[Don Pearce]

Phil Allison wrote:
"Richard Crowley"
(1) Is it ok to use this sort of coax for a microphone?
Not enough details to answer your question adequately.
First of all, the kinds of microphones used for audio
applications (reinforcement, recording, etc.) are usually
balanced and require cable with two inner wires and an
outside shield/screen. If you are trying to use a balanced
mic, then the cable is unsuitable because it is unbalanced.


** Not true at all !!

There is NO reason not to use a (suitable) co-axial type cable with a
microphone - either low or high impedance.

Despite all the nonsense you WILL have read elsewhere, co-axial cables
have as good or better rejection of external hum and noise sources as do
balanced twin wire cables.

Try it out if you don't believe this.


Of course a proper microphone cable is SCREENED balanced twisted pair,
so it enjoys the multiple benefits of electric screening by the outer,
the common mode nature of any residual interference and magnetic
interference cancellation by the twist in the balanced pair. A poorly
screened coax cable such as TV coax has only a part of the first of
those so this claim is clearly nonsensical. If it were true,
professional microphone and mixer companies would not be going to the
trouble of designing balanced kit.



The length I need to use is 3 to 4 metres.
Not really important to the question. It wouldn't make
much difference if it were 1 m or 1Km


** If the mic is high impedance ( ie 50 kohms), then more than 10 metres or
so of cable will cause high frequency response peaking and early roll off as
the cable capacitance loads the transformer inside the mic.



If the mic is low impedance ( ie circa 250 ohms), then hundreds of metres
can be used - but not kilometres.



This is true.

d