One of the oldest forms of loudspeakers are the horn loudspeakers that not only provide pure, high efficient, natural music but also fast and accurate transient response.
Basically what happens in the horn loudspeakers is that the diaphragm that is run by an electromagnet is supported by a horn, which improves the coupling efficiency between the speaker driver and the air. However, the horn is like an acoustic transformer that usually gives impedance matching between the diaphragm material and the air, having a low density. This will show the difference in density and motion of the air and of the driving element.
The first horn speaker that was invented looked very simple. It was a horn attached to a receiver and the sound quality was just awful. But it was better than that of the triode tube that was the base concept behind the horn speakers. Actually, this triode tube amplified the electric signal to the possible level and it could also produce audible output while driving the receiver. But the output power was really low. And later this conception gave birth to high efficiency loudspeakers, which produced high sound pressure level. It was in 1927 when Wente and Thuras, two Bell Laboratory engineers invented the compression horn driver, or rather say a driver.
Talking about the qualities of horn loudspeakers, the first thing that attracts is the harmonic, distortion less sound. It also offers a dramatic increase in dynamic capability in comparison to other such speakers, which suffered from dynamic compression. Horn loudspeakers have the capability to run efficiently with low powered amplifiers like single ended triode amps. Moreover, they can be designed to reproduce a wide range of frequencies using a single and small driver.
But the problem with horn speakers was that they were quite big and heavy. And soon after World War II more powerful and portable systems came into the market. But it will be wrong to say that they were completely out of demand because, although the horn loudspeakers lost the major demand but they survived in movie theatres.
These speakers are used for audio application due to the fact that horn reduces the need for exotic speakers. They are even used by audiophiles for sound reproduction. But there is a fact that not all type of horn speakers are used for this purpose. As there are ample designs that differ in length, material, drivers and many such things, so it is very confusing to state that which form is the best.
Horn loudspeakers are also used for public address and concerts. As it is mentioned earlier they provide high sound pressure level that is basically necessary for sound reinforcement and thus used for public address applications. They are used in concerts due to the high volume bass reproduction so that the bass can be heard as well felt by the concertgoers. And for this reason sometimes multiple loudspeakers in a group are used. But it should be noted that they give the same benefit as a single horn loudspeaker with a big mouth area. But off course, it should include greater power of multiple drivers.