Acousticon Model 26 (Silver Seal Symphonic) Carbon Hearing Aid The Acousticon Model 26 hearing aid, also known as the "Silver Seal Symphonic," was a carbon hearing aid manufactured by the Dictograph Corporation of New York between 1935 and 1937. This model used a mechanical (carbon) amplifier.
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| It was a bone conduction model and it was recommended to be used with a 4½ Volt battery. It is pictured here with a lead acid rechargeable battery. The microphone measures 3” in diameter. The picture at the right shows the Acousticon Model 26 with the headband as well.
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| Close-up of the front of the Acousticon Model 26 carbon microphone showing its design. The square holes around the circumference let the sound in. |  | Click picture for larger view | | | |
| The back of the Acousticon Model 26 carbon microphone. The pocket clip (top center) hides the model number (left side) and the serial number (right side). |  | Click picture for larger view | | | |
| Close-up of the upper left side of the back of the Acousticon Model 26 carbon microphone showing the Model number—Model 26—normally hidden behind the pocket clip. |  | Click picture for larger view | | | |
| The Acousticon Model 26 carbon amplifier wasn't big at all. It looks just like the plug to plug into the top of the battery—but this is the real amplifier. |  | Click picture for larger view | | | |
| The Acousticon Model 26 had a rotating volume control on the cord that plugged into the bottom of the microphone. The knob rotates to change the volume. You can see the volume level numbers faintly on the plug part.
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| The bone conduction transducer attached to the headband. A lot of the hearing aids in the 1930s and 1940s seem to have been bone conduction models rather than the air conduction models so common today.
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