In theory - if the membrane stiffens, the sensitivity of the capsule
goes down. But the noise from the following electronics doesn't go
down. So relatively, the inherent noise of the microphone goes up.
But this is deep water ... how much the membrane will stiffen depends
on the material (from metal to metal plated plastics), the membrane
diameter and all other parameters.
Do you get less bat-detections when cold?
And is the question whether there are less bat's or poor microphone
performance??
This is also a question of how the bat-detector works and I am not a
specialist.
I suggest that you get in touch with Lars Pettersson. He is a friend
of mine and I can link you further if you get in touch with me privatelly.
Klas.
At 21:00 2008-06-07, you wrote:
> >
> > How far away are those bats? In theory one may think that some of
> > them drown into the increased noise level of the mic, but I
> wouldn't think so.
> >
> > Klas.
> >
>
>Klas, likely a naive question, but can you clarify whether you are
>suggesting that
>microphone noise floor actually rises when microphones are at
>-20C or whether the
>sensitivity declines as the membrane stiffens?
>====
> >Given the attenuation with distance for these small energies, don't
> >most of the ultrasound sources have to be fairly close to be
> >recorded? How far away can you record a bat call in a very quiet
> >location? Rob D.
>
>
>You've both asked one of the basic questions that people have been
>exploring for some
>years, Mostly you can't see flying bats, so you don't know from
>visual observation. There
>is a large variation in body size (3-80+ grams). More importantly,
>from the point of view
>of attenuation, species call at quite different frequencies.
>
>In western North America there are two that have most of their call
>energy in the audible
>(peak energy near 6 KHz, 8-10 KHz for the other). There are also a
>couple of species
>with most of their energy in the audible in Europe (and other
>temperate to tropical bat
>faunas as well).Eyeball maximum distance estimates from spotlighting
>and recording big
>audible frequency bats are in the 50m range. The sounds they make
>are aesthetically quite
>interesting, but some of us have to artificially drop the frequency
>to hear them.
>
>There aren't a lot of measured call intensities for bats, but values
>are around 120-135 dB
>(see
>http://en.wikisource.org/wiki/Echolocating_Bats_Cry_Out_Loud_to_Detect_Their_Prey).
>
> Modal call frequencies for most echolocating bats are in the 20-60
> KHz range, but a few
>are much higher (e.g., 160 KHz). Practical distances for
>recording the latter species are
>quite small and very dependent on frequency sensitivity of the
>microphone. From flash
>photography combined with call recording, prey detection distances
>for smaller ultrasonic
>bats are also small, perhaps only a meter or two. Echolocation for
>most bats is a short
>range system.
>
>To get more information on how far away you can record various
>species a number of
>people have assembled microphone arrays coupled to multichannel
>recording systems and
>used time of arrival to estimate 2D or 3D position of bats flying
>within the array. There are
>many challenges in this, especially when multiple bats of the same
>species are recorded
>simultaneously. I have no experience with it, but what looks like
>one of the nicest systems
>for this is produced by Raimund Specht. With this kind of system it
>would be possible to
>explore how detection distances differ with environmental
>conditions, though there is the
>problem of steep gradients in humidity, etc. near the ground.
>
>
>We have noticed that ultrasonic range condenser mics with a fritted backplate
>unfortunately begin to pop extensively as they drop through the dew
>point while mics with
>a grooved solid backplate (and different circuitry) don't generate a
>lot of noise until ice
>starts to form on the membrane. At that point some quite startling
>oscillatory artifacts are
>generated.
>
>Bill R.
>
>
>------------------------------------
>
>"While a picture is worth a thousand words, a
>sound is worth a thousand pictures." R. Murray Schafer via Bernie Krause
>Yahoo! Groups Links
>
>
>
Telinga Microphones, Botarbo,
S-748 96 Tobo, Sweden.
Phone & fax int + 295 310 01
email:
website: www.telinga.com
"While a picture is worth a thousand words, a
sound is worth a thousand pictures." R. Murray Schafer via Bernie Krause
------------------------------------------------------------------------
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/naturerecordists/
<*> Your email settings:
Digest Email | Traditional
<*> To change settings online go to:
http://groups.yahoo.com/group/naturerecordists/join
(Yahoo! ID required)
<*> To change settings via email:
<*> To unsubscribe from this group, send an email to:
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/
------------------------------------------------------------------------
|