PHL Audio 1660NdM-SQ2
Best box: 0.5 L sealed · Fc 509.1 Hz · F3 402.9 Hz
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Comparable 6.5" Drivers
Drivers with similar piston area, resonance and Qts — useful alternatives when the PHL Audio 1660NdM-SQ2 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: 2.5 mm); set a high-pass subsonic filter at 25–30 Hz when driven with high power.
Textbook Bass Reflex — not recommended (15.1 dB bass hump)
PORT BUILDABLE| Net Box Volume (Vb) | 1.5 Liters |
| Tuning Frequency (Fb) | 306.0 Hz |
| F3 (-3 dB Cutoff) | 279.9 Hz |
| F6 / F10 Extension | 252.9 Hz / 229.4 Hz |
| Port Inner Diameter | Ø 7.5 cm |
| Port Physical Length | 4.1 cm |
| First Pipe Resonance | 4230.0 Hz |
| Estimated MOL @ F3 | 122.2 dB SPL |
Sealed (Acoustic Suspension) — compromise
SUITS INFINITE / OPEN BAFFLEWith Qts 0.9 a Butterworth (Qtc 0.707) box would be many times Vas. A box equal to Vas reaches Qtc 1.273; for a flat response this driver is better used on an infinite (IB) or open baffle.
| Net Box Volume (Vb) | 0.5 Liters |
| System Q (Qtc) | 1.273 (above Butterworth: Qtc cannot fall below Qts (0.90)) |
| System Resonance (Fc) | 509.1 Hz |
| F3 (-3 dB Cutoff) | 402.9 Hz |
| F6 / F10 Extension | 341.2 Hz / 279.2 Hz |
| Air Spring Linearity | High (Zero port compression) |
Thiele/Small Parameters
| Resonance (Fs) | 360.0 Hz |
| Total Q (Qts) | 0.9 |
| Electrical Q (Qes) | 0.975 |
| Mechanical Q (Qms) | 11.76 |
| Equivalent Volume (Vas) | 0.5 Liters |
| Diaphragm Area (Sd) | 150.0 cm² |
| DC Resistance (Re) | 5.2 Ω |
| Efficiency Bandwidth Product (EBP) | 369.4 |
| Linear Excursion (Xmax) | 2.5 mm |
| Thermal Power (Pe) | 250.0 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 PHL Audio 1660NdM-SQ2?
A simple ported box is not recommended for PHL Audio 1660NdM-SQ2: the textbook alignment (1.5 liters tuned to 306.0 Hz) needs a 4.1 cm port, and no nearby retune stays buildable without a bass hump. A sealed box, a passive radiator or a folded duct is the practical choice.
Can PHL Audio 1660NdM-SQ2 be used in a sealed box?
Yes. In a sealed (acoustic suspension) enclosure of 0.5 liters with a Qtc of 1.273 (above Butterworth: Qtc cannot fall below Qts (0.90)), the system exhibits an F3 of 402.9 Hz.
What port dimensions should be used for PHL Audio 1660NdM-SQ2 to avoid port chuffing?
A straight 7.5 cm port would need 4.1 cm of length, which does not fit a practical cabinet. Use a passive radiator or a folded/3D duct instead of a straight tube.
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