A DSP is not necessary for your car audio as it just enhances your audio, which means your stock speakers will still produce decent sound even without it. But if you want them to sound the best they possibly can then it becomes necessary. This is because, without a DSP, your car speakers will not sound nearly as close as what they are capable of. In fact, even if you change your stock speakers to a better model or a better version, you’ll still need a DSP to enhance your audio quality in the car.