Ranft, Richard wrote:
> I don't think your 20" parabola reflects sounds down to 50Hz; they mostly
> diffract around it. However, the microphone in the parabola will still pick
> up such sounds - and from all directions in the case of the omnidirectional
> Telinga mike. There may also be some directionality at 50Hz due to the
> 'shadow' effect of the parabola, but not much. Parabolas of 20" are rather
> poor for recording low frequency sounds.
> This is because the mike also receives sounds directly from the source at
> all frequencies. The parabola on its own still has a low cut off, and it
> sounds unnatural on some low-pitched sounds. I use a MKH 816 gun mike to
> record a large owl rather than my Telinga or other parabola. Sure, the owl
> sounds come over in the parabola recording, but not as well as with the
> Sennheiser. As you say, you have to get closer with a gun mike, but for me
> that's all part of the challenge of 'hunting' such sounds.
Most of the owls I've recorded have been incidental to recording frogs
at night. Before you volunteer to get close, maybe you should consider
the conditions. My "typical" recording site is from a road shoulder,
over the barbed wire fence and past the No Tresspassing sign. To go past
that sign risks gunshot, arrest, etc. I'm legal on the road edge.
Second, I'm recording frogs, typically from a wetlands, swamp, etc. The
owls are typically out somewhere the other side of the swamp. A
interesting trip in the dark. Here in Georgia slogging through the swamp
in the dark is for the truly fanatic. Ranks right up there with catfish
tickling.
I own a pair of MKH-816 shotgun mics. I like them too. Though, since
I've not worked out the stereo suspension and windscreening for the pair
I'm not using them a lot. I try to avoid mono.
Now, back to the parabola. You make it clear the parabolic reflector is
doing nothing. If that's the case, then the mic is doing it all. There
is only the mic and reflector. Now what can it do?
Well, first off most of what I record starts at 200hz or so, though
quite a bit of interfering noise goes all the way down. At a distance of
a mile, a barking treefrog's call is reduced to just the low frequency
components. All well below the 660hz cutoff that physics predicts. I
can, on numerous occasions, have picked up barking treefrogs at this
distance. Once in a while I even record them at this distance, but, they
are so faint they cannot be heard by ear at all, and on recording are
still a faint call. So, usually I use the mic to triangulate their
location. I can get the vector within a few degrees easily off that low
frequency, faint call. By moving and triangulating I can work out the
exact direction and estimate of distance. Then I can compare that with
my GPS map and my paper maps and what I can see to work out if there is
a road path to take me closer. Again, I stop periodically to verify
direction. Sometimes that mile can take several miles of driving if it's
possible at all. If I'm lucky there will be a road right past the pond
where a few of these frogs are calling. Note I'm picking up frequencies
below 660hz well, and I'm able to get a precise direction.
If the dish is not doing this, then the mic has to be. That makes it
some mic. Far more directional than a MKH-816, and super, super
sensitive. And, since it's frequency response is reasonably flat, and
there is no change in direction finding as frequencies go up, and no
breaks in response it would appear that this mic can do this for all
frequencies. If that's the case, I can throw away the dish, my mic will
be much more compact. And it will still do everything attributed to a
parabolic dish.
That is the logical extension of what you are saying. Note it does not
have to be barking treefrogs; bullfrogs, gopher frogs, etc. will do too.
Or a 50hz noise source.
Now, myself, I happen to know that the bare Telinga DAT Stereo mic
cannot pick up barking treefrogs from a mile, and that it has no
directional ability to speak of. Why, because I tried it, I don't rely
on the pronouncements of physics. Which is the same way I know for
certain what a Telinga Pro V with DAT Stereo element can really do. I
really have used this for many years, and it does what physics says it
does not.
For some 50 odd years since the first nature recordist put a mic in
front of a parabolic there has been this problem that physics predicts
it won't work. (In fact I believe that originally, when consulted
physics said it would not work for any audio frequencies) Meanwhile a
somewhat bemused nature recordist keeps right on recording. As will this
somewhat amused nature recordist. I'll trust what ends up in the
recording over any theory. Someone else can agonize over why.
And note, once you account for the change of the sound with distance,
the Telinga does a good job of recording those low sounds in the
distance. Where you can hear them by ear, what you record will sound the
same, or as close as mics can do.
Walt
________________________________________________________________________
________________________________________________________________________
|