Speaker Box Explained - Basic Parts & 7 Types Speaker Enclosure

Did you know? According to Grand View Research, the global professional audio equipment market was worth approximately $19.1 billion in 2023 and is expected to grow from 2024 to 2030.

A speaker system may look simple on the outside, but its internal design is sophisticated. Different enclosure types affect bass strength, vocal clarity, and coverage. This article explains the basics of acoustics, the main parts of a speaker, and the seven common enclosure types in simple terms. We hope you find this guide helpful.

1. Overview of a Speaker System

A speaker system is a device that converts an audio signal into sound and makes it louder.

The speaker is the endpoint of the entire audio system. Its job is to convert electrical energy into sound energy and send it into space so that a person can hear it.

2. How a Speaker Works

Sound Environment

To understand how a speaker creates sound, you need to understand how sound propagates. Sound must travel through a medium (sound doesn't travel in a vacuum). Gases, liquids, and solids can carry sound. This is similar to throwing a stone into water—waves are created. Sound waves propagate in a similar way.

Sound Wave Frequency

The human ear hears waves in the range of approximately 20–20,000 Hz. Below or above this range, sound is inaudible. Sound can travel through gases, liquids, and solids.

How a Speaker Works

A speaker converts an electrical signal into sound waves. It consists of a voice coil, magnet, diaphragm, and other components. An amplifier applies alternating current to the coil. The coil moves back and forth in a magnetic field. The coil moves the diaphragm, which pushes air, creating sound.

Why a Speaker Makes Sound

The electrical signal changes polarity many times per second. When the coil is attracted, the diaphragm moves inward. When the coil is repelled, it moves outward. This oscillating motion creates differences in air pressure. These differences form sound waves. This principle is similar to the way the human vocal cords work.

3. Main Parts of a Loudspeaker System

A loudspeaker system primarily consists of a driver, an enclosure (cabinet), and a crossover.

3.1 Driver

The driver converts the signal from the amplifier into sound and emits it.

Drivers are classified by many characteristics: operating principle, cone design, shape, frequency range, magnet type, and cone material.

3.2 Enclosure

The enclosure prevents short-circuiting of sound waves, reduces unwanted resonances, improves the frequency range, and reduces distortion.

By style, speakers can be bookshelf or floorstanding. By internal structure, speakers can be closed, bass reflex, bandpass, passive radiator, transmission line, dual-chamber, quarter-wave, symmetrical drive, and horn-loaded. The most common types are closed, bass reflex, and bandpass.

3.3 Crossover

Crossovers can be passive or electronic.

They split the frequency range, adjust the frequency response, regulate the phase, and control impedance.

A passive crossover is installed after the amplifier and uses coils (L), resistors (R), and capacitors (C) to send the correct frequency range to the correct driver. Passive crossovers are inexpensive and simple, but have higher losses and lower efficiency.

4. Seven Types of Loudspeaker Enclosures

Enclosures come in different designs. They aim to improve bass, efficiency, and reduce distortion. Below are seven common types.

4.1 Sealed Enclosure

This is the simplest design, proposed by Frederick in 1923. The speaker driver is installed in a completely sealed enclosure. This prevents the front and rear sound waves from mixing. However, the air inside creates elasticity and increases the resonant frequency.

Sealed enclosures sound tight and deep. Bass detail is higher. However, good deep bass usually requires a large volume. Newer sealed designs use drivers with better suspension. The air inside acts like a spring, which is why small sealed systems are sometimes called "acoustic suspension."

4.2 Bass-Reflex Enclosure

Invented by Turas in 1930, the enclosure has a port (opening), often with a tube. The enclosure's volume and the port's dimensions create a resonance based on the Helmholtz principle. The rear wave is inverted by the port and adds to the front wave in phase.

A bass-reflex enclosure provides a wider range, higher efficiency, and lower distortion (when properly designed). The low frequency limit can be 20% lower than the driver's resonance. This type of enclosure produces powerful bass even in a small volume and is the most common today.

4.3 Resistive Ported Enclosure

This is a variant of a bass reflex design. Sound-absorbing material is installed in the port. This slows the airflow and lowers the tuning frequency, extending the bass range.

4.4 Transmission Line

Based on transmission line theory, a long channel with sound-absorbing walls is located behind the driver. The channel's length is typically 1/4 or 1/8 of the low-frequency wavelength.

The purpose is to absorb the back wave so it doesn't return. In practice, the channel also provides damping, increases resonance output, and reduces cone movement. The internal path is often complex and maze-like.

4.5 Passive Radiator Enclosure

Introduced in 1954 (Olson and Preston). Instead of a port, a cone is used without a magnet or voice coil. The passive cone moves in phase with the main cone. The air in the enclosure and the passive cone form a resonant system, enhancing low frequencies.

This enclosure eliminates port noise and stabilizes the output. Even small enclosures produce good bass and high efficiency. Fewer standing waves result in a cleaner sound.