Sounds

Definition Sounds

Sound is one of a wave, the longitudinal wave. Longitudinal waves are waves that the direction parallel or coincide with the direction of vibration. Examples of longitudinal waves are waves and slinki waves sound in air.

The sound of the waves has the same properties with the properties of waves, namely:

a. Can be reflected (reflection)

The sound can occur when sound is reflected on the surface of a hard object, such as the surface of the stone wall, cement, steel, glass and zinc.

Example: 

• Our voices are louder in the cave due to the reflection of sound from the walls of the cave. 
• Our voices inside the building or music studio that does not use a silencer.

b. Can be refracted

Reflected is bending toward trajectory wave after passing through the boundary between two different media.

Example: At night the sound of thunder sounded louder than during the day because of the refraction of sound waves.

c. Can be combined (interference)

As well as the interference of light, sound interference also requires two coherent sources of sound.

Example: Two loudspeakers are connected to a signal generator (audio frequency generator tool) can function as two coherent sources of sound.

d. Can be bent (diffracted)

Diffraction is flexing incident sound wave when it passes through a narrow slit.
Example: We can hear the voices of different people and covered all subjects, as the sound passes through narrow slits that are passable sound.

The sound occurs when there are three conditions as follows.

1. The sound source

    Objects that can generate sound called sound source. Examples of sound sources is a variety of musical instruments, such as guitar, violin, piano, drums, trumpet and flute.

2. Substance Intermediaries (Medium)

     Sound waves are longitudinal waves that do not appear. The sound can only propagate through the medium of an intermediary. For example air, water, and wood. Without an intermediary medium sound can’t propagate so it will not be heard. Based on research, a solid sound propagation medium is best compared to liquids and gases. 

3. Listener
The sound can be heard when there are listeners. Human auditory equipped, ie the ear hearing aids.

The vibrations emanating from objects that vibrate, up to our ears in general through the air in the form of waves. Because the waves can be in the air only longitudinal waves, the sound propagates through the air is always in the form of longitudinal waves. We need to remember that it is sealing and longitudinal waves can propagate through extensional three states of matter are: solid state, liquid and gas.

 There are three aspects of sound as follows:

a. The sound produced by a source such as another wave, the sound source is vibrating body.

b. Transferred energy and sound sources in the form of longitudinal waves.

c. The sound is detected (known) or an instrument by ear wave propagation speed of sound in air is affected by the temperature and density of matter trajectory

Based on the frequency, the sound can be classified into three. There are as follows.

1. Infrasound, sound whose frequency is below 20 Hz.

2. Audiosonik, is a sound frequency between 20-20000 Hz.

3. Ultrasonic, is the sound frequency above 20,000 Hz.

The human ear has a hearing limit. Sound that can be heard is the sound man with a frequency of 20 Hz to 20,000 Hz, which is audiosonik. Infrasound and ultrasound can’t be heard by humans. Infrasound can be heard dogs, crickets, geese, and horses. Ultrasound can be heard by bats and dolphins.

Sound Reflection

The sound will be reflected if the surface of a hard object, such as a stone wall or a surface of cement, steel, glass, and zinc. In contrast, most of the sound will be absorbed if the surface is soft objects, such as cloth, rubber, foam, cork, rugs, and wool (silencer objects). If we say a few words then a few syllables or words between the sound comes with reflected sound mutually destructive, so that we only share a single audible to the last syllable of the reflected sound. This event is called reverberation or boom. In a confined space such as a cinema, concert hall music, to reduce echo, wall and ceiling mounted silencer.

Sound Reflection Law

The following two laws of reflection of light are applicable to sound waves as well

1. The incident wave, the normal to the reflecting surface and the reflected wave at the point of incidence lie in the same plane.

2. The angle of incidence ∠i is equal to the angle of reflection ∠r.  

Kinds of Sound Reflection

Reflected sound can be divided into 3 kinds. There are as follows.

1. Strengthen the reflected sound is reflected sound original sound that can amplify the original sound. It usually occurs in circumstances between the sound source and the reflective wall is not so far away (less than 10 meters)

2. The boom is reflected sound that sounded almost simultaneously with the original sound. Usually occurs at a distance of between 10 to 20 meters.

3. The echo is reflected sound is heard after the original sound. Usually occurs at a distance of more than 20 meters.

Application of Sounds Reflection

1. Detecting Defects and Cracks on Metal

    To detect cracks in metal or concrete structures used ultrasonic scanning were used to check for hidden cracks on parts of the aircraft, which later could endanger aircraft flight. In a routine examination, vital parts of the in-plane ultrasonic scanning manner. If there are cracks in the metal, ultrasonic reflections from cracks will be detected. Cracks are then examined and addressed immediately before the aircraft allowed flying.

2. Measure the depth of the sea 

    By using SONAR we can measure the depth of the sea. At the bottom of the vessel wall is installed a vibration source (oscillator). Mounted near the receiver oscillator vibrations (hydrophone). If the transmit pulse takes a long time to get back to the receiver,  in and vice versa. If the time of vibration (sound) propagating (t) for a distance second commute is 2 L meters, the propagation speed can be calculated as follows.

V = 2L / T or 2L = v x t or L = v x t / 2

Where:

v = propagation speed of sound (m / s)

L = inside the sea (m)

t = time (t)

3. Knowing the position of submarines by sending ultrasonic waves from the boat to the underwater hunter.

4. Knowing the position of schools of fish in the sea.

5. Knowing the pockets of petroleum basins by sending sound waves into the    ground.

6. The Use in Medical 

     Examination to see inside the human body using ultrasonic pulses is called ultrasound (ultrasonography).  In the human body, ultrasonic pulses are reflected by the tissues, bones and body fluids with different density. Reflecting ultrasonic pulses emitted Ulsa can produce images of body parts that were found by the ultrasonic pulses on the oscilloscope screen.

Ultrasound is particularly useful in medical diagnosis since some of the following.

• Ultrasonic much safer than X - rays that can damage the cells of the human body due to ionization, it is safer to use ultrasound to view the fetus in the mother's stomach than light - X. 
• Ultrasonic can used continuously transform and see the movement of the fetus or lever one, without injuring or pose a risk to patients. 
• Ultrasound can measure the depth of an object under the skin's surface, while the resulting image rays - X is flat with no clue about the depth. 
• Ultrasound can detect differences in the tissues in the body that can’t be done-ray - X. This ultrasonic sometimes able to find tumors or clots in the human body.

Resonance

In sound applications, a resonant frequency is a natural frequency of vibration determined by the physical parameters of the vibrating object. This same basic idea of physically determined natural frequencies applies throughout physics in mechanics, electricity and magnetism, and even throughout the realm of modern physics. Some of the implications of resonant frequencies are:

1. It is easy to get an object to vibrate at its resonant frequencies, hard to get it to vibrate at other frequencies.

2. A vibrating object will pick out its resonant frequencies from a complex excitation and vibrate at those frequencies, essentially "filtering out" other frequencies present in the excitation.

3. Most vibrating objects have multiple resonant frequencies.

Resonance and Musical Instruments

Musical instruments produce their selected sounds in the same manner. Brass instruments typically consist of a mouthpiece attached to a long tube filled with air. The tube is often curled in order to reduce the size of the instrument. The metal tube merely serves as a container for a column of air. It is the vibrations of this column that produces the sounds that we hear. The length of the vibrating air column inside the tube can be adjusted either by sliding the tube to increase and decrease its length or by opening and closing holes located along the tube in order to control where the air enters and exits the tube. Brass instruments involve the blowing of air into a mouthpiece. The vibrations of the lips against the mouthpiece produce a range of frequencies. One of the frequencies in the range of frequencies matches one of the natural frequencies of the air column inside of the brass instrument. This forces the air inside of the column into resonance vibrations. The result of resonance is always a big vibration - that is, a loud sound.

Woodwind instruments operate in a similar manner. Only, the source of vibrations is not the lips of the musician against a mouthpiece, but rather the vibration of a reed or wooden strip. The operation of a woodwind instrument is often modeled in a Physics class using a plastic straw. The ends of the straw are cut with a scissors, forming a tapered reed. When air is blown through the reed, the reed vibrates producing turbulence with a range of vibrational frequencies. When the frequency of vibration of the reed matches the frequency of vibration of the air column in the straw, resonance occurs. And once more, the result of resonance is a big vibration - the reed and air column sound out together to produce a loud sound. As if this weren't silly enough, the length of the straw is typically shortened by cutting small pieces off its opposite end. As the straw (and the air column that it contained) is shortened, the wavelength decreases and the frequency was increases. Higher and higher pitches are observed as the straw is shortened. Woodwind instruments produce their sounds in a manner similar to the straw demonstration. A vibrating reed forces an air column to vibrate at one of its natural frequencies. Only for wind instruments, the length of the air column is controlled by opening and closing holes within the metal tube (since the tubes are a little difficult to cut and a too expensive to replace every time they are cut).