At the top of this page we’ve included our video that compares the most immediate differences between these two uprights, tone and touch. That comparison sets the stage. This article goes deeper, looking at how design and construction choices shape what you hear, feel, and experience over long-term ownership.
The Boston 52 inch UP-132 and 51 inch Kawai K-500 are closely matched in size, placing them in the professional upright category. They are also manufactured in the same factory in Japan, which often leads to understandable questions about how similar these pianos really are.
The Boston line is designed by Steinway engineers and built by Kawai as an Original Equipment Manufacturer, or OEM. Kawai is hired to produce Boston pianos to Steinway’s specifications, using Steinway-directed designs, materials, and scaling concepts. Although the instruments are built in the same facility, Boston pianos are not Kawai pianos with a different name. Their design priorities reflect Steinway’s accumulated experience with musicality, durability, and long-term value.
The soundboard is the heart of an acoustic piano’s tone. Made of spruce, it converts string vibrations into the rich sound we hear. Its size, grain quality, and tapering all influence volume, sustain, and tonal richness.
The Boston UP-132 uses a solid, non-laminated spruce soundboard with straight, close grain and a tapered thickness from treble to bass. This tapering allows the board to vibrate more freely, especially in the bass, producing a fuller, richer tone with strong sustain. The design and material choices reflect Steinway’s long experience with diaphragmatic soundboards, a concept that gives enhanced resonance and balanced projection across the range.
The Kawai K-500 also features a solid tapered spruce soundboard, selected for its high-quality straight grain and natural resonance. Like Boston’s board, the tapering helps maximize vibrational response and contributes to a rich, resonant tone with good sustain. Kawai’s soundboard is a core part of its tonal design, supporting a broad dynamic range and expressive capability.
Both pianos use well-crafted, solid tapered spruce soundboards, however, Boston’s connection to Steinway’s design philosophy emphasizes lower string tension and a larger effective vibrating area, which can enhance warmth and sustain. The Kawai’s soundboard design focuses on balanced projection, responsiveness, and harmonic richness in a slightly more compact upright profile.
The piano action is the primary point of contact between the pianist and the instrument. Differences here directly affect control, repetition speed, long-term stability, and the overall playing experience. While both the Boston UP-132 and the Kawai K-500 are well-regarded uprights, they approach action design from very different philosophies.
At the core of the Kawai K-500 is the Millennium III upright action. This action incorporates ABS plastic and carbon fiber composite parts in several critical components. Kawai’s stated goal with this design is consistency and durability, particularly in environments where humidity and temperature fluctuate.
Kawai emphasizes that composite materials are less susceptible to dimensional changes than wood, which can reduce the need for regulation over time. This contributes to the K-500’s characteristically light and quick touch, which many pianists find immediately accessible, especially for fast passagework.
It is also worth noting that Kawai continues to use wood for keys and hammer shanks. This reflects a recognition that certain wooden elements still provide musical benefits that composites cannot fully replace.
The Boston UP-132 uses a traditional all-wood action designed under the direction of Steinway engineers. Wooden action parts expand and contract together in response to humidity changes. Because all parts move at the same rate, stress on glue joints is reduced. This is one reason all-wood actions have a long-standing reputation for mechanical stability when properly maintained.
Beyond durability, wood also behaves differently under tension than composite materials. Many pianists describe wooden actions as having a more organic resistance and a greater sense of connection to the hammer. This tactile feedback often becomes more apparent over long practice sessions and advanced repertoire.
The Boston action design reflects feedback gathered by Steinway engineers from music professors and conservatory environments. The goal was not just reliability, but a touch that supports expressive control over decades of use.
One of the clearest links between Boston and Steinway appears in the pinblock design, which directly affects tuning precision and long-term reliability.
The Boston UP-132 uses Steinway’s patented Octagrip pinblock, a design created by Steinway’s engineers. It is built from multiple layers of hard rock maple, laminated with the grain oriented in different directions. This structure creates more uniform torque on the tuning pins, allowing for a smoother pin turn and more precise tuning.
The Kawai K-500 uses a laminated hard maple pinblock, engineered to provide stable tuning and strong pin torque, which is standard for high-quality uprights. Kawai emphasizes consistency and durability in its pinblock construction, though it does not incorporate a patented torque-control system comparable to Octagrip.
In upright pianos, backposts are the vertical structural supports that run the full height of the back frame. They play a crucial role in stabilizing the rim and soundboard, resisting the immense tension of the strings, and helping maintain tuning and structural integrity over time. The size, spacing, and material of these posts contribute directly to how well a piano stands up to decades of string tension and environmental changes.
In the image showing both uprights from the back, the Boston UP-132 clearly has larger backposts than the Kawai K-500. This greater mass reflects a design choice focused on rigidity and longevity rather than material efficiency.
Videos and images are helpful, but tone, touch, and structure are ultimately felt, not described. The Boston UP-132 and Kawai K-500 reveal their real differences when played side by side, in the same room, under the same hands.
An in-person appointment allows you to explore how each upright responds to your touch, how the tone fills the space, and how the construction choices discussed in this article translate into a real playing experience.
Schedule a time to play both instruments with a piano consultant at our Newton or Waltham showroom, and take the next step in making a confident, informed decision.