Working with Geophones
Device: GeoSpace Technologies GS11D
Natural Frequency: 4.5Hz
Casing: GeoSpace Technologies PC-21 Land Case
Coil Resistance: 380Ω
Further Detail: http://www.geospace.com/geophones-gs-11d/
Inserted the sensor node into the top of a foam acoustic bass trap to test its potential as a signal producer. Attached the provided heavy duty crocodile clips of the negative and positive to the corresponding shielded part of a low noise 1/4″ Jack instrument cable.
Plugged the other end into an Avid/M-Audio Fast Track C600 digital audio interface:
A: Hi-Z Jack Input (50kΩ)
B: XLR Input (200Ω)
No discernible difference in signal output with minor increase in Pre-Amp Gain. The Device is only capable of converting signal from 10Hz below so the core frequency of the unit is already below the audio pre amplifiers capacity.
A notable hi frequency wave at 16kHz exists in the waveform.
Using a rubber vibrating tool, I test a number of vibrational patterns to determine the stability and sensitivity of the geophone as an audio signal. It is surprsingly powerful and accurate at frequencies between 20Hz – 45Hz.
A thunder storm starts outside. I observe the reaction of the geophone to the thunder felt through the foam mount and see it spike, responding the vibration. I start to think about a feedback loop between the geophone picking up the pressure wave movements of vibrations from a subwoofer that is playing back the amplified signal of the geophone, looping into a subharmonic frenzy. I think about Primordial/Lift, the score written by Pauline Oliveros that bases itself around subharmonic frequencies as a platform for composition with instruments.
I wonder what I might be able to discover with this Geophone.
Next I will strip the cable and attach a proper Jack cable to it so to avoid the precarious crocodile clip situation that currently exists. I will then run it in my garden flower bed and listen to the earth inside before taking it on to further adventures.