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A brief history of microphonesA brief history of microphones
By Hugh Robjohns
The humble microphone has been with us for the first transmission of intelligible speech over
well over a century and has come a long way a rudimentary telephone system – the famous
from its crude beginnings. Identifying the request by Bell of his assistant: ‘Mr. Watson,
inventor of the microphone is not a simple task, come here. I want you’. However, the true
and depends very much on the definition used. inventor of the telephone was originally disputed
since Bell filed his original patent application for
In the beginning the telephone on the same day that Gray also
The German physicist Johann Philipp Reis applied for a Caveat announcing his intention to
(1834–1874) is a strong candidate for the title. claim the same invention (a caveat being a
His design for a 'sound transmitter' (optimised means of protecting an idea in advance of a full
around 1861), used a metallic strip resting on a patent application). At this time, though, neither
membrane with a metal point contact inventor had actually succeeded in transmitting
completing an electrical circuit. It was Reis's speech over a telephone system at all! The
theory that, as the membrane vibrated, the complaint was that Bell's first demonstrations of
metal point bounced up and down ‘producing his telephone employed a 'liquid transmitter' of a
intermittent contact and thus a varying current kind previously developed and shown publicly by
synchronous with the vibrations’. He believed the Gray – and not of the type documented in Bell's
height of the bounce and the force of its return patent application. However, the courts decided
caused variations in the amplitude of the current
pulse proportional to the intensity of the sound. It
worked in a fashion, but not really well enough
for intelligible speech!
The next recorded attempt was that of Elisha
Gray (1835–1901), an American inventor and
one of the founders of what became the
Western Electric Company. The Gray design
was called a 'liquid transmitter' in which a
diaphragm was attached to a moveable
conductive rod immersed in an acidic solution.
A second, fixed rod alongside the first
continued the circuit through the solution with
a battery connecting the two. Sound pressure
variations through the diaphragm caused the
separation between the two rods to vary in
proportion to the sound, producing
corresponding changes in the electric
resistance through the cell and, therefore, the
amount of current flowing around the circuit.
On March 10, 1876 Alexander Graham Bell
employed a very similar transmitter design for Bell’s original liquid transmitter microphone
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, A brief history of microphones
The poor quality of these 'liquid transmitters' development of better quality carbon microphones.
prompted a number of inventors to pursue Perhaps the best known is an octagonal design often
alternative avenues of design – David Edward seen in photographs of the early broadcasting
Hughes (1831–1900) was one such man.. stations –– the Marconi- Reisz 'transverse-current'
Already involved in the fledgling telegraph carbon microphone. This was invented in Germany by
industry, he was granted a patent in 1855 for a a young employee of the Reisz company, Georg
type-printing telegraph instrument, his design Neumann (who went on to manufacture microphones
became very successful in America and was under his own name). In 1925 the Marconi-Reisz
widely adopted throughout Europe. By 1878 he design was employed throughout the recently formed
had designed a new kind of microphone, using BBC, where it remained in daily use for over a decade.
carbon granules loosely packed in an enclosed
space. In response to varying pressure from a However, the inherent instability problems of
sound diaphragm, the electrical resistance carbon granules provoked the search for better
through the carbon granules changed alternatives. One avenue was the piezoelectric
proportionally. Although the performance of this (crystal) transducer, based on fundamental
kind of microphone is poor by today's standards research by the Curies during the previous
(inherently noisy with high distortion), it was a century. These transmitters originally used
significant step forwards at the time and was quartz or Rochelle salt crystals but the sound
the enabling technology for voice telephony. quality was not particularly good. Today,
piezoelectric foils in contact microphones use
The modern term of 'microphone' also appears specialised ceramics with very respectable
to have been coined by Hughes. He results.
demonstrated his transmitter by mounting it on
a sound box containing insects whose The first capacitor microphone (and associated
scratchings were then perceived to be impedance converter/amplifier set) was
'amplified'. Reports in the newspapers developed by EC. Wente in 1917, based on
suggested that the device ‘...acts for the ear work at Bell Laboratories in America. This was
much in the same way that the microscope a laboratory sound intensity measurement tool
serves the eye, hence its name’. and it wasn't until the early 1920s that
precision stretched-diaphragm condenser
Thomas Alva Edison (1847–1931) is well known microphones started to be manufactured for
for his work refining the carbon granule recording and broadcast applications. The
microphone, resulting in the carbon-button thermionic valve (invented in 1907 by Lee de
transmitter in 1886. This consisted of a cavity Forest) was a key factor in this, as capacitor
filled with granules of carbonised anthracite coal microphones require impedance conversion
confined between two electrodes, one of which impossible to achieve in any other practical
was attached to a thin iron diaphragm. Edison's way. Condenser microphones were employed,
transmitter was simple and cheap to to a limited extent, in the BBC from 1926 but
manufacture, but also very efficient and durable, they had a reputation for being
becoming the basis for the telephone 'temperamental' due to their susceptibility to
transmitters used in millions of telephones moisture causing 'frying noises'!
around the world for the majority of the last
century. Electromagnetic microphones (moving coil,
moving iron and ribbons) were relatively late on
Recording and broadcasting the scene because permanent magnets were
very weak and only electromagnets could create
developments sufficient flux densities. As a consequence, the
The advent of electrical disc recording and radio
broadcasting in the early 1920s stimulated the
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