay on a 1m interconnect (around 10ns). Even 100's of reflections will do no harm, except to introduce a little delay - which can be calculated by using method 1 above.

If I were wiring a theatre or stadium I might start to think about this issue, and wonder whether I needed to add compensating inductors to the cables to reduce frequency dispersion - as used to be done on trunk telephone lines. For a short interconnect in my lounge I know that the quasi-static EM approximation is perfectly good enough so I can treat the cable as a resistor and a capacitor. This is first-year electromagnetism.
I'm sure Erno not confuses.
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Old 3rd October 2012, 05:11 PM   #47
DF96 is offline DF96  England
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Quote:
Originally Posted by marce
DF96 you forgot skin effect! tut tut
Not hugely relevant, but can be included when calculating the resistance of the cable. Net result is that the audio characteristic impedance gets slightly different frequency dependence, because R varies as well as L and C. For the RF view, skin effect increases attenuation so making transients decay more quickly which makes the Borbely model even sillier.

Quote:
Originally Posted by merlin el mago
I'm sure Erno not confuses.
Please explain why you think he is not confused. Your answer should be based on the science of transmission lines, not personalities (Catalonian or otherwise).
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Old 3rd October 2012, 05:24 PM   #48
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Because I use his point of view with great success with all my kind of interconnects, for me is enough test (real life) instead of simulated, not happy with your last phrase about personalities.
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Old 3rd October 2012, 05:34 PM   #49
DF96 is offline DF96  England
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I was concerned that you might want to quote a guru, as some do on here.

To drive a 'low impedance' line (it actually isn't low impedance at audio frequencies, as I have explained, but the termination certainly is) with a -6dB attenuation gives slightly poorer signal-noise ratio and probably higher distortion because you need a power driver. If this seems to you to be an improvement then fine. No simulations are involved; just science.
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Old 3rd October 2012, 05:40 PM   #50
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I always do the test in real life. not simulated because I didn't hear simluations, I own Borbely stuff so for me it's OK, I don't know if it's Ok for the others but it's simple and can't need to much money just several resistor.
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