Jbl 2451 j brochure

Page 1

UBL

Professional Series

Key Features:

>100 watts continuous program
above 500 Hz

D 150 watts continuous program at
1 kHz and higher

I}

eodvmium rarerearth magnet
stmcture 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 radialrrib topology

>38 mm (11/2 in) throat exit diameter

>101) mm (4 in) edgewound
aluminum voice coil

The Model 2451H/J is a 38 mm
(1 /2 in) exit diameter, compact size
and light weight addition to JBLs famr
ily of professional quality neodymium
compression drivers. The 38 mm exit
allows the Coherent Wave phasing
plug to directly couple with Optimized
Aperture BirRadialr horns to pro
vide lower distortion and better
coverage control to 20 kHz than
previous designs.

The Coherent \Vave phasing plug
structure has four equal length pasr
sages to provide inrphase 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 JBLs
exclusive threerdimensional diamond
pattern surround tuned to reduce
fatigue inducing stresses in the memr
brane and support structure This
provides predictable normal resor
nance modes, and radial reinforcing
ribs increase diaphragm stiffnessr This
diaphragm design combined with the
Coherent Wave phasing plug
increases the 2451s output in the 5
kHz to 20 kHz range

1} Pint-m 3? 4,324 312
F ergo parente pending

2 45 1 H/] Compression Driver
tr

Preliminary Specifications:

Throat Diameter:

Nominal Impedance:

38 mm (1% in)

2451H 8 ohms
2451] 16 ohms

Minimum Impedance:
DC Resistance:

Power Rating:

6 ohms (H), 12 ohms (I) @ 5 kHz
4.3 ohms (H), 8.5 (J) i 10% @ 25°C

100 w continuous program above 500 Hz
150 w continuous program above 1 kHz

Sensitivity:

111 dB SPL, 1 \X" @ 1 m onraxis on horn2
118 dB SPL, 1 mW on plane wave tube3

Nominal Efficiency:

Frequency Range:
Reeommended Amplifier Powerd:
Diaphragm:

Voice Coll Diameter:

Voice Coil Material:

Flux Density:

30% (500 Hz to 2.5 kHz)

500 Hz or higher, 12 dB/octave minimum
200 w into 8 ohms

0.05 mm (0.002 in) pure titanium

100 mm (4 in)

Ed Cwound aluminum rihhon

1.9 T (19,000 auss)

B1 Factor: 12.7 (H) *r m

18 (I) Tm
Polarity: Positive voltage to black terminal produces diaphragm

motion toward phasing plug

Dimensions: 167 mm (07/6. in) diameter
76 mm (3 in)

Mounting: Four 1/420 threaded holes, 90° apart on 114 mm

(41/2 in) diameter

Net \Yei ht: 4.5 k (10 lb)

leorrtinaon; pioprrnrt porter is defined as '5 dB prearer than tootioom pink noise and i,
transdutexs ahilit, to handle normal tpeeeh and muqt program m.

hotm duration

. t'omerrarne Lxpiusmn ot the
Hill (:onrinoas p l Holst runatl ratlnet are rested

.. pinl noee inpat having a o as trett tattor, with a hieher pro tiltei ~et to the spetitittl looer irroaener, lot too

zSensitirirt measured \Vlrh l \v inprrr at l m Lilmngc orrao. from the roonrh ot' the horn \urh a Q ot oz ateraped 1n the

2 Hlv UCIHLL hand

As Specified h) rtLogmvcd slmd'trds oipnnilattons, senotnio H measured otth the drner tonpled to a plane \Lmt tone
The 1131. sensttoitr mung repre e s the slL to a 23 mm (1 in) termloared tithe. using a l m lnpnt aerial [11126 \' mm

to ohms) orept trorn am 7 to 25 kHz,

Reeomroended [whack ampliller mung l. a pnide tor amplifier ScieCnun Lonstdulllg normal proprarn material and line

roltaee lllaxlable ro dmpllhen, although lrmcr punt! ampliii

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engages in rcsedrth related to prodnrr tnrprotement Ne rrrareoal., prodnrtion murhods
tetntenreno are ntnodnted lnlo eaitrinp pruduus wllhuur norite in a roarine L\p t
n. no torrent jBl. prodart mm turret in some

mm he null/(Li

ion ot thar phllukupil
et tront it. prihlithed destnptltm, but \ull alwins equal or

(\LLLLi rhe original tletlpn spLUfiLaluUnS unless otherwise .tared

Page 2

V 2451M Compression Driver

High temperature voice coil former materials and adhes
sives 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 JBLs rigid performance standards

The model 2451H/J is ruggedly constructed to withstand
the rigors of both fixed installations and touring applica
tions All tolerances are held to the same high levels tradis
tionally 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 hillet stoeh. The phasing plug shall be assemhled of con
centric horns to minimize phase cancellations. The diaphragm shall
he .05 mm (.002 in) pure titanium pneumatically drawn to shape and
embossed with radial reinforcing ribs to increase stiffness. High
frequency response shall he 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 he as
follows: Measured sensitivity with a 1 mW' input on a 25 mm (1 in) terr
minated tube, averaged from 500 Hz to 5 kHz, shall be at least 118 dB
SPL. Measured sensitivity with a 1 \Y' input at 1 m distance onraxis 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 he flat
within it 1 dB from 500 Hz to 3.3 kHz, with 6 dB/octave rollroff
above that point. Nominal impedaaee 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 2451HU]. Other
drivers will he considered for equivalency provided that suhmitted
data from a recognized independent test laboratory verify that the
above performance specifications are met.

Response on JBL 2352 BisRadialk Horn

«20

no

a'
.,
a
'u .
E
a
5
.
9 2
a
x
r
80 16
100 200 500 1000 2000 50m 10000 20000
lelm in Hz

Frequency reponse of the 245111 coupled to a JBL 2352 BirRadial
Horn, measured onraxis 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 PlanesWave Terminated Tube

tan

8PL as [re 2a.. Pa)

in

impedance Ohm:

Frequency response and impedance modulus of model 245m coupled
to a 38 mm (1 /z 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 JBLs 2350 series of BirRadialhorns.

UBL

JBL Professional
8500 Balboa Boulevard, PO. Box 2201)
Northridge, California 9132) USA Eiffel!

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