B&C 21SW115 – Powerful 21″ Neodymium Subwoofer Driver with 3400W Continuous Handling
If your subwoofer build needs to move serious air at serious power levels, the B&C 21SW115 is one of the most capable 21-inch subwoofer drivers available. This neodymium-powered monster handles 3400 W continuous program power through a 116 mm (4.5-inch) split-winding copper voice coil, delivering ground-shaking low-frequency output from 30 Hz with 60 mm of peak-to-peak excursion before damage.
The B&C 21SW115 produces 97 dB sensitivity from a massive 1680 cm² piston area — more cone surface than any 18-inch driver can offer. That combination of sensitivity, excursion, and cone area translates directly into the kind of deep, physical bass that you feel in your chest, not just hear with your ears.
Available in both 4 Ω and 8 Ω versions, the B&C 21SW115 gives you the impedance flexibility to match your amplifier and wiring configuration. Whether you’re building a single-driver reflex sub, a horn-loaded infrasub, or a multi-driver low-frequency array, this driver gives you the displacement, power handling, and motor control to deliver bass at a level that smaller drivers simply can’t reach.
Design and Construction of the B&C 21SW115
The B&C 21SW115 is built around a 116 mm (4.5-inch) split-winding copper voice coil on a glass fibre former. This is one of the largest voice coils in B&C’s entire driver catalogue. The split-winding design allows the 4 Ω and 8 Ω versions to share the same coil structure, while the sheer diameter provides an enormous thermal surface area for heat dissipation.
For your build, that thermal capacity is what makes sustained 3400 W operation possible without the driver compressing or overheating. A ventilated voice coil gap further reduces power compression by allowing airflow through the motor during excursion. You’ll maintain full output at the end of a punishing set just as well as at the start.
The double silicone spider suspension provides tight mechanical control over the heavy 342 g moving assembly throughout its massive stroke. The 16 mm Xvar (linear excursion) and 60 mm peak-to-peak excursion before damage give the B&C 21SW115 extraordinary air displacement. That’s how a single 21-inch driver can pressurize a room with deep bass that most dual-18 setups struggle to match.
The 30.1 Tm Bl factor is exceptionally strong, ensuring the neodymium motor maintains authoritative control over the cone even at maximum excursion. You’ll hear this as tight, defined bass rather than loose, boomy output — the driver hits hard and resets fast, giving you punchy kick drums and clean sub-bass that doesn’t smear or overhang.
An aluminium demodulating ring in the motor structure suppresses modulation distortion, keeping the output clean and linear even under extreme load. The radial cone shape and triple roll surround are optimised for maximum excursion capability while maintaining consistent compliance across the stroke.
The cone features TWP (Total Waterproof) treatment on both sides — full moisture protection for outdoor festival rigs, humid venue environments, and any build where weather exposure is a concern. The neodymium inside-slug magnet with T-pole design keeps the motor compact despite its enormous power, holding the total driver weight to 14 kg — remarkably manageable for a 21-inch subwoofer of this capability.
Performance and Applications for the B&C 21SW115
The B&C 21SW115 handles 3400 W continuous with 97 dB sensitivity and a frequency range from 30 Hz to 1000 Hz. The 2.2% reference efficiency means your amplifier watts translate effectively into SPL. Pair it with a quality 2000–3500 W amp and you’ll have a subwoofer that dominates any room.
B&C provides specific enclosure recommendations: a 250-litre vented box tuned to 32 Hz. That’s a useful starting point for your design. The Qts of 0.37 and EBP of 77 Hz confirm the driver works well in both vented and horn-loaded enclosures, giving you design flexibility depending on your application.
The 318-litre Vas is large, which is expected for a 21-inch driver. Your enclosure will be substantial, but the output-per-box ratio of a single 21-inch sub often beats a dual-18 configuration in both efficiency and low-frequency extension — with a simpler build and fewer drivers to wire.
Builders commonly choose the B&C 21SW115 for:
- High-output bass-reflex subwoofer cabinets for live sound
- Horn-loaded and bandpass subwoofer designs for maximum SPL
- Festival and touring sub stacks requiring extreme low-frequency output
- Club and venue installations needing deep, physical bass impact
- Single-driver subs that need to replace or outperform dual-18 configurations
The driver displaces 15 litres of air volume inside the enclosure, which needs to be accounted for in your cabinet calculations. At 249 mm deep and 547 mm overall diameter, the B&C 21SW115 is a large driver — but the neodymium motor keeps it significantly lighter and more compact than ferrite alternatives in this class.
Specifications
- Nominal Diameter: 530 mm (21 in)
- Voice Coil Diameter: 116 mm (4.5 in)
- Continuous Power Handling: 3400 W
- Nominal Power Handling: 1700 W
- Nominal Impedance: 8 Ω (also available in 4 Ω)
- Minimum Impedance: 6.2 Ω
- Frequency Range: 30 Hz – 1,000 Hz
- Sensitivity: 97 dB
- Winding Material: Copper (Split Winding)
- Former Material: Glass Fibre
- Winding Depth: 34 mm (1.34 in)
- Magnetic Gap Depth: 14 mm (0.55 in)
- Flux Density: 1.15 T
- Surround Shape: Triple Roll
- Cone Shape: Radial
- Spider: Double Silicone
- Cone Treatment: TWP Waterproof Both Sides
Thiele–Small Parameters
- Fs: 30 Hz
- Re: 5.4 Ω
- Qes: 0.39
- Qms: 10.9
- Qts: 0.37
- Vas: 318 dm³ (11.23 ft³)
- Sd: 1680 cm² (260.4 in²)
- η₀: 2.2%
- Xmax: 14 mm
- Xvar: 16 mm
- Mms: 342 g
- Bl: 30.1 Tm
- Le: 2.1 mH
- EBP: 77 Hz
Mounting Information
- Overall Diameter: 547 mm (21.5 in)
- Bolt Circle Diameter: 527 mm (20.7 in)
- Baffle Cutout: 503 mm (19.8 in)
- Depth: 249 mm (9.8 in)
- Air Volume Occupied: 15 dm³ (0.53 ft³)
- Net Weight: 14 kg (30.8 lb)
- Replacement Recone Kit: RCK21SW1158
Conclusion
The B&C 21SW115 is the driver to choose when your sub build demands the deepest, most powerful bass available from a single driver. Its 116 mm split-winding copper coil, 3400 W continuous handling, and 60 mm peak-to-peak excursion deliver the kind of low-frequency displacement that physically moves air and bodies in equal measure.
With a 30.1 Tm Bl factor for tight motor control, a ventilated gap for reduced power compression, TWP double-side waterproofing, and B&C’s own 250-litre / 32 Hz enclosure recommendation to get you started, the B&C 21SW115 gives you professional-grade subwoofer performance from a 14 kg neodymium platform. Whether you’re building a single-driver reflex sub, a horn-loaded infra cabinet, or a bass stack for touring, this is the 21-inch driver that delivers when nothing less than the absolute deepest output will do.
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About B&C Speakers S.r.L.
B&C Speakers products are built in Bagno a Ripoli (Florence), Italy., ensuring high quality products to suite your speaker building requirements. Their 10,500 square meter facility incorporates highly sophisticated automation and quality control. Over the years they become one of the world leaders in the Professional Audio market, a brand recognized everywhere as a premium product that offers excellent value to the consumer.
