by H. Winfield Secor, E. E.
Science and Invention,
January 1926, pp. 802-803, 875-876.
Illustration 1 - the front and rear views of the orthophonic radio phonograph. All the component parts are plainly labeled and by reading the text, you will learn all about this wonderful new development in the radio and phonograph field.
Illustration 2 - Fig. 6 shows that several loud speakers can be used with this new combination phonograph and radio set so as to reproduce the sound in any part of the house. Fig. 7 shows operation with standard phonograph reproducer and Fig. 8, with electric pick-up through amplifier and to loud speaker, result being tremendous volume.
Illustration 3 - Fig. 9 shows component parts being used for the reproduction of incoming radio signals.
Illustration 4 - the beautiful cabinet in which this new combined radio and phonograph is housed. In the view at the left, the front screen has been removed so as to show the horn openings. The phantom view at the right shows the construction of the folded horn which gives a resonating chamber 6 feet long yet is all contained within the cabinet. The dotted lines show in general the paths of the sound waves but it must be remembered that the sounds issue from both left and right of the top and bottom openings.
Illustration 5 - The phantom view at the right shows the construction of the folded horn which gives a resonating chamber 6 feet long yet is all contained within the cabinet. The dotted lines show in general the paths of the sound waves but it must be remembered that the sounds issue from both left and right of the top and bottom openings.
Illustration 6 - Fig. 1 shows standard phonograph with ordinary horn and Fig. 2 indicates how larger resonating chamber can be obtained. Figs. 3 and 4 give constructional hints for building horns of this nature for your own use on present phonograph or radio loud speaker.
Illustration 7 - Fig. 5 shows how short horn will respond to harmonics of certain wave-lengths whereas a horn ofthe same length as the wave responds to full wave.
This seems to be an epochal year in the realm of radio and phonograph development. A short time ago we described a wonderful new talking machine known as tile panatrope, in which the full volume of the original orchestra, band, organ or voice is reproduced by means of an electrical pick-up traveling over the record, together with the aid of a vacuum tube amplifier. The electrical output from this amplifier is then carried into a new cone loud speaker developed by tile General Electrical Company engineers and the results obtained with this clever combination of new scientific ideas are fully described in file November issue of this journal.
A short time ago the writer was present at a demonstration of the latest brain child of the Western Electric Company and Victor Talking Machine Company engineers, and lie was very agreeably surprised at the faithful reproduction, as well as the volume of the vocal and instrumental selections on the new orthophonic talking machine.
THE ORTHOPHONIC SOUND BOX
The two most important factors involved in the orthophonic phonograph lie first in the new folded type of horn as it is called, and which is shown in the accompanying photographs and special drawings; and secondly, in the sound box and its diaphragm. The majority of talking machine sound boxes or reproducers which pick up mechanical vibrations from the record and translate them into sound waves which are projected downward and out of the horn, have used mica diaphragms. A number of other materials have been tried from time to time, but the old stand-by has been mica. As good as this material has proven for many years in its utilization for sound box diaphragms, it was limited in the range of vibrations which it could cover, namely, about 350 to 3,000 a second, or about three octaves on the musical- scale. This means that the very low as well as the very high vibrations were never heard at all on the old style talking machine. This also holds true for all of the average type radio loud speakers.
Extended research work in the acoustical laboratories of the American Telephone and Telegraph Company and the Western Electric Company, together with the aid of the Victor Talking Machine Company experts. brought out the fact that the best of all materials for a sound box diaphragm was duralumin, now widely used for airplane construction. This new material when tried in the form of a diaphragm of the proper shape, proved that it could respond to sound frequencies over 5-1/2 octaves, or from about 100 up to 5,000 vibrations per second, which covers practically the whole scale of speech or music, so far as the human car is concerned. Mica diaphragms also had the undesirable property of vibrating in sympathy
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with certain musical notes. The new orthophonic sound box has a diaphragm which is corrugated. or ridged in a certain fashion in order to give it rigidity and also to prevent any sympathetic vibrations which the diaphragm might try to assume. This new sound box is claimed to obviate all blasting, which is common to many radio loud speakers and phonographs of the ordinary type.
THE ORTHOPHONE HORN
Taking up the new orthophonic phonograph in a general way. we find that the larger size machine costing a little under $300.00 has a massive folded wooden born within it, the length of the sound path through this horn being six feet or seventy-two inches-some horn you will agree.
One of the accompanying diagrams show the length of the average sound wave in air corresponding to, let us say, a baritone note. The sound wave here shown in connection with one of the new horns is six feet, but even a 4-1/2 foot horn, corresponding to a 4-1/2 sound wave in air will give very wonderful reproduction on the lower notes of the musical scale, as was pointed out to the writer several years ago by Professor Dayton C. Miller, of the Case School of Applied Science, who is one of our leading acoustical experts.
It will be seen from the accompanying diagram of the six foot sound wave and the long horn which is needed to allow this sound wave to vibrate or resonate with full power, that a small phonograph or loud speaker horn about one to 1-1/2 feet long can only reproduce these low notes by resonating harmonics or partial tones of the fundamental note. In some cases it is possible to get fair results by building up certain harmonics of the fundamental note, but it is not the preferred method by any means.
Another important scientific point which phonograph manufacturers have constantly ignored for years is a fact which acoustical experts have always known, which is -that there should be no air leaks or right angle bends along the sound amplifying passage. Also, the walls of the horn should be rigid -only the air column should vibrate. In the orthophonic talking machine this was one of the points particularly watched, and it was interesting to note in regard to air leaks how the tone arm had been redesigned so as to be practically air-tight at its base, where it joined the orthophonic amplifying horn; secondly, the sound passageway through the tone arm was designed to continually expand, without having any abrupt right-angle bends. With many of the old style tone arms, the sound waves coming from the reproducer diaphragm only traveled a few inches, when they were reflected sharply by a right-angle bend at a joint in the center of the tone' arm. These reflected sound waves or echoes created blasting, and also caused many of the finer notes to be weakened. or entirely destroyed by the time the music or speech emerged from the opening of the sound chamber or horn.
One of the men familiar with the experiments carried on in the laboratory in developing the new orthophonic horn said that while a six foot horn might seem long to the layman, the ultimate in sound reproduction would be obtained by means of a horn twenty feet in length. One of these days we probably will be buying phonographs with twenty feet of horn folded or spirally concentrated within its case, but the phonograph experts tell us that the new six foot horn reproduces and builds up practically all of the main vibrations over the 5-1/2 octave scale, so necessary for first-class vocal and instrumental sound reproduction.
Any phonograph will be vastly improved with a 4-1/2 to 6 foot horn placed in it, as shown in the accompanying drawing, but the ultimate in beautiful sound reproduction so particularly noticeable in some' of the lighter musical selections, where delicate shadings of the music occur, is only made possible by this clever masterpiece of the engineering laboratory.
A RADIO ORTHOPHONIC PHONOGRAPH
Instead of spending from five thousand up to fifty thousand dollars or more for an elaborate pipe organ, the palatial home owner of today may spend instead but $1,000.00 and have in his home one of the new radio orthophonic phonographs shown elsewhere. This new radio orthophonic outfit has all the necessary controls on it which enable the owner to have three different forms of musical reproduction. The first is regular acoustical reproduction of music from a phonograph record, through the medium of the usual needle, orthophonic sound box and tone arm, together with the orthophonic horn. If greater volume of sound is desired than that required for the ordinary residential living room, the electrical pick-up may be placed on the record instead of the ordinary needle and sound box, and the electrical currents produced by this pick-up device may be passed into a vacuum tube amplifier of several stages. This amplifier contains a remarkable ballast tube which compensates for changes in the alternating current line voltage, and some of the tubes serve as rectifiers, so that A, B and C current for the tubes of the radio set is supplied.
The greatly amplified voice currents coming out of the amplifier are passed into a new orthophonic loud speaker which embodies all of the qualities of the new sound box, in that it can cover 51/2 octaves of sound and will not blast or distort any of the notes. This loud speaker is also used in connection with the eight tube Super- Heterodyne built into the cabinet as the photographs show, the loop aerial for which is enclosed in the cabinet also, the loop being rotated by a disk or dial mounted in the instrument shelf at the top of the cabinet.
No batteries are required whatever, except in the event that the owner has no A.C. 110 volt supply in his district, when batteries may be placed on the shelves provided in the back of the cabinet, and the whole radio phonograph may be operated from the batteries only.
When using the radio or the electrical phonograph pick-up in connection with the orthophonic loud speaker, the sound waves are switched into the orthophonic horn by means of a three-way sound valve, the control lever of which is placed in a convenient position. The phonograph motor is driven by an induction type A.C. motor, and when using the electrical pick-up for phonographic reproduction the voice currents from the pick-up device pass through a scratch reducer filter.
One of the interesting features of the new radio orthophonic machine is that a jack is provided on the instrument board whereby one or more external loud speakers placed at any desired point about the house or hall, may be connected with the amplifier circuit when reproducing radio music or electrical phonograph music.
The radio set incorporated in this deluxe radio phonograph is an eight-tube straight super-heterodyne of the R.C.A. type, and will do most anything one could expect of a radio set. One of its features is the new uni-dial control.
RECORDS NOW ELECTRICALLY RECORDED
One of the interesting new developments in the phonograph world, particularly in view of the fact that the new orthophonic sound box will reproduce vibrations from 100 to 5,000 per second, is the newly developed electrical recording process for registering the voice or musical production. The electrical recording is done by means of a special electro-magnetic mechanism operating a cutting. needle, as this mechanism together with the needle are spirally traversed over the master' record blank in the recording studio. The voice is picked up by an ordinary radio broadcast microphone, such as we see in the studios nowadays, and this may seem very interesting in an offhand way perhaps, but the marvellous thing about this electrical recording of records, is that one or a dozen microphones, if necessary, may be used, and such gigantic selections as that of an opera at the Metropolitan may be recorded, without the least trouble. . . .
