> now I'd like to run about 500' of 3.5mm stereo cable down to
> the creek (and maybe _in the creek -- the mic in a plastic
> soda bottle)
resonances inside the bottle will dominate the sound...
> behind my place where all the marvelous
> serenades occur this time of year...
>
> I'm thinking of recording direct to DVD/computer if
> possible... or HiMD
>
> is the cable length a problem?
> recommended vendors appreciated
Any twisted pair with shield will do. I've run 100' unbalanced stereo
like that, in the city. Expected taxis to break in, but it was fine.
500' may be pushing it, but the only effect of too long will be a
rolloff of high frequencies. You'll want to keep cell phones off
around such extended unbalanced circuits.
I'm not an engineer but I play one at work. Let me try to run the
numbers (real engineers correct me if I'm wrong):
Take the very rugged Belden 8451--not a low-capacitance cable, so a
worst case. Capacitance between one conductor and other conductor plus
shield is 67 pF/ft. 500 feet is a capacitor of 33,500 pF or .033 uF.
Assume a worst-case PIP microphone source impedance of 3K Ohms.
Slide rule says that combination is 3 dB down at -- oops -- 1600 Hz.
That would sound pretty dull. A 200-Ohm source on the same cable would
be 3 dB down at 22 KHz. That would work--so you need a low-impedance
mic out there. And in that case you might as well go pro and wire it
balanced with a twisted pair for each of 2 mics.
Plan B: put the recorder down at the creek. Then run the headphone
circuit back. That has a low source impedance and should be just fine
through 500' of cable.
-Dan Dugan
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