Headphones

Headphones are a pair of small loudspeaker drivers worn on or around the head over a user's ears. They are electroacoustic transducers, which convert an electrical signal to a corresponding sound. Headphones let a single user listen to an audio source privately, in contrast to a loudspeaker, which emits sound into the open air for anyone nearby to hear. They are also known as earphones or, colloquially, cans.

Headphones connect to a signal source such as an audio amplifier, radio, CD player, portable media player, mobile phone, video game console, or electronic musical instrument, either directly using a cord, or using wireless technology such as Bluetooth, DECT or FM radio. The first headphones were developed in the late 19th century for use by switchboard operators, to keep their hands free.

Headphones are used in many places and for many purposes. Beginning in the 1980s, they became common in public places such as sidewalks, grocery stores, and public transit due to the Walkman effect. Professionals such as audio engineers, disc jockeys, aircraft pilots, and call center employees also use headphones for work.

History

Headphones began when people needed a way to use the telephone without using their hands. In the 1880s, telephone operators started using a device that held a telephone receiver next to their ear. This let them connect calls while keeping their hands free. At first, these devices only had one earpiece.

Later, more advanced headphones with two earpieces were created. By the early 1900s, people were using headphones to listen to radio signals. Over time, headphones improved, and in 1958, the first stereo headphones were made. Smaller earbuds became popular with portable radios in the 1950s and 1960s, changing how people listened to music and radio shows.

Main article: Headphones

Applications

Wired headphones can be used with many devices like CD and DVD players, home theater systems, personal computers, digital audio players, MP3 players, and mobile phones that have a headphone jack. Cordless headphones, on the other hand, don’t use a cable. They receive signals through radio or infrared waves using methods like FM, Bluetooth, or Wi-Fi. These are often used in places like silent discos.

In professional settings, headphones are important tools. DJs and sound engineers use them to monitor audio without disturbing others. Musicians and singers wear headphones in studios to hear their backing tracks. Military personnel also use headphones to monitor various audio signals. Wired headphones connect to devices using cables, with common types being 6.35 mm and 3.5 mm connectors.

Electrical characteristics

Headphones work like tiny speakers and have special electrical properties that affect how they sound. One important property is impedance, which measures how much the headphones resist the flow of electricity. Headphones can have low impedance (16 to 32 ohms) or high impedance (100 to 600 ohms). Low-impedance headphones need less power to work well and are common in modern devices like smartphones and portable music players. High-impedance headphones need more power and work better with older audio equipment.

Another key feature is sensitivity, which tells us how well headphones turn electrical signals into sound. Sensitivity is measured in decibels and shows how loud the headphones can get with a certain amount of power. Higher sensitivity means louder sound, but it’s important not to turn the volume too high, as this can damage hearing over time. Most headphones have sensitivities between 80 and 125 dB/mW, measured at a specific frequency of 1 kHz.

Specifications

Headphones come in different sizes and styles to suit different needs. The main types are circumaural (over-ear), supra-aural (on-ear), earbud, and in-ear. Circumaural headphones are large and cover the ears completely, providing good noise blocking but can be heavy. Supra-aural headphones sit on the ears and are lighter but don't block as much outside noise. Earbuds are small and fit in the outer ear, making them portable but they don't block much noise and can be uncomfortable. In-ear headphones go into the ear canal and also block out a lot of outside noise, but can fall out easily.

Headphones can also be open-back, semi-open, or closed-back. Open-back headphones let more outside sound in and sound more natural, while closed-back headphones block more noise and have stronger bass sounds. Some headphones are headsets, which combine a headphone with a microphone. These are useful for talking on the phone or communicating during activities like gaming or flying.

Main article: Headset (audio)

Ambient noise reduction

Unwanted sounds from the environment can be reduced in two main ways. The first way is called passive noise isolation. This simply blocks out sound by using the part of the headphone that sits over or in your ear, acting like an earplug. Some types of headphones, like in-ear and closed-back models, block more sound than others.

Another way to reduce noise is with active noise cancellation. These special headphones use a microphone and a small speaker to pick up outside noise and play it back in reverse. This helps cancel out the unwanted sound without disturbing the music or audio you are listening to. Active noise cancelling works best on steady, low-frequency sounds, like engine noise.

Transducer technology

Headphones use different types of transducer to turn electrical signals into sound. The most common type is the moving coil driver, often called a "dynamic" driver. It has a magnet and a coil of wire that moves when electricity passes through it, making the diaphragm vibrate and create sound waves.

Other types include MEMS speakers, which are made on small chips, and electrostatic drivers, which use a thin charged diaphragm to create sound. There are also electret drivers, which have a permanent charge, and planar magnetic drivers, which use a large membrane with wires to produce sound. Each type has its own way of working to bring audio to life.

Benefits and limitations

Headphones let you listen to music or other sounds privately, without disturbing others around you, like in a quiet library. They can also give better sound quality than regular speakers, especially for low-pitched sounds, because they sit close to your ear and don’t need to push a lot of air.

Headphones are great for video games because they help you hear where sounds are coming from, like the footsteps of someone behind you. While many headphones are made for regular music listening, some special kinds, called binaural recordings, can make sounds feel very real when you wear them. Headsets can also help people who spend long times on the phone stay more comfortable by letting them talk without holding the phone to their ear.

Health and safety

See also: Automatic volume limiter

Dangers and risks

Using headphones at high volume can harm your hearing. This is especially true in noisy places like subways or airplanes, where you might turn the volume up too loud. Experts suggest not listening to music at volumes higher than 80 decibels for more than 40 hours a week to keep your ears safe. Many smartphones now have features to help limit volume, but some people still prefer to set their own levels.

Headphones can also be distracting, especially when you're driving or cycling. Some places have laws against using headphones while doing these activities. There have been some reports of skin irritation from in-ear headphones, but more study is needed to understand this fully.

Occupational health and safety

Workers who use headphones or headsets for their jobs, like pilots or call center operators, also need to be careful about volume. Long periods of exposure to loud sounds can damage hearing. Guidelines suggest keeping sound levels below 85 decibels during an 8-hour workday. If the volume goes up, the time you can safely listen should go down.