Ear, ear: a brief history of headphones

By Mike Smyth, specialist technical writer
Thursday, 31 January, 2013

Headphones have been with us since the beginning of the 20th century when they are said to have been invented by one Nathaniel Baldwin who produced early models in his kitchen and later interested the US Navy in their adoption. They were the only way to hear the faint signals coming through the air by radio as the age of loudspeakers had not yet arrived.

With the advent of broadcast radio they again were the only way of hearing the signals, and even when loudspeakers did come on the scene, headphones created a niche for themselves which still exists today.

These early devices, which used moving iron drivers, were sensitive enough but lack of damping made for poor sound quality. The impedance needed for telegraph work was around 75 Ω but for radio reception they had to be more sensitive still and this raised their impedance to around 2000 Ω to match the outputs of the triode anodes of the receivers of the time.

Today these values have changed somewhat. Low-impedance phones are typically 16-32 Ω and high-impedance types are between 100 and 600 Ω. As the impedance increases, more voltage but less current is needed and the loudness for a given voltage decreases. With low voltage, very common in much equipment, the impedance has decreased.

Early headphones were very uncomfortable to wear for any length of time because of the hard wooden and then plastic cases that contained the workings and the usually tight headbands to which they were attached. Their very limited frequency response and construction that made them prone to distortion were strong discouragements for prolonged wearing and listening.

For a while, headphones were the only way to hear radio and telegraph signals as the early speakers were not only large and cumbersome but also very insensitive and again, prone to distortion. But as speakers got better, headphone use by the general public declined. However, it expanded in specialised industries such as the maritime and the budding aviation industry where both sound security and ease of hearing were essential.

Technology took a quantum leap forward with the advent of the moving coil, also known as the dynamic, headphone and this has become the most common device. It reduced background noise and made individual voices recognisable above the hiss and crackle of earlier devices while other technologies such as the electret and balanced armature have further improved quality.

These advancements turned makers towards making their headphones more comfortable for the wearer, recognising that this was a prerequisite for long-time wearing by specialised users. Soft surrounds, lighter units and adjustable headbands all contributed to a much more pleasant wearing experience.

Hand in hand with this came moves to exclude extraneous noise, in some cases made all the more important because by now headphones had reached a point of being a hi-fi device comparable with the best speakers.

Today, the best noise-cancelling phones are in-ear canal devices or closed back types while open back and ear bud versions give some noise isolation as well. For really effective noise cancellation, closed back phones attenuate by 8-12 dB but in-ear devices are even better at 10-15 dB.

Headphones and headsets (those with a microphone attached) are widely used in many industries. Emergency services are particularly suited to wireless headphones, as workers need to have free hands at all times and not have their movements impeded by equipment.

Mobile phone users are increasingly turning to Bluetooth for a hands-free means of communication while even office phones are going wireless for the freedom they afford. In the mining industry, especially long-wall underground mining, safety is paramount and radio/phone equipment has to be intrinsically safe because the smallest spark could cause a disastrous explosion.

Although jet engines are today nothing like as noisy as their forebears, they still represent a major source of noise in all aircraft. So for pilots, radio operators, navigators in the airforce and anyone else who has to wear a headset or headphones for a long time, both comfort and outside noise exclusion are important factors that equipment manufacturers have gone a long way to take into account.

And while the many technical improvements were going on, the price per unit has been falling and the choice has been rising.

With the advent of first the miniature, portable cassette player and later the iPod, tiny ear bud phones have taken the market by storm. They are now used by many two-way radio operators because they are so small, unobtrusive and efficient.

Two technologies seem likely to dominate the headphone market in the near to medium future. Unified communications (UC) is an integrated set of voice, data and video communications. Headset manufacturers are providing UC-certified headsets to integrate directly into certain platforms. They are now available in wireless for hands-free communication.

According to a Frost and Sullivan report on the industry, UC would appear to be a growth area that is going to provide huge versatility as it effectively links home landline phones, mobile phones, videoconferencing, email and software driven phones that allow calls to be made across the internet without specialised equipment other than a computer.

The second technology is wireless headsets, as mentioned previously. Allowing a freedom from cables and plugs, it is increasingly being used in control centres for emergency services and by the general public in a range of applications.

In whatever shape or form, headsets and headphones have provided clear hearing and communication for users in many industries. It is a safe bet that the technology will continue to improve in the near future.

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