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TCX924 Three Way Electronic Time Delayed Crossover
SECTION 1
INTRODUCTION
The TCX924 Three Way Time-Corrected Electronic
Crossover is a multi-channel electronic crossover
designed specifically for cinema use. This product
contains features not found in other products of its type.
The TCX924 contains three identical crossover channels
for the stage speakers, along with its own AC power
supply that can operate from 110-120 VAC or 220-
240VAC 50/60 Hz line voltages. Each channel has its
own adjustment for time correction of the high fre-
quency/horn driver and the low frequency woofer(s) to
align acoustically relative to the midrange speaker.
Although it is desirable to use identical stage speakers
for stereo in an auditorium, non-similar types can be
accommodated and the time correction for each
channel can be individually adjusted.
Three Way Electronic Crossover. The standard TCX924
divides an audio signal into three frequency bands: 300
Hz and lower, 300 to 2500 Hz, and 2500 Hz and higher.
Alternate "Crossover points" are available upon request
from the SMART factory. The crossover slopes are 24 dB
per octave (utilizing 4 pole active filters) to provide a
smooth blend of sounds from the low, mid and high
frequency components. The steep 24 dB slope also
provides maximum protection for the high frequency
driver during loud sound passages.
Time Correction. When a 2-way speaker reproduces a
note at (or near) the crossover frequency, both the HF
and LF speakers are working at that frequency. Be-
cause the HF driver cannot be physically aligned with
the LF woofer, the HF sound arrives at the listener’s ears
slightly behind the sound created by the LF woofer. This
creates a muddy, confused sound in the overlap fre-
quencies where misaligned pressure fronts of the
corresponding frequencies cancel each other out. For
example, if a 2.5 kHz tone is electrically delayed in
the high frequency band so that the corresponding tone
from the midrange band arrives
at the same time at the listener’s
ear, the tones combine acousti-
cally in phase and produce a
clear, transparent sound. Jumpers
have been provided in the
circuitry of the TCX924 to align
most of the common stage speakers by varying the
delay. Figure 2 shows mechanical misalignment of the
a 3 way speaker arrangement.
CD horn compensation. The
new constant directivity horns
offered by most major loud-
speaker manufacturers hold
their published dispersion
patterns very nicely. Early
design horns used in cinemas
until the early 1960’s were very
directional at higher frequen-
cies. A horn may have a 90-
degree by 40-degree pattern at
the crossover frequency, but as
the frequency tone went up, the
pattern could narrow as low as
10 degrees. You could only
hear all tones directly on-axis of
the horn.
New CD horns can hold their
pattern throughout the high
audio frequency range. Be-
cause the pattern is so wide, the
higher frequencies are spread
over a bigger and appear not to be as loud as their
lower counterparts. The TCX924 has CD horn compen-
sation built in. The smooth high frequency boost is up
12 dB at 10kHz from the Crossover frequency of 2.5
kHz. This high frequency boost is valuable for movie
theatres because of screen attenuation losses at high
frequencies. Equalization is easier and smoother with
the CD horn correction added.
SECTION 2
INSTALLATION
Mount the TCX924 in the equipment rack where it is in
proximity to the power amplifiers. An ideal location is
where the TCX924 output leads can easily reach the
Figure 1. The TCX924 Front panel with Security Cover removed.
8“
6“
Figure 2. Acoustically
unaligned 3 way speaker
system.
