JBL 560GTI, 660GTI manual Air Core Coils, Directivity Index

		Wire-Wound
	Polypropylene	Precision Resistors
Air Core Coils	Caps	With Integral Heatsink

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.

Directivity Index

Tweeter Without Waveguide Tweeter With Waveguide

20	dBSPL
15										ENGLISH
5
10
									Sound Directed
									Into Window
										Figure 10.
0
									Sound Spread
-5									Into Free Space
										Tweeter Level Adjustment
							Sound Spread
-10				Sound Directed Into			Into Free Space			+1.5dB
				Window
-15										0dB (Reference)
-20										–1.5dB
	20 Hz	50	100	200	500	1K	2K	5K	10K	20K

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.						Frequency
						Contour
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
	1K	2K	5K	10K	20K
provides nearly constant directivity over the tweeter’s range above the crossover. At the	Figure 12.
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. Bi-Amp Capable Tweeter Level Frequency

Adjustment Contour 9