details on loudspeaker

1. Practical-2
The standard dynamic loudspeaker that we know of today was first
built 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.
Types of speakers and how they work:
1. Horns
2. Electrodynamic Loudspeaker
2.1 Timeline of the Modern Speaker
3. Flat Panel Speakers:
3.1 Planar
3.2 Electrostatic
3.3 Multi-cell Diaphragm Speakers
4. Plasma Arc Speakers
5. Piezoelectric Speakers

2. 1) Horns Speakers
Horns were the earliestform 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.
Horn uses: Audio recording for entertainment and record keeping, later on for
voice radio.
2) Electrodynamic Speakers

3. What 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.
Work:
The modern speaker uses an electromagnet to turn electric signals of varying
strength into movement. The coil of copperwire moves as the magnet energizes.
This works using induction. The coil is connected to a cardboard/paper/vinyl
"cone". The coneis 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 producea specific frequency range. Not all
materials and construction designs produceall sounds the same: see tweeter, mid-
range, woofer, subwoofer.
Timeline of the Modern Speaker:
1861 - A simple type of electronic loudspeaker was developed by Johann Philipp
Reis - a teacher at Friedrichsdorf, Germany. The speaker was crudely able to
reproducenoise and just an experiment.
1876 - Alexander Graham Bell also tried to producea speaker based on Reis's
work. At this time in history there was not enough base knowledge in physics and
material engineering to allow Bell or any other inventor the ability to successfully
producean electrodynamic loudspeaker. The need to amplify sound and telegraph
signals over long distance did help spur the development of amplifiers, which is an
important component of audio systems later on.
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.
1877-1921-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.

4. The electrodynamic loudspeakertodaycomes in severaltypes in order to
produce a quality sound for a given frequency range:
Tweeter- 2kHz - 20kHz. used to produceall 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.
Mid-range Speaker - 300 - 5kHz. This speaker covers most human voice along
with most instruments.
Woofer- 40 - 1 kHz. low frequencies. The woofer goes back to work done in the
1930s at Bell Labs.
Subwoofer- 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 producesound 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/stoporreflect sound. Subwoofers
were developed in the 1960s.
3) Flat Panel Speakers:

5. There are several kinds of flat panel speakers, engineers have been working on flat
speakers for many decades as to decrease the size of speaker boxes. The standard
flat panel speaker has a exciter attached to a square panel. 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.
The standard flat panel electrodynamic loudspeaker has 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
speaker in a flat form.
Types of flat panel speakers: ribbon speaker, planar magnetic, electrostatic
Standard Flat Panel Speakers:
The diaphragm can have paper bonded on both sides of the polystyrene to help
sound production. It can also be made of PET foam, polypropylene foam,
polypropylene, ABS, glass fiber and carbon fiber.
The four corner points of the flat diaphragm are attached to a cushion. The exciter
pushes the center of the diaphragm forward causing a bending in the surface,
generating sound waves.
Planar Magnetic Speakers:
This has a conductorattached/embedded in the diaphragm of styrofoam. The
diaphragm moves forward and backward to make sound. This type of speaker has
traditionally worked better than a standard flat electrodynamic loudspeaker
because the entire styrofoam flat surface moves easily, not requiring a large
electromagnet to drive it.
Electrostatic FlatPanel:(ESL)
The 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. It has poorbass responsebut 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.

6. Ribbon Driven Speakers:
Super light (low mass) aluminum foil film is used as a diaphragm in this type of
speaker. The thin strip of aluminum on mylar (like a shiny mylar balloon) is
durable and suspended between two bar magnets. This type of speaker does not
need a transformer between the amplifier and the speaker.
Multi-cell Flat Diaphragm 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 coppercoils have been wrapped around the base of the
clear plastic bulges in the photos below. The long permanent magnets create
separate 'cells' and the whole diaphragm ends up moving uniformly. This is a
heavier speaker than the flat panel speakers above. This type of speaker requires a
tranformer becauseeach small cell has a lower impedance than a standard speaker
with single exciter.
4) Plasma Arc Speakers:
Plasma is 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.

7. 5) Piezoelectric Speakers:
Piezoelectric speakers use an expanding and contracting crystal to vibrate the air
and producesound. Piezoelectric 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. It may be possible in the future that this
technology may improve, providing a speaker with good sound characteristics and
durability, however it remains up to tomorrow's engineers to make this possible.
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.
Conclusion: In this Practical, we studied about various speakers andalso their
structure and uses at various locations. The speakersclassifiedabove are used
for many specific as well as common purposes and according to the need of
them in an environment and place.