Many of you have requested a copy of the article first appearing in my news latter “Hartman’s Fine Piano Rebuilding” It will be easier to send it to the list than to each of you individually. As regards soundboard ridges and cracks; I presented a class at last years Convention in Albuquerque “Wood behavior and Woodworking Techniques” on wood technology that contained a more detailed account of the problem. “Building a Better Soundboard” by John Hartman Copyright 1995 Building a quality soundboard requires the consideration of a number of issues; selecting and seasoning the wood, machining and joining the wooden components, considering design and proper dimensions, setting bearing, notching the bridges and finally applying a finish and installing the soundboard into the case. Each of these elements must be accomplished in a manner consistent with two goals; the production of a full and beautiful tone and the construction of a durable soundboard. This short article will show how this is achieved at each stage of soundboard building. First of all I have abandoned the practice of buying pre-made soundboard panels. The use of these pre-made panels is common to all but a few piano rebuilders. While these panels are easy to use and may be a help to busy shops that lack the knowledge and equipment to make their own, it is my experience that using them can lead to short lived soundboards. As you will see the durability of our work is a primary concern The right way to make a soundboard is to hand select the wood. Proper seasoning and drying are essential. While this requires making the panel oneself, it assures that the wood has been selected with the following concerns in mind. When selecting the wood (first done at the lumber yard or saw- mill and again before glue up) the primary concern is that the annular growth rings are perpendicular to the board’s face. Lumber yards are allowed to call some wood quarter sawn that shouldn’t be used in a soundboard. The cause for concern is that wood has unequal radial and tangential shrinkage. The glue lines will have less stress on them if the adjacent boards have similar rates of shrinkage. Another concern is the density or spacing of the growth rings. I have found it best to stick with the traditional practice of no fewer than ten rings per inch. Also, individual boards should be no wider than 5” and no narrower than 2 1/2”. The best boards should be used in the most active part of the soundboard; nearest the bridge. Obviously, wood defects such as knots, stains, worm holes, shakes and pitch pockets will be carefully culled. For appearance sake, the boards used in each soundboard will be matched in terms of color and value. I have installed special light fixtures in the shop to help with color matching. Once the wood is selected for a soundboard it will be planed on both surfaces and the edges will be carefully machined to create perfect mating surfaces for the glue. Using a pre-made panel, one would be unable to select the wood and even more important, would have to settle for a less than ideal adhesive. Because of the demands of high production most pre-made panels are glued together with a modified PVA (Titebond) type glue. This adhesive creates problems in gluing up the large, thin panels for soundboards. Tending to absorb moisture at a faster rate than the wood, it often results in raised glue lines in the humid season. I use traditional hot hide glue in all the critical joints of the soundboard. Hide glue moves at the same rate as the wood and the panels stay flatter. The glue lines are consequently less stressed .. The dimensions of all the soundboard components must be carefully considered if a full and round tone is to be obtained. The first consideration is the thickness of the panel and the tapering of the edges. I have visited shops where tapering of the soundboard was minimal at best. Without an adequately thinned edge, an otherwise well constructed board will not function at it’s full potential. The piano will sound smaller than it is; a 7’ piano will sound more like a 6’ piano. Full tapering of the soundboard edge helps more of the surface to vibrate, making the motion of the board more efficient. When more of the soundboard is vibrating more air can be set into motion and the piano will have a larger sound and an improved bass. To visualize this, consider what would happen if the edges where made thicker; the board will be stiffer and much less soundboard surface will vibrate. I use a substantial taper: 20% to 30% thinner at the edges than in the middle of the board. I have also given careful attention to the selection and dimensioning of the soundboard ribs. Each model piano has a proper rib scale that relates to the panels’ dimensions, wood species and soundboard taper. I make my own ribs individually for each soundboard. I find that the Steinway pianos (and many others) work best with pine ribs in the bass and tenor and spruce ribs in the treble. While more costly, the improvement in tone and ease of voicing are worth the trouble. Glueing the ribs onto the panel is probably the most critical part of the soundboard building process. Ribbing a board effects both the piano’s tone and it’s durability. Because the soundboard panel expands and contracts as much as 1/2” across the grain during normal seasonal changes in relative humidity, careful consideration must be given to the exact point in this cycle to glue the ribs onto the panel. If the ribs are glued on when the panel is too wet the soundboard will be prone to tension cracks in the dry seasons and may have too little crown. If the panel is too dry during the ribbing process it will compress to the point of failure during the summer, causing ridges in the panel surface. I have found that ribbing the board with the panel conditioned to an equilibrium moisture content of 5.5% to 6% will produce a durable soundboard for our North American environment. I have designed a chamber for the panels with specially calibrated gauges for conditioning the panels. Panels are brought directly from the chamber and the ribs are immediately glued in order to assure that the panel is ribbed at 5.5-6% EMC. After deciding on the best EMC for ribbing, the soundboard press must be designed to achieve adequate crown. The curve of the press should create approximately 5/8” of crown on the longest rib, measured before the board is installed into the case at 7-8% EMC. I have found the amount of crown to be a problem for many rebuilders. On a recent visit to a shop that rebuilds more than 100 pianos a year I saw two soundboards ready to be installed. Nobody seemed to be watching so I examined them for crown. Almost no crown was present, and this was in September, so excessive dryness could not be blamed! It looked as if they had no means of controlling the moisture content in the panels prior to ribbing. The raw panels were simply stacked on a shelf and allowed to acclimate to the relative humidity in the shop, whatever it happened to be. This careless approach means that the amount of soundboard crown will be inconsistent, varying from season to season. As you can see I am concerned with tonal aspects, such as crown and dimensioning, as well as the durability of the soundboard. Besides being particularly concerned about the adhesives used, wood selection and moisture content, I am equally concerned about the finish used on our soundboards. While the finish can not entirely prevent the wood from reacting to relative humidity, the right finish will slow down the rate at which the wood will react. With the proper finish, the soundboard can be protected from the temporary extremes in the environment, for example the two weeks in the summer when the relative humidity rises to 85%, or the weekend in February it dropped to 20 below zero and the indoor R.H., fell to 15%! The traditional thin finish provides almost no protection for these extremes. I am using a catalyzed varnish and building the film to a thickness that will provide a measurable degree of protection. This process has no detriment to the tone and the appearance is superior. If you are have any questions about soundboard replacement or other piano rebuilding processes please feel free to contact me: by mail John Hartman RPT, 45 Academy St., Beacon, NY 12508, By phone (914) 838-3635 or by E-mail pianocraft@aol.com.
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