Re: Listening to TC?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Jerry Chamkis <jchamkis@xxxxxxx>

Oooohh-   this is Very interesting!  I seriously doubt the bat's confusion was
a coincidence and you would certainly expect a rich ultrasonic field due if
nothing else to the sharp rise-times of the sparks.  If you really want to
explore this, start watching ebay for B&K (Bruel & Kajer) microphone capsules
smaller than 1/2 inch.  They make 1/4" capsules that are measurement grade to
~40 KHz and 1/8" that go to 60 or 80- typically used for vibration analysis
in jet engines and the like.  The price and rarity increase with decreasing
diameter-  the 1" naked capsules go for a couple hundred bucks in their
lovely wooden box and a 1/4" recently went for ~$450.  I don't seek
consistently but I've never noticed an 1/8" on auction but of course that's
the one you really want.  They behave just like an ordinary capacitive
transducer, the polarizing voltage is typically 200 v.  You can find a
(very!) wide spectrum of B&K instruments quite cheap but the capsules hold
their value depressingly well.  It wouldn't be hard at all to build a
heterodyne listening-box.  I think such things (although presumably NOT with
B&K capsules :-) are still used for detecting insects.

Good luck!

Jerry
Austin, TX

On Friday 20 June 2003 08:33 am, Tesla list wrote:
> Original poster: "by way of Terry Fritz <teslalist@xxxxxxxxx>"
> <Mddeming@xxxxxxx>
>
> Hi All,
>
>         We all know that spark gaps and streamers make some pretty awesome
> sounds, but what about "ultrasounds"? These would be sounds from 15KHz on
> up to the resonant frequency of the coil. This question is prompted by the
> following: Last night, a bat got into the instrument/people section of the
> lab. (The TC section is inside a grounded 10ftx10ftx8ft cage). With the
> coil running, the bat ran into the wall the way a bird or insect will beat
> against a window trying to get out. I turned off the coil and it
> immediately turned around and flew back out the door which was only open
> about 5 inches.  Makes me think maybe the coil was making sonar-jamming
> noises. Of course, it could be pure coincidence.
>         Seems about 35-40 years ago, I read about an "ultrasonic listening
> device" that used a very (for that time) high freq. response ceramic mike
> and heterodyned its output with ~38KHz local oscillator which made sounds
> above 20KHz audible but inverted. Example: a 32 Khz "sound" would become a
> 6Khz tweet, while a 37KHz one would become a 1 KHz beep, etc. By making the
> local oscillator a VFO, one could listen to a wide range of the audio
> spectrum up to the response limits of the microphone.
>         If nothing else, such a gizmo might add to the "Halloween value" of
> a coil. Does anyone know if such devices are still around in a modern form,
> or if there is a microphone/transducer with good well-above audible range
> frequency response for a DIY?
>
> Matt D.

--
Jerry Chamkis
jchamkis@xxxxxxx

Non-locality is spooky action at -zero- distance.
www.teslaphone.com/OTE/TIME.mp3