Re: Ambient outdoor recording (running 1000 ft of cable)
- From: "Michael R. Kesti" <mrkesti@xxxxxxxxxx>
- Date: Sun, 29 Jan 2006 10:24:41 -0800
Harry wrote:
>Hey!
>
>I would like to run a matched pair of microphones about 900-1000 feet
>away to record ambient outdoor sound.
>
>Ideally, I would like to use my (indoor) preamps, and I would like the
>option of using condensers, meaning I would need to send phantom power
>to these mics.
>
>Before I sink any cash into the 1000 ft cable to run the first tests,
>can anyone tell me if this is even feasible? i.e., would the signal be
>too weak after going 1000 feet to do anything with? What would be the
>maximum distance I could get away with?
>
>My instincts tell me it would be better to get the signal up to line
>level as quickly as possible after the mic.
>
>Do I need some kind of *battery-powered* phantom supply that could
>also get my mic signal up to line level before traveling back to my
>studio? Does such a thing even exist?
>
>Thanks for your recommendations. They are appreciated.
>
>HH
It is not uncommon for large touring acts to approach or exceed 1000 feet
of cable between their stage mics and FOH mixers so it is most definately
feasible. The limiting factor is not signal strength, however, as the
losses along the wire are minimal because of the very low amount of signal
current. Instead, the limit is a function of the amount of noise induced
along the cables and filtering caused by the cables' capacitance.
The noise issue occurs simply because longer cables provide more opportunity
to be in proximity to noise sources. The noise rejection of the balanced
lines feeding differential premap inputs is the first line of defense
against noise and routing cables away from noise sources such as motors
and lamp dimmers helps, too. Induced noise will probably not be a large
factor your outdoor ambience application.
The filter caused by the cable's capacitance is of the high-cut variety
and its cutoff frequency is dominated by the mics' source impedance and
the cables' capacitance. Lower source impedance and cable capacitance
results in higher cutoff frequency and the filtering is negligible as
long as the cutoff frequency remains above the highest frequency of
interest (about 20 KHz). This is why low-impedance mics are prefered
and why one aspect of cable quality is its capacitance.
Another concern some might have is phantom power loss. Note, however,
that phantom power is coupled to the cable through several thousand ohms
of resistance (6.8K, typically) so two or three more ohms of cable
resistance is not going to matter.
There can be some value in preamping near the source as higher signal
levels are less subject to noise and because preamps outputs can be
made with very low output impedances. The disadvantage of having such
preamps' controls located near those mics typically overrides those
considerations, however.
The bottom line is that you should be OK if you use low-impedance mics
and reasonbly good cable.
--
========================================================================
Michael Kesti | "And like, one and one don't make
| two, one and one make one."
mrkesti at comcast dot net | - The Who, Bargain
.
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