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

The JBL 2451H/J high frequency compression driver is a 38 mm (1-1/2") 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.

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.

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. 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.

JBL 2451H/J High Frequency Compression Driver Features:

• 100 watts continuous program power handling when used above 500 Hz
• 150 watts continuous program power handling when used above 1 kHz
• 8 ohm (H) or 16 ohm (J) impedance
• 500 Hz to 20 kHz response
• 111 dB sensitivity (1W/1m on 2380A horn)
• Coherent Wave phasing plug design for increased high-frequency output
• 100 mm (4") pure titanium diaphragm with radial-rib topology
• 100 mm (4") edgewound aluminum voice coil
• Net weight: 4.8 kg (10.5 lbs.)

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JBL 2451H/J High Frequency Compression Driver Specifications:

• Throat Diameter: 38 mm (1-1/2")
• Nominal Impedance: 2451H 8 ohms , 2451J 16 ohms
• Minimum Impedance: 6 ohms (H), 12 ohms (J) @ 5 kHz
• DC Resistance: 4.3 ohms (H), 8.5 (J) +/- 10% @ 25°C
• Power Rating': 100 W continuous program above 500 Hz; 150 W continuous program above 1 kHz
• Sensitivity: 111 dB SPL, 1 W @ 1 m on-axis on horn
• 118 dB SPL, 1 mW on plane wave tube
• Nominal Efficiency: 30% (500 Hz to 2.5 kHz)
• Frequency Range: 500 Hz or higher, 12 dB/octave minimum
• Recommended Amplifier Powered: 200 W into 8 ohms
• Diaphragm: 0.05 mm (0.002 in) pure titanium
• Voice Coil Diameter: 100 mm (4")
• Voice Coil Material: Edgewound aluminum ribbon
• Flux Density: 1.9 T (19,000 gauss)
• B1 Factor: 12.7 (H) T m; 18 (J) Tm
• Polarity: Positive voltage to black terminal produces diaphragm
• motion toward phasing plug
• Dimensions: 167 mm (6") diameter
• 76 mm (3")
• Mounting: Four 1/4 - 4-20 threaded holes, 90° apart on 114 mm
• (4-1/2") diameter
• Net Weight: 4.5 kg (10 lb)

JBL 2451H/J High Frequency Compression Driver