Twin Mini Compact Horn Twin Mini Compact Horn features a prewired, sealed sound unit with 304 stainless steel diaphragm and stamped 304 stainless cover. Mounting bracket can be used as a wiring template. A drop-in replacement for many common OEM horns. When installed, horns should point slightly downward to permit water drainage. At 111 decibels and a frequency (Hz) of 490±20A, this horn meets US Coast Guard's COLREGS and ABYC standard A-23 for use on vessels under 12m (39'). 12VDC. NMMA Type Accepted #2577061.