Loudspeaker

A loudspeaker, often simply called a speaker, is a device that turns electrical audio signals into sound we can hear. It consists of one or more speaker drivers, an enclosure, and electrical connections, sometimes including a crossover network. The speaker driver is an electroacoustic transducer that converts electrical signals into movement, producing sound by moving air.

The most common type of speaker driver, called a dynamic speaker, was invented in 1925 by Edward W. Kellogg and Chester W. Rice. It works by passing an audio signal through a voice coil, which moves rapidly back and forth within a magnetic field, attached to a diaphragm that creates sound waves. To work efficiently, especially for lower frequencies, speaker drivers are often placed inside a speaker enclosure or cabinet.

Speakers come in many sizes and types. Smaller ones are found in everyday devices like radios, televisions, portable audio players, and computer speakers. Larger, louder systems are used in home stereos, electronic musical instruments, theaters, concert halls, and public address systems. Some modern speakers, known as powered speakers, even have built-in amplifiers for better sound quality.

Terminology

The term loudspeaker can mean either a single part that makes sound, called a driver, or a whole system that includes a box (called an enclosure) and one or more drivers.

Most loudspeaker systems use several drivers to create the best sound. These drivers each handle different sound ranges: subwoofers for very low sounds, woofers for low sounds, mid-range speakers for middle sounds, tweeters for high sounds, and sometimes supertweeters for the very highest sounds. When there are several drivers, a special filter called an audio crossover sends the right sounds to each driver. A system with two types of drivers, like a woofer and a tweeter, is called a two-way speaker system.

History

Early loudspeakers were simple devices that turned electrical signals into sound. In 1861, Johann Philipp Reis added a speaker to his telephone, allowing it to produce clear tones and later, muffled speech. Alexander Graham Bell later created a better speaker for his telephone in 1876.

The modern speaker design using a moving coil was invented in 1925 by Edward W. Kellogg and Chester W. Rice. This design improved sound quality across different frequencies. In the 1930s, companies began combining multiple speakers into one system to create richer, louder sound for movies and public events.

Driver design: dynamic loudspeakers

A loudspeaker uses special parts called drivers to turn electricity into sound. These drivers work like tiny motors connected to a piece of soft material, such as paper or metal. When electricity flows through the driver, it moves back and forth very quickly, pushing the air around it. This movement of air creates the sounds we hear from speakers, whether they are playing music, news, or other audio.

Dynamic loudspeakers are the most common type, and they rely on a magnet and a coil of wire to create this back-and-forth motion. The coil moves when electricity passes through it, just like a magnet can push or pull certain metals. This simple design helps make speakers efficient and effective for many different uses.

Speaker systems

Speaker system design involves ideas about sound quality and measurements. Designers adjust their creations using theories from several areas of science and test them with precise tools and experienced listeners. They face challenges like distortion and phase effects.

Loudspeaker systems often combine different types of drivers to cover a wide range of frequencies. The most common types are cone, dome, and horn drivers. Full-range drivers try to handle all frequencies alone, often found in small devices like televisions and radios. Subwoofers focus on very low frequencies, while tweeters handle the highest frequencies. Each type of driver has its own role in creating a full, rich sound.

System design

Crossover

Main article: Audio crossover

In multi-driver speaker systems, a crossover separates the audio signal into different frequency bands for each driver. This ensures that each driver only receives the frequencies it is designed to handle, reducing distortion and interference. Crossovers can be passive, using components like resistors, inductors, and capacitors, or active, which includes an amplifier for better control.

Enclosures

Most loudspeakers are housed in an enclosure to prevent sound from the back of the driver from interfering with the front sound. Without an enclosure, these opposing sound waves can cancel each other out, especially at low frequencies. Enclosures can be sealed boxes or designed to allow rear sound waves to add constructively to the front sound, improving low-frequency performance.

Horn loudspeakers

Main article: Horn loudspeaker

Horn loudspeakers use a shaped waveguide to direct sound and improve efficiency. By matching the driver to the air, horns can produce louder sound with less power, focusing the sound into a narrower area. Some famous horn designs, like the Klipschorn, use room corners to extend the horn's effectiveness.

Transmission line loudspeaker

Main article: Transmission line loudspeaker

A transmission line loudspeaker directs sound from the back of the driver into a special pathway inside the enclosure. This design helps control the sound and makes better use of the speaker's energy.

Wiring connections

Most home speakers use two wiring points to connect to an amplifier or receiver. Common connections include binding posts or spring clips. Connecting wires with the wrong electrical polarity can cause sound cancellation, making stereo sound harder to enjoy.

Wireless speakers

Main article: Wireless speaker

Wireless speakers receive audio signals using radio waves instead of cables. They still need power from an outlet or batteries, but eliminate the need for audio wires.

Specifications

Speaker specifications help us understand how a loudspeaker works and what it can do. Some key specifications include the type of speaker driver, such as a woofer for low sounds or a tweeter for high sounds, and the size of each driver.

Loudspeakers also have a rated power, which tells us how much electricity they can handle without getting damaged. Another important specification is impedance, usually measured in ohms (Ω), which affects how the speaker works with an amplifier. Other details like the type of enclosure and the number of drivers help describe the loudspeaker's capabilities.

Listening environment

Main article: Room acoustics

Loudspeakers work differently depending on where they are placed. Rooms can change how sound sounds because of walls, furniture, and other objects that reflect sound waves. These reflections can make some sounds louder and others quieter, affecting what a listener hears.

The way a loudspeaker sends out sound also matters. Simple speakers send sound in all directions, but many speakers focus sound more in certain areas. This can change how balanced the sound feels, especially if the listener moves around the room. Placement and design of the speaker both play important roles in creating the best sound for a space.

Other speaker designs

While dynamic cone speakers remain the most popular choice, many other speaker technologies exist.

Moving-iron speakers use a stationary coil to vibrate a magnetized piece of metal, which is attached to the diaphragm. Balanced armature drivers are a type of moving iron driver used in high-end earphones and hearing aids. Piezoelectric speakers are often found in watches and other electronic devices, and can also be used as tweeters in computer speakers and portable radios. They are resistant to overloads and can be used without a crossover.

Magnetostatic speakers use an array of metal strips bonded to a large film membrane, while magnetostrictive speakers are often used in sonar and audio speaker systems. Electrostatic speakers use a high-voltage electric field to drive a thin membrane, providing a more linear motion but are less efficient. Ribbon speakers consist of a thin metal-film ribbon suspended in a magnetic field, offering a good high-frequency response but are often fragile. Planar magnetic speakers use a flexible membrane with a voice coil printed on it.