Scan-Speak 18M/8631T00
Best box: 11.2 L bass reflex tuned to 55.2 Hz · F3 78.6 Hz
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Comparable 6.5" Drivers
Drivers with similar piston area, resonance and Qts — useful alternatives when the Scan-Speak 18M/8631T00 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: 3.0 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) | 11.2 Liters |
| Tuning Frequency (Fb) | 55.2 Hz |
| F3 (-3 dB Cutoff) | 78.6 Hz |
| F6 / F10 Extension | 65.1 Hz / 50.0 Hz |
| Port Inner Diameter | Ø 5.0 cm |
| Port Physical Length | 13.7 cm |
| First Pipe Resonance | 1258.0 Hz |
| Estimated MOL @ F3 | 106.3 dB SPL |
Sealed (Acoustic Suspension) — compromise
SUITS INFINITE / OPEN BAFFLEWith Qts 0.71 a Butterworth (Qtc 0.707) box would be many times Vas. A box equal to Vas reaches Qtc 1.004; for a flat response this driver is better used on an infinite (IB) or open baffle.
| Net Box Volume (Vb) | 14.0 Liters |
| System Q (Qtc) | 1.004 (above Butterworth: Qtc cannot fall below Qts (0.71)) |
| System Resonance (Fc) | 91.9 Hz |
| F3 (-3 dB Cutoff) | 76.5 Hz |
| F6 / F10 Extension | 63.0 Hz / 50.4 Hz |
| Air Spring Linearity | High (Zero port compression) |
Thiele/Small Parameters
| Resonance (Fs) | 65.0 Hz |
| Total Q (Qts) | 0.71 |
| Electrical Q (Qes) | 0.821 |
| Mechanical Q (Qms) | 5.24 |
| Equivalent Volume (Vas) | 14.0 Liters |
| Diaphragm Area (Sd) | 154.0 cm² |
| DC Resistance (Re) | 6.0 Ω |
| Efficiency Bandwidth Product (EBP) | 79.1 |
| Linear Excursion (Xmax) | 3.0 mm |
| Thermal Power (Pe) | 120.0 W |
| Nominal Diameter | 6.5" |
| Catalog Source | Load Forge catalog (manufacturer datasheets and retailer listings) |
Frequently Asked Questions
What is the recommended ported (bass reflex) box volume for Scan-Speak 18M/8631T00?
Load Forge's calculated alignment puts Scan-Speak 18M/8631T00 in a 11.2 liter vented enclosure tuned to 55.2 Hz, reaching an F3 cutoff of approximately 78.6 Hz.
Can Scan-Speak 18M/8631T00 be used in a sealed box?
Yes. In a sealed (acoustic suspension) enclosure of 14.0 liters with a Qtc of 1.004 (above Butterworth: Qtc cannot fall below Qts (0.71)), the system exhibits an F3 of 76.5 Hz.
What port dimensions should be used for Scan-Speak 18M/8631T00 to avoid port chuffing?
Sized from cone displacement (Sd × Xmax), a minimum port diameter of 5.0 cm with a length of 13.7 cm is suggested; check the port air velocity at your drive level in the Load Forge Studio.
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