Two factors to consider when buying car stereo tweeters are wattage (measured in RMS) and impedance (measured in Ohms), or the power that the speakers need to be able to handle in order not to blow out. Most built-in car stereo system amplifiers are relatively low-powered, and are therefore compatible with low-powered speakers. More powerful car stereo amps, however, require more powerful speakers. When it comes to tweeters, there is usually no need to aim for high power-handling capabilities. The reason for this is that what is known as a "crossover cable" (see below) diverts the lower frequencies from the amp to the appropriate speaker (i.e. the sub-woofer) leaving the tweeters unaffected by powerful signals. Unfortunately, there is no agreed-upon standard when it comes to tweeter wattage. Prospective buyers should keep in mind, however, that the most important wattage factor to consider is the maximum RMS level, which is an indication of how much power the tweeter can deal with over time. The so called "peak" measure is not as important. When it comes to impedance, anything between 4 and 8 ohms is sufficient.
Having understood the basics of the audio frequency spectrum and where tweeters fall in the frequency range, the following sections offer a few tips on what to consider when buying component car stereo tweeters..