The human ear is a miniature receiver, amplifier and signal processor all in one. The ear is split into three main sections the outer ear, middle ear and the inner ear. The ear also plays an important part in how we maintain our balance and how we perceive things like distance, room structures and atmosphere. Hearing is one of the five human sense's and is essential for how we communicate and live our modern lives. The ears pick up sound waves which travel through the air and through different materials and this is how sound is felt rather than seen.
The outer ear acts as a funnel and sound waves are collected and then sent directly down the ear canal to the eardrum. The fact we have two ears means that two signals are sent to the brain a split second apart and at a slightly different pressure, and the brain can then detect these differences and therefore work out the direction the sound comes from. Sound waves entering the ear travel along the ear canal and strike the eardrum, which has a tightly stretched membrane covering causing it to vibrate. These vibrations are then picked up and then transmitted by the three ear ossicles. The three ear ossicle are the three smallest bones in the human body. The oval window of the middle ear is a membrane covered hole and the vibrations from the ossicles amplify the sound as the oval window is much smaller than the eardrum. The middle ear is also connected to the throat via the back of the mouth through the Eustachian tube, which is where the air pressure is equalized. After the vibrations of sound are passed through the oval window of the middle ear they are then transmitted to the cochlea of the inner ear.
The cochlea is a long, spiral shaped, fluid filled tube that is layered with sensory hair cells. The hair cells in the cochlea work differently to each other as they are all sensitive to a different frequency. The different hair cells range from shortest to longest along the length of the cochlea. The very short hair fibers in the first part of the cochlea are sensitive to the high range frequencies we are able to hear and the long hairs at the end of the cochlea are sensitive to the low end frequencies we can hear. The hair cells of the cochlea convert the vibrations into nerve signals that then travel along the auditory nerve to the brain. This information is then recognized by the brain and interoperated accordingly.
The possible amount of vibrations that occur every second are one particular sounds frequency and that rate of different available frequencies are measured in hertz. If one vibration occurred in that given second it would then be measured as 1 Hz and if two occurred in a second it would then be 2 Hz.
The dynamic hearing range of humans is approximately 20 Hz to 20 kHz, so this limits humans to not hearing any frequency lower than 20 Hz. Any frequency lower than 20 Hz will not be heard by humans but will be felt as a rhythm. Also this means any frequency that is higher than the top of the range 20 kHz human limit cannot be heard. As humans grow older the range of frequencies they can then hear will decrease with age and exposure to different levels of noise.
The dynamic hearing range can differ with different animals and this means humans can hear low bass sounds that will be inaudible to a chimpanzee for example as they have a hearing range of 60 Hz to 40 kHz. This means a chimpanzee would be able to hear one octave higher than a human.
Frequencies that are greater than the upper limit of the human hearing range are known as ultrasounds. Ultrasound is used for many different things but the best example is when it is used for generating a picture of inside the womb whilst a woman is pregnant to produce an image of the unborn baby using sonography.
Infrasound however is measured as any frequency that is registered below approximately 16 Hz. As with the ultrasound, the infrasonic sound will not be able to be heard by the human ear. Infrasounds can be dangerous as far as human health goes and there have been a number of scientific tests regarding the damage infrasonics can do.
There have been many tests for infrasonic weapons, which have been performed by the military for different types of sounds that would be able to injure or possibly kill a human being. These tests have been essential in the development of a number of possible means of causing damage to humans using extremely low frequencies.
Reverb is the continuation of sound in any given space after the original sound has ceased. The space that a sound is created in has a direct affect on the amount of reveraration that is heard and the materials that a space is made from affect the amount of reverb by the amount of absorbtion that the materials allow. The different types of materials that rooms or spaces are made from affect the amount and type of reverb. A concrete surface for example will create a sharp or bright type of reverb and an insulated studio wall would create a warm or smooth type of reverb. The size of a room will also determine the amount of reverb that is created from a sound, and a large room will create a fuller longer amount of reverb. The type of reverb that is heard in a large church hall is normally a rich, full and very clear sound as there is a greater amount of space for the sound waves to travel through, and the walls inside churches are normally lined with wood creating a small amount of absorption.
Alex Sanderson HE Access Music Group B.