Earthquake recordings?

[Sean Conolly]

Just curious if anyone happened to be recording a take as the quake hit. It
would be interesting to look for infrasonic signals in the audio - if there
was no high-pass filter being used.

Sean

[Arny Krueger[_4_]]

"Sean Conolly" > wrote in message
...
> Just curious if anyone happened to be recording a take as the quake hit.
> It would be interesting to look for infrasonic signals in the audio - if
> there was no high-pass filter being used.


*All* professional microphones have a built-in high pass filter. For
cardioids and bipolar microphones, the back side of the diaphragm is
necessarily exposed to the atmosphere. For omnis, there has to be a vent or
the diaphragm would be damaged if you changed its elevation too much. If
you want to see the true infrasonic signals in a quake hit, you want a
siesmograph, but even they have high pass filters, just ones tuned to far
lower frequencies. Ground distance measurements by a GPS lack the high pass
filter, but their high frequency response is relatively poor.

[Scott Dorsey]

Arny Krueger > wrote:
>"Sean Conolly" > wrote in message
...
>> Just curious if anyone happened to be recording a take as the quake hit.
>> It would be interesting to look for infrasonic signals in the audio - if
>> there was no high-pass filter being used.
>
>*All* professional microphones have a built-in high pass filter. For
>cardioids and bipolar microphones, the back side of the diaphragm is
>necessarily exposed to the atmosphere. For omnis, there has to be a vent or
>the diaphragm would be damaged if you changed its elevation too much. If
>you want to see the true infrasonic signals in a quake hit, you want a
>siesmograph, but even they have high pass filters, just ones tuned to far
>lower frequencies. Ground distance measurements by a GPS lack the high pass
>filter, but their high frequency response is relatively poor.

I have used B&K lab mikes for classical recording and they have some very
interesting issues that result from the very good low frequency response.

Once had a run-through that was great but then as soon as they lit all
the candles in the hall, the air currents started pegging the meters....
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Arny Krueger[_4_]]

"Scott Dorsey" > wrote in message
...

> Arny Krueger > wrote:

>>"Sean Conolly" > wrote in message
...

>>> Just curious if anyone happened to be recording a take as the quake hit.
>>> It would be interesting to look for infrasonic signals in the audio - if
>>> there was no high-pass filter being used.

>>*All* professional microphones have a built-in high pass filter. For
>>cardioids and bipolar microphones, the back side of the diaphragm is
>>necessarily exposed to the atmosphere. For omnis, there has to be a vent
>>or
>>the diaphragm would be damaged if you changed its elevation too much. If
>>you want to see the true infrasonic signals in a quake hit, you want a
>>siesmograph, but even they have high pass filters, just ones tuned to far
>>lower frequencies. Ground distance measurements by a GPS lack the high
>>pass
>>filter, but their high frequency response is relatively poor.

> I have used B&K lab mikes for classical recording and they have some very
> interesting issues that result from the very good low frequency response.

> Once had a run-through that was great but then as soon as they lit all
> the candles in the hall, the air currents started pegging the meters....

Classic case of being careful about what you wish for, as there may be
unintended consequences once you get what you wish for.

B&K apparently invest quite a bit in the venting system that they use to
obtain that kind of LF response. I hear tell of porous ceramic plugs and the
like.

[gregz]

"Sean Conolly" > wrote:
> Just curious if anyone happened to be recording a take as the quake hit. It
> would be interesting to look for infrasonic signals in the audio - if there
> was no high-pass filter being used.
>
> Sean

I was surprised how smooth it was and something just over 1 Hz. Some light
rattling in my kitchen.

Greg