JBL TM420 (c. 1990)

The JBL TM420 is a 2-way in-vehicle speaker unit - a car speaker - that JBL offered around 1990 at ¥36,000 per unit. Documentation is thin. What survives is scattered across parts listings and classified ads rather than period reviews. A few specifics are on record.

Technically, the TM420 is a 100mm (roughly 4-inch) coaxial design with a polypropylene cone for the low range and a pure titanium diaphragm for the highs. JBL spec'd it with an 80 Hz–22 kHz frequency response, 4-ohm impedance, 40W allowable input, and 90 dB output sound pressure level. The motor uses a low-distortion SFG magnetic circuit with an edge-wise wound voice coil. No crossover frequency, weight, dimensions, or production run dates have surfaced.

The original rubber edges on these drivers tend to deteriorate, as they do on many car speakers of this era. A Japanese parts supplier (hobbies-n-things.com) sells a non-original replacement edge set, catalog number SB401, for ¥2,510. It includes adhesive and an 8-page installation manual, and it fits both the TM420 and the Fostex FW100. The listing is candid that this is a repair part, not an authentic JBL piece, and that it will harden and need replacing again within a few years. The included adhesive is not meant to be used as a damping agent.

Classified listings call the TM420 "vintage" car speakers. One Dutch seller offers a used set at €0.00 (pickup or shipping), and a Russian listing asks 1,000 rubles for a set described as new and "genuine American." No substantive owner reviews or measurements from period publications have been found. Audio, High Fidelity, and the other whitelisted magazines appear not to have covered this model.

Type: 2-way in-vehicle speaker unit
Aperture: 100mm
Frequency response: 80 Hz – 22 kHz
Impedance: 4 Ω
Allowable input: 40W
Output SPL: 90 dB
Low range: polypropylene cone; High range: pure titanium diaphragm
Original price: ¥36,000 per unit (c. 1990)