vibration of a certain medium is necessary for the production of sound. For example vibratuon in the guitar's strings, vibration in vocal chord (when humans are speaking) etc etc.
Sound energy is the form of waves. Thus it requires a specific media to transmit itself. For instance sound travels fastest in solids. Sound also travels in liquids and air (gases). However, if there is no medium present. Sound will not travel.
Hope you get the answer :)
