Hi Peter,
It is mounted in the dish! Now to find a subject to test it on.
John Hartog
rockscallop.org
--- In Peter Shute <> wrote:
>
> I'd be very interested to hear the results of that, John. I had similar p=
lans to Arwen when I bought my M10, but somehow the ME66 arrived first, and=
I still don't have the dish.
>
> Peter Shute
>
>
> --------------------------
> Sent using BlackBerry
>
> ________________________________
> From:
> To:
> Sent: Mon Jan 02 14:26:14 2012
> Subject: [Nature Recordists] Fuzzy Blobs
>
>
>
> Hi David,
> Thanks for elaborating, I will look forward to your sound focusing piece.
> To give a rough estimate of the capsule spacing in the PCM-M10, I have me=
asured the microphone grills at about 57mm on center. I don't use a dish ve=
ry often so this is a bit of a diversion for me, however if it would be use=
ful for anyone here, I could mount my M10 in my Telinga dish and see what h=
appens.
>
> John
>
> --- In <naturerecordists%40yahoogr=
oups.com>, "Avocet" <brini@> wrote:
> >
> > > This is the first time I have heard the term "Airy disc" used in the
> > > context of acoustics.
> >
> > John,
> >
> > The theory is identical with any wave focussing. Knowing the size of
> > the "fuzzy blob" focus area describes most of the characteristics of a
> > dish microphone and lets you work out what is happening.
> >
> > > ... in practice it will be distorted over a measurable volume of
> > > space. From my perspective this practical "focus" will likely be a
> > > non-uniform, asymmetrical blob rather than a sphere or disc.
> >
> > It is more like an apple core shape with the narrowest bit, or best
> > image, at the focus point. This is what you see when you are focussing
> > a camera lens. Bypassing the geeky explanation, the diameter of a
> > sound Airy disc is more or less the wavelength of the frequency being
> > focussed, in other words 300mm or 1 foot at 1 KHz.
> >
> > Stick a small mic in this position and you will only pick up a
> > fraction of the reflected sound, therefore the dish gain is low, but
> > at 15KHz and 20mm diameter it is about the same area as the mic
> > capsule so the gain will be high and the focus will be narrow.
> >
> > My argument with using a dish for stereo is that a parabola loses its
> > focus pattern off center, so why not use a spherical dish and at least
> > maintain the same focus at any angle?
>
> The huge wartime concrete
> > reflectors used on the English Channel coast to listen for German
> > planes were spherical.
> >
> > Point a dish at the sun - with the mic(s) removed for safety -and you
> > can see the focus patterns with a piece of paper, or at least the
> > patterns for high frequencies. A spherical dish has a ring focus which
> > can be used for positioning the mics for stereo.
> >
> > I'm writing a full length piece on sound focussing which will give
> > chapter and verse. :-(
> >
> > David
> >
> > David Brinicombe
> > North Devon, UK
> > Cogito cogito ergo cogito sum - Ambrose Bierce
> >
>
>
>
>
>
>
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