A loudspeaker emits a longitudinal wave. Sound waves are mechanical waves that travel through a medium by compressing and rarefying the particles of the medium. In a longitudinal wave, the displacement of the particles is parallel to the direction of wave propagation. When an electric current is applied to the speaker, it causes the speaker cone to vibrate back and forth, creating areas of compression and rarefaction in the surrounding air. These pressure waves then travel through the air to reach our ears, where they are detected as sound. Therefore, sound waves are examples of longitudinal waves.