Re: Echophone
Posted: Wed Jan 19, 2011 5:15 pm
This strikes me as a perfect example of the "by guess and by golly" method of inventing. Tinkerers cobbled together all sorts of contraptions, some of which actually happened to work. When asked to describe them, the inventors really didn't understand what they had made (for example, DeForest never could correctly explain how his Audion vacuum tube worked).
In the case of reproducing the content of a phonograph record, just about any arrangement of stylus coupled to just about anything will make some kind of sound. This Echophone reproducer as originally described in the patent includes a weight to increase the tracking force rather than the spring used in the production models. The weight makes more engineering sense as it provides mass somewhere along the length of the glass tube. This mass acts like the fulcrum pivot along the needle bar of more conventional reproducers such as made by Edison or Victor. Or, even more similar to the fulcrum point of the long wooden needle bar of a Vitaphone tonearm. To be most effective, instead of being hung by threads at each end of its length (which produces a vague center of mass distributed along the glass tube), the mass should have been hung from a single point, just as the spring was attached in the production models. This arrangement would make more efficient the rocking motion of the glass tube around the fulcrum which would translate the vertical stylus tip motion to vertical motion of the back end of the glass tube which would then vibrationally compress the sandwich of the tapered rubber tubing and flat wooden clamping pieces, thus creating air pressure changes inside the tapered rubber tube.
HOWEVER, the production model with the tracking spring instead of mass seriously reduces the transmission of vibration as vertical motion at the back end of the glass tube. Instead, without the mass creating a virtual fulcrum pivot along the glass tube, the fulcrum point moves back to the end of the glass tube where it attaches to the pin in the wood. This results in the vertical motion of the stylus tip being translated to rocking motion at the back end of the glass tube rather than vertical motion. This is a much less efficient transfer of energy. The rocking motion of the pin on top of the wood clamp plate translates poorly to compressions of the air inside the tapered rubber tube. So the resulting sound made from this production model is probably pretty weak. I doubt that it would produce anything more than a whisper if attached to a horn, but it would probably be sufficient to hear with the listening tubes that were provided with the Echophone. Another "close, but no cigar" moment in inventing history.
In the case of reproducing the content of a phonograph record, just about any arrangement of stylus coupled to just about anything will make some kind of sound. This Echophone reproducer as originally described in the patent includes a weight to increase the tracking force rather than the spring used in the production models. The weight makes more engineering sense as it provides mass somewhere along the length of the glass tube. This mass acts like the fulcrum pivot along the needle bar of more conventional reproducers such as made by Edison or Victor. Or, even more similar to the fulcrum point of the long wooden needle bar of a Vitaphone tonearm. To be most effective, instead of being hung by threads at each end of its length (which produces a vague center of mass distributed along the glass tube), the mass should have been hung from a single point, just as the spring was attached in the production models. This arrangement would make more efficient the rocking motion of the glass tube around the fulcrum which would translate the vertical stylus tip motion to vertical motion of the back end of the glass tube which would then vibrationally compress the sandwich of the tapered rubber tubing and flat wooden clamping pieces, thus creating air pressure changes inside the tapered rubber tube.
HOWEVER, the production model with the tracking spring instead of mass seriously reduces the transmission of vibration as vertical motion at the back end of the glass tube. Instead, without the mass creating a virtual fulcrum pivot along the glass tube, the fulcrum point moves back to the end of the glass tube where it attaches to the pin in the wood. This results in the vertical motion of the stylus tip being translated to rocking motion at the back end of the glass tube rather than vertical motion. This is a much less efficient transfer of energy. The rocking motion of the pin on top of the wood clamp plate translates poorly to compressions of the air inside the tapered rubber tube. So the resulting sound made from this production model is probably pretty weak. I doubt that it would produce anything more than a whisper if attached to a horn, but it would probably be sufficient to hear with the listening tubes that were provided with the Echophone. Another "close, but no cigar" moment in inventing history.
Despite the limitations of the horn, this demonstrationdoes manage to show that the Echophone plays quite well for such an odd and early machine. It would certainly be more impressive if you were to visit and hear it in person.