JBL 2405H

Name: JBL 2405H
Brand: JBL

The 2405H is JBL's ultra-high-frequency slot radiator. It's the diffraction-slot tweeter from the 2400-series compression driver family, built around a 44 mm (1¾") aluminum-alloy diaphragm with an aluminum ribbon voice coil and a ferrite magnet. JBL's own literature says it "provides smooth response and exceptionally wide dispersion even at extremely high frequencies." It's rated for 40 watts above 6 kHz with 105 dB sensitivity averaged from 7 kHz to 20 kHz. The recommended crossover is 7 kHz or higher. Specified dispersion is 90° × 25° at 16 kHz, a tight vertical slot pattern, and that's the whole point of the design. JBL lists the frequency range at 6.5 kHz to 21.5 kHz (−10 dB), the flange at 121 mm diameter by 95 mm deep, and the net weight at 2.3 kg (5 lbs).

Two things need flagging. First, the impedance is muddled in the record. The "H" suffix in JBL's professional line conventionally denotes 8 ohms (the "J" suffix is 16), and JBL's spec table lists the 2405H at 8 ohms nominal. Still, a fair amount of secondary and resale material calls it a 16-ohm unit. This page goes with the manufacturer's 8-ohm figure, but check the actual unit before you buy. Second, production years and original pricing are not documented in the available sources. The 2405 platform dates to the late 1960s, but it's unclear when the "H" variant appeared and what exactly separates it from the plain 2405.

Where it was used is well documented. JBL's own system reference charts place the 2405H in the 4343, 4343B, 4344, 4350B and 4355 studio monitors, and in the 4663A theater system. It was typically paired with a 2307 horn and 2308 lens and crossed via a 3105 network at 7 kHz. The 2405H is also the factory-sanctioned acoustic equivalent for the earlier 077 ring radiator. Its standard replacement diaphragm is the D16R2405, with D8R075 and D8R076 listed as alternatives. Period coverage is thin but real. Recording Engineer (February 1983, p.93) described 2405 units being added to a system, passively crossed above 10 kHz, to add presence to the top end. That's how these drivers tended to enter service, as a retrofit enhancement rather than a full-range solution.

Known specifications:

Type: ultra-high-frequency compression driver, diffraction-slot ("split-horn") radiator
Nominal impedance: 8 ohms (per JBL spec table; some sources say 16 — verify)
Diaphragm: 44 mm (1¾") aluminum alloy; aluminum ribbon voice coil
Magnet: ferrite, 1.75 T (17,500 gauss)
Power capacity: 40 W above 6 kHz
Sensitivity: 105 dB (1 W, 1 m), averaged 7 kHz–20 kHz
Frequency range: 6.5 kHz – 21.5 kHz (−10 dB)
Dispersion: 90° × 25° at 16 kHz
Recommended crossover: 7 kHz or higher
Dimensions: 121 mm diameter × 95 mm depth · Net weight: 2.3 kg (5 lbs)
Replacement diaphragm: D16R2405