Recording - October 2016 - 42

B Y PA U L V N U K J R .

The TG D71c is a brand new boundary-style microphone from
beyerdynamic. Boundary mics, often called called PZM (Pressure
Zone Mic, which is a trademark of Crown), are used on conference desks, podiums, in stage productions with actors and
dancers, are bolted to the lids of pianos, hung on walls behind
drum kits, stuffed inside drums, and much more. Many are built
with certain sources in mind; this is the case with the new beyerdynamic TG D71c. It's designed for use in kick drum, cajon, and
piano.
On the boundary
Just what is a boundary mic? It starts with a small electret-style
condenser capsule mounted to or suspended just above a flat
plate, often made of brass. This is then placed on a flat surface,
where said flat surface aids in sound capture, especially in low
end response. It's much like a soundboard in an acoustic instrument like a piano.
While most boundary mics are designed with perforated metal
mesh and screening around the entire top surface of the mic, they
are actually front-address designs. The mic's capsule is aimed out
at the surface it is mounted on. This creates a halved polar pattern
where the boundary cuts off the other half. This can be a half-omni;
you can picture a hemispherical dome pattern above the mic. In
the case of the TG D71c, it is a half-cardioid pattern. Picture a halfheart-shaped pattern emanating above and around the mic and
offering fantastic feedback rejection.

beyerdynamic TG D71c Condenser Boundary Microphone
A great example of an often-overlooked style of mic
TG D71c: specs and sound
The TG D71c measures 35/8" x 33/8" x 1" and can fit in the
palm of your hand. It has a nice solid mass and weighs just under
a pound. The top of the mic is arched and the body is perforated
on the top and front. The XLR input is on the rear, along with a red
LED light that indicates phantom power.
As mentioned above, it uses a pressure-gradient back electret
condenser element with a half-cardioid pattern. It has a 25 Hz-
20 kHz frequency response, an open circuit voltage of 1.5 mV/Pa,
an impedance under 200 Ω, a huge maximum SPL of 148 dB (@
1% THD at 1 kHz), and a 63 dBA RMS signal-to-noise ratio.
Its frequency response plot has a gentle low end boost of roughly 1 dB from 30 Hz to 400 Hz. It's flat from 400 Hz to 1 kHz and
then has a large (11 dB!) rise from 1.25 kHz up to and peaking at
6 kHz. The frequency response then drops by a few dB with a gentle downslope to 20 kHz, broken only by a slight dip at 18 kHz.
The factory frequency response plot also shows an enormous bass
boost-up to 16 dB at 40 to 60 Hz-due to proximity effect.
Because of the broad high-end peak, this can be perceived more
as a dip in the mids than a bass/treble boost.
Because this mic is so unique, it is hard to describe its sound outside of its intended uses, but overall I found it to be detailed and
open... and nowhere near as bright as its frequency plot would
lead you to believe. It also has a nice firm low-end capture.
42

RECORDING OCTOBER 2016

In use: kick, cajon, piano, and room
I have long enjoyed using boundary mics on kick drums.
Placing one inside the kick drum is a very fast and effortless
way to mic the drum, letting the engineer arrive at a usable
kick sound quickly. Because it is not as prone to variations
due to changes in placement, you get a very natural round
tone with a great balanced beater sound. Inside the drum, it
is not very low-end heavy or boomy in its natural state,
Table of Contents for the Digital Edition of Recording - October 2016
