Siemens Model M-22 Carbon Hearing Aid The Siemens Model M-22 carbon hearing aid was made by Siemens & Halske A. G. of Germany in 1925. There appear to have been at least two versions of the Model M-22, this one and the M-22 "Booster Flat". |  | Click picture for larger view | | |  | | | |
| The front of the Siemens Model M-22 hearing aid carbon microphone. Each microphone grill consists of an outer circle of 12 diamond-shaped cut-outs and an inner row of alternating diamond-shaped cut-outs and small circles. The double carbon microphones measured 4¾" x 2⅜" x 7/16" thick. Note the leather button-hole (left). This way the microphone could be attached to any button on the wearer's shirt. Alternately, a ribbon could be threaded through the button hole so the hearing aid could be worn on a lanyard around the wearer's neck.
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| Rear view of Siemens Model M-22 hearing aid microphone. Engraved on the back just below the leather button hole are the words "Siemens & Halske A. G. Germany"
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| Front view of Siemens Model M-22 hearing aid on-off switch shown in the "on" position. There was no volume control on this model.
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| View of battery plug (left) and the top of a battery (right) showing the battery jacks. The pins and jacks were of different sizes so the plug could not be inserted with the polarity reversed.
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| The Siemens Model M-22 carbon hearing aid plugged into a 4½ volt Fortiphone No. 3-S battery.
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| The receiver and stock ear mold of the Siemens Model M-22 hearing aid. The wire ear hook helped it stay in place.
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View of stock ear mold (left) and receiver (right) of the Siemens Model M-22 hearing aid. The ear mold snapped into the hole in the receiver.
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| Side view of the Siemens M-22 receiver showing the patent number. It reads, "U.S. patent No. 1,406,510".
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| Bottom view of the Siemens Model M-22 carbon microphone showing the "foot" swung out so it could stand upright on a table instead of laying flat. When the foot is swung out it reveals the Roman numeral II and the number 264. This likely indicates this is the sub model II of the M-22 line. The 264 may be the serial number as there is no serial number visible as is the case with the Model M-22 "Booster Flat".
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