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.
--
|