Crown PZM-10 Application Manual page 15

rejection. Many vendors can heat and shape the plastic
according to your specifications. They use their own ad-
hesives which are usually proprietary.
Cyanoacrylate adhesive ("Super Glue") or RTV
("Sealastic") have worked well in some instances. Or you
can join several pieces of plastic with metal brackets,
bolts and nuts.
If you intend to hang or "fly" the boundary assembly,
drill holes in the plastic for tying nylon line. To prevent
cracks in the plastic, use ceramic drill bits or start with
small drill-bit sizes and work up. You may want to paint
the boundary edges flat black to make them less visible.
When making a multi-boundary assembly, be sure to
mount the PZM mic capsule as close as possible to the
junction of the boundaries. Let the tip of the cantilever
touch the plastic, but leave the usual gap under the mic
capsule.
NOTE: Some older PZMs include a small block of foam
under the mic capsule for acoustical adjustment. If your
PZM has this foam block, trap it under the mic capsule
before screwing the PZM cantilever to the boundary.
The PZM model used for multi-boundary assemblies is
the PZM-6D. When drilling the screw holes for the can-
tilever, make them 5/32" diameter, .563" center-to-cen-
ter, and countersunk .250" x 90°.
2-Foot-Square Flat Panel
This boundary (Fig. 25) is most often used for direc-
tional pickup of solo instruments, choirs, orchestras,
and bands. Two PZMs back-to-back on a panel form a
"bipolar" PZM for coincident stereo. Place the assembly
about 14 feet above the stage floor.
Fig. 25 – A two-foot square flat panel
For near-coincident stereo miking, place two panels
with edges touching to form a "V" (Fig. 10). Aim the
point of the "V" at the sound source. Mount a PZM
about 4" off-center on each panel, toward the point of
the "V" for better stereo imaging. This assembly pro-
vides a higher direct-to-reverb imaging. This assembly
provides a higher direct-to-reverb ratio (a closer per-
spective) than the bipolar PZM mentioned above. It also
rejects sounds approaching the rear of the panels.
The frequency response of a flat panel is the smoothest
of all the boundary assemblies in this booklet. For a 2-
foot square panel, there is a 10-dB rise above the low-
frequency shelf at 497 Hz for direct sound at normal in-
cidence (Fig. 23). F
-6
The polar pattern is omnidirectional at low frequencies,
supercardioid at mid frequencies, and hemispherical at
high frequencies (see Fig. 26).
Fig. 26 – Polar response of a 2 foot-square boundary.
Random Energy Efficiency = –3 dB at high frequencies.
The assembly has 3 dB less reverb pickup than an omni-
directional microphone in open space at the same dis-
tance.
Distance factor =1.41. That is, the microphone/panel
can be placed 1.41. times as far from the source as an
omnidirectional microphone for the same direct-to-
reverb ratio.
PZM-2
This model uses two panels at right angles to each other.
One of the panels is placed on a large flat surface such as
a table or floor.
One configuration uses a 1'x2' vertical panel. When this
vertical panel is placed on a horizontal surface, the verti-
cal panel is "reflected" in the horizontal surface. The
panel and its reflection appear to be a 2'x2' panel with a
94-Hz shelving frequency.
Random Energy Efficiency =–6 dB. The assembly has
6 dB less reverb pickup than an omnidirectional mic in
open space as the same distance.
13
=94 Hz.
Fig. 27 – PZM-2