Number of woofers
The number of main speakers installed in the subwoofer. Most models are equipped with a single speaker, which is considered sufficient for quite decent bass reproduction.
Models with two speakers sound louder and have better sensitivity, but are complex in design (as a result, more expensive) and more difficult to install, and therefore are relatively rare.
Rated power
The average (root mean square — RMS) power of the input signal, at which the subwoofer is able to work continuously without negative consequences (damage, failure) for at least an hour. The rated power of the subwoofer must be greater than the power of the amplifier connected to it — in order to avoid overloads.
Max. power
The maximum signal power that the subwoofer is able to withstand for a short time (up to several seconds) without any negative consequences. When selecting an amplifier-subwoofer pair, it is recommended to take a subwoofer with a maximum power of at least twice the maximum power of the amplifier. In general, the higher the maximum power, the more resistant the subwoofer is to overloads.
Impedance
The electrical resistance of a subwoofer when a signal is applied to it. This parameter is important primarily for selecting a subwoofer-amplifier pair: at a lower impedance than that of the amplifier, the subwoofer will distort the sound, at a higher impedance the sound will be too quiet.
For dual voice coil models (see above), the impedance is specified for one of the voice coils.
