Mechanical or acoustic telephones.
This is an updated collation of work from issue 33 of the journal of the Telecom Heritage
I will begin with an article on string telephones by Jon Kolger, originally published in the June 1986 ATCA Newsletter.
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 behaviour 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 home-made, 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.
Here are two short contemporary pieces on mechanical telephones.
Source: the Lancaster, Pennsylvania Agricultural Almanac for the Year 1879, printed by John Bater's Sons.
How to Construct a Farmer's Telephone.
A form which may be called the farmer's telephone for communications less than one thousand feet may be stated for the benefit of agricultural readers, who can easily construct it for themselves.
Take tape such as is used by the ladies for their dresses, either in long roll or else in pieces sewed together flatwise. Whenever it is necessary to support it, fasten it flatwise to the top of a spiral spring about one and one-half inches long, made by winding close small steel wire round a lead pencil.
Kerosene lamp chimneys make the best mouth pieces. Over one end stretch a piece of old kid glove or stout paper in the manner of a drum head by winding a string tightly around. Fasten the tape flatwise against the outer surface of the diaphragm of leather or paper thus formed, when conversing keep the tape stretched. The sound vibrations will travel across the supporting points of steel springs without interruption and the flat surface of the tape prevents the musical ring which destroys the distinctiveness in such contrivances made of strings. Such lines of tape can be carried in every direction, round corners, up stairs and down without much affecting the sound except by the distance.
Source: Telephone Experiences of Harry J. Curl as told by him to E. T. Mahood, During the summer of 1933 at Kansas City, Missouri.
First Telephone Experience
I was born in Elwood, New Jersey April 23, 1863. My father was a telegrapher, as were several of my uncles. In 1879, when I was sixteen years old, my father and I built a pole line one and one-quarter miles long between the railroad station at Elwood, New Jersey, where he was employed as Agent, and our farm, in order to establish what I believe to be one of the first telephone lines in this section of the country.
We went into Philadelphia to buy some wire. We didn't want to use iron wire and the only copper wire available was #50 soft drawn, which we bought. We suspended this wire from the poles with string loops and at each end connected up an acoustic telephone. These telephones were available in Philadelphia as toys. They had no batteries associated with them and no way of signalling over them.
They operated by direct physical impulse. When my father wanted to call home, he would start calling 'hello' into his telephone and when we heard it we would answer.
The transmission was good and we had no difficulty in hearing. We used to invite the neighbors in to hear vocal and instrumental music from the railroad station one and one-quarter miles away. This was the first telephone experience that I had. The copper wire sagged between poles quite a bit and we frequently had to go out and pull it up and cut out a lot of the slack and, of course, in time its diameter shrunk to such an extent that we had to take it down."
¨ Mechanical telephones were also used to some extent (I cannot say what) in Britain. I remember see one thirty years ago at the old railway museum in York and I assume it is still in the collection of the present, much enlarged railway museum there. There is also a description in Baldwin's book History of the Telephone in the United Kingdom. the Science Museum has a pair have identified a pair in the telecommunications collection (not on display); these came from the GER section of the LNER in 1923. Mike Horne has discovered that a pair were in use at Earls Court on the Metropolitan District Railway for linking the telegraph office on the westbound platform with the ‘east’ signal cabin, which was beyond the station. This was in 1881
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