The Wheelock cluster speakers are designed for ceiling or wall mount applications for high ambient noise environments. The cluster speakers are available in multiple configurations-a speaker/visual (Series STH-MSR) and speaker only (Series STH-R or STH-G). All cluster speakers are equipped with UL listed STH-15SR or STH-15S supervised horn loudspeakers and the speaker/visual system has a UL listed DC-MAX-C strobe, mounted to a steel enclosure. STH-4MSR and STH-4R supplied with four STH-15SR Horns STH-3MSR and STH-3R supplied with three STH-15SR Horns STH-2MSR and STH-2R supplied with two STH-15SR Horns STH-2G supplied with two STH-15S Horns All STH MSR series cluster speakers are supplied with oneDC-MAX-C strobe with clear lens. The SHMP-R is a UL listed adapter plate designed for mounting oneSTH-15SR horn to a series RSSP strobe mounting plate. For surfacemount applications, the SBL-R surface mount backbox is required.