With all the extremely capable subs being built and tested, I figured I'd share a measuring mic that I came across so that we can get accurate measurements. This is extremely capable (SPL from 50 dB to 130 dB with no ranging or preamp, frequency from the single-digits to >20 KHz +/- 3 dB with no corrections) and extremely inexpensive. The only downside? You gotta make it, but this is the DIY Forum.
Pretty much anyone familiar with a soldering iron should be able to put one of these together and have change left out of a $20, maybe even a $10, depending on what you've got sitting around.
Anyhow - I can not claim the design - that is all from Linkwitz
. This is 1/2 of the microph2.gif
from the linked page, with a 10uF capacitor substituted for the 2.2 uF to lower the low corner to ~4 Hz.
The other use of these mics? Bootleg recordings of live shows. This is known as a "battery box".
Without further ado - here is the schematic:
EDIT: This is the corrected schematic.... 4-7-2011
Pin 1 of J2 is the (+) signal to the sound card (tip of the RCA or miniplug), pin 2 is the ground (ring of the RCA or miniplug).
Panasonic WM-61A Mic Capsule, modded per Linkwitz
R1 10 KOhm resistor
R2 100 KOhm resistor
C1 10 uF/16V capacitor
9V battery clip
plug compatible with your PC Sound Card
perf board and small project box
Deluxe versions can have switches, LEDs and attenuators too
Point to point wiring worked fine on mine, notnyt made one too, and he took better pictures than I did.
Anyhow - here are the parts:
Here it what it looks like all put together with one of my plumbing-aisle wands:
Detail of the back side of the circuit board I used: