JBL 4330/4331
The JBL 4330 and 4331 are professional studio monitors introduced in 1974. They were built for playback monitoring and mixdown in recording studios, broadcasting stations, and halls. Both are two-way, two-speaker bass reflex systems in large bookshelf-style enclosures, and they share the same basic drivers. The woofer is a 38 cm cone, the 2231A, noted for its improved cone paper density and mass. The high-frequency section is horn-loaded: a 2420 compression driver, a 2312 exponential horn, and a 2308 acoustic lens. The center pole piece of the 2420 is coated with pure silver. It acts as an impedance control ring and keeps the high-frequency response smooth.
The difference between the two is the crossover. The 4330 was set up for multi-amplifier use. It needed an external electronic crossover: a power amplifier plus a 5231 or 5232 divider and a 52-5123 filter board. The 4331 ran on a passive network. The 4330's non-network configuration eventually got it discontinued. The 4331A, released in 1976, added switch-based multi-amplifier capability and let you rotate the acoustic lens 90 degrees for horizontal placement. Both models came in gray and walnut finishes, with the WX suffix marking walnut.
Around 1980, the 4331B appeared. It swapped the alnico-magnet 2231A woofer for the ferrite-magnet 2231H. The reason was trouble with alnico magnets under high-power studio drive, particularly magnetic flux instability and terrestrial magnetism protection issues, and those pushed JBL toward ferrite. The 2231H used JBL's new SFG (Symmetrical Field Geometry) magnetic circuit, which included a stabilizer ring to reduce distortion. The alnico circuit tended to lose response in heavy bass and lacked smoothness in the mid-low range. The SFG circuit addressed that. Otherwise, per period documentation, the 4331B was identical to the 4331A.
Specifications for the 4331A/4331B are documented as follows:
- Frequency response: 35 Hz – 15 kHz ± 3 dB
- Crossover frequency: 800 Hz
- Impedance: 8 Ω
- Output sound pressure level: 93 dB (new JIS)
- Allowable input: 75W program (network / below 800 Hz), 30W above 800 Hz
- Directivity: 60° horizontal × 30° vertical (at 12 kHz)
- Enclosure volume: 127 liters (4330/4331 original); 156L (4331A)
- Dimensions: 600 × 780 × 510 mm (4330/4331); 619 × 778 × 497 mm (4331A/B)
- Weight: 43 kg (4330), 44 kg (4331), 57 kg (4331A/B)
Original Japanese pricing around 1975 was ¥420,000 for the 4330, ¥443,000 for the 4330WX, ¥488,000 for the 4331, and ¥511,000 for the 4331WX, per unit. The 4331A later listed at ¥380,000 (¥395,000 for the WX) around 1978, and the 4331B at ¥450,000 (¥470,000 for the BWX).
Collector sources say the multichannel 4330 is quite difficult to obtain today, and the 4331BWX turns up less often than the 4331B. Units in good condition are scarce. Some owners have converted 4331Bs to 4333B configuration by adding supertweeters, which requires no cabinet changes. One owner on a forum described replacing 4330s with Tannoy DMT monitors and praised the Tannoys' neutral, phase-coherent sound. Another owner on Audiofanzine was less kind and suggested the used price wasn't justified given the alternatives available. These are the only owner perspectives that have surfaced. No formal period reviews of the 4330/4331 have been located in the available documentation.
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