AUDIO DEVICES AND APPLICATIONS Prepared by:DURGESH CHANDANMAL BANDHARA Enrollment no

. The Microphone is a transducer which can converts sound pressure variations into electrical signals of the same frequency, phase and of amplitudes in the same proportion as in pressure variations.

CHARACTERISTICS OF MICROPHONES Sensitivity : output in mV for the sound pressure of 0.1 Pa at 1000Hz frequency. Signal to Noise ratio: some noise generated inside the microphone due to resistance of ckt.,Transformer etc. S/N = 20 log ( o/p in pressure of sound / o/p in absence of sound) Frequency response :the BW of audio frequencies in the o/p of microphone within + 1 dB at 1000Hz frequency. 40 to Hz is considered good fore Hi-Fi Audio Systems. Distortion : un even frequency response. Two types 1. Non linear 2. phase

Non linear distortion: It distorts the amplitude of audio signal,which result in production of such harmonics which are not present at the input. For better quality it should be less than 5% Phase distortion : input and o/p not in same phase is called phase distortion. Output impedance: it has o/p imp. So that type of transformer needed to transfer power efficiently.

Directivity (d) : it define with polar diagram. The angle for half power point in polar diagram is called as directivity. D=e/e 0 e = direction for max.o/p e 0= o/p in omni direction

Requisites of good microphones High sensitivity High s/n ratio Flat freq. response Very low impedance Very low distortion Directivity suite the the requirement

From the point of view impedance,the microphones are divided into 3 categories Very low Impedance (fraction of Ω to 50 Ω ) Ribbon, Moving coil ---they need step-up Tx. medium Impedance (100 Ω to 600 Ω ) Carbon microphone High Impedance ( 750 Ω to higher ) Crystal, capacitor---they need emitter follower amp. For matching.

Types of Microphones There are three main types of microphones: 1) Dynamic/Moving Coil 2) Ribbon 3) Condenser/Capacitor

Dynamic/Moving Coil microphone

Electrical Equivalent circuit

Basic Principle Electromagnetic Induction When sound pressure variation move a coil placed in a magnetic field, there is a change of magnetic flux passing through the coil, an E.M.F. is induced in coil and this E.M.F forms output of microphone

The main component of these type microphone are magnet,diaphragm and coil. POT type permanent magnet with center pole piece (south pole)and the peripheral pole piece (north pole) this type of magnet gives uniform magnetic field in the gap between the pole pieces. Diaphragm is thin circular sheet of non magnetic material and is of light weight. it is fixed to the body of the magnet with the help of spring. the spring provides compliance(equivalent to electrical capacitance) to the motion of diaphragm. mass of diaphragm and coil assembly provides inductive effects. a protective cover is used to save diaphragm and coil assembly. A silk cloth partition is used to separate upper chamber from the lower chamber.

WORKING When sound waves strike the diaphragm,it moves and hence, coil moves in and out magnetic field. This motion change the flux through the coil which results in EMF is Induced. The value EMF depends on rate of change of flux and hence on motion of coil. the displacement of coil depends on pressure of sound waves on diaphragm So induced voltage across coil in microphone is given by e =B*change of area /sec = B* length of conductor *distance move/sec =B*l*v

Characteristic Sensitivity : 30 micro volt for 0.1 Pa sound level s/n ratio : 30 dB freq. response: 60 Hz to 8000 Hz for +1dB. output impedance: about 25 ohm distortion: <5% Directivity : omni directional

Application It is suitable for use in PA system and broadcast studio  In moving coil microphone,high freq. response is poor because of mass of diaphragm and coil assembly. Mechanical mass is equivalent to electrical inductance,and these response to high freq.  A very light Aluminum ribbon is use in place of diaphragm and coil assembly.the ribbon act as conductor as well as diaphragm. such microphone is called “Ribbon microphone”

Ribbon microphone

Construction Main parts are 1. permanent magnet 2. ribbon conductor…. Magnet is specially designed horse-shoe magnet.it provide strong magnetic field. The ribbon is light (0.2 mg and 3 mm wide)aluminum foil.which is vertically placed. It suspended in magnetic field of permanent magnet and this suspension is very small. The whole unit is enclosed in circular or rectangular baffle. the shape is not purely circular or rectangular but it depends on structure of magnet.

Working When ribbon placed in magnetic field is made to move at right angle to magnetic field by force of sound pressure,there is a change of magnetic flux through ribbon conductor. Due to this EMF is induced across ribbon. This EMF is proportional to rate of change of mag. Flux which is proportional to the force of sound wave sticking the ribbon. In ribbon microphone,the driving mechanical force is proportional to difference of pressure acting of the sides of ribbon, or velocity of sound waves. hence it called as “pressure gradient ” or “velocity ” microphone.

Characteristic Sensitivity : 3 µv volt for 0.1 Pa sound level s/n ratio : 50 dB freq. response: 20 Hz to Hz for +1dB. output impedance: about 0.25 ohm distortion: < 1 % Directivity : Bidirectional

Application It is suitable for dramas. Orchestras These are due to weightless ribbon…

Capacitor microphone

principle When capacitance of capacitor change,the change on the capacitance tends to remain the same, and hence voltage change in accordance with …. V= Q/C (1) V = VOLTAGE ACROSS THE CAPACITOR Q = CHARGE IN COULOUMBS C = CAPACITANCE IN FARADE (1) Shows when C is increase V will be decrease and vicaversa…. Diaphragm of the microphone act as one plate of capacitor. The other plate,called back plate,is fixed. When sound pressure moves the diaphragm in, the capacitance is increase,and when it moves out,the capacitance will decrease. The change in capacitance result in change in voltage.the capacitor microphone is pressure microphone

Construction It consist light weight metal diaphragm (Al) which suspended above a fixed metal back plate. The plates are near each other and form a capacitance of few pF V is applied back plate and the movable plate. these plates are insulated each other. The diaphragm is attached by the supporting spring. The capacitance of these microphone is about 30 pF.

Working When sound wave strikes the diaphragm,it moves,the compression increase the capacitance.and rarefaction decrease it. The change in capacitance result in change in voltage across the capacitor. C = kA/d and V=Q/C So, V = Q/(kA/d) V = Qd/kA A= area k =dielectric constant d=distance between two plates Q= charge in coloumbs.

Q/kA = constant So, V ∞ d The variation in output voltage depends on change in distance between the plates. which in turns depends on the pressure variation due to sound waves.

Characteristic Sensitivity : 3 mv volt for 0.1 Pa sound level s/n ratio : 40 dB freq. response: 40 Hz to Hz for +1dB. output impedance: high, 100 Mega-Ohm distortion: about 1 % Directivity : Omni directional

Application As standard microphone for calibrating other microphone. As sound level meter. As high fidelity recording

ELECTRET MICROPHONE

ELECTRET MICROPHONE(contd…) External DC suppply is not required. Back plate  Tefflon  holds negative charge  capacitive effects.

CRYSTAL MICROPHONE

Special microphones Lavalier microphone : it suspended on the chest by mean chord around the neck. it is small moving coil microphone. It is applicable where mobility is necessary, example-Lecturer Tie-clip microphone: it is electret type tiny microphone which can be clipped on the tie. Radio microphone : Noise cancelling microphone :

LOUDSPEAKERS

Loudspeaker is transducer which converts electrical signal of audio freq. into sound wave of same freq.

Characteristics Efficiency : ratio of output sound to input audio signal. Its value depends on proper matching of mechanical impedance with acoustical imp. Noise : the unwanted sound, not contained at input side but present at the output of the loudspeaker Frequency response : it indicate the loudspeaker’s response for the audible freq. range of sound. Distortion : any change in frequency (phase or freq.) of the output sound as compare to the input audio signal is called “Distortion”

Directivity : it is the ratio of actual sound intensity at a point in the direction of max. intensity to the sound intensity that would be have available there, had been omni directional. Impedance : the input impedance is the important parameter as its matching with the impedance of source amplifier.

Some types of loudspeaker Moving coil cone type Electrodynamics Horn type

Moving coil cone type

Equivalent circuits

Principle Interaction between magnetic field and current in the same way as an ac motor works. A coil, called voice coil,is placed in uniform magnetic field When current pass through the coil. There is Interaction between magnetic field and current, resulting in a force working on the movable coil. This force is proportional to the audio current and hence cause vibratory motion in the coil. which makes the conical paper diaphragm to vibrate and produce pressure vibration in air, resulting in sound waves. F=b*l*I sin α; α =angle between coil and the field α =nearly 90

Construction It consist voice coil which placed in a magnetic field. POT type magnet which has center pole is south pole and north pole is as peripheral poles. which has a good uniform magnetic field. It is also called as “Permanent magnet type speaker” The coil is attached to conical diaphragm,made of paper. it is called paper cone. A flexible strip of rubber round its periphery used to support it. A spider springs are used to support the diaphragm. The whole paper in cone type loudspeaker act as diaphragm and causes pressure variation direct in the listeners area hence it called Direct radiating type loud speaker.

working When audio current flow through the voice coil placed in magnetic field, then the force F=Bli, act on the coil and moves it Back and fro. The paper cone attached to the coil also moves and cause compression and rarefaction cycle in the air. thus sound wave produces. thus finally audio current converted into the sound waves. Two transformation 1. electro- mechanical 2. mechano- acoustical

CHARACTERISTICS Efficiency: low, about 5% S/N ratio : 30 db Frequency response : 60 Hz-2000Hz Distortion : 10%(non linear output) Directivity : basically, Omni-directional Impedance: 2-32 ohm Power handling capacity: low

ELECTRODYNAMIC LOUDSPEAKER

HORN TYPE LOUD SPEAKER

High frequency HORN TYPE

LOW freq. horn type

BAFFLES

Sound Mixers: Overview Sound mixer is a device which takes two or more audio signals, mixes them together and provides one or more output signals. The diagram on the right shows a simple mixer with six inputs and two outputs.

Input channels 12-channel 12 input channels. 16x2 16 input channels, 2 output channels. 24x4x2 24 input channels, 4 subgroup channels and two output channels.

It is used to combining signals, mixers allow you to adjust levels, enhance sound with equalization and effects, create monitor feeds, record various mixes, etc. Mixers come in a wide variety of sizes and designs, from small portable units to massive studio consoles. The term mixer can refer to any type of sound mixer; the terms sound desk and sound console refer to mixers which sit on a desk surface as in a studio setting. Sound mixers can look very intimidating because they have so many buttons and other controls. However, once you understand how they work you realize that many of these controls are duplicated and it's not as difficult as it first seems.

Advanced Mixing

Principle of magnetic recording

for more on magnetic tape recoarding, Refer book: Audio Video Systems by R.G. Gupta. Also in the Techmex book it is available.

(Public Address system) PA SYSTEM

PA(Public Address system)

Precautions for Public Address system or Requirements of Public Address system Acoustic feedback: Distribution of sound intensity: Reverberation : due to over lapping of sound. It solve by using small power L.S. Orientation of Loudspeaker : direct to audience Selection of microphone: directive microphones(Cardioid type) Phase delay(>45 ms) (>16 meter) Matching: Grounding of cable:

PA Installation for public meeting

PA Installation for Debating Hall

PA Installation for Football Stadium

PA Installation for college Sports

Digital Consoles 1. Digital Manipulation k1&k2 are multiple coefficient

Digital Manipulation The simplest form of digital audio mixer is illustrated in Figure. In this case, two digital audio signals are each multiplied by coefficients (k1 and k2) the two functions of addition and multiplication, plus the ability to delay signals easily within digital systems, allow us to perform all the functions required within a digital sound mixer, even the equalization functions. That’s because equalization is a form of signal filtering on successive audio samples, which is simply another form of mathematical manipulation

2. Digital Filtering

Digital Filtering the basis behind all digital filtering and may be extended to include several stages of delay and By using a combination of adder and variable multiplication factors. it is possible to achieve a very flexible method of signal filtering in which the shape of the filter curve may be varied over a very wide range of shapes and characteristics. Here in lies the greatest benefit of digital signal processing—that by simply reprogramming the coefficients in the multiplier stages, a completely different filter may be obtained. Not only that, but if this is done in real time too, the filter can be made adaptive, adjusting to demands of the particular moment in a manner that might be useful for signal compression or noise reduction.