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Re: extension cables

Subject: Re: extension cables
From: "Rob Danielson" danielson_audio
Date: Fri Jan 22, 2010 4:10 pm ((PST))
Posting this again as its not showing on the list for me. I must have 
forgotten to perform an obligatory, arcane "yahooism" on it when 
sending it early this p.m. ;-)

At 1:01 PM -0800 1/22/10, Robb Nichols wrote:
>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.

Sorry Vicki. Robb is absolutely right. I didn't read back far enough 
and I compared apples to oranges: 3000 ohms (WL183) to 200 ohms 
(NT2000). I know just enough about electronics to get into trouble.

I assume that running her WL183's on a 9 volt battery box (max is 10 
volts) wouldn't affect the inherent capacitance in the wire and the 
HF loss?

>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.

Some folks of the miclist reported HF loss on this order too but I 
was cautioned that some gear combinations can fare much better than 
calculators predict. Testing may provide one the most relevant answer 
to the, "how much cable can I,.."  question. :-)  Rob D.

>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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