When we hear the same sound again and again in a medium it is called Echo. The sound or echo persists in our brain for 0.1 seconds. This means that the difference between sound and its echo should be at least 0.1 seconds. It is produced as a result of reflection of sound through a medium. If sound reflects more than once we may hear multiple echoes.



It is the persistence of a sound after a sound is produced. A reverberation is created when a sound signal is reflected multiple of times until it reaches a sound wave that cannot be heard by human ears. Auditoriums and big halls often have to deal with reverberation. That is why the roofs are made up of soundproof materials like Flipboard and the chairs in the halls are also made up of fabrics that can absorb sound.



 Advantages of Multiple Reflection of Sound

Horns, trumpets, loudhailers or megaphones are designed in such a way that sound can travel in a particular direction only without spreading out everywhere. This makes it easier for the audience to listen to the speaker. All these instruments work on the phenomena of multiple reflections of sound.



The multiple reflections in a stethoscope tube make it possible for the doctors to listen to a patient’s heartbeat.


Concert halls are generally covered so that sound can reflect through it and reach the wider audience.

The range of sound – on the basis of the range of frequency of a sound, it is categorized into ultrasound and infrasound.

Human auditory range is between 20 Hz and 20000 Hz.


Difference between Ultrasonic and Infrasonic:



Sounds of frequencies below 20 Hz are called infrasonic sound or infrasound.

Frequencies higher than 20 kHz are called ultrasonic sound or ultrasound.

Examples:1.we would hear the vibrations of a pendulum .

2 .we hear the vibrations of the wings of a bee.

3.Rhinoceroses communicate using infrasound of frequency as low as 5 Hz.4.Whales and elephants produce sound in the infrasound range



Examples: 1.Ultrasound is produced by dolphins, bats and porpoises.2.Moths of certain families have very sensitive hearing equipment. These moths can hear the high frequency squeaks of the bat and know when a bat is flying nearby, and are able to escape capture.

3. Rats also play games by producing ultrasound.

Applications of Ultrasonic Waves:

  • Ultrasounds are used extensively in industries and for medical purposes.
  • Ultrasound is generally used to clean parts located in hard-to-reach places,for example, spiral tube, odd shaped parts, electronic components etc.
  • Objects to be cleaned are placed in a cleaning solution and ultrasonic waves are sent into the solution. Due to the high frequency, the particles of dust, grease and dirt get detached and drop out. The objects thus get thoroughly cleaned.
  • Ultrasounds can be used to detect cracks and flaws in metal blocks.Metallic components are generally used in construction of big structures like buildings, bridges, machines and also scientific equipment.
  • Ultrasonic waves are made to reflect from various parts of the heart and form the image of the heart. This technique is called ‘echocardiography’.• Ultrasound scanner is an instrument which uses ultrasonic waves for getting images of internal organs of the human body.
  • Ultrasound may be employed to break small ‘stones’ formed in the kidneys into fine grains. These grains later get flushed out with urine.