Choosing the car audio speakers for your vehicle can be a daunting task, especially without actually hearing them. However, paying attention to certain specifications can give you a good idea of a speaker's capabilities.
Frequency Range
The reason a low note from a bass guitar sounds so different from the shrill sound of a loud whistle is because of their frequency. Sound waves behave like ripples in a pond. If you throw a large stone into the pond, you get a deep plunk that creates large waves. But if you throw in a pebble, you get a higher-pitched sound and smaller waves that are closer together. The number of waves that cross a point in a given time frame is known as the frequency of the waves. The higher the frequency of a sound wave, the higher its pitch.
Different models of car audio speakers are capable of producing different frequencies of sound. Woofers focus on deep, low-frequency sounds, while tweeters are used for high-pitched sounds.
A car audio speaker's frequency range details the highest and lowest notes it's capable of producing. In general, humans can hear sounds ranging from 20 to 20,000 Hz. While the frequency range of many car audio speakers extends beyond the 20,000 Hz limit of our hearing, the high notes in this range can harmonize with the notes we do hear, modifying our listening experience. Just because a speaker can produce a wide range of frequencies doesn't mean it will sound good doing so. Unfortunately, the complexity of speakers prevents us from measuring their quality with a simple, single metric.
Impedance
For speakers to produce sound, they need power in the form of electrical current. A car audio speaker's impedance is a measure of its resistance to this current, dictating the amount of power it pulls from the amplifier. The lower a speaker's impedance, the more power it will pull. Measured in ohms (Ω), the impedance of car audio speakers generally ranges from 2 to 4 ohms. Amplifiers will push twice as much power to speakers with 2 ohms of impedance as to those with an impedance of 4 ohms. A speaker's impedance changes constantly based on the frequency of the sound it's producing at any moment. Rather than publishing a speaker's impedance curve, which details its impedance at any given frequency, speaker companies offer "nominal" impedance, a constant that's typically slightly higher than the speaker's minimum impedance. This simplification makes it easier to pick the right combination of speakers and amps.
