Question

How do digital signals work?

I am trying to explain how a simple coil speaker works, I understand that a current creates an electromagnet in the coil whose magnetic field interacts with that that of the permanent magnet... however I am confused as to how the electricity is sent from the phone and into the coil, can someone explain this please?

Does this relate to motion of waves? are they electromagnetic waves being converted in to vibrational waves? im confused!!!

Answer 1

A simple coil speaker comprises of three components, namely, a permanent magnet, a cone diaphragm (usually made of plastic or paper) ,and an electromagnet carefully placed between the two of these. The electromagnet is a simple coil which has two leads, as shown in the figure below.

When current passes through the coil in one direction, a magnetic field is induced in the electromagnet whose North and South poles are in certain orientation. Hence, the electromagnet gets attracted to the permanent magnet. Alternatively, when the current passes through the coil in the opposite direction, the magnetic field of electromagnet reverses its orientation. Therefore, it gets repelled. This electromagnet is attached to the cone diaphragm which also moves, along with the electromagnet.

The amount of current (in ampere) determines how far the electromagnet moves (and in turn the diaphragm moves) and frequency with which the current changes direction determines how fast the electromagnet vibrates.

• When you hear a high frequency sound from the speaker at a low volume, a current that changes its direction rapidly (say 500 Hz) with a low magnitude of current (say, 10 mA) passes through the coil.
• When you hear a low frequency sound from the speaker at low volume, a current that changes its direction slowly (say 50 Hz) with a low magnitude of current (say 10 mA) passes through the coil.
• When you hear a high frequency sound from the speaker at high volume, a current that changes its direction rapidly (500 Hz) with a high magnitude of current (1000 mA) passes through the coil.
• Similarly, A low frequency current and high magnitude of current produces a low frequency sound at high volume.

This current that is passed through the electromagnetic coil comes from a microphone that converts sound to electric current. It has a very similar arrangement as the speaker, but in reverse. The sound makes the diaphragm vibrate and this in turn makes the electromagnet vibrate. This vibrating electromagnet produces a current with an amplitude and frequency that corresponds to the incoming sound. This current is often called signal. The signal is amplified, i,e. its strength is increased by the amplifier. And then this amplified signal goes into the speaker.

These are not electromagnetic waves. Here the sound wave, which is simply small change is pressure in the surrounding air, is converted to a changing current in a coil in the microphone. This changing current is sent to the electromagnet in the speaker which produces back the sound (after amplification).