With GRAMOPHONE and RADIO

Radio Record, Volume III, Issue 41, 24 April 1930, Page 7

With GRAMOPHONE and RADIO

BY

B NATURAL

No radio-gram enthusiast nowadays uses an ordinary steel needle more than once on a record which is of any value. The habit of using a steel needle for more than one side of a record has long ago been shown to be a very injurious one. Many Types of Needles. HE radio-gramophonist has an ample choice in the variety of needles which are marketed nowadays, and although the "loud," "medium," and "soft" descriptions of these articles apply more particularly to their use in an ordinary sound-box, such Leedles do give rise to different volumes of sound when employed in a pick-up-a constant degree of amplification being, of eourse, understood. Look at the typical loud, medium and soft-toned needles. It will be seen that the loud-tone needle is comparatively

The top illustration shows the tapering point of the soft needle. It ean be readily understood why this needle will have less effect on the grooves of the record that the loud needle shown underneath. The lowest photograph depicts a rusty needle seen through a powerful magnifying glass. Its effect on the records is quite apparent, short and stubby, whilst the soft-toned needle has a thinner shank and a more gradually tapering point; the mediumtone needle, of course, effecting a compromise between these two extremes. It is not merely the actual mass of the needle which governs the tonal volume of the reproduction, but its. actual shape also. The thinner the needle and the more tapering its point the less will be the intensity or ampliude of its vibrations. Effect of Length. (CON SEQUENTLY, the feebler will be the vibrations which are communicated to the pick-up mechanism or the diaphragm of the ordinary soundbox. And, conversely, the thicker the needle and the shorter and:stubbier its point the greater will be the amplitude of its vibrations. Hence such a needle will exert a stronger effect upon the pick-up or sound-box. It is not so generally known that various degrees of tonal volume can be obtained from one type of needle mere-

ly by altering the distance the needle is allowed to protrude from its socket. For instance, if a loud-tone needle ‘is extended as far out of its socket as the needle-screw will permit, a considerably reduced volume of sound will be obtained at any given amplification .of the pick-up system. Sometimes when a maximum volume of tone is required needles of the collar type are used, the collar on the needle ‘serving to increase its mass. Examine the Points. ALTHOUGH: steel needles are very hard, they are fairly brittle. Due to the brittleness of the needles, one or two of them may be found with their points broken away. It is a good plan to make a habit of running the finger over the point of the needle before use in order to feel if the point is intact. . Sometimes, also, a rusty needle finds its way into the box. The point of one of these is illustrated here, and from a glance.at the photograph it will be obvious that such needles are unfit for ‘use. The Best. Policy. [f is always the best policy there- , fore to examine, either by sight or by touch, every needle before it is used; so that record wear may be kept down. to the minimum. ‘When wear. does ultimately set in on’ the record it is always the outer playing grooves which show the first signs of wear by becoming scratchy. This is due to the fact that the tip of ‘the needle never fits the track quite accurately at first.

The needle-point has to be rounded off slightly, and this "grinding in" is accomplished during the first few grooves of the record. However, wear at this portion of the record can be reduced considerably by getting into the habit of allowing the needle to run on the plain edge of the record for half a dozen revolutions or so, and then gently pushing it into the track, The steel needle is a tried and trusted article. During the playing of-an average twelve-inch record it has to traverse approximately 750 feet of playing grooves, and to bear upon its point a weight of anything from three to six ounces, which, in the former instance, represents a pressure of nearly twelve tons per square inch.