JBL 2121 (Mid-1970s)

The JBL 2121 is one of those models that sits in the shadow of its more famous siblings — the L100 Century gets the attention, but the 2121 was the compact studio monitor that JBL positioned just below it in the mid-1970s lineup. It was the successor to the JBL 2100 "Dynagarde" system, and the main goal was straightforward: keep the dynamic character of the 2100 but smooth out the response and improve dispersion by swapping in a dome tweeter.

What the record shows is a 2-way, acoustically-suspended (sealed) bookshelf system built around a 10-inch 123A-1 woofer with a ribbed-butyl surround and heavy ferrite magnet, a 5-inch LE-5-2 midrange, and a 3-inch 033 concave-dome tweeter with an edge-wound aluminum voice coil. The crossover sits at 1.5 kHz with a 12 dB/octave slope, and both midrange and tweeter have L-pad attenuators for level adjustment — a nice touch for tailoring the balance to the room. Rated sensitivity is 89 dB at 1W/1m, impedance is 4 ohms, and it handles 60 watts continuous program material. The cabinet is internally damped, measures 12.5″ H × 26.5″ W × 11″ D, and weighs about 32 lbs. Finish options were oiled walnut veneer or a walnut "utility" finish.

One honest caveat: the source material describes the enclosure as both "acoustically-suspended (sealed)" and "slot-ported" in the same passage, which is contradictory. I've gone with the sealed description since it's the more prominent claim and consistent with the acoustic-suspension tradition JBL was known for in this era, but the ported mention remains unresolved. Frequency response is rated at 45 Hz – 20 kHz (±4 dB), which is respectable for a cabinet this size.

Surviving documentation on the 2121 is thin — no production years, no original price, and few published reviews from the period have surfaced. Contemporary coverage of JBL's professional line in Sound and Communication (March 1991, p.42) discussed the company's coaxial drivers and sealed-enclosure designs, though it did not specifically address the 2121. Most of what's known comes from a single enthusiast source, so there's no multi-source corroboration for the specs listed above. If you own a pair and have documentation, the Archive would love to hear from you.