Don't most mics, regardless of polar pattern,
become nearly omni-directional in response to the
lowest 3-4 octaves?
Curious if you might have time to elaborate on this,..
>so just at the point where the six db boost due to the boundary
>effect starts to disappear, the microphone is sampling
>a much larger sound space.
Thanks,
Rob D.
=3D =3D =3D=3D
At 8:33 AM -0800 11/5/05, umashankar wrote:
>a microphone on a boundary does not necessarily
>accentuate low frequencies. a small boundary in fact
>works as a very effective low cut filter (i have often
>used microphones mounted on six inch boundaries for
>dialogue).
>
>what happens is actually quite interesting. there is a
>transition frequency (i think it the wavelength in
>question is six times or five times the dimensions of
>the boundary) where the boundary no longer works. the
>microphone then becomes omnidirection. before the
>transition the pick up is a hemisphere. so just at the
>point where the six db boost due to the boundary
>effect starts to disappear, the microphone is sampling
>a much larger sound space.
>
>umashankar
>--- Curt Olson <> wrote:
>
>> Rob Danielson wrote:
>> >
>> >>> ... Curt Olson has some great wooden
>> wedge/boundary designs
>> >>> http://www.trackseventeen.com/mic_arrays/ which
>> could probably be
>> >>> modified/made out of lighter materials.
>>
>> I replied:
>>
>> >> FYI, that page badly out of date. Soon after
>> posting it in May, I
>> >> realized that the wedge/boundary array at the
>> bottom of the page was
>> >> giving me too much bass response,
>>
>> Dan Dugan added:
>>
>> > Were they omni mics mounted in the boards? I'm
>> curious about the
>> > nature of "too much bass response."
>>
>> 183s flush-mounted through 1/2" holes in 1x6 pine
>> stock, thus
>> incorporating the capsules into a boundary. My
>> seat-of-the-pants
>> observation is that this seems to accentuate the the
>> already-ample low
>> end of the 183s. I believe mic theory would predict
>> this too, if I
>> understand correctly.
>>
>> I'll continue beyond the scope of your question. The
>> reason for the
>> boundaries is that in my experience, spaced omnis
>> can give terrific
>> stereo imaging in an enclosed space with a specific
>> targeted sound
>> source, such as a choir or orchestra. But for
>> outdoor ambience, phase
>> interaction between the mics makes imaging a mess
>> and destroys mono
>> compatibility every time. (I'm talking about close
>> spacing here -- say
>> 4" - 9" -- that someone can easily carry in the
>> field, not wide
>> spacing.) But when the mics are incorporated into
>> boundary, this phase
>> interaction at close distances seems to be virtually
>> eliminated while
>> the distinct and desirable omni characteristics seem
>> to be preserved --
>> with a little low-end boost thrown in.
>>
>> I've focused most of my tinkering on learning the
>> effects of boundary,
>> size, shape, material, spacing, angles, and
>> positioning of the mics
>> relative to the edges of the boundary. The idea is
>> to end up with a
>> nice stereo spread that is spacious and also
>> accurate as to sound
>> source vectoring. I suppose I could go buy a SASS
>> and be done with it,
>> but that would spoil all the fun!
>>
>> Incidentally, Dan, I appreciated your PDF about the
>> mic vest. You
>> showed us a photo of it a long time ago, and I've
>> thought about if
>> often since. I'm still resisting a strong urge to
>> start down that road
>> too...
>>
>> Curt Olson
>>
>>
>>
>> ------------------------ Yahoo! Groups Sponsor
>>
>>
>> "Microphones are not ears,
>> Loudspeakers are not birds,
>> A listening room is not nature."
>> Klas Strandberg
>> Yahoo! Groups Links
>>
>>
>>
>>
>>=A0
>>
>>
>>
>>
>
>
>
>
>__________________________________
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>
>
>"Microphones are not ears,
>Loudspeakers are not birds,
>A listening room is not nature."
>Klas Strandberg
>Yahoo! Groups Links
>
>
>
>
--
Rob Danielson
Film Department
University of Wisconsin-Milwaukee
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