Driver size and RMS power rating speak to a home theater speaker system's performance. Nominal impedance is also an important specification to consider, though most modern systems feature similar impedance levels.
One of the most important considerations in home theater speaker systems is the wattage rating. This is most important for the subwoofer, but applies to all speakers. A home theater's power rating dictates the signal level that can be passed before encountering distortion. Power ratings are measured in watts. Because the number of watts pumping through a speaker changes at any given moment, manufacturers provide a suggested average power level, called the RMS power rating. Modern speakers typically have RMS power ratings between 80 to 125 watts.
Another important consideration is the size of the driver, or the speaker cone. Larger speakers are bettered suited to bass frequencies, while small speakers prefer higher frequencies. In general, users want a range of speaker sizes in a home theater system, usually ranging from 8 to 10 inches for the subwoofer and 2 and 4 inches for satellite speakers. Systems should also be set up so that higher signals go exclusively to the satellite speakers, while bass frequencies are played through the sub. This can be done by adjusting the crossover frequency on the receiver.