MLA

Koch, Frederick R. (Frederick Robinson). Music/Sérénade (chorus, male voices). Box 329, folder 1847. n.d.. https://collections.library.yale.edu/catalog/2039614.

APA, 6th edition

Koch, Frederick R. (Frederick Robinson). (["Box 329, folder 1847"])(n.d.)[Music/Sérénade (chorus, male voices)]. https://collections.library.yale.edu/catalog/2039614.