Gerard Cheshire (2006). Sound and Vibration. Black Rabbit Books. p. 25. ISBN 1-58340-997-1. 1-58340-997-1
Joseph P. Olive; Alice Greenwood & John Coleman (1993). Acoustics of American English Speech: A Dynamic Approach. Springer. p. 64. ISBN 0-387-97984-0. 0-387-97984-0
Dorita S. Berger (2002). Music Therapy, Sensory Integration and the Autistic Child. Jessica Kingsley Publishers. pp. 86–87. ISBN 1-84310-700-7. 1-84310-700-7
John Watkinson (1998). The Art of Sound Reproduction. Focal Press. ISBN 0-240-51512-9. 0-240-51512-9