Soundboard Racks and Cracks
As we mentioned in the last post, perhaps the most critical component in the piano for determining its final tone and resonance is the soundboard, If there were no soundboard under the strings to amplify their vibrations, the piano would sound as thin as a banjo. Actually, this wide slab of wood under the strings (or behind them in an upright) is usually not one piece of wood, but made up of several quarter-sawn spans of spruce, glued together.
We also emphasized the importance of the ribs glued to the back of the soundboard, critical because they hold the soundboard in a slightly convex bowed shape, or "crown." The soundboard isn’t really flat as it may appear, it’s raised slightly towards its middle. If the soundbaord flattens out and loses its “crown” (which it most certainly will in time – anywhere from 50-100+ years,) the string pressure against the bridge and soundboard will become loose and the tone will suffer greatly.
So the better piano manufacturers use the best quality wood they can find for the soundboard and ribs, and cut & glue the ribs with precision to insure the longest possible life for the soundboard’s crowned shape.
Almost exclusively, the wood of choice for soundboards is spruce. And not just any spruce, but spruce carefully chosen for close grain (for better sound conducting) and that perect balance between strength and suppleness. It must be strong enough to withstand the immense pressure from the strings, but supple enough to vibrate freely with resonant tone.
Piano makers since the 18th century have scoured the world’s finest spruce forests, looking for spruce that would make the most resonant soundboards. An overwhelming majority of this soundboard spruce for American pianos has come from the Sitka region of Alaska. European and Japanese pianos have also used Sitka spruce, and have found great stands of spruce in European forests also.
Because of the immense pressure of the soundboard, as well as wide humidity fluctuations wherever you live, it is not uncommon for soundboards to develop lengthwise cracks in them, often running right along the glued seam between any of the quarter-sawn spans. Henry Steinway once said he’d be surprised to see any of his soundboards over 15 years old that didn’t have a least a crack or two running through them. Although these cracks can look ugly, curiously, they often have little or no effect on the piano’s sound. The overall area of resonating wood is so large, the string vibrations still get evenly distributed over the soundboard despite the cracks.
One condition where soundboard cracks do effect the sound negatively is when the split is not only side-to-side, but where the wood one or both sides of the crack lifts upward, coming loose from the rib below it. Not only can this result in a dead resonance in that spot, but a nasty buzz can occur where the now-unglued rib just barely contacts the soundboard. Often, if you hear a buzz when playing an older piano, most prominent in one section of your keyboard, this loose rib is the cause. Fortunately, it is often a straightforward repair to work some glue between rib and soundboard and draw the two of them together with a screw, which can later be removed
Below we can see some examples of cracks running through a grand piano soundboard, then across the back of an upright soundboard:
In later posts, we will talk about completely rebuilding older top-name grand pianos, what’s involved and whether it’s truly worth it. It cetainly involves installing all new hammers and damper and other felts, and competely restringing the piano, often with a fresh new pinblock. Many fine technicians know how to do these replacements, and consequently offer their services as a piano rebuilder. But almost none of these have the skill and heavy equipment necessary to replace the entire soundboard of a piano…it’s really a factory job. So it’s critical that each technician measures how much crown is left in the current soundboard, because restoring all the rest of a piano that has a flat or soon-to-be-flat soundboard is certainly a waste of much time and money.
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