Microphones
Riley White 20742356
Contents
Definition & Overview............................................................................................................................. 1
History & Requirement ........................................................................................................................... 1
Measurement.......................................................................................................................................... 2
Types ....................................................................................................................................................... 2
Condenser Microphone ...................................................................................................................... 2
Cost ................................................................................................................................................. 2
Dynamic Microphone.......................................................................................................................... 3
Cost ................................................................................................................................................. 3
Ribbon Microphone ............................................................................................................................ 3
Cost ................................................................................................................................................. 3
Piezoelectric Microphone ................................................................................................................... 3
Fibre Optic Microphone ...................................................................................................................... 3
MEMs Microphones ............................................................................................................................ 4
Further Reading ...................................................................................................................................... 4
References .............................................................................................................................................. 4
Definition & Overview
A microphone is defined as “An instrument for converting sound waves into electrical energy
variations which may then be amplified, transmitted, or recorded.” [1] Sir Charles Wheatstone was
the first person the coin the phrase “microphone” in 1827. [2]
Microphones (also known as mics or mikes), have a variety of uses in a variety of industries. A
microphone can refer to the unit one holds when talking or singing in order to amplify voice or
sound, as well as the sensor that can be found in electronic circuits to pick up sound. Some
microphone sensors (such as the ones used in hearing aids) can be as small as 7.3 cubic millimeters.
[3]
History & Requirement
In 600BC, the first device that attempted to increase the volume of the spoken word was invented in
Greece, in an effort to communicate with large groups of people in amphitheatres. This device had
specially designed mouth openings that acoustically augmented the voice. [4]
Microphones were first used with early telephones and radio transmitters. In 1876, the first
microphone was invented by Emile Berliner for use as a telephone voice transmitter. [2] This was
known as a carbon microphone. Thomas Edison then refined this carbon microphone into his carbon
button transmitter in 1886, which was used in the first ever radio broadcast in 1910. [5]
The condenser microphone was invented in 1916 by C. Wente, followed by the first practical moving
coil microphone in 1923 invented by Captain H.J. Round, and later the ribbon microphone was
introduced by Harry F. Olson. [6] [7] [8] Development of the microphone as well as inventions of
different types came quickly in the second half of the 20th century, to get us to where we are today.
Measurement
Microphones are essentially sensors that
detect sound, like our ears. Sound is
defined as “Vibrations that travel through
the air or another medium and can be
heard when they reach a person’s or
animal’s ear”. [9] Basically, sound can
travel as a pressure (or vibration) wave
through some medium, and is detected by
the microphone sensor by vibrating some
Figure 1: Sound as a pressure wave. Source:
membrane. In humans, this membrane is http://www.mediacollege.com/audio/01/sound-waves.html
our ear drum. Different types of
microphones have different types of membranes to pick up these vibrations. The vibrations of the
membrane are then transformed into electrical signals. The method in which this is done varies on
the microphone.
Types
Condenser Microphone
The condenser microphone gets its name from the old name for capacitors (they were historically
called condensers). The diaphragm in the condenser microphone acts as one plate of a capacitor,
and the vibrations due to the sound changes the distance between the plates. [10] The plates are
given a charge, and the distance between them is inversely proportional to their capacitance, and so
the voltage maintained across the capacitor plates changes with the vibrations in the air, according
to the equation (C = Q/V).
As the plates have to be given a charge, condenser microphones require a power source, whether
that be from a battery or from the microphone input. These microphones are popular in a wide
range of sources, from cheap karaoke microphones to expensive high-quality recording studio mics.
This popularity is mainly due to the small mass that has to vibrate for sound to be detected. [10] This
means weaker sounds can be picked up.
Cost
As the condenser microphone is used in a variety of applications, in varying quality, the price can
range from cheap inexpensive units to sets costing upward of $1700 available commercially. [11]
Dynamic Microphone
“Dynamic microphones work via electromagnetic
induction. They are robust, relatively inexpensive and
resistant to moisture. This, coupled with their
potentially high gain before feedback, makes them
ideal for on-stage use.” [10]
Essentially, a small induction coil placed inside the
magnetic field of a permanent magnet is attached to
the diaphragm, which when vibrated via air pressure
through the grate, moves, inducing a current.
Figure 2: Dynamic Microphone. Source:
undergraduate.csse.uwa.edu.au
Cost
Relatively inexpensive when compared to condenser microphones, many dynamic microphones can
be purchased in the $30 - $100 range. [12]
Ribbon Microphone
Similar to the dynamic microphone in that it works on electromagnetic induction, the ribbon
microphone uses a thin metal ribbon suspended in a magnetic field, connected to the device output.
When sound vibrates this ribbon, a current is produced via electromagnetic induction and travels to
the output. Ribbon microphones are bi-directional (typically), in that they only detect sound from
certain directions. [10] This makes them appealing to certain applications when sound from only a
particular source may be desired (for example wanting to record the cymbal and not the tom-tom on
a drum set).
Cost
Somewhat more expensive than the dynamic microphone, units can be found online ranging from
$100 to upward of $1000. [13]
Piezoelectric Microphone
A piezoelectric microphone uses a crystal that produces an electric signal under pressure (known as
piezoelectricity). “An example of this is potassium sodium tartrate, which is a piezoelectric crystal
that works as a transducer, both as a microphone and as a slimline loudspeaker component.” [10]
This particular type of microphone is used nowadays in contact vibrations, such as drums or guitar
pickups, or in challenging environments, such us underwater. The cost for these mics range from
very inexpensive to upward of $500, depending on the application and encompassing kit.
Fibre Optic Microphone
This microphone uses changes in light intensity to detect sound. “[A] light from a laser source travels
through an optical fiber to illuminate the surface of a reflective diaphragm. Sound vibrations of the
diaphragm modulate the intensity of light reflecting off the diaphragm in a specific direction. The
modulated light is then transmitted over a second optical fiber to a photo detector, which
transforms the intensity-modulated light into analog or digital audio for transmission or recording.
Fiber optic microphones possess high dynamic and frequency range, similar to the best high fidelity
conventional microphones.” [10]
The fact that these microphones don’t require any electromagnetic induction or use magnets of any
kind means that they can be used in magnetism-sensitive environments, such as MRI scans and
other medical fields.
MEMs Microphones
The smallest of all microphones, the MicroElectro-Mechanical (MEM) microphone is made by
etching a pressure sensitive diaphragm onto a silicon chip, along with an integrated amplifier. They
are usually of the condenser design, and have an analogue to digital converter integrated into the
device to make them compatible with most modern digital devices. [10] These are ideal for use with
hearing aids and other applications that require a small, low-power device for sound detection, and
can be as small as 7.3 cubic millimetres. [3]
The cost for these units can range from less than $10 to more than $100, depending on the
accompanying circuitry and quality of sensor. [14]
Further Reading
1) Microphone - Wikipedia
http://en.wikipedia.org/wiki/Microphone
2) Smallest MEMs Microphone… - Analog Devices
http://www.analog.com/en/pressrelease/03_25_13_Smallest_MEMS_Microphone_Designed/press.html. [Accessed 3 August
2014].
3) How Do Microphones Work? – Media College
http://www.mediacollege.com/audio/microphones/how-microphones-work.html
References
[1] Oxford Dictionaries, “Microphone,” Oxford Dictionaries, [Online]. Available:
http://www.oxforddictionaries.com/definition/english/microphone. [Accessed 3 August 2014].
[2] M. Bellis, “The History of Microphones,” [Online]. Available:
http://inventors.about.com/od/mstartinventions/a/microphone.htm. [Accessed 3 August
2014].
[3] E. L. Kramer, “SMALLEST MEMS MICROPHONE DESIGNED FOR HEARING AID APPLICATIONS
FEATURES LOW EQUIVALENT INPUT NOISE (EIN) AND POWER CONSUMPTION,” Analog Devices,
[Online]. Available: http://www.analog.com/en/pressrelease/03_25_13_Smallest_MEMS_Microphone_Designed/press.html. [Accessed 3 August
2014].
[4] H. Montgomery, “Amplification and High Fidelity in the Greek Theater,” The Classical Journal,
1959.
[5] A. A. Huurdeman, The Worldwide History of Telecommunications, Wiley-IEEE Press, 2003.
[6] M. Fagen, A History of Engineering and Science in the Bell System: The Early Years (1875 1925), New York: Bell Telephone Laboratories, 1975.
[7] B. Hennessy, The Emergence of Broadcasting in Britain, 2005.
[8] Mix Online, “1931 Harry F. Olson and Les Anderson, RCA Model 44 Ribbon Microphone,” Mix, 1
September 2006. [Online]. Available: http://mixonline.com/TECnology-Hall-of-Fame/olsonanderson-rca-090106/. [Accessed 4 August 2014].
[9] Oxford Dictionaries, “Sound,” Oxford Dictionaries, [Online]. Available:
http://www.oxforddictionaries.com/definition/english/sound. [Accessed 4 August 2014].
[10 Wikipedia, “Microphone,” Wikipedia, [Online]. Available:
] http://en.wikipedia.org/wiki/Microphone. [Accessed 4 August 2014].
[11 Kosmic Sound, “Studio Microphones-Recording,” Kosmic, [Online]. Available:
] http://www.kosmic.com.au/recording/studio-microphones/?arrow=1&dir=desc&order=price.
[Accessed 5 August 2014].
[12 Google, “Google Shopping- Dynamic Microphone,” Google, 5 August 2014. [Online]. Available:
] https://www.google.com.au/search?q=dynamic+microphone&source=lnms&sa=X&ei=yLbfU78NoK68gWz6YHoCg&ved=0CAcQ_AUoAA&biw=1280&bih=611&dpr=1.5#q=dynamic+microph
one&tbm=shop. [Accessed 5 August 2014].
[13 Google, “Google Shopping - Ribbon Microphones,” [Online]. Available:
] https://www.google.com.au/search?q=dynamic+microphone&source=lnms&sa=X&ei=yLbfU78NoK68gWz6YHoCg&ved=0CAcQ_AUoAA&biw=1280&bih=611&dpr=1.5#q=ribbon+micropho
ne&tbm=shop. [Accessed 5 August 2014].
[14 Google, “Google Shopping- MEMs Microphone,” Google, [Online]. Available:
] https://www.google.com.au/search?q=dynamic+microphone&source=lnms&sa=X&ei=yLbfU78NoK68gWz6YHoCg&ved=0CAcQ_AUoAA&biw=1280&bih=611&dpr=1.5#q=MEMs+microphon
e&tbm=shop. [Accessed 5 August 2014].
Figure 1: Sound as a pressure wave. Source: http://www.mediacollege.com/audio/01/soundwaves.html .............................................................................................................................................. 2
Figure 2: Dynamic Microphone. Source: undergraduate.csse.uwa.edu.au............................................ 3