JBL W12GTI Supplementary Manual
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USING THE W12GTi IN SPL COMPETITION
The enclosures presented here provide maximum
SPL over a narrow range of frequencies and are
optimized for SPL competition. These designs use
a non-classical alignment in which the vented
enclosure’s resonance is carefully aligned with the
response of a sealed box of the same volume to
produce a peak in the system’s output slightly
above the tuning frequency. This peak may be as
much as 12 dB when compared to a sealed box
aligned for flat response.
Because all woofers operate as though they were
unbaffled below vented enclosure resonance
(i.e., tuning frequency) and because the tuning
frequencies of these boxes is higher those of
vented enclosures optimized for low-frequency
extension and flat response in the passband, these
woofer/enclosure combinations will not handle
rated power below resonance.
If you use these enclosures for competition and
everyday listening, you may find the sharp
response peak unsuitable when listening to music.
Try closing the vent(s) to provide an acceptable
response for music reproduction. However, do
not forget to open them for the next competition!
When you are competing (using one of these
woofer/enclosure combinations), choose a short-
duration sine wave test signal that corresponds in
frequency for the enclosure you have selected.
Be careful not to apply too much power at
frequencies more than one-half octave below the
enclosure’s tuning frequency.
ABOUT POWER COMPRESSION
For best performance in SPL competition, we
recommend minimizing the time a woofer is
played at exceedingly high input levels. As the
woofer’s voice coil heats, its dc resistance will
temporarily increase and cause the amplifier to
produce less power.
GTi woofers employ dual voice-coils, dual
ultra-long gaps, and a magnet heatsink to quickly
dissipate heat generated in the voice coil, and are
less susceptible to power compression than
ordinary woofers.
Ideally, the test signal should be very short and
repeated only after the voice coils have cooled,
as the first test will be the loudest.
NOTE: Exciting the system after the voice coil is hot will
result in lower SPL readings.
VENTED BOX VOLUME FOR 6O HZ TEST
(
INCLUDES DRIVER/PORT DISPLACEMENTS
)
VENTED
FREQUENCY RESPONSE @ 2.83 V
continued on the back...
JBL, Incorporated • 250 Crossways Park Drive • Woodbury, NY 11797 • VOICE: 516-496-3400 • FAX: 516-496-4868 • www.jbl.com
W12GTi 12" Woofer – Technical Data
W12GTi
(side view)
Port
F
b
= 55 Hz
diameter = 6.0"
length = 3.25"
V
BOX
=
2.75 ft
3
(77.88 liters)
(all sides lined with 1-inch fiberglass or fiberfill)
C
dB
105
100
95
90
85
80
75
70
65
20 Frequency 50 100 Hz 200 500 1k 2 k
60 Hz Peak