How often this needs to be done depends on how much the piano is used and the level of performance expected from it. Changes in action regulation occur so slowly that pianists generally remain unaware of them until they suddenly realize that their playing has become difficult to control. It may be years before the average amateur musician playing a piano in the home realizes this, but working concert instruments are regulated (and voiced) almost as often as they are tuned, and a fine piano in the home is no different if a professional level of performance is expected from it. The regulation will remain much more stable if very fine adjustments are made frequently, rather than infrequent wholesale changes made only in response to emergencies.
Piano actions have many points of adjustment that control the positions of the parts. The regulation procedure involves adjusting these so that each key feels the same when depressed. That may sound simple, but with keys being of different lengths, the hammers graded in size from bass to treble, hammer and action wear varying from section to section, and other variables, action regulation can be a daunting task involving thousands of steps. Most manufacturers provide regulation specifications for the actions of their current models; but for older instruments, when parts have been replaced, or when the pianist requests a particular touch, these specifications may no longer work and must be modified, which only increases the difficulty of the job.
Sometimes pianists’ complaints about the tone, such as a lack of dynamic range or power, or the inability to play softly, are best remedied with fine action regulation instead of voicing. In particular, power in the action is the result of accurate and close regulation, not simply the hardening of the hammers (a voicing technique).
The touchweight, or downweight, is the amount of force needed to depress a key to the point of escapement with the damper pedal depressed. Most manufacturers today aim for a consistent touchweight across the keyboard of 47 to 52 grams, with slightly more weight acceptable in the bass than in the treble, due to the heavier bass hammers.
In weighing off a keyboard, gram weights are experimentally placed on each key to measure its downweight; other, permanent weights, of lead, are inserted in or removed from holes drilled in the side of the key, to bring it to its proper downweight. A keyboard can be weighed off only after the action’s friction and geometry have been checked and corrected, and the action regulated. Frequently, after the fine regulating is finished, only minor weight changes are necessary to even out the touchweight.
Many touchweight problems are the result of installing replacement hammers that are heavier than the originals. Heavier hammers can be used, but the added weight must be offset by changes in action geometry, which will often necessitate replacing other action parts as well. Simply adding lead weights to the keys to counterbalance heavier hammers, even when this results in nominally correct touchweight, may make the action sluggish during rapid playing due to increased inertia in the action system.
Voicing, or Tone Regulation
When the action regulation and weighoff have been completed, the tone regulation can proceed. However, if the strings have worn deep grooves in the hammers, the hammers must be filed before action regulation and weighoff, because removal of so much felt reduces a hammer’s size and weight. Deep string grooves cause the tone to suffer, both from slight damping of the strings and because the hard, crusted felt creates noise on the attack.
After filing, the hammers must be fitted to the strings, a painstaking process that must be done before any needling of the hammer felt. Due to slight inconsistencies in the heights of the strings, the hammer angles, and/or any previous filing, tiny amounts of felt must be filed off the top surfaces of the hammers so that each hammer strikes both or all three of the strings assigned to it at precisely the same time. This ensures that all that hammer’s strings are put in motion simultaneously, which will greatly improve the tone. Some technicians might initially address this problem on a new or newly rebuilt piano by leveling the strings, but eventually this fitting must also be done by minutely filing or ironing the felt.
Once the hammers are filed and fitted to the strings, the actual work of setting the tonal level and evenness can begin. This is the part of the job most likely to require and benefit from customer input, to ensure that the customer’s tonal preferences are satisfied. If radical changes to tone are desired, I prefer to do several voicing sessions, gradually changing the sound each time. Between visits, it’s important that the pianist have an opportunity to listen carefully to what I’ve done, and to play-in the hammers to settle the felt.
Harder hammers produce a brighter sound, softer hammers a mellower sound, but many other shades of tone are possible between bright and mellow. Needling the hammers evens out the consistency of the hammer felt so that each hammer has the same amount of compression and tension and, therefore, should sound the same. Needling different areas of a single hammer will give different results; here, an experienced voicer can make all the difference.
Adding a hardening lacquer to the hammers can add body and depth to the tone. Some pianists prefer the brighter, more complicated sound of lacquered hammers, while others prefer a cleaner sound, without lacquer. Over the years, tastes in tone have changed significantly; in recent years, I have had fewer requests for a bright tone.