Frequency range
The range of audio frequencies reproduced by the subwoofer. It is believed that the human ear is capable of perceiving a frequency range of the order of 16 – 20,000 Hz, but in this case note that the subwoofer is designed to reproduce the lower frequency band (up to 200 Hz). Accordingly, in the case of the lower limit of the range, everything is simple: “the lower, the better”; the upper one should not be lower than the lower limit of the main car audio — otherwise there will be "gaps" in the frequencies, which will affect the sound quality.
Sensitivity
Sensitivity determines the loudness of the subwoofer when a signal of a certain power is connected to it: with equal signal power and impedance (see below), the subwoofer with the higher sensitivity will sound louder.
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.
Resonant frequency
The natural frequency of the cone in the subwoofer speaker, namely the frequency with which the cone will oscillate if the speaker is suspended freely in the air and a single impulse is transmitted to the cone (for example, by clicking on it with your finger). In subwoofers, this parameter determines, in particular, the lower limit of the frequency range (see above): at frequencies below the resonant sound power drops sharply. Accordingly, for deep rich bass, the resonant frequency should be as low as possible. This parameter is also used to calculate the size of the enclosure for the subwoofer.
Woofer depth
The size of the main subwoofer speaker from the front (usually the frame protruding beyond the diffuser) to the rear edge (where the magnet is usually located). In practice, it matters when selecting enclosures for frameless models, as well as when installing Free Air (see "Design"): this is the depth to which the speaker will be "recessed" into the enclosure or trunk. And
a flat subwoofer will not always produce less bass than its more voluminous counterpart.
