JBL 4310 (1970)

Name: JBL 4310
Brand: JBL

A compact control-room monitor that traded home-fi politeness for studio honesty.

Overview

Pick up a 4310 and the first thing you notice is the weight. It ships at 51 pounds, per the manual, in a box barely two feet tall. JBL built it as a tool for control rooms, not living rooms, and every decision follows from that: ¾-inch stock throughout the enclosure, lock-mitered, wood-welded joints, and a ducted port working the very bottom octave. The 4310 was developed by JBL in cooperation with leading recording studios to meet the need for a powerful yet compact professional monitor. JBL's own manual pitched it squarely at control room installations, small studios, mixdown facilities, and portable playback rigs.

It's a three-way, direct-radiator system that covers 45 to 15,000 Hz within ±3 dB on axis, with a nominal 8-ohm impedance and a 50-watt program power capacity. The low end comes from a 12-inch long-excursion woofer with a 3-inch edgewound copper ribbon voice coil in a magnetic field of 9,200 gauss. The magnetic assembly alone weighs six pounds, and free-air cone resonance is a very low 27 Hz. A 5-inch midrange transducer takes over above 1,500 Hz, with a ⅞-inch edgewound copper ribbon voice coil in a 16,500-gauss field. Its 4-inch edge-damped cone runs as a true piston. Above 3 kHz a third direct radiator fades in, reaching full output above 7 kHz. It has an effective diameter of about 1⅜ inches and a gap flux density of at least 16,000 gauss.

The crossover points sit at 1,500 and 7,000 Hz. Dispersion is a full 90 degrees both horizontally and vertically, so the 4310 works laid on its side or standing up. JBL designed it that way on purpose. The manual quotes sensitivity the old-fashioned way: approximately 42 dB at 30 feet with one milliwatt input, averaged from 500 to 2,500 Hz with controls set for flattest response. JBL's documentation points out that because the 4310's response is uniform across the full audible range, its sensitivity below 500 Hz or above 2,000 Hz may be considerably greater than systems with higher published sensitivity ratings. That reads as a dig at the spec-sheet games of the era.

Key Features

Front-Panel Presence and Brilliance Controls

Recessed into the front baffle are two continuously variable controls. One shapes the 1,500-7,000 Hz "presence" range, the other the 7,000-15,000 Hz "brilliance" range. Both run from maximum to full off. They're there to compensate for the room, not to tweak tone for taste. A 4310 in a bright, reflective control room can be dialed back in the brilliance band without touching the console. The scales are clearly marked so a specific setting can be logged and reset exactly. That tells you who JBL was selling to: engineers who needed repeatability.

Raised Auxiliary Baffle for the High-Frequency Transducers

The mid and ultra-high drivers don't sit flush with the main baffle. They're mounted on a raised auxiliary baffle, JBL's fix for cavity resonances and diffraction effects that would otherwise smear the high end. Combined with the wide-angle characteristics of the transducers, this shows up off-axis. Response measured up to 45 degrees off-axis, horizontally or vertically, doesn't deviate more than 6 dB from on-axis at 2 kHz or more than 10 dB at 8 kHz. That matters for a monitor meant to be heard by more than one person in a room.

Ducted-Port Enclosure with Front-Removable Drivers

The enclosure is built of ¾-inch stock throughout, with lock-mitered, wood-welded joints to prevent unwanted resonance. A ducted port provides added acoustical loading in the very low frequency range to increase efficiency and reduce distortion. Every loudspeaker is removable from the front, so no one has to pull the cabinet apart to service a driver. The manual includes a stress test: driven by a 50-watt sine wave at 35 Hz, the 4310 produced an almost perfect replica of the input signal. JBL notes that this is a far harder job than its rated 50 watts of program material. Below 50 Hz, most monitor loudspeakers produce substantial distortion with only a few watts input. Finish was oiled walnut or textured gray with charcoal grille fabric. Dimensions came in at no more than 24" × 15" × 12" deep, with the manual quoting 23⅜" × 14½" × 11¾" (60 × 36 × 30 cm).

Historical Context

JBL's own later documentation dates the line back to 1968 with the original 4310, the year most commonly associated with its introduction. Catalog references generally place the model at 1970. Either way, the 4310 arrived as the recording industry was expanding fast and studios needed a compact monitor that could be trusted at volume. JBL's advertising in the period leaned hard on the studio credentials and ran the same copy across multiple titles. The 4310 was "especially designed for mastering, control room installations, mixdown facilities, portable playback systems," and had been "developed with the enthusiastic assistance of leading recording engineers." High Fidelity (June 1971, p.36) and Audio (March 1971, p.44) both carried the line that beneath its mild-mannered charcoal-gray exterior sat "the finest compact studio monitor money can buy." That's marketing copy, not an independent verdict. The studio-engineer consultation claim is repeated in the company's own manual.

Collectibility & Value

The 4310 is the ancestor of a long line of JBL bookshelf studio monitors, and the 4311, 4312, and 4313 followed it. Because so many were built for professional use, survivors range from clean original pairs to heavily gigged cabinets with tired drivers. Condition drives price more than anything else. Buyers should inspect the front-panel controls for scratchiness, check the woofer cone and surround for age, and confirm the raised high-frequency baffle hasn't been tampered with. Original grille cloth and the oiled walnut finish are commonly degraded after five decades of studio life. Collectors prize the 4310 as the origin point of the series rather than as a spec-sheet champion. The 50-watt rating and 45 Hz bottom end are modest by later standards, but the build quality and the presence/brilliance flexibility keep them in service.