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the tweeter's output at low frequencies in the listening window and decreases its out-
put in the off-axis response. That's a much closer match to the directivity of the woofer,
which is focused into the listening window in the crossover region. The crossover region
is also indicated in dark green in the frequency response plot in Figure 9.
dBSPL
20
15
10
5
0
-5
Sound Directed Into
-10
Window
-15
-20
20 Hz
50
100
200
Figure 9. The waveguide provides a smooth and gradual increase in tweeter directivity in the
crossover region and a reduction in tweeter directivity at higher frequencies.
At higher frequencies, the waveguide's gentle curve (indicated in orange in Figure 9)
spreads the sound over all the angles, increasing the high-frequency content of the
off-axis response and decreasing it in the listening window. This region is also indicated
in light green in the frequency response plot in Figure 9. Essentially, the directivity of
the waveguide is the inverse of the tweeter's directivity, and the combination of the two
provides nearly constant directivity over the tweeter's range above the crossover. At the
highest frequencies (to the right of the orange region), the waveguide has no effect
because the dispersion pattern is narrower than the waveguide.
THE CROSSOVER: MORE THAN A DIVIDING NETWORK
The crossover included in GTi competition speaker systems is more than a set of
simple filters. The filter frequencies, slopes and Q values are carefully chosen to
provide a phase-aligned transition between woofer and tweeter with optimally
flat frequency response at the design axis and throughout the listening window.
Additionally, the tweeter's high-pass filter circuit includes a level control and
frequency contour to optimize the system's response when the waveguide is used
or when the tweeter is conventionally mounted.
Capacitor, inductor and resistor types have been selected to minimize distortion
and maximize power handling. Air-core coils minimize saturation, which can cause
distortion at high input power. Low-loss, low-ESR polypropylene capacitors provide
crystal-clear high frequencies, while wire-wound precision resistors with integral
heatsink ensure filter stability at high input power.
Finally, for systems that will include a separate amplifier channel for each speaker, the
GTi competition system crossover includes bi-amp capability. For instructions in setting
up the crossover for bi-amp systems, see "Adjusting the Crossover" on page 11.
Figure 11.
Tweeter Without Waveguide
Directivity Index
Tweeter With Waveguide
Sound Directed
Into Free Space
Sound Spread
Into Free Space
500
1K
2K
5K
Bi-Amp Capable
Air Core Coils
Into Window
Figure 10.
Sound Spread
Tweeter Level Adjustment
0dB (Reference)
10K
20K
Figure 12.
Wire-Wound
Polypropylene
Precision Resistors
Caps
With Integral Heatsink
+1.5dB
–1.5dB
1K
2K
5K
10K
Tweeter Level
Frequency
Adjustment
Contour
Frequency
Contour
20K
9
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