long cable

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If you have a microphone cable partially left on a cable drum/reel it
will form a coil. Is its inductance negligeble or can it in any way
affect the sound quality?

Lars


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"Lars Farm" wrote ...
> If you have a microphone cable partially left on a cable drum/reel it
> will form a coil. Is its inductance negligeble or can it in any way
> affect the sound quality?
>

Low-impedance, true balanced source and destination?

 

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In article <1gx8241.1izvnoc1s9pd8tN%see.bottom.of.page@farm.se> see.bottom.of.page@farm.se writes:

> If you have a microphone cable partially left on a cable drum/reel it
> will form a coil. Is its inductance negligeble or can it in any way
> affect the sound quality?

Sheesh! Some people worry about the most trivial things! Usually you
can ignore the inductance. The capacitance is more likely to cause
high end rolloff - the longer the cable, the more the capacitance, but
it won't matter whether the cable is straight or coiled.




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Lars Farm <see.bottom.of.page@farm.se> wrote:
>If you have a microphone cable partially left on a cable drum/reel it
>will form a coil. Is its inductance negligeble or can it in any way
>affect the sound quality?

It will not affect the sound quality, BUT the inductance can help
block common mode RF noise. Wrapping it around a steel mike stand
is even better.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

 

[mark]

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we're going to have to get into the difference between the common mode
inductance which will block RF and the differential inductance which
would (could) effect the audio.

To the RF, the two or more wires within the cable act as one wire and
if you coil the cable it makes a big inductor.

To the audio, the wires are independent and coiling the cable has
virtually no inmpact on them.

Similar to putting a big ferrite bead over the cable, it does not
impact the audio at all because the audio is differential within the
cable but the bead does impead the RF because the RF typicvally travels
common mode.

Mark


Mark

 

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On Fri, 27 May 2005 11:17:29 GMT, see.bottom.of.page@farm.se (Lars
Farm) wrote:

>If you have a microphone cable partially left on a cable drum/reel it
>will form a coil. Is its inductance negligeble or can it in any way
>affect the sound quality?
>
>Lars

You don't get any increased inductance by winding a cable on a reel.
Each signal going in one direction is exactly balanced by the signal
in the other wire going the other way, and there is no net inductive
effect.

d

Pearce Consulting
http/www.pearce.uk.com

 

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Richard Crowley <rcrowley7@xprt.net> wrote:

> "Lars Farm" wrote ...
> > If you have a microphone cable partially left on a cable drum/reel it
> > will form a coil. Is its inductance negligeble or can it in any way
> > affect the sound quality?
> >
>
> Low-impedance, true balanced source and destination?

yes, phantom powered condenser mics into pre-amp.


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lars is also a mail-account on the server farm.se
aim: larsfarm@mac.com

 

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"Lars Farm" wrote ...
> Richard Crowley wrote:
>
>> "Lars Farm" wrote ...
>> > If you have a microphone cable partially left on a cable drum/reel
>> > it
>> > will form a coil. Is its inductance negligeble or can it in any way
>> > affect the sound quality?
>> >
>>
>> Low-impedance, true balanced source and destination?
>
> yes, phantom powered condenser mics into pre-amp.

Then I would concur with Mr. Pearce's reply:
Any inductive effect is cancelled by virtue of the
balanced line.

 

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Mike Rivers <mrivers@d-and-d.com> wrote:

> Sheesh! Some people worry about the most trivial things!

Well ... Now I don't have to worry (and note that I'm not arguing
against your infinite wisdom, just asking I've seen people describe
how they uncoil their cables and couldn't really see why.

Inductance follows from current. Input impedence in a pre is high so
there ought to be little current and therefor little effect from
coiling, but is that line of reasoning valid? No harm in quantifying is
there (which hasn't been done yet)?

OTOH Pierce's explanaiion seems good enough. Whatever effect there is
should be canceled for all practical purposes with balanced signals.

Lars


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lars is also a mail-account on the server farm.se
aim: larsfarm@mac.com

 

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Scott Dorsey <kludge@panix.com> wrote:

> [...] the inductance can help block common mode RF noise. Wrapping it
> around a steel mike stand is even better.

I get the part with the rod, but blocking RF...?


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lars is also a mail-account on the server farm.se
aim: larsfarm@mac.com

 

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Lars Farm <see.bottom.of.page@farm.se> wrote:
>Scott Dorsey <kludge@panix.com> wrote:
>
>> [...] the inductance can help block common mode RF noise. Wrapping it
>> around a steel mike stand is even better.
>
>I get the part with the rod, but blocking RF...?

See, you are basically making a choke in the microhenry range. This
does form a low-pass filter, but it forms one in the MHz region. And
this can be useful sometimes.
--scott

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In article <1gx8erw.15nwk82jwoe1wN%see.bottom.of.page@farm.se> see.bottom.of.page@farm.se writes:

> Inductance follows from current. Input impedence in a pre is high so
> there ought to be little current and therefor little effect from
> coiling, but is that line of reasoning valid?

Good theory, but engineers tend to put theories aside when they don't
matter in practice. You're correct that the current is so small that
the inductive effect can be ignored under any reasonable
circumstances.

> No harm in quantifying is
> there (which hasn't been done yet)?

No, but it's going to be mighty hard to measure.


--
I'm really Mike Rivers (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo