B&C Speakers 21SW115 8Ω
Best box: 275.0 L bass reflex tuned to 30.8 Hz · F3 30.1 Hz
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Comparable 21.0" Drivers
Drivers with similar piston area, resonance and Qts — useful alternatives when the B&C Speakers 21SW115 8Ω does not fit your target box volume or tuning. Each entry links to its full enclosure design and Thiele/Small parameters.
⚠️ Engineering Notice for Builders
- Large enclosure volume (275.0 L) requires extensive internal matrix bracing to prevent panel resonance.
Recommended Bass Reflex (Vented)
PORT BUILDABLE| Net Box Volume (Vb) | 275.0 Liters |
| Tuning Frequency (Fb) | 30.8 Hz |
| F3 (-3 dB Cutoff) | 30.1 Hz |
| F6 / F10 Extension | 26.7 Hz / 23.5 Hz |
| Port Inner Diameter | Ø 20.0 cm |
| Port Physical Length | 21.8 cm |
| First Pipe Resonance | 789.0 Hz |
| Estimated MOL @ F3 | 124.2 dB SPL |
Recommended Sealed (Acoustic Suspension)
MAX TRANSIENT DAMPING| Net Box Volume (Vb) | 119.9 Liters |
| System Q (Qtc) | 0.707 (Butterworth) |
| System Resonance (Fc) | 54.6 Hz |
| F3 (-3 dB Cutoff) | 56.1 Hz |
| F6 / F10 Extension | 42.3 Hz / 31.9 Hz |
| Air Spring Linearity | High (Zero port compression) |
Thiele/Small Parameters
| Resonance (Fs) | 30.0 Hz |
| Total Q (Qts) | 0.37 |
| Electrical Q (Qes) | 0.383 |
| Mechanical Q (Qms) | 10.9 |
| Equivalent Volume (Vas) | 318.0 Liters |
| Diaphragm Area (Sd) | 1680.0 cm² |
| DC Resistance (Re) | 5.4 Ω |
| Efficiency Bandwidth Product (EBP) | 78.3 |
| Linear Excursion (Xmax) | 14.0 mm |
| Thermal Power (Pe) | 1700.0 W |
| Nominal Diameter | 21.0" |
| Catalog Source | Load Forge catalog (manufacturer datasheets and retailer listings) |
Frequently Asked Questions
What is the recommended ported (bass reflex) box volume for B&C Speakers 21SW115 8Ω?
Load Forge's calculated alignment puts B&C Speakers 21SW115 8Ω in a 275.0 liter vented enclosure tuned to 30.8 Hz, reaching an F3 cutoff of approximately 30.1 Hz.
Can B&C Speakers 21SW115 8Ω be used in a sealed box?
Yes. In a sealed (acoustic suspension) enclosure of 119.9 liters with a Qtc of 0.707 (Butterworth), the system exhibits an F3 of 56.1 Hz.
What port dimensions should be used for B&C Speakers 21SW115 8Ω to avoid port chuffing?
Sized from cone displacement (Sd × Xmax), a minimum port diameter of 20.0 cm with a length of 21.8 cm is suggested; check the port air velocity at your drive level in the Load Forge Studio.
Shareable Acoustic Card for Forums & Social Media
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