Rated power
Rated power of the acoustic system. Most often, the average (root mean square) sound power is indicated as rated.
The most obvious point related to this characteristic is the volume of sound: the more powerful the sound system, the louder the sound it can produce, all other things being equal. In addition, compatibility with an external amplifier depends on this indicator: its power should not exceed the power of the sound system, otherwise overloads and damage to the speakers are possible.
Max. power
The maximum power of a short-term (up to several seconds) incoming signal that the speaker can withstand without physical damage. Just like the nominal power, it matters for the selection of acoustics for an amplifier (or vice versa): it is believed that the maximum power of the speakers should be at least 2 times higher than the maximum power of the signal source.
Sensitivity
This parameter determines the volume of the sound of a particular speaker when a certain standard signal is fed to it. Typically, this is considered a 1 W signal with a frequency of 1000 Hz. The higher the sensitivity, the less the speaker is demanding on the power of the amplifier. So, it is believed that for acoustics connected directly to the car radio, the sensitivity should be 80 dB or more; for less sensitive systems it is recommended to use a separate amplifier.
External crossover
Crossover is part of acoustic system that divides the overall signal into separate frequency bands fed to the corresponding speakers (for more details, see "Bands"). All multi-band speakers (component and coaxial, see "Type") have their own crossover; it is usually located directly in the speaker body. However, in some models, usually the most advanced ones, the crossover can be made as a separate device, in its own body.
External crossovers are considered to provide better sound quality and introduce less distortion into it; in addition, they often provide the ability to fine-tune the sound.
Woofer size
Size of the low-frequency speaker(s) provided in the speaker system.
This size is specified only for models with separate bass speakers. In such acoustics, it is the LF emitter that is the largest (this is due to the physical characteristics of the bass range). Accordingly, the space occupied by the entire system is determined mainly by the diameter of the LF speaker. And since the power and richness of the bass also directly depends on the size of the emitter, then when choosing, you have to proceed from a compromise between the capabilities of the acoustics and the available space in the car.
