Other

92.07 - Musical instruments, the sound of which is produced, or must be amplified, electrically (for example, organs, guitars, accordions). 9207.10 - Keyboard instruments, other than accordions 9207.90 - Other This headin covers musical instruments in which the sound is generated or amplified electrically Indudin electronically) (i.e., those which cannot be layed for normal hearin without their electrica or electronic components, even though the vi rating devices with whic they are fitted may produce faint sounds). h this res ect, they differ from certain other instruments (e. ., pianos, accordions, pitars) which, w ile they may be e uipped with an electrical soun pick-up and am Iifylng device, are nevertheless indepen ent instruments suitable for laymg wthout sucl! devices, in the same wa as similar conventional-type instruments. I? lectrically operated automatic pianos are excludec i (heading 92.01). R f f ! The instruments of this heading are usually based on the use of : (A) Electro-magnetic generators. In one of the systems based on this principle, the enerator has a drive shaft connected by a flexible coupl~ngto a synchronous motor which fives it at constant speed. Different sized gear wheels are laced in airs along the shaft, each wheel driving toothed wheels known as " tone " whee s. When e instrument is connected to the mains, the synchronous motor turns the tone wheels at speeds which vary according to the diameter of the gear wheels. A permanent magnet carrying a coil at one end is fitted near each tone wheel and arallel to ~ t When . the wheels rotate, the teeth placed at replar intervals around their e ges under the ole of the associated magnets; this causes vanations in the fields which in turn set up wea current changes in the coils. These currents, which are of predetermined frequencies, are electrically amplified and transmitted to loudspeakers. f' This principle is used in particular for the " organ " type of instrument. In another system, a harmonium-type " free-reed "moves across a pole of a permanent magnet, its vibrations roducing variations in the ma etic field set up in a coil wound around the magnet. d e resulting current is electrica ly amplified and transmitted to a loudspeaker. Y (B) Electrostatic generators, of which there are severaI types : (1) Stretched wire generators. In these the vibrations produced when a wire carrying an electric current is struck by a hammer, give rise to variations in capacitance between the wire and metal parts (studs) adjacent to it. The variations in capacitance correspond exact1 to the vibrations of the stnng, so that they provide faithfid reproduction when ampli ed. i (2) Vibrating reed generators, in which the current is carried by reeds instead of strings. (3) Variable-condenser generators, in which the condensers (capacitors) are rotated at constant speed by a motor. (C) Oscillating electronic valve (or tube) generators, including gas discharge tube oscillators. (D) Photoelectric generators, in which a light ray passing through a perforated disc is thrown on a cell. By careful1 calculating the number of apertures in the discscreen, a corres ondin number o current vanations is obtained and these, amplified, produce the desire: souncf r Some of these instruments are called electro-magnetic, electrostatic, electronic, radio-electric, photoelectric ianos, or ans, accordions, carillons, etc., but are nearly always known by their registered tracfe names. fhey enable faithful sound reproduction of most rnuslcal instruments to be obtained b simply changing registers. Such instruments may be described as " monophone " when they on y give a succession of separate notes, or " polyphone " when they produce several notes at once (e.g., organs "). i " Some may be played separately; others may be adapted to an ordinary piano, the instrument being played with the right hand while the piano accompaniment is played with the left hand. Such instruments are classified here, whether or not presented with the piano. Although they may generally be essential for the normal o eration of the instruments of this heading, electrical or electronic ap aratus (in particular J e amplifier and loudspeaker) are excluded and fall in their respective eadings (Cha ter 85) whenever they are not built into the unit itself. When, however, they are incorporate in or housed in the same cabinet as the instrument they are classified with the instrument, even though they may be packed separately for convenience of transport. YI a This heading does not cover conventional e clocks (with dials showing the hours) which are used with certain electronic chimes to strike autornatica ly the hours, half-hours, etc. (Chapter 91). -