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Re: Making a parabola

Subject: Re: Making a parabola
From: "NordicNature" nordicsounds
Date: Thu Sep 20, 2012 2:41 am ((PDT))
Hi Martin!
I just have to ask one thing.
Did you intend to buy a parabola just for recording one single specie of bi=
If you are going to record more bird species I still think a parabola is th=
e best choice. 95% of the time it's a great tool for recording bird species=
. The cormorant also have other sounds that are higher than 400hz so those =
will get a little higher gain, but that's often not a problem because lower=
 frequencies travel further so it will probably end up nice. If the sounds =
are very weak you need a low noise microphone and a recorder with good spec=
s that doesn't add noise.

I don't know what you believe, but a few people I have talked to that wante=
d to record bird species, read around on internet and then thinks that para=
bolas can't record below 1000hz AT ALL... but they do... yes, you don't get=
 the same gain like with the higher frequecies, but it still works.

The same goes for the frequency range of a microphone.
Some people think that if the specs is 100-18000hz it can't record anything=
 below or above that range...
It's like one of my microphones that have specs that goes to 17000hz, but I=
 still record bats at 60000hz with it... yes, there is probably better micr=
ophones for recording bats, but it works.

The best thing of course would be if you could compare gunmics with a parab=
ola side by side and then make your choice.

/H=C3=A5kan O.

--- In  "MARTIN" <> wrot=
> Hi David,
> Thanks for your interesting and detailed reply - it looks like parabolas =
are not the solution for my cormorant colony. The best results I've had so =
far are with a pair of Sennheiser ME 66s spaced about 20 cm apart and angle=
d at about 60 degrees. Although it's a very quiet site, there is not enough=
 signal for a really good recording. Would the 815T's be that much better a=
nd if so what do you need to power them?
> Best wishes,
> Martin
> --- In  "Avocet" <brini@> wrote:
> >
> > > I'd like a large enough parabola to successfully record cormorants
> > > nesting on a tall cliff not far from me here in north Wales. The
> > > cormorants have quite low frequency calls starting at about 400Hz.
> >
> > Martin,
> >
> > The frequency response of a parabolic mic rig is very complex, but
> > there are some "bare bones" guidelines.
> >
> > You need a number of wavelengths to get anything like a focus and
> > directional amplification. As a rough guide, the wavelength at 1Khz is
> > 340mm or about two wavelengths for a dish diameter of 700mm. You won't
> > get much focussing at this frequency, or much gain.
> >
> > Another factor is direct mic pickup mixing with reflected pickup on
> > the mic at the focus. This will cancel out when the 700/4 focal length
> > equals half a wavelength, theoretically 1Khz, but other factors can
> > move this null point. Using a cardioid mic reduces this effect, but
> > cardioids are designed for free air, not a messy reflection pattern.
> > The bottom line is that you will get a comb filter response rising in
> > sensitivity with frequency becoming very directional in the higher
> > kHz.
> >
> > > Any ideas as to how large a dish I'd need?
> >
> > At 400Hz, several metres wide. :-)
> >
> > A more sensible suggestion would be to use a long gun mic in a blimp.
> > I bought as couple of old beaten up but working MKH 815 T's for under
> > =EF=BF=BD100 recently, but T powered mics are good value for money as m=
> > recordists are now using phantom power.
> > See eBay Item number: 300777364229
> > Search for Sennheiser MKH-815
> >
> > Unfortunately, your cormorants are a bit too far away and I'm a bit
> > lame, or I'd be up there with my stuff.
> >
> > David
> >
> > David Brinicombe
> > North Devon, UK
> > Cogito cogito ergo cogito sum - Ambrose Bierce
> >

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