I presume you mean your SASS with the 2 MKH20??
Klas.
>
>However, I don't use my stereo parabolic mike + barrier for soundscapes
>because it doesn't sound near as good as the SASS. I only use that setup i=
n
>the parabola, when I really do want loud closeups of individual species.
>
>Lang
>
>What about having the barrier between the mics, but not extending down
>into the dish between the mics. Thus sound reflected from both sides of
>the dish would reach each mic but there would remain a separation
>between the two preventing direct crossover. For example Lang, what
>would you get if you pointed your SASS setup into the dish?
>Kevin
>
>-----Original Message-----
>From: Lang Elliott
>Sent: Friday, February 14, 2003 7:26 AM
>To:
>Subject: Re: [Nature Recordists] How parabolas do work.
>
>My ears tell me that the barrier definitely improves stereo response
>when
>using two mono mikes. To prove this, one has only to put two omni mikes
>side
>by side and listen to a broad soundfield using headphones. You will
>notice
>only a very minor stereo effect. Then slide a barrier between the mikes.
>The
>stereo effect is hugely improved.
>
>It's as simple as that.
>
>When such a mike setup is placed in the parabola, with mikes pointing
>forward, one records a nice stereo soundfield that is independent of the
>parabola. The on-axis sounds concentrated by the parabola are then added
>to
>the stereo soundfield. The result is quite pleasing.
>
>I don't think the same result could be obtained without use of the
>barrier.
>I base this on simple listening tests.
>
>Lang
>
>
>Thanks Marty, I'll give it a try.
>
>Kevin J. Colver
>114 N. Clark Lane
>Elk Ridge, UT 84651
>801-423-1810
>
>
>-----Original Message-----
>From: Marty Michener
>Sent: Thursday, February 13, 2003 2:40 PM
>To:
>Subject: [Nature Recordists] How parabolas do work.
>
>At 10:18 AM 2/13/2003 -0700, it was written:
>>I've used a similar system of 2 mono mics mounted in a parabola with a
>>barrier between. It works fairly well, however it has less magnifying
>>power than a single mic because each mic in the pair only receives the
>>amplified sound from 50% of the parabola surface area. Thus it has a
>>bit less "reach" than the single mono mic. The stereo effect is more
>>pleasing however, and you will need to get a bit closer to your sound
>>source.
>>Kevin
>
>Hello:
>
>There is absolutely no physical reason why, FOR INCOMING FOCUSED SOUND,
>one
>needs to put a barrier between two mono mics in a parabola; it just gets
>in
>the way. For non-focused background sound, the barrier will have about
>the
>same effect as in non-parabola usage, some slight contralateral damping.
>
>I don't mean to pick on anyone, here. This is a widely stated and used
>misconception. I have posted to clarify this point on at least two past
>
>occasions (see attached notes below, from this list Sept 2000).
>Parabolas
>do NOT "gather" and they do not "amplify". These words have specific
>meanings other than focusing, and apply to things and to signals, but
>not
>to waves. The focused light or sound may be brighter or dimmer than the
>
>intensity of the object itself, it depends on the ratio of object
>distance
>to image distance. In all our REAL-LIFE nature recording settings, the
>image is much brighter - louder - than the object intensity, so we can
>use
>noisier mics.
>
>Please lets be clear that a parabola is a reflecting lens. Putting a
>barrier between the mono mics is like putting a small card inside your
>SLR
>camera to keep the light from the lens that is supposed to fall on one
>spot
>from also falling on the spot next to it. The physics and the practice
>is
>nonsense. The card just cuts down the light you WANT getting to the two
>spots, making the lens effectively a larger "f-number" (smaller
>numerical
>aperture, e.g. f/8 instead of f/5.6.). This is why Kevin finds LESS
>sound
>than with ONE mic, because of the ill-conceived barrier. In principle,
>you
>could put an ARRAY of mics, like the array of light sensors in a digital
>
>camera.
>
>I even prepared a diagram of the focusing process, and privately mailed
>it
>to some folks. Placing two small mono mics two inches apart, with no
>barrier, means they gather ALL the sound from ALL the parabola, each
>from
>two divergent incoming paths. This is just like a camera. It is the
>incoming DIRECTION of the sound that determines where it will focus.
>
>Who ever dreamed up the idea of using the "sound from one half of the
>parabola" that I keep hearing. I bet it was G*** B*****, at LNS, I
>could
>never get him to understand this when I talked to him in the 80's or
>90's
>either. ;^)
>
>As with sounds to your two ears, the waves all cross in the air, they
>don't
>bounce on each other. You are holding this huge reflector out in front
>of
>you, so you want ALL the reflected sound getting to ALL your mics for
>maximum focused signal per background (non-reflected) sound.
>
>If the focal length is 20 inches, and the spacing between mics is two
>inch,
>the angle will have a tangent of 1/10, of about 6=B0. With my 48 inch
>giant
>parabola, I usually used two or three inches, depending on what I was
>recording. When you point the parabola at a pond, for instance,
>subtending
>an arc of six degrees, you point the center to the pond's middle. Then
>the
>focused sound from the left end of the pond focuses squarely on the
>right
>mic, and the right end of the pond is focused on the left mic. And the
>sound in the earphones is a really clear stereo. I have hundreds of
>really
>old cassettes of it. Good, live sounding stuff.
>
>Please, no more barriers!
>
>my best regards,
>Marty Michener
>MIST Software Associates PO Box 269, Hollis, NH 03049
>EnjoyBirds.com - Software that migrates with you.
>http://www.EnjoyBirds.com
>
>Folks:
>
>Let us be really clear about how a parabola works and how it
>may be configured to make a stereo recording.
>
>First, a parabola is mathematically not that different from
>a (transparent, biconvex refractive) lens - both do focus sound to
>a plane, with predictable aberrations from a plane as covered in
>any high school physics book under optics. We recordists use
>the reflective medium for sound because it is just about impossible*
>to make a transparent lens that is linear for sound. To do so
>you would need a predictably different sound velocity (inside the
>lens) from that in air, with a surface medium also totally
>transparent to sound, separating the two media. So we always
>use a parabola as a reflector. Under some conditions a helium
>balloon seems to act as a very non-linear sound lens.
>
>But both a refractive lens and a parabolic reflector focus
>parallel waves (in our case of sound) to a single 3D point
>in space. Parallel waves correspond to a near flat wavefront,
>that is, from a point source that is so far away that the waves
>appear to have a single arrival time in the neighborhood of the
>parabolic dish. This is like assuming for an optics lesson
>that the object is at infinity.
>
>To say that you can't focus incoming sound on two separate
>points would be like saying a camera can only take a picture
>of a single point of light. Not true. If the waves arrive from
>different directions, corresponding, let us say, to two frogs
>singing from 100 ft away are 6 ft apart, the two focus
>points will be several centimeters apart - one corresponding
>in this simple example to the left mic, the other to the right mic.
>
>NO separation device between mics is in fact needed.
>The two mics are like two nearby grains of silver halide in
>a camera film emulsion. One records the singing of the
>left frog (the mic on the right, because the image reverses)
>and the other from the other frog.
>
>The mics do not need any separation device because
>sound waves, like light waves, freely cross in space, yet
>arrive concentrated at but a single point - at least in the ideal
>case where the sound wavelength is much less than the
>dimensions of the mic and dish.
>
>I have recorded from two omni mics in the focal PLANE
>(not point) of my 48 inch (70 pound) dish, many bird and frog
>flocks and choruses. The spacing of the stereo separation of
>the sources is by the same ratio to the separation of the two
>mics as are the relative distances from the reflector. This is
>identical to the formula for magnification of an image with
>an optical lens Object size/image size =3D Object dist/Image distance.
>
>If the frogs are 6 ft apart at 100 ft distant, and the parabolic focal
>plane is 2 ft from the dish, the ratio would simply be 2/100
>or 1/50, and the 6 ft would be represented by a mic
>placement of 6/50 ft or the mics about 1.44 inches apart.
>
>. . . and he went on and on . . .
>
>and from a private note I wrote on the same subject following up to
>somebody else:
>
>I attach a diagram of how they really work. Sound waves
>bounce off (and refract around small ) solid objects. This is true,
>because the impedance to travel in a solid is so radically
>different from that of air. Waves pass by objects small
>with respect to their wavelength, like ocean waves
>wash past a post or wharf by a dock. They reflect off objects
>much larger than their wavelength, in a mirror-like manner.
>In between sizes, they bend and curve in a manner
>much harder to visualize.
>
>Sound is not "gathered" as you state. It is reflected,
>jut like light in a flashlight, sort of in reverse. Angle of
>incidence equals angle of reflection. If you simply
>place to bulbs in a flashlight, against each other, side by
>side, you would have two diverging beams of light - make
>one bulb red on the right and one green, on the left, and you
>would produce a green beam of light to the right and a red
>to the left of center. This is exactly what you do with two
>mics side by side in a parabola. No barriers, no membranes.
>
>Correction, that is what **I** have been doing with my parabolas for
>over 30 years. The analogy with a refractive lens is much better.
>
>Each lens, whether refractive or reflective focuses waves to a point.
>The location of the point only depends on the entry angle of the
>sound waves to the lens's diameter and center axis. Just like
>a camera lens, sound is focused by every parabola, regardless
>of who makes it, to a point. You are absolutely correct that this
>point is spread to a globe by the inherent diffusion factor which
>depends directly on wavelength. Longer wavelength, larger
>the globe. In photographic optics, this is actually called the
>"circle of confusion".
>
>To put a barrier in a parabola I would say is worse than useless:
>it prevents each half from providing directional sound focusing
>to each mic, so makes the sound amplification less by 3 dB
>at each mic. Why do it? I have read the explanation of
>the PZM effect, and it is all new to me, so I don't pretend to
>understand it. If what you say about it is all true, then
>you are also correct that the sound at which you aim the
>axis would be recorded mono in both mics, and the off
>axis sound would be blocked differentially to the two mics.
>I am not convinced yet that this would amount to a stereo
>recording. It would be nothing like what I am showing in
>my diagram and what I can provide you with hours of from
>my old recordings.
>
>
>To unsubscribe from this group, send an email to:
>
>
>
>
>Your use of Yahoo! Groups is subject to
>http://docs.yahoo.com/info/terms/
>
>
>
>
>To unsubscribe from this group, send an email to:
>
>
>
>
>Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service
><http://docs.yahoo.com/info/terms/> .
>
>
>
>
>[Non-text portions of this message have been removed]
>
>
>To unsubscribe from this group, send an email to:
>
>
>
>
>Your use of Yahoo! Groups is subject to
>http://docs.yahoo.com/info/terms/
>
>
>
>
>To unsubscribe from this group, send an email to:
>
>
>
>
>Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service
><http://docs.yahoo.com/info/terms/> .
>
>
>
>
>[Non-text portions of this message have been removed]
>
>
>To unsubscribe from this group, send an email to:
>
>
>
>
>Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/=
>
>
>
Telinga Microphones, Botarbo,
S-748 96 Tobo, Sweden.
Phone & fax int + 295 310 01
email:
________________________________________________________________________
________________________________________________________________________
|