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MECHANICAL or ACOUSTIC TELEPHONES
This
is an updated collation of work from Issue 33 of the Journal of the
Telecom
Heritage
ACOUSTIC
TELEPHONES
Bill Jacobs (bjacobs@mintaka.sdsu.edu), from the Internet 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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