At 8:11 AM -0600 11/5/05, 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 FYI, that page badly out of date.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.
When I look at the spectral displays of field recordings made with a
range of different mics, they all reveal that a very, very high
percentage of the total sonic energy in our environments is below 300
Hz-- even in remote areas in the middle of the night. Very low
frequencies are powerful and travel great distance and our powerful
machines generate tons of it. I can roll-off everything above 1000Hz
in a field recording and still retain 90% of the amplitude. If I use
shelf filtering to "roll-off" below 150Hz, I'll be left with 10-25%
of the sound recorded. Its traditional to "roll off." The harmonics
produced by these Hz's are lost and the ability to define the mid
range is adversely affected. Of course, the intrigue of recording,
"space" has only been considered possible for about 15-20 years.
In short, "I never met a low Hz I didn't like" -- that I couldn't
find something useful in or about. Very, very few people have
subwoofers that can reproduce this energy with smooth response, but
I'm not sure that recordists need to attenuate this energy in the
field unless its really dominate and one is interested only in the
high register info. I feel there are bound to to be gains in low Hz
tech. Perhaps mic systems that use multiple capsules similar to
bi-amplified speaker systems. But today, the topic of low Hz
representation is still largely a practice of "Bass Management."
>
>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
If it helps to make this a lower priority, you can use an M-S
processing based Stereo Image plug like Waves S-1 in post to achieve
mono compatibility when needed.
>(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'm not sure your front-facing, flush with boundary mics behave
similarly, I know that PZM boundary mics need at least 4' X 4'
collectors for full frequency response. A 12" area produces much less
low Hz. Crown lit mentions using smaller collectors for low Hz
attenuation. Likewise, the SASS collector seems too small to use as
free-standing suspended boundary mic rather than on a stage where the
floor creates a large collector. Maybe I'm totally wrong.
Feel free "roll off" my observations if you're applications dictate
different needs/solutions. Rob D.
>
>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
>
>
>
>
>"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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