B&C Speakers 21SW152
Best box: 94.7 L bass reflex tuned to 47.6 Hz · F3 46.7 Hz
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Comparable 21.0" Drivers
Drivers with similar piston area, resonance and Qts — useful alternatives when the B&C Speakers 21SW152 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 (94.7 L at 39.7 Hz) would need a 58.1 cm port; the recommendation is retuned to 94.7 L at 47.6 Hz so the port can be built.
Recommended Bass Reflex (Vented)
PORT BUILDABLE| Net Box Volume (Vb) | 94.7 Liters |
| Tuning Frequency (Fb) | 47.6 Hz |
| F3 (-3 dB Cutoff) | 46.7 Hz |
| F6 / F10 Extension | 42.0 Hz / 37.1 Hz |
| Port Inner Diameter | Ø 23.6 cm |
| Port Physical Length | 44.2 cm |
| First Pipe Resonance | 389.0 Hz |
| Estimated MOL @ F3 | 125.9 dB SPL |
Recommended Sealed (Acoustic Suspension)
MAX TRANSIENT DAMPING| Net Box Volume (Vb) | 43.9 Liters |
| System Q (Qtc) | 0.707 (Butterworth) |
| System Resonance (Fc) | 72.7 Hz |
| F3 (-3 dB Cutoff) | 79.0 Hz |
| F6 / F10 Extension | 58.5 Hz / 43.5 Hz |
| Air Spring Linearity | High (Zero port compression) |
Thiele/Small Parameters
| Resonance (Fs) | 32.0 Hz |
| Total Q (Qts) | 0.3 |
| Electrical Q (Qes) | 0.313 |
| Mechanical Q (Qms) | 7.0 |
| Equivalent Volume (Vas) | 200.0 Liters |
| Diaphragm Area (Sd) | 1680.0 cm² |
| DC Resistance (Re) | 3.3 Ω |
| Efficiency Bandwidth Product (EBP) | 102.1 |
| Linear Excursion (Xmax) | 15.0 mm |
| Thermal Power (Pe) | 2000.0 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 21SW152?
Load Forge's calculated alignment puts B&C Speakers 21SW152 in a 94.7 liter vented enclosure tuned to 47.6 Hz, reaching an F3 cutoff of approximately 46.7 Hz.
Can B&C Speakers 21SW152 be used in a sealed box?
Yes. In a sealed (acoustic suspension) enclosure of 43.9 liters with a Qtc of 0.707 (Butterworth), the system exhibits an F3 of 79.0 Hz.
What port dimensions should be used for B&C Speakers 21SW152 to avoid port chuffing?
Sized from cone displacement (Sd × Xmax), a minimum port diameter of 23.6 cm with a length of 44.2 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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