In a message dated 2006/11/01, gmvoeth@........... writes:

> These are some speculations into making a good geophone installation.
> I looked further into the clossal caves of
> Tucson Arizona USA and this is what i found:
> "Today visitors take a fifty-minute, one-half mile guided tour down six 
> stories into Colossal Cave to see the beautiful formations."
> 
> It seems that to get a stable temp of 70F at 90% to 100% RH you need to be 
> about 6 stories underground. I am not sure what a story is but if it is 15 
> feet then thats about 100 Feet underground.
> If I could i would bore a 6inch hole 50 feet to 100 feet deep then somehow 
> place my geophone there.
> 
> Otherwise I would isolate the geophone with very good insulation and 
> moisture protection on a tripod of metal stakes driven into the base of the hole 
> with a ceramic tile glued with liquid nails or something. Try to vibrationally 
> isolate the body of the geophone from the sides of the hole.

       You want the geophone to be in very good contact with the ground.

> It seems to me a proper installation is not really possible for the average 
> person.
> It is too expensive.

       Do some 'vertical thinking'? Hire an auger, preferably motorised, to 
dig a hole maybe 6ft or a bit more deep, install a plastic drain pipe already 
containing the seismometer with sealed ends. Then backfill with slurry around 
the pipe? This won't get you away from surface vibrations entirely, but it 
should help reduce the wind noise? Looking at published noise data, you may need 
to get to over 100 m to really get away from surface noise. That is a long way 
down.

>     Have you ever seen a geophone that is resistant to higher freq 
> vibrations by being placed on a foam like material instead of hard ground ?

       No. You don't usually bother. You rely on a fairly linear axial sensor 
response, a low cross response and electronic low pass filters. I suspect 
that you would have problems getting full vertical sensitivity just over the 
range that you want. And it would need to be fairly independant of temperature 
effects.

>     Such a thing might if it can be adjusted right might reduce higher freq 
> noise without affecting the range we desire to look at ?

    I don't know when / where this has been a problem? Have you had problems 
of this sort?

>     Sort of like the submarine makers isolating moving machinery from the 
> hull etc...
> The sound radiation is reduced but the item / machinery still travels with 
> the sub whose motions are relatively slower then the vibrations.

       But in a submarine you want to isolate all vibrations, not just 
selectively the high frequency ones. Building high performance mechanical low pass 
filters might not be too easy?

       Regards,

       Chris Chapman
In a me=
ssage dated 2006/11/01, gmvoeth@........... writes:



These are some speculations int=
o making a good geophone installation.

I looked further into the clossal caves of

Tucson Arizona USA and this is what i found:

"Today visitors take a fifty-minute, one-half mile guided tour down six stor=
ies into Colossal Cave to see the beautiful formations."



It seems that to get a stable temp of 70F at 90% to 100% RH you need to be a=
bout 6 stories underground. I am not sure what a story is but if it is 15 fe=
et then thats about 100 Feet underground.

If I could i would bore a 6inch hole 50 feet to 100 feet deep then somehow p=
lace my geophone there.



Otherwise I would isolate the geophone with very good insulation and moistur=
e protection on a tripod of metal stakes driven into the base of the hole wi=
th a ceramic tile glued with liquid nails or something. Try to vibrationally=
 isolate the body of the geophone from the sides of the hole.



       You want the geophone to be in very go=
od contact with the ground.



It seems to me a proper install=
ation is not really possible for the average person.

It is too expensive.




       Do some 'vertical thinking'? Hire an a=
uger, preferably motorised, to dig a hole maybe 6ft or a bit more deep, inst=
all a plastic drain pipe already containing the seismometer with sealed ends=
.. Then backfill with slurry around the pipe? This won't get you away from su=
rface vibrations entirely, but it should help reduce the wind noise? Looking=
 at published noise data, you may need to get to over 100 m to really get aw=
ay from surface noise. That is a long way down.



    Have you eve=
r seen a geophone that is resistant to higher freq vibrations by being place=
d on a foam like material instead of hard ground ?




       No. You don't usually bother. You rely=
 on a fairly linear axial sensor response, a low cross response and electron=
ic low pass filters. I suspect that you would have problems getting full ver=
tical sensitivity just over the range that you want. And it would need to be=
 fairly independant of temperature effects.



    Such a thing=
 might if it can be adjusted right might reduce higher freq noise without af=
fecting the range we desire to look at ?




    I don't know when / where this has been a problem? Have=20=
you had problems of this sort?



    Sort of lik=
e the submarine makers isolating moving machinery from the hull etc...

The sound radiation is reduced but the item / machinery still travels with t=
he sub whose motions are relatively slower then the vibrations.
=




       But in a submarine you want to isolate=20=
all vibrations, not just selectively the high frequency ones. Building high=20=
performance mechanical low pass filters might not be too easy?



       Regards,



       Chris Chapman