There is a new ringtone that can’t be heard by most people over the age of twenty. The tone is used for the noble purpose of driving hooligans away from places where grownups are attempting to ply an honest trade. The tone emits a 17 kilohertz buzz, a pitch that is too high for older ears to register but is “ear-splitting” for younger people. A copy of the mosquito buzz has been produced for use as a cellphone ring tone, evidently with the idea that it will enable students to receive notification of new text messages while sitting in class, without the knowledge of the teacher.
The audible reach of sound for human beings extends from about 20 Hz to 20000 Hz. Children below the age of five and some animals, such as dogs,cats can hearup to 25 kHz (1 kHz = 1000 Hz). As people grow older,their ears become less sensitive to higher frequency sounds. Sounds of frequencies below 20 Hz are called infrasonic sound or infrasound. If we could hear infrasound,we would hear the vibrations of a pendulum just as we hear the vibrations of the wings of a bee. Rhinoceroses communicate using infrasound of frequency as low as 5 Hz. Whales and elephants produce sound in the infrasound range.
It is generally observed that some animals get disturbed well before earthquakes. Earthquakes produce low-frequency infrasound before the main shock waves commence which possibly alert the animals. Sounds operating with frequencies from 20 kHz upto several gigahertz are ultrasonic or ultrasounds. Ultrasound is produced by animals such as dolphins, bats and porpoises. Moths of certain types 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 hence able to escape. Rats also play games by producing ultrasounds.
Ultrasounds are high frequency waves. They are able to travel along well defined paths even in the presence of obstacles. Ultrasounds are used extensively in industries and for medical purposes.
Here are a few sounds of varying frequencies. Go ahead and check your hearing ability. [The high-frequency tones (or mosquito ringtones) are those above 17 kHz. Most people over the age of 30 will not be able to hear them]
8 kHz Frequency sound (Audible to everyone)
10 kHz Frequency sound (60 year old & younger can hear)
12 kHz Frequency sound (50 year old & younger can hear)
14 kHz Frequency sound (45 year old & younger can hear)
15 kHz Frequency sound (40 year old & younger can hear)
16 kHz Frequency sound (30 year old & younger can hear)
17 kHz Frequency sound (24 year old & younger can hear)
18 kHz Frequency sound (24 year old & younger can hear)
19 kHz Frequency sound (24 year old & younger can hear)
20 kHz Frequency sound (24 year old & younger can hear)
21 kHz Frequency sound (20 year old & younger can hear)
22 kHz Frequency sound (18 year old & younger can hear)
23 kHz Frequency sound (cannot be heard)
High frequency tones (or mosquito ringtones) emit high-frequency tones that are not audible to adults but can be heard by teenagers. It is very normal for people to lose their hearing as they age. The loss of hearing is gradual in most people, while others may experience more severe hearing loss.