JBL 4642A User Manual

4642A

Dual 460 mm (18 in)
Subwoofer System

Key Features:

䉴

1200 Watts Continuous Pink Noise,
2400 Watts Continuous Program
Power Handling

䉴

Usable response to 22 Hz (-10 dB,
no EQ), flat to 22 Hz (-3 dB) with
External EQ

䉴

2241H VGCTMVented Gap Cooled
Drivers
– High Sensitivity
– Low Power Compression
– High Maximum-SPL Capability
– Low 2nd and 3rd Harmonic

– Distortion

– Symmetrical Field Geometry SFG

TM

– Magnet Structure

– Long Excursion Capability

䉴

Approved by Lucasfilm, Ltd. for
THX®installations

The JBL Model 4642A is a high
quality subwoofer system, featuring an
advanced technology 460 mm (18 in),
low frequency transducers mounted in
a direct radiator, bass-reflex enclosure
for smooth response to the lowest
audible frequencies. The 4642A is
ideal for low-frequency augmentation
of either analog or digital soundtracks
in motion picture theaters and for
general sound reinforcement
applications.

Transducer:

The 2241H transducer utilizes the
patented Vented Gap Cooling (VGC)
process*, which pumps air through the
magnetic gap and directly over and
around the voice coil, providing
immediate heat transfer and a
reduction in operating temperature.
This increases power handling while
reducing power compression.

Through the use of computer-aided
magnet optimization and analysis
techniques, JBL engineers were able to
optimize magnet weight, flux density
and field saturation, resulting in a 2.6
kg (6.5 lb) reduction in overall driver
weight and a significant reduction in
harmonic distortion. This magnet
structure offers much of the weight
advantage of rare earth magnet
structures without the prohibitive cost,
enabling the system to carry a 1200
watt continuous AES pink noise power
rating.

*U.S. Patent #5,042,072. Foreign Patents Pending.

Specifications:

TRANSDUCERS: Two JBL Model 2241H 460 mm (18 in) Low

Frequency Transducers

SYSTEM:

Rated Impedance: 4 ohms

Minimum Impedance: 3.2 ohms

POWER HANDLING CAPABILITY:

Continuous Pink Noise1: 1200 Watts

Continuous Program2: 2400 Watts

Peak Power3: 4800 Watts

OUTPUT CAPABILITY:

Axial Sensitivity4: 50 Hz to 500 Hz; 101 dB, 1W @ 1m

40 Hz to 100 Hz; 100 dB, 1W @ 1m

Power Compression5:

At -10 dB power (120 W): 0.8 dB

At -3 dB power (600 W): 2.6 dB

At rated power (1200 W): 4.3 dB

Single Two Four
Module Modules Modules

Half-Space Reference Efficiency6: 5.8% 8.7% 11.6%

Max. Continuous Acoustical

Power Output: 70 W 209 W 557 W

Maximum Continuous SPL @ 1 meter7: 131 dB 136 dB 140 dB

Maximum Peak SPL @ 1 meter7: 137 dB 142 dB 146 dB

FREQUENCY RESPONSE8: Lower Frequency Limits (no EQ):

-10 dB: 22 Hz

-3 dB: 35 Hz
Lower Frequency Limits (with EQ):

-10 dB: 20 Hz

-3 dB: 22 Hz

Recommended Crossover Frequencies: High-pass: 20 Hz, 12 dB/octave or greater

Low-pass: 80 Hz to 150 Hz, 12 dB/octave or greater

Distortion9:

2nd harmonic: <2%

3rd harmonic: <2%

System Polarity: EIA Standard. Positive voltage to RED terminal

produces forward cone motion.

Input Connectors: Color-coded push terminals

Net Weight: 98 kg (216 lbs.)

Shipping Weight: 109 kg (240 lbs.)

ENCLOSURE:

Materials and Finish: 19 mm (¾ in) particle board with 25 mm (1 in) baffle

and back panel. Extensive bracing on all panels

Enclosure Tuning Frequency: 25 Hz

Net Internal Volume: 506 liters (18 cu. ft)

Dimensions: 762 mm x 1219 mm x 610 mm

H x W x D 30 in x 48 in x 24 in

See footnotes on back ☞

Professional Series

JBL Professional
8500 Balboa Boulevard, P.O. Box 2200
Northridge, California 91329 U.S.A.

A Harman International Company

SS 4642A
CRP 10M
10/98

䉴 4642A Dual 460 mm (18 in) Subwoofer System

4642A frequency response, 1 watt at 1 meter, with 150 Hz Linkwitz­Riley 4th order low-pass filter and 2nd order high-pass filter at 25 Hz
with Q=2. 1␲ (upper curve) and 2␲ (lower curve) conditions.

4642A frequency response and impedance (bottom curve), 1 watt at
1 meter, with 150 Hz Linkwitz-Riley 4th order low-pass filter
measured under 4␲ ground plane conditions. 1␲ (upper curve) and
2␲ (center curve) loading condition predictions also shown.

JBL continually engages in research related to product improvement. New materials,
production methods, and design refinements are introduced into existing products
without notice as a routine expression of that philosophy. For this reason, any current
JBL product may differ in some respect from its published description, but will always
equal or exceed the original design specifications unless otherwise stated.

The 100 mm (4 in) voice coil benefits from a new
winding technique which offers greater thermal stability
with increased power handling. All elements of the
cone, voice coil and suspension system have been
carefully optimized and controlled to ensure smooth high
frequency response.

The magnet structure and compliance allow for long
peak-to-peak excursions without damage to the speaker.
Symmetrical Field Geometry (SFG) minimizes second
harmonic distortion.

Enclosure:

The enclosure is constructed of dense stock and is
extensively braced on all panels. It has a net internal
volume of 506 liters (18 cu. ft.) and is tuned to 25 Hz
with a very large port to minimize port compression and
to reduce distortion due to turbulent air flow.

Frequency Response:

The 4642A features high sensitivity. It is intended for
use as a subwoofer with a low-pass filter and appropriate
high-pass filtering for protection and equalization.

Note: Drawing not to scale. All dimensions are reference
only.

1

AES continuous pink noise (25 - 250 Hz), 2 hours duration.

2

Continuous program power is defined as 3 dB greater than AES continuous pink noise
and is a conservative expression of the transducer’s ability to handle normal music
program material.

3

Peak power is defined as 6 dB greater than AES continuous pink noise, reflecting the
6 dB crest factor contained in the pink noise signal.

4

Averaged half-space (2␲). Quarter-space (1␲, wall/floor junction placement) is 6 dB
higher.

5

Power compression is the sensitivity loss at the specified power, measured from 50 Hz
to 500 Hz, after a 5 minute AES standard (50 to 500 Hz) signal at the specified power.

6

Based upon specified half-space 40 Hz to 100 Hz sensitivity; 50 Hz to 500 Hz reference
efficiency is higher.

7

Per industry practice, maximum long-term SPL is a calculation that references half-space
1W/1m sensitivity, scaled by the long-term continuous power rating.

8

Based upon specified sensitivity, 40 Hz to 100 Hz.

9

100 watt sine wave input, averaged from 40 Hz to 100 Hz.