Headphones: A Soothing Exploration & History

Welcome to the I Can't Sleep Podcast,

Where I read random articles from across the web to bore you to sleep with my soothing voice.

I'm your host,

Benjamin Boster.

Today's episode is from a Wikipedia article titled,

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.

Headphones are also known as earphones,

Or colloquially,

Cans.

Circumural,

Around the ear,

And supra-aural,

Over-the-ear headphones use a band over the top of the head to hold the drivers in place.

Another type,

Known as earbuds or earpieces,

Consists of individual units that plug into the user's ear canal.

Within that category have been developed cordless earbuds using wireless technology.

A third type are bone conduction headphones,

Which typically wrap around the back of the head and rest in front of the ear canal,

Leaving the ear canal open.

In the context of telecommunication,

A headset is a combination of a headphone and a microphone.

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.

Initially,

The audio quality was mediocre,

And a step forward was the invention of high-fidelity headphones.

Headphones exhibit a range of different audio reproduction quality capabilities.

Headsets designed for telephone use typically cannot reproduce sound with the high fidelity of expensive units designed for music listening by audiophiles.

Headphones that use cables typically have either a quarter inch or an eighth inch phone jack for plugging the headphones into the audio source.

Some headphones are wireless,

Using Bluetooth connectivity to receive the audio signal by radio waves from source devices like cell phones and digital players.

As a result of the Walkman effect beginning in the 1980s,

Headphones started to be used in public places such as sidewalks,

Grocery stores,

And public transit.

Headphones are also used by people in various professional contexts such as audio engineers mixing sound for live concerts,

Or sound recordings and DJs who use headphones to cue up the next song without the audience hearing,

Aircraft pilots,

And call center employees.

The latter two types of employees use headphones with an integrated microphone.

Headphones grew out of the need to free up a person's hands when operating a telephone.

By the 1880s,

Soon after the invention of the telephone,

Telephone switchboard operators began to use head apparatuses to mount the telephone receiver.

The receiver was mounted on the head by a clamp which held it next to the ear.

The head mount freed the switchboard operator's hands so that they could easily connect the wires of the telephone collars and receivers.

The head-mounted telephone receiver in the singular form was called a headphone.

These head-mounted phone receivers,

Unlike modern headphones,

Only had one earpiece.

By the 1890s,

A listening device with two earpieces was developed by the British company Electrophone.

The device created a listening system through the phone lines that allowed the customer to connect into live feeds of performances at theaters and opera houses across London.

Subscribers to the service could listen to the performance through a pair of massive earphones that connected below the chin and were held by a long rod.

The French engineer Ernest Mercadier in 1891 patented a set of in-ear headphones.

The German company Siemens Brothers at this time was also selling headpieces for telephone operators which had two earpieces,

Although placed outside the ear.

The Siemens Brothers' headpieces looked similar to modern headphones.

The majority of headgear used by telephone operators continued to have only one earpiece.

Headphones appeared in the emerging field of wireless telegraphy,

Which was the beginning stage of radio broadcasting.

Some early wireless telegraph developers chose to use the telephone receiver's speaker as the detector for the electrical signal of the wireless receiving circuit.

By 1902,

Wireless telegraph innovators such as Lee de Forest were using two jointly head-mounted telephone receivers to hear the signal of the receiving circuit.

The two head-mounted telephone receivers were called in the singular form head-telephones.

By 1908,

The headpiece began to be written simply as head-phones,

And a year later the compound word headphones began to be used.

One of the earliest companies to make headphones for wireless operators was the Holzer Cabot Company in 1909.

They were also makers of head-receivers for telephone operators and normal telephone receivers for the home.

Another early manufacturer of headphones was Nathaniel Baldwin.

He was the first major supplier of headsets to the U.

S.

Navy.

In 1910,

Motivated by his inability to hear sermons during Sunday service,

He invented a prototype telephone headset.

He offered it for testing to the Navy,

Which promptly ordered 100 of them.

Wireless Specialty Apparatus Company,

In partnership with Baldwin Radio Company,

Set up a manufacturing facility in Utah to fulfill orders.

These early headphones used moving iron drivers with either single-ended or balanced armatures.

The common single-ended type used voice coils wound around the poles of a permanent magnet,

Which were positioned close to a flexible steel diaphragm.

The audio current through the coils varied the magnetic field of the magnet,

Exerting a varying force on the diaphragm,

Causing it to vibrate,

Creating sound waves.

The requirement for high sensitivity meant that no damping was used,

So the frequency response of the diaphragm had large peaks due to resonance,

Resulting in poor sound quality.

These early models lacked padding and were often uncomfortable to wear for long periods.

Their impedance varied.

Headphones used in telegraph and telephone work had an impedance of 75 ohms.

Those used with early wireless radio had more turns of finer wire to increase sensitivity.

Impedances of 1000 to 2000 ohms was common,

Which suited both crystal sets and triode receivers.

Some very sensitive headphones,

Such as those manufactured by Brands around 1919,

Were commonly used for early radio work.

In 1958,

John C.

Koss,

An audiophile and jazz musician from Milwaukee,

Produced the first stereo headphones.

Smaller earbud-type earpieces,

Which plugged into the user's ear canal,

Were first developed for hearing aids.

They became widely used with transistor radios,

Which commercially appeared in 1954 with the introduction of the Regency TR-1.

The most popular audio device in history,

The transistor radio,

Changed listening habits,

Allowing people to listen to the radio anywhere.

The earbud uses either a moving iron driver or a piezoelectric crystal to produce sound.

The 3.

5 millimeter radio and phone connector,

Which is the most commonly used in portable applications today,

Has been used at least since the Sony EFM-117J transistor radio,

Which was released in 1964.

Its popularity was reinforced by its use on the Walkman portable tape player in 1979.

Wired headphones may be used with stationary CD and DVD players,

Home theater,

Personal computers,

Or portable devices,

E.

G.

Digital audio player,

MP3 player,

Mobile phone,

As long as these devices are equipped with a headphone jack.

Cordless headphones are not connected to their source by a cable,

Instead they receive a radio or infrared signal encoded using a radio or infrared transmission link,

Such as FM,

Bluetooth,

Or Wi-Fi.

These are battery-powered receiver systems,

Of which the headphone is only a component.

Cordless headphones are used with events such as a silent disco.

In the professional audio sector,

Headphones are used in live situations by disc jockeys with a DJ mixer,

And sound engineers for monitoring signal sources.

In radio studios,

DJs use a pair of headphones when talking to the microphone,

While the speakers are turned off to eliminate acoustic feedback while monitoring their own voice.

In studio recordings,

Musicians and singers use headphones to play or sing along to a backing track or band.

In military applications,

Audio signals of many varieties are monitored using headphones.

Wired headphones are attached to an audio source by a cable.

Most common connectors are 6.

35mm and 3.

5mm phone connectors.

The larger 6.

35mm connector is more common on fixed-location home or professional equipment.

The 3.

5mm connector remains the most widely used connector for portable application today.

Adapters are available for converting between 6.

35mm and 3.

5mm devices.

As an active component,

Wireless headphones tend to be costlier due to the necessity for internal hardware,

Such as a battery,

A charging controller,

A speaker driver,

And a wireless transceiver.

Whereas wired headphones are a passive component,

Outsourcing speaker driving to the audio source.

Some headphone cords are equipped with a serial potentiometer for volume control.

Wired headphones may be equipped with a non-detachable cable or detachable auxiliary mail-to-mail plug,

As well as some of the two ports to allow connecting another wired headphone in a parallel circuit,

Which splits the audio signal to share with another participant,

But can also be used to hear audio from two inputs simultaneously.

An external audio splitter can retrofit this ability.

Various types of specially designed headphones or earphones are also used to evaluate the status of the auditory system in the field of audiology for establishing hearing thresholds,

Medically diagnosing hearing loss,

Identifying other hearing-related disease,

And monitoring hearing status in occupational hearing conservation programs.

Specific models of headphones have been adopted as the standard due to the ease of calibration and ability to compare results between testing facilities.

Supra-aural style headphones are historically the most commonly used in audiology as they are the easiest to calibrate and were considered the standard for many years.

Commonly used models are the Telefonics Dynamic Headphones TDH-39,

TDH-49,

And TDH-50.

In-the-ear or insert style earphones are used more commonly today as they provide higher levels of inter-aural attenuation,

Introduce less variability when testing 6,

000 and 8,

000 Hz,

And avoid testing issues resulting from collapsed ear canals.

A commonly used model of insert earphone is the Etymotic Research ER-3A.

Circum-aural earphones are also used to establish hearing thresholds in the extended high-frequency range,

8,

000 Hz to 20,

000 Hz.

Along with Etymotic Research ER-2A insert earphones,

The Sennheiser HDA-300 and COS-HV-1A circum-aural earphones are the only models that have reference equivalent threshold sound pressure level values for the extended high-frequency range,

As described by ANSI standards.

Audiometers and headphones must be calibrated together.

During the calibration process,

The output signal from the audiometer to the headphones is measured with a sound level meter to ensure that the signal is accurate to the reading on the audiometer for sound pressure level and frequency.

Calibration is done with the earphones in an acoustic coupler that is intended to mimic the transfer function of the outer ear.

Because specific headphones are used in the initial audiometer calibration process,

They cannot be replaced with any other set of headphones,

Even from the same make and model.

Electrical characteristics of dynamic loudspeakers may be readily applied to headphones,

Because most headphones are small dynamic loudspeakers.

Headphones are available with high or low impedance,

Typically measured at 1 kHz.

Low impedance headphones are in the range of 16 to 32 ohms,

And high impedance headphones are about 100 to 600 ohms.

As the impedance of a pair of headphones increases,

More voltage at a given current is required to drive it,

And the loudness of the headphones for a given voltage decreases.

In recent years,

Impedance of newer headphones has generally decreased to accommodate lower voltages available on battery-powered CMOS-based portable electronics.

This has resulted in headphones that can be more efficiently driven by battery-powered electronics.

Consequently,

Newer amplifiers are based on designs with relatively low output impedance.

The impedance of headphones is of concern because of the output limitation of amplifiers.

A modern pair of headphones is driven by an amplifier,

With lower impedance headphones presenting a larger load.

Amplifiers are not ideal.

They also have some output impedance that limits the amount of power they can provide.

To ensure an even frequency response,

Adequate damping factor,

And undistorted sound,

An amplifier should have an output impedance less than 1 8th that of the headphones it is driving,

And ideally as low as possible.

If output impedance is large compared to the impedance of the headphones,

Significantly higher distortion is present.

Therefore,

Lower impedance headphones tend to be louder and more efficient,

But also demand a more capable amplifier.

Higher impedance headphones are more tolerant of amplifier limitations,

But produce less volume for a given output level.

Historically,

Many headphones had relatively high impedance,

Often over 500 ohms,

So they could operate well with high impedance tube amplifiers.

In contrast,

Modern transistor amplifiers can have very low output impedance,

Enabling lower impedance headphones.

This means that older audio amplifiers,

Or stereos,

Often produce poor quality output on some modern low impedance headphones.

In this case,

An external headphone amplifier may be beneficial.

Sensitivity is a measure of how effectively an earpiece converts an incoming electrical signal into an audible sound.

It thus indicates how loud the headphones are for a given electrical drive level.

It can be measured in decibels of sound pressure level per milliwatt,

Or decibels of sound pressure level per milliwatt.

Both definitions are widely used,

Often interchangeably.

As the output voltage,

But no power of a headphone amplifier,

Is essentially constant for most common headphones,

DB over MW is often more useful if converted into dB over V,

Using Ohm's law.

Once the sensitivity per volt is known,

The maximum volume of a pair of headphones can be easily calculated from the maximum amplifier output voltage.

For example,

For a headphone with a sensitivity of 100 decibels,

SPL over V,

An amplifier with an output of one root mean square RMS voltage produces a maximum volume of 100 decibels.

Pairing high-sensitivity headphones with power amplifiers can produce dangerously high volumes and damage headphones.

The maximum sound pressure level is a matter of preference,

With some sources recommending no higher than 110 to 120 decibels.

In contrast,

The American Occupational Safety and Health Administration recommends an average SPL of no more than 85 decibels A to avoid long-term hearing loss,

While the European Union Standard EN 50332-1 2013 recommends that volumes above 85 decibels include a warning,

With an absolute maximum volume defined using 40 to 4000 Hz noise of no more than 100 decibels to avoid accidental hearing damage.

Using this standard,

Headphones with sensitivities of 90,

100,

And 110 decibels SPL over V should be driven by an amplifier capable of no more than 3.

162,

1.

0,

And 0.

3162 RMS volts at maximum volume setting,

Respectively,

To reduce the risk of hearing damage.

The sensitivity of headphones is usually between about 80 and 125 decibels over MW and usually measured at 1 kHz.

Headphone size can affect the balance between fidelity and portability.

Generally,

Headphone form factors can be divided into four separate categories,

Circum-aural over-the-ear,

Supra-aural on-ear,

Earbud,

And in-ear.

Wired headphones make a direct electrical connection to the source device using a cable,

Typically connected with a headphone jack.

Modern wireless or cordless earphones have no cord connecting the two earphones to the device or to each other.

They receive audio by means of a wireless technology such as Bluetooth.

In historical usage,

Wireless referred to a connection to a radio receiver,

Which was known as a wireless.

On some models,

Both audio streams are transmitted to one earphone,

Which forwards one stream to the other earphone.

On other models,

Each earphone receives its audio stream directly from the source device.

The former arrangement has the advantage of being capable with legacy systems,

While the latter arrangement has the advantage of causing less power drain in the earphone that has to forward one audio stream.

Connection between the two earphones,

Also being wireless,

May be referred to as True Wireless Stereo,

TWS,

Offering longer battery life and complete transmission on left and right channels,

Avoiding possible source signal emission if only one is worn.

Circum-aural headphones,

Sometimes called full-size headphones or over-ear headphones,

Have circular or ellipsoid earpads that encompass the ears.

Because these headphones completely surround the ear,

Circum-aural headphones can be designed to fully seal against the head to attenuate external noise.

Because of their size,

Circum-aural headphones can be heavy,

And there are some sets that weigh over 500 grams,

Or one pound.

Ergonomic headband and earpad design is required to reduce discomfort resulting from weight.

These are commonly used by drummers in recording.

Supra-aural headphones,

Or non-ear headphones,

Have pads that press against the ears rather than around them.

They were commonly bundled with personal stereos during the 1980s.

This type of headphone generally tends to be smaller and lighter than circum-aural headphones,

Resulting in less attenuation of outside noise.

Supra-aural headphones can also lead to discomfort due to the pressure on the ear as compared to circum-aural headphones that sit around the ear.

Comfort may vary due to the ear cup material.

Earphones sit in the outer ear.

Earphones are very small headphones that are fitted directly in the outer ear,

Facing but not inserted in the ear canal.

Earphones are portable and convenient,

But many people consider them uncomfortable.

They provide hardly any acoustic isolation and leave room for ambient noise to seep in.

Users may turn up the volume dangerously high to compensate at the risk of causing hearing loss.

On the other hand,

They let the user be better aware of their surroundings.

Since the early days of the transistor radio,

Earphones have commonly been bundled with personal music devices.

They are sold at times with foam or rubber pads for comfort.

The use of the term earbuds,

Which has been around since at least 1984,

Did not hit its peak until after 2001 with the success of Apple's MP3 player.

In-ear headphones,

Also known as in-ear monitors,

IEMs,

Or canal phones,

Are small headphones with similar portability to earbuds that are inserted in the ear canal itself.

IEMs are higher quality in-ear headphones and are used by audio engineers and musicians as well as audiophiles.

The outer shells of in-ear headphones are made up of a variety of materials,

Such as plastic,

Aluminum,

Ceramic,

And other metal alloys.

Because in-ear headphones engage the ear canal,

They can be prone to sliding out,

And they block out much environmental noise.

Lack of sound from the environment can be a problem when sound is a necessary cue for safety or other reasons,

As when walking,

Driving,

Or riding near or in vehicular traffic.

Some in-ear headphones utilize built-in microphones to allow some outside sound to be heard when desired.

Generic or custom-fitting ear canal plugs are made from silicone rubber,

Elastomer,

Or foam.

Such plugs in lower-end devices may be interchangeable,

Which increases the risk of them falling off and getting lodged in the ear canal.

Custom in-ear headphones use castings of the ear canal to create custom-molded plugs that provide added comfort and noise isolation.

Some wireless earphones include a charging case.