QSC SB-15121 High-Output 21-Inch Cinema Subwoofer for Premium Low-Frequency Performance
1500W Continuous | 139 dB Peak SPL | 23.8 Hz Extension | 21" Transducer
Overview
The QSC SB-15121 is a premium 21-inch cinema subwoofer engineered for high-impact low-frequency reproduction in large-format theaters and post-production environments. Designed to deliver deep, distortion-free bass without the need for B6 EQ filters, the SB-15121 extends cleanly below 25 Hz and reaches a peak SPL of 137 dB—making it one of the most powerful subwoofers in its class.
Its vented enclosure is tuned to 25 Hz and features a symmetrical port design to minimize turbulence and port compression at high drive levels. The 21" transducer incorporates a vented 6-inch copper voice coil on a fiberglass former, neodymium magnet structure, and high-excursion suspension—resulting in exceptional thermal stability, low distortion, and long-term reliability.
With a nominal impedance of 4 ohms and a sensitivity of 99 dB (40–100 Hz), the SB-15121 integrates easily into high-power cinema systems. It includes barrier strip terminals for flexible wiring and is compatible with QSC DCP, DCM, and SF-3 signal processors. The enclosure is constructed from heavily braced MDF and includes vandal-resistant mounting hardware for secure installation.
Technical Specifications
| Category | Specification |
|---|---|
| Transducer | 21" (533 mm) high-efficiency subwoofer |
| Voice Coil | 6" (153 mm) copper, vented, on fiberglass former |
| Frequency Response (-6 dB) | 23.8 Hz – 250 Hz |
| Frequency Response (-10 dB) | 21.5 Hz – 250 Hz |
| Sensitivity (40–100 Hz) | 99 dB SPL (1W/1m, half space) |
| Maximum SPL (Peak) | 137 dB |
| Maximum SPL (Continuous) | 131 dB |
| Nominal Impedance | 4 Ohms |
| Power Handling | 1500W Continuous / 2500W AES / 3400W Max Recommended |
| Recommended Amplifier | 1200W min / 3400W max |
| Nominal Coverage | Omnidirectional (80 Hz) |
| Recommended Processing | HPF at 20 Hz, 12 dB/octave minimum |
| Input Connectors | Barrier strip (accepts up to #10 AWG), 2 in / 2 out |
| Enclosure Type | Vented, symmetrical port, tuned to 25 Hz |
| Enclosure Construction | MDF, heavily braced, vandal-resistant mounting bolts |
Physical Data
| Dimension | Value |
|---|---|
| Height | 48.8 in (1238 mm) |
| Width | 30 in (762 mm) |
| Depth | 24 in (610 mm) |
| Net Weight | 231 lbs (105 kg) |
| Shipping Weight | 257 lbs (114 kg) |
