There is one change in terminology which has occurred since this article appeared -- the "transmitters" mentioned in the article would be called "microphones" today.
Telephony, September 10, 1910, page 293:
The Telephone in Opera and Church Service Transmission
By C. E. Fairbanks
It is not of recent development that music and spoken parts have been delivered simultaneously to two audiences--one within the building and the other at some distance.
As early as June 10, 1878, at Bellinzona, Switzerland, the opera "Don Pasquale" was transmitted by telephone to an audience entirely separate from that within the theater. At about that same period, the transmission of the music from the opera in Paris to a point some distance away, is a matter of record. At Halifax, in this same year, church services were transmitted, for some months, a distance of about two miles. These early, and even more recent attempts, were only partly successful on account of the difficulty of transmitting the spoken parts. Furthermore, the acoustic properties of the building enter into the subject far more than is ordinarily suspected and a resonant effect which may be unnoticed by the ear affects the transmitter to rather considerable extent. This is also frequently the cause of even musical numbers being difficult to transmit clearly.
As the telephonic art has progressed, attempts along these lines have improved. With the advent of the solid back transmitter the nearest approach to success was reached.
Best results are obtained by removing the mouthpiece and substituting for it a "plug" with as many holes through it as may be empirically determined in each case. One method of making this "plug" is to cut off the free end of the present type of mouthpiece and fill as many of the holes in the remaining stub as may have been previously decided. The transmitter should be enclosed in felt or cotton of about ¾ in. thickness and then placed in a box which is weighted with about 3 lbs. of lead to give it stability. This box is in turn placed upon a felt pad ¾ in. thick. Of course, an opening is provided through the side of the box, somewhat larger than the exposed plug or mouthpiece.
Better results are obtained if the diaphragm is of mica, so as to avoid the possibility of any fundamental tones inherent in a metal diaphragm. Locating an equipment of this type in the footlights of a stage has demonstrated by test that a piano recital by Paderewski, a minstrel, and any other class of either musical or spoken sounds can be transmitted distances of from 3 to 15 miles and farther without any confusion of words or music.
Church services have been particularly hard to transmit on account, usually, of the interference due to acoustic properties of the building. By making the adjustments previously outlined and locating the transmitter on the pulpit as shown in the illustration, no trouble has been experienced in overcoming these troubles.
Transmitters constructed with pencils of carbons and other super-sensitive types produce an effect indicating that they are entirely too sensitive for some portions of the program and also give trouble in other ways. The placing of several transmitters in series does not add to but rather interferes with the clearness of transmission. Any number of circuits may be supplied from the one transmitter by connecting in series with it and with each other, the primary windings of the induction coils.
To obtain the best results, the primary current should be maintained at .03 ampere and the source of supply should be such that the current will remain constant. Storage batteries, Edison-Lalande, or large sizes of dry battery cells, are good for this purpose. Placing several banks of dry cells in parallel is effective.
The induction coil is necessarily important; the primary winding should consist of three layers (330 turns) of No. 17 B. & S. gage wire and the secondary of four layers (1,250 turns) of No. 26 wire. The length of the core (between heads) 6 in., diameter ½ in., core consisting of the best grade of No. 26 annealed iron wire.
The standard common battery circuit is not adapted for obtaining the best results for this class of service.
In some cases it is necessary to locate the transmitter at one side of the room or building. This is never desirable and is to be avoided if at all possible. The main point is to keep the body of the transmitter from touching any hard substance and to prevent sound waves striking any portion other than the mouthpiece.
In church work one of the best methods of attaching the transmitter to the pulpit without making it conspicuous or in any way marring the woodwork, is shown in the illustration.
This consists of a support of 5/8 in. brass tubing colored to match the woodwork and attached to a plate ¼ in. by 2 in., which should be long enough to reach under the book rest; a screw combined with the weight of the book rest will hold it. At the top of the piece of the tubing is brazed a plate to which is attached the back of the transmitter, between the two being a ½ in. piece of felt. The holes for the machine screws are bushed with felt washers to prevent vibrations other than those due to sound waves being transmitted to the diaphragm.
In order to get the transmitter as near as possible to the speaker, it is sometimes necessary to suspend it from the ceiling. This can be done by using two No. 18 bare copper wires which will serve both as a means of support and for current transmission. It very frequently happens that the reverbratory effect is such as to seriously interfere with clear transmission. Repeated tests may be necessary to find a location such that this effect is negligible or a minimum.
At the receiving end, four 80-ohm receivers connected in series, constitute the maximum number which should be in series. If more receivers than this are required, they should be connected in parallel banks of four per bank. Twenty receivers, five sets in parallel of four in series per set, are the greatest number that should be connected to any one circuit. If the number of persons listening will permit, placing a receiver to each ear heightens the effect as well as increases the volume of sound received.
In this connection it may be of interest to know that at a dinner given by a prominent New York business man, the forty guests were each provided with a watch case receiver hung from the table cloth by means of a small pin hook, such as is used for supporting eye glasses. The cords were carried to the under side of the table where a running board lashed in position was equipped with the necessary terminals. The receivers were not noticed by the guests until they were requested to take them up. Music was transmitted from Philadelphia and other points, as well as a twenty-five minute speech by a prominent absentee located in Boston. In this case the forty receivers were treated as twenty, that is, in ten sets of four per set.
The church arrangement illustrated is one of several similar installations which have served for invalids or others in permitted "attendance" at all times and in all weather. Large bodies of persons located at a distance have frequently been addressed by an individual, among which may be mentioned the recent gathering of newspaper men in New York addressed by Commander Peary, Mr. Carnegie, and other prominent men in Washington. On one occasion a large number of people were entertained in this manner by a minstrel show ten miles away and another by a vaudeville entertainment twenty-five miles away.
As a single transmitter is sufficient for any number of circuits there is a large field for pleasure and profit in the transmission of concerts and services as above outlined to hospitals or private invalids, besides numerous other uses which suggest themselves.