Electronics > Beginners
Does cable impedance add to source or load impedance?
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fonograph:
Lets imagine we have amplifier with 2 ohm output impedance connected to 8 ohm impedance load, headphone for example. Becose the amp impedance is 2 and headphone is 8, then the damping factor is 4.

How will the cable affect our system? If the cable has 2 ohm resistance, does it add up to the source impedance and decrease damping factor from 4 to 2 becose 2 ohm source + 2 ohm cable = 4 ohm output impedance divides 8 ohm load = 2x damping factor.

Or does it add to the load impedance and increase the damping factor becose 8 ohm headphone + 2 ohm cable = 10 ohm load divided 2 ohm amp output impedance = 5x damping factor?
Doctorandus_P:
Damping factor gets worse (lower) by cable resistance.
If high resistance would increas damping factor everybody would use open connections between the amplifier and speakers.
Audioguru:
Simply try it. A modern audio amplifier has an output impedance at low frequencies of 0.04 ohms or less for excellent speaker resonance damping. A pulse sounds like a "thump". With a poor damping factor caused by the amplifier output or cable resistance then the pulse sounds boomy like a bongo drum.

The amount of damping required depends on the speaker and on your hearing.


Your example of a 2 ohm amplifier or cable resistance feeding an 8 ohm speaker also reduces the maximum undistorted output level a little.
Richard Crowley:
Remember that series resistance has nothing to do with cable impedance.

Cable impedance is of no importance down at audio frequencies.

OTOH, series resistance does indeed affect damping factor:


--- Quote ---The damping factor is affected to some extent by the resistance of the speaker cables. The higher the resistance of the speaker cables, the lower the damping factor. When the effect is small, it is called voltage bridging.
https://en.wikipedia.org/wiki/Damping_factor#Effect_of_cable_resistance

--- End quote ---
fonograph:
So cable impedance adds up to and counts as source output impedance? I expected it will add up to load impedance.
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