Raimund Specht wrote:
> Walt,
>
> thanks for the reply. I was afraid, that the discussion turned into
> a unpleasant emotional debate...
I hope not.
> I can not provide the complete derivation of the sound wave theory
> here. Read a textbook on technical acoustics. You will find the
> rules describing how sound travels in air (and all other stuff
> including reflection and so on). I admit, that it is difficult to
> understand these effects from viewing at single molecules.
> Nevertheless, this acoustic wave theory has proven in practice.
>
> I will do the frequency response measurements in the near future. At
> the moment I have no calibrated sound level meter. However, it
> should be possible reference all parabola measurements to the bare
> MKH 800, which came with a individual frequency response plot. This
> would compensate the bad frequency response of the speaker. I will
> use a slowly sine sweep signal played back from a laptop PC and I
> will record the microphone signal directly into the same computer.
> It would then be possible to create a frequency response plot from
> these data.
I have a pretty good modern sound meter. I wish it had the octave filter
block, but that's hugely expensive and a little hard to justify. I got
more meter for my money by buying one that's 2nd level calibrated. The
difference is primarily in that the top level has a calibration paper
trail suitable for court cases and other legal wrangling. The 2nd level
is generally the same meter calibrated just as good, but you don't get
the same piece of paper. I've also got a calibrator, which carries it's
own certification. I use it a fair amount when out recording. I'm trying
to get a handle on the dB level for each of Georgia's species. It's just
as bad to try and get a sound meter close to a frog as a regular mic,
and more essential for the measurements, so it's slow going.
You should be able to get a relative gain figure of some sort without
calibrating the input sound. You would not be controlling the variables
as much as the scientist in me expects. When I manage to get a good
portable sound source that can work the low frequencies cleanly at the
necessary volume I'll do the metered version. That can be compared to
the version in the citation.
Meanwhile I'll continue to record these things the parabolic can't
record. Several years of using the Telinga has given me a very good
working knowledge for what it can and can't do. At least as far as the
frequency range of frogs we have (200hz - 7500hz) I'm extremely familiar
with those.
Walt
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