B & C BAC21SW115C
Best box: 222.2 L bass reflex tuned to 34.8 Hz · F3 33.8 Hz
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Comparable 21.0" Drivers
Drivers with similar piston area, resonance and Qts — useful alternatives when the B & C BAC21SW115C 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 (222.2 L) requires extensive internal matrix bracing to prevent panel resonance.
Recommended Bass Reflex (Vented)
PORT BUILDABLE| Net Box Volume (Vb) | 222.2 Liters |
| Tuning Frequency (Fb) | 34.8 Hz |
| F3 (-3 dB Cutoff) | 33.8 Hz |
| F6 / F10 Extension | 30.1 Hz / 26.5 Hz |
| Port Inner Diameter | Ø 20.0 cm |
| Port Physical Length | 20.7 cm |
| First Pipe Resonance | 831.0 Hz |
| Estimated MOL @ F3 | 124.6 dB SPL |
Recommended Sealed (Acoustic Suspension)
MAX TRANSIENT DAMPING| Net Box Volume (Vb) | 97.3 Liters |
| System Q (Qtc) | 0.707 (Butterworth) |
| System Resonance (Fc) | 61.7 Hz |
| F3 (-3 dB Cutoff) | 63.2 Hz |
| F6 / F10 Extension | 47.4 Hz / 35.6 Hz |
| Air Spring Linearity | High (Zero port compression) |
Thiele/Small Parameters
| Resonance (Fs) | 33.0 Hz |
| Total Q (Qts) | 0.36 |
| Electrical Q (Qes) | 0.378 |
| Mechanical Q (Qms) | 7.7 |
| Equivalent Volume (Vas) | 278.0 Liters |
| Diaphragm Area (Sd) | 1680.0 cm² |
| DC Resistance (Re) | 3.6 Ω |
| Efficiency Bandwidth Product (EBP) | 87.4 |
| 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 BAC21SW115C?
Load Forge's calculated alignment puts B & C BAC21SW115C in a 222.2 liter vented enclosure tuned to 34.8 Hz, reaching an F3 cutoff of approximately 33.8 Hz.
Can B & C BAC21SW115C be used in a sealed box?
Yes. In a sealed (acoustic suspension) enclosure of 97.3 liters with a Qtc of 0.707 (Butterworth), the system exhibits an F3 of 63.2 Hz.
What port dimensions should be used for B & C BAC21SW115C to avoid port chuffing?
Sized from cone displacement (Sd × Xmax), a minimum port diameter of 20.0 cm with a length of 20.7 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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