JBL 2404H

Five pounds of ferrite and aluminum with a diaphragm that looks like a baby's backside, and a Bi-Radial horn that put controlled 100° dispersion in a package small enough to bolt to a baffle.

Overview

The 2404H is JBL's ultra-high-frequency compression driver. It has one of the best nicknames in the catalog. The diaphragm is two concentric annular rings moving together, and the "Baby Butt Cheeks" name explains itself. Collectors shorten it to "BBC" and use it as a shorthand identifier.

On to the numbers. It's an 8-ohm nominal driver with a rated frequency range of 3,000 Hz up to 21.5 kHz, and it weighs 5 lbs. The magnet is an 8 oz. barium ferrite unit. The voice coil is a 2½-inch edgewound aluminum ribbon with a DCR of 5.7-6.7 ohms. What sets the 2404H apart in the 2400 series is the front end: a Bi-Radial horn that holds a 100° by 100° coverage angle. That gives tightly controlled dispersion across the passband, rather than the narrowing beam of a simple conical horn.

Power handling is where the arguments start, because the record conflicts. One source cites 10 W RMS and 40 W peak. Other references, including a Japanese specification listing and a US speaker retailer, give 40 W continuous program at 3 kHz or higher. The figures may not be contradictory so much as measured differently: one is a conservative thermal rating for the voice coil, the other a program-power figure tied to a crossover point. Either way, this is a driver for domestic and project-studio duty, not for high-SPL reinforcement work. Sensitivity is split too. A 1988 trade listing (Sound and Communication, January 1988, p.32) shows 105 dB, and 110 dB SPL (1 W @ 1 m) is cited elsewhere. The same 1988 trade listing (Sound and Communication, January 1988, p.32) also documents the companion 2402H at 110 dB with a 40 W rating and a 205 Hz - 15 kHz range. Both point the same way: the 2404H is efficient enough that a few watts go a long way.

Key Features

Twin Annular Diaphragm

The twin annular diaphragm is the core of the 2404H. Two concentric rings move as one, rather than a single dome or cone. JBL's literature claimed the arrangement delivers excellent high-frequency dispersion while holding smooth, flat response and very low distortion. The look is unmistakable, and anyone who has spent time around JBL pro gear can pick the driver out before reading a model number.

The diaphragm is aluminum alloy, and the coil is an edgewound aluminum ribbon. That construction packs more conductor into the magnetic gap than a round-wire coil of the same size, which improves efficiency and power handling for a given coil diameter. The gap is driven hard: a Japanese spec listing gives the flux density at 17,500 gauss.

100° x 100° Bi-Radial Horn

The horn is the other half of the 2404H. JBL's Bi-Radial profile is designed to hold constant directivity of 100° in both the horizontal and vertical planes, from roughly 3 kHz to 20 kHz. That keeps the driver's output consistent as you move off-axis. The same source notes that the rapid expansion of the horn flare keeps second-harmonic distortion extremely low.

The horn aperture measures 13 x 13 cm, and the complete driver measures 130 mm in diameter with a 130 mm depth. That's compact for a professional compression driver. It's why the 2404H could be dropped into baffles and multi-element systems where a larger horn wouldn't fit.

Coil-in-a-Magnet Construction

Know what the 2404H is not. The related JBL 2402 used a piezoelectric element, a completely different transduction method with its own limitations. The 2404H uses a conventional coil in a magnetic field, and the magnet is barium ferrite rather than alnico. That matters for long-term ownership: barium ferrite holds its charge well and doesn't suffer the partial degaussing that can afflict vintage alnico assemblies after decades of use and mishandling.

The other family difference is at the front. The 2402H carried a small metal horn built into the driver body. The 2404H does not - its Bi-Radial horn is a separate, larger structure. That helps when you're identifying loose drivers at a swap meet, and it changes how the two units behave in a system.

Flush Mounting and 4-Bolt Pattern

Installation is straightforward. The 2404H is a flush-mount driver, and the baffle is drilled for JBL's 4-bolt pattern with four threaded inserts, the same layout used across much of the professional line. There are no nuts to fish around behind the baffle; a bolt and washer finish the job. Polarity follows the standard JBL convention: positive voltage produces positive acoustic pressure and cone movement into the room. That matters when you wire multiple drivers and want them to sum rather than cancel.

Crossover advice varies. One factory figure recommends 5,000 Hz, while other documentation lists 3 kHz or higher as the crossover point. Owners tend to push higher still, suggesting 8 kHz or above to protect the voice coil from excessive power. Given the modest thermal rating, that caution is sensible. The response extends well past 20 kHz, so there's plenty of top octave left above a high crossover point.

Historical Context

The 2404H belongs to JBL's 2400 series of high-frequency drivers, a family that includes the 2402 and 2402H. It was built for professional monitor duty and served as the high-frequency driver in JBL's professional monitor systems. It also appears as the compression driver in the VT4887 loudspeaker system.

It was also designed as an ultra-high-frequency driver in multi-element, wide-range loudspeaker systems, and it shows up in that role as an optional add-on. JBL's 4770A Sound Power system, for instance, came pre-drilled and wired for optional three-way active operation with one or two 2404H drivers. A Japanese specification listing prices the driver at ¥62,000 per unit around 1983. Production years and a US original MSRP are not documented in available sources.

Collectibility & Value

The 2404H has a loyal following, and the nickname has only added to its desirability. Market prices are anecdotal but reasonably consistent. Listings have run from roughly $150 to $250 per driver depending on condition, with pairs fetching more: observed sales include a tested pair at $319 and a pair of 2404H-2 units at $535. Single drivers with original factory diaphragms have turned up around $125, and used examples as low as $110. A Canadian listing sat at CA$300. The spread reflects condition and, above all, whether the diaphragm is genuine JBL or aftermarket.

That last point is the real risk. There is no documented spare-parts availability, and JBL does not sell the replacement diaphragm as of this writing. Blow a diaphragm and you're hunting NOS or a donor driver. Aftermarket diaphragms are widely sold and inexpensive, but experienced owners note that genuine JBL parts are specified to perform the same while the aftermarket units are an unknown quantity. Owners also report a known pattern of low-output problems with these drivers, though no confirmed root cause appears in the available documentation.

Reception among long-time users is warm but clear-eyed. One JBL veteran calls it a very good driver that sounds good, while noting it lacks the top-end sizzle of newer designs; another describes it as a wonderful-sounding high-frequency driver with smooth, flat response that nonetheless gives up a bit of air at the very top. The Gearspace consensus, quoted via Vintage Audio Barn, is an excellent driver — very smooth, flat, and very low distortion — and one that pairs well with the 2402H bullet tweeter. For a home monitor system, a small studio, or a vintage JBL restoration, the 2404H delivers smooth response, low distortion, and high sensitivity at a price that keeps it within reach. Just respect the power rating and cross it high.