This is a Bossman BSX-221 dual-21-inch subwoofer.
Model: BSX-221
LF drivers: 2 × 21-inch
Power (Pro): 2,000 W
Impedance: 4 Ω
Sensitivity: 100 dB (1 W/1 m)
Maximum SPL: 140 dB
Frequency range: The plate appears to say 37 Hz–800 kHz, but that upper figure is almost certainly a printing/specification error; a dual-21 subwoofer would normally have a much lower upper operating limit.
This is a very large, high-output subwoofer designed for serious PA systems. Two 21-inch drivers give it considerably more cone area than a single 18-inch sub, so it is intended to produce powerful low-frequency output for:
Large churches
Outdoor events
Concerts
DJs
Live bands
Large sound reinforcement systems