The two-way speaker has a system that has mounted within the same acoustic box two different speakers:
Tweeter: smaller speaker (usually a capacitor or electrostatic loudspeaker), specializing in high frequencies (3 to 20 kHz). That is, optimized to reproduce the treble.
A woofer, larger speaker (usually a dynamic speaker or voice coil), specializing in low and middle frequencies (30 to 3,000 Hz). That is, optimized to reproduce bass and mid tones.
In an active speaker and active filters are applied before amplifying the audio signal in order to divide the frequencies in certain ranges to be applied to the appropriate speaker cone.
There are also used crossing filters (crossover) on the speaker box itself, in this case working on the amplified signal.
The three-way speaker has a system that has mounted within the same acoustic box three different speakers:
Tweeter: Speaker of smaller size (usually capacitors), specializing in high frequency (4 to 20 kHz) optimized to reproduce the treble. The vibration of the coil is very weak amplitude (only displaces a portion of the membrane), light speakers are small and rigid, the domes are generally up to two cm, cones up to 6cm. Ferrofluid cooled (controlled viscosity oil loaded with iron particles, is placed in the gap), they also have very little excursion, in fact spoken of vibration and only a portion of the membrane, the allowable power range from 20 to 70W
A Middle: mid-size speaker specializing in midrange (800 to 5000 Hz) can be cone or dome, these are very common, and its operation is a vibration of the whole mobile.
A woofer, larger speaker (usually moving coil), specializing in low frequencies (30 to 800 Hz), optimized to reproduce the bass, have a large diameter 15 “(38cm) and 18” (46cm). Its membrane is heavy, should be possibility of elongation, the diameter of the coil is up to 10cm, contains a powerful magnet and weighed (to maintain the magnetic flux density in the gap), also contain highly developed cooling circuits. It works like a piston, the moving assembly moves in a single block.
The audio signal is divided by active or passive crossovers, to apply a certain range of frequencies to the appropriate speaker.
While optimizing the mid band, usually neglected, are very expensive speakers, and its high market price, have a limited deployment.