Modern headphones are indispensable accessories for private audio transmission at home, in the office, or on the go. Headphones are especially prominent equipment among carriers of laptops, cell phones, analogue and digital music players, audio recorders, and many other personal electronic devices. Perhaps no other headphone in history has gained more attention than the fashionably white earbud-style headphones made popular by Apple’s now virtually ubiquitous iPod. But headphones were not always a technology readily available for general use. The individual components of headphones are technological innovations that are vital to modern electronics for many more uses beyond the transmission of sound.

Headphones, in other words, while taken for granted today—from inexpensive versions packaged with electronic devices to the highest quality models—are achievements in human invention that coincide with other critical innovations without which headphones as we know them would not be possible. Like many histories of modern invention in physics and electronics, the history of headphones has roots in the experimentation of Thomas Edison. Though he did not know it at the time, some of his work with electrical currents indirectly led to innovations that made possible the amplification of audio signals.

Invention from the Amplifier to the Transistor

The history of the amplifier begins with none other than Thomas Edison, though he was unaware how to treat the electrical flow that occurred as a result of inserting a metal plate near the filament of his direct-current light bulb (McGrath 1999). Edison’s objective was to stop the transfer of heated carbon filament particles into the middle of the bulb, and he did not realize the effect was a result of excited electrons crossing the space between the metal and the filament. While the discovery of the electron would be credited to British physicist Joseph John Thomson, one of Edison’s men, the British scientist John Ambrose Fleming, working independently, modified Edison’s two-element bulb and created an “oscillation valve,” or vacuum tube, that could not only detect alternating current, but also received incoming radio waves. The radio signals were transformed into electrical signals that created a faint sound (Evans 2004).

Later, the American scientist Lee de Forest added a third, zigzagged element into Fleming’s tube creating a direct-current grid he called the “Audion,” or “triode,” that Edwin Howard Armstrong, the technical “father of radio,” discovered could be amplified using two circuits linked between a stronger and a weaker current. Armstrong discovered that the stronger current can be drawn out and converted to sound waves in a loudspeaker--and so the amplifier was born, a technology that would gradually be developed to replace the highly sensitive early mechanical headphones (Evans 2004). Modern headphones are simply miniature versions of loudspeakers and, while they have “evolved…to re-create the breadth and depth of the original sound,” the basic headphones are little more than miniature signal-propelled diaphragms sending air vibrations into the ear canal (McGrath 1999).

Still, the loudspeaker was a device that only gradually replaced the “acoustical horn” of early twentieth-century phonographs. The loudspeaker’s earliest patents were actually submitted in England and Germany near the end of the nineteenth century. But the first modern loudspeaker relied upon the development of a transducer to convert mechanically created signals into electrical energy. Based upon that innovation, C.W. Rice and E.W. Kelley discovered, in 1924, that electrical energy could be sent to a coil surrounded by a magnetic field, which then reproduced the electrical signal’s variations in the form of sound waves. Later, loudspeakers were evolved to eliminate distortion and improve total sound quality. Finally, researchers replaced bulky and fragile vacuum tubes with solid-state electronic transistors, which provided greater range of frequency and power by using material such as silicon to conduct and resist currents (McGrath 1999). Using tiny transistors, loudspeakers convert electrical signals into sound and, in the case of headphones, are designed to send out controlled, directional audio—though the evolution of headphones involves ever-increasing quality and personal experience of the reproduction of the original sound.

Innovation in Early Headphone Technology

In the 1930s, Beyerdynamic began marketing some of the world’s first headphones designed for use by the public. The company Web site states that they invented the “first dynamic headphones” in 1937 and continue to produce a modified version of that model today. However, Beyerdynamic’s DT 48, now immensely popular headphones among professionals in video and sound production, were not initially used as they are now. DT, an abbreviation for “Dynamic Telephone,” had not been put into use for high-fidelity sound reproduction. But by 1950, the company demonstrated the product’s acoustic sensation and so had the archetype of the world’s first high-fidelity headphones (Beyerdynamic.com). Dynamic audio devices express the range of audio sound from the loudest possible to the softest possible without distortion (Holmes 2006).

However, according the World of Invention, Jazz musician John C. Koss invented stereo headphones—that is, headphones providing a “full amplitude” of sound—in 1958. Koss’s avid interest in audio technology spurred him to enlist the assistance of an audio engineer to put together a complete audio listening system, including a portable phonograph, speakers, and headphones (McGrath 1999). Prior to Koss, audio playback equipment was bulky and difficult to move. The success of Koss’s design was their transportability. As such, the “first commercially viable high-fidelity headphones,” found an instant market among musicians and listeners alike (Holmes 2006). These rudimentary headphones, however, were “little more than tiny loudspeakers covered in cardboard and held in place by a military headband.”

Still, the success of Koss’s early headphones launched a family business that continues to thrive to the present day. Meanwhile, other companies, most notably in Japan, soon adopted the Koss design and began to develop innovative products of their own. These portable loudspeakers contained tiny amplifiers converting and sending out the audio signal. In truth, however, from their invention in the late 1950s, most headphones remained rather large by today’s standards until the Sony Walkman appeared on the portable audio device scene in 1979 and new accessories were developed to complement the emerging portable cassette player. In the next decade, Koss would go on to develop cordless headphones using infrared signals, though other manufacturers developed cordless headphones using radio transmitters of the kind used in cordless telephones (McGrath 1999).

Bluetooth Wireless Technology

In 1998, an organization called the Bluetooth Special Interest Group developed prototypes of the short-range wireless technology now popular in numerous devices from headphones to automobile security. Bluetooth, like other wireless technologies, are modeled on frequency hopping for secret communication, an idea first conceived by actress Hedy Lamarr and George Antheil, for which they were awarded a patent in 1942. Bluetooth further reduces interference between wireless devices by implementing the Adaptive Frequency-hopping Spread Spectrum (AFH), which works with the spectrum of frequencies to find the most available frequency for efficient transmission (Edlund 2008). Wireless headphones, one application of the technology, have faced the difficult challenge of matching the sound quality of corded headphones. But as AFH has evolved and further reduced signal dropouts and interference, proponents of wireless headphones may finally get comfortably unplugged, even where numerous other signals are present.

The first commercially available Bluetooth products (including the first headset) only appeared in 2000, but within the next eight years, companies have produced and shipped nearly two billion devices featuring Bluetooth technology. The privately held not-for-profit group has also grown from its initial five members (IBM, Intel, Nokia, Toshiba, and Ericsson) to 10,000 participating members today, and their responsibilities include publishing Bluetooth specifications and protecting the trademark for protected implementation in their products. Since the technology originates in Scandinavia and it is used to unite multiples devices, the founders codenamed the company after the tenth-century Danish King Harald Blatand (“Bluetooth” in English) who was influential in uniting the oft-feuding region. The codename stuck and has remained a leader in Personal Wireless Network communication technology by continuing to improve the original core specifications. Bluetooth headphones have found a niche with the development of modern portable audio devices, from enabled MP3 or other digital media to cell phones with music capabilities.

Looking Forward

One future of headphone technology is already being developed. New Scientist describes headphones using “human body communication” (according to Sony’s patent application), which uses the body to transmit an electric signal to headphones, effectively eliminating the need for both wires or interference-prone synced Bluetooth products. The body becomes the capacitor for the electrostatic charge tiny enough to allow specially designed “conductive ear pads in the headphones” to receive and convert a fluctuating signal sent from the music device, but without having any effect on the body (Fox 2006). Other manufacturers are exploring further merging mobile phones and headphones using digital radio technology. Such moves seem natural given the current trends in personal electronic device integration, which see wired mobile phones capable of performing every task from music playback to accessing the Internet.

In the meantime, headphones and earphones already have become tiny technological masterpieces. Higher-end models feature everything from noise reduction or noise cancellation to surround sound, which implement multiple tiny speakers on each side “creating the effect of space in sound” (McGrath 1999). Headphone amplifiers are also available to further reduce audio distortion and hiss that develops between the music source and the phones, making the listening experience as pristine as possible. Of course, all these features and accessories come with a monetary price, but the future of diminutive electronic technology may eventually build everything into a tiny, inexpensive model that will come standard with every gadget requiring this audio-personalizing accessory.

-- Posted August 20, 2008

References

"Headphones/Headsets." Beyerdynamic.com. Accessed: July 18, 2008.

"History." Beyerdynamic.com. Accessed: July 18, 2008.

"The Essentials of the Bluetooth SIG." Bluetooth.org. Accessed: July 18, 2008.

Edlund, Anders. “Bluetooth Technology: The True Hollywood Story.” Bluetooth SIG at Bluetooth.org. 2008. Accessed: July 18, 2008.

Evans, Harold. 2004. They Made America. New York, NY: Little, Brown and Company.

Fox, Barry. “Invention: Body-Wired Headphones.” NewScientist.com news service. New Scientist Tech. November 27, 2006. Accessed: July 9, 2008.

Holmes, Thom, ed. 2006. The Routledge Guide to Music Technology. New York, NY: Routledge.