Engineered for applications with limited plenum space incorporating a SoundTube specific shallow backcan with an installed depth of only 3.5 inches. One 4 inch (102 mm) treated fiber woofer with cloth surround and one 0.75 inch (19 mm) silk dome tweeter. Easy-access six-position tap switch for 25/70.7/100-volt and 16 ohm transformer bypass position allows for easy ordering, stocking and installation. Reduced amplification costs with maximum efficiency including 87.5 dB sensitivity and 16 ohm impedance. Superior voice intelligibility with an average coverage angle of 100 (210 kHz, independently verified). Cost-effective 16 ohm settings allows for the use of multiples of two, four, or six speakers in a system using a standard amplifier without a transformer. Incorporates a painted steel grille for lasting durability. Ceramic input terminal accepts up to 10 gauge plenum rated signal wire and includes thermal fuse. Suitable for use in voice alarm applications subject to EU regulations EN60849 and BS5839-8. EN54-24 listed. Clamping allowance from 0.00 in. (0.0 mm) to 1.50 in. (38.1 mm). UL 1480 (UEAY) and 2043, CE (EMC Directive 89/366/EEC, EN55020, EN55013) approved.