JBL Project EVEREST DD66000 User Manual page 10

T
RANSDUCERS
The 1501AL Low Frequency Driver
See Figure 2
The 1501A L Low Frequency driver is very similar to the 1500A L used in the
S9800 system. It incorporates a new high impedance voice coil to allow a pair
of woofers to be used while still maintaining an 8 ohm system impedance. The
voice coil length has been increased to 30.5 mm (from 20.3 mm) and its milling
width has been reduced slightly. This was done to allow greater clearance from
the outer diameter of the coil to the laminated top plate and to provide a larger
surface area of coil surface for heat dissipation. These coil improvements allow
the 1501A L to handle up to 25% more power than the 1500A L.
Figure 2 – 1501AL section view
The 1500AL LF driver is a 380 mm diameter device with a 100 mm voice coil
completely immersed in a radial field generated by an Alnico 5DG magnet.
Alnico was chosen because of its stable operating point. This material is
insensitive to temperature changes and back EMF from the coil. JBL has
overcome the tendency of Alnico to demagnetize with high drive by utilizing a
massive shorting ring at the base of the motor assembly. The top plate is
constructed of alternating copper-steel laminations. The presence of the copper
rings linearizes the magnetic properties of the gap to all but eliminate eddy
current distortion.
The outer suspension is made of EPDM foamed rubber, which has the
longevity and frequency response characteristics of traditional rubber surrounds,
but with a low density very close to that of foam surrounds. Low loss EPDM
material was chosen so that the transient detail of musical signals could be
preserved. Dual inverted Nomex spiders are employed for the cancellation of