There are a few things to consider when purchasing an amplifier for car door speakers. The first is the type of speaker. Some amplifiers are designed specifically for car door speakers, while others work with a variety of speakers. The second is the size of the amplifier. Some amplifiers are small enough to fit in a small car, while others are larger and require a larger vehicle. The third is the type of speaker. Some speakers are designed for use with car door speakers, while others are designed for use with other audio devices. The fourth is the price. Some amplifiers are affordable, while others are more expensive. The fifth is the quality of the amplifier. Some amplifiers are designed for high-quality sound, while others are less reliable.