OK to use TV coax for microphone?

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.

This is true.

Good quality coax will do the job if you don't mind the impedance mismatch and if you want balanced line then you could use a pair of coax feeds in parallel (impedance about 100 ohms for rg58). Also there's coax and there's coax, I've seen rg58 like TV down-lead and others like shrunk down UR67M.

A pair of coaxes in parallel is balanced, but you miss out on the close proximity and twist. The first makes the magnetic loop very small, while the second causes the polarity of any residual pickup to swap every inch or so, giving a net cancellation.

As I said in my first reply, if I was forced to use coax for a microphone, domestic TV grade would be a very poor choice because in general it has perhaps no more than 10% screening (just enough in fact to give the cable a stable characteristic impedance, but no more). Microphone signals are too small to mess around this way. Decent audio grade cable has screening approaching 100%.

Um, yes. It is exactly like that. I had thought maybe they were using very thin wires and that way getting a reasonable amount of physcial screening but the wires I found were so sparse that it must be more like what you describe!

Er, not in every case. In any case my point about the mic being regarded as a voltage source remains true.

For speech use (3K) you can get away with just about anything!

Les.

This cheapo coax is quite flexible. It may an indication of poor physical resistance to squashing and also of limited copper content.

I am the OP and as you can probably tell I am no electronics or radio expert. However even my limited knowledge struggles to believe some of the points you have made.

Forgive me if it's more obvious to others but your's is not some sort of funny posting is it?

I too have started to feeling that there is a heck of lot more variation than I realised in how coax cables can be made and yet are still conform to some particular technical specification.

I came across some interesting articles at "abc cables". Here are some which caught my eye.

Wire? or Cable? RG6 Copper vs. Copper Clad Steel RG59 vs. RG6 Better Copper?

I would like to get other (supplier's) info as that site is quite useful. Has anyone got any links to these sort of explanatory articles?

Maplins selling crap merchandise doesn't surprise me. (Though to be fair, it does sell the odd good item too.)

But where would I go to get half-decent cables in relatively short lengths (not 50m drums) without paying a fortune for ultra quality dedicated-hobbyist stuff or exhorbitant delivery charges?

yeah but there is no "mag loop" outside of the shield with coax.

no pickup inside coax.

fully agree.

"don pearce PITA smug wanker "

Mic cable IS a balanced twin wire cable.

Do learn to read sometime - f****it.

Do learn to read sometime - f****it.

so this claim is clearly nonsensical.

your irrelevant & asinine claims are nonsensical

- f****it.

" 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. "

Obviously YOU need to do this too - f****it.

Since you are so PIG ignorant of the basic physics of co-axial cable.

...... Phil

Having trouble spotting the capital letters, are you? (yes, I saw yours, and that is what prompted this question, the relevance obviously passed you by).

we know exactly what this cable is - and yes it is poorly screened. Do try to follow the threads. And if you want to post about something else, start a new thread.

Irrelevant is it? Tell that to Neve, Neumann, Shure, Sennheiser, Leevers Rich - need I go on?

I appear to have a vastly better grasp of the topic than you, not surprising really when you consider that I have designed ultra low noise microwave measuring equipment.

"Chris Siz"

Cos the truth is never as simple as you would like to be.

Looks every inch like some piss head's pathetic troll.

...... Phil

You can slap RG- numbers on anything. It stopped being a military standard a long time ago. Belden, Alpha, Times wire websites should have some good white papers. RG meant 'Radio Guide', and all early coax was braided copper shielding. Their is still some RF coax made this way, but it uses teflon and silver plated copper and is VERY expensive.

is the coaxial cable part of the Belden catalog. about 4 MB download.

is their full catalog, about 38 MB download.

Copper 'work hardens' when flexed. Over time it develops cracks, then breaks. Stranded wire uses smaller conductors and has less problems per conductor, due to a larger bending radius VS the diameter of the conductor. The steel center conductor is meant for permanent installation, but it holds up better on the bench that solid copper coax.

Really? Then you don't know much about Coaxial cables, shielding effectiveness, signal ingression and a dozen other topics. In other words, no single shield is 100% effective.

And of course unless it is made of soft iron or mumetal, it doesn't shield magnetically at all.

Don, please don't feed the troll.

The signal-to-noise ratio from Mr. Allison is so poor that he is better to be filtered completely out.

"Dead Paul" wrote in ...

There is no "impedance mismatch" at audio frequencies in this application.