Transcript microphone
Shri Navsari Paschim Vibhag Koli Samal Kalyankari Trust Sanchalit MAHATMA GANDHI INSTITUTE OF TECHNICAL EDUCATION & RESEARCH CENTER NAVSARI NPE Campus , Bhanunagar , Eru-Aat Road , Po.Bhutsad , Tal.Jalalpore, Dist. Navsari- 396450 1 Group no: 15 AUDIO VIDEO SYSTEM TOPIC:MICROPHONE PREPARED BY: Name: Enrl no. 1. Miss. Gite Jagruti N. 140333111005 2. Miss. Patel Shreyanshi N. 140333111014 3. Miss. Patel Urvashi A. 140333111015 GUIDED BY: Mr. Kaushik Patel 1 CONTENT 1) 2) 3) 4) 5) Introduction Requirements of Good Microphone Characteristics of A Microphone Types of Microphones Comparison of Microphones 1 2 1.INTRODUCTION • A Microphone is a transducer that converts acoustic energy to electrical energy. • When choosing the optimum microphone, the parameters to look at include the type of response field, dynamic response, frequency response, polarization type, sensitivity required, & temperature range. 1 4 2.Requirements of A Good Microphone 1) 2) 3) 4) 5) 6) 7) The Frequency response should be as flat as possible over the frequency range. The electrical output should be as high as possible. The self generated electrical noise is called the equivalent acoustic noise. The directivity pattern should not vary with freq. A Microphone should be mechanically robust. A Microphone must not be too expensive. The Electrical output should be high as possible so that audio signal produced by the microphone is high. 1 3.Characteristics of A Microphone 1) 2) 3) 4) 5) 6) Sensitivity Frequency response Directivity or directional patterns Impedance Signal to noise ratio Distortion and temperature range 1 4.Types of Microphones Dynamic (moving coil)Microphone 2) Ribbon (velocity)Microphone 3) Carbon Microphone 4) Condenser(capacitor) Microphone 1) 1 (1)Dynamic (moving coil) Microphone The Principle of Operation: The Moving Coil microphone uses the principle of electromagnetic induction. When a coil placed in the magnetic field is moved with sound pressure variations, there is a change of magnetic flux through the coil. This change is magnetic flux induces an emf. e=dflux/dt=B*change of area per second = B*length of conductor*distance Thus ,the copper wire coil moves in the magnetic field a voltage as given by, V=B/v 1 The microphone consist of a permanent magnet, a diaphragm and a coil. Construction: As shown in figure, the magnet is a permanent magnet with a central pole piece[B] & the peripheral north piece[A].The gap between the pole piece gives a uniform magnetic field. The coil is a thin fine aluminum wire with 10 to 20 turns. 1 Advantages: These are inexpensive and resistant to moisture. • This coupled with their high gain. • They are suited for the close making of Bass & Guitar speaker & Drum kits. • Disadvantages: • • A single dynamic does not respond to all audio frequencies. Combining the multiple signals correctly is difficult & designs that do this are rare & tend to be expensive. 1 (2) Ribbon (velocity)Microphone Principle of Working: The Ribbon Microphone is called as the pressure gradient microphone because driving mechanical force is proportional to the difference of the pressure acting on two sides of the conductor. It can also be said as Velocity Microphone. Construction: Ribbon microphone use a thin, metal ribbon which is mounted between the poles of a permanent magnet. Ribbon or corrugated aluminum, typically 2.5 cm long, 0.6cm wide and 0.00006cm thick. 1 Advantages: • • • Good response Does not need external bias Figure of 8 response is ideal for stereo recording Disadvantages: • • This conductor is very delicate, so it damaged easily. This microphone is delicate so cannot be blown into for checking. 1 (3) Carbon Microphone Principle of Working: The resistance of the carbon granules changes when they are subjected to the pressure variations. A double button carbon microphone has a push pull action that cancel second harmonics. Construction: This type of microphone was used in telephones. A single button carbon microphone as a telephone transmitter as shown figure. in 1 Advantages: It is cheap. It gives high output. For many years this microphone was used in telephones. Disadvantages: There is a considerable background noise called “carbon hiss” that cannot be eliminated. The carbon granules can get damaged & even fused together. Frequency response is not good. 1 (4) Condenser(Capacitor) Microphone Principle of Working: A Condenser Microphone operates on a capacitive design. The cartridge from the condenser microphone utilizes basic transduction principles and will transform the sound pressure to capacitance variations, which are then converted to an electrical voltage. The voltage between the capacitor plates is V=Q/C V=Q/EA/d =QD/EA since Q, A & E are constant We get,V=Kd where K=constant 1 Construction: It consist of a stretched aluminum diaphragm suspended above a fixed metal back plate as shown in figure. By taking a small thin diaphragm & stretching it a small distance away from a stationary metal plate called a “back plate” 1 Advantages: • • The absence of a high bias voltage permits the use of a diaphragm with looser tension. lower electrical impedance . Disadvantages: DC biased microphones cannot be used in damp conditions as it can contaminate insulating surfaces. 1 5.Comparison of Microphones PARAMETERS CARBON MOVING COIL CAPACITOR RIBBON Directivity Omni directional Omni directional Omni directional Figure of 8 Distance of speaker close 25-30cm close 50cm size small large large Fairly large cost cheapest Not very high high high Frequency response 200-5000 Hz 6 -8000 Hz 40-15000 Hz 20 to 12000 Hz Distortion Highest 10% 5% 1% Very less 1% Bias Voltage Required Not required Required Not required Noise Highest Lower than carbon Lowest Lower Application Cheap radio sets, telephones P A system orchestra Professional recording In conference halls 1 1