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
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