The phonoscope (Nov 1896-Dec 1899)

8 THE PHONOSCOPE September, 1899 effort during this period has been for greater volume of sound. In this direction the art has been painfully struggling for many years, and the results have seemed to indicate that a practical limit had been reached. But within a few months a new development had taken place, which produces results in volume of sound and in fidelity to the original, far exceeding the limits of what was previously, and by those best able to form an opinion, deemed possible. What is of peculiar interest in this connection is the fact that the result in question is produced by an apparently slight variation from previoiis practice, and the attempt to trace the observed result from the apparent cause will form the concluding portion of my remarks. It is appropriate at this point to offer a practical demonstration in order that your ears may judge of the extent of the advance that has been made. I shall first show the result that has been attained by the standard Graphophone, and from which a comparison can be made. (A demonstration was here given, using a record made by the old process and one of the same selection made by the new process.) The difference observable between the two machines before you (overlooking unimportant details of construction) is that the cj-lindrical tablet of the loud-sounding machine is larger than that of the other. No one in this audience will for a moment suppose that the volume of sound is in any way affected by, or dependant upon , the size of the recording tablet. It would be as reasonable to suppose that characters written on a large piece of paper would be visible farther than characters of the same kind written on a small piece of paper. The other mechanisms are substantially the same in the two cases ; that is to say the same recording devise is used, the same material for the tablet, and the same reproducer. The difference is that the recording tablet of the "Grand" moves with a surface velocity of from two and a half to three times that given to the small tablet. The former is made large because, for practical reasons, it is preferred to obtain the high surface speed by increasing the diameter of the tablet rather than by increasing its axial speed The known conditions, therefore, lead us to inquire how the mere increase in speed can bring about so remarkable a result? Superficial con. sideration would indicate that such change in operation could only have the effect of producing a corresponding elongation of the undulations ; and in order to see a logical connection between the cause and effect we must observe, a little more closely, the conditions under which records of sounds are made and reproduced. An important factor here is the resistance which the substance of the tablet offers to the action of the cutting style, which will conform absolutely to the movement of the acoustical vibrations only if absolutely free and unimpeded. This resistance is very slight, owing to the properties of the substance employed, which is an insoluble soap, and to the fact that a very sharp jewel point is used, whose normal penetration is not much more than one thousandth of an inch, so that the style has to cut away an exceedingly small amount of material having very slight cohesion. When the speed is increased a proportionately greater amount of material is cut away in a given lime, i. c., more work is done and more resistance overcome, during the period occupied by the utterance of a given sound. It would appear to follow that increased velocity does not diminish the resistance to the movements of the style, but just the reverse. The factor of resistance, however, has had an influence in determining the angle of inclination of the style to the recording surface and the shape of the cutting point. The latter is formed by a small cylinder of sapphire cut off in a plane nearly at right angles to the axis, so that the cutting edge is approximately an arc of a circle. With such a cutter the resistance to its action would be greatest when it operates in a position normal to the recording surface, and least when placed tangential thereto. This theoretical position of least resistance is, however, inadmissible in the operation of recording sounds. In this operation we have two movements to consider. The first is the straight ahead movement of the tablet which results merely in the removal of the material in front of the cutting point and the formation of a groove. If the stylus were stationary during the operation it could manifestly, and with great advantage, occupy a position almost tangential to the cylinder. But there is a second and all important movement, namely, that due to the vibrations of the diaphragm, which movement is substantially radial of the cylinder. It would be manifestly impossible for the stylus to perform this movement at all if it occupied the ideal tangential position, for that would imply forcing the stylus side-wise into the hard body of the tablet, a task far beyond the strength of the feeble sound-waves. In practice, therefore, the stylus has been inclined at an angle of about thirty -five degrees to the tangent at the point of contact. Under these conditions, what takes place in the operation of making a sound-record may be roughly described as follows : the cutting stylus, performing its pendulous motion corresponding to the sound waves, cuts a sinuous line, composed of alternate elevations and depressions. As the cutting edge begins to descend to cut a depression it at first encounters practically no resistance the sharp edge alone being in contact with the material of the tablet ; but as the movement continues the crest just being formed by the descent of the cutting edge comes in contact with the shank of the cutting stylus, that is the smooth cylindrical surface forming the periphery of the stylus. As soon as this occurs a check is imposed upon the further penetration of the stylus, which is no longer free to follow the movements of the atmospheric impulse. The effect of this check or damping influence is not merely to diminish the penetration of the stylus, but also to modify to some extent the form of the undulations. The effect of increasing the velocity of the recording tablet will now be easily understood. If that velocity be made sufficiently great the crest of the undulations as they are formed, are, so to speak, carried away so rapidly that they do not come in contact with the shank of the stylus at all. More exactly stated, the descending slope becomes very gradual as distinguished from a very abrupt one, the curve approaching more nearly to parellelism with the recording surface. It follows that the resistance or check being removed, the stylus will penetrate to a much greater depth than formerly, and will form undulations of much greater amplitude. The volume of sound being dependent upon the amplitude of the vibrations, the increased volume of sound is thus accounted for. Methodical experiments have shown that, beyond a certain critical speed, there is no gain either in loudness or quality, but that, on the contrary the results deteriorate upon further increase of velocity. The improvement in quality resulting from this new method is apparently due to the fact already stated, namely, that the diaphragm and cutting stylus are at all times free to move in accordance with the acoustical vibrations. The test of the ear convinces us that the records made by this process correspond very closely to the form and amplitude of the actuating vibrations. But in all probability they correspond more closely than that test would indicate, for the conclusiveness of that test would imph a perfect-acting reproducer. It is appropriate, therefore, to notice the construction of the reproducer and the conditions under which it operates. It will appear from this examination that the operation of reproducing the recorded sound is materially affected by the invention under discussion. The reproducing stylus has an end of spherical curvature which rides in the record groove, being automatically held therein by the weight of the mounting of the reproducer, which is supported on a universal joint. The object sought is to give to the device such weight that the stylus will at all times rest in the record groove and follow accurately the undulations thereof. With the low speed record it could not do this. The crests, when very close together (as in high pitched sounds) did not afford the point (which must have a relatively large area in order not to cut the record) opportunity to descend fully into the intervening depressions. Moreover, when an abrupt ascending slope impinged against the reproducing point, the effect was that of a blow, throwing the point away from the record and causing an interruption of the operation. With the gentle slopes and wide curves of the high speed record this irregularity is largely eliminated, and we approach much nearer to the theoretical condition for perfect reproduction, namely, that the diaphragm should be at all times controlled by the sound-record, and should move in strict accordance with the form of its undulations. Not the least remarkable and interesting fact connected with our subject is that the discovery of a relation between the velocity of the recording material and the volume and quality of the reproduced sounds has so long escaped attention. It appears strange indeed that, with so many observers, and with so strong an incentive to increase the volume of sound, this simple law has not sooner been discovered. It seems, however, that variations of speed within ordinary limits produce no noticeable difference and obviously, other things being equal, it is desirable to use as low a speed as practicable and thus obtain a record of maximum length upon a surface of given area. *A Paper Read before the Franklin Institute, Wednesday, March 15. 1899, By Philip Mauro, Counsel for American Graphophone Company. ♦ ♦ -♦ IRovel Ma? of Hbvertismg Working Street Car Fender Shown in a Mutoscope A Boston man has hit upon a novel way of advertising a streetcar fender which the Hip woodBarrett Company is introducing in the West, from a Chicago branch office. He carries a Mutoscope around with him, catches a street-rail way man, and makes him put his eyes to the peek-hole. Then he turns a crank and the street-railway man sees the fender in the act of picking up two dummy figures on the Newton-Boston electric tracks. The smaller dummy weighs thirty pounds and lies across the tracks ; the larger one, fifty pounds, stands upright with its back to the rapidly approaching car. The fender does its work in great shape ; the exhibitor explains that the small dummies are much harder to pick up than real men, and the street-railway man has to believe the evidence of his own eyes as to the merits of the fender.