Loudspeaker

A loudspeaker, often simply called a speaker, is a device that turns electrical audio signals into sound we can hear. It has one or more speaker drivers, an enclosure, and electrical connections, sometimes including a crossover network. The speaker driver is an electroacoustic transducer that changes electrical signals into movement, making 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 sending an audio signal through a voice coil. This coil moves quickly back and forth inside a magnetic field. It is attached to a diaphragm that creates sound waves. To work well, especially for lower sounds, 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, 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 tools that changed electric signals into sound. In 1861, Johann Philipp Reis added a speaker to his telephone, helping it make clear tones and later, muffled speech. Alexander Graham Bell made an even better speaker for his telephone in 1876.

The modern speaker design with a moving coil was created in 1925 by Edward W. Kellogg and Chester W. Rice. This design made sound clearer across many notes. In the 1930s, companies started linking many speakers together to make richer, louder sound for films and big 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 soft material, such as paper or metal. When electricity flows through the driver, it moves back and forth quickly, pushing the air around it. This movement of air creates the sounds we hear from speakers, like music or news.

Dynamic loudspeakers are the most common type. They use a magnet and a coil of wire to make the back-and-forth motion. The coil moves when electricity passes through it, like a magnet can push or pull certain metals. This simple design helps make speakers work well for many uses.

Speaker systems

Speaker systems are made to create good sound. Designers use science and special tools to make speakers better. They test speakers with people who know a lot about sound.

Speakers often use different parts to play many kinds of sounds. Common parts are cone, dome, and horn drivers. Some speakers try to play all sounds by themselves. These are often in small devices like televisions and radios. Subwoofers play very low sounds, and tweeters play very high sounds. Each part helps make the sound rich and full.

System design

Crossover

Main article: Audio crossover

In speakers with more than one driver, a crossover splits the audio signal into different frequency bands for each driver. This helps each driver work better by giving it only the sounds it is made for. Crossovers can be passive, using parts like resistors, inductors, and capacitors, or active, which uses an amplifier for more control.

Enclosures

Most loudspeakers are placed in a box to stop sound from the back of the driver from mixing with the front sound. Without a box, these sounds can cancel each other out, especially at low pitches. Enclosures can be sealed boxes or designed to let rear sound waves mix well with the front sound, which helps with low-pitched sounds.

Horn loudspeakers

Main article: Horn loudspeaker

Horn loudspeakers use a special shape called a waveguide to direct sound and make it louder. By matching the driver to the air, horns can produce louder sound using less power, focusing the sound into a smaller area. Some famous horn designs, like the Klipschorn, use room corners to make the horn work better.

Transmission line loudspeaker

Main article: Transmission line loudspeaker

A transmission line loudspeaker sends sound from the back of the driver into a special path inside the box. This design helps control the sound and uses the speaker's energy more effectively.

Wiring connections

Most home speakers have two points to connect to an amplifier or receiver. Common ways to connect include binding posts or spring clips. Connecting wires with the wrong electrical polarity can cause sound problems, making stereo sound less enjoyable.

Wireless speakers

Main article: Wireless speaker

Wireless speakers get audio signals using radio waves instead of cables. They still need power from an outlet or batteries, but they don’t need audio wires.

Specifications

Speaker specifications help us learn about how a loudspeaker works and what it can do. Key specifications include the type of speaker driver, like a woofer for low sounds or a tweeter for high sounds, and the size of each driver.

Loudspeakers also have a rated power, which shows 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. Details like the type of enclosure and the number of drivers help describe what the loudspeaker can do.

Listening environment

Main article: Room acoustics

Loudspeakers sound different based on where they are placed. Rooms change how sound sounds because walls, furniture, and objects reflect sound waves. These reflections can make some sounds louder and others quieter.

The way a loudspeaker sends out sound also matters. Simple speakers send sound in all directions, but many speakers focus sound 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 help create the best sound for a space.

Other speaker designs

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

Moving-iron speakers use a stationary coil to move 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 strong and can be used without extra parts.

Magnetostatic speakers use 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 move a thin membrane, but they are less efficient. Ribbon speakers have a thin metal-film ribbon suspended in a magnetic field, giving good high-frequency response but they can be fragile. Planar magnetic speakers use a flexible membrane with a voice coil printed on it.