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The "truth" about different speaker cables - Page 13

post #181 of 309
7/10/09 at 6:23pm
Quote:
Originally Posted by Koyaan I. Sqatsi View Post
There is no 50 ohm standard for audio interconnects. The fact that an RCA plug has a characteristic impedance of 50 ohms and the fact that consumer audio gear uses RCA plugs have absolutely nothing to do with one another.
Really? I've read otherwise in the audio press. Also about the 75-ohm standard for S/PDIF cables. I can't judge it myself, I'm no expert. But many experts claim 50-ohm cables and RCA plugs/jacks to be problematic for digital connections. Moreover, what is the 50-ohm standard for RCA plugs worth for if it is worthless in your opinion?

In any event we're getting off topic. Actually I was just trying to counter your earlier statement...

Quote:
Originally Posted by Koyaan I. Sqatsi View Post
Why would you want half of your amplifier's power going into driving the cables rather than driving the speakers?
...a conception that doesn't apply to «20-ohm» speaker cables like the ones in the linked patent paper (read it!).
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post #182 of 309
7/10/09 at 7:27pm
Intrigued and investigating speaker cable impedance further, I found this site which does some simulations:
Loudspeaker Cable Characteristic Impedance
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post #183 of 309
7/10/09 at 7:34pm
Quote:
Originally Posted by JaZZ View Post
I'm not sure what you're talking about. Wave resistance (in German Wellenwiderstand) is a product of capacitance and inductance. The higher the capacitance with respect to inductance, the lower the wave resistance. And vice versa. That's why there are cables specified as 50- and 75-ohm cables (and that's not their ohmic resistance, which may still be near zero!). So you can easily build an 8-ohm cable (with ~0 ohm ohmic resistance), as demonstrated by the link.
So you mean characteristic impedance, Leitungswellenwiderstand ? It is not the product (which means "multiplication") of capacitance and inductance. For a lossless line (and even if you have a really large mansion, your audio cables will probably fall under this), it is sqrt(L/C), where both are measured per some unit length. It is also purely resistive and independent of frequency. Again, you can convince yourself of the unimportance of the difference by using the "full" formula Z=sqrt((r+2*pi*f*j*L)/(g+2*pi*f*j*C)), where g is the conductance of the dielectric surrounding the wire. Audio cables of 8-ohm characteristic impedance are indeed easy to build - just pick one where inductance per meter is 64 times larger than capacitance

The reason there is a standard characteristic impedance for interconnects is for termination. Which most important application in case of audio is to keep shoddy amplifiers from oscillating
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post #184 of 309
7/10/09 at 7:57pm
Quote:
Originally Posted by JaZZ View Post
Really? I've read otherwise in the audio press. Also about the 75-ohm standard for S/PDIF cables. I can't judge it myself, I'm no expert. But many experts claim 50-ohm cables and RCA plugs/jacks to be problematic for digital connections. Moreover, what is the 50-ohm standard for RCA plugs worth for if it is worthless in your opinion?
The frequency at use in s/pdif cables is 100-300 times higher than that for audio. It is an entirely different world cables wise, and things from it don't really apply to audio frequencies. The impedance match is needed to eliminate reflections.
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post #185 of 309
7/10/09 at 8:14pm
Quote:
Originally Posted by sanderx View Post
Audio cables of 8-ohm characteristic impedance are indeed easy to build - just pick one where inductance per meter is 64 times larger than capacitance
The easier it is to build one of 20 ohm. I have no idea if a speaker connection would benefit from it, but I give the idea the benefit of the doubt. After all cables are generally said to make no sonic difference, whereas in fact, you know...
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post #186 of 309
7/10/09 at 8:17pm
Quote:
Originally Posted by JaZZ View Post
Really? I've read otherwise in the audio press.
Which audio press is this? I've been reading the audio press for going on 30 years now and I don't recall any mention of a 50 ohm "standard" for analogue interconnects.

Quote:
Also about the 75-ohm standard for S/PDIF cables. I can't judge it myself, I'm no expert. But many experts claim 50-ohm cables and RCA plugs/jacks to be problematic for digital connections.
50 ohm cables and RCA plugs/jacks can be problematic if used on a 75 ohm high speed digital interface. Any impedance mismatch in such an interface can be problematic.

Quote:
Moreover, what is the 50-ohm standard for RCA plugs worth for if it is worthless in your opinion?
RCA plugs weren't intentionally designed to have a 50 ohm characteristic impedance. They were designed because they were cheap to make. They were originally designed back in the 1930s for the purpose of allowing owners of RCA radios to plug in an RCA record player, which is why they are also referred to as "phono plugs."

They then ultimately became the ipso facto standard connector for consumer audio equipment. But it had nothing to do with their 50 ohm characteristic impedance.

Quote:
...a conception that doesn't apply to «20-ohm» speaker cables like the ones in the linked patent paper (read it!).
I read it.

The whole gist of it is that that cable's impedance should match the loudspeaker's impedance.

And even if you're talking 20 ohms, you're still talking about wasting about a third of the amplifier's power driving the cable.

k
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post #187 of 309
7/10/09 at 8:42pm
Quote:
Originally Posted by Koyaan I. Sqatsi View Post
And even if you're talking 20 ohms, you're still talking about wasting about a third of the amplifier's power driving the cable.
Huh? You stated yourself that the audio band is not affected by the cable impedance, so why does the cable eat up energy? Remember, it still has ~0 ohm ohmic resistance. And capacitance should only have an effect in the ultrasonic range, no?
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post #188 of 309
7/10/09 at 10:01pm
Quote:
Originally Posted by JaZZ View Post
Huh? You stated yourself that the audio band is not affected by the cable impedance...
I didn't say any such thing.

What I said was that matching the cable's impedance to the loudspeaker's impedance was irrelevant at audio frequencies.

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...so why does the cable eat up energy?
Technically the reactive elements (i.e. inductance and capacitance) don't actually eat up the energy. Energy is only eaten up by resistance, which converts the energy into heat.

However because of the cable's impedance, it's still drawing power from the amplifier. And in the case of 20 ohms, about a third of the amplifier's power is going into the cable, and not the loudspeaker. Which means the amplifier has to provide a third more power with a 20 ohm cable in order to get the same amount of power delivered to the speaker if the cable's impedance was much higher.

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Remember, it still has ~0 ohm ohmic resistance.
It's not the ohmic resistance we're concerned with. It's the impedance.

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And capacitance should only have an effect in the ultrasonic range, no?
Depends on how much capacitance there is. The greater the capacitance, the greater its effect on impedance at lower frequencies.

k
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post #189 of 309
7/10/09 at 10:22pm
Quote:
Originally Posted by Koyaan I. Sqatsi View Post
Technically the reactive elements (i.e. inductance and capacitance) don't actually eat up the energy. Energy is only eaten up by resistance, which converts the energy into heat.

However because of the cable's impedance, it's still drawing power from the amplifier.
How this?


Quote:
And in the case of 20 ohms, about a third of the amplifier's power is going into the cable, and not the loudspeaker. Which means the amplifier has to provide a third more power with a 20 ohm cable in order to get the same amount of power delivered to the speaker if the cable's impedance was much higher.
So the power is converted into heat as well, or what? I can't imagine anything else than capacitance acting as (sort of) short-circuit between the cable poles, but that would require heavy capacitance with effect deep down into the audible range. And this scenario makes it impossible to consider a fixed percentage (which you provide with your «third»), since the actual capacitance of a 20-ohm cable is dependent on the counterbalancing inductance. When I think about it: According to your theory every speaker cable draws considerable power from the amplifier because of its impedance, even normal speaker cable (let's say of 60 ohm impedance), just not as much as one with 20 or 8 ohm. Or did I get it wrong?
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post #190 of 309
7/10/09 at 11:41pm
Quote:
Originally Posted by JaZZ View Post
How this?
Simple. Ohm's Law.

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So the power is converted into heat as well, or what?
Eventually, yes.

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I can't imagine anything else than capacitance acting as (sort of) short-circuit between the cable poles
Yes.

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but that would require heavy capacitance with effect deep down into the audible range. And this scenario makes it impossible to consider a fixed percentage (which you provide with your «third»), since the actual capacitance of a 20-ohm cable is dependent on the counterbalancing inductance.
The percentage is for wherever the cable impedance is 20 ohms and the load is 8 ohms.

Quote:
When I think about it: According to your theory every speaker cable draws considerable power from the amplifier because of its impedance, even normal speaker cable (let's say of 60 ohm impedance), just not as much as one with 20 or 8 ohm. Or did I get it wrong?
The lower the impedance of the cable, the more power is drawn from the amplifier by the cable and vice versa.

k
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post #191 of 309
7/11/09 at 5:48pm
Quote:
Originally Posted by JaZZ View Post
The easier it is to build one of 20 ohm. I have no idea if a speaker connection would benefit from it, but I give the idea the benefit of the doubt. After all cables are generally said to make no sonic difference, whereas in fact, you know...
You should also consider the "monster cables vs wire coathanger" test. Or what the fact that which one was the coathanger wire was not apparent 100% of the time implies about any short interconnects.
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post #192 of 309
7/11/09 at 6:14pm
Quote:
Originally Posted by Koyaan I. Sqatsi View Post
However because of the cable's impedance, it's still drawing power from the amplifier. And in the case of 20 ohms, about a third of the amplifier's power is going into the cable, and not the loudspeaker. Which means the amplifier has to provide a third more power with a 20 ohm cable in order to get the same amount of power delivered to the speaker if the cable's impedance was much higher.
You are confusing impedance and characteristic impedance. You need a rather long run of cable for its impedance to be 20 ohms. Even for a cable with characteristic impedance of 75 Ohms. Cables you usually meet in you home all measure (essentially) 0 Ohms and as a result consume essentially 0% of the output power of the amplifier.
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post #193 of 309
7/11/09 at 6:43pm
Quote:
Originally Posted by sanderx View Post
You are confusing impedance and characteristic impedance.
No, I'm not. I'm simply addressing the idiocy of Goertz's assertion that the cable's characteristic impedance should be close to that of the loudspeaker's impedance.

First, the cable's characteristic impedance doesn't revert to the square root of L over C until well above the audio range, at which point the speaker's nominal impedance is completely irrelevant.

Second, if the cable's impedance in the audio band where the speaker's nominal impedance would be relevant, you'd be wasting a lot of power just driving the cable, not the speaker.

k
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post #194 of 309
7/11/09 at 7:17pm
Yeah, I must confess that I still doubt this scenario.


Quote:
Originally Posted by sanderx View Post
You should also consider the "monster cables vs wire coathanger" test. Or what the fact that which one was the coathanger wire was not apparent 100% of the time implies about any short interconnects.
Well, this test wasn't done with my ears, but somebody else's, and possibly it was a DBT. So it has no validity to me.
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post #195 of 309
7/13/09 at 7:19pm
Quote:
Originally Posted by JaZZ View Post
Well, this test wasn't done with my ears, but somebody else's, and possibly it was a DBT. So it has no validity to me.
So... if it doesn't match your preconception about things you will simply not accept it as evidence?
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