Woofers are used to handle the lower frequencies (sound waves) of a speaker system, and there are several different types, depending on your needs. Although they are very similar in design, there are significant differences between the different types.
Standard subwoofer:
A standard subwoofer reproduces frequencies from 20 Hz to 2000 Hz (2 kHz or 2 kHz). Subwoofers are usually characterized by a coppery sound caused by lower frequency sine waves. A standard subwoofer is usually used as part of a high-end speaker and includes a subwoofer and tweeter (a setup known as a 2-way speaker) or a subwoofer, tweeter, and midrange driver (a setup known as a 3-way speaker).
Subwoofer:
In consumer systems, subwoofers can only reproduce tones below 200 Hz. They consist of one or more subwoofers, usually mounted in a wooden cabinet. Although the human ear can only perceive frequencies below 12 Hz, subwoofers operating at lower frequencies can only be perceived, if not heard. Subwoofers are the most common complement to consumer speakers. They are usually housed in their own isolation cabinets and provide a low level of sound that a standard subwoofer cannot provide.
Midwoofer:
The midrange driver is located right in the middle of the woofer's range, from 200 Hz to 5 kHz. With such a wide frequency range, this speaker will produce the highest quality sound in the 500 Hz - 2 kHz range, and will begin to degrade at either end of the spectrum.
Rotary woofer:
A rotary woofer is a speaker that uses the movement of an oscillating coil to change the height of a set of fan blades, rather than using a cone shape. Since the height of the blades is changed by the sound amplifier, the power required is much less than that of a conventional subwoofer. In addition, they are better able to produce sound at frequencies well below 20 Hz, which is below normal human hearing, and by compressing air in a confined space, they can produce frequencies as low as 0 Hz.
In most consumer speakers, you will probably find a standard subwoofer as part of the main speaker, and possibly an additional but separate subwoofer.
Midrange speakers are intended to handle the "middle" range of the frequency spectrum, between 500 Hz and 4 kHz. This is probably the most important frequency range, as it is where most audible sounds are produced, such as musical instruments and the human voice.
Because the human ear is more sensitive to midrange, speakers can maintain lower power levels and still provide good sound quality and volume. Because midrange speakers can't produce very low or high frequencies, they tend to sound dull or flat and need the support of a woofer or tweeter to achieve full sound levels.
Midrange speakers are used as part of a loudspeaker that also includes a woofer and tweeter, and they are also used as a center speaker typically used in surround sound systems.
At the upper end of the sound spectrum is the tweeter, named for the higher tones of the bird. Loudspeakers typically cover a range between 2 kHz and 20 kHz, although some special speakers can reach 100 kHz.
Traditionally, speakers are designed in the same way as other speakers, but in a smaller size. The problem is that the sound at these frequencies is quite directional, which means that the highs in music sound best when the tweeter is pointed directly at you. Modern speakers are starting to come out in cone versions, using soft cones made of polymer resin, silk or polyester foil impregnated with polyester fabric. Dome tweeters are capable of spreading sound over a larger area.
