Working of Speakers

We have always shown keen interest in buying the best electronic stuffs like CD’s, tapes and also computers. No one has bothered much to know about the quality of the speakers that bring the ultimate output. Even if any high end amplifier and other devices are used, it will all become a waste if the proper loud speaker is not used to present the output. The speaker is mainly responsible for changing the electronic signals that are produced by the CD’s and other devices into audible sound.

Sound

To know more about the speaker, it is important that you know the basics of sound. We have to know how a sound produced is intercepted by the human ear.

Objects can produce sound in all mediums like solids, liquids and gases. As the best practical way of transmission is through air, this method has been used for the design of speakers.

An object produces a sound only by vibrating in the air. This vibration cases a disturbance in the air particles surrounding it. This disturbance is further passed on to the next set of air particles. This cycle continues depending on the strength of the sound made.

Suppose a telephone is ringing. We can hear the ringing even if we are standing a few meters away from the telephone. As soon as the telephone is rung, it causes a disturbance in the air. This disturbance is sent to the nearby particles and travels further. By moving further, there occurs a pressure drop in the air which pulls in particles that are even farther out and so on. This decrease of pressure is known as rarefraction.

When these air particles reaches our ears it strikes a very thin layer of skin known as the ear drum. When the air particles strike them, it vibrates causing those particular signals to reach the brain. These signals are interpreted as pure sound by the brain, which helps us to hear. The difference in each sound is produced due to the difference in the air pressure that strikes your eardrum.

When the brain intercepts these sounds there are two parameters that should be checked. They are

• The speed in which we hear the sound.
• The loudness of the sound.

The speed can be intercepted with the help of the sound wave frequency. If the sound wave frequency is low, it means there are fewer fluctuations in a period of time, which in turn causes the pitch to be lower. The opposite of this occurs if the sound wave frequency is high.

The loudness of the sound can be determined by the amplitude of the wave (air-pressure level). If the amplitude is greater, it strikes more into our eardrums, causing a louder sound. Opposite happens if amplitude is lesser.

Parts of a Sound System

A sound system mainly consists of three parts. They are

Microphone – A microphone is used to make the original sound that is later heard through the speakers. Its working is similar to our ears. A sound made is changed into vibrations that is converted into electrical signals and sent to the next stage.

Tape/CD/DVD – This device collects the sound from the microphone and amplifies it and sends it to the speaker.

Speaker – The speaker receives the electrical signals from the Tape/CD/DVD and converts them into physical vibrations. A good speaker provides the exact sound that was produced in the microphone. An amplifier will also be used to amplify the sound to a higher level.

Speaker Drivers

A speaker driver mainly consists of a speaker and driver. It is generally called as a speaker, as this is the part that produces sound. The driver is actually a transducer that uses an electronically induced reciprocating motion to make pressure waves, which are used to create the original sound. The motion is created with the help of a diaphragm. The diaphragm is a flexible cone or also a dome which is usually made of paper or plastic. It also has two magnets out of which one is mounted to the diaphragm and is made up of tightly wound electrical wire. It is used to receive the electrical signals from the amplifier so as to move the voice coil. The voice coil then interacts with the second magnet which is a permanent magnet. The permanent magnet is usually larger than the moving magnet. The drivers produce lower frequencies when they are larger in size.

Take a look at the cross-sectional view of a speaker driver. From the figure we can see that the cone is attached to the wide end of the suspension. The suspension is designed in such a manner that it is attached to the driver’s metal frame called the basket. The suspension also helps in moving the cone, whose narrow end is connected to the voice coil. The connection between the basket and coil is made with the help of a ring of flexible material called spider. The spider helps the coil to move back and forth.

There are many types of speaker drivers which are classified according to their accuracy in different frequency ranges. They include woofers, subwoofers, mid-range speaker drivers and also tweeters.

Both the diaphragm and the voice coil work on the principle of an electromagnet. That is, a magnetic field is produced when an electric current s passed through the wire. The voice coil works as an electromagnet and thus produces a magnetic field with a polar orientation. The current flow has to be reversed so as to switch the north and south ends of the magnet. Thus two output wires are needed for a speaker.

A speaker may have more than one driver units. As air is produced when the cone moves, a rear vent is made in some speakers for the air to move out. A dust cap is also made in the cone so as to prevent air from getting in through the front. The dust cap can also be kept as the vent. A rubber, foam, or sometimes cloth surround at the outer edge of the cone allows for flexible movement.

Depending on the movement of current through the voice coil, the north and south pole of the magnetic field will be at one end of the voice coil or the other. Since the permanent magnet also has magnetic poles, its magnetic fields will push the coil outwards if all the magnetic fields are lined up together. If the magnetic fields are lined oppositely, the coil will be pushed outwards.   Thus the voice coil will be pushed outwards and inwards according to the music. This push-pull of cone will increase-decrease ait pressure in eardrum creating music.

There are speakers with one-way drivers and two-way drivers. Speakers like tweeters need two-way drivers as they handle high frequencies. One way drivers are usually found in pocket radios. There are also three way speakers which have a combination of one way and two way drivers. This combination is usually found in home theatres.

Making of a Speaker – Video

Speaker Sound Coloration

There are a lot of speakers available which has prices varying from a hundred dollars to thousands of dollars. Many may think what makes the speakers so expensive. Well, the only answer is accuracy and simplicity. The most expensive speakers will be having custom made speaker drivers and also small amount of electrical quantities. The accuracy refers to the tonal characteristics which will be different for different speakers.  There is no speaker that can reproduce the same sound as the audio spectrum.  These differences will be according to the designer’s choice and also the price. Selecting the right speakers for your ears is a time taking process as the some will have bright sounds, while others with strong mid-range and others with very deep bass.

Speaker Driver Configuration

The speaker drivers are configured in two ways. They are the sealed box design and the bass-reflex design.

Sealed box design is a basic design in which the woofer is simply mounted inside a box with no openings. This is a single resonant system. Through this configuration the output from the back of the driver is kept out of phase from the output in front of the driver. Thus the bass is prevented from cancelling out. The internal air acts like a spring and thus the stiffness for the suspension of the driver is increased.

Bass-reflex design on the other hand is used for hi-fi speakers and home theatres. This is a two-resonant system consisting of the driver and the reflex system. The reflex system works by sucking acoustic output from the rear of the active driver, and then looping that energy back out of the cabinet, either through a tube or a passive radiator. Thus more bass is produced while all other parameters are equal.