2.0 Speakers (Stereo Speakers):
Low end speaker system for basic computer usage and music. 2.0 Speakers tend to lack base and are usually very low power, sometime a bass enhance button is included; however, this may create audio distortion. There is also the possibility of power supply noise on low end speakers, even when connected through USB.
2.1 Speaker Audio System:
Three Speakers - A subwoofer (bass unit) and two satellite speakers. Sound quality of a 2.1 is better than a 2.0 system, however, these are still lower end speakers and may distort at higher volumes.
4.1 Speaker Audio system:
A subwoofer, two front satellite speakers and two rear speakers. 4.1 Speaker systems are medium to high-end. Please take note of the real power rating and not the PMPO value.
5.1 Speaker Audio System:
Six Speakers - A subwoofer, a central front speaker, two front satellite speakers and two rear speakers. Please take note of the real power rating and not the PMPO value.
Power expressed as PMPO: Peak Music Power Output - This is calculated by the manufacturer and there is no set standard for determining PMPO. Power expressed as PMPO = a constant number multiplied by the actual power, where the constant number is determined entirely by the manufacturer. A single manufacturer will therefore have speakers expressed in the same way and comparing their own speakers to each other is fine, however, different manufacturers will have different ratings for the very same speaker.
PMPO = k x Actual Power
Power expressed as RMS: Power is a standard scientific formula. When comparing speakers from different manufacturers, the RMS will reflect a far more accurate power rating for the speakers.
Power should only ever be measured with no clipping. When an amp clips, there is more available power, but higher distortion. It is not uncommon to see amplifier powers rated at 10% distortion. This is quite unacceptable, as this indicates that there is severe clipping of the signal. A good quality amplifier will have less than 0.1% distortion just before clipping, somewhat higher for push-pull valve amps, and a lot higher for single ended triode valves.
Power(RMS) = V (RMS)2 / R where V is the voltage into the speaker and R is the speaker impedance (resistance) value. For example 12V(rms) across 8 Ohms = 18 W(rms)