I am not responding right away because I have to digest this info
from Sten a bit.
I am taken back a bit with it and need to recompute as it would be
said. It appears that my ears have lied to me where they have served
me well in the past.
Marty M. from our group and whos work was posted here does need to be
noted as taking the stereo image with parabolics beyond what either
Sten or Randy has done. The simple fact that there is one focal point
for one point in infinity yet still being other focal points for
other points in infinity is a very important concept. It is a tool I
do not wish to be without. The same principal needs to be worked on
for an array for a stereo noise cancelling parabolic. It that has
great potential.
But for now I need to read and re-read the presentation and play with
it in the field to confirm what I have used as a guide in the past is
wrong and determine why in my own head and get a proper perspective.
Rich
--- In "Randolph S. Little"
<> wrote:
> NatureRecordists,
>
> Sorry for being slow to respond to Rich Peet's invitation to join
this thread, but I have been rather pre-occupied with publication of
my new book on the history of the Cornell Laboratory of Ornithology,
For The Birds, (URL: http://RSL.HOME.ATT.NET) and am about to head to
Florida for a week.
>
> Rich refers to my "Acoustic Properties of Parabolic Reflectors"
thesis at Cornell's School of Electrical Engineering. Unfortunately,
it is even harder to get than Sten's paper (Sten cites it), so
perhaps I could be coerced into transcribing it and posting it on my
website some day. In the meantime let me offer one all-important
point about all of these theoretical analyses, at least all that I
know of to date. And this I have discussed with Sten who also agrees.
>
> Key point:
> Whereas the mathematical analyses attempt to predict the
acoustic pressure at the focal POINT, the actual microphones that we
use to transduce this acoustic pressure into an electrical signal are
sensing the mean acoustic pressure over some finite area
approximating that of the diaphragm.
>
> Thus, the net acoustic pressure over a certain focal area (I have
previously called this "focal volume") is what counts, and this does
NOT increase monotonically with frequency. In fact, it levels off
for wavelengths shorter than the diameter of the microphone.
>
> So, if there are any hot-shot mathematicians among you who would
deign to include finite microphone size in the theoretical analysis,
Sten and I would both welcome your contribution.
>
> Good recording,
> Randy
> -----
> Randolph S. Little <>
> 111 Berkeley Circle, Basking Ridge, NJ 07920-2009
> Phone: (908)221-9173 Fax: (908)630-0871
>
> [Non-text portions of this message have been removed]
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>From Tue Mar 8 18:27:06 2005
Message: 4
Date: Sun, 22 Feb 2004 11:50:12 -0500
From: Walter Knapp <>
Subject: Re: parabolic alternatives
From: "thorley_tom" <>
> I have not been following thread so forgive me if you have already discus=
ed it
> but there is one microphone that will do just as you ask. The Audio Techn=
ica
> AT-895 RK, developed for the Sydney Olympics it has better off axis rejec=
tion
> than any commercial parabola that I know of and unlike parabolas is broad=
> frequency. Walter I am sure you have investigated this mic and rejected i=
t for
> it's downfall - very high self-noise but I have used it in conjunction wi=
th Cedar
> audio noise removal systems (I have a mate who works in the Sony masterin=
g
> departement) and the noise is very stable and hence you can get very good=
> results this way.
You are talking one huge hunk of change. The mic itself lists just under
$3000, though that does include a full windscreen. The the Cedar system
is not exactly chicken feed either.
Note also it's frequency response 60-12,000. That would not be a
problem with frogs, but might be with a few birds.
Yes, I was not happy with it's self noise. If one turns up priced
appropriately for it's specs on ebay I'd probably buy it. But that's a
huge lot less than it's price. At it's core this is a fairly low end mic
oriented toward voice. The idea looks promising, and as you say, I'd
looked at it already.
The real test is if it can fully reject a busy highway nearby, or
airplane noise. Partial rejection I have.
It's more a shotgun mic replacement. Not near the gain of a parabolic.
So, it might work in place of a parabolic up close, but unlikely if the
subject is far and not all that loud. That self noise would really get you.
If you want to dream, think about a Sennheiser MKH version of this. Say,
based on a MKH60 core and using MKH80 capsules for the side mics. Hugely
expensive, but that would be a killer. That's the first thing I thought
about when looking at the AT895.
The other way is to baffle a parabolic. Pretty bulky, but might work if
done well enough.
Note the Telinga is directional all the way down to it's gain limit.
Just not enough off axis rejection. Even with the dual science mic. I
have some ideas about experimenting with a baffle on it. I need the gain.
Walt
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>From Tue Mar 8 18:27:06 2005
Message: 5
Date: Sun, 22 Feb 2004 12:05:18 -0500
From: Walter Knapp <>
Subject: Re: non-professional setup
From: Rob Danielson <>
> I too noted that that the manuf's specs for the AT835 were better
> than the ECM-44's [32 dB(A) self noise and 10 mV/Pa sensitivity]. We
> bought one to try and I did a left/right channel comparison between
> the AT835 and the Sony ECM-44 and the AT835 had much more noise, very
> evidently, grungy, full bandwidth. I sent it back. Its possible I
> could have gotten a lemon but I'm suspicious of AT's specs based on
> some of their other mics I tried too.=20
I've never been much of a Audio Technica fan. But, I have heard some
ambiance recordings and small group acoustic music from this Sound
Professionals design that sure indicated to me the specs were pretty
good. Not really quiet ambiance, mind you, but I'd not expect any of
these mics to do that well.
The AT specs are right in with the rest of the mics in this class. So I
don't think they are fudging them. Though if their quality control is
not up to snuff that's another problem.
If you don't like AT, you can go with Core Sound's DPA based ones. Six
times the price, same specs. Same tiny size. No interchangeable capsules.
Walt
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