HELIX Ci7 C165.2FM-S3
Best box: 20.0 L bass reflex tuned to 42.4 Hz · F3 49.7 Hz
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Comparable 6.0" Drivers
Drivers with similar piston area, resonance and Qts — useful alternatives when the HELIX Ci7 C165.2FM-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
- Limited linear excursion (Xmax: 3.7 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) | 20.0 Liters |
| Tuning Frequency (Fb) | 42.4 Hz |
| F3 (-3 dB Cutoff) | 49.7 Hz |
| F6 / F10 Extension | 37.7 Hz / 32.3 Hz |
| Port Inner Diameter | Ø 5.0 cm |
| Port Physical Length | 12.8 cm |
| First Pipe Resonance | 1344.0 Hz |
| Estimated MOL @ F3 | 103.5 dB SPL |
Recommended Sealed (Acoustic Suspension)
MAX TRANSIENT DAMPING| Net Box Volume (Vb) | 20.4 Liters |
| System Q (Qtc) | 0.707 (Butterworth) |
| System Resonance (Fc) | 73.7 Hz |
| F3 (-3 dB Cutoff) | 73.2 Hz |
| F6 / F10 Extension | 55.7 Hz / 42.3 Hz |
| Air Spring Linearity | High (Zero port compression) |
Thiele/Small Parameters
| Resonance (Fs) | 59.0 Hz |
| Total Q (Qts) | 0.55 |
| Electrical Q (Qes) | 0.638 |
| Mechanical Q (Qms) | 3.99 |
| Equivalent Volume (Vas) | 13.3 Liters |
| Diaphragm Area (Sd) | 131.0 cm² |
| DC Resistance (Re) | 3.0 Ω |
| Efficiency Bandwidth Product (EBP) | 92.5 |
| Linear Excursion (Xmax) | 3.7 mm |
| Thermal Power (Pe) | 150.0 W |
| Nominal Diameter | 6.0" |
| Catalog Source | Load Forge catalog (manufacturer datasheets and retailer listings) |
Frequently Asked Questions
What is the recommended ported (bass reflex) box volume for HELIX Ci7 C165.2FM-S3?
Load Forge's calculated alignment puts HELIX Ci7 C165.2FM-S3 in a 20.0 liter vented enclosure tuned to 42.4 Hz, reaching an F3 cutoff of approximately 49.7 Hz.
Can HELIX Ci7 C165.2FM-S3 be used in a sealed box?
Yes. In a sealed (acoustic suspension) enclosure of 20.4 liters with a Qtc of 0.707 (Butterworth), the system exhibits an F3 of 73.2 Hz.
What port dimensions should be used for HELIX Ci7 C165.2FM-S3 to avoid port chuffing?
Sized from cone displacement (Sd × Xmax), a minimum port diameter of 5.0 cm with a length of 12.8 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.
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