Earphone

     A headphone consists of two receiver units joined together with an iron strip in such a way that the strip rests on the head and both the receiver units  rest  close to the  ears of the listener. An earphone consists if a single receiver unit. Some earphones are made so small in size that they can be easily fitted inside the external cavity of the ear.

    An earphone is the miniature form of a loudspeaker. It is used with transistorized receivers and hearings aids.

Loudspeaker

The instrument which converts electrical a.f. waves into sound waves is called a loudspeaker. there are mainly following two types of loudspeakers:

1     Magnetic loudspeaker 

2    Dynamic loudspeaker

1.       Magnetic loudspeaker: It consists of a permanent magnet and a voice coil wound on it. A diaphragm made of fine iron sheet and a paper cone is mounted in front of the magnet. Its working is identical to that of headphone. It is also known as cone type loudspeaker.

Sometimes, a horn is also attached to the loudspeaker for increasing the loudness of the sound. Such loudspeaker is called horn type loudspeakers.

Both the above explained loudspeakers are outdated since the performance of dynamic loudspeaker is more satisfactory than magnetic loudspeakers.

2.       Dynamic loudspeaker: This type of loudspeaker consists of moving or dynamic loudspeakers. There are following two types of loudspeakers :

1.      Permanent magnet dynamic loudspeakers :

2.       Electro magnet dynamic loudspeakers :

Permanent Magnet Dynamic Loudspeaker   

1.       Principle. If two magnetic fields are acting at one place than a magnet or magnetic field producing coil can be moved of vibrated due to attraction or repulsion between the two fields.

2.       Construction: Its construction is similar to that of a dynamic microphone. The only difference is this that the size of loudspeaker is much bigger than that of a microphone. The diameter of the cone of a microphone is usually 2-3 cm while that of a loudspeaker is usually 3 to 30 cm. it employs an ALNICO magnet. 

3.       Working: the voice coil established an alternating magnetic field on applying a.f. voltage to it. The coils magnetic field will start to be added to or subtracted from the magnetic field of the permanent magnet consequently, the voice coil will start to vibrate to and fro. The cone sound waves. The frequency and amplitude of cones vibration and the corresponding sound waves are exact replica of a.f. waves applied.

4.       Users: Loudspeaker are used for listening a broadcast program from a receiver or for listening a public address through an a.f. amplifier by more than one person at a time.

Electro Magnet Dynamic Loudspeaker  

   In this of loudspeaker an electromagnet is used in place of the loudspeaker construction is the is same as of a p. m. dynamic loudspeaker.

       The coil used in electromagnetic is called humbeking coil of field coil. It is excited with a D.C. source. This type of loudspeaker were used in early type of receiver since the technique of making small sized powerful permanent magnets was not developed till then. Now, those loudspeakers are obsolete.