WIRELESS NEWS

Press, Volume LXVI, Issue 20086, 15 November 1930, Page 10

WIRELESS NEWS

(By "MAX.") The Radio Society has staged some very interesting demonstrations this year, but the one given last week will be hard to beat. Mr Eric Shipley took along an assortment of old and new apparatus to show members the difference between early and recent amplifiers of the audio variety. The first combination was a two stage outfit as used some five years ago and the speaker was also antiquated. i'iie "music"'\vas thin and the volume poor, whilst the real bass notes were mot reproduced. Two other later model speakers were tried on the same amplifier and with better results. With the next test, a bias battery was connected up and. then the same speakers were tried again. No. .1 speaker was but little better, but the others showed improved volume and qualitv. these being still better when a valve capable of handling more power was inserted in the second stage socket and the plate voltage put up. Incidentally, readings were taken of the milliainperes of current taken in the tests and showed that where increased volume was required and the semi-power valve used, the consumption of current from the "B" battery was very much greater. All the tests were made with an electric pick-up and the next one was with a different amplifier, a modern one of moderate power handling capabilities and with a modern dynamic speaker. The improvement of the bass was especially noticeable, but the high notes were not suppressed. Two 210 type valves in a push-pull circuit with 400 volts, on, the plates of the second stage of amplification shows that considerably more energy was handled. Next there were two push-pull stages to give still more power in the speaker, which was also a Magnavox, but in a special baffle, and was completely boxed in at the back to prevent the sound waves from the rear from escaping and mixing with the sound waves from the front. This provision is very desirable under most conditions, as two waves beating out of step would spoil the 'miisie. When turned on full, the volume was unpleasant, even in the. fairiv large room, but the quality was excellent, the notes coming out clearly and distinctly. imt.h in the deepest i Lase and liigTicst treble. ■* v The Had in Olviiipja reccntiv ! eld I.orfdon was full of up-to-date receivers. etc.. of k!I descriptions, .ain! apparently those of the Home manufacturers are now . able to compare favourablv witli foreign makes. I lie Radio Society of Great Britain had stand and amongst the features of interest were two ultra short wave transmitters. one for five metre work and Che other for one to li metres. •» # Ac has been stated, before, permanent magnets for loud' speakers of the moving coil typo are being developed by a number of firms. One maker claims that the parts of his particular magnet are held together entirely by the strength of the magnetism, no screws being f-mploved.' and that a straight pull of over one ton is required to separate the parts. JjC ' # This week-end a Blue Spot type RGG speaker wa.s tried out with the LoftinWhite, both on 3YA>. a crystal being used as the rectifier, and with a electric pick-up: ' The Blue Spot has a four pole balanced armature and handles more volume than the average listener can stand in a room of ordinary size. The base js'not as' pronounced as 'with a dynamic (with its' appropriate baffle), but the tost was not quite fair as a baffle was not handy and so its effect could not be compared, but one of the right design •would improve the low tones. An output. transformer was in use to keep the D'.C. out of the speaker, and then the five-year-old Amplion was given fl trial again now thfit a suitable output r:oupli"cr wgs nvnilnhlp/ *nH- it was surprising how well this old speaker shows up. A deficiency ill base, of course, was to be expected, as the earlier speakers would not go down much below about a 100 cycle note and the average listener's ear makes up the deficiency, curiously enough. •i> * Whilst on tlifr subject: of loudspeakers, it should be remembered that one gets accustomed to a speaker P.rtd when one of the modern dynamics is tried out the "trial should extend over n period of several days to get away from the habitual use of the one generally used. For dancing purposes it is often advisable to choose a batHe which deepens the base a little more than is desirable for ordinary reproduction. * >k The re-broadcast of the Melbourne Cup was a particularly fine one, the' Australian shor* wave station coming through excellently The broadcast of. the King's speech last Wednesday was also well received in Christefmrrh. Conditions must have improved at. midnight, because . static was almost continuous on the forty and eighty metre bands round about 8 p.m.- and amateur transmission, according to reports. was* difficult, even when signals were strong. * * Jiif>t a /few hints for intending purchasers offmmiature receivers. The larger models are generally designed to facilitate repairs or servicing, and so it is advisable to make sure that ,-tlje parts of a . midget are get-at-able and that it-is not necessary to pull half the set to pieces to locate or rectify a fault. Tt comes rather expensive if proper regard is not paid to accessibility. Another point is that parts should be of a good quality, commensurate with the price. Quite a good dea{. of the price of a set is absorbed by the cabinet. This is to be expected with the duties and freights which have to be'paid and there will •he a strong appeal by the midgets to those wn.o want most of their money to go into a capable receiver and not for rnuqh ornamentation. It is surprising how compact these new sets are. # >Je At last the 8.8.C. seems to have discovered another studio equalling the acoustic brilliance of the Grahd Hotel at Eastbourne Listeners were to be given an opportunity to judge ' for themselves in the middle of last month when the new National Orchestra o? 114. players was billed to give their first broadcast from a disused ware-

Notes From Far and Near

house adjoining Waterloo Bridge on tlio south side of the Thames. - ' The warehouse was found after a ! feverish search for a building capable of containing the 225 musicians and singers composing the new National Orchestra and Chorus. When, the necessary transformation is comniptprl this will be the largest studio in the country, with an area of over 4000 square feet and a height of 30 feet It is said that the building is acoustically perfect. It is being connected by private wire with Savoy Hill which is barely a quarter of a mile distant. It will be used fairly frequently as an auxiliary studio until the opening of Broadcasting House. * - New Zealand is not the onlv country, where care is taken to prevent the broadcasting of matter which might annoy the political views of listenersNews regarding religious conferences is permitted, but anything likely to caus6 strife must not be put over "the air in Holland. * " * The question as to whether a man's or a woman's voice is the more pleasant when broadcasted it is hard to say, and is largelv a matter 6i individual taste. Actually, a good woman announcer is more clear cut in enunciation than a man. The pitch of the voice of the average woman is about equal to the middle "C of the piano and that of a man, is nearer the next "C" below, with the corresponding overtones in each case. It is the overtones which five individuality to a voice and makes it distinguishable from another.