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Author Topic: cables - facts and fiction  (Read 52219 times)

jneutron

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Re: cables - facts and fiction
« Reply #105 on: March 29, 2005, 08:16:30 AM »

danlavry

I see what you are saying. I do not know if a human can tell a change in position of a speaker by 3 inches (left to right) when the overall distance is 10 feet. I am ready to accept that is the experiments show it to be the case. However, we should keep that delay issue very separate from the audio bandwidth of a system and the ear.

I also do not know if a human can detect at 3 inches ten feet away.  The derivation was simply to show the level of ITD required to simulate the side movement at that level.  The research pointing to 1.5 usec sensitivity implies something like half an inch localization, which I simply discount as not humanly possible...just my guess, of course.

I point out the relative size of the delays, as they are not consistent with a 20 Khz bandwidth...I concur that we do not need half megahertz bandwidth audio reproduction, but the system has to be capable of 1 to 5 uSec temperal accuracy if we wish to provide good virtual image reconstruction.
danlavry

 I am sure the experiments of delay were not done with speakers that can pass 1MHz signal… But my real question is regarding practicality of caring about delay to 1.5uSec. You said: “the thought that we are indeed sensitive to low microsecond deltas, means electrical testing effective bandwidth to see this, needs consideration.”

Most of the research I've seen, at least the neural/auditory researchers, used headphones to test localization..it seems that they desire eliminating the crosstalk inherent in two speaker reception..the cost of eliminating that confounding issue is the image is stuck in a line between the ears, hence the term lateralization, vs exterior localization.  I conjecture that when ITD is combined with IID, the localization will take up a 3 dimensional aspect, but I've not yet modelled that..just a gut feeling.

As for do we need 1.5 uSec delay accuracy?  Probably not to that level, but I would test beyond that level for result accuracy.  My concern with loads is, what is the current being delivered to the load, not the voltage...the acceleration of a moving coil in a magnetic field is directly proportional to the current within the coil, so viewing the voltage is viewing where we want the force to be, but not the actual force..and, in low impedance systems, viewing the current, especially at high current slew rates, is a bear..I've experienced 1.5 volt errors in a 60 hz, 6 kiloamp current waveform across a 250 micro-ohm resistor, then with 20 Khz 1 amp drive, still got volts of error..that error being the intercept of the vtap loop picking up the mag field of the CVR.  And, also at 22Khz, into a .1 ohm resistor.
danlavry

I do not see the connection here between bandwidth and delta.

I don't think I've stated a relation between the human bandwidth of hearing, and the ITD (delta) we are capable of resolving for sound localization.. In fact, the two numbers are seemingly disjoint..
danlavry

B. What are the practical aspect of tiny delay? We do not have real life mechanism that suddenly changes delay by 1.5uS. The speakers don’t “jump to the side by 3 inches, The data does not “jump” either. It is probably impossible to keep the ears steady in space to .149 inch…  Am I still missing your point?

Yes, you are still missing it..
The 149 mil number is the difference in path length between a point source at that position, and each ear..

What I have done via that graph, is show what the difference in delay ear to ear is, as a point source is moved in y...the line between speakers.  In a two speaker setup, if you delay one signal 80 uSec, for example, you will image the sound 22 inches or so off center. Consider: If you have two instruments, A and B, and feed A into left straight, into right delayed 40 uSec...and feed B into right straight, and into left delayed 40 uSec, the virtual soundstage will have instrument A 22 inches to the left of instrument B.  This is the temporal equivalent of using levels via a pan pot, but a pan pot does not change ITD, just the intensity..
danlavry

I am sure you did not mean to focus on the wires themselves in terms of delay. With wires we are talking about the range of 8nsec per foot delay. Someone may misunderstand that your focus is on  “two independent channels” not on wire delay.

I am not in any way discussing prop delay..that would be insane, and I do not think I am insane..of course, I don't think I would be in a position to have that statement taken at value.. Rolling Eyes

I am speaking only of RLC....and how those parameters can affect the imaging cues we pick up on for localization.
danlavry

 So we don’t get to look at a waveform with enough accuracy. But we do have some approaches to measuring audio, that free us from confronting some difficulties head on. For example, we use sine wave testing, dual tone testing, multi tone testing, and by doing so we know ahead of time what the ideal outcome must be. The test gear is designed to measure deviation from ideal outcome. For example, if I pass a 1KHz 10V sine wave, and wonder how good it is to 10uV accuracy, a scope will not do it. But if I can cleanly filter the 1KHz and look at what is left (the residual), I will be able to look at 10uV of distortions, and even analyze the nature of such distortions (second, third…)


Consider:  two channels, standard speaker loads, reflex type..
Left running 100 hz sine, 200 watts, with a rider of 10Khz, 20 watts.  On right, the same 100 hz sine, 200 watts, but 180 degrees out w/r to the left..and, the same 10Khz rider, same phase, same power..

Speaker is quite reactive at 100 hz, forcing the amp to operate in all four quadrants...meaning, alternate pass die are running well off their load lines, die temp variation is running at 100 hz, this fast transient heating not being seen at the die package bottom, yet affecting the chips...the bias circuit is unknowing of this die stuff, bias is still a long term average..

Look at the hf stuff..subtract the two 10Khz signals, and see the residual..do they cancel perfectly throughout the 100 hz signal?..or, is the high power stuff causing the 10Khz signals to move temporally, modulated by the 100 hz, either by field loop coupling within the amps, or by damping factor variations across quadrants, or indeed, by the current slew the load is actually drawing..

If the 10K stuff is being time modulated by the 100 hz, will an FFT actually see it buried within the signals?

And, first and foremost, how does one measure the current in this experiment, when the measurement of the high slew current has an error component which is proportional to the current slew?

First, I see the need to learn to walk...I am working to develop a high power load that I can trust to provide an accurate current draw at the .1 to 1 uSec level, an accurate voltage, and an accurate measure of the current itself, at 4 and 8 ohms..that is not as easy as it seems..but, it is a first step.

Cheers, John
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acorec

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Re: cables - facts and fiction
« Reply #106 on: March 29, 2005, 10:43:51 AM »

danlavry wrote on Mon, 07 March 2005 19:06

I found that on the web:

"Audience's other products, the Au24 line of speaker cables and interconnects, take a different tack from many other cables in the same price range. Their construction is intentionally low mass -- connectors, insulation materials, and conductors. The conductors are so-called "single-crystal copper" with polypropylene insulation and a cross-linked polyethylene jacket. Audience says the geometry of the conductors lowers eddy-current resistance compared to other designs. Eddy current is produced in conductors when the electrical field around a wire collapses. This happens constantly with audio cables as the signal varies continuously between negative and positive. Each time the signal heads towards and reaches zero volts, the field collapses around the wire. This collapse induces a current in the wire. Audience believes the reduction or elimination of this induced current is one of the keys to making a good-sounding audio cable with excellent performance in the time domain. Audience found that in achieving low eddy-current resistance, they also minimized inductance and capacitance in the cables. Audience also believes that low eddy current is one of the keys to accurate time-domain performance: All frequencies are delivered from one component to another at the same speed, so there is no smearing in time caused by high frequencies traveling faster than low frequencies, as could happen in some conventional cable designs."

Can you belive it?

Regards
Dan Lavry










Sounds like a load of shit to me. I can't believe that anyone would question any good cable as all the music industry have used them for decades. If anyone can hear a difference between a $10 cable and a $1000 cable, they should find out why their $10 cable is broken.
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weihfool

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Re: cables - facts and fiction
« Reply #107 on: March 30, 2005, 12:00:38 PM »

Speaking of MIT cables, the company I work for has a demo sound room where they show off their latest and "greatest" home audio crap.  

They have some pair of MIT cables (can't recall the exact model offhand) that also have some sort of a box that is inline between the cables and the speaker itself.  

So one day, a friend's curiosity gets the better of him.  He opens the box and sketches a quick circuit.  He takes that circuit to one of our old timers here who looks at it and figures out that it's a low pass filter at 23KHz.  

I thought this audiophoolery nonsense was all about getting "everything" that the recording has on it???  Well, I suppose they're trying to filter out any digital aliasing outside of the audio band or something?!  Who the hell knows... ridiculous.  Why doesn't the FTC clamp down on these scam artists for their snake oil claims?  

Not saying it doesn't sound different, but put some FACTS behind the claims.
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bblackwood

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Re: cables - facts and fiction
« Reply #108 on: August 20, 2006, 08:16:51 PM »

*bump*
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Brad Blackwood
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Tom C

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Re: cables - facts and fiction
« Reply #109 on: August 21, 2006, 04:42:08 AM »

bblackwood wrote on Mon, 21 August 2006 02:16

*bump*



Thanks for bringing that (and 'the otherTM') thread up again so I can redirect people to here.
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Tom

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lucey

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Re: cables - facts and fiction
« Reply #110 on: August 27, 2006, 03:13:10 AM »

Dan I didn't read all of this thread but I hear cable tone fairly easily in many cases so I'm asking:

What about the obvious differences between silver and copper analog cable?

And the reasons why mic cables can be so obviously different from one another whereas line levels are more consistent?
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Brian Lucey
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danlavry

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Re: cables - facts and fiction
« Reply #111 on: August 28, 2006, 02:17:00 PM »

lucey wrote on Sun, 27 August 2006 08:13

Dan I didn't read all of this thread but I hear cable tone fairly easily in many cases so I'm asking:

What about the obvious differences between silver and copper analog cable?

And the reasons why mic cables can be so obviously different from one another whereas line levels are more consistent?


You say "obvious differences". I consider such a phrase as "loading the dice". I am not going to argue about subjective "sounds better" remarks. No one can, and that is why in this thread we do not talk about how things sound.

But I would be interested in repetitive double bind ABX results (which I bet there are non supporting your suggestion).

Take equal gauge silver and copper, and the silver is a couple of percent less resistive, which is very tiny difference at standard loads. But if you go to the next gauge in copper, the copper has a lot less resistance, and is much cheaper.

Line level is more consistent because the signal level is much higher then mic levels. Therefore, you are a lot less susceptible to all sorts of interference, which alters the sound, often in indirect and subtle ways. I would suggest that the physical construction is of much importance (the shield, the distance between internal wire pair, the insulation material, the tolerance...) The conductor material (silver or copper) for audio frequencies is NOT important.

Regards
Dan Lavry  
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