It depends on the speakers and the audio system in your car. Some car speakers are designed to be powered directly by the head unit or radio, while others may require an amplifier to work properly. If your car's audio system does not have an amplifier, and the speakers you want to install require one, then you will need to install an amplifier as well. If you are unsure about whether or not your speakers require an amplifier, you should consult the manufacturer's documentation or a professional car audio installer.