Radio Digest (Oct 1923-July 1924)

February 2, 192k RADIO DIGEST — Illustrated Simple Explanation of Radio for Everybody Chapter X — Part I — Loud Speakers By M. W. Thompson THE following article is the nineteenth of a series for Radio beginners, written by Marvin W. Thompson, well known in airphone circles for his understandable style of approaching his subject. The remaining chapters will be: Chapter XI— Dry Cells and Storage. Batteries. Chapter XII — Radio Frequency Amplification. WE MAT begin this chapter by asking a question. "Why does man set up an elaborate network of wires on his roof, carefully insulate the lead-in wire, put $200 or $300 worth of apparatus in a cabinet, constantly add to and refine that which he has and spend his evenings, week in and week out, twirling dials and called fundamentals and overtones. This is similar to dividing colors into primary colors and their tints and shades. Every tore of music or speech is a composite. The separate component tones are called partial tones or partials; the partial having the lowest frequency of vibration is the fundamental, while Uie others are overtones. Those overtones having frequencies which are exact multiples of that of the fundamental are called harmonics; others are designated inharmonic partials. Frequencies of Tones The piano has a range in fundamental notes between the frequencies of 27 vibrations per second and 4,138 per second. The human voice has a range in fundamental notes over those having vibration > LU Z UJ <! 5 5 2 Ol 1 0 50< 3 IOC )0 151 DO 20 30 E5 00 30 0O 35C )0 4000 FREQUENCY PITCH Figure 76 — To affect us with equal intensity, the notes of the scale must be started with amplitudes shown by the curve. adjusting knobs? To what end all this expenditure of money and time? There is but one answer: To obtain clear, strong reproduction of audible sounds created miles away. After his antenna and outfit are electrically as perfect as human ingenuity can make them, what is the device that changes minute, invisible, inaudible electrical impulses into sound waves which are supposedly faithful reproductions of those made at the far-away microphone? The loud speaker — and if that is imperfect in either design or construction, the first expenditure of money and time is all for naught. Tones Not Perfect In the writer's opinion there is no loud speaker on the market that could honestly be called excellent. Each one dodges some problem, certain groups of notes in the scale are distorted or reproduced in a volume that is out of proportion to others. These facts, however, are no reflection on the engineers and designers of loud speakers. Much research and careful check on reproduction have been spent, but the problem is a difficult one. Let us look at music from its scientific side, forgetting for awhile the sharps and flats, the lines and spaces. Then we will not only have learned What the engineer is up against but also to analyze loud speakers and judge with fair accuracy what they will do. All speech and musical notes are a matter of air vibrations, in waves whose number per second determines the pitch. Most of the sounds which we hear are really combinations of notes called chords, and a chord is a very complex thing when analyzed. For purposes of discussion let us divide musical sounds into what are rates between 60 and 1,300 per second. Though the pitch of the highest fundamental commonly used in music is 4,138, overtones with frequencies of 10,000 or more enter into the composition of a great many of the sounds of music and speech. A noted authority, Helmholtz, has said that the quality of a musical tone depends solely on the number and relative strength of its partial simple tones (harmonics). Given the fundamental which is known to musicians as C2 and is placed on the second space of the base staff, and has a frequency of 129, there are nineteen harmonic overtones, viz., C3, 259; G3, 388; C4, 517; E4, 647; G4, 776; B flat 4, 905; C5, 1,035; D5, 1,164; E5, 1,293; G flat 5, 1,423; G5, 1,552; G sharp 5, 1,681; B flat 5, 1,811; B5, 1,940; C6, 2,069; C sharp 6, 2,199; D6, 2,328; D sharp 6, 2,457; and E6, 2,586. The above figures are approximate, decimal fractions having been omitted, and multiplying 129 by 19 will not give 2,457. The note C2 is slightly less, by a few hundredths of a vibration per second, than 129. The diaphragm of a loud speaker should, to be perfect, be able to handle all 20 frequencies at once, not for one note alone, but for many notes. Characteristics of a Tone What is it in an audible tone that makes us exclaim, "That is beautiful — perfect!" The characteristics of a tone are (1) pitch or frequency; (2) loudness or intensity, and (3) quality or tone color. A tone to have ideal tone color should have a strong fundamental containing about 50 per cent of the total energy or intensity, accompanied by a complete series of nineteen or twenty overtones of successively diminishing intensity. If the overtones are A*200,000.°° COMPANY stands squareli; h&ck of the guarantee on every Scientific headset END NO MONEY? ZO.OOO TURNS Ai.J«.TnnAV equivalent to WOf* TODAY 3,ooo ohms bu Postcard j^HP and Pay Postman on arrival POST* PAID LOUD SPEAKER UNIT*!®5 We Gliai*antee The Scientific Headset to be the greatest value on the market. Try it for five davs. If not satisfactory send it back and your* money0 will be refunded immediately. Circular0 on request. Dealers wanted. THE SCIENTIFIC ELECTRIC WORKS 98 Brookline Ave dept. w. BOSTON, MASS. Agents for New York and Vicinity— AMBASSADOR SALES CO., 74 Cortlandt St., Phone Cortlandt 6296 removed, the remaining fundamental is of a dull, lifekss, colorless, droning quality. Docs that description fit much of the music you have heard through Radio loud speakers? Since intensity is one of the important tcteristics of a musical tone we will is the acoustical problems that remain to be solved. Some time, an inventor will evolve a practical, economical method of sound reproduction that does not include a diaphragm. The present-day diaphragm cannot be made so that it will respond Figure 77 — A diaphragm is checked by putting sand on it; three of the forms the sand takes are shown here. now see how it may be altered and how it affects the beauty of what we hear. It will be a surprise to many to learn that if a high note and a low note are both started with equal strength (amplitude), the high note has a much greater intensity or loudness to our ears. Two factors enter into intensity and their effect is clearly stated in this rule: Intensity varies as the square of the amplitude, the frequency remaining constant; it varies as the square of the frequency, the amplitude remaining constant. To make a chord which affects us pleasantly, each of the notes of which it is composed must, to us, have tbe same intensity, but to give that effect, the low notes must be started with more energy contained in their waves. (See Figure 76.) Design of Loud Speaker Now, as to the design of the various parts in a loud speaker, there are the diaphragm, the chambers behind and before it, the material of wbich the horn is made and its shape. The electrical components in several makes of loud speakers have been very well worked out and the magnetic field which affects the diaphragm, either directly or through a link, will respond and vary with every change in tone quality and intensity. It ACE Type 3C Consolette The Most Satisfactory Radio Set For Real Entertainment ""PHIS is the last addition to * the Ace Family. Has beautiful solid mahogany, wax finished cabinet. Set consists of a regenerative tuner, detector and two stages of amplification with built in loud speaker. Due to the particular method of winding Crosley coils it is exceptionally selective. Has sufficient room inside cabinet for dry batteries making a complete self contained long range receiving outfit. Licensed under Armstrong U. S. Patent No. 1,113,149. Phone jack for tuning with head phones; Crosley multistat; filament switch; engraved Formica panel. Uses all kinds of tubes. An efficient set at a remarkable price, $125.00 — without tubes or batteries. The Precision Equipment Co. Powel Crosley, Jr., President 127 Vandalia Ave., Cincinnati, Ohio equally well to all frequencies; its chief defect is that it has a natural frequency of its own at which it vibrates freely and vigorously. At higher frequencies various parts of the circular disc vibrate independently of each other and each with far less energy than if the whole diaphragm vibrated to a lower note. The action of a circular diaphragm made of either metal or mica is examined by sprinkling fine sand upon it and ihen setting it into vibration at gradually increasing frequencies. As the rate per second becomes higher, the sand will begin to assume regular, symmetrical figures, the areas of which are quite large at low notes and very small at higher notes. In Figure 77 we see samples of these Sll.ct.T56S (TO BE CONTINUED.) RAdindijNE "The Voice of the Nation" NO LOOPS NO ANTENNA THE RADIODYNE is operated by simply grounding to a water pipe or radiator, and throwing a few feet of wire on the floor. Uses any standard tubes — dry cell or storage battery. Extremely selective. Simple to operate — only two controls. Stations within a radius of 2000 miles can be picked up on the loud speaker ; any wave length from 200 to 700 meters. PRICE $150.00 For use in apartments, boats, automobiles, railroad trains, etc., the RADIODYNE is enjoyable where other receiving sets would not be practical. When interference, strays, static. etc., make other types of reception utterly useless, the RADIODYNE picks up broadcast programs clear and distinct. Write for illustrated folder which describes the RADIODYNE in detail. Every radio fan will be interested in this new type (antennaless) receiving set. Western Coil & Electrical Co. 312 5th St. Racine, Wisconsin