Instructions: Ever wondered how speakers work? This is what you need to know.

But how do speakers work? Let's start with the basics.

Wikipedia
The speaker driver: a simple yet brilliant electromagnetic motor

An amplifier feeds a signal to two terminals on the back of a speaker. These terminals pass the current into a cylindrical coil of wire, which is suspended in the circular gap between the poles of a permanent magnet. This coil moves back and forth inside the magnetic field as the current passing through it alternates in direction with the signal applied, per Faraday`s law. The center of the speaker cone is attached to one end, which gets driven back and forth by the moving coil. This cone is held at its edges by an airtight suspension or surround. As the cone moves, it pushes and pulls the surrounding air; by doing so it creates pressure waves in the air, called sound. So that`s how the speaker driver works.

Why are speakers mounted in boxes?

As a speaker driver's cone moves, it creates a pressure wave from both the front and from the back. As it moves towards you, pushing the air and creating a positive pressure, it simultaneously pulls the air behind it, creating negative pressure. If the wavelength that corresponds to the frequency of the reproduced signal is large relative to the size of the driver, the pressure generated by the two sides of the driver will effectively cancel each other out. So at any useful distance, the low frequencies (bass) are rendered inaudible. If you want to try this at home, remove a driver from its enclosure. You`ll notice a [tinny" sound quality compared to how the speaker sounded when assembled.

For a speaker to function well at all frequencies, we must prevent the pressure wave created by the back of the speaker cone from cancelling out the wave created by the front of the cone. If you were to mount the driver in a large, rigid sheet of material (a baffle), you could achieve the same effect. A baffle needs to be large to prevent low-frequency cancellation, so this is impractical in most applications. Closed boxes allow a more practical way of doing this.

A combination of the mechanical properties of the driver and the size of the box define the low-frequency behavior of an assembled closed box loudspeaker system. Without getting super technical, the air in the box acts like a spring that the cone pushes and pulls against, and that system has a resonant frequency below which its output drops off considerably.