“Echoes Through Time”
“Tracing the Evolution and Innovations
in Microphone Technology from Robert
Hooke to Digital Age”
Terrence Cheng 11A
Introduction
A microphone is a marvellous invention; it is a transducer that converts sound into an electrical
signal. Telephones, hearing aids, public address systems, sound recording, speech
recognition—all these applications are based on this product, but how exactly are the
microphones we see today built? Does it look the same as it did a hundred years ago? This
essay will delve into the history of microphones and explain the scientific theories behind.
Timeline
With the need of larger voices to speak to more people, acoustic megaphones were used to
achieve this. One of the first examples is introduced was from fifth-century-BC Greece- horn
shape theatre masks wear on actors in amphitheatres, although it seems not relevant to
microphones but it is the very first method that use a medium to concentrate sound energy into
a wider field. However, in 1665, a closer apparatus was introduced. English physicist Robert
Hooke set experiment with a non-air medium to transfer sound energy with “Lovers
Telephone” by only stretched wire with a cup at each end. Moving on, in 1861, German
inventor Johann Philip Reis used metallic strip to
attach on a vibrating membrane which produced
an intermittent current. This invention was known
for the “Reis telephone”. Although similar
products like “Liquid Transmitter” was also in
early telephones, these systems all presented a
poor quality.
(Reis Telephone)
The first microphone that gives a proper sound was the
carbon microphone developed by English inventor
David Edward Hughes and Thomas Edison and Emile
Berliner in the US, despite the fact that Thomas Edison
was the person who patented this invention, Hughes
was the one who got credit by people by several
evidences that he was the one who actually invented it.
(Two Carbon Microphones)
2
Varieties
With better methods to transfer proper sound, different kind of microphones were introduced.
After the condenser microphone was invented in 1916 by E.C. Wente, microphone technology
suddenly bloomed.
In a DC-Biased condenser microphone, the plates are altered
with a fixed charge (Q), and the voltage across the capacitor
plates changes with air vibrations. The capacitance equation
(C = Q⁄V) is used, where Q is the charge, C is capacitance, and
V is potential difference. However, the condenser microphone
knowledge is relevant to Cambridge International AS & A
Level Physics, particularly in the context of electronic circuits.
The voltage changes across the capacitor as the capacitance
changes, this voltage difference is amplified into sound signal
which could for to recording and performance.
(Senal SCM-66 DC-Biased Condenser Microphone)
However, In a dynamic microphone (moving-coil microphone) works with electromagnetic
induction, it is a strong type of microphones and it is not very expensive, the high gain makes
this kind of microphone ideal for stage performing.
A very classical example is a Shure SM-58 Dynamic
Microphone, this kind of microphone is also called
cardioid type microphone, it is widely using in vocal
because its polar direction and sensitivity and it is just
right to quickly respond with a natural, soft voice.
3
Dynamic microphones use the same physics principal as in a loudspeaker, a permanent magnet
wrapped with induction coil, when the
sound was transmitted, the membrane
vibrates and create coil movement
along the magnet, which produces a
varying current in the coil through out
the electromagnet. However, this kind
of membrane does not collect all audio
frequencies.
And that is the reason why some microphones use several membranes to combine multiple
signals, but this method is difficult and expensive. On the other hand, there are also examples
of microphones that designed to be collect only part of the sound. The AKG D112, designed for
bass respond instead of treble.
Further Research
(Polar Patterns)
Different types of microphones could use in different application fields with its material and
internal design by presenting different polar patterns. A SM-58 is a Cardioid microphone,
which accept sound from 130 angel in the range above. The polar pattern of the microphone is
indicative of its sensitivity to sound from a variety of angles. When a sound pressure level is
released, the illustrated patterns show points that have identical signal values. The microphone's
orientation is dependent on its design; for example, larger membrane types such as Oktava are
"side fire," while the smaller diaphragm like Shure are "end fire." Designs may combine
principles, using housing for shielding or electronically merging dual membranes.
4