What Is Audio?
Audio is loosely defined as an electrical representation of sound.
Sound is described as mechanical waves that vary the localized pressure within a medium. A sound wave travels through a medium, causing peaks of maximum compression and troughs of maximum rarefaction at varying locations within the medium.
Analog audio signals reproduce these waveforms as AC voltages (electrical signals). Digital audio signals represent the analog signals by sampling the amplitude (bit depth) many times per second (sample rate).
Audible sound waves and audio signals have a frequency range between 20 Hz – 20,000 Hz (Hz = Hertz, which measures cycles per second). Sounds naturally have many frequencies (harmonics and others) that make up the sound's timbre and pitch. These frequencies each typically have their own transients and amplitudes to make up the character of the sound.
Sine waves are single-frequency waves and are the easiest way to represent sound. Here is an illustration of a sine wave:
Regardless of the driver type, an electrical circuit must be made with the driver in one way or another. This requires at least two electrical lead wires to be connected to the conductive part of the driver.
With moving-coil dynamic drivers, the lead wires are connected to either end of a conductive coil of wire.
Planar magnetic driver diaphragms have embedded conductive material, and so the electrical leads are attached to the diaphragm at either end of the conductive element.
Electrostatic drivers have parallel stators that act as a sort of capacitor. An amplified signal is sent via two electrical lead wires: one attached to each stator.
Balanced armature drivers also use a conductive coil. This coil is wrapped around the armature and has lead wires attached to each of its ends.
Finally, the piezoelectric crystal of the bone conduction driver has two electrical leads attached to it to complete the electrical circuit.
Explaining these driver types gives us a good idea of how audio signals interact with headphones. Beginning with the end in mind, let's explore how audio signals are carried through headphone cables.
