problem at the source. The cone transducer’s tempo-
ral smear is corrected by precisely aligning the cone/
dustcap/surround geometry to maintain temporal
unity. The distance to the dustcap is slightly longer to
compensate for differences in material density.
The phase plug, whose geometry is matched to
the cone, then serves to leave this unity intact. Expand-
ing radial slots within a compressing frame lower the
mechanical reactance of the load facing the transducer
without modifying the directivity associated with the
source. This allows for faithful reproduction of the upper
mid-frequencies without any narrowing of beamwidth.
The wavelets (below) illustrate the difference
between old and new mid-frequency cone/phase plug
technologies. These wavelets represent data gathered at 1
meter from devices mounted in a pseudo-infinite baffle wall. The vertical axis indicates frequency, the hori-
zontal indicates time, and color indicates dB SPL with each color change indicating a 1 dB drop in level. The
first illustration represents data obtained from a conventional midrange transducer. Particular attention
should be paid to the upper midrange above 1 kHz. Note that the energy at the top of the passband centered
around 2.1 kHz is
slightly leading the
rest of the broadband
energy and also
remains considerable
after.
This difference of
microseconds is
difficult to observe
without precision
measurements, but the
phenomenon is quite
audible. The resulting
reproduction would
take a finite sonic
event (a Foley door
slam, gunshot, or footstep, for example) and reproduce it over a longer period of time than it had actually
taken. The source has been compromised and the events’ clarity and impact degraded. With the harmonics
leading and/or lagging the fundamental tone, the timbral quality of the acoustic event is lost.
The next illustration results from an identical measurement taken on a new CSC mid-range trans-
ducer. Needless to say, the temporal inconsistencies have been eliminated through the implementation of a
more logical transducer geometry.
In the end, the mid-frequency sub-system of the CSC Series exhibits the temporal clarity of a com-
pression driver alone
(as in a two-way
system) and the
natural low distortion
sonic reproduction of a
cone transducer (as in
an EAW three-way
system) while remov-
ing crossover transi-
tions from the vocal
region and maintain-
ing the spatial perfor-
mance required for
broad band constant
directivity.
Dustcap
Surround
Cone
Voice Coil
Traditional Mid Cone with Phase Plug, Side View Cutaway
Voice Coil to Surround = 6.3 inches
Voice Coil to Dustcap = 6.8 inches
Radial Slots
VA4 Phase Plug uses Radial Slots to Maintain Source Directivity
page 5
