 Ilya Arjanjani, Assistant Professor from the Department of Electronics, Valchan Institute of Technology, Solapur. Today we are going to see the topic sound waves from audio video systems. So what are the learning outcomes from this topic? At the end of this topic, student is able to select and convert sound systems as per application, analyze the characteristics of sound. The student can compare between loudness and intensity of the sound. So first we are going to see what exactly is meant by sound. So sound is nothing but sound is produced by a vibrating source around which the carrying media example that is air is caused to move. That means here the channel through which the sound propagates is nothing but the air. From the vibrating source a sound wave radiates in omnidirectional way which is away from the sound source. The sound energy is then transferred to the carrying media through the compressions and rare fractions. These are similar to the waves moving on the surface of the sea. So for this as we can take an example when we throw a stone on the surface of the sea then there are waves which are propagating on the surface of the sea. So these are these waves are nothing but the compressions and rare fractions. So here this diagram will give you a clear cut idea about compressions and rare fractions. So here the high pressure of air is nothing but crest on sinusoidal wave and the waveform. That means for the upper crest the compression is maximum and when you look at the low crest the compression is minimum. Hence the upper crest is called as compression and the lower crest basically denotes the rare fractions. So the main difference between these two compressions and rare fractions is that the compressions are having high sound pressure of the sound and rare fractions are having low pressure sounds. So this is the diagram for compressions and rare fractions. So how does the sound propagate? So here as you can see there is an example. So here if the phone is ringing so this phone is when this particular phone is ringing. So the person which is nearer to the phone he can hear the sound in a large amount of quantity whereas the sound then propagates through the different molecules of the air. So A, B, C these are the points which basically denote the position of the person. When the person is standing nearer to the phone he can hear the sound very much clearly. When the person goes to the point B then the sound gets decreased and so on. So what we can conclude from this? We can conclude that as we move away from the source the sound gets decreased. Hence the propagation of sound through air sound from the source reaches surrounding particle A of the air medium then at A what exactly happens particle A then pushes against particle B and comes back to its original position. So as a result of this particle B what it will do? It will push the particle C again and it will come back to its original position. This is how the vibrations are transferred from the source towards the destination or towards the human ear. For this we can take an example of a tuning fork. So when we bang a tuning fork on a wooden plank then the prong of the tuning fork moves right and comes back. So as you can see here the tuning fork is vibrating and the vibrations are denoted by the colors which are contrast which are shown in contrast and the dark color basically denotes the exact position of the tuning fork tongs. So it compresses the air particles around it and hence resulting in the form resulting in the formation of compressions. When prong moves left and when it comes back the air particles are separated again forming the rare factions. So this is the most basic example of how sound propagates. So in the similar way here you can see there is a drum when the drum is banged then the air compressions are formed and the variations in air pressures are shown at this particular point and the rare fractions which are nothing but these are the waves which are between the two air compressions. So where is the exact position of the rare fraction? It is between the two compressions. So the next point is loudness of sound. So whenever we consider sound then we have to consider this basic parameter which is called as loudness. So loudness of sound increases with the amplitude of the sound. So as you can see here there are two sound waves which are shown. One is having the less amplitude whereas the other another is having the maximum amplitude. So the sound wave with less amplitude basically denotes the quiet sound and the sound wave which is represented with maximum or high amplitude basically denotes the loud sound. So here we can say that the loudness of the sound is directly proportional to the amplitude of the sound. So loudness of sound. So what exactly is loudness? So loudness is the characteristic of sound by which loud and faint sounds can be distinguished. Loud and faint sounds is nothing but loud and quiet sounds can be distinguished. So for this if we can take an example of two communication between two friends. When two friends are having a talk then at that particular point their voice is low but when these two persons or two friends are speaking want to communicate in a public meeting then what exactly is happening their voice their loudness of the voice gets increased. Loudness of sound basically depends on two major factors. First is amplitude of the vibrating body. The loudness of the sound varies directly with the amplitude of the varying body. For this we can take an example as the sound produced by sitar which is nothing but a musical instrument will be loud if we pluck its wire more violently. That means if we pluck or if we move the strings of this sitar in a random manner or in a very high frequency at high frequency then it will create a sound which is more loud and it is more violent. The second factor on which loudness of sound depends is area of vibrating mode. The loudness of the sound depends upon the area of the vibrating body. So here if we can consider that if there is a device example the sound which is produced by large drum is louder than that of the small one. So the area whenever we are considering the area here we are considering the drum which is having large circumference area and the another drum which is having small circumference area then the large drum will produce the sound which is very much loud and the small drum which is having less circumference of area will produce the small sound. And the third important factor is distance from the vibrating body. So loudness of sound also depends upon the distance of the vibrating body from the listener. That means loudness basically depends upon the distance between the device or the sound source and the person itself. So it what basically does it is caused by the decrease in amplitude due to the increase in distance. So whenever the distance goes on increasing there is the decrease in amplitude of the sound. The next point is loudness also depends upon the physical conditions of the ears of the listener. That means if a person is having certain physical problem regarding his ears then loudness also depends upon the physical condition of the ears. If the person is partially deaf he can hear around about 50% of the sound. If the person is completely deaf he will not hear any sound so for that he will require a device by which he can listen the sounds. So these are the three major factors on which loudness of the sound depends. So what are sound waves and what are the characteristics of this? So the characteristics of this of the sound waves are as you can see here first is amplitude, phase and wavelength. We have seen amplitude of the sound goes on decreasing as the distance increases. Similarly the phase of the sound also plays an important role whenever the sound wave is considered. Also the wavelength the distance between the upper crest and the lower crest basically it is denoted as the wavelength of the sound. So amplitude height or loudness of the wave it denotes height and loudness of the wave. The amplitude of the sound which is basically measured in decibels. The second characteristics is frequency. Number of waves that passes in one second is called as frequency. Also it is measured in Hertz wavelength. The length of the wave from crest to crest is basically called as the wavelength or the frequency. Phase basically it refers to the point at which the wave cycle begins and it is measured in terms of degrees. Here for example we are seeing changing a wave cycle from crest to trough corresponds to 180 degrees phase shift. So these are the characteristics of sound. Similarly the amplitude frequency time period phase wavelength velocity these can be correlated by using a relation which is called as relationship between velocity and temperature which is given by v2 is equal to v1. Route of t2 by t1 where v1 and v2 are the two different velocities for the two different temperatures t1 and t2. So here there is a change in medium hence the velocities and the velocities and the temperatures differ. So intensity of the sound this is also one of the characteristics of the sound. So intensity of the sound can be defined as average rate of flow of sound energy through the cross sectional area. It is also calculated in terms of decibels. In terms of power it is calculated as p1 and p2 is equal to log of p1 by p2 where p1 and p2 are initial and final power. In terms of amplitude also the intensity of the sound can be calculated as 20 log a1 upon a2. So this diagram will give you a brief or a good explanation that this is the sound source and from this sound source the sound is radiating basically the green basically the red arrows what they denote they denote the sound which is having the higher intensity and the green arrows basically these denote the dark green arrows basically they denote the smallest intensity of the sound. So these are the references for you people for the further study. Thank you for watching.