How speakers produce sounds at different volumes and frequencies
When the cone vibrates more, the speaker produces a loud sound, and when it moves less, the speaker produces a soft sound. Why? Think drums. Hitting the head harder causes the head to vibrate a greater distance and produce a louder sound. Likewise, sending a larger electrical impulse to the speaker will move the cone farther and create a louder noise. Smaller sounds are made by smaller electrical pulses.
We can come to the same conclusion by thinking about energy. The laws of physics tell us that we cannot create energy out of thin air. So if we want to make loud sounds (sounds that carry a lot of energy), we first need to generate vibrations with a lot of energy (in other words, hit something hard).
Some drums have pedals that make the skin tighter or looser. If the skin is tight, it will vibrate faster and produce a higher pitched sound when you strike the drum; if the skin is loose, the opposite will happen and you will get a lower note. Something similar happens with speakers. Larger speakers with large cones (called woofers) move more slowly than smaller speakers with smaller cones (called tweeters)—so they are better at producing lower frequencies. Any speaker can produce a variety of different sound frequencies by moving it back and forth quickly (for treble) or slowly (for bass). A typical home speaker, in a wooden box, will contain a large woofer and a small tweeter so it can produce the full range of frequencies. It uses a circuit called a crossover to split the incoming electrical signal into a low-frequency portion, which is sent to a woofer, and a high-frequency portion, which is sent to a tweeter.
Speakers that need to produce high-frequency sound (or ultrasound, far beyond the range of human hearing) sometimes use piezoelectric transducers based on vibrating crystals, rather than the traditional magnetic coil setup. Commonly known as crystal speakers or simply "buzzers," they're also used to make blaring sounds in devices like telephone ringers and smoke alarms, where the effectiveness of the alarm is far more important than its quality.
