(((Bill Jacobs remarks: I have recently visited the Museum of Independent Telephony in Abilene, Kansas, where they have displays regarding the history of telephony, excluding Bell's corporate monster. One display that particularly interested me regarded mechanical telephones. They graciously allowed me to look through their files on the subject, copied for me a variety of information, and gave me permission to forward it to the Dead Media Mailing List.
(((I will begin with an article on string telephones by Jon Kolger, originally published in the June '86 ATCA Newsletter (which is affiliated with the museum).)))
"Mechanical or String Telephones"
by Jon Kolger
"Acoustic telephones or 'string' telephones as they are often called, are misunderstood by many collectors. Since they transmit sound purely by mechanical means, they embody none of the pioneering electrical innovations that many collectors find so interesting. Truthfully though, very early telephones performed poorly; and during these years, the acoustic telephone represented a truly viable alternative for relatively short, private-line telephone systems.
"Since they contained no electrical transmitting or receiving devices, they did not infringe on the Bell patents. Thus they were able to enter the telephone industry during the protected years of the late 1870s and 1880s, carving out a small niche for themselves.
"Acoustic telephones literally work on the 'two tin- cans on a string' principle. Two (or sometimes more) firmly mounted instruments, each containing a flexible diaphragm, are connected by a taut wire of high tensile strength. Any vibrations acting upon one diaphragm are mechanically transmitted through the line wire to the other diaphragm, making it vibrate in unison. Thus, sound energy is physically transmitted from one point to another.
"The diaphragms themselves were made of many materials, notably wood, metal, animal membrane, fiberboard, and even tightly woven cloth. Those instruments designed for longer lines, perhaps one-half mile or more, would have relatively large diaphragms, up to a foot or so in diameter. Conversely, short-line instruments would have smaller diaphragms, approximately 2 or 3 inches in diameter.
"Although ordinary line wire could be used, it was common for manufacturers to recommend special types of wires. Typically it would possess high tensile strength, to minimize stretching and breaking. Many were galvanized to combat corrosion. Wire for longer lines might have two or three conductors twisted together for maximum strength. The line wire would be strung aerially from point to point, attached to poles with special insulators designed not to dampen the vibrations.
"The line wire itself had to be banjo-string tight in order to transmit vibrations.
"Obviously the straightest and shortest line wire run would perform best. However, the straightest path was not always practical. To overcome this, special insulators were available which allowed the line wire run to include right and even acute angles.
"Signalling the other party could be as simple as rapping on the diaphragm with a pencil or a small mallet, provided of course that the called party was within earshot.
"Other sets might be found with a small bell attached to a curved wire extending from the instrument. This device was intended to jingle at the slightest signal from the other end. These additions were inventions of the owner, and were not manufactured as such. Still more elaborate sets included magneto signalling, just as with more conventional telephones.
"The line wire itself would be one side of the ring circuit, the other side being an earth return.
"Since the taut line wire was exposed to the elements, acoustic telephones were quite dependent upon fair weather. Acoustic telephones would exhibit unusual behavior during adverse weather conditions. They were known to howl and sing during windy periods, the diaphragm responding to vibrations induced into the wire by the wind. Heavy ice or snow could make the telephones inoperable, and the line would groan under the weight of ice on the wire. Rain was known to produce tapping sounds as raindrops hit the wire. Acoustic telephones were also susceptible to lightning, as there was rarely any type of lightning protection, except with those sets equipped for magneto signalling.
"When conditions were right, however, great claims were made as to the efficiency of acoustic telephones. Testimonials report the ability to carry on a conversation over an acoustic telephone from anywhere in a room, much like the speakerphone of today. It is also said that clocks could be heard ticking over the line.
"Despite the inherently simple principles behind acoustic telephony, well over 300 patents were issued detailing supposed 'improvements' in this technology. Many of these dealt with the aforementioned signalling mechanisms, earpieces, methods of construction, diaphragm placement, etc.... In spite of all this innovation, the very heart of acoustic telephony, the diaphragm and the taut line wire, remained unchanged.
"By far, the best known manufacturer of acoustic telephone equipment is J.R. Holcomb & Co. of Cleveland, Ohio. They designed and manufactured many different models of acoustic telephones, some exhibiting patent dates as early as 1878. They also carried a complete line of accessories such as line wire, insulators, magneto call bells, etc. Other manufacturers include, but are not limited to: Watts Telephone Co., Louisville, Ky.; Mechanical Telephone Co., Albion, Ill.; O. Hamblins Mechanical Telephone, Newton, Ill.; Shaver Corporation, New York; and Lord Telephone Mfg. Co., Boston Mass.
"Many, perhaps most, acoustic telephones are unmarked. By the same token, many sets were homemade, as the simplicity of acoustic telephony made home-built telephones practical.
"With the expiration of the Bell patents in 1893 and 1894, the hey-day of acoustic telephony was on the wane. Hundreds of new telephone manufacturers entered the industry, resulting in furious competition and steady technological progress. It was not long before the acoustic telephones' small niche, that of the short, private telephone system, was challenged by newer, more efficient apparatus."
Bill Jacobs \ firstname.lastname@example.org / killing time in Delaware