A 4 ohm version of the popular Sigma Pro 18, recommended for professional audio as a woofer in vented enclosures.

Specification
Nominal Basket Diameter18", 457 mm
Nominal Impedance*4 Ω
Power Rating**
Watts700 W
Music Program1400 W
Resonance32 Hz
Usable Frequency Range32 Hz - 2 kHz
Sensitivity***97.6 dB
Magnet Weight120 oz.
Gap Height0.375", 9.5 mm
Voice Coil Diameter3", 76 mm
Thiele & Small Parameters
Resonant Frequency (fs)32 Hz
DC Resistance (Re)3.35 Ω
Coil Inductance (Le)0.85m H
Mechanical Q (Qms)14.79
Electromagnetic Q (Qes)0.3
Total Q (Qts)0.29
Compliance Equivalent Volume (Vas)360.84 liters / 12.74 cu.ft.
Peak Diaphragm Displacement Volume (Vd)695 cc
Mechanical Compliance of Suspension (Cms)0.2 mm/N
BL Product (BL)16.54 T-M
Diaphragm Mass Inc. Airload (MMs)121 grams
Efficiency Bandwidth Product (EBP)107
Maximum Linear Excursion (Xmax)7 mm
Surface Area of Cone (Sd)1140 cm2
Maximum Mechanical Limit (Xlim)18.0 mm
Mounting Information
Recommended Enclosure Volume
SealedN/a
Vented84.95-212.38 liters / 3.00-7.50 cu.ft.
Driver Volume Displaced0.234 cu.ft. / 6.62 liters
Overall Diameter18", 457.2 mm
Baffle Hole Diameter16.56", 420.6 mm
Front Sealing GasketYes
Rear Sealing GasketYes
Mounting Holes Diameter0.28", 7.1mm
Mounting Holes B.C.D.17.25", 438.2mm
Depth8.15", 207 mm
Net Weight24.5 lbs, 11.11 kg
Shipping Weight28.1 lbs, 12.75 kgs
Materials of Construction
Coil ConstructionCopper voice coil
Coil FormerPolyimide former
Magnet CompositionFerrite magnet
Core DetailsVented and extended core
  
Basket MaterialsDie-cast aluminum basket
Cone CompositionPaper cone
Cone Edge CompositionCloth cone edge
Dust Cap CompositionSolid composition paper dust cap