On Dec 1, 2004, at 8:50 AM, wrote:
> Message: 10
> Date: Wed, 01 Dec 2004 12:23:39 +0100
> From: Terry King <>
> Subject: RE: MHK 800 prelim field test discussion
>
> -----------------------------------------------------
> OK, this is almost exactly what I need to do to characterize mikes I
> have,
> the Transit 24-bit interface recording to a laptop, and a preamp I will
> probably be building.
>
> I was considering building a 'foam-lined box' for this purpose. Can
> Rudy or others give some info on how you did this, size, material
> etc??
>
Nothing special, I had a foam-lined road case which had 1/4" plywood
walls covered with that "roadcase" plastic outer skin. I figured it
would do an excellent job attenuating any ultrasonic in the acoustical
environment, but is not effective at lower frequencies. I think any
sturdy foam-lined (or blanket wrapped) box would work, just remember
that as the frequency of interest drops, so to will the acoustic
isolation offered by your sound-proof box.
> Next: I have a couple of Shure 183's that I'd like to characterize.=20
> They
> have a rated output impedance of 1800 ohms, higher than I expected.=20
> Am I right that I'd need to terminate the 'other' input in 1800 ohms
> to fairly
> assess the residual noise from the preamp? Is 1800 ohms high enough
> to require a special low-noise resistor for accurate results?
I'd defer to Dan Dugan on this point. Dan?
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