PSN-L Email List Message
Subject: Re: OT: an alternative use for a geophone
From: james fisher kd6iwd@.........
Date: Thu, 13 Jul 2006 02:10:22 -0700 (PDT)
Hi, a piezo disk will pick up the higher frequencies
you are interested in. use a 100 gram weight on top of
the piezo disk and bury in a 1' deep hole to isolate
disc from direct sound pickup. Superglue a strong
magnet to disk and stick on a iron rod driven into the
ground. Insulate everything well. See past posts on
piezo disks. They really work well for picking up
seismic waves as well as sound waves.
--- Mark Robinson
> Nicholas Ward wrote:
> > Hi,
> > I realise this is probably not the kind of request
> you get everyday and
> > would like to say thanks in advance for any advise
> you folks might be
> > able to offer.
> > Im a multimedia artist working here in ireland. I
> have an installation
> > which will be part of a music festival here in
> > http://www.electricpicnic.ie/flash.html
> > For the installation i have proposed to capture
> the sound of 10000 or so
> > people all jumnping in unison to the music and
> play it out through small
> > speakers situated at the far end of the festival
> from the main stages. i
> > also anticipate picking up some of the music as it
> is transmitted into
> > the ground via the mainstage (if he had ears)
> would hear under the
> > festival.
> > I was thinking a geophone would be the right
> device to capture the sound
> > with. Im most interested in the 20 to 1200Hz range
> of frequencies.
> > I have no experience with this type of equipment
> and was hoping you
> > might be able to advise me on a suitable device
> for this project? Also
> > what type of amplification would i need to bring
> the output signal up to
> > a line level, (around 100mV).
> > Any advise such as whether a geophone would be
> sensitive across this
> > frequency range, where i might get one, how much
> they cost etc that
> > could be offered would be really great.
> > Many thanks
> > Nicholas
> Hi Nicholas,
> Geophones are well suited to your application
> although there are some pitfalls.
> They would be unlikely to capture much above about
> 100Hz. Ground doesn't
> transmit such frequencies well anyway.
> A geophone will do a good job of capturing
> vibrations in the ground and yes the
> effects are interesting through a *large* PA. It
> gives the whole venue more
> "feel". You can connect it straight into the
> microphone input of a sound desk
> and get excellent results.
> Small speakers will not give good results as the
> frequencies you are dealing
> with are very low.
> You could feed the geophone signal through a music
> synthesizer to generate a
> signal in the audible spectrum.
> Most oil exploration companies and university
> geophysics departments will have
> some. Larry's for sale list at
> http://psn.quake.net/geophone/index.html seems
> to say he has none in stock.
> http://www.tenrats.org/geo.shtml lists possible
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