The piezo disk transducer is a suitable device for
urban search work where it is  necessary to listen for
tapping or other noises in collapsed buildings. The
transducer when coupled to an op27 audio amp and a 386
power amp will yield incredible sensitivity. 

In an experiment i conducted, it was easy to detect
the noise caused by merely toutching a countertop with
one finger. The countertop had a piezo disk transducer
attached to it. The piezo disk had a thumbtack glued
to it and no weight was placed on the piezo disk. The
head of the thumbtack was glued to the piezo side of
the disk. This setup is also sensitive to ambient
noise and will feed back if the earphones used to
listen are within 10 feet of the pickup. Note that you
must use earphones with good audio isolation because
the sound from the earphone will feed back.
Loudspeakers will not work. The electronics for this
application could be put together very inexpensively
less than $25. Another approach for an amplifier is to
tap into an inexpensive amplifier on a tape player or
other similar consumer device. If you can lift the
leads going to the read head on a tape player you
should be able to feed the piezo disk output directly
into the player. If the tape drive motor leads are
clipped off the batteries will last much longer. 

best regards
james fisher 
--- Larry Cochrane  wrote:
> From John Lahr. -Larry
> 
> ----- Original Message -----
> From: "The Lahrs" 
> To: ; 
> Sent: Thursday, August 16, 2001 8:33 PM
> Subject: Re: geophone for urban search work
> 
> 
> > (Larry, could you forward this to the PSN? 
> Thanks!)
> >
> > Hi Rick,
> >
> > I don't think a 1 Hz geophone would be the best
> tool to pick up a tapping
> > noise.
> > You might want to use a less expensive 4.5 or 8 Hz
> geophone or even a
> > microphone.  In 1992 I used microphones to locate
> neighborhood gunshots.
> > The recording system digitized the signals at
> 2,000 samples per second.
> > A high sampling rate would also be required for a
> your search and rescue
> > system, both to record the high frequencies and to
> allow very accurate
> > timing for locating the source with three sensors.
> >
> > There is information on the gunshot system here:
> > 
> >
> > Cheers,
> > John
> > At 02:29 PM 8/12/2001 , you wrote:
> > >Rick,
> > >
> > >I'm not sure if a geophone would be good for this
> type of thing,
> > >maybe....I'm CCing the PSN mailing list. Maybe
> someone on the list has
> some
> > >ideas for you.
> > >
> > >PSN'ers, please CC Rick at seadog@....... since
> he is not on the list.
> > >
> > >-Larry Cochrane
> > >Redwood City, PSN
> > >
> > >
> > >----- Original Message -----
> > >From: "Rick Howard" 
> > >To: 
> > >Sent: Sunday, August 12, 2001 12:43 AM
> > >Subject: geophone for urban search work
> > >
> > >
> > > > Larry,
> > > >
> > > > Please advise whether you feel a geophone like
> the Mark
> > > > Products L10B you have for sale might prove
> useful as
> > > > a device to detect a person tapping on a
> collapsed structure
> > > > when buried under rubble.
> > > >
> > > > I'm a Technical Search Specialist for one of
> the FEMA
> > > > Urban Search & Rescue Task Forces, and we use
> a
> > > > sophisticated device (http://www.delsar.com)
> as a person
> > > > locator, but this equipment is expensive and
> limited as
> > > > far as access for training.  How might a
> geophone work as
> > > > as a detector if someone was tapping on a
> structure (pipe,
> > > > concrete, etc) 20-100 feet away?  The general
> frequency
> > > > range the Delsar unit calls for is 1-3000 Hz. 
> I'd love
> > > > to buy a geophone to experiment with.  I can
> solder circuits
> > > > pretty well, if you can recommend a circuit to
> go with it.
> > > >
> > > > Any advice would be appreciated.  I serve in
> search and
> > > > rescue as a volunteer; you'll incur no
> liability in
> > > > giving me your recommendation - I'm just
> looking to
> > > > experiment with other available, cheaper tools
> in a
> > > > quest to do my search job better.
> > > >
> > > > Thanks -
> > > >
> > > > Rick Howard
> > > > Tech Search Specialist
> > > > California Task Force 3, Menlo Park
> 
> 
>
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