Rockville MS40W
Best box: 6.0 L bass reflex tuned to 103.7 Hz · F3 95.0 Hz
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Comparable 4.0" Drivers
Drivers with similar piston area, resonance and Qts — useful alternatives when the Rockville MS40W 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 (1.5 L at 103.7 Hz) would need a 32.9 cm port; the recommendation is retuned to 6.0 L at 103.7 Hz so the port can be built.
- Limited linear excursion (Xmax: 1.5 mm); set a high-pass subsonic filter at 25–30 Hz when driven with high power.
Recommended Bass Reflex (Vented)
PORT BUILDABLE| Net Box Volume (Vb) | 6.0 Liters |
| Tuning Frequency (Fb) | 103.7 Hz |
| F3 (-3 dB Cutoff) | 95.0 Hz |
| F6 / F10 Extension | 89.4 Hz / 84.8 Hz |
| Port Inner Diameter | Ø 5.0 cm |
| Port Physical Length | 5.5 cm |
| First Pipe Resonance | 3101.0 Hz |
| Estimated MOL @ F3 | 100.9 dB SPL |
Sealed (Acoustic Suspension) — compromise
SUITS INFINITE / OPEN BAFFLEWith Qts 1.611 a Butterworth (Qtc 0.707) box would be many times Vas. A box equal to Vas reaches Qtc 2.278; for a flat response this driver is better used on an infinite (IB) or open baffle.
| Net Box Volume (Vb) | 0.85 Liters |
| System Q (Qtc) | 2.278 (above Butterworth: Qtc cannot fall below Qts (1.61)) |
| System Resonance (Fc) | 172.5 Hz |
| F3 (-3 dB Cutoff) | 188.4 Hz |
| F6 / F10 Extension | 171.1 Hz / 149.7 Hz |
| Air Spring Linearity | High (Zero port compression) |
Thiele/Small Parameters
| Resonance (Fs) | 122.0 Hz |
| Total Q (Qts) | 1.611 |
| Electrical Q (Qes) | 2.571 |
| Mechanical Q (Qms) | 4.32 |
| Equivalent Volume (Vas) | 0.8 Liters |
| Diaphragm Area (Sd) | 54.0 cm² |
| DC Resistance (Re) | 3.2 Ω |
| Efficiency Bandwidth Product (EBP) | 47.5 |
| Linear Excursion (Xmax) | 1.5 mm |
| Thermal Power (Pe) | 50.0 W |
| Nominal Diameter | 4.0" |
| Catalog Source | Load Forge catalog (manufacturer datasheets and retailer listings) |
Frequently Asked Questions
What is the recommended ported (bass reflex) box volume for Rockville MS40W?
Load Forge's calculated alignment puts Rockville MS40W in a 6.0 liter vented enclosure tuned to 103.7 Hz, reaching an F3 cutoff of approximately 95.0 Hz.
Can Rockville MS40W be used in a sealed box?
Yes. In a sealed (acoustic suspension) enclosure of 0.85 liters with a Qtc of 2.278 (above Butterworth: Qtc cannot fall below Qts (1.61)), the system exhibits an F3 of 188.4 Hz.
What port dimensions should be used for Rockville MS40W to avoid port chuffing?
Sized from cone displacement (Sd × Xmax), a minimum port diameter of 5.0 cm with a length of 5.5 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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