![Acoustics
It is known as the science of sound including three
process:
(I) Generation (Production).
(II) Transmission
(III) Reception.
Acoustics is related to different branches as follows:
[1] Engineering: (i) Mechanical Engineering (vibration – noise).
(ii) Electrical Engineering: Electro-acoustics.
(iii) Material Engineering.
[2] Arts: (i) Architecture, such as theater.
(ii) Music Instruments.
[3] Life Science: (i) Medicine (i.e. UI=Ultrasonic Imaging).
Note: In biology, this science is called
Bioacoustics.](https://image.slidesharecdn.com/ec522lectureone-230103201249-e4964ba9/85/EC522-Lecture-One-ppt-2-320.jpg)
![(ii) Psychology: Leading to reduction of concentration
and an aggressive behavior.
(iii) Physiology: Affecting upon some of human's body
systems (i.e. Cardiac system and hearing system).
[4] Earth Science: (i) Underwater acoustics.
(ii) Forecasting (acoustic antenna).
(iii) Seismic acoustics.
Acoustics (Cont.)](https://image.slidesharecdn.com/ec522lectureone-230103201249-e4964ba9/85/EC522-Lecture-One-ppt-3-320.jpg)
EC522 Lecture One.ppt
- 2. Acoustics It is known as the science of sound including three process: (I) Generation (Production). (II) Transmission (III) Reception. Acoustics is related to different branches as follows: [1] Engineering: (i) Mechanical Engineering (vibration – noise). (ii) Electrical Engineering: Electro-acoustics. (iii) Material Engineering. [2] Arts: (i) Architecture, such as theater. (ii) Music Instruments. [3] Life Science: (i) Medicine (i.e. UI=Ultrasonic Imaging). Note: In biology, this science is called Bioacoustics.
- 3. (ii) Psychology: Leading to reduction of concentration and an aggressive behavior. (iii) Physiology: Affecting upon some of human's body systems (i.e. Cardiac system and hearing system). [4] Earth Science: (i) Underwater acoustics. (ii) Forecasting (acoustic antenna). (iii) Seismic acoustics. Acoustics (Cont.)
- 4. Course Contents Introduction of acoustics, acoustic wave equation and its solution. Chapter One Sound intensity, power, energy, density level and loudness. Chapter Two Environmental acoustics. Chapter Three Electro-acoustics Chapter Four Underwater acoustics Chapter Five
- 5. What is the definition of sound? Sound is generated by the mechanical disturbance of the medium’s particles. It is found that the particles near the source of sound vibrate back and forth and due to the elastic collision between particles, the sound propagates. Factors affecting speed of sound Temperature: Sound moves through hot air faster than cold air due to the increased speed of the particles. Type of medium or medium characteristic: Sound moves well through dense material and material that returns quickly to its original position. Thus, sound moves fastest in a solid and slowest in a gas. Chapter One
- 6. Reason Sound travels more quickly through solids and liquids because the individual molecules are closer together than the molecules in gas. Sound waves CANNOT move through a vacuum – they need a medium! Notes: 1. Sound wave is independent on the motion of sound source (such as car siren) but depends on the propagation of waves. 2. For the waves propagating through a rope, its velocity depends on the rope characteristics (tension and rope elasticity). 3. Sound waves travel as compression waves.
- 7. What are the types of waves? - When the wave particles vibrate back and forth along the path that the wave travels. It is known as longitudinal waves. -When the wave particles vibrate in an up-and-down motion. It is called transverse waves.
- 8. Decibels The decibel (dB) is the unit utilized to measure sound intensity or loudness. Loudness corresponds to the amplitude of a wave and can be measured by instruments such as an oscilloscope. Sounds greater than 120 dB can cause pain in human ears. Sounds with an amplitude between 0 and 120 dB are called audible. While, anything below 0 dB is considered sub-audible. Humans can hear frequencies in range between 20 Hz and 20 kHz. It is known that frequencies above 20 kHz are called ultrasonic. While, frequencies below 20 Hz are called infrasonic
- 9. Decibels (Cont.) Source of Sound Level (dB) Normal Breathing 10 Close Whisper 20 Library 40 Normal Speech 60 Busy Street Traffic 70 Subway Train 100 Loud Rock Music 115 Threshold of Pain 120 Jet Engine 140
- 10. It occurred when, more than one wave can exist in the same place at the same time and it is found that resulting wave may be increased, decreased, or cancelled. Types of interference 1. Constructive Interference: Crest of one wave overlaps the crest of another results in increased amplitude as shown in the figure. Interference
- 11. 2. Destructive Interference: Crest of one wave overlaps the trough of another results in cancellation of amplitude as shown in the figure. Interference (Cont.)
- 12. - A receiver may hear two sound waves at the same time: In phase: Compressions and rarefactions overlap each other Out of phase: Compressions and rarefactions of each wave are offset. If the crest of one wave overlaps the trough of another, they will cancel. Interference (Cont.)
- 14. Standing Waves Created when a wave reflects on itself. Nodes: Parts of a standing wave which remain stationary. Antinodes: Positions on a standing wave with the largest amplitudes. Node Antinodes
- 15. Standing Waves (Cont.) Harmonics To determine the harmonic of a standing wave, count the antinodes.
- 16. Is the apparent change in the frequency of a sound caused by the motion of either the listener or the source of the sound. If the source is moving as fast or faster than the speed of sound, the sound waves pile up into a shock wave called a sonic boom. A sonic boom sounds very much like the pressure wave from an explosion. Doppler Effect
- 17. {To Be Continued} Good Luck