Eighteen Sound 21iD

• Sensitivity (1W, 1m, infinite baffle) SPL1W 96.2dB
• Frequency response 29 - 1600Hz

Thiele & Small parameters

• Resonance frequency (free air) fS 38Hz
• Mechanical quality factor QMS 5.60
• Electrical quality factor QES 0.24
• Total quality factor QTS 0.23

Large signal parameters

• Maximum linear excursion xmax 14mm
• Air volume displaced at xmax VD 2324cm³
• Power handling P 1800W
• Program power Pmax 3600W

Voice Coil

• Nominal impedance Z 2Ω
• DC resistance RE 1.3Ω
• Inductance (1kHz) LE 1.08mH
• VC Diameter 135mm
• Winding material Copper

Magnet

• Force factor Bl 25.2N/A
• Motor constant Bl/√RE 22.1N/√W
• Material Neodymium

Diaphragm

• Effective diameter 460mm
• Effective area SD 1660cm²
• Moving mass MMS 489g
• Moving mass (without air load) MMD 442g
• Material Water,UV repellent

Suspensions

• Stiffness KMS 27.8N/mm
• Compliance CMS 36µm/N
• Equivalent volume to the compliance VAS 143L
• Mechanical resistance RMS 20.9N·s/m

Dimensions

• Nominal diameter 21″
• 533mm
• Overall diameter 545mm
• Baffle cutout diameter 492mm
• Overall depth 250mm
• Flange thickness 18mm
• Mounting depth 232mm
• Volume occupied by the driver (estimated) 9.2L
• Net weight 13.6kg