"Buzz" is the most important of the minor defects of a piano, as it is generally also the most persistent. The conditions under which it may occur are various, and for the most part, simple and easily removed: -
(6) The cause may be found in a loose fit of the upper or lower panel, or of the fall, or of the bar upon which the fall rests, or of the lining under the key-board; or the fall may not truly lie back when opened, or the lid may not rest evenly upon the sides and front. Any defect in the fitting is sufficient to cause a buzz.
To discover the cause: first raise the lid. If the buzz ceases, the cause lies in the fitting of the lid, which must be adjusted by raising or lowering one, or both, of the hinges at the back. If not, remove the upper panel. If the buzz ceases then, find out what part of the front causes it. The panel being replaced, the buzz will probably again be heard: it may happen that by merely taking out the panel and putting it in again the defect in the fit has been remedied. If not, the part whose looseness causes the buzz, will be found by pressing the panel in its frame, or the frame itself downwards, inwards, outwards, or sideways, until the disagreeable noise ceases. It is possible that a piece of ordinary writing paper gummed or glued on at the spot, where pressure has stopped the buzz, will be sufficiently thick to produce a perfect fit. If the manipulation of the front does not bring about the desired result, proceed in the same manner with the lower panel, the key-board lining the fall, and the bar on which the fall rests. The fall is removed by simply raising it: if the fit is perfect, this is not easily removed. The bar beneath is fixed by a sunk screw at each end to the frame of the piano.
The key-board lining is usually sprung into position, wedging itself into the slits which receive it, and the defect will be an imperfection of the wedging. A thin slip-wedge is the remedy.
(c) Torsion of the sound-board may arise from the woodwork adjoining the iron studs which, when the lower panel is removed, are visible at the base of the piano, projecting through the soundboard. This is originally cut away just enough to admit the passage of the studs without contact. These studs, however, have a very sharp rise, and it may happen that the tension of the strings produces in the lower part of the board a certain amount of torsion, and very little suffices to bring the two into contact. When this takes place, a buzz results. The remedy is obvious, by means of a thin narrow sharp knife.
(d) Great difference is to be noticed in the tone of different pianofortes, and even of different notes on the same piano. These differences are largely dependent upon the material of the frame and bridging; and it may be said broadly that coeteris paribus, the tone will vary between sharpness and shortness, and softness and rotundity, according as metal or wood predominates. But quite distinct from these qualities, accidental to the material, is the clearness of note given by a perfect instrument, the result of effective toning. The operation is simple, but delicate in the extreme, and the affected part is the felt covering the hammers. This felt, which is of a very fine kind, varies occasionally in density, and this variation may sometimes produce a buzz. An operation which improves the quality of the tone, and removes the buzz (when attributable to the cause under consideration) by equalising the density, consists in pricking the felt on the upper part of the hammer with the toning tool, which, in its simple form, is a fine steel fork of 3 short sharp prongs.
The felt is not perpendicularly prodded, but the points of the fork are stuck into the felt as often as is requisite to produce the correct tone, and in the direction shown in Fig. 190, the motion being that indicated by the darts. This operation depends for its success upon delicate hand and ear: over-prodding is injurious to the felt, and ruinous to the tone.
If the buzz does not yield to one or other of the remedies indicated, the cause will probably be insufficient tightening of leading screws, or defective fixing of the foundations, or imperfect glueing, and the instrument must be handed over to a pianoforte-maker.
Another common defect is in the "repetition": a key will not rise to the level instantly the finger is raised, it rises either slowly or not at all. This may result from one of two causes; either the key has warped or it has swollen.
(a) The warping of the key will probably be the result of the piano having been subjected to extremes of temperature - great heat in summer, and great cold in winter; or perhaps one day the room is without warmth of any kind, the next it has a roaring fire. In time the keys will stick. To remedy this, raise the lid and remove the front, the fall and the bar, raise the key by the forepart, above the pins which keep it in position, and draw it forwards. Where the key rubs its neighbour, it will generally appear chafed, but if no chafing is apparent, just rub the side lightly with blacklead, and replace the key - it will now blacken its neighbour at the point of contact, and at the corresponding part of itself it may be rubbed down very slightly with glass-paper, first No. 1 then No. 0.
(6) Swelling of the key is the result of damp alone, which operates by decreasing the size of the holes into which the fixed pins fit, and these are accordingly more or less gripped by the key. Perhaps only one is tightened, more likely both. On taking the key out, it will be at once apparent whether both pins are gripped or only one, as the piece of cloth in the forward hole, and the wood itself in the case of the other, are dented and blackened. The hole may be enlarged to the necessary extent by shaving the wood with a fine penknife, but preferably by filing it with a fine fret-file of oblong section. No more should be taken off than is just sufficient to enable the key to work freely, as otherwise the key will rattle and work unevenly.