Sound is a form of energy that is caused by a vibrating object. It can not travel through a vacuum and requires a medium such as air for its transmission. Sound is useful for communication due to the enormous variety of sounds that can be produced. Sound is a useful and versatile form of communication due to a number of factors. These include:
a variety of sounds can be made by an individual; sound travels well in air and water; the sender doesn’t have to be visible to the receiver; it’s useful at night and in dark environments; it can go around objects; it provides directional information; it works over long distances. Sound is emitted by many animals for sending messages as well as detecting them. For example animals may inform each other of their presence or the presence of a predator.
Figure 1.1 displays how sound is the vibration of an object, and the various frequencies at which it is emitted. It is shown by the movement of dust on the sound board.

Fig. 2.1 - Sound

The vibration caused by a vibratin object set up vibrations of the same frequency in the medium through which the sound is passing. The
number of vibrations per second is measured in Hertz. The amplitude (height) of a wave determines the loudness of a sound. This is demonstrated in the video above (Figure 1.1). The vibrations in the medium are detected by a structure such as the ear and converted into sound. For example, when, hypothetically, the sound board is vibrating at 256Hz, it sets the air particles at 256Hz.
Fig. 2.2 - Sound waves

The Human Larynx

The larynx is a special part of the body that functions as an airway to the lungs as well as providing us with a way of communicating (vocalizing). These functions are all possible because of the skeletal components and the muscles that act on them. The anatomy of the larynx is displayed below in Figure 1.3.1 and 1.3.2.

Fig. 2.3.1 - The larynx
Fig. 2.3.2 - The laryx from above

The larynx is a complex structure situated in the throat-neck region in front of the fourth, fifth and sixth cervical vertebrae, and forms part of the trachea. Its main function is to produce sound. It is a complex arrangement of 9 different cartilages. The vocal cords are connected by some of these cartilages extending across the tracheal opening, these are made of elastic fibres. The vocal cords and the larynx surround a narrow opening called the glottis. As air passes through the glotis the vocal cords vibrate. The pitch of the sound is altered by the length and tension of the vocal cords and the opening of the glotis. Other structural components within the body also assist in altering the quality of the sound. These include: the pharynx, nasal caivty and oral cavity.

Detection of vibrations by insects, fish and mammals

How it detects Vibration
The tiny hairs on their antennae are able to detect minute vibrations in the air.

Tympanic membranes
Tympanic membranes on the abdomen or legs have a similar role to that of the ear drum. This specialized sound detector is
formed by a thin membrane overlying an air sac containing sensors.

Some such as the ant have mechanoreceptors on their legs that are able to detect vibrations in the ground
Internal ears
fish have two internal ears filled with fluid and lined with cilia. The cilia detects the movements in the fluid which are caused by the vibrations in the water

Swim bladder
The swim bladder detects the sound, sends the signal on to the ear which then sends it to the brain

neuromasts have hair cells like the inner ear. It is situated near the head and the side of the body
The ear
it is used to detect vibration, the external ear collects the vibrations, the middle ear transmits the vibrations and the inner ear, i.e the cochlea and the organ of Corti, converts them into electrical impulses