B&C Speakers 21SW150
Best box: 79.8 L bass reflex tuned to 55.2 Hz · F3 54.3 Hz
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Comparable 21.0" Drivers
Drivers with similar piston area, resonance and Qts — useful alternatives when the B&C Speakers 21SW150 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
- The textbook alignment (79.8 L at 40.9 Hz) would need a 68.9 cm port; the recommendation is retuned to 79.8 L at 55.2 Hz so the port can be built.
Recommended Bass Reflex (Vented)
PORT BUILDABLE| Net Box Volume (Vb) | 79.8 Liters |
| Tuning Frequency (Fb) | 55.2 Hz |
| F3 (-3 dB Cutoff) | 54.3 Hz |
| F6 / F10 Extension | 49.3 Hz / 43.8 Hz |
| Port Inner Diameter | Ø 25.4 cm |
| Port Physical Length | 44.3 cm |
| First Pipe Resonance | 388.0 Hz |
| Estimated MOL @ F3 | 126.0 dB SPL |
Recommended Sealed (Acoustic Suspension)
MAX TRANSIENT DAMPING| Net Box Volume (Vb) | 39.7 Liters |
| System Q (Qtc) | 0.707 (Butterworth) |
| System Resonance (Fc) | 76.2 Hz |
| F3 (-3 dB Cutoff) | 80.4 Hz |
| F6 / F10 Extension | 59.0 Hz / 43.7 Hz |
| Air Spring Linearity | High (Zero port compression) |
Thiele/Small Parameters
| Resonance (Fs) | 29.0 Hz |
| Total Q (Qts) | 0.26 |
| Electrical Q (Qes) | 0.269 |
| Mechanical Q (Qms) | 8.1 |
| Equivalent Volume (Vas) | 254.0 Liters |
| Diaphragm Area (Sd) | 1680.0 cm² |
| DC Resistance (Re) | 3.0 Ω |
| Efficiency Bandwidth Product (EBP) | 108.0 |
| Linear Excursion (Xmax) | 15.0 mm |
| Thermal Power (Pe) | 1500.0 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 21SW150?
Load Forge's calculated alignment puts B&C Speakers 21SW150 in a 79.8 liter vented enclosure tuned to 55.2 Hz, reaching an F3 cutoff of approximately 54.3 Hz.
Can B&C Speakers 21SW150 be used in a sealed box?
Yes. In a sealed (acoustic suspension) enclosure of 39.7 liters with a Qtc of 0.707 (Butterworth), the system exhibits an F3 of 80.4 Hz.
What port dimensions should be used for B&C Speakers 21SW150 to avoid port chuffing?
Sized from cone displacement (Sd × Xmax), a minimum port diameter of 25.4 cm with a length of 44.3 cm is suggested; check the port air velocity at your drive level in the Load Forge Studio.
Shareable Acoustic Card for Forums & Social Media
Embed this design card on DIYAudio, AVSForum, Reddit, or Facebook. It shows the calculated F3, MOL (when the power rating is published) and box parameters.
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