- Thread Starter
- #61
I am certainly not demanding or forcing anyone. I was just asking to see if there was interest. I am sorry if that was not clear.
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- Thread starter jensgk
- Start date
Nope, my statement was absolutely correct, as written, and yours perhaps has some errors.
Most engineers forget that impedance has a frequency term to it:
the jwL and jwC terms dominate at high frequencies and the cable, within the limits of the frequency linearity of the capacitance and inductance reaches an asymptote. For practical purposes that typically happens from about 5K - 50K. For most cables, the impedance is highly variable (as per the equation) at audio frequencies and hence is impossible to "match".
W.R.T. to most simplifications of where transmission line effects have effects, they are just that, simplifications. The ones w.r.t. it only mattering if the cable is > 1/10th or 1/20th the wavelength is just one of those simplifications and has been around from the days of long telephone and telegraph wires where the SNR was <40db, and stayed around into the digital era where again, 40db would be for most applications more than sufficient.
At 3m, limiting the bandwidth to the audio bandwidth, 20-20KHz, even at a -160db scale I do not think you will measure a difference. At a 100K bandwidth and 10 meters you may. I have done the calculations before, not worth doing them again
The cable and speaker were calculated
Look at a speaker |Z| and phase plot
Phase swings typically -30 to +30, 8 ohm nominal
Lead lag depending on filter region
The net is (Xl - Xc) at that point
The equations are basic textbook stuff
you know that this is an foolish attempt to measure resistance in this order of magnitude.
well ok yes i was neglecting DC resistance and Leakage.
not talking about magnitude errors alone there is also phase.
assuming there is significant impedance mismatch there can be reflections for some time.
At what frequency are all this effeckts below lets say relative 160dB? i don't know but if you have done the math pleses share it.
What "speaker" or evaluated? You marked as Zol (impedance of load). I have never seen a speaker with an impedance of 158 ohms at 1000 KHz, and 0.08 ohms at 100Hz, and the phase only changes the real/reactive component so not sure what you are calculating / referencing hence why I asked.
No one forgot thatNope, my statement was absolutely correct, as written, and yours perhaps has some errors.
Most engineers forget that impedance has a frequency term to it:
View attachment 198299
the jwL and jwC terms dominate at high frequencies and the cable, within the limits of the frequency linearity of the capacitance and inductance reaches an asymptote. For practical purposes that typically happens from about 5K - 50K. For most cables, the impedance is highly variable (as per the equation) at audio frequencies and hence is impossible to "match".
W.R.T. to most simplifications of where transmission line effects have effects, they are just that, simplifications. The ones w.r.t. it only mattering if the cable is > 1/10th or 1/20th the wavelength is just one of those simplifications and has been around from the days of long telephone and telegraph wires where the SNR was <40db, and stayed around into the digital era where again, 40db would be for most applications more than sufficient.
At 3m, limiting the bandwidth to the audio bandwidth, 20-20KHz, even at a -160db scale I do not think you will measure a difference. At a 100K bandwidth and 10 meters you may. I have done the calculations before, not worth doing them again
R and G are small and ignored
The freq component then cancels
My grad textbook
You don't understand Zo
No use explaining
Did a quick look, but could not find quickly. The reflections themselves represent step functions but the underlying "frequency" is related to mismatch and cable length. My calculations were effectively related to settling time as I could related that back to resolution and bandwidth. Accurate enough for the discussion at the time. Pick the worst case mismatch for settling, then determine how many reflections till you settle to a sufficient accuracy.
Humor me and all the other people reading your calculations and going "huh?" because they can't read your mind, and suspect your either made a mistake, you don't understand the problem, or are willing to give you the benefit of the doubt that perhaps you are a bad communicator.
You don't have to read my mind.
Read a textbook
The 158 Ohm is the characteristic or surge Z, not the Z
I do not need any benefit
8 x sin (30) = Xl
Xl = 2 Pi f L j, L is net at the phase point or C = unit 1
Zo = sqrt(L/C) as shown on the sheet
Or you simply do not have the background to comprehend the calcs?
You say I made a mistake about something you do not understand.
That is rich lol
what accuracy?
Your metes?!
you seam to ignore the +1 count
And the contact resistance from your "calibrated" probing setup surly is not.
Use the proper technique
Four-terminal sensing - Wikipedia
DonR
Major Contributor
Anything less than an ohm needs a Kelvin connection to measure properly.
