Horn speaker

At the most fundamental level, a horn speaker uses a "horn" to get more sound (volume) from the driving loadspeaker. Note however that the horn is not amplifying anything in the sense of adding energy, rather it gets more sound from the driver by improving the coupling between the driver (typically made of paper or more recently more exotic materials up to and including titanium, and consequently rather dense) and the air (which has a very low density).

In this sense some people have described a horn as an "accoustic transformer". Stated another way, it converts large pressure variations in a small amount of air into a low pressure variation (the human ear is very sensitive indeed to pressure variations - even quite load sounds are actually ver small pressure variations !) in a large amount of air.

The most well known early horn speakers are those on 78 RPM phonographs. in this case the record moved a heavy metal needle that excited vibrations in a metal disk typically a couple of inches in diameter. If played without the horn, this sounds very quiet. The horn improves the loading and thus gets a better "coupling" of energy from the metal diaphram into the air, and the pressure variations then get smaller as the vlume expandds as the sound travels up the horn.

A modern electric horn speaker works the same way, but just replaces the mechanically excited diaphram with a dynamic loadspeaker (or sometimes piezo speaker).

As usual once a principle of operation has been defiend, the technology can be adapted and improved almost without limit

The horn should not just be a cone of fixed length, since this would resonate at the natural frequency of its length. Typically modern horns have some form of exponential flare, notably the tractrix taper.

Some claim that the small amplitude high pressure environment makes it possible to build better drivers than "normal" dynamic speakers, which are hampered by the need to make the rotor as light weight as possible. In particualr the driver can be very small, even for bass frequencies. This makes it possible to produce wide range drivers and in some cases avoid crossovers entirely

Horn speakers can provide very high efficiencies, making them especially desirable for very low powered amplifiers, such as single ended triode amplifiers. See also Voight, Lowther, Foster, Bruce Edgar.

Horn speaker efficiency is also applied to provided very high sound pressure levels needed for sound reinforcement and public address applications, although in these applications fidelity is usually severely compromised and large multi speaker combinations/arrays are used (see also bass bins).

See also: JBL, Altec Lansing, Voice of the Theatre