To find out how the ears detect sound, we must look at what is contained in the ear, and what functions each part of the ear has to offer. Sound waves travel through the outer ear, making there way into the middle ear by way of the ear canal. The middle ear turns the sound waves to vibrations, which are processed to the inner ear. Contained within the ear is the eardrum, which is a thin piece of skin, the eardrum helps to take the vibrations and turn them into sound so that humans can hear.
The ear drum seperates the middle ear from ossicles, these are three tiny bones located inside the ear. These bones are called the malleus, the incus, and the stapes, which is the smallest bone in the human body. In Latin these small bones are known as the hammer, anvil, and stirrup. As the eardrum vibrates it moves these small bones, from the hammer, to the anvil, to the stirrup, helping the sound move to the inner ear. Each part of the ear has its own purpose in helping us detect sound.
There is a small curled tube in the inner ear, called the cochlea, this tube is filled with liquid. As the ossicles vibrate the liquid in the cochlea moves around. The tiny cells that cover the cochlea are covered in small hairs, so small that they can't be seen by the naked eye. These microscopic hairs are an important factor, they vibrate, sending messages to the brain to enable us to hear. To see a diagram of the ear, and explanations of parts of the ear you can look here.
Sound is measured in decibels. humans can hear very quiet sounds. as low as 0.1 decibels. At the other end of the scale we can hear up to 120 decibels, but this extreme noise can actually hurt the ears. People hear different sounds depending on the wave frequency that sound creates. A higher frequency is caused by the air pressure going back and forth quickly, the ears receive this as a high pitched sound. The slower the air pressure moves, the lower the sound will be, this is how the ears hear low volumes of sound.
Your brain will allow the ears to determine what direction the ears will be detecting sound from. If the sound is coming from the left, the left ear will hear it slightly quicker than the right, and vise versa. The pinnae (cartilaginous projecting portion of the external ear) faces forward, making it easier to hear when facing forward. It is more difficult to detect sound from behind, than it is from the front. The human ears are amazing, we tend to take them for granted at times, but they should be protected and taken care of at all times.