The Electric Gramophone

Radio Record, Volume IV, Issue 21, 5 December 1930, Page 9

The Electric

Gramophone

Some important

considerations

concerning

selection

and

Weal

A talk broadcast from Z2YA

by

COLIN W.

SMITH

B.A.

a HIS last year or so we have heard a great deal about the radio and gramophone combination, and it now appears that these two industries are rapidly mergD ing into one. The quality of reproduction from reeords now possible is so very near natural that the electric reproducer must become very popular. We all remember a few years ago when gramophones first came on the market. They were small, and the tone, at least in the extremes of the musical scale, was very thin and unnatural, and yet it was all very wonderful. We all know that it was Edison who introduced the first gramophone, and I want to quote to you Edison’s account of the discovery. "T was experimenting on an auitomatic method of recording telegraph messages on a dise of paper laid on a revolving platen, exactly the same as the dise talking-machine of to-day. The platen had a spiral groove on its surface, like the disc. Over this was placed a circular dise of paper; an electro-magnet, with the embossing point connected to an arm which travelled over the disc; and any signals given through the magnets were em- bossed on the dise of paper. "If this dise was removed from the machine and put on a similar machine provided with a contact point, the embossed record would cause the signals to be repeated into another wire. The ordinary speed of telegraphic signals is thirty-five to forty words a minute; Mut with this machine several hundred jrords were possible. "From my experiments on the telephone, I knew of the power of a diaphragm to take up sound vibrations, as I made a little toy which, when you recited loudly in the funnel, would work a pawl connected to the diaphragm, and this engaging a ratchet wheel, served to give continuous rotation to a pulley. This pulley was connected by a cord to a little paper toy representing a man sawing wood. Hence, if one shouted "Mary had a little lamb," et ectera, the paper man would start sawing wood. I reached the conclusion that if I could record the movements of the diaphragm properly, I could cause such record to reproduce the original movements imparted to the diaphragm by the voice, and thus succeed in recording and reproducing the human voice. "Instead of using a disc, I designed a littie machine, using a cylinder proyided with grooves around the surface,

Over this was to be placed tinfoil, which easily received and recorded the movements of the diaphragm. A sketch was made and the piecework price, eighteen dollars, was marked on the sketch. I was in the habit of marking the price I would pay on each sketch. If the workman lost, I would pay his regular wages; if he made more than the wages, he kept it. "The workman who got the sketch was John Kruesi. I didn’t have much faith that it would work, expecting that I might possibly hear a word or so that would give hope of a future for the idea. Kruesi, when he had nearly finished it, asked what it was for. I told him that I was going to record talking, and then have the

machine talk back. He thought it absurd. "However, it was finished, the foil was put on; I then shouted "Mary had a little lamb," et cetera. I adjusted the reproducer and the machine reproduced it perfectly. I was never so taken aback in my life. Everybody was astonished. I was always afraid of things that worked the first time. Long experience proved that there were great drawbacks found generally before they could be got commerciai; but here was something there could be no doubt of." That was the beginning ef the gramophone, and since then gradually improved until we had the instrument of a year or two back, but the intro-

duction of radio changed everything and since the combination of the two instruments both have gone ahead very rapidly. Making Sound Solid. ET us for a moment examine the method in which sounds are made solid. You will remember in my second talk I told you how the microphone picked up the minute vibrations in the air and transformed them into electricity. A microphone is used in. the production of gramophone records and in the sound recordings for the talkies. The sounds are picked up, transferred to electricity, and then an _ instrument that may be regarded as the opposite of the pick-up is used to transform the electric vibrations back to mechanical vibrations which cut the grooves of the record. For best results a triangular needle must be used, and if we could use such a needle in reproducing our results would be much better, but we cannot because they would cut the records too deeply. When a deep note is registered the’ impression in the groove being cut, swings widely, and when a high note comes through the impressions are small and close together. Now this is important, and later on I shall come back to this point for you will realise that these wide notes caused by the bass will have a definite limit, because the grooves must be kept fairly close together. Furthermore, it will be apparent that it is going to be difficult for a needle to reproduce the fine variations caused by the high notes. We shall not pause to consider how records are commercially made from this original record, but pass on to consider the more useful points in gramophone reproduction. EPRODUCTION is the exact opposite to recording. A needle moves in the grooves, and if the proper speed is attained, the impressions cause the needle to vibrate in the groove at the same rate as did the waves in the air when sound was made. Now if the needle is attached to a diaphragm the vibrations will be transferred to it, and so to the air, and we hear them. This is how the earlier gramophones worked. A horn was used to somewhat magnify the sounds. Nowadays, the needle moves between two electric magnets, and causes an electric current to flow in _ the fine wire round these magnets. This current, of course, will yary in

proportion to the movement of the needle in the groove. This feeble . electric current is magnified \by the audio stages of our receiver. The Wear of Records. FroR a few moments we will consider the important aspect of wear. The variations in the grooves are made upon their sides, not from the bottom, and so the first requisite of the needle is that it fits right down in the groove and ean move freely from side to side. If it is stiff or whips it is bound to damage the fine variations in the groove. Actualy there is a pressure of over 40,000lb. per square inch on your record, so you can see that if the point is not fine and thin something is going to be damaged and the chances are that it will be the grooves of the record. . There must be nothing to hinder the side-to-side movement of the needle, and this is where the old style of reproducer failed. Attached to the needle you will remember is a diaphragm which takes quite a considerable amount of energy to move it. It has neither the plasticity to respond to the deep notes nor the fineness to respond to the upper notes. It consequently missed them. Our needle, then, must be fine ‘enough to respond to the high frequencies, hard enough not to whip and tough enough not to wear rapidly. Measurements have shown us that a: -worn needle not only damages the ‘groove, but actnally reproduces less ‘signal than an unused one. Only the other week I evolved a very interesting set of figures bearing out this fact. Furthermore, a used or blunt needle, which cannot fit down into the groove,

is very likely to cross where two bass notes are in adjacent grooves. If you examine a record you will gee some of the grooves have a very big swing, and if you notice the space between these lines you will see how very narrow it really is. You will remember we mentioned this point a few moments ago when we were speaking of the manufacture of the records. At these narrow places a blunt or whipping needle -will break through very easily, and you will get the familiar repetition of a bar or so. Our perfect needle, then, must have a very fine point, and of the commercial types probably the spear point is the best. The soft is also. good, but some of these are made very thin, and are inclined to whip. The medium is, considering everything, the best type of needle to use. If you want to play safe and stand no chance of damaging your records, use the fibre needle. They will positively not harm the records, but they will not reproduce as loudly, nor will they bring in the high notes as well as do the steel needles. Nevertheless they are very good, and certainly must be recommended where wear is excessive. If they will not fit your pickup the shanks may be trimmed, but do not interfere with the point. It may, of course, be resharpened when it becomes dull. Types of Pickups. O much. for the needles. Let us examine a few of the types of pickups. Of paramount importance in selecting one of these instruments is its construction. It must be robust and yet all the joints must work perfectiy. The pickup head should weigh little more than 50z., and preferably should be hinged on a more rigid type

of arm. Usually pickups, the heads of which are tightly connected with the arm, are hard on records. Another type of pickup is the one with ‘the bent arm, and these minimise wear more so than any other type. Technically speaking, they can track to Within 3 degrees of a constant tangent. These are not hinged in the usual way, but there is no necessity for them to be so. Quite worth noting in considering one of these pickups that tip back is that the head should be capable of staying in a backward position. You will find it very handy. In selecting a pickup for tone, see that it is connected with a good ampli-

fier, such as the Loftin-White or a modern push-pull arrangement, ‘then listen for notes at both ends of the scale. Do not let a heavy bass reproducticn influence you in buying. Before long you will become very tired of it and wish for the clearer and purer reproduction brought about by a really good pickup. But the bass must be there and the pickup should be able to go down into the deeper registers like those in an organ solo without any difficulty and without distortion. It must be able to bring through such instruments as the violin, flute, and piccolo, and reserve the characteristic overtones, that is to say, you must be able to recognise a flute when it is playing and realise that it isnot a piccolo. Most first-grade pickups will do this, but as a deciding point, listen for the separation of the notes. Many good pickups will not separate one instrument from another but run all notes together-"garbled," as we speak .of them. You must be able to hear the individual instrument without any difficulty. Of course this statement is relative, and I do not mean to suggest that at a band fortissimo you can pick ‘that the cornet is a quarter of a note out of tune. We have now covered the main points in electric reproduction and the selection of needles and pickup. There are many points I have not had time to dwell upon and if there are any further points that occur that any ‘listener especially wishes to have explained, a letter to me will have the desired effect.