JBL 2451-H, 2451-J Brochure

Professional Series

Key Features:

100 watts continuous program
above 500 Hz

150 watts continuous program at
1 kHz and higher

Neodymium rare-earth magnet
structure provides high output, light
weight, and compact size

Coherent Wave™ phasing plug
design for increased high frequency
output

100 mm (4 in) pure titanium

diaphragm with radial-rib topology

38 mm (1½ in) throat exit diameter

100 mm (4 in) edgewound
aluminum voice coil

The Model 2451H/J is a 38 mm
(1½ in) exit diameter, compact size
and light weight addition to JBL’s fam­ily of professional quality neodymium
compression drivers. The 38 mm exit
allows the Coherent Wave™ phasing
plug to directly couple with Optimized

Aperture™ Bi-Radial® horns to pro­vide lower distortion and better

coverage control to 20 kHz than

previous designs.

The Coherent Wave™ phasing plug
structure has four equal length pas­sages to provide in-phase summation
of diaphragm output at the 38 mm
exit, This optimized configuration
produces coherent acoustical power
up to much higher frequencies than
more conventional designs.

The diaphragm design includes JBL’s
exclusive three-dimensional diamond
pattern surround’ tuned to reduce
fatigue inducing stresses in the mem­brane and support structure. This
provides predictable normal reso­nance modes, and radial reinforcing

ribs increase diaphragm stiffness. This
diaphragm design combined with the
Coherent Wave™ phasing plug
increases the 2451’s output in the 5
kHz to 20 kHz range.

2451H/J

Compression Driver

Preliminary Specifications:

Throat Diameter: 38 mm (1½ in)

Nominal Impedance: 2451H 8 ohms

Minimum Impedance:

DC Resistance: 4.3 ohms (H), 8.5 (J) ± 10% @ 25°C

Power Rating’: 100 W continuous program above 500 Hz

Sensitivity: 111 dB SPL, 1 W @ 1 m on-axis on horn²

Nominal Efficiency: 30% (500 Hz to 2.5 kHz)

Frequency Range: 500 Hz or higher, 12 dB/octave minimum

Recommended Amplifier Powerd:

Diaphragm: 0.05 mm (0.002 in) pure titanium

Voice Coil Diameter:

Voice Coil Material: Edgewound aluminum ribbon

Flux Density: 1.9 T (19,000 gauss)

B1 Factor: 12.7 (H) T m

Polarity: Positive voltage to black terminal produces diaphragm

Dimensions: 167 mm (6 in) diameter

Mounting: Four ¼-20 threaded holes, 90° apart on 114 mm

Net Weight: 4.5 kg (10 lb)

¹Continuous program power is defined as 3 dB greater than continous pink noise and is a Conservative expression of the

transducer’s ability to handle normal speech and music program material Continous pink noise power ratings are rested
with a pink noise input having a 6 dB crest factor, with a higher pass filter set to the specified lower frequency, for two
hours duration.

²Sensitivity measured with 1 W input at 1 m distance on-axis from the mouth of the horn with a Q of 6.3 averaged in the

2 kHz octave band

³As specified by recognized standards organizations, sensitivity is measured with the driver coupled to a plane wave tube

The JBL sensitivity rating represents the SPL in a 25 mm (1 in) terminated tube, using a 1 mW input signal (0.126 V into
16 ohms) swept from 500 Hz to 2.5 kHz.

4

Recommended power amplifier rating is a guide for amplifier selection considering normal program material and line

voltage available to amplifiers, although lower power amplifiers may be utilized.

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

2451J 16 ohms

6 ohms (H), 12 ohms (J) @ 5 kHz

150 W continuous program above 1 kHz

118 dB SPL, 1 mW on plane wave tube³

200 W into 8 ohms

100 mm (4 in)

18 (J) Tm

motion toward phasing plug

76 mm (3 in)

(4½ in) diameter

¹U.S. Patent # 4,324.312.

Foreign patents pending

2451H/J Compression Driver

High temperature voice coil former materials and adhe­sives enable the 2451H/J to handle higher power levels
over extended periods of time. The voice coils themselves
are identical to previous JBL models, so that impedance
and network matching will be the same. After manufacture,
the frequency response of each transducer is tested for
conformity to JBL’s rigid performance standards.

The model 2451H/J is ruggedly constructed to withstand
the rigors of both fixed installations and touring applica­tions. All tolerances are held to the same high levels tradi­tionally associated with JBL designs. The JBL manufacturing
process permits the use of rim centered diaphragms for
instant interchangeability and ease of field service.

Architectural Specifications:

The compression driver shall consist of a neodymium magnetic

structure with all magnetic assembly parts machined from cast or

extruded billet stock. The phasing plug shall be assembled of con­centric horns to minimize phase cancellations. The diaphragm shall
be .05 mm (.002 in) pure titanium pneumatically drawn to shape and
embossed with radial reinforcing ribs to increase stiffness. High
frequency response shall be controlled through the use of a three
dimensional suspension structure. The voice coil shall be edgewound
aluminum ribbon of not less than 100 mm (4 in) diameter, operating
in a magnetic field of not less than 1.9 T (19,000 gauss).

Performance specifications of a typical production unit shall be as
follows: Measured sensitivity with a 1 mW input on a 25 mm (1 in) ter­minated tube, averaged from 500 Hz to 5 kHz, shall be at least 118 dB
SPL. Measured sensitivity with a 1 W input at 1 m distance on-axis from
the mouth of a horn with a Q of 6.3 averaged in the 2 kHz octave band

shall be at least 111 dB SPL. As an indication of electromechanical

conversion efficiency, the B1 factor shall be at least 18 Tesla meters.

Frequency response, measured on a terminated tube, shall be flat
within ± 1 dB from 500 Hz to 3.3 kHz, with 6 dB/octave roll-off

above that point. Nominal impedance shall be 8 [16] ohms and power

capacity shall be at least 100 watts normal speech or music program

material.

The compression driver shall be the JBL Model 2451H[J]. Other
drivers will be considered for equivalency provided that submitted
data from a recognized independent test laboratory verify that the
above performance specifications are met.

Response on JBL 2352 Bi-Radial® Horn

Frequency reponse of the 2451H coupled to a JBL 2352 Bi-Radial
Horn, measured on-axis at a distance of 1 meter with a 1 watt (2.83
V RMS) input in a reflection free environment, with impedance vs.
frequency curve.

®

Response on Plane-Wave Terminated Tube

Frequency response and impedance modulus of model 2451H coupled
to a 38 mm (1½ in) diameter terminated plane wave tube. This is the
power response of the transducer, and is the frequency response that
will be obtained on a true full range constant directivity horn design,
such as JBL’s 2350 series of Bi-Radial® horns.

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

A Harman International Company

SS 2451H/J
CRP 5M
10/96