Sonotone Model 400 Eyeglass Hearing Aids Sonotone Model 400 eyeglass hearing aids were manufactured by Sonotone International, Inc., of Ossining, New York beginning in September 1957. This was a 4-transistor hearing aid amplifier. It also had automatic gain control (AGC). The Model 400 was all contained in one temple piece. Thus a person could now wear two hearing aids—one in each temple piece as with the example shown here. With hearing aids in each temple piece, the whole eyeglass assembly only weighed 4 oz. without the batteries. |  | Click picture for larger view | | | | | | |
Side view of the Sonotone Model 400 eyeglass hearing aid. As was common during the late 1950s, the temple pieces were thick and heavy-looking. Even so, this was quite an attractive pair of eyeglasses.
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| Inside view of the temple piece showing the Sonotone name and model number. The ear mold tube slide over a short stub at the bottom of the temple piece.
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| Outside view of the Sonotone Model 400 eyeglass hearing aid showing the microphone port facing out to the side.
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| Bottom view of the Sonotone Model 400 eyeglass hearing aid showing the volume control wheel (right). |  | Click picture for larger view | | | |
| View of the back of the Sonotone Model 400 eyeglass hearing aid showing how the battery door swung out and down to open (left), and the on/off switch (top right). This hearing aid took a No. 675 battery.
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