how do horn's work?

This should get you started!
http://melhuish.org/audio/horn.html

A horn does have a dynamic driver like most other speakers. The difference is that the horn acts somewhat as an amplifier after that sound has been produced. It is like cupping your hands around the outside of your mouth to scream accross a football field. Because the low frequencies of bass notes are so long bass-horns often have to be folded as in the Klipsch K-horn. This speaker uses the corner of the room as the final fold in teh horn. There is also a website for the "worlds largest subwoofer" which uses a horn design.

Horns are highly efficent which means that you can power them with modest amplification. Check out old Klipsch or Avangarde.

Good one Bignerd...Bob

A horn speaker uses a conventional cone. The difference is the cabinet. One of the disadvantages of electromagnetic drivers is impedence mismatch. You have a relatively small cone trying to push a large air mass in the room. A horn speaker uses a tapered tube like a bullhorn to get greater acoustical power. Thus the horn speaker is quite efficient in that you can get loud volume from a small amp. There is a disadvantage however. Bass can be poor, not poor in the quality of what it reproduces, but poor in how low it can go. The mouth of the horn is one-quarter of the wavelength of its lowest frequency. The speaker has to be physcially big to accommodate the horn to reproduce deep bass. That is why, as Bignerd100 states, it is placed in the corner of the room. The corner is used as the mouth of the horn in order to increase its ability to reproduce lower bass frequencies.