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The answer to your set seems to be at this link - the summary seems to explain 
the function of the set.

http://archotol.jamanetwork.com/article.aspx?articleid=546479

'The introduction of the phonograph audiometer1 (Western Electric No. 4-A) made 
possible the testing of the hearing of a large number of persons at one time. This 
instrument is now used in many cities for the examination of school children.'

Jolyon