Longitudinal wave means the vibration is in the direction of the wave motion, i.e. back and forth instead of perpendicular, such as, up and down. The velocity of the wave depends on the medium and not on the frequency. The higher the temperature the higher is the velocity. The human ear hears vibration from about 20 to 20,00 Hz. The sound we hear is the combination of many superimposed waves.
Sound waves have energy and are measured in decibels.
Every 10-decibel change the energy levels by a factor of 10. Music is a combination of sound waves pleasing to the ear. In string equipment, such as the violin, the sound is made by means of a stretched string. In wind instruments, such a trumpet or an organ, the vibration source is the air. The equipment determines the wavelength.