Posted by: "Mark R."
>>>The clipping problem I had was on thunder that was a bit further away an=
d
>
> far below the
>
>>>level of distortion according to my 722 meters. That's what confounds me
>
> and makes me
>
>>>wonder if it's a mic overload issue.
>
>
>
> it wouldn't surprise me at all if the mic's frequency range wasn't being
> compromised during those far off rumbles. the energy that these storms
> display with these low rumbles is staggering. BTW i would love to hear wh=
at
> you recorded... can you post them?
The rumbles extend way down into the infrasound. The highest energy is
infrasound, not audible. You don't hear the infrasound, but more feel
it. The mic definitely gets the force on it's diaphragm.
I know the SASS/MKH-110 handles this rumble far better than the
SASS/MKH-20 (the MKH-20 still does a good job). The MKH-110's are
designed with a range that extends down to 1Hz. They cleanly reproduce
the infrasound down to that whereas many mics mess up with a heavy load
of infrasound. In doing so they don't pass on a high overload spike to
the pre, but act as a non distorting limiter, or it could be some built
in limiting in the Portadisc which is only rated to 15Hz. They are also
designed for handling pretty high sound levels in general as they were
designed originally for high levels of sound from machinery under test.
The capsule vent on the MKH-110 is hair thin and probably limits
diaphragm movement from the shock waves of the infrasound. Sennheiser
once gave a talk on how this mic was designed and pointed out the vent
was a critical design component. Unfortunately I've never found a copy
of that talk.
I'd expect the VP88 is being overloaded by the infrasound. It's not
designed for really high levels anyway, and probably even less so in the
infrasound. Mic overload like this will not show up as characteristic
clipped waveforms. The mic simply cannot process the high sound
pressures accurately and limits out in it's output with distortions that
are often similar to wind gusts. You need a mic that's capable of
smoothly handling high levels of infrasound. The MKH-110 is good, but
it's also a 40+ year old mic and hard to come by one in good condition.
There are some newer mics used for infrasound recording that should be
tried.
With any mic a good deal of wind protection may also moderate the
highest infrasound pressure. Breaks up the shock wave front a little.
Walt
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