• Double-tuned, quarter-wave loaded high-impact subwoofer system
  • 21” woofer with all-carbon cone for high pressure loading
  • Large, rounded vent for improved breathing and low compression
  • Force-ventilated 5.3” voice-coil for low power compression prolonged performance
  • 15mm birch with extensive bracing brings lightweight yet rigid cabinet construction
  • SIS™ pre-wired for very high damping and further reduced distortion (with ALC)
  • Durotect™ flexible and scratch-resistant coating


BQ211 The BQ211 is a quarter-wave loaded subwoofer system, extending the low frequency response of Alcons’ pro-ribbon systems, in both permanent and portable applications. Featuring a state-ofthe- art 21” Neodymium transducer, this subwoofer is designed to offer maximum, prolonged high impact SPL performance from a relative small footprint. For this, the latest materials and innovations have been applied: A very large displacement transducer with all-carbon fiber cone + dust cap, 5.3” voice-coil with vented triple-spider frame plus optimized low resistance impedance, and port-vented magnet structure to maximally reduce power compression.

The extensively internally-braced cabinet features features double-tuned, high-pressure loading, through a rounded 236mm diameter low-tuned bass-reflex vent and a wide, high-tuned quarter wave tunnel. This provides optimised breathing at high SPLs, yet keeping the total system weight to a minimum.
Slider feet on cabinet bottom and side enable stacking of multiple BQ211’s into vertical LF arrays: The additional front-positioned NL4 connector caters for easy “reverse connection” in cardioid arrays.

The BQ211 is powered and controlled by the ALC amplified loudspeaker controller; Through the SDP™ (Speaker Drive Processor) circuit, the ALC offers BQ211-specific drive processing with response optimisation, dedicated power and excursion protection, hybrid filtering and cardoid processing.

Through the SIS™ (Signal Integrity Sensing) circuit, the cable-length and connector resistance between the BQ211 and ALC is completely compensated (damping factor 10.000), further increasing response accuracy.
The quarter wave pipe principle in combination with a low tuning frequency, forms a true wideband subwoofer with high SPL performance down to the lowest frequencies.

Typical applications for the BQ211 include groundstacked sub-bass extension of main sound systems, used in multiples depending on the application and sound pressure level / dispersion pattern control requirements.

Dimensional Drawing »

Technical Specifications

Frequency Response
+/- 3 dB 33 Hz – 150 Hz
+/- 10 dB 27 Hz –
Sensitivity (SPL 1W/M) 100 dB
Nominal Impedance 4 ohms
Recommended drive ALC4 min., 1 pce. per channel (4 ohms)
SPL program/peak (nom.) 135dB (ALC 6) / 140dB (comparative)
Dispersion H x V (array) omni / (hyper) cardioid in array with processing

Physical Specifications

System subwoofer, bass reflex + quarter wave pipe
Drivers LF 1 x AW21.6NDC/4 21″ double vented
Connectors 3 x Speakon NL4 input / link (rear)
cardioid (front)
Physical dimensions mm
Height 560
Width 747
Depth 986
Weight (approx.) BQ211 82kg
Weight (approx.) BQ211i 72kg
Warranty 6 years limited