Radio Digest (Oct 1923-July 1924)

February 9, 192J, R A D I O D F G E S T — Illustrated Simple Explanation of Radio for Everybody Chapter X — Part II — Loud Speakers By M. W. Thompson THE following article is the twentieth 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. THE perfect diaphragm, or one that would be sufficiently good for most of us, would have an intensity curve like that shown in Figure 78. For notes below 50, the efficiency would be gradually rising and it would reach maximum on notes around 100. The intensity line would be flat to notes around 5,900. after which it would drop to zero at 6,000. True, some of the higher harmonics of the upper fundamentals would be lost, but reproduction would be most satisfactory. Unfortunately, due to the increasingly di 10OO 20 OO SCOO FREGIUENCY 4O0O 50OO 6000 Figure 79 — The diaphragm response is usually as shown here, the natural period being at 990 cycles. other means of setting the air in vibration is essential. The small chamber behind the diaphragm receives but little consideration in most loud speakers, although it can play quite an important part in the faith 1000 2O0O "3000 4000 5000 FREQUENCY Figure 78 — The efficiency curve of a perfect loud speaker would show equal response at all frequencies. 60OO vided response on higher notes, the curve for even the best present-day loud speakers looks much like Figure 79. The peak at about 990 is due to the natural frequency of the diaphragm; those at 2,500 and 5,000 are due to certain harmonics at which the diaphragm vibrates well. The intensity, for the reasons given above, falls off and there is a pleasure-wrecking weakness of the high notes and a flat shrillness to them due to the elimination of their harmonics. The elimination of the diaphragm with the necessary substitution of some JhordarsoN POWER AMPLIFYING TRANSFORMERS Price per pair, $13.00 The new Thordarson Power Amplifying Transformers (push pull) are designed for use as third stage audio frequency amplifiers, to provide high power amplification for operating loud speaking devices. With power amplification, not only is it possible to increase volume, but, since two tubes replace the usual one, the distortion and howling which usually accompany the overloading of a single tube on the third stage is done away with entirely. The Thordarson Power Amplifying Transformers are well constructed electrically and are capable of indefinitely carrying the additional load without breaking down. In tonal purity these transformers equal the Thordarson Super Audio Frequency transformer whose rich quality and even amplification has made it the popular transformer of the day. JhordarsoN ELECT. MFG. CO. fulness of the reproduction. It is, as a rule, air-tight, and the air within it must expand and contract with the diaphragm. This air has a natural resonant point. Both of these factors react on the diaphragm, adding more bumps to the reproduction curve, which mean distortion. The Horn Part This brings us to the horn. Contrary to the general impression, the amplifying action on sound waves is not due to the horn vibrating and acting as a sounding board. The effect of the horn is to CLEAR RECEPTION ASSURED, A Crosley brings in distant Stations Easily. Listen to Crosley Broadcas ting Station WLW. 500 W. Huron St. CHICAGO "N^TO MATTER which Crosley Receiver you choose, you can be assured of unexcelled performance at the lowest price. The Model X-J has proven especially popular. With it, Stations in all parts of the United States and Canada may be clearly heard. Even Honolulu has been frequently brought in from the eastern seaboard. Compare These Prices Crosley Model VI — a Two Tube Set $ 30 Crosley Model X-J — a Four Tube Set $65 Crosley Model X-L — a Four Tube Consolette $140 Special Mahogany Stand for Model X-X, $25 For Sale by Good Dealers Everywhere. Write for free Catalog. The Crosley Radio Corporation Powel Crosley, Jr., President Formerly The Precision Equipment Company and Crosley Manufacturing Company 2492 Alfred St., CINCINNATI, OHIO The largest Manufacturers of Radio Receivers hi the World LnilimiUll!llllinilll!«»lli!llilllll]il"lllllll!Nlllllllllll!IIIIIUniIil!lllllllilllllllllllllllllllllll[IIIIIIIIIIUIIllll reinforce the vibrations which enter it due to the resonance properties of the body of air inclosed by it. The quantity and quality of this resonance depends mainly upon the volume of the inclosed air and somewhat upon its shape. Con nant to any of the frequencies found in the musical scale, is not completely d and lifeless. Unusually rigid material, such as stone or thick metal or compositions mad' wood fiber, gives the best results. If the walls of the horn are smooth and rigid, they produce no appreciable effect upon the tone. If, on the other hand, they .ugh or flexible (resonant), they may absorb or rapidly dissipate the energy of of the air vibration and thus, by subtraction of certain harmonic overtones, have a marked influence upon tone quality. This would inject depressions or valleys into our curve of Figure 79 and make it appear as in Figure 80. A resonant point on the 1,750 notes will give the depression noted at that point and also a marked weakening on the first multiple, or 3,500. Shape of the Horn The shape of the horn also affects that which comes out. Every curve and corner, twist and surface on the inner side 10O0 4-0OO 500O eooo 3000 FREQUENCY Figure 80 — Many horns dissipate energy at certain frequencies, causing dips in the curve 6000 sideration of the speakers on the market gives one some idea of the divergence of opinion on the subject. The aim is to produce a horn that, while it is not reso changes the direction of the outpouring waves. The flare of the horn has a great influence upon the response; widening the (Continued on page 2*6) Worlds BuMest BattercrBs ■■ » 1 oj w'(///M?'«m m™$?ffy M*"*M "R » l Hydrometer and \ 4|ir \ Proof «rf Performance "B" Battery FREE V»«~-~ ....„...'/ Written Guarantee READ THIS SPECIAL NEW YEAR'S OFFER. THEN ACT! Thousands of Badio Digest Headers will profit by this amazing offer. They will buy the famous 2-year guaranteed World Battery at the lowest pure ever Quoted. They will g.-t a hydrometer and a "B" Battery FBEE. And they set the best battery built. It Is "World" quality thai makes possible our 2-year ironclad guarantee. It is "World" onality that makes "World" owners "tell their friends." That's the best proof of performance any product can hate. SEND NO MONEY COMPARE THESE PRICES: You need not send a penny. Just clip this ad and Special 200-hour Rechargeable Storage attach your name and addiess. Tke Batteries battery will be shipped to you the , v , , „._. ", _ , c ay your order is received. When 2 Vo t for WD-ll and 12 Tubes. $ 5.00 the battery arrives, inspect it — 4 Volt for UV199 Tubes 8.00 read our 2-ye*. guarantee be g Vo,t 6„ A g 5„ fore you pay one i.enny. Con v . £ fines yourself you are pro » »°« J» Amp 10.BO tected from every angle — that 6 Volt 100 Amp 12.50 the World battery price saves 6 Volt 120 Amp 14.50 you 50%. Get the "B" Bat 6 Volt 140 Amp 16.60 tery and hydrometer FREE. Order today. 5% Discount for Cash with Order. New' W. Ofte^^. W°r,d Battei*y C°> ^ ^ 60 L R°0SeVelt Rd" ChfcagO, III. tery order and get this \\ ^k/W «. W * U. %JBr ^*^^. order hydrometer and "B" bat \N, ▼ ▼ X^ * W ^**" ^^ -"J""r tery FREE. ^ today. Coto Special Audio Frequency Transformer $050 A MARVEL of manufacturing economy brings this remarkable audio transformer to you at a popular price. Turn ratio is 3 to I . Gives you ample volume and full, rich tone. Finest of materials. Coto quality throughout. If your Dealer cannot Supply you write us giving his Name COTO -COIL CO. 87 Willard Ave., Providence, R. I. BRANCHES Los Angeles: 329 Union League Building; Minneapolis: Geo. F. Darling, 705 Plymouth Building; Atlanta: C. P. Atkinson, Atlanta Trust Co. Building. c£gt CANADA: Perkins Elec. Co., Ltd., Montreal. Toronto. Winnipeg Type 4500 real, loronro. winnim-y. | ^^ff '/ Jt Jt n If It 11 WWW WllTWWK