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Blue Jeans 5T00UP Cable Measurements

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Using our Wayne Kerr 6420 Impedance Analyzer which graces our Reference System 1, I measured all of the critical metrics which directly affect cable performance.

Cable Metric Definitions

Rdc

Commonly referred to DCR which is the series resistance of a cable at zero frequency.

Rac

The resistive portion of the cables series resistance as a function of frequency due to skin effect.

Rs

Total Series Resistance (mohms) measured tip to tip at one end of the cable while the other end is shorted. Note: Rs = Rac + Rdc (minus instrumentation inaccuracies identified below)

Ls

Series Inductance (uH) measured tip to tip at one end of the cable while the other end is shorted.

Cp

Parallel Capacitance (pF) measured tip to tip at one end of the cable while the other end is open circuited.

Cable Measurement Test Set-Up Notes
All of the above measurements were completed on a fully calibrated and certified, Wayne Kerr 6420 Impedance Analyzer . The 6420 was calibrated for full frequency bandwidths and for greater accuracy the measurements and calibration process was repeated twice for consistency.

All cable lengths measured were 20 feet and divided by their length for a normalized per foot measurement. At low frequencies the results illustrate Rs being lower than Rdc, which is inaccurate, as Rs tends towards Rdc as frequency approaches zero or DC. The LCR measurement derives Rs from signal phase and amplitude, while a DC meter measures exactly what it is looking for, thus this discrepancy is likely due to a meter resolution issue, as the meter in AC mode does not sport the high accuracy it would in DC mode. The cable should ideally be modeled as multiple parallel resistors, and those resistors treated as a lumped element in series with an ideal inductor.

Each resistor is a frequency dependent element, and the inner ones fall out as the frequency increases. It is important to note the difference in measuring techniques, and caution the reader not to attempt to derive any relationships with the two numbers, as the absolute accuracy between the methods has not been established. However, the rising trend of Rs vs frequency is indicative of increased Rac due to skin effect and should also be noted.

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Inductance was about what I expected - around 0.160uH/ft. We like to see cable inductance below .200uH/ft to minimize high frequency rolloff for long cable runs. This cable is well within our guidelines. The slight decrease in cable inductance above 20kHz is a result of minimized internal inductance due to skin effect. This is an inaudible and barely measurable phenomenon and is only discussed herein for academic purposes.

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The DC resistance of the 5T00UP measure just a tad under 2mohms/ft which is 10AWG equivalent at DC as specified by Blue Jeans Cable. This is an extremely low resistance speaker cable making it ideal for long runs throughout the home with minimized losses.

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We see a slight rising AC resistance with frequency above 20kHz attributed to skin effect, but practically speaking a non-issue for the application of high fidelity audio especially since even at 50kHz it maintains an equivalent 14AWG resistance.

For a more detailed discussion on Skin Effect, see our article on Skin Effect Relevance in Speaker Cables.

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Capacitance was about what I suspected, ringing in at 25pF/ft. We like to see cables measure under 50pF/ft. This ensures there won't be any stability issues for long runs on marginally stable amplifiers with high unity gain crossing, or excessive high frequency roll off on amplifiers with high output impedances driving a reactive loudspeaker load. The reason for the slight decrease in capacitance with increasing frequency is likely attributed to measurement error of measuring a distributed device (speaker cable) with a measurement tool (Magnetics Analyzer) designed to measure lumped elements (magnetics, electrical circuits, etc).

Cable Assembly

Blue Jeans Cable offers you the option of buying cable in bulk which gives you cost savings and allows you to pre-terminate and cut each cable your desired length or buy them pre-terminated by them into whatever lengths you desire. If you are tight on time, you may wish to opt for having them pre-terminate your cables and pay the extra in favor of wasting time for assembly. It took me about five minutes per cable to cut and terminate both ends. Do this 50 or 100 times and you've just wasted a days worth of work and inherited tired hands and a dirty floor sprinkled in conductor flaxes and cable jacket refuse. Given the choice, I would go pre-terminated and I am sure the wife wholeheartedly agrees.

For those DIY-ers here is how you terminate these cables:

  • Step #1: Cut the cables to desired length
  • Step #2; Using a utility blade, make about a 3 inch slit in the center of the PVC jacket .

    Note: Be careful not to slice the conductors.

  • Step #3: Cut away excessive PVC tubing.
  • Step #4: Shave off about 3/4" insulation from all four conductors on each cable
  • Step #5: Using a small flat head screw driver, loosen the two screws in the locking banana plug
  • Step #6: Remove the green pvc tube insert (why they have these I have no idea, but they are frustrating to remove after doing it more than a half dozen times)
  • Step #7: Insert the termination barrel into the cable conductor (make sure you do this before attaching the connector assembly).
  • Step #8: Tighten down the screws on each connector (double check your polarity is consistent on both ends of the cable)
  • Step #9: Give a tug on all connectors to ensure a tight fit has been achieved.
  • Step #10: Repeat steps #1-9 for next cable.

Blue Jeans cut jacket Blue Jeans Cable solder
(Step #2)                                                       (Step#6)

 

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