The Influence of Solid Wood Soundboards vs. Composite (Laminated) Soundboards on Sound

June 30, Mr. Huscher

There are fundamental differences between solid wood soundboards and composite/laminated soundboards in pianos in terms of structural construction, acoustic performance, and physical stability.

Differences in Structure and Manufacturing Process

Solid wood soundboard: Typically made from edge-glued strips of quarter-sawn softwood (most commonly spruce, such as Sitka spruce or European spruce), each strip being approximately 10 cm wide. This type of soundboard exhibits enormous stiffness along the grain direction but is considerably weaker across the grain, resulting in pronounced anisotropy.

Composite (laminated) soundboard: Usually constructed by gluing face layers and a core layer together at specific angles, forming a three-ply or multi-ply structure. The core layer of a composite soundboard can be arranged with vertical, horizontal, or diagonal grain orientation, with the grain directions of the face layers and core layers alternating with one another.

Effects on Acoustic Vibration and Sound (Timbre)

Acoustic power and frequency response: In the mid-to-high frequency range above 1 kHz, solid spruce soundboards exhibit significantly stronger vibration and acoustic response than composite soundboards, radiating approximately 3 to 5 decibels more acoustic power. Overall, composite (plywood) soundboards have lower acoustic efficiency, with notably weaker bass response compared to solid wood soundboards.

Regularity of vibration modes: The vibration modes of solid wood soundboards (such as nodal line patterns) are primarily oriented along the longitudinal direction of the glued strips, appearing more regular and symmetrical. In contrast, due to the complex grain angles across the various layers, the vibration modes of composite soundboards are less regular and less symmetrical, making it difficult to simply determine their vibration patterns.

Uniformity of tonal consistency: If plywood is used as the soundboard, although its performance in the low-frequency range is similar to that of solid wood, its acoustic radiation characteristics undergo a drastic change in the high-frequency range. This abrupt shift in radiation mechanism is undesirable in musical instrument manufacturing, as it disrupts the uniformity of volume, sustain, and spectral structure across different notes of the piano.

Differences Across Piano Sizes: In smaller upright pianos, where the string and soundboard dimensions are inherently limited, the tonal differences between solid wood and composite soundboards are not particularly pronounced. However, in larger pianos, the sound quality of solid wood soundboards is noticeably superior—to the extent that even a solid wood soundboard with minor cracks can outperform an intact composite soundboard.