声学基础课件许肖梅fundamentalsofacoustics07-1.ppt

Basic Knowledge
In following pages, we will learn:
Introductions of this course.
What is sound.
What sound is caused by.
What a sound wave is.
What a cycle is.
Prerequisites:
An understanding of basic mathematics.
The fundamental principles of mechanics.
Electricity and access to a scientific calculator.
Objective:
Throughout the course, emphasis is placed on the fundamental of acoustics, with discussions and problems extending into some phases and applications of acoustics
The Generation, Transmission and Reception of Acoustic Waves
pletion of this course, students will be able to understand:
the terms used to describe sound waves, the generation, transmission, and reception of acoustic waves and their application to numerous fields.
the relationship between sound pressure, sound intensity and sound power.
the terms used to describe sound fields.
What is sound?
Sound is mechanical wave of energy that changes the pressure of its medium (air or water) as it moves. These changes of pressure are detected by our sense of hearing and transmitted to our brains for interpretation. Sound waves are described by their wavelength, amplitude and frequency and intensity (in decibels).
Any sound, whatever it might be, is caused by something vibrating. Without vibration there can be no sound. The vibrating body causes the air particles next to it to vibrate.
Those air particles, in turn, cause the particles next to them to vibrate. In this way a disturbance of the air moves out from the source of the sound and may eventually reach the ears of a listener.
The Transmitting Medium
When we hear a sound, air vibrates against our eardrums causing them to vibrate also.
These vibrations are detected and analyzed by our brains. Although it is usually the air that acts as the transmitting medium, sound can be transmitted by other media, . water, building structures, etc.
Sound Wave
Sound does not consist of air moving towards us in bulk. It travels through the