slightly ot: battery driven microphone

[Rory McDonald]

The cheapest route for an "omni" room ambience mic isnt really a omni,
but a "hemispherical"- the PZM, or Pressure Zone Microphone.
While not nearly as accurate or pristine as the earthworks or B&K, 
they can be had for a heck of a lot less.  The now off-market (I think)
Radio Shack (AHHH!) PZM was in fact a Crown PZM, but not balanced.
There are mods to this mic to make it balanced, increase s/n etc.
They are battery powered (AA) but not phantom.  I have used these and
the "real" Crown PZM's, especially when I was in recording school where I
met Dr. Wahrenbrock, the inventor of the PZM. Our class did some demo
recordings
to be used by Crown when they bought the PZM technology from Dr W.
They can be great as room, piano, some percussion, auxilliary mics, choir
type
vocals etc. I made  a stereo plate mic from two of them on a 2x2 ft piece of
plexiglass.
There are a lot of tricks you can do with a PZM, but I dont recommend it for
a primary vocal mic.
The last time I used mine was for vibes, and it sounded quite good-nice and
airy.
The Radio shack version was about $50 US, significantly less than the
earthworks etc (but you
DO get what you pay for, somewhat). So what I am saying here is if budget is
an issue,
or you just need a room ambience mic, consider a PZM or two. Check eBay
possibly for the
old RS type, or spring for the balanced Crown version.

Another mic I have used a bit is the CAD e-100, which goes for around
$250US.
A little cold, but I liked it on Piano and some general uses. It is a
Cardioid pattern however.
It runs off Phantom power (48v), but has a self-charging internal battery
that it will run without Phantom for 
about 6 hrs. It has more spunk with the Phantom, I think.

Rory Mc Donald
-----Original Message-----
From: Steve Ridley [mailto:spr at spridley.freeserve.co.uk]
Sent: Tuesday, August 08, 2000 7:41 AM
To: synth-diy at node12b53.a2000.nl
Subject: Re: slightly ot: battery driven microphone



The best choice would probably be a Bruel & Kjaer 
omnidirectional mic, perhaps the Model 4006, but these 
are very expensive.  I think they are now marketed by 
DPA (Danish Pro Audio).  B&K also make special 
measuring microphones, but these are extremely
expensive and require special powering.
 
The Earthworks omnidirectional mics are cheaper,
but still quite good.  A good Omnidirectional mic needs a
small capsule to avoid corrupting the polar response.  The
Earthworks has a smaller capsule than the B&K, but that 
means less signal, more gain and therefore more noise.

I suspect the B&K will be way too expensive, and maybe the 
Earthworks too, but you may be able to hire them.  Studio Hire
companies will usually rent microphones by the day or by the 
week.  They could probably rent you a phantom power box
too.

A phantom power supply is simple to build.  All you need is a
48v supply - it's not critical - five 9v batteries would be fine -
plus two 6K8 resistors and two capacitors.  The resistors go
from the +48v to the signal pins of the mic (pins 2 & 3), with the
caps stopping the 48v going into the mixing desk.  The negative
side of the 48v goes to screen (pin 1).


Steve Ridley