HELIX Ci3 C100.2FM-S3
Best box: 3.4 L bass reflex tuned to 104.9 Hz · F3 110.7 Hz
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Comparable 4.0" Drivers
Drivers with similar piston area, resonance and Qts — useful alternatives when the HELIX Ci3 C100.2FM-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 (1.7 L at 116.5 Hz) would need a 21.9 cm port; the recommendation is retuned to 3.4 L at 104.9 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) | 3.4 Liters |
| Tuning Frequency (Fb) | 104.9 Hz |
| F3 (-3 dB Cutoff) | 110.7 Hz |
| F6 / F10 Extension | 89.9 Hz / 78.4 Hz |
| Port Inner Diameter | Ø 5.0 cm |
| Port Physical Length | 12.2 cm |
| First Pipe Resonance | 1415.0 Hz |
| Estimated MOL @ F3 | 107.8 dB SPL |
Sealed (Acoustic Suspension) — compromise
SUITS INFINITE / OPEN BAFFLEWith Qts 0.66 a Butterworth (Qtc 0.707) box would be many times Vas. A box equal to Vas reaches Qtc 0.933; for a flat response this driver is better used on an infinite (IB) or open baffle.
| Net Box Volume (Vb) | 2.1 Liters |
| System Q (Qtc) | 0.933 (above Butterworth) |
| System Resonance (Fc) | 193.7 Hz |
| F3 (-3 dB Cutoff) | 163.4 Hz |
| F6 / F10 Extension | 132.0 Hz / 104.1 Hz |
| Air Spring Linearity | High (Zero port compression) |
Thiele/Small Parameters
| Resonance (Fs) | 137.0 Hz |
| Total Q (Qts) | 0.66 |
| Electrical Q (Qes) | 0.777 |
| Mechanical Q (Qms) | 4.37 |
| Equivalent Volume (Vas) | 2.1 Liters |
| Diaphragm Area (Sd) | 57.0 cm² |
| DC Resistance (Re) | 3.0 Ω |
| Efficiency Bandwidth Product (EBP) | 176.2 |
| 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 C100.2FM-S3?
Load Forge's calculated alignment puts HELIX Ci3 C100.2FM-S3 in a 3.4 liter vented enclosure tuned to 104.9 Hz, reaching an F3 cutoff of approximately 110.7 Hz.
Can HELIX Ci3 C100.2FM-S3 be used in a sealed box?
Yes. In a sealed (acoustic suspension) enclosure of 2.1 liters with a Qtc of 0.933 (above Butterworth), the system exhibits an F3 of 163.4 Hz.
What port dimensions should be used for HELIX Ci3 C100.2FM-S3 to avoid port chuffing?
Sized from cone displacement (Sd × Xmax), a minimum port diameter of 5.0 cm with a length of 12.2 cm is suggested; check the port air velocity at your drive level in the Load Forge Studio.
Shareable Acoustic Card for Forums & Social Media
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