Walt,
please do not misunderstand my postings. I really appreciate your
broad and impressive knowledge on recording techniques and your long
experience in sound recording.
However, I'm sure, that you are completely wrong at these points:
>Essential or not, there are reflections internally in a microphone
at
>ALL frequencies. For reflections to occur from any of these
surfaces
>which are tiny compared to the wavelengths, proves you absolutely
wrong
>that the vastly larger surfaces of a parabolic reflector will not
>reflect things longer wavelength than their size.
>Note that reflection in a microphone, which you do admit occurs, is
>exactly the same thing as reflection off a parabolic surface. If it
>occurs in a microphone, it definitely occurs off the much larger
surface
>of a parabolic.
I guess, that you got your impression on the directionality of the
parabola at all frequencies from the fact, that our brain is able to
restore information that got lost during the travel through air.
For instance, we can determine the pitch of a sound, that contains
harmonics (e.g. human speech) even if the signal has been high-pass
filtered with a cutoff-frequency higher than the fundamental
frequency of that sound. This effect can be heard in a telephone
speech. The transmitted bandwidth ranges from 300 to 3500 Hz only.
Male speech may have a pitch lower than 300 Hz and we can still
understand what one says (and have teh impression of a low-pitched
voice). Another example would be piano music broadcasted over a
cheap radio. Thanks to the harmonics in a piano note, we can still
determine the pitch of the note, even if the fundamental frequency
of that note is not transmitted.
I guess, that the same happens when you listen to your parabola
recordings. Because the parabola is very directional for the high-
frequency components of a sound, you may have the impression, that
the parabola is also very directional at lower frequencies (which is
not true).
As I have seen from your website, you have been recording frogs and
toads, that may have strong harmonics and can be very noisy (broad
frequency spectrum). This would explain your impressions.
Please also note, that I use parabolas too (just purchased one from
Telinga). Nobody says, that parabolas were bad. But I would not use
them for recording signals with wavelengths smaller than the dish
(because of the distortion in the frequency response curve).
Perhaps I will conduct some measurements using a sine sweep
generator, a speaker and a MKH 800 microphone both with and without
the dish. I will then post the results.
Raimund
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