Q: How can a speaker recreate any sounds, such as people's voices?
It's quite simple really.
First we must understand what sound is. Sound is vibration waves in air. In some ways similar to ripples and waves in a pond. When a stone is thrown into a pond, it makes a series of waves that move away from where the stone dropped into the water. The stone contacting the water is the SOURCE of the vibration waves.
Sound in air is similar. It has a source, let's say the human voice. The human voice is created by the vocal cords which vibrate and the sound is changed by the shape of the mouth. The vocal cords vibrate back and forth as we speak and that movement is like the stone repeatedly hitting the surface of the pond making wave after wave.
The distance between the waves and the time it takes from one wave to the next wave is called the FREQUENCY. The closer the waves and the faster they are, becomes what we call higher frequency and the farther apart and slower they are, is called lower frequency. Frequency is measured in Hertz (Hz) and is the time from one wave peak to the next. If the wave peaks are one second apart, we consider it to be 1 Hz. If there are ten waves in one second, then it is 10 Hz and if there are 100,000 wave peaks in one second, then it is 100,000 Hz. Humans generally can hear from 20 Hz to 20,000 Hz.
A rough guide to frequency and sound would be, a low organ note, or a very large drum has low frequency notes from around 18 Hz to 100 Hz, while the human voice is generally in the 500 Hz to 1,000 Hz range and small bells and cymbals are in the 3,000 Hz to 18,000 Hz range. These are very rough estimates of how different frequencies sound.
Of course, the sound vibration waves are not simple waves and include different frequency waves at the same time. You can have many different frequencies in the human voice at the same time. If you listen very carefully you can hear them.
So, sound is vibration waves in air and it can have different frequencies, and can even be a combination of many different vibration waves and frequencies.
To recreate the sound wave, we need a surface that can move the air and recreate the vibration waves. That is what the speaker does. A speaker is simply a push-pull motor and a diaphragm (surface) to push the air to recreate the vibration waves in the air. The push-pull motor is driven by an electrical signal. That electrical signal can be anything, a simple sine wave, the sound of a bell, or very complicated music, or that of a human voice.
Where can we get an electrical signal from a human voice? We use an instrument we call a microphone. A microphone is the reverse of a speaker. It has a very light diaphragm attached to a very sensitive generator (a reverse motor - a generator). The voice vibration waves in the air, push the very light and delicate diaphragm which moves the very sensitive generator and a small electrical signal of the human voice is generated.
Very simply (there are many more steps to this process) if this signal was then connected to the appropriate amplifier (to increase the signal strength) and connected to a speaker, the speaker diaphragm would move almost the same as the waves that generated the signal and the sound will sound waves in the air will be very similar to the original human voice that caused the signal.
Basically that is how speakers can recreate sounds.
The source vibration waves become an electrical signal that drives the speaker which then becomes the recreated sound we hear.
But they really can't create "any" sounds. Speakers are generally more limited in the frequencies they can recreate or reproduce than the human ear can hear. That is why some 'speakers' have many component speakers which we call TWEETER (for high frequencies) and WOOFER (for low frequencies), etc. There are more types of component speakers, but tweeter and woofer can easily show that to reproduce more of the frequencies, we need different types of speakers, each better at producing different frequency ranges to cover the large range that the human ear can hear. Very few speakers and reproduce the very low pipe organ notes and the very high cymbal sounds clearly and accurately.
This was very basic and I hope clear enough to make sense.
