Dear Richard Ranft,
Thanks for useful information.
Pratap Singh
On Mon, 17 Feb 2003 Ranft, Richard wrote :
>Dear Pratap
>
>The relationship between sound wavelength and parabola diameter
>is probably
>more important than parabola focal length, in that parabolas
>simply won't
>reflect sounds whose wavelength is greater than the parabola
>diameter. In
>effect, the parabola has a severe bass cut below a frequency
>determined by
>its diameter.
>
>wavelength =3D speed of sound divided by frequency
>
>so if the speed of sound in air is 332 m/s, to record frequencies
>above 500
>Hz you will need a parabola of diameter (332/500=3D) 0.664 metres
>(=3Dabout 26
>inches). Many owls and larger pigeons have frequencies below 500
>Hz. In
>practice, however, the larger the parabola the more unwieldy it
>is to use in
>the field, which is why many recordists settle on a 20-inch
>diameter dish
>with a bass cut off below 650 Hz. The parabola is better for
>recording the
>higher-pitched sounds especially those that are far away, and is
>more
>directional, but I use a gun mike when recording larger birds or
>mammals
>because its frequency response extends into the lower
>frequencies. Many
>times when recording in remote places I find I have taken the
>'wrong' mike
>out on a recording session and the more appropriate one I left
>back at camp!
>
>--------------------------------------------------------------------------=
--
>-------------------
>Richard Ranft
>Wildlife Section,
>The British Library Sound Archive,
>96 Euston Road,
>London NWI 2DB, UK.
>email:
>voice: +44 (0)20-7412-7402/3
>fax: +44 (0)20-7412-7441
>WWW pages with fully-searchable on-line catalogue at:
>http://www.bl.uk/nsa
>--------------------------------------------------------------------------=
--
>--------------------
>
>
> > -----Original Message-----
> > From: pratap singh
> > Sent: 16 February 2003 08:21
> > To:
> > Subject: [Nature Recordists] sound wavelengh and parabola
>size
> >
> >
> >
> > I request knowledgeable members to explain to me or direct me
>to
> > relevant website for understanding the physics of focussing
> > soundwaves using parabola and in particular the relationship
> > between sound wavelength and parabola focal lenth for good
> > focussing.
> >
> > I use an old Telinga parabolic microphone for birdsound
>recording.
> > The results are very good for high frequency sound but for
>low
> > frequency owls, pigeons etc. I do not get desired intensity.
>What
> > can be the options for me within a budget of $400 or so.
> >
> > Pratap Singh
> >
> >
> >
> > To unsubscribe from this group, send an email to:
> >
> >
> >
> >
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> >
> >
>
>
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