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4. Re: mbho MBP 648 PZ

Subject: 4. Re: mbho MBP 648 PZ
From: "Dan Dugan" dandugan_1999
Date: Sat Jul 17, 2010 11:30 am ((PDT))
> <<Sure, but I question the use of the concept "zone" when the more
> useful concept is wavelength.>>
>
> Wavelength is what it truly is about, but "Pressure Zone" is
> patentable market-speak.
>
> <<Question: what is the depth of the "zone" that will not produce comb =

> filtering below 16kHz?>>
>
> That would involve math & I'd rather visit a dentist than revisit my
> college physics notes. IIRC it's around 1/8" to 1/4".
> Ever used an Electro-Voice Mic Mouse? That was boundary miking long
> before anybody thought to give it a name. Since it was intended
> primarily for voice pickup with PA systems, the fact that the capsule =

> is held perpendicular to the stage floor & about a half inch away
> probably isn't that critical. I used a lot of these for years with a
> touring tap dance ensemble & if we were losing as much high end as
> Paul's test set up showed, nobody would ever be able to say the
> rendering of clacking tap shoes on Masonite wasn't sufficiently "pure".

Thereby hangs a tale, if you will indulge me.

To clarify, in the EV Mic Mouse the mic body was parallel to the stage floo=
r so the diaphragm was perpendicular to the floor.

I made an XY stereo "mouse" by slitting and gluing together two of them, an=
d used AKG C-451E mics. I thought that would be ideal for an unobtrusive re=
cording of an -a capella- vocal group. They performed in a semicircle with =
the mic array on the floor front center.

I was chagrined to find that the recording had an awful coloration. Apparen=
tly the approximately 45-degree pickup angle and the spacing of the capsule=
 from the floor brought a cancellation notch right down into the upper voca=
l harmonics range, where it really sucked.

I think one of the reasons that we get away with crude boundary mic schemes=
 in nature recording might be that we don't have principal sources with rec=
ognizable harmonic structures--a colored bird song still sounds like a bird=
 song to us. I suggest that boundary array experimenters set up their rigs =
outdoors, listen to just one channel on both ears, and walk around in front=
 of the mics with a speaker playing broad-band noise. If as you move you he=
ar "swishing" effects, you have a comb filter problem.

-Dan





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