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Re: extension cables

Subject: Re: extension cables
From: "Robb Nichols" robb_nichols
Date: Fri Jan 22, 2010 1:01 pm ((PST))
I'm not sure you're comparing apples to apples here. Your test included 
mics with a low-impedance balanced source, where as the original 
question came up regarding PIP mics.

This, by coincidence, is a fresh subject for me. I have been asked to 
help set up some remote hydrophones in Nigeria where we'll need a 
300-meter cable. On Monday of this week, I did some kind of quick and 
dirty tests where I placed the mic in the earcup of a decent headset 
providing white noise. Then I tested for spectral losses with and 
without extension cables and subtracted the results. With a 1000' spool 
of a low-capacitance coaxial extension cable in a PIP powered 
application, I saw almost a 20dB loss above 1KHz and a 10dB resonant 
peak at about 225Hz. Then, using the same mic, I set up our UPA-1 as a 
phantom-powered line driver at the source and measured losses with a 
1500' balanced cable (I didn't have a 1000' spool on hand to make a 
similar comparison) and found a pretty smooth response curve that began 
to roll off at about 1K and extended to about -20dB @20KHz. The 
low-impedance source and balanced line didn't maintain a particularly 
compelling response with such a long cable, but it was substantially 
better and quite useable in our application.

Rob Danielson wrote:
> At 9:54 AM -0800 1/22/10, Dan Dugan wrote:
> Next time I install a long cable run, I'm going to record the test I
> did where I connected two Rode NT2000's (7dB[A] self noise)-- one to
> a 20' mic and the other to a 1000' role of cable and placed the mics
> side by side. Prior to this, I looked at all the charts and did the
> HF loss computations and then Richard Lee (miclist) suggested the
> obvious perception test. Result: to my aging ears (significant loss
> above 9-10Khz), I could not detect any loss of signal or HF. I use
> Symetrix SX202 Mic preamps. RFI-wise on my two 700'+ runs, I
> sometimes get very faint radio on one mic from a station in Western
> Texas when the conditions are just right-- its very,very rare. The
> other 3, same model mics get none. I'm running 5 conductor
> studio-grade wire ~$180 for 1000'. Rob D.
> -- 

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