Recording - May 2018 - 53

the audience would have heard each
instrument twice: once through the backline, and again, delayed, through the
vocal mics and speakers. That's a perfect recipe for phase cancellation and
comb filtering, and in fact earlier
backline-plus-vocal PAs were prone
to that problem. The Wall of Sound
used high-quality measurement mics in
noise-cancelling configuration, and the
musicians were always careful to sing
into only one mic of the pair.
I never got to hear the Wall of Sound,
though I heard the Dead several times over
the years, but scuttlebutt says that vocals
always sounded weird and "phasey". I
suspect the problem was those fancy measurement mics; they were omnidirectional,
and a vocal sung into one of a noisecancelling pair could easily bleed into the
other, causing comb filtering. That's what
led me to suggest using hypercardioid mics

for noise-cancelling setups; the tight pickup pattern (and singing where the arrow
shows) would keep leakage to a minimum.
By the way, another good mic for
noise-cancelling arrays would be the
Electro-Voice RE16. It's also hypercardioid,
and was designed by Lou Burroughs,
closing the circle nicely. Burroughs had a
long and illustrious career in the mic biz,
and he was fond of the noise-cancelling
technique-during World War II, in fact,
he designed a noise-cancelling array that
greatly improved voice intelligibility for
fighter pilots who were talking against the
incredibly noisy background of a plane's
cockpit. It's nice to know that there are
more benign applications of the idea.
Paul Stamler (stamler@recordingmag.
com) is a musician, engineer, educator,
and collector of wonderful bits of audio
history, living and working in St. Louis.

If your preamp or interface doesn't have a polarity-flip switch, this easy-to-build
project will do the job. The wiring diagram is shown in Figure 5; it's really just a
mic cable that swaps the connections for XLR pins 2 and 3. In the picture, the red
line represents the mic's non-inverted output (normally pin 2), while the blue line
represents the mic's inverted output (pin 3).
The easiest way to build a Flipper is to buy a short (~12") mic cable and modify the
connections to one of the XLR plugs. (You can also build it into a barrel connector,
but I don't recommend that; if a barrel connector is plugged into a preamp/
interface, one good sideways tug can torque the socket, possibly pulling it off
its circuit board.) The tools you'll need include a soldering iron, a small set of
needlenose pliers, a jeweler's screwdriver (if your XLR connectors are made by
Switchcraft, which I find easiest to modify), and a set of Visegrip pliers.
Take one of the cable's XLR connectors apart. I recommend the female, but do
whichever is easiest for you. Heat up your soldering iron and use needle-nose pliers
to desolder the wires connected to pins 2 and 3 (see the picture for a guide), while
holding the insert in the jaws of the Visegrip. (You may want to line those jaws with
gaff tape to minimize damage.). Now swap the two wires and resolder them, routing
the one formerly attached to Pin 2 to Pin 3, and vice versa. Use a magnifier to check
your solder joints, then put the connector back together. Label both ends with a
permanent parker or engraving tool so you don't mix it up with other mic cables!
To use the Flipper, plug it into the channel you want to flip, and plug the mic
cable for that channel into the Flipper; when you want to return the mix to normal,
unplug the Flipper from the preamp/interface and the cable; plug the cable back
in without the Flipper. It's that simple, and dolphin-safe, too.-PJS
FIGURE

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RECORDING May 2018

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Table of Contents for the Digital Edition of Recording - May 2018
