Tech Basics: AUDIO DEVICES

 In our last few articles, we have discussed the working and functionalities of various day to day using technology. We covered up history, development and manufacturing of various technologies that of course we use but we don't usually think about how they work. With the continuation of our ongoing series 'tech basics,' this article will clear your doubts regarding a very basic technology that we may be using from over a century. This article covers the information about the working, history, development for various kinds of audio technology. We have been using microphones, speakers, and other audio gears from almost two centuries. But it sounds crazy to think about the working of all these items, as it seems easy but they are very much sophisticated. And that's the reason why they so much well performed in delivering such quality of sounds to our ears. In this decade we use microphones and speakers like technology almost everywhere taking from computers, mobiles and music players where the role of speakers are supreme. Now let's get into the topic and know about the working of audio gears.

Working of Speakers

Speakers are the lifeline of today's sound system. A good quality sound depends on the quality of the speaker, encoding, and recording. The main function of speakers is to convert the electronic signals stored inside CDs, DVDs, hard drives of computers etc to actual sounds that we can hear. To learn the working of speakers we need to understand how sound works. Inside our ears, there is a small membrane known as the eardrum. When the eardrum vibrates, our brain measures that vibration and interprets it as sound as we know. The vibration in eardrums can be created by changing sudden air pressure.

The cause of sound can be defined as a vibrating object causes the air particles around it to move and in turn, those air particles also cause the particles around them to move. The rapid movement of these air particles causes disturbances in the atmosphere. When our eardrums come in contact with those atmospheres, they vibrate and we call it as sound. The vibrating atmosphere sends a wave in the air which is caught by our eardrums to produce actual sound. These waves are known as sound waves. As these waves are carried out by particles in the air, sound waves never travel in vacuum.

The intensity of sound can be explained as:

•  Frequency of sound wave: Frequency can be defined as the number of vibration in one second. The intensity of sound can be increased by increasing the frequency that means the air fluctuates faster as a result we hear high volume sounds.

• Air pressure: The intensity of sound depends upon the air pressure level. This is called the wave's amplitude simply means a sound wave of higher amplitude reaches our ears faster and it sounds like higher volume.

The sound waves that travel in the air are captured through microphones(covered later in this article) and encoded electrically and stored in the memory. A speaker does the reverse of this, it decodes the stored data to produce sound waves that we hear.

Speakers use drivers to produce vibrations. Vibrations are produced by drivers which produce sound waves by rapidly vibrating some structure called cone or diaphragm. The diaphragm made up of plastic, paper or metal attached to a wide end. The surround is a rim of flexible material which allows the diaphragm to move freely. The ending of the diaphragm is attached to a voice coil. The frame of the driver is called a basket. The coil is attached to the basket through a spider, basically a ring of flexible material. The spider holds the diaphragm in position and allows it to move freely.

When the electric current flowing through the voice coil changes, the polarity of the voice coil also changes. The voice coil is an electromagnet. An electromagnet is a piece of a coil wrapped around some kind of magnetic material like iron. Moving electric current produces a magnetic field around the coil magnetizing the metal. Unlike a permanent magnet which have two poles I,e north and south, electromagnet has poles that can be oriented by changing the flow of current. an amplifier that is connected to the speaker constantly changes the flow of current throughout the speaker. As the orientation of the poles changes, this moves the diaphragm and coil back and forth.

The electromagnet is situated in a constant magnetic field created by the permanent magnet. The positive end of the electromagnet is attracted to the negative end of the permanent magnet and the negative end of the electromagnet is repelled by the negative end of the permanent magnet. So when the direction of current changes, it changes the electromagnet's polar orientation changing the direction of attraction and repulsion. This pushes the coil to and fro.

When the coil moves, it pushes and pulls the speaker cone and this vibrates the air in front of the speaker creating sound waves. The electrical signal can also be interpreted as a wave. Frequency and amplitude of this wave decide the rate at which the voice coil moves. Various drivers sizes are available of different types of frequencies and amplitudes.

There are various sizes and types of drives available for different sound qualities some of them are:

• Woofers
• Tweeters
• Midrange

Woofers are the drivers whose frequency is the lowest but they are the largest. Tweeters are the smaller drivers but their frequency is quite high. And midrange drivers produce a variety of frequencies.

To get the best quality sound modern speakers breaks the sound frequency into small quantities that are handled by different drivers. Good quality speakers would have a woofer, a tweeter and even a midrange which handles different frequency at the same time.  

The speakers break the audio signals into a different range of frequencies i.e low, high and midrange to dedicate all the present drivers.

The most famous audio crossover is called passive. In this crossover, the speaker runs on the same audio signal and don't need an external electric source. It contains capacitors and inductors and of course for its functioning it requires a frequency of particular range as the crossover will only conduct the current when the sound is of the minimum range of frequency.

There is also an active crossover which picks up the frequency of different ranges through the audio signal before it goes to the amplifier. They have various advantages over their passive counterparts, the first one being frequency can be adjusted in the active crossover, while in passive crossovers frequency is constant. But active crossover is no so widely popular as a passive crossover because they are way more expensive as they need multiple amplifiers output for speakers. 

In all sound systems, all the drivers and crossovers are kept in enclosures. Enclosures deals with several functions. In an enclosure system, it's easy to set up all the components in the right position in one unit to produce the best quality sound. Most of the enclosures are made with wood or some kind of metal which can easily absorb the driver's vibrations. The most common type of enclosure is sealed enclosure or acoustic suspension enclosure. As it is sealed, no air can escape through it. As no air can escape, the air pressure inside is constantly changing. The forward waves travel outwards and the backward waves travel inside the box.

Other types of enclosures redirect the inward pressure outward resulting in the sound wave to move forward. This can be done by building a port in the speaker body. The backward direction of the diaphragm pushes the sound wave out of the port and boosts the overall sound level. These type of speakers are called bass reflex speakers.

There is one more type of enclosure known as the passive radiator enclosure. In this system, the backward waves instead of moving outward move an additional passive driver. The passive drivers are moved by the waves coming from the active drivers. These works more efficiently then sealed and bass reflex driver models.

How microphones works?

Well now as we know about the working of speakers, it's important to know about the working of microphones. Microphones are devices that trap or records the sound waves and convert them to electrical signals to store them into a storage area like CDs, DVDs and hard drives. Until the late 19th century there was no good way to send sounds to long distances. As we have discussed the functioning of speakers, now its easier to know the working of microphones because what speakers do, microphones do the same task in a reverse manner. As we know, in speakers there is a coil wrapped around a permanent magnet. The changing pattern of electricity around the coil creates a magnetic field that pushes the field created by the permanent magnet and that moves the coil moves. The movement of the coil moves the diaphragm and that pushes the airflow back and forth creating sound waves. In microphones also all the parts are almost the same by they all works the reverse way.

When we speak, sound waves(that carries energy from the vibrations in air) hits the microphone. By this, the diaphragm moves back and forth, the coil attached to the diaphragm moves as well. The coil moves in the region of the magnetic field created by the permanent magnet. This creates an electric current that flows through the coil. This electric current flows through the circuit and goes to the amplifier that records this data into some sort of storage area. Further, this current can also be fed into speakers resulting in loud sounds.

Like speakers, most of the microphones work in the same way, but there are some types of microphones whose working process is slightly different. The most common type of microphone is a dynamic microphone that uses diaphragm, magnets and coil. This works exactly the opposite way a speaker works. Condenser microphones are designed with a different approach. They use a diaphragm to move the plates of a capacitor.

Most of the microphones that we see are Omni-directional that means they are designed to pick up sound from all directions. This is pretty useful but in some cases, the situation is like that we need to record the sound of a particular direction like wildlife photography, news-making etc. In this type of cases, unidirectional microphones are used which records the sound of a particular direction. There are also some microphones called cardioid and hypercardioid that are specifically designed to record the sound of only a particular direction.

The most popular microphone these days are wireless microphones that uses radio waves to transmit and receive data from the amplifier and other audio devices.

Intercom

Intercom is a small stand-alone voice communication device that works separately from the normal telephone network. Usually, they are used in buildings and offices where people can contact each other without any interference for long-range. They are attached with a long copper wire connected across the length of the device and at each end, there is a receiver, microphone and speakers. Usually, the speakers in the intercom system work for sound delivering as well as sound recording depending upon who is speaking and who is listening. In early days most of the intercom systems used to be wired but now wireless intercom is in use. Basically, intercoms are the application of microphones, they work the same way as microphones and speakers do. Wireless intercoms use radio signals to transmit data. They have several advantages over the wired once. First, they are very much portable and easy to install as they are small and no wiring is required. Second, the data is encrypted so no loss or leak of data. Third, they are easy to exchange and setup.

Telephones

Well till now we were busy in speakers and microphones but now its time to know and understand some of their great applications. Telephones are such a technological approach that changed the world. Today when we can't even imagine a day without having a call with family and friends, we should thank that technology what brought us this telephone what connects us to our beloved once. But its working is quite familiar to us as we already know the working of speakers and microphones. A telephone is not just a simple box, it's a complete machine. So many essential parts like handsets, connection apparatus, switching apparatus need to work in a proper way then only a telephone can work. As we know the working of microphone and speaker, a telephone uses microphones and speakers to record the voice at one end and transmit it to another end where it sounds out of the speaker. As we know that microphones convert the energy from sound waves to electrical energy and speakers do the opposite of it, the process of conversion of energy from one form to another is called transducing.

Parts of an old telephone:

• Dial mechanism

In old-style telephones, there were dials. When we rotate it, it creates some sort of interruptions in the circuit between the telephone and it also creates dialling pulses. If 4 is pressed then it will create four pulses.

• Bells

Old telephones had shiny metal bells on it which rung when the telephone receive an incoming call.

• Circuit board

All the wiring and controls meet at one area known as a circuit board in telephones. The circuit board is responsible to dial and receive outgoing and incoming calls respectively.

• Electromagnet

When the telephone receives an incoming call the electromagnet in it switches on and off rapidly which moves the clapper in between the bells which makes the bell ring.

• Tilting switch mechanism

When the handset is lifted or put back, this mechanism detects it. When the handset is put back, this mechanism cuts the connection from the local exchange. It makes the circuit with the local exchange complete when the handset is lifted.

Now summing up all the above parts to function together makes the telephone works. In short, the sound energy from the voice makes the air vibrates. The sound waves carry the energy into the phone. The energy is converted into electrical energy by the diaphragm in the mouthpiece microphone. The voice is then transmitted to the other phone that is being called via the telephone exchange. When the voice finally reaches the other phone, the diaphragm present in the speaker of the handset finally converts the electrical energy to sound waves that can be heard.

History of speakers

Well, the speakers that we use today are not a new technology, they are almost one and a half-century old. From the last century, we have been using these speakers for every type of job, whether it is a football game, making a phone call, delivering speeches and everywhere we use speakers. In 1861, Johann Phillip Reis installed an electric speaker on his telephone which was able to produce clear tones. In 1876, Alexander Graham Bell patented his first electric loudspeaker which was a part of his telephone research. In 1898, compressed air was used to drive a loudspeaker, this patent was developed by Horace Short. This design was not so popular as the sound quality was not so good.

The era of the dynamic speaker came in the 20th century. Peter L. Jensen and Edwin Pridham in 1915 made the first dynamic loudspeaker that became popular over the years. These speakers were designed to produce sound by horns that could amplify it. In 1924, Chester W. Rice and Edward W. Kellogg patented the moving coil technology that is used in speakers. In 1937, the first speaker design that could be used in film industries was introduced.

 In 1943, Altec Lansing introduced his 604 loudspeaker that was very much popular in film industries as it was able to offer better clarity sound and loudness. In 1954, Edgar Villchur developed the acoustic suspension system of a loudspeaker in Cambridge, Massachusetts. This design was capable of producing better bass and fantastic quality audio. 

History of microphones

Speakers and microphones both brought down a revolutionary change in the technical aspects. Both are now such a prominent part of the technology that we use today. Microphones are such technology that made it possible to record our voices. Its first invention began in 1861 when Johann Philipp Reis successfully designed a device capable of converting sound to the electrical signal. It has a transducer which converts sound energy to electrical energy. This was the first design of the microphone. Later in 1876, water microphone was invented which was a part of Alexander Graham Bell's telephone project. The carbon microphone was also invented in 1876 that was a true design of the microphone. It has a variable resistance that converts audio signals to electrical signals. In 1877, the famous moving coil microphone was invented by Ernst Werner Von Siemens. This microphone was designed to use magnet and diaphragm. In 1916, a condenser microphone was introduced by Edward Christopher Wente which contained a capacitor that would act as a diaphragm. In 1931, the moving coil dynamic microphone that we use today was invented. This microphone was able to capture noise-free quality sound. In 1941, the shotgun microphone was invented by Harry F. Olsen which had a tube that was used to capture sound. The generation of wireless microphones started in the 1950s. In 1957, the world's first wireless microphone was developed by Raymond A. Litke.

 After this many companies manufactured various wireless microphones like Shure introduced it's Vegabond 88 and Sennheiser introduced its Telefunken in 1958. In the 21st century, the trend of digital microphones stared. The first-ever digital microphone was Solution D, D-01 in 2003.

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