Ladefoged, Peter. 1968. A phonetic study of West African languages: An auditory-instrumental survey. Cambridge University Press, 2nd edition. ISBN 0-521-06963-7
Ladefoged, Peter (1996). The Sounds of the World's Languages. Oxford: Blackwell. ISBN 0-631-19814-8. Parameter |coauthors= yang tidak diketahui diendahkan (|author= dicadangkan) (bantuan)
Amanda Miller, Levi Namaseb, Khalil Iskarous. 2003. Tongue Body constriction differences in click types.
Traill, Anthony & Rainer Vossen. 1997. Sound change in the Khoisan languages: new data on click loss and click replacement. J African Languages and Linguistics 18:21-56.
