Subwoofers have been the best kept secret in professional audio history, even though they have been around for several decades.
In brief, subwoofers are very large speakers, at least 18 inches in diameter that carry the lowest signals on the sound spectrum.
They have been in use for professional performances since the advent of radio and electric music, along with being incorporated in sound systems in movie theaters and large churches.
Recently, the awareness of subwoofers is increasing along with the increasing popularity of home theater audio systems.
The normal sound range for a standard commercial audio system is high, mid, and low-range, and the subwoofer increases the sound presence in the audio system.
A standard stereo system has had the same capacity for many years and never really changed until the addition of subwoofers in commercial home theaters.
Thus the subwoofer offers an audio additive that has become popular in parallel with the common use of home theater audio systems.
Subwoofers aren't only characterized by the speaker size.
The magnets are also very heavy.
They are normally powered with a designated amplifier, whether connected to a four-way active crossover or a passive single amp setup.
Active crossovers provide the possibility to reduce the power ohmage (or resistance) to 2 ohms.
Subwoofers are also characterized by power capabilities.
They usually have at least a 100 watt minimum power level and can handle upwards to 2000 watts at the peak.
However, the range of power depends on the speaker size, or the cone, and the magnet size.