Radio Broadcast (Nov. 1925-Apr 1926)

JANUARY, 1926 WHERE SHOULD THE MICROPHONE BE PLACED? 329 of them. As the soloists stood in front of all the other performers, this microphone was well removed from the rest of the musicians and singers. By all accounts the transmission was firstclass. Even the slight rustling sound as the audience turned the pages of the programs in unison, while reading the words of Haydn's masterpiece, was distinctly heard on the air. Some years ago weaf broadcast the " Messiah" oratorio from Carnegie Hall in New York, also turning out an excellent piece of work. And wjz in the same city did Beethoven's Ninth and Verdi's "Requiem" last summer, outdoors, with an orchestra of no men, five soloists, but with a smaller chorus — 200 in number. We should like to hear from other broadcasters regarding large pick-ups they may have tried, and their estimate of the results. CKCO DR. G. M. GELDERT of Ottawa, the president of the Ottawa Radio Association of 600 members which operates CKCooutof pure interest in broadcasting, was in New York during the week of the radio expositions, looking over the field and visiting the metropolitan broadcasters The Doctor is a prominent physician of Ottawa. If I knew as much about cyanosis and streptococci as he knows about microphones and audio frequency, 1 should feel proud of myself. Studio Microphone Placingther Consideration -Fur THE interest shown in the problems of microphone placing in the studio has been sufficiently marked to warrant interrupting the progress of our technical series for broadcasters to give further discussion of this important subject. Among the letters received is one from Mr. Ralph S. Hayes, of Ardmore, Pennsylvania, Teading as follows: While I have never had anything to do with "broadcasting, nevertheless, from a study of speech, music, and acoustics, I would like to submit some ideas relevant to the article, "Microphone Placing in Studios." (In the September issue.) 1. I notice the basses and percussion instruments are placed comparatively far from the microphone. Should it not be just the opposite on account of the fact that the bass tones are invariably attenuated more in their transmission through the station amplifiers and receiver amplifiers? 2. It is a proved fact that the basses carry much of the pleasant roundness of music — as well as the energy. 3. The excess of energy in the lower pitches ■ — isn't it the usual cause of the "blasting" mentioned? 4. Wouldn't a better placement be — (a) microphone farther away from or chestra; (b) basses closer to microphone than trebles. 5. A possible objection to such an arrangement would be carbon frying, but it either need not be carried to such extremes, or a condenser transmitter could be used. At any rate shouldn't you aim toward "basses front" instead of "basses rear?" As to Mr. Hayes's first point, I believe the general feeling among broadcast engineers is against trying to compensate for losses of essential frequencies in the audio channels of transmitters and receivers, by exaggerations in the pick-up or elsewhere. As far as the transmitter is concerned no such losses should be tolerated in any considerable degree. Plenty of stations :find it possible to send out their stuff flat be tween 60 and 6000 cycles, and those who haven't learned how, should acquire that ability quickly, while they still have an audience. As for receivers, what degree of deficiency is to be taken as a criterion? In some cases the loss of low frequencies is so complete that a slight gain in bass at the start wouldinot help appreciably. Again, just as many receivers lose the higher frequencies as well as the lower, passing only a band of three octaves or so in the middle. Following out Mr. Hayes's theory, there is just as much reason for emphasizing the violins at the start in order to retain the natural quality of the treble strings with their wealth of overtones. This brings us to the second point. It is true that loss of bass notes makes music sound "tinny," "canned," and disagreeably sharp, and strident. But dropping the band from 3000 cycles up is quite as bad. All the instruments merge into a dull, soft, lifeless harmony, like a bad orjran heard with one's ears stuffed full of cotton. Finally, receiving sets are now on the market which are capable of reproducing sounds sensibly as they are broadcast, and the number of these sets will naturally increase. They are the only safe criterion. It is obviously a saner procedure to work with a horizontal frequency characteristic all along the line. Answering the third point, I believe that blasting is most frequent with instruments possessing a steep wave front. The cornet is about the worst offender. Cutting off the higher frequencies tends to reduce blasting. One type of carbon microphone, which cuts off on the high end at about 2500 cycles, is relatively free from blasting, but the loss of intelligibility and tone brilliancy makes the net result undesirable in high quality work. To point 4a, I should answer " No," for reasons well stated by Mr. Julius Weinberger, one of the leading electro-acoustic and broadcast engineers in the East. (" Broadcast Transmitting Stations of the Radio Corporation of America." Proc. Institute of Radio Engineers, Vol. 12, No. 6, December, 1924.). Mr. Weinberger writes: It may appear that less work would have to be done with regard to proper placing of the performers if the microphones were not used relatively close up, being placed instead, for example, at the opposite end of the studio. In the latter case, the relative distance of the microphone from each of the several performers would be nearly the same and there would apparently be less of a problem so far as proper "balance" is concerned. However, it has been found that this cannot be done for a number of reasons. First, the farther away the microphone is from the performers, the greater is the proportion of sound which reaches it by reflection from the room walls, compared with that reaching it directly from the source of sound. These reflected sounds are generally distorted, since they not only are reflected in a variable fashion with respect to frequency, but interference phenomena occur between reflected sounds coming from various reflection points. Thus, it is found that the sounds as heard from a microphone located, say, twenty feet from the source, are more distorted than those heard when the microphone is placed relatively close. Secondly, the sounds reaching the microphone must be strong enough to give an output far exceeding the hiss due to the use of carbon, and this again necessitates fairly close placing with all performers except orchestras or large choruses. Sharp "Wave Broad V*£we wiih. Double Hump Waveler^lh FIG. I It will be observed that I am not attempting to controvert Mr. Hayes's idea that the bass instruments may advantageously be moved closer to the microphone. No doubt in some studios something might be gained by work in this direction. I do not believe, however, that some of the theories on which Mr. Hayes bases his conclusion, would work out in practical broadcasting. There is no doubt that the carbon microphone is not the final answer to the pick-up problem. What is needed is an inherently hissless and noiseless transmitter, reasonably flat from say 50 to 6000 cycles, if not better, and insusceptible to blasting. Preferably, also, it should be a low impedance instrument, so that it can be used with a long, relatively high capacity lead. Finally, it should be capable of producing a voltage output comparable to that of a good carbon microphone, which is, incidentally, a fine amplifier in itself. Such an outfit would simplify many of our pick-up problems, and personally I pray for it night and day. If someone will invent it, I hereby offer $25 in gold, out of my own pocket, toward a statue of the great man, to be erected at the site of his labors, be it East Pittsburgh; 463 West Street, New York; Schenectady; Van Cortlandt Park South, New York, or any other place. Radio Lingo, Past and Present IN THE December issue of this magazine, the writer considered the source of some of the terminology of radio. In the group of figurative expressions we considered were phantom and dummy antennas, and the counterpoise. Numerous figurative expressions along the same lines will occur to the reader. We speak cf the "fading" and "swinging" of distant signals as they vary in strength in their journey over great distances. A reactance coil is termed a "choke" for alternating currents. Interrupted continuous wave signals are sent with a "chopper." A transmitting station has a "broad" wave or a "sharp" wave; it is violating the radio regulations if it has a "double hump" or "peak." These terms are derived from the curve of response of a wavemeter or receiver to such a transmitter, as shown in Fig. 1. The word "wave" with its combinations, as used in radio, is itself in the nature of a simile, for an electric wave is some sort of displacement or stress in a figurative medium, quite inconceivable to the non-mathematical mind, and the comparison with the waves of the sea and other material wave motions is simply a convenient but rather inaccurate means of tuition. The same hydraulic analogy persists when we