Woofer speakers are specially designed to handle low and low-mid frequencies of the audio specter. They are also known as “bass speakers”. In most cases, their frequency range is set between 40 Hz and 500 Hz. The word “Woofer” comes from the onomatopoeic English word for a dogs bark “Woof”. At ordinary sound pressure levels (SPL), most humans can hear down to about 20 Hz.
Woofers are generally used to cover the lowest octaves of a loudspeaker’s frequency range. In two-way loudspeaker systems, the drivers handling the lower frequencies are also obliged to cover a substantial part of the midrange, often as high as 2000 to 5000 Hz; such drivers are commonly termed mid-woofers. Since the 1990s, a type of woofer (termed subwoofer), which is designed for very low frequencies only, has come to be commonly used in home theater systems and PA systems to augment the bass response. They usually handle the very lowest two or three octaves (from as low as 20 to 80 or 120 Hz).
Although all woofer speakers are built similarly, there are some differences which are listed below.
A standard woofer produces frequencies from 20 Hz up to 2,000 Hz (2 kilohertz, or 2 kHz). The woofer is often characterized by its bassy sound which comes from the lower frequency sine wave. You’ll typically see standard woofers as part of higher-end speakers that contain either a woofer and tweeter (a setup known as a 2-way speaker) or a woofer, tweeter, and mid-range speaker (a setup known as a 3-way speaker).
Subwoofers are only capable of producing tones lower than 200 Hz in consumer systems. They are made up of one or more woofers, often mounted inside a wooden enclosure. Although the human ear is only able to pick up a frequency as low as 12 Hz, subwoofers working at lower frequencies can only be felt, if not heard. Subwoofers are the most common add-on to a consumer speaker setup. They have typically placed in their own, isolated enclosure and provide the low-level thump that you just can’t get with standard woofers.
Midwoofers land right in the middle of the ‘woofer’ range, coming in from 200 Hz -5 kHz. Having such a wide range of frequencies, this speaker will produce the best quality sound from 500 Hz-2kHz and start to deteriorate at either end of the spectrum.
A rotary woofer is a woofer-style loudspeaker that uses a coil’s motion to change the pitch of a set of fan blades, instead of using the cone shape. Since the pitch of the blades is changed by the audio amplifier, the power required is much less than that of a conventional subwoofer. They are also far superior at creating sounds well below 20 Hz, below the normal level of human hearing. They are able to produce frequencies down to 0 Hz by compressing the air in a sealed room.