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A high-purity copper sleeve is used for the polepiece. This greatly improves the
electrical conductivity of the copper sleeve for lower coil inductance and thus
greater high-frequency output at 15kHz and above. The copper-sleeved pole
quickly wicks away heat generated by the coil, thereby contributing to a
reduction in dynamic power compression. To compensate for the higher
resistance caused by the use of a copper-sleeved polepiece, a large magnet area
has been used, in conjunction with special high-grade and high-temperature-
grade neodymium.
The phasing plug is of JBL’s traditional rapid-flare, coherent-wave four-slot
design. This coherent-wave design shapes the wave output, producing a truly
coincident wave front as the sound enters the Bi-Radial horn. The diaphragm
is formed of pure beryllium foil that is manufactured with a proprietary high-
temperature and pressure-forming process. This process enables the integrated
JBL diamond-pattern surround to be formed as one piece with the dome.
Compared to other methods, forming the diaphragms out of sheets of
beryllium foil yields greater reliability and resistance to failures due to fatigue.
If breakage ever does occur, the diaphragm does not shatter into pieces or
harmful dust. Beryllium has a stiffness-to-density ratio of about five times that
of aluminum, magnesium, titanium and iron. This maintains pistonic behavior
up to 20,000Hz, eliminating diaphragm modal breakup and keeping the upper
frequency response very smooth, with minimal distortion spikes. Compared
to the 475Nd compression driver used in JBL’s original K2 S9500 system,
this is about a 45 percent reduction in moving mass. With such a low mass,
the moving assembly is able to respond even quicker to musical transients,
to further enhance detail and microdynamic nuances.
JBL’s proprietary diamond-pattern surround is utilized to maintain proper
control and tuning of the second diaphragm resonance (the surround resonance
mode). The proper control and placement of this surround resonance is critical
for good high-frequency shape, extension and level.
These features, when taken as a whole, create a new large-format compression
driver with the greatest high-frequency extension, lowest distortion, smoothest
response and greatest sonic detail.
