Most of the “high-end” pianos use the low-tension scale design. Pianos such as Steinway & Son, Baldwin, Bosendorfer, Bluthner, and C. Bechstein use low tension designs. The cornerstone of a low tension scale design is a dense rim. Most of the pianos in this category use dense woods such as hard rock maple, and beech wood, although there are other variations to these two woods. The use of a dense rim allows the sound to resonate in the case, which in turn allows the manufacturer to place less tension on the strings. The less tension on placed on a string the more it can vibrate therefore the longer the sound will sustain.
Most of the “entry level” pianos use high-tension scale designs. These pianos use softer, less expensive woods in their rims. Woods such as Philippine mahogany are soft and absorb sound into the rim itself. In order to preserve the sound output in pianos with soft wood rims the manufacturer pulls the strings tighter. This increased tension produces a tone that is brighter and more strident in tone. When a string is pulled tight it cannot vibrate as much so the sustain is rather short.
Many people talk about differences is soundboards. There are a few different aspects that can be talked about in soundboards. The number of growth rings per square inch is sometimes addressed. The theory says the more growth rings the better the sound, a piano with 10 to 13 growth rings per square inch tends to be considered the best you can get. However, my experience using this guide has not been very impressive so I hesitate to even mention this. There are several other factors that would outweigh the growth ring theory. Solid spruce soundboards are considered to be the best for sound transfer and resonance. Most pianos in production today use solid spruce soundboards so this is not something that will really guide in one direction or another when looking for a piano.
The ribs of the soundboard are perpendicular to the grain of the wood. This allows them to help the vibrations become distributed across the soundboard faster. They also help keep the soundboards shape, which is concave, not flat.
The piano uses a harp or plate to hold over 20 tons of string tension in place. There are two types of plates on the market today; a sandcast and a v-pro plate. The solid or sandcast plate does not participate in sound production, and is the plate most used in “high-end” pianos. The solid sandcast plate is made using a sand cast procedure which requires a thicker more dense plate, this also allows any air bubbles in the molten metal to work their way out leaving only metal. Sand Casting plates therefore allows the manufacturer to produce a piano with a more solid and pure tone without getting ringing from the plate. The v-pro plate production is like flash freezing, allowing air bubbles to get trapped in the metal. When producing a v-pro plate the manufacturer can produce a much thinner plate then required when building a sand cast plate. These plates will ring and will typically interfere with the pure tone of the piano.
There are three different types of actions, a drop action, a direct action and a grand action. A spinet piano uses a drop action and is the least responsive action on the market, because it has the most moving parts. The direct action is the best vertical action and is used in consoles and studios. This action is quicker, with less moving parts it allows faster repetition. The grand action used in both baby grands and grands is the most responsive action using gravity more and relying less on springs then the drop and direct actions.
The action is one of the most subjective areas when choosing a piano. Some people like a very heavy action others like a very light action. My opinion for those who are just learning to play the piano is to try to find an action somewhere in the middle. An action that is too light will not give the player enough resistance. A pianist who plays a piano with very little resistance will have a hard time playing softly. There must be enough resistance to allow a wide range of dynamic control.
One notable action on the market is the Renner Action. Renner is a German manufacturer of actions, and their actions are used in some of the finest instruments in the world. I mention Renner with a hint of caution. Many piano companies imply a full Renner action when only a few parts are made by Renner. Also Renner makes actions to order so a Renner action in a ‘high-end” hand made piano is probably not the same Renner action found in an entry level piano. The regulation of the action by a highly skilled technician can sometimes make more of a difference then a name brand action.
The pinblock or rest plank is the section of the piano where the tuning pins are held in place. This section of the piano has over 20 tons of pressure on it. The pinblock is usually made of several layers of hardwood to handle all of this pressure and tension.