WIRELESS NEWS.

Press, Volume LX, Issue 18195, 4 October 1924, Page 11

WIRELESS NEWS.

LOUD SPEAKERS. HOW TO GET EFFICIENT REPRODUCTION. (CXCULLY VBITTXX JOB "THE NU639.") (By Electra.) Many people have changed their minds about buying a radio set, after listening-in on a friend's set to what he has been pleased to call "music." They usually say: "I may have been listening to a wireless concert, but I am disappointed. It sounded like a bad gramophone reproduction." I have heard this remark often, and the result has been the loss of a potential enthusiast. Dealers are sometimes as much to blame as the amateur for .this state of affairs. Sft long as the demonstration produces a big noise the operator is delighted; but not so the audience, who liavo the punishment inflicted upon them. For a professional to continue to offer to the publie low-grado telephony and class it as a demonstration is to alienate public sympathy, which will damage sales in an incredibly short spaee of time. With the amateur and experimenter it is a different matter. t His shortcomings are caused by ignorance. His research work is conducted only in his leisure hours," and it is a marvel that he has progressed as far as he has, since it so often necessitates the burning of the midnight oil. It is onlv natnral that users of valve sets should desire to discard head 'phones in favour of the loud-speaker. The speaker will afford enjoyment, to a very much larger assembly Bimultan* eouslv, and its initial -cost, as compared with "a number of pairs of 'phones, is verv small—to say nothing of the inconvenience which the wearing o any sort of head-gear occasions. pnrfty Bafore Strength. , The flv in the ointment is the tendency 'to sacrifice tone and quality for volume. SigMl strength is very necessary. but it must be- borne' in mind that it " a much greater strain upon the ears to have harsh noises thrust upon them than to hear clearly a purer but weaker transmission. Numerous factors go to the makeup of perfect loud speaker work, as in the case of the transmitting studio, echo and damping must be seriously considered in their effect .upon the quality of the reception. A _ loua speaker giving perfect results m a heavily-draped room will, upon _ the same adiustments, be unbearable iu a bare dance hall or similar structure whose • hollowness causes the <seho cfleet to bo • predominant. Very careful attention should always be paid to the acoustic properties of the room to be used, and experiments iu this direction will yield surprising results. The. operation.and adjustment of.the apparatus is, however, of paramount importance!: Better far a distribution of sound from several points comparatively eoft than a blare from one central position. Overloading is. thq most common fault in operating a loud speaker. The aim should .be to .reproduce the m the> identical' intensity at which it is conveyed to the microphone. It it is magnified It becomes unnatural and dis--1 pleasing, even given that reproduction otherwise -perfect. •

\, Several Better Thap One. Two srnskll loud speakers in an ordinary room,' suitably arranged, are much preferable to on© large mstrumerit. A safe rule is to connect as many in series a3 possible, and distribute tliem. as far a& is convenient. ■ Puritv and clarity of tone must take procedenoe over vol'ume if a pleasing result is aimed at. Thore are always two sides to a bargain, and in fairness to those, who are striving to tlie uttermost to Rive us of i their best i»r the way of transmission, it is tip to everyone of 11s individually to reproduce what tney give us as nerfoctly as possible, and so efface from'the public mind the false •impression .that dfetortion and harshness are inevitable - results in the use of & loud-speaker. A "badly designed power ampmier, too many stages of audio frequency, badly designed A.F. transformers, and an overloaded detector valve are some of the most common causes >of distor-! ■ tion, apart from a cheap and inefficient ( loud-talker. ' • j

WEATHER FORECASTS. The following stations transmit regular weather reports, on a, 600 metre wave-length, in New Zealand and Australia:— „ ■ . . Adelaide, S.A., call VIA, 11 p.m. New Zealand time. Brisbane, Queensland, VIB, 11.30 New Zealand time. . Melbourne, \ ictona, VIM, 10.31) New Zealand time. Perth, W.A.j VIP, 12.30 New Zealand time. , Sydney, N.S.W., VIS, 10 a.m. and 10 p.m. New Zealand time. Awanui, .New Zealand! VLA, 10.10 p.m. Wellington, New Zealand, VlAl. 9.3 ' p.m. AN UNUSUAL SET FAULT. , The receiving set that developed.the following fault was one possessing only two valves, one detector with reaction, and one low frequency amplifier. Although only one stage of low frequency amplification was used most persistent lowifrequency howling "was occurring. It should perhaps be explained at this stage how it was decided that howling was pJaoe in tlie low frequency circuits, since this discrimination! is one which ofteri has to be made. , The discrimination is made by bringing tie tickler coil right oat irom the secondary coil and observing whether alterations of the filament current of the low-frequency valve make any dif- | ference in the pitch of the note. It the - howling is taking, place a* low frequency, swfa variations in pitch will usually take plase, ajid, further, numerations of aerial tuning will leave it quite unaffected. The particular fault which was pwJsent in this case is one which is exceedingly, .difficult to locate .by means of <uiy system of testing, but it is one which, once experienced, is never forgotten. It "sr&s pr&rknasly discovered thutibei use of' a very high internal resistance "B" battery would produce this effect in.a circnit.of titis type, and therefore the first 8/Ooesßory which was investigated was the' high-tension battery. Tbe method of testing was quit© simple, but unfortunately one which' is not twuojly possible to the experimenter. Measurement of the "3&" battery voltage ww first made by mean® ofavohsnetarof a very high internal resistance. The result was practically tshe foil reading which might hare been expected from a number of cells in use. locating the Fault Upon a farther reading hang token with a' comparatively low internal resistance voltmeter (thia being amply one of tlie cheap type sold at about 7s 6d)' scarcely aiiy deflection at all wei6 observed.' Tho obvious inference was a ljiJ t jij(iif 11fil iimjultnii iatbobaiioxj.-

but its location proved unusually difiU colt. The battery consisted of an assembly of separate flash lamp refill cells, connected together by means of somo of tlie patent strip connectors now on the. market. Each individual cell tested out qui to satisfactorily by means of a small torch bulb, and it therefore seemed that tho trouble must bo in ono of tlie connexions. Th© trouble was ultimately found by the us© of smother low resistance voltmeter, reading up to 12 volts, applied across tlx? ends of two of th© cells a£ a time, the readings being 9 volts. A pair was ultimately found which gave scarcely any reading at till upon this voltmeter, although their individual readings were quite up to standard. Closer examination then revealed the fact that thero was a patch of verdigTis immediately beneath the clamping screw of one of the connecting strips, and upon tho removal of this tho fault was cleared. Moral: Overhaul connexions periodically, and do not overlook the smallest detail.

HERE AND THERE.

A sinipl© expedient for marking the position of valve holders is to place o fipot of white paint on tho tip of each screwed leg, and then impress tliem oveuly on tho panel. Carefully lift off, avoiding smudging, and the oantres should 1« dearly marked and may bo centre-punched in th© usual way by a li£ht tap. Tho sain© procedure also a polios where valve. legs arc used. Simply slip th© four rockets on tho pins on the valve, make them all level, and proceed as above. Motorists may bo able to ooen the doors of their garages when they are still s(>yds away, if a recent invention is taken up. A transmission from tho car on a short wave is received in the garago. where a relay starts an electric motor that opens the doors. Why not use the discharge of tho plugs, it would savo extra gear? Because at ono time or another radio amateurs have received stations, sav. 1000 miles away, they think that this is the receiving range of their sate, and if asked what tho range is they will givo this mileage. This is th© wroner way to estimate th© rang© of a set. The proper method is to see how far tho sot "can receive signals ia tho daytime, between 11 o'clock in th© morning and 4 p.m. Stations be picked no regularly between thea® hours are tlfe ones upon which th© receiving range should he based. THE CLOSING DOWN OF SERVICES. In the Legislative Council yesterday ■afternoon the Hon. Mark Cohen asked "whether, seeing that Amalgamated Wireless (Australasia), Ltd., had by threats of legal process, succeeded ia closing down all broadcasting services in the Dominion on account or an alleged infringement of the Association's patent rights, the Government would take steps to prevent if possible the continuance of such a dangerou# monopoly?" The Hon. Sir Francis Bell Tepliea that the Government had the matter under immediate consideration.