Piano Wippens blog post

How Action Design Affects Piano Touch & Performance Piano action design plays a critical role in how an instrument feels and responds to a pianist’s touch. The weight and geometry of action components determine the touchweight (the force needed to depress keys) and the ability to execute fast repeats or delicate dynamics. Modern grand piano actions are built on the double-escapement principle (invented by Erard in 1821 ), which uses a complex assembly of levers to allow rapid note repetition and fine control. Below, we examine five key design factors – repetition lever weight, key length, material of action levers, hammer weight, and stack height – and how they influence touch and performance. Comparisons between different piano design schools (European, American, Asian/Korean) are included to highlight various engineering approaches. Illustration: Diagram of a modern grand piano action (English double-escapement type) with major parts labeled. The pianist’s finger presses the key (1), which pivots and raises the capstan (2). The wippen (3) (whippen) transmits this motion to the jack (5), pushing the hammer (10) toward the string. Just before striking, the jack escapes from under the hammer butt, allowing the hammer to fly freely. The repetition lever (9) supports the hammer as it falls back, enabling a note to repeat even if the key is only partially released (the core feature of double escapement). Other parts like the drop screw (7), hammer shank (8), backcheck (11), and damper mechanisms (12–15) work in concert to reset the system and damp the string. Small adjustments in this mechanism’s design or weights can significantly change the piano’s feel. In general, most well-regulated grand actions have a downweight (force to press a key) around 50–60 grams and an upweight (force the key returns with) around 20 grams . The action leverage or action ratio (hammer travel to key travel) typically ranges about 5.3 to 6.0:1 , and it must be balanced with hammer mass and key counterweights to achieve the desired touch. With this overview, we can delve into each focus area: Repetition Lever Weight and Repetition Speed The repetition lever (also called the balancier) in a grand action is the small horizontal lever that lifts the hammer via the jack and supports it for quick repeats. Its weight and moment of inertia directly affect repetition speed and responsiveness. A heavy repetition lever requires more force (from springs or gravity) to reset quickly, potentially slowing down the action’s return and making the touch feel less snappy. By contrast, a lighter or more optimally balanced repetition lever can improve repetition by reducing the mass the key must overcome when repeating notes rapidly. • Repetition Speed: A grand piano can repeat a note faster than an upright partly because of the repetition lever mechanism – it allows a hammer to be re-struck when the key is only halfway up, rather than fully released as in an upright . However, if the repetition lever is too heavy, the key’s return (upweight) might be insufficient for very fast repeats. An action can only repeat as fast as the key returns to position, which is why technicians target at least ~20g of upweight for good repetition . Upweight is largely provided by the falling mass of the hammer and repetition assembly pushing the key back up . Excess lever weight or friction will diminish upweight, slowing key return. In practice, about 20g upweight is a minimum for reliable rapid repetition – any drag from a heavy repetition lever or tight center pins will reduce this, capping the repetition speed. • Inertia vs. Weight: It’s not just the static weight, but the moment of inertia of the repetition lever that matters. Modern action designers (e.g. Wessel, Nickel & Gross and Kawai) have addressed this by using lighter or stiffer materials for these parts. Notably, composite repetition lever and wippen assemblies can be engineered with lower rotational inertia even if their total weight is similar to wood . In one comparison, an advanced composite repetition lever (WNG) had slightly lower effective weight at the key interface than the best wooden parts, when measured in a lever test . By concentrating mass near the pivot and using lighter materials, the lever’s rotating mass is reduced, allowing quicker movement . This means the repetition lever can lift and reset faster, directly improving repetition speed and the responsiveness felt by the pianist. • Touch and Responsiveness: A lighter, well-balanced repetition lever makes the action feel more responsive to small key movements. The pianist can play trills and rapid note repetitions with less effort, because the key doesn’t have to fully rise to re-engage the jack under the hammer knuckle. Historically, the introduction of the repetition lever (in Erard’s double-escapement action) was credited with facilitating rapidly repeating notes – a revolution in touch that allowed techniques impossible on earlier single-escapement (Viennese) actions. If a repetition lever is overly heavy or its spring too weak, the pianist might feel a sluggish or “dampened” return, making quick passages harder to execute. Technicians will often adjust repetition spring tension to compensate, but an optimal solution is to design the lever to be as light and friction-free as possible without sacrificing strength. Comparative Approaches: Most European and American grand actions use wooden repetition levers (often hardwood). These are finely balanced, but can vary in weight. American makers like Steinway traditionally used wooden parts with an eye toward durability, sometimes resulting in slightly heavier actions. Japanese makers Yamaha and Kawai standardized very consistent repetition springs and part weights, yielding reliably fast repetition in their pianos. Kawai in particular moved to composite (ABS-carbon) repetition levers in its Millennium III action, achieving lighter parts that are 25% faster in key return than traditional designs. This faster return is directly linked to easier repetition and “effortless” touch in fast passages. Korean-built grands (e.g. older Samick or Young Chang models of the 1980s) often copied Western action designs but sometimes ended up with heavier repetition assemblies and springs that made their out-of-the-box touch a bit stiff. In recent years, many of those designs have been refined (some even incorporating parts from Renner or WNG) to lighten the repetition, bringing them closer to the European/American standard for fast repetition. Key Length and Leverage (Evenness & Control) The length of the key (often called the key stick) – from the front where the pianist presses, to the back where it meets the action – has a profound effect on leverage and touch. A piano key is essentially a class 2 lever, pivoting on the balance rail pin. The ratio of the front length (forward of the balance point) to the rear length (between balance pin and capstan) determines the mechanical advantage the pianist has in moving the action. Longer keys generally yield greater leverage, more control, and more even touch across the keyboard. • Leverage and Power: Lengthening the key gives the player more leverage, meaning the same finger force produces greater force on the action. As one piano reviewer explains, “Just like any other lever, as you extend the lever, you’re able to apply more force with the same amount of motion or pressure, increasing the dynamic potential of the instrument” . In practice, a longer key allows the pianist to play more powerfully (louder) without feeling as much resistance, because the key amplifies their input. For example, when Kawai lengthened the keys by nearly one inch on their 5′11″ GL-40 grand (compared to the older RX-2 model), they noted an immediate improvement in the piano’s dynamic range and ease of playing forte passages . • Control at Soft Dynamics: Extended key length also improves control, especially in soft playing and at the top of the key (closer to the fallboard). With more leverage, the pianist can finely modulate the force – the key doesn’t “fight back” as much – which is crucial for pianissimo and nuanced expression. Testers of the GL-40 noted the longer keys “improve the speed of repetition as well as the control you have in the lower dynamic range”, making it easier to play quickly and very softly . In general, a pianist will find an action with long keys more responsive to small variations in touch. • Evenness Across Keyboard: One challenge in piano design is ensuring that the touch feels consistent from one end of the keyboard to the other. On many small grands or uprights with shorter keys, the extreme bass and treble can feel different – often heavier and less controllable – than the center, because the keys in the extremes are shorter (or effectively shorter due to the geometry inside the case). Longer keys mitigate this. They maintain a more uniform leverage ratio for all keys, including the black keys and the far ends of the keyboard. This reduces the common issue of the uppermost notes feeling “stiff” or the bass keys feeling “wooly” to the touch. High-end European grands like Bösendorfer or Fazioli often emphasize their extended key sticks. For instance, the Bösendorfer 214VC (7′ model) has longer keys than smaller Bösendorfers, explicitly to achieve a more even touch and greater control similar to a concert grand. American Steinway concert grands (Model D, 8′11″) also have very long keys – considerably longer than those in a baby grand – which is one reason concert pianists find them more even and responsive than smaller instruments of the same brand. • Downsides and Practical Limits: “Generally speaking, there are almost no downsides whatsoever to extending a key,” notes one expert . The main limitation is simply the size of the piano’s cabinet – smaller grands physically cannot accommodate very long keys. Key length behind the fallboard is one of the reasons a larger grand requires more depth. In the Kawai GL-40 example, the piano itself was made an inch longer purely to fit the extended keys . Thus, in design, makers strike a balance: a compact baby grand (under ~5′) will have shorter keys and inevitably a slightly compromised action leverage, whereas a concert grand (~9′) will use the longest keys feasible for optimal touch. From a technician’s perspective, key length and action spread (the lateral spacing of action rails) also tie into regulating aftertouch and even voicing, but the fundamental point is that a longer key provides a mechanical advantage to the player. Comparative Approaches: European makers have long pursued longer keys for their top instruments. For example, Fazioli prides itself on actions with very even touch across all 88 notes, partly due to careful key stick design. Yamaha and Kawai both advertise “extended length keys” on many models to simulate the control of a larger grand even in mid-size instruments . Yamaha’s mid-size C3/C5 grands and Kawai’s SK/EX series all have key lengths optimized for balance. Historically, some American pianos in the mid-20th century (like certain Baldwin models or smaller Steinways) had slightly shorter keys which, combined with heavy hammers, made the touch weight in the high treble quite high. Modern American designs (e.g. Steinway’s latest redesigns or Mason & Hamlin) have addressed this with improved key geometry. Korean and other Asian manufacturers initially followed whatever design they inherited or copied – e.g., a 5′2″ Korean grand from 1985 might feel uneven compared to a German 5′8″, partly due to key length differences. But today, thanks to global design knowledge, even these manufacturers often incorporate longer keys in larger models and promote the evenness of touch. In summary, key length is a key factor (no pun intended) in providing the pianist with leverage – the longer the key, the more power, control, and uniformity a piano can offer, all else being equal . Wood vs. Composite in Action Levers (Weight, Feel, Stability) Traditionally, almost all piano action parts – keys, wippens, repetition levers, hammer shanks, etc. – have been made of wood. Wood was used because it’s light, can be very strong (especially hard maple, hornbeam, or beech in critical parts), and was readily available. However, wood parts come with variability and issues related to climate. In recent decades, manufacturers have explored composite materials (plastics with carbon fiber) to address these issues. The choice of wood vs. composite for action levers significantly affects the weight of the action, the touch feel, and long-term stability. • Weight & Strength of Materials: Different woods have different densities and strength-to-weight ratios. For the keys themselves (the long wooden levers the pianist presses), many manufacturers historically used fir, sugar pine, or basswood, which are relatively light softwoods. Yamaha, for example, uses Sitka or Japanese spruce for its keys – the same high-quality spruce used in soundboards – because it has “virtually free from warpage and [an] excellent strength-to-weight ratio” . Spruce keys are both lightweight and stiff, which gives a nice solid feel without excess mass. Keys need some mass (to convey a sense of substance under the fingers) but not so much as to slow repetition . Other action parts like wippens and repetition levers are typically made of hardwood for durability: common choices are hornbeam, maple, walnut, or mahogany, which can be machined thin yet remain strong. Interestingly, for hammer shanks and moldings, lighter woods are preferred – “light woods such as walnut, mahogany and hornbeam are commonly used for hammers. The lighter the wood, the faster the hammer can accelerate” . This highlights that reducing weight in moving parts (hammers, levers) improves speed. A lighter hammer shank or repetition lever can start and stop more quickly, contributing to a more responsive action. • Feel and Inertia: The materials used influence the action’s overall inertia and touch. Heavy or dense woods in the keys or wippens will raise the action’s static touchweight (requiring more lead counterweights in keys to compensate) and increase its dynamic inertia (making the action feel sluggish in fast motion). Conversely, lighter materials yield a lighter feel and faster response, assuming the parts are strong enough not to flex or break. This is where modern composites come in: ABS plastic infused with carbon fiber (used by Kawai) can be made into action parts that are lighter than wood but also extremely rigid. Kawai reports that by using ABS-Carbon for action parts, they “reduced their weight, facilitating a faster overall action – a crucial element for control during rapid note repetition or trills” . The reduction in mass directly translates to an action that feels more agile under the fingers. Pianists often describe composite-action pianos as having an “effortless” or “quick” touch, partly due to this weight optimization. • Stability (Humidity and Wear): Wooden action parts are sensitive to humidity changes. Wood can swell or shrink with seasonal changes, affecting critical tolerances – keys might stick, center pins might tighten (causing sluggish keys) or loosen (causing wobble or noise). According to Kawai, “wood is susceptible to breakage from continual stress and can shrink and swell dramatically with changes in climate,” which can “impair a piano’s tone and touch” over time . They introduced ABS parts precisely to combat these issues. Composites like ABS-Carbon are impervious to humidity shifts, so the action regulation remains stable year-round . Additionally, wooden parts rely on cloth bushings for pivot points (which can develop friction issues like verdigris over decades if old lubricants react with copper in the cloth), whereas composite parts often use self-lubricating polymers or precise tolerances to maintain low friction without traditional felt bushings. In terms of wear, composite parts are extremely durable – Kawai notes their ABS-Carbon is “over 50% stronger” than the equivalent wooden parts. This means they are less likely to break or deform under heavy use (like repeated glissandi or percussive playing). For piano technicians, this stability can mean less frequent need for regulation adjustments and fewer issues in very damp or dry environments. • Feel and Sound Considerations: Some pianists and technicians note subtle differences in feel or even sound between wood and composite actions. Wood has a certain damping characteristic – it can absorb a bit of vibration – whereas hard composites might transmit more shock or noise. Early composite actions (and Steinway’s ill-fated Teflon bushings in the 1960s) drew some criticism for feeling a bit different (some said “plasticky” or too quiet mechanically). However, modern implementations have largely resolved these issues, and any difference in feel is minor compared to the benefits in consistency. The mass distribution is far more critical: for example, Wessel, Nickel & Gross (WNG) composite wippens are designed so that their weight is distributed optimally. Even though the flange of their wippen is heavier (due to composite material) than a wooden flange, the overall lever has lower inertia, because they removed weight from the moving portions . The net effect is a lever that feels light and responsive. From a tonal standpoint, the choice of wood vs composite in the action doesn’t directly change the piano’s tone (which is more influenced by hammers, strings, soundboard), but it can affect how connected a pianist feels to the production of sound. A well-regulated action, wood or composite, should provide predictable control of the hammer – that is the ultimate goal. Comparative Approaches: European makers have traditionally stuck with wood for actions (often using high-quality spruce for keys and hornbeam or beech for actions). They rely on precision craftsmanship and seasonal adjustments to manage wood’s quirks. For instance, Blüthner and Steingraeber tout the resonance and tradition of wood actions, and some technicians feel there is a familiar “organic” feel to these. American makers like Steinway experimented with improving wood action stability – notably Steinway’s Teflon action (1962-1981) replaced cloth bushings with Teflon to avoid friction changes. While the Teflon itself didn’t swell or shrink, that experiment had mixed results (Teflon could click when gaps emerged). Steinway returned to traditional felt bushings, but with improved seasoning of wood and climate-controlled factories, modern Steinway actions are quite stable if maintained. Japanese makers led the composite charge: Kawai’s use of ABS (from the 1970s) and ABS-Carbon (from 2002) is a major departure from wood. They advertise “ABS-Carbon produces more dynamic power, greater durability, improved control and unparalleled speed” compared to wood . Yamaha, on the other hand, has mostly stayed with wood, but with extremely careful material selection (e.g. Yamaha’s keys are spruce for high-end models , and they use hardwood (mahogany) for hammer cores to keep weight low). Yamaha actions are famously consistent – a result of precise machining and treatment of wood to reduce variance. Korean/Chinese manufacturers initially used cheaper woods (sometimes lower-cost pines or even plywoods in actions), which led to heavy, inconsistent touch and more susceptibility to humidity. In recent years, many have improved: for example, Pearl River (China) now uses maple and spruce in critical parts and some carbon fiber in its higher models, and Samick has models featuring Renner (German) actions or parts to elevate performance. Overall, the trend in the industry is toward maintaining the beloved touch of wood while leveraging modern materials to solve age-old problems. A striking example is the hybrid actions in some pianos (like Steingraeber’s optional carbon-fiber shanks, or Mason & Hamlin’s use of WNG composite parts in rebuilds) – these combine wood keys with composite levers or shanks to get the “best of both.” A technician evaluating an action will always consider the material of the levers because it informs how to regulate and voice the piano for optimal feel. Hammer Weight and its Influence on Touchweight and Tone The piano’s hammers are where mechanics meet music – their weight and design affect both the touchweight (heaviness/lightness of the action) and the tone produced when they strike strings. Hammer weight is usually graduated across the scale (heavier in the bass, lighter in the treble), but the overall weight profile and how heavy the hammers are relative to the action’s leverage is a crucial aspect of design. • Effect on Touchweight: Hammer mass is one of the largest contributors to key resistance. The keys must lift the hammers (through the intervening levers), so a heavier hammer will require more force. In fact, there’s a roughly linear relationship: “A 1 gram increase in hammer weight causes a 5–7 gram increase in both downweight (D) and upweight (U), and vice-versa” . This rule of thumb is widely appreciated by piano technicians. For example, if you replace a set of hammers with new ones that are 1g heavier each (not uncommon if say original hammers were heavily filed/lightened over time), the keys might suddenly require ~5g more force to press – a very noticeable change, often making the action feel heavy or fatiguing. Likewise, as hammers wear and are filed smaller, they lose weight; even a 0.25g reduction from filing can reduce downweight by about 1.5g . Over many filings (say 1g total lost), the touch can lighten by 5–10g , which is why an older piano sometimes feels “lighter” than a factory-new one. Because of this, designers carefully match hammer weight to the action ratio and key leverage so that downweight ends up in a desired range (often ~50g midrange). If hammers are too heavy for a given action, the manufacturer must add a lot of lead weights to keys to compensate – achieving the target downweight but at the cost of increased inertia. In the Spurlock analysis, it’s noted that if a high action ratio piano (more hammer motion per key motion) uses heavy hammers and then lots of key leads to offset the static weight, “the action will feel terribly heavy when played fast” due to the added inertia . A better approach is to use lighter hammers or fewer leads, even if static downweight measures slightly higher, because the action will feel lighter in motion . This highlights that heavy hammers can make an action feel sluggish, especially in quick passages, whereas appropriately light hammers keep the action lively. • Tone Production: The weight of the hammer also influences the tone and volume the piano can produce. Heavier hammers carry more momentum for a given velocity and can drive the strings harder, yielding greater potential volume and often a richer tone, especially in the bass. However, simply making hammers heavier is not a free ticket to big sound – beyond a certain point, a too-heavy hammer can actually reduce efficiency (the key can’t throw it fast enough) and can create a muffled tone if the hammer is so heavy that it doesn’t rebound quickly. Manufacturers balance hammer weight and hammer felt hardness to voice the piano. Lighter hammers, on the other hand, require less force to get moving, aiding the pianist in playing fast and softly, but if too light, the piano might lack power or sound thin. This is why concert grands often have heavier hammers than small grands: the large soundboard and longer strings can handle and benefit from that extra hammer mass to create a full fortissimo. For instance, American Steinway hammers (especially the NY Steinway hammers) have been known to be relatively heavy and hard (as voiced from factory) to maximize the powerful American tone. Technicians sometimes even lighten Steinway hammers by filing or swapping for slightly lighter hammer sets to achieve a more responsive touch without greatly sacrificing tone. In contrast, some European makers (like older Bösendorfer or Blüthner) used slightly lighter hammers made of softer felt – this contributed to a lighter touch and a warm, singing tone, albeit with somewhat less raw volume. It’s a tonal philosophy difference: American = bold sound, willing to accept heavier touch; European (historically) = more transparent sound, lighter touch. • Dynamic Touch and Control: Hammer weight affects the dynamic control a pianist has. A heavier hammer provides more resistance which some pianists like when playing loud – there’s something to “dig into.” But that same resistance makes pianissimo harder. Very light hammers make the action feel easy in quiet playing but can feel lacking in substance when playing loud. Upweight is also largely the hammer weight returning: heavier hammers will increase upweight (good for repetition up to a point) but only if the repetition lever and springs can support them. If the hammers are too heavy, you might see the repetition lever not catching the hammer properly (because the spring can’t push it up in time), leading to “babbling” notes on fast repetition. Thus, an overweight hammer can actually hinder repetition if not balanced by an appropriately strong repetition spring – but a too strong spring then makes the action stiff on the upstroke. Everything is a balance. From a builder’s perspective, the ideal is to use the lightest hammer that still produces the desired tone and volume. Modern hammer felt technology allows even lighter hammer molds (wood cores) with hard-pressed felt to produce big tone without as much mass. For example, Yamaha and Kawai pianos often have slightly lighter hammers than Steinway, but their felt (and voicing techniques) can still generate brightness and volume. This contributes to the characteristically lighter Yamaha touch. On the flip side, if a piano’s hammers are replaced with the wrong spec (too heavy), it can “end up ruining the touch response”, as even a few grams off can make the piano feel extremely heavy . One must match replacement hammers to the original weight spec or be prepared to re-weight the action accordingly. Comparative Approaches: American pianos historically favored heavier hammers with denser felt – part of the American “big tone” ethos. Steinway, Mason & Hamlin, and old Baldwin pianos often have substantial hammer mass. They rely on skilled weighting of keys (with lead) to keep downweight reasonable, typically aiming around 52–55g. When regulated well, these can feel solid and controlled, but if anything is off (friction high, or keys not adequately weighted) the pianist will notice heaviness. European/German pianos (Bosendorfer, Bechstein, etc.) tend to use slightly lighter hammers with a bit more bounce; Renner (a German hammer/action supplier) offers various hammer weights and many German scale designs opt for a middle ground that yields a refined touch around 48–50g and a singing tone. Asian makers calibrate hammer weights carefully: Yamaha designs its hammers in gradient, and part of why lower notes have higher downweight is that bass hammers have more felt mass which adds weight, whereas treble hammers are tiny. Yamaha actions are known for uniformity – each hammer’s weight is exactly as needed for its string, producing a very even grading of touch from bass to treble (heavier touch in bass, lighter in treble, but smooth). Kawai took a different path by combining somewhat heavier hammers with their lighter ABS action: the Millennium III action can thus produce a warm, strong tone (hammer mass contributing) while the lighter wippens and shanks keep the touch from feeling too heavy. Korean pianos in the past sometimes had inconsistencies here – e.g. a mid-90s Samick might have hammer weights copied from a Steinway design, but an action ratio not adjusted for it, resulting in a heavy touch. Over time, these companies have improved by consulting scale designers and often using hammer sets from established suppliers (like Abel hammers from Germany or Japanese hammer felt). Today’s mid-tier pianos from Asia typically achieve standard touchweights and don’t suffer the extreme issues of older mass-produced instruments. In summary, hammer weight is a pivotal factor: it must be orchestrated with the action mechanism. Too heavy, and the pianist feels like lifting a barbell (and may get a louder but harsher tone); too light, and the pianist might enjoy the easy touch but at the cost of tonal body. The best pianos find the sweet spot where the hammers are as light as possible for agility, yet heavy enough to pull a full, beautiful sound from the strings. Technicians often measure strike weight (the weight of the hammer plus shank as felt by the key) and will modify or swap hammers during rebuilds to optimize this if the original design missed the mark. Stack Height and Action Geometry (Regulation & Responsiveness) The term “stack height” in a grand piano refers to the vertical position of the action stack (the assembled action mechanism: keys, wippens, hammer flange rail, etc.) relative to the strings and keybed. In simple terms, it’s how high or low the action sits. This geometric parameter, along with related dimensions (key dip, hammer blow distance, let-off, etc.), has a big impact on how the action regulates and feels. Even small deviations in geometry can cause an action to feel wrong – too shallow, too deep, or sluggish in response. • Geometry Basics: In a well-designed action, the hammer blow distance (distance from hammer to string at rest), the key dip (how far the key travels down), and the points of let-off and drop are all coordinated. Stack height comes into play here: if the entire action is set too low (far from the strings), then the hammers have to travel farther to hit the strings. The technician might then have to increase key dip (so keys push hammers higher) to compensate, but too much key dip can cause the touch to feel sunk and slow (and as Spurlock notes, very low action ratios or geometries require “deep key dip and short hammer blow” – a compromise scenario). Conversely, if the action stack is too high (close to the strings), the hammer blow distance is short – the piano may feel shallow (little aftertouch) and possibly lack power because the hammer can’t accelerate enough. There is an ideal range (for many grands, blow distance ~1.75″ and key dip ~10 mm) that yields proper aftertouch and dynamic control. • Regulation Issues from Improper Stack Height: A mis-set stack height can make certain regulation steps impossible. For example, one technician working on a Steinway Model B found “it’s impossible to get the jacks to align with the knuckles… without making the hammer blow over 2 inches or having the hammers rest on the rest felt”, and considered raising the stack slightly to fix the geometry . In that case, the factory geometry might have been off due to a slight error in hammer boring or action spread, and the remedy was to shim the action brackets (raising the whole action by 1/16″) so that jack and knuckle met correctly at the point of let-off . This illustrates that even a small discrepancy (1/16″) in stack height can throw off jack alignment and let-off timing. With the stack at the correct height, the jack will properly reset under the hammer knuckle after a note is struck, enabling smooth repetition. If too low, the jack may stay too far and not reliably re-engage (causing misfires on repeats); if too high, the jack may jam into the knuckle or not escape cleanly (causing aftertouch to vanish or notes to block). Another way stack height shows up is in the aftertouch – the slight additional key travel after the hammer lets off the string. Proper aftertouch (a few tenths of a millimeter) gives the pianist feedback and ensures the repetition lever catches the hammer. If stack height or action spread is wrong, aftertouch can be zero (the key stops dead at let-off, very unforgiving feel) or too much (wastes motion). Technicians often adjust stack height in restorations by shimming the keybed or action rails to dial this in when other regulation parameters are maxed out. • Action Ratio and Lines of Convergence: Stack height is part of the overall action geometry that includes the “lines of convergence” – imaginary lines through the key, wippen, and hammer that ideally intersect near the string. When a piano is built, the geometry is set so that at the point of hammer strike, the alignments are optimal. If the stack (which holds the wippen and hammer flange rails) is moved, it changes where these lines meet. A higher stack moves the hammers closer to the keys, effectively increasing the action ratio (slightly) and altering how energy is transferred. A lower stack does the opposite. Designers use these adjustments to fine-tune an action’s feel. For instance, some rebuilders of older pianos will intentionally raise an action stack slightly and rebalance things to increase hammer leverage, making a formerly stiff action play better. However, one must be careful: any change in stack height means recalibrating let-off, drop, and possibly key dip to maintain the proper escapement timing. • Responsiveness: Assuming the piano is regulated to spec, a correct stack height yields the crispest response. The pianist will feel a clean key escapement (a slight “notch” of let-off followed by a bit of aftertouch cushion) and the note will respond immediately when the key is depressed. Incontrast, an action with poor geometry might feel either mushy (if blow is too long and aftertouch too great) or brittle (if blow is too short and there’s no cushion). In extreme cases, improper stack height can even cause double striking (hammer bobbling against the string) or blocking (hammer getting caught against the string without enough momentum) because the timing of the let-off vs. hammer travel is off. Thus, the stack height indirectly affects consistency of touch and tone – each note regulated at correct geometry will behave the same. Comparative Approaches: Most manufacturers have standardized geometry for each model, and they usually get it right in the design stage. European makers often design actions with slightly shallower key dips and moderate aftertouch, which some pianists find faster (but sometimes harder to control at very soft dynamics). American makers historically favored a tad more aftertouch – which can give a comfortable feel – at the expense of a bit more key travel. These differences are subtle. Where we see big differences is in older pianos or certain designs: Spinets and consoles (small uprights) infamously have compromised action geometry (drop actions, etc.), resulting in a less responsive touch. On grands, Steinway in the mid-20th century sometimes had variations (as seen in the Steinway B example) that required correction by techs; Steinway has since refined its manufacturing to avoid such issues. Asian makers like Yamaha and Kawai place great importance on precise geometry – Yamaha actions are often praised for being “textbook” in regulation out of the box, meaning stack height and all parameters are spot on, contributing to their consistent feel. Korean grands made in the 70s/80s might not have had the benefit of such precise engineering – some had issues like shallow blow distance to make the pianos more compact, resulting in a hard touch. But again, modern designs (often supervised by or copied from experienced scale designers) have corrected these. An interesting innovation in recent years is the use of adjustable action brackets (e.g. bolts that allow slight height tweaking) in some high-end pianos or restorations, giving technicians a way to fine-tune stack height without shims. In essence, stack height and action geometry are about aligning the mechanism for optimal performance. When correctly set, the pianist shouldn’t have to think about it – the piano will feel responsive, even, and controllable. When mis-set, the action will fight the pianist in subtle or not-so-subtle ways. It’s a testament to piano engineering that in a well-scaled instrument, all these geometric factors coalesce so that each note has the same reliable “feel” – enabling the artist to play with confidence from the lowest A to the highest C. Design Philosophies: European vs. American vs. Asian Throughout the above discussions, we’ve hinted at regional or manufacturer-specific philosophies in action design. While every piano is unique, broad trends have historically distinguished European, American, and Asian (particularly Japanese/Korean) piano design approaches: • European Tradition: European makers (Germany, Italy, Austria) often emphasize refinement and balance. They tend to use high-quality traditional materials (spruce keys, hornbeam or beech actions, wool felts) and aim for a lighter, very responsive touch. For example, a Hamburg Steinway or Bösendorfer might come from the factory with downweights in the high 40s (grams) and extremely smooth repetition. European actions (many built or designed by Renner) commonly feature lighter hammers with softer press felt, long key sticks, and meticulous hand-finishing. The result is a touch known for sensitivity – great for nuanced control in soft playing – and an even feel across the keyboard. The stability of wood is managed by climate seasoning and precision (Renner, for instance, ensures their wood parts are properly aged and machined to tight tolerances). European pianos also sometimes incorporate innovative ideas: Fazioli uses a Renner action but with small custom tweaks (like titanium hammer shanks in some cases) to further lighten the action inertia. Steingraeber offers optional carbon-fiber shanks to reduce hammer weight. These show a willingness to improve repetition and lightness without abandoning wood elsewhere. In summary, the European school values an action that a pianist can “float” on with ease, with clarity of tone – often requiring less brute force and rewarding finesse. • American Approach: American pianos, epitomized by Steinway (NY) and historically Mason & Hamlin, Baldwin, etc., have aimed for power and durability, sometimes at the expense of a heavier touch out of the box. Steinway’s design, for instance, uses quite heavy hammers (for tonal power) and a moderate action ratio ~5.5:1. Factory Steinways might measure ~55g downweight in the middle – a tad heavier than some European counterparts – which some artists like for its robustness in fortissimo playing. The American ethos often is that a pianist can work with a slightly heavier action, and it will hold up under hard playing. Steinway also infamously tried Teflon bushings to combat humidity issues, showing a penchant for innovation – though that particular idea was not well-received by technicians due to noise issues (the clicking when no friction at all). American actions traditionally use rock maple or similar hardwoods for action parts, ensuring longevity (many 100-year-old Steinways still have original actions functioning). That said, American makers have evolved: Steinway now uses accelerated action (a subtle alteration with shaped balance weights) to improve repetition, and others like Charles Walter (an American maker) adopted composite parts from WNG to modernize their actions. The Mason & Hamlin pianos, now made with some composite action parts, show that the line between American and other schools is blurring, with emphasis on both power and improved touch. So, one might say American pianos aim for a bold tone and a solid feel – and with modern tweaks, they’re managing to achieve a lighter touch while preserving that character. • Asian (Japanese/Korean/Chinese) Approach: Japanese makers Yamaha and Kawai have become two of the most influential in action design. Yamaha’s approach is very much about precision engineering: they use jigs and machines to ensure every action is nearly identical, and they choose materials scientifically (e.g. Yamaha’s use of spruce keys vs. others using basswood is a conscious quality choice ). Yamaha actions typically have medium hammer weights, medium action ratios, and very consistent regulation – resulting in what many call an extremely reliable and predictable touch (neither notably heavy nor light). Kawai took a more radical approach with its ABS-Carbon actions, prioritizing speed and stability: their design claims a 25% faster action response due to lighter parts, and indeed many pianists feel Kawai grands have an especially quick repetition and a slightly lighter touch than a Steinway of similar size. Kawai also markets the longevity and climate stability – their actions won’t stiffen in high humidity or loosen in low, a big selling point for institutional pianos. Korean makers (such as Samick, Young Chang, and their various sub-brands) in the late 20th century often based their actions on American or Japanese designs. Early on, some had a reputation for a heavier touch – possibly from using somewhat heavier woods and not finely balancing the keys. For example, a 1980s Young Chang grand might have downweights in the 60+ gram range, which is high. Over time, these companies hired consultants to improve their actions. By the 2000s, many Korean and Chinese pianos come with actions designed by Renner or using parts from companies like Louis Renner or Abel. As a result, their touch has become more in line with Western standards. It’s not uncommon now to find a 6′ Korean-made grand with a perfectly respectable 50g/20g weight and good repetition. Some Asian makers have even partnered with or bought European brands to acquire that know-how (e.g. Young Chang’s association with Pramberger, or Pearl River’s joint venture leading to the Ritmüller premium line with Renner actions). • Key Differences Today: In modern high-end pianos, differences in action feel have narrowed. A concert pianist can jump between a Steinway (American), a Fazioli (European), and a Shigeru Kawai (Japanese) and find all of them responsive – each with a slight unique touch flavor, but none feeling out of place. Those differences: European might feel a tad lighter and quicker on release, American a bit more resistance and “grunt” in fortissimo, Japanese extremely even and smooth. Lower-tier or older designs still show differences: a well-worn 1920s upright from Europe might have a very light touch and soft voice, whereas an old American upright might feel like a truck spring but produce a big brassy tone. Asian entry-level pianos from the 1980s often were heavy and inconsistent, but current production has improved vastly. In summary, European builders lean toward touch refinement and tradition, Americans blend power with innovation (willing to try new tech to improve actions), and Asian manufacturers have moved from imitation to innovation, now driving some of the most stable and fast actions in the industry. All these approaches seek the same goal: an action that allows the pianist to produce the desired sound with ease and reliability. For the piano technician or builder, understanding these design choices – repetition lever weight, key length, materials, hammer weight, stack geometry – is essential to maintain or improve any piano’s performance. A well-designed and well-regulated action is the product of countless such choices, each contributing to the instrument’s ultimate touch and tone. Sources: • Spurlock, “Grand Action Touchweight” – technical paper on action ratio, hammer weight, and touchweight . • Yamaha Music (hub.yamaha.com), “Piano Tonewoods” – on woods for keys and hammers . • Kawai Piano Technical Info – ABS-Carbon action benefits (faster repetition, stability) . • Merriam Piano Blog – Kawai GL-40 extended key benefits . • Piano Technicians Journal – Wessel, Nickel & Gross on composite action parts (weight vs inertia) . • Lynn’s Wagon blog – Diagram and explanation of grand action parts . • Living Pianos – Article on action weight and regulation factors . • Piano Technicians Guild resources – on repetition lever function and regulation .