JBL DD66000 - Manual (Page 12)

A high purity copper sleeve is used for the pole piece. This greatly
improves the electrical conductivity of the copper sleeve for lower coil
inductance and thus greater high frequency output at 15 kHz and above.
The copper sleeved pole quickly wicks away heat generated by the coil and
contributes in reduction of dynamic power compression. To compensate
for the higher reluctance gap caused by the use of a copper sleeved pole
piece, large magnet area was used in conjunction with special high-grade
and high-temperature grade Neodymium.
The Phasing plug is of JBL’s traditional Rapid Flare, Coherent Wave 4-slot
design. This Coherent Wave design shapes the wave output producing a
truly coincident wave front as the sound enters the 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 proprietary integrated JBL diamond 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 against 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 about 5 times that of Aluminum, M agnesium,
Titanium, and Iron. This enables to maintain pistonic behavior up to
20,000Hz, eliminate diaphragm modal breakup and keep the upper
frequency response very smooth with minimal distortion spikes. Compared
to the 475Nd compression driver use in JBL’s original K2 S9500 system,
this is about a 45% 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 micro dynamic nuances.
JBL’s 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.