When the audio system attempts to reproduce a sound louder than it can accommodate, it goes into "clipping" and produces a distorted version of the sound. One thing to remember is that even the most powerful instruments can be driven into clipping if played loudly with the volume turned all the way up. Aside from distorting the sound, overdriving the system can damage the speakers and amplifiers. The key is to set the volume no higher than 75 to 80% of its maximum level.
If you've already peeked at the specification charts toward the end of this book, you know that only a few digital pianos produce 100-plus watts of output power per channel (left and right). Many of the models that do have that much power also separate the low-demand treble frequencies from the power-hog bass frequencies by providing each frequency range with its own amplifier and speaker(s). A very few go so far as to divide the audio system into three separate subsystems, for the bass, midrange, and highs. These designs, called "bi-amped" or "tri-amped," can make a noticeable difference in sound and power efficiency by using amplifiers and speakers optimized for specific frequency ranges rather than sending the entire frequency spectrum to a single full-range audio system.
Because all of the digital pianos we'll consider in this publication have stereo audio systems, all discussions of speakers will assume matching left and right channels.
The least expensive digital pianos employ a single full-range speaker per side. While these speakers are typically described by the manufacturer as "full-range," they are in fact a compromise dictated by cost and, in the case of the most compact designs, space. While a full-range speaker may reproduce much of the 20Hz–20kHz frequency range required by the piano samples, those frequencies will not be treated equally. The frequency response of a speaker is judged not only by its range, but also by its "flatness," or accuracy. If we send to a speaker multiple signals at different frequencies but at the same volume level, then measure the speaker's output volume when producing those sounds, we will see the speaker's "frequency-response curve." The full-range speaker will usually be acceptably flat through the middle of the frequency range, but will fall off in volume at the upper and lower reaches of the spectrum. In other words, the speaker will not accurately reproduce the full range of the signal sent to it. This is not the result of poor speaker design. As a matter of fact, I'm frequently amazed at what the engineers can coax out of these speakers. But the fact remains that they are inaccurate, and in ways that color our perception of the instrument's sound. Even the best sample set is rendered unimpressive if the sparkling highs and thunderous lows are weak or missing.
For this reason, most upper-end models use three speakers, one of each optimized for the bass, midrange, or treble frequencies. Accurate reproduction of bass frequencies requires the movement of a great deal of air. This is accomplished by combining a relatively large surface area with a high degree of in-and-out movement. These bass speakers, or woofers, are largely responsible for our impression of an instrument's "guts."
At the opposite end of the frequency spectrum is the high-frequency speaker, or tweeter. The tweeter, which is physically quite small, is responsible for reproducing the nuances of the upper range of the instrument. Besides the obvious frequency difference between the outputs of the woofer and tweeter, they also differ in their placement requirements. Whereas low frequencies tend to radiate in all directions, the higher the frequency of the sound, the more directional it is, which means that the precise placement of the tweeter is much more important. Most of the low- and mid-frequency speakers on digital pianos are located below the keyboard because there's plenty of room there. The more directional nature of the high frequencies requires pointing the tweeters directly at the player's head, usually from somewhere on the instrument's control panel.
The newest twist in speaker systems — one that appears to be unique to digital pianos — is the soundboard speaker. This technology will be discussed in the article "Hybrid Pianos," elsewhere in this issue.
So we now have all the makings of a digital piano: a sound source, and the means to control and hear it. But none of the current crop of digital pianos stops there; all of them have additional capabilities. These extras range from a handful of additional voices to direct Internet access. Even if your current needs don't extend past the basics, you should understand the other features present on your instrument, and how they might surprise and lure you into musical adventures you've never contemplated. To continue, please read "Digital Piano Basics, Part 2: Beyond the Acoustic Piano."
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