solderdude
Grand Contributor
We don't need the reference as we now have a graph showing voltages. Input voltage 55.5mV, and 1.1mV cable loss @ 10kHz. What's the formula that gives 23dB cable loss using these input parameters?
(There might be some error margin on the 55.5mV input voltage, but that error would need to be really huge to get a 23dB cable loss).
There is no reference as the 2i2 input pot can be in any position. Also the 55.5mV is not accurate.
Let's say the 55.5mV is correct. Then at 200Hz the impedance of the load = 8 Ohm.
55.5mV over 8 Ohm = 6.9mA. Do note this is the total signal containing the entire frequency band.
at 200Hz the used cable has a voltage drop of 90uV (the small 10uV bump is mains hum)
90uV / 6.9mA = 13mOhm and given the fact that his cable is 8.4 mOhms per meter (so the measured side 4.2Ohm/meter) would mean the cable is 3meter long.
The article states 7m long so something is fishy and the reference is not correct, the 7m is not correct, the Ohm/meter is incorrect, the load is incorrect.
Acc to mr. Townshend the 7m Isolda is 2.45uH, 65.8nF, 189mohm (= 13.5 Ohm/meter for 1 conductor and not the 4.2 Ohm per meter).
Apples and pears, no reference.
To really be able to tell something you need the sweep also with 2i2 of the input signal. Certainly because the RMS value is measured over the entire frequency range (a total, well not total as >500Hz it doesn't register correctly) and the 90uV value is (most likely) not calibrated and is only part of the entire 'energy'.
You really cannot use the data as there is no actual reference.
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