Greater responsive qualities in the reproducer itself being called for, research determined that the ordinary flat or single diaphragm should be replaced by one of dual construction, having two responsive zones, the purpose being to give equal value to both the high and low frequencies. An inner zone, cone-shaped, is tuned to a peak resonance of 3,000 vibrations per second, the outer annular zone being tuned to a peak resonance of 110 vibrations per second. The two responsive zones are combined to give equal amplification throughout a range of six octaves.

Fig. 77.

The stylus bar, unlike the usual mounting of this detail, is so constructed and proportioned that it transmits all musical vibrations to the diaphragms, whatever their amplitude or frequency. It is mounted between hardened steel ball bearings so adjusted as to be practically frictionless, and is perfect to such a fine degree that a movement of 1/100,000 of an inch can be transmitted from the needle point to the diaphragm and can be clearly heard in a quiet room.

A resilient anti-vibratory coupler is employed for the attachment of the sound-box to the tone-arm, this coupler being so proportioned that it will absorb all shocks due to loud passages in music and so preclude the sound distortion inevitable in the usual semi-rigid coupling.

The tone-arm is carefully proportioned to conduct the pure musical vibrations set up in the soundbox to the amplifying chamber.

With such a phenomenal range secured in reproduction, it was necessary that its amplification and projection should be effected with positive equality throughout the entire scale of frequencies. The ideal was an absolute replica of the original performance-in volume and quality of tone.

The mere adoption of a large interior horn was never contemplated. It was not in accordance with true acoustic principles, for it lowered the pitch of the reproduced music, which was unnatural. Further, it robbed cabinets of valuable record-storage capacity.

The amplifying chamber of the Viva-tonal Columbia is, therefore, also revolutionary in character, albeit it occupies no greater space than before. It is a scientifically proved application of stereoscopic principles allied with curvilinear sound conduits so proportioned that they gave synchrophase and equal amplification of all frequencies within the full acoustic range of recorded music. This stereoscopic horn (actually a double horn) eliminates any possibility of exaggerating the intensity of some notes out of proportion to others, as is usually noticeable in long horns.

It will be seen that the above described sound box differs considerably from the ordinary sound box, which has a flat circular diaphragm, generally of mica.

The stylus bar on the new sound box described above will be noted as having ball-bearings. In sound boxes of low cost the pivot of the stylus bar will generally be found to be secured in a more or less tight bearing, while in the more expensive types the stylus bar is balanced on two knife edges, and held thereon by two small springs; undoubtedly the ball bearing method must allow more freedom of movement to the stylus bar, and, without actual slackness, all this must make for more sensitiveness. We spoke above of a resilient anti-vibratory coupler between the sound box and the tone-arm, this is generally a moulded rubber tube, a very good coupler can be made out of a piece say 11/2 inches long, of thin flexible garden hose pipe, the inside diameter fitting the outside of the sound box tube it can be tightened on to the sound box by a turn of wire round it if necessary, the other end is slipped over the end of the tone arm. It should not be pushed so far on that the sound box end can touch the end of the tone arm. Generally it will be found to give a decided advantage to the sound quality, properly moulded couplers can be readily bought for the purpose. The length of stylus bars and their proportions as against the length of the needle, has been determined by many experiments, and present practice has been found to give the best results, although at first sight it might appear that, if the needle leverage were altered so that on a standard record it could increase the diaphragm movement, that this would increase the volume of the sound, but this does not happen, the volume appears unaltered, acting as though the limit had been reached.

Revolutions Per Minute

Some records state the speed at which they should be run, or do so in the catalogue dealing with them, but in any case it is important to get the right speed in order to get the best results, perfectly true music does depend upon the proper speed being used. The speed can best be checked by sticking a pin in the cover of the turntable, letting this pin touch a finger held near the edge of the turntable, and timing the number of touches felt per minute. The minute should be started when a touch is felt and that touch called " nought," the next touch being " one " and so on, this will make certain that the number recorded at the end of the minute is really the number of revolutions made per one minute.

Spring Motors

These may have one or more springs, two is a popular number, four is generally the maximum. The springs are of the best flat steel, and may be from fin. to 11/4 ins. wide, there is no one standard. These springs are generally secured in a steel cup-like container, one end of the spring being fastened to the container, and the other end being fastened to the shaft or spindle running through it. In a two-spring motor it is usual to wind round the first container by the handle, this tends to wind up the first spring, but its other end being secured to the central shaft, likewise the end of the other spring, the effect of turning the handle is to wind up both springs at the same time. When the motor is started running, then both springs are working in tandem, and run down equally, thereby j giving twice the time of running that could be given by each one separately. In the case of even four-spring motors the same principle is used. If now one spring should break, then it will not be easy by simple outward inspection to tell which is the broken one. The motor must be taken off the baseboard of the machine, and taken to pieces so that the spring containers can be separated, it will then be easy to detect the broken spring, and after obtaining its exact size, to replace it with a new one. The speed regulation method of most gramophones is simple and ingenious; a train of gear wheels is supplied and on the highest speed axle is fitted a spring controlled set of three small weights, i.e., a governor. When the motor is stopped these small weights lie near to the axle, equally round it. Each weight has a flat spring from one side anchored to the axle, and rotating with it, from the other side of each weight another flat spring is fastened to a sliding collar upon the same axle; to this collar a circular disc is secured. When the motor rotates the above-mentioned high speed axle causes the weights attached to it to also rotate at a high speed, and due to this they fly round at a distance from the axle depending upon the speed. A small rubbing finger or brake is brought into contact with the above-mentioned disc and by pressing it lengthwise along the axle it regulates the position of the flying weights and therefore the speed of the axle, and through this fact it clearly regulates the speed of the whole motor. If then a gramophone refuses to run up to speed, it may be due to the disc being unable to slide along the high speed axle, or it may be that the regulating finger had remained in the low speed position for some reason; examine for either of these faults. Equally well it may be that something has got into the gear wheels and causes them to bind and slow down. If a gramophone will not run slowly enough, examine to see whether the friction pad on the regulator has worn away, or come out, thereby releasing the friction on the disc. It is not difficult to get perfect speed regulation on a gramophone, expensive or otherwise, but it is another matter to get quietness of running. This implies well cut, properly adjusted gear wheels, but much can be done to reduce noise by adjusting the centres of the various wheels from one another, and giving them grease rubbed on the teeth. The quietest running machines will be found to have worm drive whereever possible, also ball-bearings on the main shaft, also an eccentric adjustment to the governor shaft.

Fig. 78.

Fig. 78 shows a two-spring motor having a worm-driven governor, and showing the above-mentioned three weights spring held on the speed regulating shaft, i.e., the governor.