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 FYI, that page badly out of date.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
>
>
>
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>
>
> "Microphones are not ears,
> Loudspeakers are not birds,
> A listening room is not nature."
> Klas Strandberg
> Yahoo! Groups Links
>
>
>
>
>=20
>
>
>
>
=09=09
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