Estimated Date: 1930
Description: 3×1” bell on binaural rubber tubing to a standard binaural metal ear piece with ebony ear plugs. The bell is made of hardened rubber with metal tubes to connect to the rubber tubing. In addition to the basic instrument, there are two additional screws in bells, one for pediatric use and the other with a small hole. The main bell can be used with the diaphragm adaptor.
Reference 1: 259