The term "impedance" refers to the electrical resistance of AC systems whose DC resistance is very low, such as loudspeakers. In modern car audio, the most common impedance is
2,
4 or
8 ohms. This parameter has practically no effect on the sound quality — it serves to select the optimal combination of acoustics and an external amplifier. If the speaker impedance is higher than that for which the amplifier is designed, the sound will be quieter than necessary, and if the impedance is lower, distortion in the sound is possible.
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.
The mounting depth of car audio is, in fact, the size of the speaker in depth. Note that for component sets (see "Type") this parameter is given for the largest speaker, and for case models it is generally irrelevant.
The mounting depth, along with the diameter of the speaker (see above), determines the amount of space needed to mount the speaker — in this case, how deep a niche would be required for normal mounting. At the same time, the larger the speaker, the larger, usually, the installation depth. And with similar diameters of equal size, a more powerful model is likely to be more “deep”.
The smallest amount of space —
up to 15 mm deep — is required by some tweeters. A depth
of 16 – 30mm is normal for tweeters and very shallow for general range speakers, most of these models have a depth
of 30mm or more. At the same time, full-range speakers are usually "recessed" by
less than 60 mm, component systems — by
less than 90 mm, and
more depth may be required only for some coaxial and mid-range models and, oddly enough, tweeters.
