Calculation - cable length and mic cable capacity cutoff frequency microphone wire - sengpielaudio Checker
 
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Calculation: Cable Length, Cable Capacitance,
and
Treble Loss (Attenuation, Cutoff Frequency) •

mic cable

This is not about coaxial cables, antennas and satellite frequencies,
here we have a look at a normal audio, mic or
microphone cable.

Cable and treble damping
treble cut filter (low pass)
Simplified principle
C = Cspec ·
d
RC-pad = cable

A frequently asked question is at which cutoff frequency fc the microphone cable has
a (−) 3 dB loss of treble (Treble frequencies are attenuated)? Which length d a cable
can have to reach this damping? How are high frequencies damped by the length of
the cable?
Cables are characterized by the capacity of the cable between the conductors, the
resistance, inductance of the cable along the conductor, and the current crowding,
which boost the resistance at high frequencies. The
microphone cable usually has a
capacitance from wire to wire of about Cspec = 100 pF per meter.
The line resistance, and the inductance is usually negligible in practice. Each wire
has an unavoidable cable capacitance, that leads to the damping of high
frequencies (
cable loss). Because the input resistance (load) is large against the
small output impedance (source), the input impedance (load) can be neglected.

Calculating the treble cutoff frequency of a cable

 Source impedance Zout   ohms
Capacitance C per m   pF/m
Cable length d   meters 
     
                        
     
Cutoff frequency fc   Hz
Zout = Output impedance of microphone, source impedance
Cspec = Specific capacitance of the cable in pF per m cable lenghth
d = Length of the cable in m            C = Cspec · d

Formula for the cutoff frequency of the treble damping:
Cable cutoff frequency - sengpielaudio

Another frequently asked question is of how long can the microphone cable be,
without having treble loss?

Cable length

Calculation of the length of a cable at 3 dB treble attenuation

 Source impedance Zout   ohms
Capacitance C per m   pF/m
Cutoff frequency fc   Hz
     
                        
     
Cable length d   meters 
Formula for the length of the cable d and a given cutoff frequency fc:
Cable length - sengpielaudio

fc = Cutoff frequency at (−)3 dB treble loss
Zout = Output impedance of microphone, source impedance
Cspec = Capacitance in pF per m cable lenghth     C = Cspec · d

If you want to know how long the cable can be and permit a level damping
of only 1 dB, you need to enter the double value of the cutoff frequency.

Cable characteristic impedance is a cable characteristics which is only
valid for high frequency signals. Multimeters use DC current for resistance
measurements, so you cannot measure the cable impedance using your
multimeter or other simple measurement equipments.

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