Manual JBL Project Everest DD67000 (page 10 of 26) (English)

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The 1501AL-1 employs a pure pulp straight sided cone body

attached to an outer suspension made of special foamed rubber.

This suspension material has the longevity and frequency-response

characteristics of traditional rubber surrounds, but with a low density

very close to that of foam surrounds. This material was chosen to

preserve the transient detail of musical signals while still providing

the movement required for high output at low frequencies. Unlike

traditional foam surrounds, the foamed rubber has a very long

service life and will not deteriorate. The cone consists of a special

layered paper-pulp matrix with proprietary Aquaplas damping,

which offers more pistonic behavior throughout the woofer’s

operating bandwidth, and controlled cone breakup beyond it.

The 1501AL-2 uses an “accordion pleated” high strength Poly-

Cotton cloth outer suspension. This material is then coated with a

sealing/damping compound to render it air-tight and provide the

appropriate amount of damping control. This surround is attached

to a composite cone body consisting of an inner and outer layer of

pure pulp stock with an inner foam injection core. This sandwich

construction creates an incredibly stiff, but still relatively light cone

body with extremely good distortion characteristics.

Both woofers employ dual inverted Nomex® spiders for the

cancellation of even-order distortion components. The design

and material of these spiders have been further optimized for the

DD65000 and DD67000 systems to offer even greater freedom

of motion and dynamic range, specically at low playback levels.

All suspension elements are tailored for maximum mechanical

displacement linearity.

All together, these design factors provide reduced harmonic

distortions at very low and very high acoustic output, improved

power handling, reduced power compression, and more

consistent spectral balance with varying input drive level.

476Mg, 476Be HIGH-FREQUENCY

COMPRESSION DRIVER

The 476 family of high-frequency compression drivers make

use of a 4-inch (100mm)-diameter formed diaphragm with a

4-inch (100mm) aluminum edge-wound voice coil, operating into

JBL’s existing rapid-are-type, coherent-wave phasing plug. The

476Mg (DD65000) has a 95% pure magnesium alloy diaphragm.

The 476Be (DD67000) has a 98% pure beryllium diaphragm.

The use of an efcient neodymium rare-earth motor structure

with a new copper-sleeved polepiece maintains maximum gap

ux and reduced coil inductance at a minimal size and weight.

The combination of these features has resulted in drivers that can

deliver superior sound quality with very little distortion and power

compression, regardless of acoustic power output.

A high-purity copper sleeve is used for the polepiece. This greatly

improves the electrical conductivity of the polepiece for lower coil

inductance and thus greater high-frequency output at 15kHz and

above. The copper-sleeved pole piece quickly wicks away heat

generated by the voice coil, thereby contributing to a reduction

in dynamic power compression. To compensate for the higher

resistance caused by the use of the copper-sleeved polepiece, a

new magnet with special high-grade and high-temperature-grade

neodymium has been used.

The phasing plug is of JBL’s traditional rapid-are, 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 very high purity magnesium alloy

foil (476Mg, DD65000) or pure beryllium foil (476Be, DD67000)

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 magnesium or beryllium foil yields greater reliability and

resistance to failure due to fatigue. If breakage ever does occur, the

diaphragm does not shatter into pieces or harmful dust. Beryllium

has a very high stiffness-to-density ratio of about ve times that

of aluminum, magnesium, titanium or 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 more quickly to musical

transients, further enhancing the reproduction of musical detail

and microdynamic nuances.

Like the beryllium diaphragm in the 476Be, a proprietary thermal

forming process is used to form thin magnesium alloy sheets into

a 100mm magnesium dome shape of exacting dimensions for

the 476Mg. This includes the integrated JBL diamond surround.

The 95% pure magnesium alloy diaphragm of the 476Mg also

uses small percentages of aluminum, zinc, and other alloys to

improve characteristics such as diaphragm forming, fatigue

strength, corrosive and acoustic properties. Magnesium has very

low density, slightly lower than even beryllium, but with much lower

stiffness. However, with such a low density the thickness of the

magnesium alloy diaphragm can be increased to 130 microns,

greatly improving its stiffness. In fact, when compared to the

titanium diaphragms used in JBL’s original K2 S9500 and M9500

systems, this new magnesium alloy diaphragm is 2.5 times thicker

but maintains about the same moving mass of 3.4 grams. This is

benecial because with high stiffness, pistonic behavior extends

up to higher frequencies than is possible with current aluminum

or titanium diaphragms. Another benet of the magnesium alloy is

greater internal loss or damping when compared to aluminum or

titanium diaphragms. This greater internal loss quickly minimizes

the amplitude of resonances when the driver is asked to produce

frequencies beyond its acoustic limits.

Die-Cast Aluminum Front Cover

4" Edge-Wound

Aluminum Voice Coil

Copper-Sleeved

Pole Piece

Foam Damping Pad

Diaphragm Assembly

Acoustic Seal

Die-Cast Aluminum Back Cover

5-Way, Gold-Plated Terminals

Coherent-Wave, 4-Slot Phase Plug

Diamond Surround

Neodymium Magnet

Top Plate

476-series Compression Driver Section View

3-Layer Pure Pulp

Sandwich Cone with

Foam Injection Core

Layered Paper-Pulp

Matrix Cone with

Aquaplas Damping

1501AL-1

(DD65000)

1501AL-2

(DD67000)

High-Strength Sealed

Poly-Cotton Cloth

Accordion-Pleated

Suspension

Special Low-Density

Foamed Rubber

Half-Roll

Suspension

1501AL-1/1501AL-2 Cone and Suspension Comparison

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JBL Project Everest DD67000 Manual

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