JBL Synthesis Everest DD67000 - Manual (Page 11)

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JBL’s proprietary diamond-pattern surround is utilized to maintain
proper control and tuning of the diaphragm’s second 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.
045Be-1 And 045mg uLTrAhigh-Frequency
compression driver And Bi-rAdiAL
® horn
Like the original 045Be used in the Everest DD66000, the 045Be-
1 used in the Everest DD67000 incorporates a 1-inch (25mm)
beryllium diaphragm and 2-inch (50mm) neodymium magnetic
structure. The pure-beryllium diaphragm is less than 0.04mm
thick and has a mass of only 0.1 gram. The single-layer aluminum-
ribbon voice coil is wound without a former and is attached
directly to the diaphragm. This driver employs the smallest
annular-slit phasing plug that JBL has ever designed. The 045Be-
1 has been re-designed to improve manufacturing efficiency and
consistency. Small changes have been made to the top plate and
some significant improvements were made to the surround shape
and clamping methodology. As a result, the driver’s output above
30kHz has been increased by nearly 5dB.
Newly created for Everest DD65000, the 045Mg incorporates
a very high purity magnesium diaphragm – the same material
used on the 476Mg. This material was selected to maintain
acoustic consistency between the high-frequency and ultra-high-
frequency drivers. Also new to the 045 family is a new precision
cast magnesium phasing plug. Compared with the plastic phasing
plug used in the previous design, this new magnesium phasing
plug offers improved stiffness and better ability to wick heat away
from the voice-coil/diaphragm assembly. The extremely low
mass of the moving system combined with the high magnetic flux
density and high rigidity of diaphragms produces response that is
very smooth from below 8kHz to beyond 50kHz in the DD65000,
and beyond 60kHz in the DD67000.
The response curve has a slight downhill tilt, due to the constant-
directivity nature of the horn used in this system. The Bi-Radial
®
horn used with the 045-series driver is properly scaled to maintain
a coverage angle of 60 degrees in the horizontal plane and 30
degrees in the vertical plane over the frequency interval from
10kHz to 50kHz.
inTernAL crossover neTwork
The circuit topology, combined with the acoustic behavior of the
1501-series and 476-series transducers, provides a 24dB-per-
octave transition at 750Hz in the DD65000 and at 850Hz in the
DD67000. This is the primary crossover point of the system.
Additionally, the 045-series transducer is active above 20kHz to
provide extended response to beyond 50kHz in the DD65000,
and beyond 60kHz in the DD67000. A second 1501AL woofer
is active from below 30Hz to around 150Hz, at which point it is
gently rolled off at 6dB per octave. The design intent is to use both
woofers in the bass frequencies and slowly transition to a single
woofer in the midrange. This technique allows a primary crossover
point between just two drivers and permits proper control of the
system’s directivity pattern, while providing tremendous power
and air movement capabilities at the lower frequencies. As a
result, the speed and power of the Project Everest systems are
unmatched from the lowest to the highest frequencies.
All of the electrical components are of the highest quality and exhibit
the lowest internal loss. Air core inductors are incorporated to avoid
nonlinear hysteresis effects. Capacitors are constructed using
polypropylene foil, which is known for having minimal distortion
caused by dielectric absorption nonlinearities. The mid-, high- and
ultrahigh-frequency networks employ DC voltage bias to operate
the capacitors effectively in a Class A mode. Every attempt is made
to present as smooth a system impedance as possible to the
driving amplifier. This design element is often overlooked in many
loudspeaker systems, yet amplifiers work their best when they are
given a smooth, level load impedance in which to deliver current.
The aggregate of these attributes allows the DD65000 and
DD67000 systems to translate the electrical signal from source
material into an accurate and unencumbered three-dimensional
sound field. These systems can do this at any desired listening
level, from whisper-quiet to big-band loud, while at the same time
maintaining unchanged acoustic characteristics.
045-Series Compression Driver Section View
surround
back Plate/
Driver exit
gold-Plated
input terminals
Die-cast
aluminum-alloy
back cover
1" edge-Wound
aluminum voice-coil
1" Diaphragm
magnesium
Phase Plug
stainless-steel
mounting bracket
top Plate
neodymium magnet
20Hz 50 100 200 500 1k 2k 5k 10k 20k
Ohm
0
5
10
15
20
25
30
35
40
45
50
Impedance vs Freq
DD65000 System Impedance