Sonotone Model 35:15 Carbon Hearing Aid The Sonotone Model 35:15 carbon hearing aid was manufactured in 1935 by Sonotone International, Inc. of New York. This hearing aid consisted of a double carbon microphone unit in an oval imitation tortoiseshell case that measured 5 3/16" by 2 9/16" x ¾" (13.2 x 6.5 x 2.0 cm) and weighed 7.4 oz. (212 g) without the battery. The picture (above) shows the Sonotone 35:15 bone conduction carbon hearing aid attached to a 3 volt Sonotone X42 battery.
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| Front view of the Sonotone Model 35:15 carbon hearing aid plugged into a higher-powered 4½ volt Sonotone X65 battery (right). Since increased battery voltage meant higher current, which in turn gave increased amplification, the user's manual recommended that the wearer use a 3-volt battery (above) when at home in quiet situations, and a 4½ volt battery (right) when more amplification was needed such as in a public place, church or theatre. |  | Click picture for larger view | | | |
To get even more amplification, you could add a carbon amplifier. When using a carbon amplifier, the battery cord plugged into the amplifier (right) and the amplifier plugged into the top of the battery. This way if you had a mild hearing loss you used the Sonotone Model 35:15 carbon hearing aid without the amplifier. If you had a more severe loss, you plugged in the amplifier.
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| Top view of the carbon amplifier showing the amplifier jack and the plug from the Sonotone Model 35:15 carbon hearing aid (unplugged). |  | Click picture for larger view | | | |
| The picture on the right shows the Sonotone Model 35:15 carbon hearing aid plugged into a carbon amplifier which is plugged into the higher-powered Sonotone X65 battery. Note that this hearing aid came in both air conduction and bone conduction models, and with, or without, a mechanical (carbon) amplifier. This picture shows the Sonotone Model 35:15 carbon hearing aid with an air-conduction earpiece (right). |  | Click picture for larger view | | | |
| Front view of the Sonotone Model 35:15 carbon hearing aid with air-conduction earpiece (top). The microphone openings consist of four narrow slots around the perimeter of the raised portion of the case, thus being virtually invisible.
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| Left side view of the Sonotone Model 35:15 carbon hearing aid showing the microphone slots. There were two slots on each side. You can see them (blue slots near top on each side of center. The foot partially obscures the left one). This was a rather unusual design as most microphones had a grill on the face of the hearing aid rather than almost invisible slots on the side as this one has. |  | Click picture for larger view | | | |
| Right side view of the Sonotone Model 35:15 carbon hearing aid showing the volume control with its positions marked "off," "soft" and "loud." The volume control was a slider giving an continuous range of volume as you slid it from soft to loud. The metal "foot" is shown turned at right angles (the way it is used when standing the hearing aid on a table). When not it use, it turned 90° counterclockwise so it didn't stick out.
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| Rear view of the Sonotone Model 35:15 carbon hearing aid showing the spring-loaded pocket clip (top). Below the pocket clip faintly engraved into the plastic is "SONOTONE/REG. U.S.P.O./ MADE IN U.S.A.". Below the midline is the serial number "S-S 88833". The S-S stood for "Super Sonotone" but that was more correctly used for Models 33 and 34. Perhaps they used the same backs for the Model 35 series as well and thus they were part of the S-S serial number continuum. Near the bottom is engraved, "U.S. PAT. No. 1,811,638/OTHER PATS PEND".
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| End view of the Sonotone Model 35:15 carbon hearing aid showing how the foot let the hearing aid stand on its own. Note, carbon microphones wouldn't work if they were laid flat on a table as the carbon "shot" inside wouldn't then touch both the metal diaphragm and the back of the case to complete the circuit. When held at an angle or vertical, the carbon shot "flowed" down and filled the space between these electrodes, thus touching both surfaces which completed the circuit. The pocket clip sticks out to the right. |  | Click picture for larger view | | | |
| Left side view of the Sonotone Model 35:15 carbon hearing aid showing the battery/earphone/transducer cable plug. The left pin and jack were larger that the others so you couldn't insert the plug the wrong way. |  | Click picture for larger view | | | |
| Left side view of the Sonotone Model 35:15 carbon hearing aid showing the battery/earphone/transducer cable plugged in. |  | Click picture for larger view | | | |
| The bone conduction transducer and headband of the Sonotone Model 35:15 carbon hearing aid. The user placed the transducer behind the ear where the springy headband held it tightly on the mastoid bone. This allowed the vibrations it produced to reach the inner ear. |  | Click picture for larger view | | | |
| The Sonotone Model 35:15 carbon hearing aid in its original carrying case. |  | Click picture for larger view | | | |
| Inside view of the empty carrying case of the Sonotone Model 35:15 carbon hearing aid showing the pull-tab (top center) to access the hidden compartment below the false floor. |  | Click picture for larger view | | | |
| View of the hidden bottom compartment of the carrying case of the Sonotone Model 35:15 carbon hearing aid showing the headband stored there.
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| Outside view of the original case for the Sonotone Model 35:15 carbon hearing aid. The case measured 5⅝" wide x 4⅞" deep x 1⅝" high (14.2 x 12.5 x 4.2 cm).
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