Vehicle horn horn. Bicycles often have a classic "bulb horn", operated by squeezing a rubber bulb attached to a metal horn. Squeezing the bulb forces air through a steel reed located in the throat of the horn, making it vibrate, producing a single note. The flaring horn matches the acoustic impedance of the reed to the open air, radiating the sound waves efficiently, making the sound louder. Other types of horns used on bicycles include battery-operated horns (sometimes even car horns on 12-volt circuits are incorporated) and small air horns powered by a small can of compressed gas. Oliver Lucas of Birmingham,
Registered jack models require additional power (~6 V AC) for operation of the incandescent dial light. This power is delivered to the telephone set from a transformer by the second wire pair (pins 2 and 5) of the 6P4C connector. RJ21 is a registered jack standard using a modular connector with contacts of up to 50 conductors. It is used to implement a 25-line (or less) telephone connection such as that used in the 1A2 key telephone system. The miniature ribbon connector of this interface is also known as a 50-pin telco connector, CHAMP(AMP), or "Amphenol" connector, the latter being a genericized