Acousticon Model "D" Carbon Hearing Aid The Acousticon Model "D" carbon hearing aid was manufactured between 1905 and 1910 by the Hutchison Acoustic Company (1904), which later became the General Acoustic Company (1906). This hearing aid is similar to the Model "A", except that it has a double carbon microphone (center) (there is no volume control), and an earphone (left) with a detachable handle. It is connected to a 3-volt Acousticon battery (right). |  | Click picture for larger view | | |   | | | |
| Rear view of the Acousticon Model "D" carbon microphone. |  | Click picture for larger view | | | |
| Close-up of the Acousticon Model "D" earphone. |  | Click picture for larger view | | | |
| Rear view of the Acousticon Model "D" earphone showing the on/off switch on the right side. (Switch is in the "on" position.) |  | Click picture for larger view | | | |
| Inside view of the empty Acousticon Model D carrying case with the earphone handle clipped to its place on the lid (center).
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| The Acousticon Model D in its carrying case. |  | Click picture for larger view | | | |
| Front view of the Acousticon Model "D" carrying case. |  | Click picture for larger view | | | |
| A 3-volt Acousticon No. 5 battery powered the Acousticon Model D carbon hearing aid.
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