JBL MI-15
The JBL MI-15 is a 15-inch woofer from JBL's MI ("Music/Industrial") series, built for cinema sound systems. It's a component driver, not a complete speaker cabinet. It would have sat behind a theater screen alongside a high-frequency horn, crossed over somewhere around 800 Hz. The "MI" designation and its documented use in motion picture installations place it in JBL's professional theater lineup. Exactly which cinema systems used it isn't recorded.
Here is what's known about the driver itself. It's an alnico magnet design with a 4-inch voice coil and a cast aluminum frame, fitted with a paper cone. It's rated at 16 ohms, handles 35 watts, and is efficient at 98 dB (1W/1m), which is typical of the era's theater drivers, built to get loud from modest amplifier power. It was meant to be used in a bass reflex (ported) enclosure. The frequency response figures in the record conflict slightly - one source says 50 Hz to 8 kHz, another 50-9,000 Hz - so take either as approximate.
The MI-15 also found a second life among hobbyists. DIY audio forum users have repurposed pairs as guitar speakers, reporting "great tone" with a clean, articulate top end, and noting the driver's efficiency pairs well with low-power tube amps. Collectors describe it as hard to find and sought after - a "great old JBL driver" in the words of one Audiokarma poster, who also notes it shares its alnico magnet structure with other JBL 15-inch drivers of the period. No production years, original price, dimensions, or weight have surfaced in the available documentation. Period coverage in EQ Magazine (September 1995, p.86) documents JBL's use of polypropylene in contemporary designs, a contrast to the paper cone of the MI-15.
Known specs:
- Type: 15" woofer (component driver)
- Impedance: 16 ohms
- Power handling: 35 watts
- Sensitivity: 98 dB @ 1W/1m
- Voice coil: 4"
- Magnet: Alnico
- Frame: Cast aluminum
- Cone: Paper
- Recommended enclosure: Bass reflex, crossed over ~800 Hz to a HF horn
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