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Barry Baker The Digital Piano Soundboard
The Final Step in Paralleling the Acoustic Piano

Ever since pianos first became available as "digital," the goal has been to create a sound as close to a traditional acoustic piano as technology would permit. Early digital representations of pianos were fairly primitive by today's standards. But, like all technology, the results of digital replication gradually evolved over the years. Kawai's process of digital piano tone production, referred to as Harmonic Imaging, involves an interesting technique outlined here:


Besides sound, there are other elements of the acoustic piano that serve as a model for incorporation in the digital instrument, such as the mechanical feel ("hammer action") of the keyboard – a crucial part of a pianist's ability to successfully produce proper tones. Accordingly, many physical properties of the grand piano action were tooled for Kawai's line of digital pianos.

There's actually quite a bit that's fascinating about the key action's hammers, counter-balanced weights, and wooden key stick material that have found their way into many of Kawai's digital models. Here's a glimpse into the tactile side of the Kawai digital:


Now, let's return to the tonal aspect of a piano: To nudge the "acoustic experience" to the next plane in a digital, Kawai began contemplating, "what if..." in relation to a radical departure from the standard speaker system found in digital pianos.

When you meet a Kawai CA91 model digital piano face-to-face (looking at the front of the instrument), you'll see 88 keys in an attractive cabinet. But, let's take a walk around the back for a minute.

Just as every vertical acoustic piano has a soundboard that stretches most of the surface area of the piano's back, the CA91 digital, too has an expansive soundboard. However, it's not just a cosmetic accent. It's a "live" functioning basis for the piano's tone. You see, the soundboard is a speaker. To achieve this, there's a transducer mounted to the board. A transducer? We'll get into defining "transducer" in a moment.

In the CA91 digital piano, the so-called transducer takes everything you play at the keyboard and sends it directly to the soundboard. The soundboard then reacts by vibrating and producing sound waves in the same manner as a speaker cone would. This is a fascinating technology of tone production, because it mirrors the principal of the acoustic piano.

Tom Love, Electronics Marketing Manager at Kawai, has a most insightful manner of explaining a transducer and its function in the CA91 piano:

"When the strings of an acoustic piano are struck, the resulting vibrations are transferred, or transduced, onto the soundboard via the wooden bridge over which the strings are strung. You'll find bridges on all stringed acoustic instruments, from violins to guitars.

"In the case of the Kawai CA91, there are no strings, but a digital 'recording' of the sound instead. To transfer this electronic signal onto the soundboard (thus turning it into an acoustic sound that you can hear), the signal is sent to the transducer. Acting like the bridge on an acoustic piano, the transducer converts the signal to vibrations and transfers them to the soundboard, thus creating the warm acoustic sound that you hear." A fascinating analysis, Tom.

In terms of positioning the CA91's cabinet to achieve optimal listening results, one possibility is placing the piano so that the back of the cabinet (the soundboard part) is facing a wall (a common configuration for a vertical acoustic piano in a home). There's a certain warmth to "enclosing" the sound this way.

However, other situations may find the CA91 soundboard facing an open space, such as in a church sanctuary or school classroom. (Depending on the acoustical properties of the room, this "open space" placement for the soundboard may actually be preferable...experiment.) Either configuration is fine--against a wall or an open area. However, when sound waves strike a surface head on (like with the back of the piano against a wall), there is an acoustical effect vastly different from the projection of sound into an open space (when the soundboard faces a room).

Because these two circumstances produce radically contrasting tonal results, Kawai has found that it's helpful to make sound system adjustments to the CA91 that take into account the piano's position: To the left of the CA91's display screen are two "Menu" buttons. If you press the upper menu button, you'll see the function of "Wall EQ" displayed in the screen. The two buttons to the right of the display screen labeled, "Value," allow you to turn "on" or "off" this specialized equalization of the sound system, according to whether you have the piano's soundboard positioned directly against a wall (turn the function "on") or facing a more open space (turn the function "off").

The CA91 features dozens and dozens of sounds in addition to the piano (strings, organs, choir, etc.), as well as one hundred built-in drum patterns (for you to jam along with!). To support the tonal characteristics of these sounds while providing heightened "articulation" for the piano (that is, the upper frequency range), the soundboard's natural warmth is supplemented by six small speakers. Four of these speakers are positioned above the soundboard, facing upward, for direct tone. The other two are "tweeters," facing the pianist. Thus, the soundboard delivers the resonant sonority for the bass through the mid-range (as you'd probably expect a large soundboard to produce), while the small speakers render "crispness" to the tone. It's also important to note that the speakers are creating a stereo image for the piano and the other sounds.

When you play Kawai's CA91, I think you'll agree that the whole sound system works symbiotically to produce a tone that's in a different realm than the traditional speaker system. Because of the soundboard, you might call it more "organically-derived" listening.

If for no other reason than for the fun (and unique experience), I encourage you to take a listen to the CA91 piano live and in person...here's an easy way of finding one near you:


In closing, I hope you won't find it too forward of me to toot the horn of the CA91's success (after all, it's a piano--helpless in its ability to toot its own horn!). This instrument's sound system is so unique in design and tone that the piano won the prestigious Dealers' Choice Award for 2007 in the category of "Digital Home Keyboard of the Year" from Music Merchandise Review (MMR), a leading industry trade journal.

— Barry Baker

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