REVERBERATION :
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 can not be heard by human ears.
It usually takes place in a big hall or auditorium.
Excessively reverberation is highly undesirable due to which the roofs and walls of the auditorium are generally covered with sound-absorbing material like compressed fireboards, rough plaster for draperies.
The material of the seats is also selected on the basis of their sound-absorbing property.
Advantages of Multiple Reflection of Sound :
Horns, megaphones, loudhailers, musical instruments like trumpets, and Shehanais all are designed to send sound in a particular direction without spreading it in all directions.
It helps listeners and audience to listen to the speaker.
This all could become possible just because of Multiple Reflection of Sound.
Medical instrument “stethoscope” which is used for the listening sound produced within the body and specially used for heart and lungs, works on the same phenomenon that is multiple reflections of sound.
The ceiling of conference halls, cinema halls, concert halls are made curved so that sound after reflection can and even curved soundboard may be placed behind the stage so that sound after reflection can reach all corners of the hall and can spread evenly across the width of the hall.
Range of Hearing :
The audible range of sound for human beings is between 20 Hz to 20000 Hz (one Hz = one cycle/s)
The children under the age of five and some animals, such as dogs can hear up to 25 kHz (1 kHz = 1000 Hz)
As people grow older their ears become less sensitive to higher frequencies.
On the basis of the range of frequencies of a sound, it has been categorized as “infrasonic sound” or “infrasound” and “ultrasonic sound” or “ultrasound”.
| infrasound | ultrasound |
|---|---|
| It refers to sound with a frequency below 20 Hz that can't be heard by humans. | It refers to the sound with a frequency higher than the upper limit (20 kHz) which is audible to humans. |
| Rhinoceros whales and elephants can communicate using infrasound range. | Bats, dolphins, porpoises, and moths of certain families can produce this frequency. |
| It is observed that some animals get disturbed before the earthquake as they can hear low-frequency infrasound which possibly alert the animals. | It is observed that certain animals can hear each other using high-frequency ultrasound which helps them to escape & capture. |
| ·It can be used to monitor some natural calamities like earthquakes, volcanic eruptions before it occurs by infrasonic waves. | ·It can be used to detect cracks and flaws in metal blocks and also to clean parts located in hard-to-reach places. |
| It is also used to stabilize myopia is young kids. | It is used to break small stones formed in the kidneys. |
| It is also used in charting rocks and petroleum formation below the earth. | It is also used to get images of the internal organs of the human body. |
| It is also used in ballistocardiography and seismocardiography to study the mechanics of the heart. | It is also used in “ultrasonography” to examine the fetus during pregnancy. |
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