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Sound waves and Characteristics

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Lady Bustamante

on 20 May 2014

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Transcript of Sound waves and Characteristics

Lady Bustamante
The Basics
In order for us to hear the radio:
The radio encodes information on a radio wave, Known as modulation.
Then they broadcast the radio waves with the encoded information onto a certain frequency.
The radio antenna then picks up the broadcast based on the frequency which your radio dial is tuned.
The radio decodes the information from the wave and plays it trough the speakers.
Their are two basic parts.
The Concept of Modulation
Modulation is the basis for AM and FM radio signals.
AM - Amplitude modulation
FM- Frequency modulation

Modulation-the act or process of superimposing the amplitude, frequency, phase, etc, of a wave or signal onto another wave (the carrier wave) or signal

What is a Radio Wave ?
A radio wave is an electromagnetic wave broadcast by an antenna. Radio waves have different frequencies, and by tuning a radio receiver to a specific frequency you can pick up a specific signal.
Radio Waves are used to transmit music, conversations, pictures, and data invisible trough air.
Size of Radio Waves
Sound waves and Characteristics
Oscillator: Generate sine waves which are also known as carrier waves.
Modulator: adds information to the carriers wave . The information is added to AM and FM waves.
Amplifier: Increases the power of the modulated carrier wave. The more powerful the amplifier the more power the broadcast.
Antenna: converts the amplified signal to radio waves.

Antenna: Captures the radio waves. When the wire in the antenna is exposed to the radio waves the waves make a small alternating current in the antenna.

RF amplifier: An amplifier that amplifies weak radio frequency signals from the antenna so the signal can be prepared by the tuner.

Tuner: A circuit that can extract signals of a particular frequency from a mix of different frequencies.

Detector: Responsible for separating the audio information from the carrier wave.

Audio amplifier: Amplifies the weak signal that comes from the detector so that it can be heard.
What does WZMX Hot 93.7 mean?
In the United States, the FCC (Federal Communications Commission) decides who is able to use which frequencies for which purposes, and it issues licenses to stations for specific frequencies.
When we listen to a radio station and they say, "You are listening to WZMX Hot 93.7!," that means you are listening to a radio station broadcasting an FM radio signal at a frequency of 93.7 megahertz, with FCC-assigned call letters of WZMX.
Megahertz means millions of cycles per second, so 93.7 megahertz means that the transmitter at the radio station is oscillating at a frequency of 93,700,000 cycles per second.
FM radio stations transmit in a band of frequencies between 88 megahertz and 108 megahertz.
AM radio has a band from 535 kilohertz to 1,700 kilohertz.
AM radio station that says, "This is AM 680 WPTF" means that the radio station is broadcasting an AM radio signal at 680 kilohertz and its FCC-assigned call letters are WPTF.
How do we hear the sound waves?
Amplitude Modulation, AM -transmitting radio signals by varying the size (amplitude) of the radio wave while the speed (frequency) of the radio wave remains constant
* Signal transmitted trough AM can carry great distances, but are exposed to interference.
Frequency Modulation, FM - a method of transmitting radio signals by varying the frequency (speed) of the radio wave while the height (amplitude) of the wave remains constant.
* An FM wave is approximately 20 times wider than a AM wave . Therefore, FM system has a finer tonal quality. However, FM signals do not carry for long distances.
How do the antennas work ?
The transmitter moves the electrons in the antenna four ring times during one cycle of the sine wave.

If the transmitter is running on 680,0000 hertz, every cylce is being completed in 1/680,000 or .00000147 seconds.
At the speed of light, electrons can travel 0.0684 miles (0.11 km) in 0.0000003675 seconds.
The size of the antenna capable of transmitting 680,000 Hertz is about 361 feet .
This is why antennas are larger at the stations then on our cars.

Heterodyne Principle
Heterodyning is a method for transferring a broadcast signal from its carrier to a fixed local intermediate frequency(IF) in the receiver so that one radio receiver can be tuned to any of the locally broadcast radio stations, if it wasn't for heterodyning, we would have to have one receiver for each station.
a beat (or heterodyne) frequency combines the high-frequency current produced by the incoming wave with a low-frequency current produced in the receiver.
The different frequency, is called intermediate frequency (IF), In the process of projecting the sound out, the signals go trough the IF amplifier and filter where the signals on one frequency is separated from those on the next.
Beat Frequency
Outer Ear
Channels sound waves that reach the ear trough the ear canal and to the eardrum.
Because of the ear canals length it is possible to amplify sounds with frequencies of 3000 Hz.
The sound traveling trough the outer ear stays in the form of a pressure wave.
When the sound hits the eardrum its not until then that it turns into a mechanical wave.
Middle Ear
Consist of an eardrum and the hammer,anvil, and stirrup.
As the pressure wave comes toward the eardrum it vibrates at the same frequency of the sound wave.
SInce the eardrum is connected to the hammer, anvil and stirrup they also start to move at the same frequency of the sound wave.
The vibrations of the stirrup are transmitted to the fluid of the inner ear which creates a compression wave within the fluid.
The three tiny bones of the middle ear act as levers to amplify the vibrations of the sound wave.

The Inner Ear
The inner ear consists of a cochlea, the semicircular canals, and the auditory nerve.
The cochlea and the semicircular canals are filled with a water-like fluid.
The fluid and nerve cells of the semicircular canals provide no role in the task of hearing, they help detect movements and to maintain balance.
The cochlea is lined with over 20 000 hair-like nerve cells.
As a compressional wave moves from the interface between the hammer of the middle ear and the oval window of the inner ear through the cochlea, the small hair-like nerve cells start to move.
Each hair cell has a natural sensitivity to certain frequency of vibration.
When the frequency of the compressional wave matches the natural frequency of the nerve cell, that nerve cell will resonate with a larger amplitude of vibration.
The increased vibrational amplitude makes the cell release electrical impulses tha pass trough the auditory nerve towards the brain.
The brain interprets the sound.
Hearing Loss

Hearing loss usually happens to be conductive, sensorineural, or mixed.
Conductive Hearing Loss- not being able to conduct airborne sound trough the middle ear to the inner ear
sensorineural hearing loss-the impermanent of the sensory unit consisting of the auditory nerve and the hair cells that excite it .

Causes of Hearing loss
Genetic causes: Hereditary loss occurs in approximately one in 2,000 children. Most hereditary hearing loss is a result of an inherited autosomal recessive gene (80 percent) and is not associated with any type of syndrome.

Prenatal causes: Exposure to viruses, bacteria, and other toxins before or after birth can result in hearing loss. During delivery or in the newborn period, a number of complications, such as lack of oxygen, can damage the hearing mechanism, particularly the cochlea.

Postnatal causes: Infections in infancy and childhood also can lead to a sensorineural hearing loss. The most common cause of hearing loss in children is middle ear disease.

Post lingual causes: A blow to the skull can cause trauma to the cochlea and may lead to a sensorineural hearing loss. It can also damage the middle ear bones, resulting in a conductive loss. Excessive noise can also result in damage.
The frequency of sound
If a note from a pure tone is decreasing in amplitude, it will be percieved as a higher pitch than another than an identical pulse that has a steady amplitude.
Characteristics of Sound waves
Doppler effect
when the pitch of a sirennm etc.suddenly passes you and pitch drops.
Interference of sound
Two wave exist in the same medium will interfere with one another.
Constructive interference- The amplitude adds
Destructive interferance= The amplituded doesn't add up
Natural frequency of vibration determined by the physical surroundings of the vibrating object .
Each natural frequency of the object is associated with one of the many standing wave- a vibrational pattern created within a medium when the vibrational frequency of the source causes reflected waves from one end of the medium to interfere with incident waves from the source.
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