Eighteen Sound 21NLW4000
Best box: 263.7 L bass reflex tuned to 29.8 Hz · F3 29.0 Hz
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Comparable 21.0" Drivers
Drivers with similar piston area, resonance and Qts — useful alternatives when the Eighteen Sound 21NLW4000 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 (263.7 L) requires extensive internal matrix bracing to prevent panel resonance.
Recommended Bass Reflex (Vented)
PORT BUILDABLE| Net Box Volume (Vb) | 263.7 Liters |
| Tuning Frequency (Fb) | 29.8 Hz |
| F3 (-3 dB Cutoff) | 29.0 Hz |
| F6 / F10 Extension | 25.8 Hz / 22.7 Hz |
| Port Inner Diameter | Ø 20.0 cm |
| Port Physical Length | 25.9 cm |
| First Pipe Resonance | 664.0 Hz |
| Estimated MOL @ F3 | 123.3 dB SPL |
Recommended Sealed (Acoustic Suspension)
MAX TRANSIENT DAMPING| Net Box Volume (Vb) | 115.0 Liters |
| System Q (Qtc) | 0.707 (Butterworth) |
| System Resonance (Fc) | 53.1 Hz |
| F3 (-3 dB Cutoff) | 54.5 Hz |
| F6 / F10 Extension | 41.0 Hz / 30.9 Hz |
| Air Spring Linearity | High (Zero port compression) |
Thiele/Small Parameters
| Resonance (Fs) | 29.0 Hz |
| Total Q (Qts) | 0.37 |
| Electrical Q (Qes) | 0.376 |
| Mechanical Q (Qms) | 22.0 |
| Equivalent Volume (Vas) | 305.0 Liters |
| Diaphragm Area (Sd) | 1660.0 cm² |
| DC Resistance (Re) | 4.9 Ω |
| Efficiency Bandwidth Product (EBP) | 77.1 |
| Linear Excursion (Xmax) | 15.0 mm |
| Thermal Power (Pe) | 1600.0 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 Eighteen Sound 21NLW4000?
Load Forge's calculated alignment puts Eighteen Sound 21NLW4000 in a 263.7 liter vented enclosure tuned to 29.8 Hz, reaching an F3 cutoff of approximately 29.0 Hz.
Can Eighteen Sound 21NLW4000 be used in a sealed box?
Yes. In a sealed (acoustic suspension) enclosure of 115.0 liters with a Qtc of 0.707 (Butterworth), the system exhibits an F3 of 54.5 Hz.
What port dimensions should be used for Eighteen Sound 21NLW4000 to avoid port chuffing?
Sized from cone displacement (Sd × Xmax), a minimum port diameter of 20.0 cm with a length of 25.9 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.
Not sure if 21NLW4000 fits your physical space?
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