You wrote:
have been playing with piezo's a bit.
The linked recording is from putting one in a ant mound.
The ants were about 1/8" and the hill about 1/2" tall.
The clicks are when they walk on the pickup.
The roar is the minidisc motor on the ground about 2 feet away.
They don't seem to happy with my mic being there.
I obviously have some more work to do on a resonator to even out some
freqs but thought the mad ants were kind a neat and I have not seen
many posts on micro targets. Rich
Dear Rich:
As a note, you may probably remember I have posted several times perviously=
to this group that in the early 1970's, I listened to vibrations in several=
mature hardwood trees using crystal phono cartridges as sensors.
I made a tree-mounted copper covered box out of 3 inch pipe cut in half
lengthwise. The tree-mounted base part was a two by six inch rectangle of=
sheet copper, flat but slightly concave to conform to the outer bark. This=
was screwed to the bark through a rubber gasket, and had a turned up lip
around the rectangle to hold the gasket in place. It also had a large hole=
near the center, through which a deeper brass screw went into the tree wood=
itself. [I found that the sound velocity in brass matches very closely that=
of hardwoods, and therefore could obtain very little acoustic impedance
loss going from wood to brass.] So the two-inch brass screw brought
acoustic vibrations from the heart-wood into the water-proof box. The box=
was electrically grounded to a driven rod at the tree base to prevent
lightening problems.
On the head of the main screw rested the sensor of the phono cartridge
(where the diamond or sapphire phonograph needle was supposed to
go). Since piezo devices are by nature high electrical impedance, and
long-distance high-impedance mic lines invite horrible electrical
interference from various sources, I mounted an emitter-follower FET
pre-amp right on the cartridge to reduce the impedance from megs to a few
hundred ohms. The cartridge was anchored directly to a 20 gram lead
weight, and mechanically suspended by packing urethane foam all around
it. The whole unit then was capped with the half-round cylinder of copper,=
pressed into the lip of the rectangle against the rubber gasket, held to
the tree with elastic bands over the top, each anchored at each end with
short bark-deep (one inch) screws.
[This is where I jokingly claim to have started the field of "xylophonics"=
=3D wood-sounds, ;^) I showed the setup to Roger Payne and tried to get him=
and his students interested in working on it at the time as part of
acoustic ecology (he was transitioning from owl and moth hearing to whales,=
but he only wanted to study vocalizations of ocean-going mammals, oh
well! :=3D( I used the same electrical impedance-reducing trick for his=
modified sonabouys for Roger's Argentina right whale studies]
The one-conductor shielded cable was strung from the house out to the tree=
mount. DC power for the emitter-follower pre-amp went out the same cable,=
and the emitter follower resistor was inside the house, with the (DC-gain
of one) AC signal being picked off this with a blocking capacitor. The
output was quite strong, and the low impedance prevented much humm. You
could head a chickadee land on the top-most branch of a 60 foot oak with
this, as a loud "thunk!". You could also hear people walking within 30
feet of the tree (crunch, crunch), and squirrels on the bark were
deafening, but I never heard boring beetles or any chewing which is what I=
had hoped for.
I send my best regards,
Marty Michener, MIST Software Assoc. Inc., P. O. Box 269, Hollis, NH 03049
"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety." - Ben Franklin, 1775
"Pues cuando ardi=F3 la p=E9rdida reverdecieron sus maizales"
----------
---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.708 / Virus Database: 464 - Release Date: 6/18/2004
[Non-text portions of this message have been removed]
________________________________________________________________________
________________________________________________________________________
|