HELIX Ci3 M100FM-S3
Best box: 2.2 L bass reflex tuned to 111.7 Hz · F3 123.5 Hz
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Comparable 4.0" Drivers
Drivers with similar piston area, resonance and Qts — useful alternatives when the HELIX Ci3 M100FM-S3 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 124.1 Hz) would need a 21.9 cm port; the recommendation is retuned to 2.2 L at 111.7 Hz so the port can be built.
- Limited linear excursion (Xmax: 2.0 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) | 2.2 Liters |
| Tuning Frequency (Fb) | 111.7 Hz |
| F3 (-3 dB Cutoff) | 123.5 Hz |
| F6 / F10 Extension | 95.2 Hz / 83.4 Hz |
| Port Inner Diameter | Ø 5.0 cm |
| Port Physical Length | 17.9 cm |
| First Pipe Resonance | 963.0 Hz |
| Estimated MOL @ F3 | 106.7 dB SPL |
Sealed (Acoustic Suspension) — compromise
SUITS INFINITE / OPEN BAFFLEWith Qts 0.83 a Butterworth (Qtc 0.707) box would be many times Vas. A box equal to Vas reaches Qtc 1.174; for a flat response this driver is better used on an infinite (IB) or open baffle.
| Net Box Volume (Vb) | 1.1 Liters |
| System Q (Qtc) | 1.174 (above Butterworth: Qtc cannot fall below Qts (0.83)) |
| System Resonance (Fc) | 206.5 Hz |
| F3 (-3 dB Cutoff) | 169.5 Hz |
| F6 / F10 Extension | 142.6 Hz / 115.9 Hz |
| Air Spring Linearity | High (Zero port compression) |
Thiele/Small Parameters
| Resonance (Fs) | 146.0 Hz |
| Total Q (Qts) | 0.83 |
| Electrical Q (Qes) | 1.018 |
| Mechanical Q (Qms) | 4.49 |
| Equivalent Volume (Vas) | 1.1 Liters |
| Diaphragm Area (Sd) | 53.0 cm² |
| DC Resistance (Re) | 3.0 Ω |
| Efficiency Bandwidth Product (EBP) | 143.4 |
| Linear Excursion (Xmax) | 2.0 mm |
| Thermal Power (Pe) | 80.0 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 HELIX Ci3 M100FM-S3?
Load Forge's calculated alignment puts HELIX Ci3 M100FM-S3 in a 2.2 liter vented enclosure tuned to 111.7 Hz, reaching an F3 cutoff of approximately 123.5 Hz.
Can HELIX Ci3 M100FM-S3 be used in a sealed box?
Yes. In a sealed (acoustic suspension) enclosure of 1.1 liters with a Qtc of 1.174 (above Butterworth: Qtc cannot fall below Qts (0.83)), the system exhibits an F3 of 169.5 Hz.
What port dimensions should be used for HELIX Ci3 M100FM-S3 to avoid port chuffing?
Sized from cone displacement (Sd × Xmax), a minimum port diameter of 5.0 cm with a length of 17.9 cm is suggested; check the port air velocity at your drive level in the Load Forge Studio.
Shareable Acoustic Card for Forums & Social Media
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