MadSci Network: Anatomy
Query:

Re: Can human beings MAKE sounds that are infrasonic or ultrasonic?

Date: Tue Mar 24 16:48:26 1998
Posted By: Andrea Zardetto-Smith, Asst Prof -faculty, Physical and Occupational Therapy and Biomedical Sciences, Creighton University
Area of science: Anatomy
ID: 889639817.An
Message:

Ultrasound is above the 20 kHz limit of our hearing, so normally, humans do 
not hear them, but some animals (like dogs) can hear these high 
frequencies.  For instance, dog whistles work because dogs can hear up to 
about 40 kHz.  Less well known is infrasound, or sound at low frequencies, 
below about 20 Hz.  Some animals hear these frequencies; one is the 
elephant, which can detect 15 Hz tones at sound levels inaudible to humans. 
 Whales produce low-frequency sounds, which are thought to be a means of 
communication over distances of kiolometers.  Low-frequency vibrations are 
also produced by the earth, and it is thought that some animals may sense 
an impending earthquake by hearing such a sound.  Even though we usually 
cannot hear very low frequencies with our ears, they are present in our 
environment and can have unpleasant subconscious effects.  Infrasound is 
produced by such devices as air conditioners, boilers, aircraft, and 
automobiles.  Though intense infrasound from these machines does not cause 
hearing loss, it can produce dizziness, nausea, and headache.  Many cars 
produce low-frequency sound when they're moving at highway speeds, making 
sensitive people carsick.  At very high levels, low-frequency sound may 
also produce resonances in body cavities such as the chest and stomach, 
which can damage internal organs.  You might want to think twice before 
standing in front of a large speaker at a concert!

By the way, in case you are not familar with the term "hertz": sound 
produces variations in air pressure that are periodic. The frequency of the 
sound is the number of compressed patches of molecules that pass by our 
ears each second. One cycle of sound is the distance between successive 
compressed patches; the sound frequency, expressed in units called hertz 
(Hz), is the number of cycles per second. Our auditory system can respond 
to pressure waves over the remarkable range of 20 Hz -20,000 Hz (this can 
also be expressed as 20 kilohertz, abbreviated kHz). Thus, ultrasound is 
above 20kHz (20,000 Hz); infrasound, under 20 Hz.

This information was taken from Neuroscience: Exploring the Brain, by Mark 
Bear, Barry Connors, and Michael Paradiso; William and Wilkins, Baltimore, 
MD; 1996.


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