Re: photo-voltaic power for audio equipment
- From: "Richard Crowley" <rcrowley@xxxxxxxxx>
- Date: Mon, 3 Mar 2008 17:40:15 -0800
"David@liminal" wrote ...
"David@liminal" wrote in message
I'm involved in an installation which is to be permanently sited in
woodland. We're hoping to install small mics in a bird box which will
be amplified near-by in a listening area. The mics won't be exposed
to the weather directly, but they will be exposed to damp, cold air.
I've used DPA4060s a lot and was thinking of using these, not least
because DPA make bold claims about their tolerance to damp - but I
doubt they had this kind of treatment in mind. There's no power on
site so we're thinking of use PV cells to power everything and I
think we'll be fine for generating enough power with the light
available. A few questions then: Any suggestions for small, high
quality mics which have a good tolerance to damp? Suggestions for 2
similarly resilient, 12 volt powered, 2 channel mic pre-amplification?
and lastly recommendations for amps (I was thinking about car amps)
and weatherproof speakers? Not specifically a 'recording' question I
know, but I thought there might well be some valuable experience on
this list none the less. Thanks. David
The Sennheiser MKH series is uniquely resistant to moisture, far more so
than any of the other alternatives. These microphones do not use DC bias
the diaphragm. Any of the MKH series are are also much, much quieter than
the DPA 4060.
For two channel preamplification off one rail, a "production mixer" is
way to go. Something like this is
and will run on 5-18V. Because it has such flexible power ability, you
hook it directly to a panel buffered by a supercapacitor.
There are cheaper mixers available, but you will need to examine them
carefully, as many do not have the ability to run off external single
The amplifier is problematic, as most have significant idle power draw. I
would look for a switcher design.
All great stuff - a kind of desert island spec but I think beyond my
means (this time). Nice to have advice towards both ends of the
Condenser mikes are extremely sensitive to moisture. If stored in dry
conditions, a condenser mike can, if not directly exposed to moisture,
work outside for some length of time, but always less than a day, unless
the humidity is extremely low. There is a process called "adsorption", by
which water molecules form a thin layer on the diaphragm insulators. The
most minute contaminations of ionic compounds, typically salts, makes this
layer conductive. The charge is supplied to the diaphragm by an extremly
high value resistor, and it cannot be replenished quickly enough under
these conditions. Sporadic discharges cause what are referred to as
I hate to be negative about this, but the only condenser technology
that can beat this is MKH. Before you proceed with the project, I suggest
you test-mount microphones in conditions of exposure and humidity similar
to the installation.
You also need to consider self noise. Some of the suggestions are not
appropriate for nature-ambience. Condenser microphones with diaphragms
less than 16mm in diameter are utterly unsuited for such applications, and
there is a good chance that typical 3/4" diaphragms will not provide
satisfactory results -- MKH excepted.
If the OP were recording ambient sounds for production,
I would agree with you.
But he's piping sounds from a bird-box into some sort of
pubic viewing area which is likely subject to *the same*
background noise as the recording "site" (a few feet away).
I can't see any reason why an inexpensive electret capsule
and a simple 12V-powered simple amplifier circuit with a
halfway-decent speaker wouldn't do the trick.
All this talk of microphones that cost hundreds/thousands
of dollars and fancy mic preamps, etc. etc. is not only gross
overkill, but also an attractive theft target in an isolated
installation such as the one that the OP has described.
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