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Source :- http://simple.wikipedia.org,http://www.edisontechcenter.org,
Computer Spaker
A pair of speakers for notebook computers that are powered and audio-connected to the computer via USB
Computer speakers, or multimedia speakers, are speakers
external to a computer, that disable the lower fidelity built-in
speaker. They often have a low-power internal amplifier. The standard
audio connection is a 3.5 mm (approximately 1/8 inch) stereo phone connector often color-coded lime green (following the PC 99 standard) for computer sound cards. A few use an RCA connector for input. There are also USB speakers which are powered from the 5 volts at 500 milliamps provided by the USB port, allowing about 2.5 watts of output power. Computer speakers were introduced by Altec Lansing in 1990.[1]
Computer speakers range widely in quality and in price. The computer speakers typically packaged with computer systems are small, plastic, and have mediocre sound quality. Some computer speakers have equalization features such as bass and treble controls.
The internal amplifiers require an external power source, usually an AC adapter. More sophisticated computer speakers can have a subwoofer unit, to enhance bass output, and these units usually include the power amplifiers both for the bass speaker, and the small satellite speakers.
Some computer displays have rather basic speakers built-in. Laptops come with integrated speakers. Restricted space available in laptops means these speakers usually produce low-quality sound.
For some users, a lead connecting computer sound output to an existing stereo system is practical. This normally yields much better results than small low-cost computer speakers. Computer speakers can also serve as an economy amplifier for MP3 player use for those who wish to not use headphones, although some models of computer speakers have headphone jacks of their own.
A common computer icon representing a speaker
Features vary by manufacturer, but may include the following:
Despite being designed for computers, computer speakers are electrically compatible with the aforementioned stereo components. There are even models of computer speakers that have stereo RCA in jacks.
History and Types of Loudspeakers
Computer speaker
From Wikipedia, the free encyclopedia
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This article does not cite any references or sources. (July 2010) |
Computer speakers range widely in quality and in price. The computer speakers typically packaged with computer systems are small, plastic, and have mediocre sound quality. Some computer speakers have equalization features such as bass and treble controls.
The internal amplifiers require an external power source, usually an AC adapter. More sophisticated computer speakers can have a subwoofer unit, to enhance bass output, and these units usually include the power amplifiers both for the bass speaker, and the small satellite speakers.
Some computer displays have rather basic speakers built-in. Laptops come with integrated speakers. Restricted space available in laptops means these speakers usually produce low-quality sound.
For some users, a lead connecting computer sound output to an existing stereo system is practical. This normally yields much better results than small low-cost computer speakers. Computer speakers can also serve as an economy amplifier for MP3 player use for those who wish to not use headphones, although some models of computer speakers have headphone jacks of their own.
Contents
Common features
- An LED power indicator.
- A 3.5 mm headphone jack.
- Controls for volume, and sometimes bass and treble.
- A remote volume control.
Cost-cutting measures and technical compatibility
In order to cut the cost of computer speakers (unless designed for premium sound performance), speakers designed for computers often lack an AM/FM tuner and other built-in sources of audio. However, the male 3.5 mm plug can be jury rigged with female 3.5 mm TRS phone connector to female stereo RCA adapters to work with stereo system components such as CD/DVD-Audio/SACD players (although computers have CD-ROM drives of their own with audio CD support), audio cassette players, turntables, etc.Despite being designed for computers, computer speakers are electrically compatible with the aforementioned stereo components. There are even models of computer speakers that have stereo RCA in jacks.
History and Types of Loudspeakers
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The 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.
1. Horns
2. Electrodynamic Loudspeaker & about sound
3. Flat Panel Speakers: planar, electrostatic
4. Diaphragm Speakers
5. Plasma Arc Speakers
6. Piezoelectric Speakers
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Horns 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. |
 
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The 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.
Video
Below: Steve Ainlay speaks into a horn to record onto a wax cylinder:
The horn and loud speaker development were pushed forward by the advent of voice radio:
 
Left:
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
Station)
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. |
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.How 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.Why 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 regulation.About Sound:
Sound is a form of energy passing through a gas or liquid medium. Understanding sound is in the realm of physics.There are two main measurements in sound: frequency and decibels.Frequency is responsible for the quality of sound in a speaker, decibels measure the 'loudness' of the speaker.Frequency: 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 to infinity.A 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 second.The 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.Decibels: 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.
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 reproduce sound and just an experiment.
1876 - 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.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.1921The first modern loudspeaker
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Above: The first prototype loudspeaker, finished in May 1921. The speaker cone is damaged. Inside the cabinet is a groundbreaking power amplification system.
C.W. 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.
Above: 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.
 An early speaker in a household radio, it uses a simple cardboard cone and small amplifier (the transformer) |
RCA: 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 other. |
RCA was 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.
Watch the video below to see the first prototype of the first loudspeaker:The electrodynamic loudspeaker today comes in several types in order to produce a quality sound for a given frequency range:
Tweeter - 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.
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 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.
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Electrostatic flat panel speaker (no photos yet):
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 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.
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 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.
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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.
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. 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.
Source :- http://simple.wikipedia.org,http://www.edisontechcenter.org,
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