I don't think this question is "dumb" at all but rather an interesting one. |
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Lplayer, thanks for providing the link to that paper, which is excellent IMO. When I wrote my earlier comments, I hadn't thought of the fact that propagation velocity will slow at low frequencies. However, as can be seen in Figure 2 of the paper, it will still be about 5,000,000 meters per second at 20Hz, meaning that propagation times through cables at that worst case frequency are still utterly insignificant in a home audio system. For those who don't want to bother with all the technical stuff, IMO the bottom line of the paper is expressed in its last two sentences: Thus, at audio frequencies, a cable less than 2,000 ft long is no more complicated than its series resistance and parallel capacitance. As the cable becomes longer, or as frequency increases, the cable will BEGIN to behave as a transmission line.
I would add that in a speaker cable, in particular, inductance can also sometimes have audibly significant effects. The focus of the paper is mainly on transmission of line-level signals through coaxial or balanced cables. Regards, -- Al |
http://www.audiosystemsgroup.com/TransLines-LowFreq.pdf
might be a little complicated for most...but read between the lines. |
How many things does "db" stand for? I can think of two, one is a logarithmic unit of sound intensity, the other can be bought in a pharmacy. |
You guys are obviously new to this forum thing. "Great Job!" "Excellent Answers, THANKS!!!" Sheesh!!
The whole point here is to attack the opinions of others and prove how intelligent you are, not some idealistic search for the truth. I think the last two administrations proved that the truth doesnt matter, so get with the program;) |
Elizabeth and Al, you guys rock!
I have really had a great time reading the forums tonight with responses like yours.
Thanks.
Best,
Dave |
Great work, Elizabeth and Al. If this site had "stickies"I would nominate your answers for the cable section. |
Public A ha moment - pretty clear to me now why performance of speaker wire is contingent on impedance curve of speakers, amplifier capability and properties, and to a lesser (or greater) degree, the sensitivities and proclivity of the listener. Given all this difficult to see how anybody could recommend gear and wire combinations without first hand (or ear) experience with all in specific set up. I got that as a matter of common sense previously, but this series of lectures provides some theoretical and practical foundation. Nice. |
Great job. I sat back and watched to see if anyone would tackle this one. |
I read that a signal takes the easiest path. Hi Ken, That's actually a bit of an oversimplification. In the case of dc, if two parallel paths are present the current will divide up between the two paths in inverse proportion to the resistance of each path. In the case of ac, the current will divide up between the two paths in inverse proportion to the impedance of each path, "impedance" at audio frequencies essentially being the combined effects of resistance, inductance, capacitance, and to a slight degree skin effect, at each particular frequency component that is present in the signal. Paralleling two wires for each leg of the run will have the net effect of reducing overall resistance and inductance, and increasing capacitance. Except in extreme cases, capacitance is usually unimportant in a speaker cable, while resistance and inductance can be important. Whether two parallel conductors would perform better than, worse than, or the same as a single conductor having the same values for those parameters is IMO probably not technically predictable, and experimental comparisons would probably give results that are both system-dependent and listener-dependent. Best regards, -- Al |
Please, a follow-up question about signals "moving" through wire. I read that a signal takes the easiest path. If you pair two wires for, say, the positive run - one wire with fine strands, the other with large strands - will that create some difference in signal transfer, no difference, or will it provide more "bandwidth" for all frequencies? |
I have fretted about this in certain applications in the past and it has cost me in wasted lengths of speaker wire. I haven't ever noticed a difference in sound with differential lengths of wire, but since I was fretting about everything else, I thought I should worry about this too. Apparently not. Thanks again for your analysis. You're welcome! Keep in mind, though, that my comment only addressed the question of arrival time differences. If other parameters, such as resistance, inductance, capacitance, and possibly skin effect, are not small enough to be negligible in the longer cable (all of those effects are proportional to length) a length disparity could conceivably have audible consequences. And of course there is also the practical factor of resale value being less if lengths are unequal. The likelihood of those effects being audible, btw, besides being dependent on the design and length of the cable, is also highly dependent on speaker impedance, and the variations of speaker impedance with frequency. Everything else being equal, higher speaker impedance can be expected to result in smaller cable effects. Best regards, -- Al |
Thanks Al, very cool logic. Your analysis would of course hold best in scenario of an anechoic chamber. In the average listening room, reflections and nodes etc. would further diminish any vanishing differences in sound imparted by differences in speaker wire length.
I have fretted about this in certain applications in the past and it has cost me in wasted lengths of speaker wire. I haven't ever noticed a difference in sound with differential lengths of wire, but since I was fretting about everything else, I thought I should worry about this too. Apparently not. Thanks again for your analysis. |
Thanks Elizabeth, that was a great explanation. From your explanation I would guess that connections (e.g., spades) also would affect the wave especially if the connector was a huge hunk of different material? I assume material "density" (or resistance) would impede some frequencies more than others? |
Elizabeth, come clean, you must be a teacher by trade. Well done. |
Excellent answers by Elizabeth! How different would wire lengths have to be for the acute listener to notice a difference in the arrival time in a pair of a stereo signals at the speakers? Several miles or more, by which point timing differences would of course have long since been swamped by other effects (frequency-dependent signal losses caused by resistance, inductance, capacitance, among many other effects). Electrical signals (as opposed to individual electrons, whose movement is irrelevant to the question) propagate through wires at roughly 60% to 90% of the speed of light in a vacuum, which in turn is about 186,000 miles per second. If we assume 75% as being typical (the actual number depends mainly on the dielectric constant of the cable's insulation), the corresponding propagation time is about 1.36 nanoseconds per foot of cable. 1.36 nanoseconds is 0.00000000136 seconds. The speed of sound in room temperature dry air is approximately 1126 feet per second. Based on the 1.36 ns/foot figure, a 20 foot difference in cable length between the two channels, for example, would result in an arrival time difference at the speakers of 27.2 ns. Based on the 1126 ft/sec figure for the speed of sound in air, 27.2 ns corresponds to the arrival time difference at the listener's ears that would result from his or her head being 0.00037 inches closer to one speaker than to the other. In other words, not likely to be audible! Regards, -- Al |
That was a very helpful explaination(s).
"But the signal all gets to the end of the wire at basically the same time"
This makes me think, how different would wire lengths have to be for the acute listener to notice a difference in the arrival time in a pair of a stereo signals at the speakers? Answers based on complex theoretical calulations, general principles or SWAGs all entertained here. |
elizabeth...i don't think i have seen it explained any better then what you just did...thanks |
Added: the wave of different frequencies moves down the wire at the same speed. just the waveform of each frequency is a different shape, added together and constantly changing shape of waves as the multiple parts have different fequencies in the waveform. But the signal all gets to the end of the wire at basically the same time.
(only the tiny effect of the depth of the frequency of the wave into the wire affects the parts a very very tiny bit)
I tried to both explain what is happening in simple terms, and satisfy the demands of the others who will read this and protest various shortcomings in my explaination.
The science of waves/wires/electrons/music.. is very simple AND complicated at the same time. But the simple fact that we can enjoy the music is really great. |
Think of it like a wave.
If you threw a rock into a pond, the splash makes waves. The water is only moving up and down as the wave passes bye, only a little water is moved horizontally when the stone hits, the 'wave' is the motion transmitted without the water going anywhere.
Similar thing with electrical waves in a wire. The current in a music signal is a form of alternating current(a wave movement, where Direct Current is like a straight line movement), so the electrons pretty much stay in the same place in alternating current. Just the waveform moves down the wire.
The waveforms can be extremely complex. So if the music of an orchestra is being transmitted, the wave form of the sound of each instrument is added together and all of them, together, are travelling in a very complex wave through the wires to where they are going.
Electrical current in a wire is a complex phenomonon. The frequency of the waveform determines how the wave travels. The higher the frquency, the more the wave stays on the top surfaces of the wire. (each strand if multi-stranded) So the wave passes down the wire mostly on the surface, with varying degrees of penetration into the wire depending on the frequency. So wire can make a difference in how well the signal (the waveform) travels without getting messed up. The electrical energy also generates a field around the wire, and that field can affect, or be affected by it's surroundings. So good insulation on the wire also helps the waveform to reman intact.
Badly made wires can distort the waveform by slowing down some frequencies of the waveform slightly, and insulation can also affect the waveform. because as the waveform passes, it is affected by the insulation, and also the surface of the wire. (if the wire is dirty, or corroded, or is not pure, it interferes with the signal too)
All of those 'errors' in the transfer of the signal down the wire as a waveform are extremely tiny, so some folks say wire is wire, and other sayy different wires change the way the music sounds, because the wires affect the wavefoms a tiny (but significant bit)
Hope this helps. |
