Through proven performance, the patented VT/VTF series has earned worldwide recognition for its service reliability. These cost-effective units offer compact size, functional flexibility, optimal intelligibility, effective sound distribution and high-level output. All models contain a high-efficiency compression driver with maximum acoustic conversion efficiency. (A quality that reduces the number of units needed to achieve specific sound pressure levels and provides substantial savings in amplification power requirements and labor costs.) The die-cast, water-sealed construction resists vandalism, vermin, moisture, corrosion, and vibration for indoor or outdoor use. Selection includes a basic 8-ohm version and 70.7 or 25-volt transformer models with DC blocking capacitor (C), where indicated. All models are finished with barrier strips. The VT series models are surface mount units; The VTF Series are flush-mounted units for recessed installation. The VT Series mounts standard 4" EO backboxes; the VTF Series mounts 4" or 4 11/16" SQ backboxes and requires Model AR or MR adapter rings respectively (order separately). Optional mounting accessories are offered and include: indoor and outdoor enclosures, a bi-directional housing, adapter plates and rings. Model color suffix: Red (R) or Neutral Gray (N) Ex: VT-157UCS.