In this note, we are going to discuss about Moving Coil Loudspeaker or Cone Type Loudspeaker and Its Construction, Working Principle, Characteristics, Advantages, Disadvantages, and Applications. Welcome to Poly Notes Hub, a one stop solution for Diploma Engineering Notes for Polytechnic Students.
Author Name: Arun Paul.
What is Moving Coil Loudspeaker or Cone Type Loudspeaker?
One kind of audio transducer that is frequently used to transform electrical data into sound waves is a moving coil loudspeaker. A permanent magnet, a voice coil (a coil of wire), a diaphragm (usually made of paper, plastic, or metal), and a suspension system are its main parts.
The voice coil creates a magnetic field that interacts with the permanent magnet when an electrical audio signal is applied to it. The voice coil and diaphragm move back and forth as a result of this interaction, producing sound waves that match the electrical signal. The suspension mechanism aids in diaphragm movement control, guaranteeing precise audio signal reproduction.
Construction
Below we describe the Construction of Moving Coil Loudspeaker of Cone Type Loudspeaker –
- Frame: The entire speaker assembly is structurally supported by the frame, sometimes referred to as the basket. It holds the other components and is often constructed of plastic or metal.
- Permanent Magnet: Within the frame is a fixed permanent magnet. It supplies the steady magnetic field required for the speaker to function.
- Voice Coil: A wire coil fastened to a paper or plastic former, which is cylindrical in shape, is the voice coil. The permanent magnet’s magnetic field has this coil suspended within it.
- Diaphragm: Paper, plastic, or metal are common lightweight, rigid materials for the diaphragm, also known as the cone. It is attached to the voice coil and oscillates in reaction to the electrical signal’s fluctuating magnetic field.
- Suspension System (Spider and Surround): The suspension system consists of the spider and surround. The spider is a flexible, corrugated structure that supports the voice coil and allows it to move linearly within the magnetic field. The surround is a flexible ring that connects the diaphragm to the frame, providing additional support and allowing the diaphragm to move freely.
- Dust Cap: To keep polluted air out of the voice coil and other internal components, a dust cover is typically positioned in the middle of the diaphragm.
Working Principle
Similar to how a motor functions, the moving coil loudspeaker operates on the interaction of a magnetic field and electricity. A voice coil is a coil that is submerged in a steady magnetic field. A force acts on the movable coil as a result of an interaction between the magnetic field and the current as the audio current flows through the voice coil. Due to the force’s proportionality to the audio current, the coil experiences vibratory motion, which in turn causes a conical paper diaphragm to vibrate and alter air pressure, producing sound waves.
Given the current flowing through the coil and the magnetic field, the force acting on it is as follows:
F = B.i.l.sinα
Where,
- F = force in Newton,
- B = Flux density in Tesla,
- i = Flowing current in Amperes,
- l = Length of the coil in meter,
- α = angle between the coil and the field
Normally, α = 90°, and hence
F = B.i.l (as sin90 = 1)
The coil will stay inside the uniform flux density area when its velocity is minimal. Thus, the output is linear for modest coil motion. Electromagnetic induction causes a reverse EMF when the coil travels in a magnetic field. The coil’s motion becomes stable as a result.
Characteristics
Here are some important characteristics of Moving Coil Loudspeaker –
- Efficiency: The efficiency of a cone speaker is quite low, about 5% only.
- Signal to Noise Ratio: 30 dB or Better.
- Frequency Response: From 60Hz to 2000 Hz.
- Distortion: Up to about 10%.
- Directivity: It is omni-directional.
- Impedance: Varies from 2 ohm to 32 ohm.
- Power Handling Capacity: From a few milliwatts to about 25 watts.
Advantages
- It has wide frequency response.
- High efficiency.
- Compact in size.
- Higher durability.
- It has excellent transient response.
Disadvantages
- Heavier in weight.
- Costlier.
- Power supply needed for field coil.
Applications
- Used in home audio system.
- Used in Telecommunication system.
- Used in Public Address System.
- Used in Automotive systems.
- And Many More.
