What does hertz mean in reference to car audio?

while previous answer correct, there many more uses of hertz involved in car audio.
hertz unit of measure of frequency, or number of cycles per unit of time. in sound number of times per second wave of pressure passes.
in sound itself, determines pitch of sound. high number of hertz implies high pitch, while low number implies low pitch. while accepted range of human hearing 20 hertz 20000 hertz, sum of frequencies produced outside of range has effect of on hear within range.
within acoustics, frequency has larger implications sound heard itself. example, vehicle has resonant frequency, frequency @ car naturally vibrates. characteristic can either add or detract sound being produced @ time. in spl competition common contestants use advantage tuning system resonant frequency using natural vibrations enhance spl. on other hand, audiophiles battle resonant frequency , try minimize effects can cause unnatural peak in sound @ given frequency , harmonics, deteriorating quality of on sound.
hertz can refer sample rate of source of sound. refers number of samples taken continuous audio signal create discrete audio signal, applies digital media. dvd has higher sample rate cd in turn higher mp3. important cause rather analog signal , sound sinusoidal waveform, digital media square or step waveform. in converting digital media, amplitude of original sinusoidal wave measured say, simplicity, every second (in reality, more that). when play media, puts these samples recreate original wave. problem if happens between 2 samples (say @ half second point), missing digital media, , therefore, missing when original waveform recreated. higher frequency of sound, more missed in sample. why higher sampling rate considered better quality of sound, while @ same time requiring larger storage space.
in class d amplifier, hertz can refer number of times amplifier pulses power per second. above information applies these amplifiers, however, instead of being in recording phase, reproduction phase. class d amplifiers suffer same pitfalls , therefore commonly reserved subwoofer use, low frequency waves not suffer severe degradation of quality caused pulse rate high frequency waves are.
while no means limit of application of term, gives more information.

are more or less better?

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