Barry Cooper (8 October 2008). Beethoven. Oxford University Press. str. 407–. ISBN978-0-19-531331-4. Pristupljeno 15 April 2012.
doi.org
dx.doi.org
Ealy, George Thomas (Spring 1994). „Of Ear Trumpets and a Resonance Plate: Early Hearing Aids and Beethoven's Hearing Perception”. 19th-Century Music17 (3): 262–73. DOI:10.1525/ncm.1994.17.3.02a00050. ISSN0148-2076. JSTOR746569.
Ealy, George Thomas (Spring 1994). „Of Ear Trumpets and a Resonance Plate: Early Hearing Aids and Beethoven's Hearing Perception”. 19th-Century Music17 (3): 262–73. DOI:10.1525/ncm.1994.17.3.02a00050. ISSN0148-2076. JSTOR746569.
worldcat.org
Ealy, George Thomas (Spring 1994). „Of Ear Trumpets and a Resonance Plate: Early Hearing Aids and Beethoven's Hearing Perception”. 19th-Century Music17 (3): 262–73. DOI:10.1525/ncm.1994.17.3.02a00050. ISSN0148-2076. JSTOR746569.