Fi Car Audio MT Series 18
Best box: 127.0 L bass reflex tuned to 29.9 Hz · F3 28.8 Hz
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Comparable 18.0" Drivers
Drivers with similar piston area, resonance and Qts — useful alternatives when the Fi Car Audio MT Series 18 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 (127.0 L at 28.5 Hz) would need a 104.3 cm port; the recommendation is retuned to 127.0 L at 29.9 Hz so the port can be built.
- Port length (98.6 cm) exceeds a straight internal run; use an elbow bend, slotted vent or 3D folded duct to fit the enclosure.
- Large enclosure volume (127.0 L) requires extensive internal matrix bracing to prevent panel resonance.
Recommended Bass Reflex (Vented)
PORT NEEDS ELBOW / 3D| Net Box Volume (Vb) | 127.0 Liters |
| Tuning Frequency (Fb) | 29.9 Hz |
| F3 (-3 dB Cutoff) | 28.8 Hz |
| F6 / F10 Extension | 26.6 Hz / 24.4 Hz |
| Port Inner Diameter | Ø 23.6 cm |
| Port Physical Length | 98.6 cm |
| First Pipe Resonance | 174.0 Hz |
| Estimated MOL @ F3 | 125.5 dB SPL |
Recommended Sealed (Acoustic Suspension)
MAX TRANSIENT DAMPING| Net Box Volume (Vb) | 56.0 Liters |
| System Q (Qtc) | 0.707 (Butterworth) |
| System Resonance (Fc) | 51.1 Hz |
| F3 (-3 dB Cutoff) | 98.3 Hz |
| F6 / F10 Extension | 63.7 Hz / 40.4 Hz |
| Air Spring Linearity | High (Zero port compression) |
Thiele/Small Parameters
| Resonance (Fs) | 31.7 Hz |
| Total Q (Qts) | 0.43 |
| Electrical Q (Qes) | 0.45 |
| Mechanical Q (Qms) | 9.91 |
| Equivalent Volume (Vas) | 95.4 Liters |
| Diaphragm Area (Sd) | 1210.0 cm² |
| DC Resistance (Re) | 0.75 Ω |
| Efficiency Bandwidth Product (EBP) | 70.5 |
| Linear Excursion (Xmax) | 33.0 mm |
| Thermal Power (Pe) | 4500.0 W |
| Nominal Diameter | 18.0" |
| Catalog Source | Load Forge catalog (manufacturer datasheets and retailer listings) |
Frequently Asked Questions
What is the recommended ported (bass reflex) box volume for Fi Car Audio MT Series 18?
Load Forge's calculated alignment puts Fi Car Audio MT Series 18 in a 127.0 liter vented enclosure tuned to 29.9 Hz, reaching an F3 cutoff of approximately 28.8 Hz.
Can Fi Car Audio MT Series 18 be used in a sealed box?
Yes. In a sealed (acoustic suspension) enclosure of 56.0 liters with a Qtc of 0.707 (Butterworth), the system exhibits an F3 of 98.3 Hz.
What port dimensions should be used for Fi Car Audio MT Series 18 to avoid port chuffing?
Sized from cone displacement (Sd × Xmax), a minimum port diameter of 23.6 cm with a length of 98.6 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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