New Points For Listeners and Dealers

Radio Record, Volume I, Issue 40, 20 April 1928, Page 2

New Points For Listeners and Dealers

By

Meter

The aim of this section is to give listeners information of new and’ interesting devices and sets on the local market. It is free of advertising intent or influence and to the best of our ability will convey only absolutely reliable statements. Names, prices and sources of supply are mentioned for the benefit of readers and to save individual Inquiry, : .

IIROUGH the courtesy of the National Electrical and Engineering Co., Ltd., Wellington, I have been enabled to test one mec of their Fada 415 B cone loudspeakers with a electro-magnetic driye, which, it is claimed, reproduces all frequencies faithfully. It has been my experience to test over a dozen different makes and types of cone speakers since the advent of that type of reproducer, and I have been unconverted from my preference for a highclass standard large loudspeaker of the horn type. My preference was not due to any prejudice, but was always based on a desire for faithful tone reproduction. It came, therefore, as a surprise to me to discover in the tone of the Fada cone a remarkeble approximation to fidelity right along the whole gamut. ‘he deep tones of the bass were mellow and resonant, and the shrill treble tones were clear and true in timbre. The operating principle of a cone speaker is widely different to that of the horn type, which depends upon the vibrating medium of a small disc. The cone type of loudspeaker depends upon a distinct principle of sound amplification, The loudness of a sound, at a given distance from its soutce, may be increased by increasing the ‘amplitude of the vibration (increasing the actuating forces), or by increasine the area of the vibrating object. The cone accomplishes its object by substituting its larger surface for the small diaphragm, which is the source of sounds in the horn type of speaker. Such a large vibrating surface disturbs a much larger volume of air than is possible with the diaphragm, so that the amount of energy reaching the ear is increased without the use of amplifying horns. ‘The material of the cone must vibrate in numerous irregular scgments if it is to amplify all the elements of the complex tones. The higher the frequency of a note sounded, the smaller must be the vibrating segment. Since the factors of texture and elasticity, generally speaking. establish a limit to which the segments may be reduced, such a vib.®/ing cone cannot usually amplify sounds whos: — frequenéies pass a fixed upper limit, if it is at the same time to amplify the bass notes, for which it is especially suitable. The ahsen e of the upper partials in sound reproduced by some cone speakers gives them the peculiar "empty-barrel’"’ effect. The Fada Company, however, employ a special fabric which is evidently of a texture and elasticity which overcome the get.eral infirmities of many cone speakers. The Fada cone also proved decidedly sensitive, whieh is a virtue in New Zealand, -vhcre rzception of the long-dis-¢ance stations of Australia is so much

in vogne. The Fada 415 B cone speaker is rvtailed at £12 10s. MAGNAVOX COMPANY RECOVERS. Bo TR ae ~ "HE Magnavox loudspeaker of the 7 electro-dynamic type made quite a hit in New Zealand when it was introduced a few years ago, for it certainly marked a new departure in radio reproduction. ‘he Magnavox Company, which is a Califorian concern, however, exjerienced a rather precarious existence for reasons not apparent at this distance. ‘the merit of their goods was undisputed, but evidently business is not always won solely on the merit of one’s wures. News has just arrived from San I'rancisco that according to a published report: "Magnavox is staging a real comeback. ‘Shis little company that was a sensation several years ago, and whch subsequently fell by the wayside, has forzht its way back to solid footing, anu an inspection of the company’s returns revealed one of the most interestiz:g biis of pluck that Western financial nistory has recorded. "Whe story is told in the fact that Magnavex, in the last six months of 1927, earned at the rate of 25 per cent. on par despite the fact that it was being reorganised, had not attained its momertum, and was still suffering from previous errors in judgment. The semi-annual report, just released, shows a current position of 4 to 1, with net liquid assets of 358,892 dollars. Current assets totalled 477.197 dollars, compared with current liabilities of 118,804 dollars on December 31, 1927. Sales of the comnanv in the last half of 1927 were 438,567 dollars; expenses, including all charges, were 347,938 dollars, and net profit availatte for sur plus totalled 90.568 dollars, or eaual to 124 cents for the half-year period on the one doliszr par value stcck. WD tate per day, manufacturing 600 loudspeakers daily, is six weeks behind in its orders, is shipping to every point on the globe mionthly, is providing its loud-speal:inz units for the finest receiving sets manufactured, is employing 250 pecpil:, and has more than 500,000 dollars in «unfilled orders on hand." OVERLOADING VALVES. . A LARGE percentage of the distortion, in most radio receivers, even when a "C" battery is employed, is caused by overloading the valve in the last stage of audio amplification, When yalyes of the 201A or 112 type are used, the only ways to reduce the distortion may be to substitute a larger valve or to decrease the volume ; but with valves of the 171 and 210 types, the distortion can usnally be remedied by correctly adjusting the grid-bias voltage = ("C" battery) on the last stage. The instruction sheets, which are packed with the valve, give approximately values of gtid-bias voltage suitable for use with various plate potentials; but, in order to make sure that the valve is not being overloaded, it is mecessary to connect a milliammeter in the plate circuit of the last valve. If there is no appreciable movement of the necdle of the imilliammeter when loud signals are being received, the grid is correctly biased. On the other hand, when the needle of tlie meter oscillates as the intensity of the signal is intreased, the valve is hinge urerloaded, and the bias must be increased or decreased, as the case may be. If it is impossible to prevent the needle from oscillating by any adjustment of the grid bias, this fact indicates that too much volume is being obtained from the amplifier. The meter used for this purpose should have a range from 0 to 25 milliamperes, aud the maximum fluctuation of the plate current should not be greater than 10 per cent. of the total current. In the case of the 171-type valye, the plate current should be 20 milliamperes with a plate potential of 180 volts, and the correct grid bias is approximately 40 volts. THE "HUM" BOGEY. QCCASIONALLY traders are called upon to answer the question whether such-and-such a "B’"’ battery eliminator causes a hum to emit from the loudspeaker, and the same question as to the andibility of hum from electrified sets and A.C. valve sets is now current. While there are efficient eliminators, electrified sets and A.C. valve sets which de give out the very faintest hum I have interested myself to the extent of ascertaining just how much a vestige of a hum affects broadcast reception. I have found by several experiments that the faint hum disappears completely when a_ broadeast station is tuned in, no matter how weak reception is. This peculiarity has been obtained with equipment of different makes submitted to me for testing. Further, testing with an ordinary battery-supply set I found I got more hum from the "carrier" wave of certain Australian stations than when I operated the new equipment which works without batteries, but obtains its electrical supply from the house-lighting system. This is a phenomenon which must not be ascribed to the greater sensitivity of the battery set, for the battery-less equipment proved doubly sensitive, No, this talk of hum is easily silenced by actual demonstration. On the other hand there are, of course, certain lines which

are inherently bad offenders where humming is involved, but, speaking generally, the radio trade in New Zealand are wide awake to these infirmities, and are displaying good discretion in selecting their lines._ Anyhow, private persons who feel disposed to be caught by enticing ad--vertisements appearing in American radio journals lauding the alleged efficiency of certain low-priced "B"’ eliminators should hesitate before sending their good money abroad on a sheer gamble. One of these lowpriced "B’* elnninators recently imported by a Wellingtonian drowned all distant reception with its hum ‘and had to be discarded. In con‘trast the better quality lines ‘recently tested by me proved an unqualified suecess, and, as previously ‘stated, the hum never once obtruded. | THE EXPONENTIAL HORN. ‘FRADIO traders in New Zealand should sit up and take notice of the ‘"‘exponential horn" type of loudspeaker which is now in the boom stage in the United States. I have lately put this type of loudspeaker through prolonged tests, and it has emerged from them triumphantly. There is no patent covering the exponential horn, which is merely indebted for its remarkable volume

and delightful tone to its shape, the expansion of the horn from the loudspeaker unit to its large bell being made according to scientific principles. It is truly astonishing to hear how faithfully this horn reproduces all pitches of musical notes. The rumble of a grand organ deepest note and the high-pitched piping of a piccolo receive equal expression. One ean only describe the experience of hearing one of these exponential horns as "thrilling." A brass band playing atthe 2YA studio seems by magic to be transferred from the studio to one’s sitting room. The timbre of the instruments is reproduced with striking fidelity and neighbours were de‘luded into believing that the band was in the vicinity. Now, this is a lot to say for a loudspeaker which comprises only a large composition horn curled up somewhat like a bugle and fitted with a regulation loudspeaker unit of a type which has been in vogue for years. "Meter" ventures to prophesy that the ‘‘exponential horn" is going to have a big run in New Zealand, and radio traders will advisedly make inquiries about them. A few of the larger type, which ‘Meter’ prefers, have been snapped up in the Wellington market, and at the moment buyers will have to wait some weeks before a few more will arrive. And I know of other types of loudspeakers, which are of the electro-dynamic type, and of a make quite new to the New Zealand market, now on the water so that connoisseurs of good tone will have more than one new type from which to select. For my part, if the good name of broadcasting is to be preserved, I would condemn all inefficient loudspeakers to the corporation destructor. More harm to broadcasting than anything else is due to "tin-pot" loudspeakers. It would seem that many people in a community are as "tone-deaf" as others are colour-blind, judging from the satisfaction they profess to obtain from their loudspeakers. One of the saddest experiences imaginable is to hear a listener proclaim the supremacy of his own "tin-pot" loud-

‘ing polisned surfaces. ‘This speaker is made in two types-2000 ohms and 750 ohms-thougu identical in outward appearance. The latter type is more suitable for use in conjunction distorter over a loud-speaker which is acclaimed by the world. This has been my experience on more ~2n one occasion. I feel sorry. vp these people, and I feel sorry that they are able to inflict an injustice to broadcasting on their guests whose appreciation of the difference between good and bad tone is quite normal, There is room for good missionary work in the loudspeaker department. THE ETHOVOX LOUDSPEAKERS. The British loudspeakers of the horn type haye a well-deserved reputation for purity of tone, sensitivity and freedom from distortion, and in these characteristics the Ethovox stands out prominently, I have heard several of these speakers lately under varying conditions, and coupled to sets of various types, and I can safely state they were a pleasure to listen to. ‘The deepest tones and the tones of the highest pitch were reproduced with a distinctive mellowness which must make a strong appeal to lovers of music. ‘The Ethovox is a triumph of British faithfulness of workmanship, and one need not wonder at its popularity. This speaker is about 26in. in height, and the bell has a diameter of 15in. There is a system of adjustment for extra sensitivity on weak signals or, on the other hand, for prevention of "chattering"? when the volume is considerable. The Ethovox horn is of metcl with mahogany colouring, and the swan-neck is gracefully curved from the hase to the flair. ‘There are rubber pads on the fect of the Ethovox to prevent them scratchwith power valves. Both lines are retailed by Messrs. ‘Tolley and Soy Ltd., Wellington, at £5 5s.,° and al that figure are exceptional value. TO CURE DISTORTION. 2ADIO dealers and service men have many opportunities of performing ‘‘missionary’? work in — the course of their business. ‘The position would not be exaggerated if one said that there are thousands of radio sets in New Zealand which are utterly out of date, yet these sets could be modetuised by a relatively small expenditure, imall, obsolete audio-frequency transformers are not capable of faithful reproduction, and many of the_ complaints that reception is distorted are due to this cause. The substitu--tion of only one trausformer-in the last stage-would work wonders pro--viding the new transformer is of Ingh--grade and of cerrect ratio. Then, also, | many sets are being operated without a C2? battery, an omission which is fatal to good \eproduction. No wideavake service man should pass over a recciving svt with these dcficiencies without explaining to the owner the | | urgent need for reform. Not only does reproduction wnder these disabilities do an injustice to the broadcast station, the voevlists, and the instrumen-_ talists, but to 1adio as a whole, and, so, indirectly the trader is affected. Not long since au English lady vocalist took | successful action against a gramophone | company for marketing a record of hersinging which, owing to the poorncss | of the record, was a travesty of fer) vocal art. Her reputation was involved, and the Court decided in her fayour. One can casily conceive thie aunorance and disgust which some broadcast vocalists would express if they heard the reproduction of their voices from some of the archaic radio cets sprinkled around New Zealaud. ‘There is a crying need fer reform, and it is in the interests of the trade and the owners of these sets that the position should Jic: explained to the lattcr. A.C., OR BATTERY SETS. } T45t year many people hesitat--ed to buy light-socket sets, be--cause of the contention that this type | of instrument was in the experimental» stage. ‘Those who visited the recent_ Sydney Radio Exhibition found about 30 per cent. of the new sets were electrified (says the Sydney ‘‘Wireless Weekly’), and the other 70 per cent. designed to operate with batteries. The exhibitors say that those desirous of purchasing batteryless receivers need not fear that the 1928 circuits are in the experimental stage, or that this type of set will require too frequent servicing. hev contend that the development of new alternating current valves, and improvements made i rectifier valves, have made practical the building of dependable — light-socket! sets. ""Flowever, it would be well for radio purchasers to be guided by the advice of a merchandisers’ oracle which recently sounded a warning to dealers, advising that they should proceed with utmost caution in stocking alternating current receivers. ‘Consider the system employed, tite construction of the unit, and the integrity of the manufacturer,’ is the suggestion. ‘This is excellent advice to follow, not only for dealers, but for the public buying any type of radio set, whether it be electrically or battery operated. ‘It is expected that next sear thie percentage of electrical sets will be greater, However, there is no doubt that there will be a large demand for battery-operated receivers {for many years to come, because the | electric | facilities are not available in every

home. ‘The great advantage of the light-socket set is in the fact that its power supply is available by the snap of a house lighting switch. lurthermiore, there are no batteries to charge or replace, aud the power supply is constant. ‘he advantages pointed out for the batteries are ‘"‘pure direct current, steady, quiet, noiseless, nniform operation, taking nothing from and adding nothing to radio reception -no line troubles or blown-out fuses can stop reception-you need never miss a single concert from a batteryrun receiver.’ " CAUSES OF NOISES IN A SET. [¥ a client complains of excessive noises in his set, the service man should not, forget to go over all soldered conuections, and valve ptongs should be examined for corrosion. The first importent factor for getting the best results from a receiving set is soldered connections. Every point. should be carefully cleaned and then securely soldered. Aerial joints should be carefully soldered and a proper carth or earth clamp installed. There are at least twenty-two contacts in a five-valve set which cannot even be soidered. ‘Twenty of them are’ valve prong contacts, aud the other two are the battery switch and the ilicostat. Iirt on any one of these will be a fruitful source of noise. Many valves have solder (lead alloy) on their base prongs. ‘This solder rubs off on to the socket contacts, oxidises, and makes a high-resistance noisy connection, The battery switch is often liable to ‘dirty up’? ‘after continued switching, and must be cleaned. The same with tlie rheostat. A dirty switch or rheostat contact causes noise in a receiving s¢t.