A sound wave traveling in one mediummay be partly reflected, refracted or absorbwhen it strikes another medium. Sound alsoexhibits the properties ofdiffraction, interference and the Dopplereffect.
The waves bounce back when a train ofwaves encounters a barrier. They are said tobe reflected. Sound waves may be reflected fromwalls, mountains, the ground and otherobjects. The direction of reflected soundsmay be accurately predicted using the basiclaw of reflection. The angle of incidence =the angle of reflection
Angle of Incidence – angle between the incident wave and the normal to the reflecting surface. Angle of Reflection – angle between the reflected waves and the normal. We call the reflection of sound “echo”. › Echo is the sound used by SONAR or Sound Navigation Ranging in detecting and locating object. SONAR devices emits sound and measure the time required for the echo to return. SONAR is used to determine the depth of water.
Refraction occurs whenever soundpasses from one medium intoanother, where it changes its velocity. During daytime when the air need theground is warmer than the air above, soundis refracted from the ground, while atnight, the reverse happens. That is why wehear better at night than during the day.
The ability of waves to travel around thecorners or obstacles in their path is what wecalled as diffraction. It can be easilyobserved because the wave width of theopening, or size of the obstacle, is nearly thesame order as the wavelength of sound.
Constructive interference – two pulses moving in opposite direction along a stretched string are unaffected by their crossing. Destructive interference – complete cancellation occurs when identical pulses with opposite displacement by the edges of the barrier.
The Doppler effect is the apparent changein the frequency of sound due to the motionof source of sound and/or the observer.
Sound may be described by four perceptual characteristics: Pitch – refers to the highness or lowness of a sound. It depends upon the frequency of the sounding object. Higher frequency sounds produce high pitch while lower frequency sounds produce low pitch. Loudness – is a physiological sensation that varies from one person to another. It depends on the sense of hearing, the distance from the source and the material through which the sound travels.
Intensity – depends on the amplitude of pressure variations within the sound waves. The unit for this is decibel(dB), named after Alexander Graham Bell. Quality – property of a tone that distinguishes it from another tone of the same pitch and intensity produced by a different instrument. It enables you to identify the source of sound because tones differ from one another.
The ear is our organ of hearing. It is dividedinto three parts: outer, middle and inner.
The outer ear is shaped like a funnel and is called the pinna or auricle. It is that part of our ear that we have at the side of our head. The middle ear is an air-filled space containing the eardrum or tympanic membrane, the Eustachian tube and the bridge of auricles. The eardrum separates the outer ear from the middle ear. The inner ear contains a coiled fluid-filled tube called the cochlea.
The pinna collects the sound waves andtransmits them to the auditory canal. The auditorycanal acts like a closed-tube amplifier producing aresonant frequency with a wave length equal to fourtimes its length. The sound waves push on theeardrum. The pressure variation resulting from thecompression and rare fractions in sound wavescauses the eardrum to vibrate. These vibrations aretransmitted to the liquid in the inner ear. Thesevibrations are then received by the nerves andconverted to electrical nerve impulses, the onessent to the brain. In the brain, these nerve impulsesare analyzed and interpreted .