Voicing, or tone regulation, comprises a variety of techniques that technicians use to change a piano's tone. Most involve adjusting the hardness, density, tension, and surface of the hammer felt to produce a spectrum of tonal qualities ranging from bright to mellow. Slight repositioning of the strings may also be part of this process.
Voicing differs from tuning, which is the adjustment of the strings' tensions to produce the proper pitches. In voicing, it is the timbre of each note, not its pitch, that is addressed. Voicing must also be distinguished from action regulation, i.e., the mechanical adjustment of the keys and action for evenness of touch and response. However, a piano needs to be tuned and its keys and action regulated before being voiced because these procedures themselves clear up many tonal problems. For example, a piano can sound tinny simply because it is out of tune — something that no amount of voicing can correct. An inability to play softly may be caused by a poorly regulated action, which can make the touch difficult to control.
Why Pianos Need to Be Voiced
Any piano's sound will gradually brighten over time, as its hammer felts are repeatedly packed down by the impact of the hammers on the strings; it will need regular voicing to maintain good tone. Since hammer felt absorbs moisture, the tone can become mellower in more humid weather, brighter in drier weather. The voicing can become uneven when some notes are played more often than others. Heavy use of the una corda pedal in grands also causes the voicing to become uneven. I usually do some voicing during each tuning. If this is done consistently, the tone of the hammers will remain good until wear demands that they be changed.
Alexander Kobrin, the 2005 Van Cliburn International Piano Competition Gold Medalist, explains how an uneven tone can affect the performer. According to Kobrin, when the pianist can be distracted by notes that stick out or are weak in the scale, he or she has to remember which notes don't perform like the others. This inhibits the performance, and ultimately, the audience doesn't get the full benefit of the artist's interpretation of a piece. The student practicing on instruments with this problem will have much more difficulty performing on other instruments. Kobrin also states the need for young pianists to have a properly prepared piano for practice, because that is where they develop an appreciation for the quality of tone that, as future professionals or advanced amateurs, they will be responsible for producing.
Here are some terms commonly used by piano technicians, in the voicing context, to describe tone:
Timbre is the particular blend of harmonics in a piano's tone, or in the tone of a single note. The timbre is said to have color when it contains a blend of harmonics that is pleasing to the ear. The piano is said to have a broad spectrum of tonal color when the hammers are voiced in such a way that the timbre changes with minor differences in touch by the pianist, making accessible a broad range of timbres over the instrument's full range of volume. This is achieved by using hammers of very high quality that have been carefully voiced so that very slight increases in the speed of the hammer increase not only the sound's volume, but also, slightly, its brightness. Pianos with a broad spectrum of tonal color provide the pianist with a larger expressive range. However, producing the same degree of change in timbre for each hammer so that the voicing is even across the keyboard and throughout the piano's range of volume requires that the voicer be very skilled.
Bright describes tone with a concentration of higher harmonics. Bright pianos that have been properly voiced have a clear, clean, brilliant brightness that still has lots of tonal color, whereas pianos whose bright sound is a result of the hammers needing reshaping and voicing tend to lack such color. This latter, unpleasant brightness is described by terms such as brassy, metallic, glassy, and tinny. (Note that the word sharp is not used because it refers to pitch, not tone.) Making a piano brighter is referred to by technicians as voicing up.
A mellow tone has a stronger fundamental frequency and fewer upper harmonics. Pianos that sound mellow, but that still have articulation and color, are described as sounding sweet, round, dark, or rich; those whose mellowness is without these redeeming qualities can be described as dead, dull, weak, or without power. The latter kind of mellowness is the result of the instrument needing voicing or new hammers, or lacking in tone-producing capability for other reasons — such as worn bass strings, loss of soundboard crown, or poor scale design. Voicing pianos to be mellower is referred to as voicing down.
Hammers in European pianos, or by European hammer makers such as Renner and Abel, and those in Asian pianos, are generally harder than American hammers; e.g., those in older American pianos from the early 20th century, in current Steinway (New York) instruments, and from American hammer-maker Ronsen. European and Asian hammers are traditionally voiced by voicing down, American hammers by voicing up.
Even and uneven describe how similar or different the timbre is from note to note on the same piano. The process of evening out the timbre is usually a much faster one than making a wholesale change in the instrument's tone.
Big describes a piano sound with greater-than-average volume and projection (power) — the qualities needed, for example, for the sound to reach the rear of an auditorium. These factors are not usually problematic in pianos in the home, but are of critical importance in a concert setting. Power is primarily a function of the instrument's size and ability to sustain, the latter being dependent on the piano's design, and the composition of its rim and soundboard. But the choice of hammer can also greatly influence sustain and therefore power, and voicing can be used to improve these characteristics in a high-quality instrument with very good hammers. With instruments and hammers of lesser quality, sustain, power, and projection should be considered inherent in the design of the instrument, and amenable to little change through voicing.
It's important to distinguish brightness from power, but they overlap, especially in the concert setting. Concert instruments must usually be voiced brighter than home instruments in order to cut through the sound of an orchestra. Brightness can also partially substitute for power when the latter is lacking. But an overly bright instrument will lack color, and attempts to voice it down could sacrifice its power. Eric Schandall, an American technician living and working in Europe, describes the newer Hamburg Steinways as generally having a bigger sound than those of even ten years ago: "There is a wider envelope of sound and more variety of timbre. This allows more room to voice the piano less bright and still have a big sound, not relying on brightness in place of a big sound."
Similarly, Alexander Kobrin speaks about the larger spectrum of tonal color available in a piano with a big sound, and how that affects the choice of concert instrument. In comparing two concert grands, Kobrin says he would choose the one with the bigger sound and greater tonal color for Romantic works, but one with a clean attack and less color for Classical compositions.
Here are some of the techniques used to change a piano's tone:
Hammer shaping, filing, and sanding — This is the process of removing with sandpaper the grooves in the top of the hammer made by the impact of the hammer on the strings, and restoring the hammer's elliptical shape so that only the very small area of the crown at the top of the hammer strikes the string. When the grooves are very deep and wide, they not only damp the sound but also produce a louder impact noise, commonly characterized as metallic, brassy, or even woody.
Mating the strings and hammers — When a tenor or treble hammer doesn't strike its three strings simultaneously, the result can be buzzing or other odd sounds, as well as a loss of power. Mating the strings and hammers can be achieved by a combination of leveling the strings and sanding very small amounts of felt off the hammer crowns.
Needling the hammers — Careful insertion of needles into the hammer felt releases tension in the hammer and makes it softer, resulting in a mellower tone. Many techniques can be applied, with varying results. For example, needling the lower shoulder area can actually increase the volume of sound, while needling lightly into the crown of the hammer can make the sound sweeter on a soft blow. With older hammers that have hardened, lost tension and compression, or are excessively worn, the technician must be more cautious about making changes. Older hammers react more radically to needling, and could be very difficult to maintain at optimal levels if there is not enough felt left to work with, hastening the need for replacement.
Hardening the hammers — Lacquer solutions, typically thinned with solvent, can be applied to the hammer felt to increase its hardness and brighten the tone. Needling to even out the tone after the lacquer dries is then necessary. Applying lacquer is a highly skilled job for an experienced technician, who must make an informed judgment about the mixture, amount, and placement of lacquer for best results. One reason experience is called for is that using lacquer to increase a piano's power and sustain can actually make the tone worse if the tonal problem actually is in the soundboard and strings. Technicians call the adding of lacquer "building the tone"; for some manufacturers, such as Steinway, the use of lacquer is necessary to achieve the brand's traditional sound.
Ironing the surface of the hammer compresses the fuzzy surface and makes the hammer produce a cleaner sound. Though less common in North America, ironing of hammers is still done extensively in Europe, and can add moderate brightness without the use of chemical hardeners. In some cases, ironing hammers in very humid conditions will dry them out, making the action feel lighter and restoring the tone.
Voicing an older piano in which a new set of hammers has been installed is quite different from voicing a brand-new instrument. The pre-voicing and prep of a fine new piano at the factory by a skilled voicer can take days, and the technician servicing the piano in the field encounters hammers that have already been fully prepared. However, the technician who installs new hammers in the field must possess the skills of the factory and field technicians to be able to set up the hammers correctly, then voice them to the customer's preferences.
Tonal Considerations When Purchasing a Piano
I encourage customers, prior to shopping, to attend concerts and listen to high-quality recordings of the type of piano music they typically play in order to establish a concept of tonal aesthetics. Older voicers called it "having a sound in your ear" — that is, establishing a mental standard of what you like with which you can evaluate the tone of the instruments you encounter.
I recommend that you purchase a piano that, on the dealer's floor, sounds reasonably close to what you desire. Don't buy a piano with unsatisfactory sound based on a promise that radical changes in its voicing will make it sound good in your home. It's true that the tone will be different in your home due to differences in environment; e.g., carpeting and drapery instead of the dealer's hardwood floor and bare walls, as well as the rooms' different sizes. But you're buying a piano whose tonal goal has been established by the manufacturer and has been built to that standard; you shouldn't expect anything more than minor voicing in the home to even out the tone or make small changes in its brightness, If a greater change in the instrument's tone isattempted, it may well not be effective.
There's one exception to this: A large piano can, within reason, be voiced to sound good in a smaller space (though the opposite is unlikely to be true). I have many clients with 9' grands in their living rooms, and many piano studios in universities have one or two 7' grands in rather small spaces. The concern that a piano that large will be too loud can be alleviated by regulation and judicious voicing.
The above notwithstanding, it's probably best to err a little on the mellow side when purchasing a new piano. The really bright-sounding piano in the showroom will get only brighter with time. It's easier to maintain the tonal quality of hammers that start out mellow because, eventually, they will naturally brighten with use to the desired level, and will tend to stay at that level longer. Overly bright hammers will require more voicing maintenance over time, and in extreme cases, can be responsible for broken strings.
The better the piano, the more voiceable its hammers and the more malleable its sound. Manufacturers have to make decisions about materials as they increase or decrease the quality of the product to meet various price points. The hammers in the least expensive models just won't produce the quality of sound heard from the more expensive instruments. This can make separating a piano's voicing issues from its tonal potential much more challenging for the consumer.
In addition, because tone depends not only on the quality and voicing of the hammers, but also on the other sound-producing parts of the instrument (such as the rim, soundboard, and bridges), one should have realistic expectations about smaller, less expensive pianos. No amount of voicing will make an entry-level grand sound like a 9' concert grand. And because hammers tend to revert to their originally designed tone, scaling deficiencies in older or smaller models that may have been hidden by careful voicing may return as harsh changes in tone when the voicing deteriorates, exposing awkward transitions in the scale.
Following purchase of a piano, it should be ready for touch-up voicing and regulating after having been played for 50 to 100 hours, depending on repertoire and on how much playing and touch-up it received in the store before purchase. After that, the tone and voicing will evolve throughout the life of the hammers.
Choose a technician experienced in voicing your particular brand, especially for performance-quality instruments. Many manufacturers have specific tonal goals for their instruments, and technicians who regularly work with those brands' hammers are more attuned to their expectations — and the expectations of the client who has chosen that brand based on its tone.