standard dynamic loudspeaker that we know of today was developed
in the 1920's and uses a magnetic field to move a coil or magnet which
is connected to a diaphragm. There are other kinds of speakers/sound
amplification devices besides the standard round speaker, in this article
we cover just a few of the entire list: Horns, Piezoelectric
speakers, Magnetostrictive speakers, Electrostatic Loudspeakers,
Ribbon and Planar Magnetic Loudspeakers, Bending Wave Loudspeakers,
Flat Panel Loudspeakers, Heil Airl Motion Transducers, Plasma
Arc Speakers, and Digital Loudspeakers.
The dynamic loudspeaker in the photo above outperforms many other types
of speakers, and is lower cost to produce. For these reasons it is the
most popular. We will outline some other types in this page.
were the earliest form of amplification. Horns do not use
electricity. Thomas Edison, Magnavox, and Victrola all developed
advanced and well-performing horns from 1880 to the 1920's. The
problem with horns is that they could not amplify the sound very
much. With the use of electrical amplification in the future loud
sound could be generated to fill large public spaces. Horns remain
a novelty for collectors today.
uses: Audio Recording for entertainment and recorded keeping,
later on for voice radio
a straight copper horn used with wax cylinders.
Above:Left: An Edison horn made from strips of tin Right:
a small straight brass horn and wax cylinder phonograph, this
type was manufactured by Edison's companies until 1913. It was
replaced by the record. The smaller horn was used in smaller rooms
of the home.
needle moves up and down and forces the metal device above it to vibrate
on the clear diaphragm (similar to a speaker). This vibration pushes
air and makes a small amount of sound. This sound is channeled in the
brass arm down under the Victrola to a wooden horn inside the box (right
photo). The horn amplifies the sound to an impressive level. Opening
or closing the wood doors on the front controls loudness by blocking
the horn inside.
Below: Steve Ainlay speaks into a horn to record onto a wax cylinder:
horn and loud speaker development were pushed forward by the advent
of voice radio:
Pre-1925: The first voice radios
used a horn, and very quickly the horn was replaced by the electrodynamic
loudspeaker invented in Schenectady at General Electric. (WGY Radio
Right: 1927: Ernst Alexanderson
- inventor of broadcast television tests the first television broadcast
from the GE plant to his home. To his right you will see a standard
radio of the time used for the audio.
The Electrodynamic Loudspeaker (The Modern Speaker)
is an electrodynamic loudspeaker?A:
This is a device that uses an electromagnetic coil and diaphragm to
create sound. This is the most common type of speaker in the world today.
does it work?
The modern speaker uses an electromagnet to turn electric signals of
varying strength into movement. The coil of copper wire moves as the
magnet energizes. This works using induction.
The coil is connected to a cardboard/paper/vinyl "cone". The
cone is a diaphragm that vibrates along with the coil. Sound is created
and amplified by the diaphragm. There are variations on how to build
the speaker. A given speaker is designed to produce a specific frequency
range. Not all materials and construction designs produce all sounds
the same: see tweeter, mid-range, woofer, subwoofer.
did it take so long to invent the speaker?
It sounds simple, but to build a speaker one needs to have an understanding
of electricity, radio, sound waves, mechanics, chemistry and physics.
Today an engineer is trained after a few years of college in these areas
if they choose. Back in the early part of the 20th century the basic
knowledge of math and frequencies was still being explored. While the
electromagnet part of the speaker was invented early on in the 1860s,
it took 40 more years to develop a knowledge of acoustics and materials.
C.W. Rice and E.W. Kellogg finally invented it by solving the final
part of the puzzle. The final work was on how to shape the diaphragm
and what materials to use. The recent developments in vacuum tubes in
the 1910s helped to do sophisticated control of frequencies and power
Sound is a form of energy passing through a gas or liquid medium. Understanding
sound is in the realm of physics.
are two main measurements in sound: frequency and decibels.
is responsible for the quality of sound in a speaker, decibels
measure the 'loudness' of the speaker.
Humans can hear audio from 20 - 20,000 Hertz. Hertz is a measure of
cycles per second. Sound is is a wave ranging from 0 level of energy
middle 'C' tone on an instrument is not a solid constant level of energy
is it sounds to our ears, it is a wave which peaks every 278 times per
human ear does NOT hear all frequencies with the same sensitivity. It
is most sensitive to 2000 - 4000 Hz range. So a 100 dB (loudness level)
sound at 20 Hz will not damage the ear as much as a sound at 3000 Hz.
Most sounds fall in the lower range of our audible frequency range,
however sounds at 16,000 or 20,000 Hz are important. These upper frequencies
give us other information about a sound, such as the environment of
the sound. If someone is speaking in a small room or auditorium we can
tell thanks to the high frequencies. Developing a speaker which could
reproduce the low and very high frequencies was the greatest final challenge
in inventing the speaker. Of course since 1921 the speaker's abilities
to reproduce frequencies got even better.
The other measure of sound which is important for a speakers performance
is the loudness measured in decibels (dB). Decibels measure sound pressure.
The higher the pressure, the more your eardrum pushes inward. Decibels
is a logarithmic unit, which means that each unit indicates an increase
in power by x10. The 'bel' in decibel originates from telecommunications
pioneer Alexander Graham Bell. The need to measure sound efficiency
in gave rise to the unit in 1923.
0 dB is set at .0002 microbar (pressure). 120 dB is enough to cause
permanent damage to the human ear, however the ear will be more easily
damaged at the 2-4kHz range. This aspect of the human body being more
sensitive to certain frequencies is related to the species evolution.
A baby's cry is located in the 4-5 kHz range. We are programed to be
sensative to a baby's cry and human's scream. Similarly when we talk
about the electric light, the human eye is more sensitive to frequencies
in the green-yellow spectrum. You can read all about the development
of the electric light on our page here.
of the Modern Speaker:
- A simple type of electronic loudspeaker was developed
by Johann Philipp Reis - a teacher at Friedrichsdorf, Germany.
The speaker was crudely able to reproduce sound and just an experiment.
- Alexander Graham Bell also tried to produce a speaker
based on Reis's work.
1877 - The idea of the electromagnetic
coil driven speaker is formulated by Werner Von Siemens, he used
it with input signals of DC transients and telegraphic signals. He had
no way to amplify sound to create a useful speaker, but he theorized
that this could eventually be done.
- Various inventors and engineers played with the idea of
the electrodynamic loudspeaker but could only create rough distorted
sounds. There was no way to electrically amplify the signal to create
very loud sounds. The industry continued to rely on more advanced horns
to create amplification.
first modern loudspeaker
The first prototype loudspeaker, finished in May 1921. The speaker cone
is damaged. Inside the cabinet is a groundbreaking power amplification
Rice of General Electric and E.W. Kellogg of AT&T worked together
in Schenectady, New York to develop the modern speaker and first electric
amplification system. They created a working prototype in 1921. Rice
and Kellogg solved the final problems which led to a nice crisp sound.
Previous attempts to make the loudspeaker created an unacceptable muffled
sounding audio. This muffled sound was not good enough to compete with
the horn which was well established in the market. Rice and Kellogg
were able to fully understand the reproduction of all the frequencies
necessary to create an accurate audio sound. Their prototype had enough
of a dynamic range in frequencies to be better than the horn, while
possessing the ability to greatly increase loudness (dB). In 1925
they filed for patents and made a speech in St. Louis to the AIEE. After
several years of work they perfected it as the first commercial product
of it's kind called the Radiola Loudspeaker #104. It sold in 1926 for
$ 250 (about $3000 today (US dollars)). The speaker was produced under
the company name of RCA.
The first speaker. The coil was stationary unlike modern speakers, the
moving magnet was inside. Copper wires were insulated with cloth. This
prototype was built by C.W. Rice and E.W. Kellogg in 1921. The speaker
worked, but needed improvement to make it smaller so it could fit into
radio sets. Within a few years they improved the speaker so it could
fit into a radio 20 x 12 x 16" high.
early speaker in a household radio,
it uses a simple cardboard cone and small amplifier (the transformer)
The Radio Corporation of America sold the first speaker
instead of General Electric because the RCA was created as a consortium
of many US companies. RCA was created under pressure from the
US government as a way of having the major electric technology
companies work together on patents in order to more easily create
finished products which could compete with state-sponsored European
companies. European companies like Philips and Siemens had a leadership
which could easily mobilize patents for creation of products.
Under the more true capitalist systems in the US at the time,
companies fought over patent royalties and kept secrets from each
able to collectivize research in order to create better technology.
In addition to having a strong US company to compete internationally
in the radio market, having better technology was important for the
US during escalating war tensions prior to WW2. World War 1 taught the
important lesson not to be left behind, and that radio technology could
mean the difference between winning or being crushed.
the video below to see the first prototype of the first loudspeaker:
electrodynamic loudspeaker today comes in several types in order to
produce a quality sound for a given frequency range:
- 2kHz - 20kHz. used to produce all high end frequencies. There
are many ways to construct a tweeter today. Most are electrodynamic
(magnetic) speakers however there are piezo-electric, electrostatic
and plasma tweeters.
Speaker - 300 - 5kHz. This speaker covers most human voice along
with most instruments.
- 40 - 1 kHz. low frequencies. The woofer goes back to work done in
the 1930s at Bell Labs.
- 20 - 200 Hz. very low frequencies. The human ear can only hear down
to 20Hz. low frequency sound is unidirectional. This means that it can
be placed anywhere in a room and be heard from any point with the same
sound quality. Subwoofers also produce sound waves that penetrate walls
easily. Noise from this type of speaker is even known to penetrate vertically
through 5+ floors of concrete apartment buildings. Needless to say it
is easy to get in trouble with local noise ordinances. If you plan your
next loud event you may want to think about frequencies and the ability
of objects to absorb/stop or reflect sound. Subwoofers were developed
in the 1960s.
Panel Speakers use voice coils or other apparatus mounted to flat
panels to act as the source of sound. The flat panel acts as a diaphragm.
Below are some examples of different designs. Different materials can
be used as a diaphragm, from vinyl to Styrofoam. This is different from
a diaphragm speaker in that the moving voice coil is not wrapped around
the same material as the flat panel. The panel part is adhered to the
flat panel electrodynamic loudspeaker have been difficult to make because
it is difficult to vibrate the entire flat surface evenly while creating
good frequency response. Thus other speaker types have evolved to try
to make a flat speaker.
of flat panel speakers: ribbon speaker, planar magnetic, electrostatic
magnetic speaker: Has a conductor attached/embedded in the
diaphragm of styrofoam. The diaphragm moves forward and backward
to make sound. This type of speakers works better than a standard
flat electrodynamic loudspeaker because the entire styrofoam flat
surface moves easily.
flat panel speaker (no photos yet):
electrostatic flat panel speaker uses two metal grids with a diaphragm
made of a plastic sheet. The sheet is coated with graphite which is
electrically conductive. The diaphragm has a constant charge, high voltage
audio signal is created by the grids which are really electrodes.
has poor bass response but the speakers look interesting as a rectangular
flat screen. If combined with a regular electrodynamic woofer it can
be made into a full sound system.
Speakers. This speaker is related to the electrodynamic loudspeaker
in that it uses magnetic fields to move an element, however its shape
is different. This speaker has the coil directly mounted on the diaphragm.
Below is an example of a flat panel style diaphragm speaker.
The copper coils have been wrapped around the base of the clear plastic
bulges in the photos below. The entire clear plastic sheet below moves
to create sound. See the diagram below. This is a heavier speaker than
the flat panel speakers above.
Plasma Arc Speakers
ionized gas, or current sent through a gas. Plasma is responsive to
electrical fields, therefore you can turn electric signal of sound into
an electric field which manipulates the plasma. The plasma does have
mass and will vibrate creating sound similar to how a diaphragm moves
air to make sound. This kind of speaker is visually quite interesting
but limited in sound quality. The speaker has reliability problems and
therefore remains just a novelty.
speakers are limited in frequency response therefore they are only used
as tweeters or in small electrical devices like watches/clocks to make
simple sounds. Piezoelectronics are a solid state technology which makes
them durable and good for use as a microphone underwater. These speakers
are used as microphones in submarine warfare, they can detect other
microphones and hear sounds of other vessels.
We are expanding this page, so expect more
photos, speaker types and materials in the future. Help us by volunteering
material to publish.
Research - Steve Normandin
Writing, photos and graphics - M. Whelan The Physics Factbook by Glenn
Elert and Students
Decibel, Loudspeaker- Wikipedia
/ Video: -Copyright 2011-12 The Edison Tech
-Videos from the Edison Tech Center
Commercial entities must pay for use of photos/graphics/videos in their
No one commercial or public is allow to alter Edison Tech Center photos/graphics/videos.
Educational Use: Students and teachers may use photos and videos
for school. Graphics and photos must retain the Edison Tech Center watermark
or captions and remain unmanipulated except for sizing.
- Videos: We do not email, FTP, or send videos/graphics to anyone
except in DVD form. Payment is needed for this service. See our donate
page for pricing, and our catalogue
for a listing of videos on DVD.
Professional video production companies may get videos in data form
with signed license agreements and payment at commercial rates.
2012 Edison Tech Center, Schenectady, New York