The early diaphragm models resembled the older bell models but had a rigid membrane covering the bell. These mini-phonendoscopes were very popular in Europe in the early part of the 20th century. On the left is an Oertel model signed F. Davidson, London, c. 1905. The entire stethoscope is made of metal, including the flexible metal tubes, and came in a leather pouch. On the right is a similar Oertel design, but with rubber tubes attaching the ear pieces to the chest piece. It came in a canvas pouch, c. 1900.