Horn

in acoustics, a section of a tube with a variable cross section, used to increase the power radiated by sound sources and to concentrate the radiated acoustic power in a specific direction, in which case the sound source is coupled to the narrow end of the horn, or to amplify received sound, in which case some sort of sound receiver is attached at the narrow end.

Horns are most often used in horn loudspeakers, where they substantially increase the radiated acoustic power, especially in the low-frequency region, thus improving the loudspeaker’s efficiency. This is achieved as a result of the better matching between the radiator and the medium. The simplest horn has a conical shape. A more advanced type—the exponential horn—is used for operating over a broad frequency range, for instance, in amplifying and reproducing sound. In exponential horns, the cross-sectional area S varies along the horn’s axis x according to the formula S(x) = S₀e^mx, where S₀ is the cross section of the throat and m is a constant for the rate of taper of flare of the horn. Horns are used much less often for sound reception.

Horns are employed for the direct amplification of the human voice in megaphones. The principle of the horn is the basis for horn antennas in radio engineering.

one of the most ancient of the mouthpiece wind instruments. The earliest horns were made from the hollow horns of bulls. Later, horns were made out of wood, bark, ivory, or metal. The horn was a signal instrument used chiefly by shepherds, hunters, and the postal and military service. The first horn band, which consisted of perfected hunting horns, was formed in 1751. The horn was the prototype of many of the wind instruments with conical bores. The French horn evolved from the hunting horn.

a hard protuberance on the head of many extant ungulates and certain fossil reptiles (for example, horned dinosaurs) and mammals (Titantheria, Dinoceras), serving mainly as an organ of defense and, in the males of many species, as a weapon in the battle for a female.

There are several different types of horns in ungulates. Rhinoceroses bear one or two unpaired horns on the frontal and/or nasal bones; the horns consist of conical thickenings of cornified epidermis. Bovids have paired horns consisting of bony cores that develop on integumental bone which fuses with the frontal bone. The bony cores are covered with hollow, horny sheaths that grow continuously as the animal grows and the horn wears out. Only in the pronghorn do the horns periodically fall out. The paired horns of giraffes are formed of bony cores fused to the frontal bone and covered with soft skin and hair.

Deer have paired horns, or antlers, whose bony cores rest on pedicels of the frontal bones. The antlers of young deer are covered with soft skin, which later dries and falls off, revealing the bony foundation. It is characteristic for deer to shed their antlers periodically as a result of resorption of bony tissue at the site where the pedicels join the cores of the antlers. They grow new horns owing to the activity of the periosteal cells of the pedicel. Branching of the antlers increases with age. In all deer except the reindeer, only the males are antlered. The shedding and development of antlers is closely related to the activity of the sex glands. Hence, the antlers of castrated deer are not shed and do not grow. The horny sheath is used in the manufacture of various products, and the bony process yields bone oil, bone meal, and glue. The antlers in the velvet are a source of pantocrine.