Science of Sound and Musical Tone

all sound whatever they are originated vibrations any substance can vibrate if it has elasticity or the tendency to return to its usual shape after being distorted by some outside force sound vibrations are transmitted through various media sound waves reach us through the air through a solid or through a liquid sound waves spread outward like ripples and water in all directions fanning out from their source this is the famous Museum of Science and Industry in Chicago we are here to take a look at one of the new exhibits on the science of sound and musical tone hello you know sound is a fascinating thing there's so much to learn about it and there's no better place to learn than right here at this exhibit of the science of sound and musical tone let's start with sound generation how sounds are created and to illustrate that fundamental principle let's start with our old friend the tuning fork as we know to form any sound something has to move back and forth in quivering movements or vibrate and if these vibrations which form waves of sound and these waves of sound are transmitted through solid liquid or air the only medium sound can't travel through is a vacuum the dial indicates the amount of air in the Bell as the air is pumped out you'll notice that the sound guys let's suppose this panel is magnified air the lights represent the air particles let's suppose to that sound waves created by a giant tuning fork are passing through the air as the blade of the tuning fork vibrates it first pushes the particles of air near it outward these particles collide with neighboring particles which move outward and collide with their neighbors and so on then as the blade returns to complete its vibration the air particles rush back to fill the space left by the blade of the tuning fork in other words it's a bump and a rebound bump and a rebound of air particles vibrations create alternate compressions and partial vacuums of air particles when the vibrations are sound waves stop the air is exactly as it was yet the sound waves have traveled completely through it sound travels approximately 1,100 feet per second through the air of course light travels very much faster that's why the flash of lightning is often seen before you hear the accompanying Thunder sound travels roughly four times faster in water about 4,800 feet per second knowing the speed of sound and water helps the sonar engineer in the submarine to navigate underwater now the sound must be received or heard by the ear we really have six years three on each side the outer ear the middle ear and the inner ear the outer hear catches the sound waves and directs them and along the auditory canal where they bombard the eardrum setting up vibrations that are passed on to three tiny bones in the middle ear the hammer the anvil and the stirrup with increased force the sound waves enter the compressed fluid of the inner ear called a cochlea where sounds are received and transformed into nerve impulses racing to the brain no one knows exactly how this happens but the mechanism that transforms their sound into nerve impulses is called a basilar membrane uncoiled here to study it better this membrane which is actually very tiny supports about 23,000 hair like nerve endings when any part of it vibrates nerve endings are thrust against the overhanging tectorial membrane and we hear of course we can't see sound waves but scientists have developed an instrument which translates sound waves into visual patterns this instrument is called an oscilloscope the lines or pattern you see here is in effect a picture of my voice the movement of these lines indicates among other things the number of vibrations per second that the sound of my voice creates every different sound or tone creates a different number of vibrations per second and it is the number of vibrations per second that determines the pitch of its own here's another pattern created by a pure musical tone it's called a sine wave watch the oscilloscope as this tone creates more vibrations per second or a higher pitch than the one just played watch the oscilloscope again see how this tone creates fewer vibrations or a lower pitch here's another example of pitch or frequency a bicycle wheel and a playing card the card is setting the vibration by the rotating spokes when the rotating wheel is speeded up the card vibrates more rapidly and your ear recognizes a higher pitch than when the wheel rotates more slowly the pitch falls as the speed decreases intensity or loudness can also be seen on the oscilloscope by the height of the sine wave or curve at the opening of the film we heard the bark of a dog the noise of a car the music of a violin now let's discuss these different kinds of sound one is noise like you heard from the dog in the car another is musical tone watch the oscilloscope you can see how noise sends out irregular vibrations now see how musical tones produce a regular looking sound wave the instrument sends out regular vibrations whenever we hear any musical sound were actually hearing a complex combination a fundamental or basic tone and harmonics or overtones these harmonics or overtones are highly important they affect the quality of a tone because it's the difference in the number and intensity of harmonics or overtones that makes a violin sound different from a clarinet a trumpet sound different from an oboe and so forth you this Hammond organ here in the museum is an ideal instrument upon which to demonstrate fundamentals and overtones because use of the drawbars or tone bars permits us to isolate the fundamental tone from harmonics or we can blend the fundamental tone with combinations of harmonics or overtones to obtain thousands of variations of musical homes there's an animated film with in this exhibit which explains is very well let's go take a look at it interested in music kemon gives the organist the whole orchestra to work with in these tone bars every musician in fact just about everybody would like to have his own Orchestra to conduct of course they'd like to play the instruments to the orchestra is yours let's start with our string sections that's a picture of what the strings look like hold on maestro if you were a conductor that is if you were an orchestra you could vary the Harmony change the tone color according to your taste indeed you can like flutes just pucker up your white tone bars and blow like it invite a few more frames call out the whole Orchestra perhaps you prefer the reeds gentleman a little might read work please let's do it in blue a short tour professor say a little percussion allow me how about drums telephones so you're not only all the sections of the orchestra you're the conductor to like I said friend you are the orchestra interesting story now let's see how musical tone is generated by various instruments the percussion instruments such as the drum are probably the oldest instruments of all skin has stretched tightly across either one or both ends of a hollow cylinder when the drum had his rep sharply it vibrates drums may sound lower or higher according to their size and tension of their skin the musical tones of a violin and other bowed string instruments are generated by pulling the bowl back and forth over the strings causing the strings to vibrate at the same time that one hand moves the bowl the fingers of the other hand pressed the strings against the fingerboard to determine the pitch of the tone the brass slide trombone represents a still different method of tone generation the player blows into the mouthpiece and his lips act as the vibrator to generate the trombone tone different pitches are made by altering the position of the slide and changing the lippie the clarinet is a member of the woodwind family it's a reed instrument consisting of a cylindrical tube with a bell-shaped opening at one end and a mouthpiece at the other the mouthpiece has a flat can read attached it vibrates when blown thus generating a tone the tube contains open holes holes covered by T's the fingers open and close the holes and manipulate the keys to change the pitch of the clarinet tone the Greeks had an early form of pipe organ as far back is 500 pc pipe organs as we know them today generate tone much in the same manner as the wind blown instruments the flute for example in the pipe organ wind is driven over pipes of varying lengths the length of the moment determines the pitch the electric organ like this one we've been using here at the Museum of Science and Industry who was invented by Lorentz Hammond in 1935 it introduced a completely new method of electrical tone generation known as the tone wheel generator when I pull out one of these tone bars and press a key a minut electrical current generated in the organ is carried along a wire to the amplification system this amplified current is in turn connected to speakers whose vibrations in the air produce audible musical sounds thus the organs operation is entirely electrical in character until the final speaker is reached now let's look at the tone generator and see how it produces these minut electrical currents this cutaway section of the tone wheel generator shows how this disc or tone wheel is so placed that it rotates or spins right next to a magnet notice that the magnet has a coil of wire wrapped around it also note that the tone wheels are not true circles but have a number of high spots or notches around the edges as the discs rotate they do not touch the magnets but pass very close to them each time a high spot passes the magnet it induces or generates a minut electrical current in the coil one of the wheels rotate so that 440 high spots past the magnet each second generating a varying current which one it activates the speaker causes it to vibrate at 440 vibrations per second which is designated a on the musical scale the generator in this organ has 86 stone wheels all of which are permanently geared together and driven by a constant speed motor because the tone wheels are driven by a constant speed motor the pitch of the tones generated remain constant and no tuning is ever required the high spots on the tone wheels are so shaped that pure tones are generated that means tones that have no harmonic or overtones of their own now this purity is essential in order to attain pleasing tonal mixtures between fundamental tone and harmonics through the use of the drawbar when a key is depressed it closes nine small electrical switch contacts there are nine such contacts under every playing key on the organ now these contacts are connected to appropriate generator magnets as well as to the drawbars the settings of the drawbars determine the intensities of the small electrical currents generated by the tone wheels when a drawbar is pulled out all the way it generates a current of greater intensity thereby making that tone louder then if the drawbar or tone bar were pulled out on a part way very drawbar settings then actually call on up to nine different tones at one time each tones loudness or intensity being determined by how far the drawbars pulled out thus thinking of nine different draw bars each with eight different positions of intensity or loudness it's mathematically possible to create literally thousands of tones or on a more practical basis an individualized variety of organ or orchestral tone effects so we've covered what musical tone is and how it's generated we've covered pitch pitch is determined by the number of vibrations created within a given length of time intensity is the loudness or the softness of the top quality is what distinguishes one tone from another a drum from a violin a noble from a trombone a harp from a tuning fork and that's where we started at this interesting exhibit of Chicago's museum of science and industry but just hearing sound and musical tone is only half the real pleasure and satisfaction of music the other half is in your creating sound pleasant sound musical sound you