JBL M9500 - Manual (Page 5)

The JBL model 475Nd compression driver used in the M9500
has a smooth titanium dome 101 millimeters in diameter that
has been lightly coated with Aquaplas™ damping compound.
Its aluminum ribbon voice coil operates in a magnetic flux field
of 1.65 tesla (16,500 gauss). Mid-band efficiency is 20%, while
at the peak value of driver impedance it is in excess of 50%.
The driver uses JBL’s Coherent Wave™ phasing plug, which
provides equalized path lengths from all sections of the
diaphragm to the driver's output. The driver is mounted on the
H9500 horn, a design used only in this system that provides
smooth loading down to 500 Hz and exhibits consistent
horizontal dispersion over its operating range.
There are two JBL model 1400Nd low-frequency transducers
in each loudspeaker system. A single 1400Nd is capable
of handling instantaneous input signals of 600 watts,
corresponding to a midband peak output of 118 dB Lp at a
distance of one meter. The transducer’s second and third
harmonic distortion have been reduced through the use of
JBL’s traditional aluminum shorting ring at the base of the pole
piece, as well as through the use of a copper shorting ring on
the top plate adjacent to the voice coil. The transducers make
use of JBL’s Vented Gap Cooling™ in which forced air,
generated by cone motion, removes heat produced by the
voice coil. Each driver is mounted in its own ported enclosure,
and the two enclosures are “stagger tuned” to provide
smoother and more extended low-frequency response.
Cutaway views of the high-frequency and low-frequency
transducers are shown in Figures 2 and 3.
Typical System Performance Measurements
The high-frequency response of the M9500 system was care-
fully established by making a series of measurements over
frontal angles of 60° in both vertical and horizontal planes. This
allows for optimal listening over a wide area. The frequency
response averaged over the 60° horizontal and vertical angles,
measured from 200 Hz to 20 kHz, is shown in Figure 4. Here,
the network High Frequency trim is set in its zero position.
The slight downward trend was incorporated, based on
extensive listening tests to contemporary pop/rock and
classical recordings.
dB
+10
0
–10
–20
–30
2 3 4 5 6 7 8 9 10 1.5 2 3 4 5 6 7 8 9
100
10 1.5 2 2 3 4 5 6 7 8 9
1000
10 1.5
10000
Relative level (dB)
Figure 4. Averaged frontal
angle response (60°,
horizontal and vertical) of
M9500 from 200 Hz to 20
kHz.
Version 9/14/95 7/27/98 2:58 PM Page 5