How a horn loudspeaker works. (A) (B) horn A horn loudspeaker is a or loudspeaker element which uses an to increase the overall efficiency of the driving element(s). A common form (right) consists of a which produces sound waves with a small metal diaphragm vibrated by an, attached to a horn, a flaring duct to conduct the sound waves to the open air.
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Another type is a driver mounted in a which is divided by internal partitions to form a zigzag flaring duct which functions as a horn; this type is called a folded horn speaker. The horn serves to improve the coupling efficiency between the and the air. The horn can be thought of as an 'acoustic ' that provides between the relatively diaphragm material and the less-dense air. The result is greater acoustic output power from a given driver. The narrow part of the horn next to the driver is called the 'throat' and the large part farthest away from the driver is called the 'mouth'. The angular coverage () of the horn is determined by the shape and flare of the mouth.
A major problem of horn speakers is that the radiation pattern varies with frequency; high frequency sound tends to be emitted in narrow beams with poor off-axis performance. Significant improvements have been made, beginning with the ' horn invented in 1975. The main advantage of horn loudspeakers is they are more efficient; they can typically produce 10 times (10 ) more sound power than a cone speaker from a given amplifier output.
Therefore horns are widely used in,, and sound systems for large venues like theaters, auditoriums, and sports stadiums. Their disadvantage is that their is more uneven because of peaks, and horns have a cutoff frequency below which their response drops off. To achieve adequate response at bass frequencies horn speakers must be very large and cumbersome, so they are more often used for midrange and high frequencies. The first practical loudspeakers, introduced around the turn of the 20th century, were horn speakers. Due to the development in recent decades of cone loudspeakers which have a flatter frequency response, and the availability of inexpensive amplifier power, the use of horn speakers in high fidelity audio systems over the last decades has declined. Various horn prototypes in the lab of, 's chief horn designer. From about 1888 to 1925, a horn was used to concentrate sound waves in the process of recording onto, and another horn was used to amplify the recordings during playback.
An acoustic horn converts large pressure variations with a small displacement area into a low pressure variation with a large displacement area and vice versa. It does this through the gradual, often increase of the cross sectional area of the horn. The small cross-sectional area of the throat restricts the passage of air thus presenting a high to the driver. This allows the driver to develop a high pressure for a given displacement.
Therefore the sound waves at the throat are of high pressure and low displacement. The tapered shape of the horn allows the sound waves to gradually decompress and increase in displacement until they reach the mouth where they are of a low pressure but large displacement. A modern electrically driven horn loudspeaker works the same way, replacing the mechanically excited diaphragm with a dynamic or loudspeaker. Modern horn designs typically feature some form of conical, exponential or taper. Roughly speaking, the slower the flare rate, the deeper and lower frequencies the horn will reproduce for a given length of horn. For example, a horn area growth rate of 30% per foot will allow reproduction down to about 30; 10 times area per foot provides midrange reproduction; 100 times area per foot is used in high frequency horns.