Spring-loaded piano actions are the most basic of the 5 types, and are often found in portable keyboards, normally in the 61-note or 73-note configurations.  Very occasionally, pianos with 88 keys will offer this, but only by specialty. They offer minimal resistance, and do not simulate the sensation of an acoustic in any way, other than the overall shape and dimension of the key. They can often be found in hobby-like settings, or very young players who are not yet taking any lessons. As a rule, most piano instructors or schools will either refuse or strongly discourage the use of spring-loaded key actions on the home instruments of their students, since it is impossible to teach the muscle control needed for acoustic piano playing.

Waterfall actions are not particularly common, and were popularized by the home electric organ as well as the Hammond B and C series of electric organs. They normally offer no or little sensitivity to your touch velocity, and in some cases can even have a lighter touch than a spring-loaded ‘tab’ style key as discussed above. Typically not found on most hobby / beginner level instruments, and generally a highly specialized and esoteric application.

The most common 88 key action in the digital piano world. It also has the greatest variance in quality of components and engineering. Every major manufacturer currently makes several different quality levels of this type, however the basic design has been in wide-spread use for more than 30 years. It involves the use of a key connected to a counterweight, which simulates the resistance of an action. The use of the counterweight was first successful attempt to properly simulate the dynamic resistance of a real piano action.

One of the drawbacks of these actions is their relative complexity; the high number of moving components and impact points has translated into short shelf-lives under heavy usage, as the bushings, hinges, rubber pads, and springs tend to wear down, loosen, and in some cases break. The majority of improvements by manufacturers has been in the strength and overall durability of the action, as well as the authenticity of feel.

A recent trend has been the replacing of the actual key material with alternate materials such as wood, while maintaining the same overall geometrical design as before. This has lead to a great deal of confusion in the marketplace regarding these “wood” actions, particularly in comparison to Yamaha’s higher end wood actions of the N-series, and Kawai’s CP/CA series, both of which use wood, but of an entirely different design.

What began as an experiment nearly 25 years ago on a single stage piano model, has now grown into an industry-leading design from Kawai. The principal was a fairly simple one: they took acoustic keys off of their upright production line, built a simple key-bed with the same overall elements of an acoustic (balance rail, front pins/bushings, key punchings, cap-stand), and then attached it to a simple hammer mechanism instead of a full repetition, which then struck a sensor. Kawai has continued to develop the concept and now includes it on their MP10, CA series, and most of the CP series of pianos. Whether it is primarily cost, or patent issues which have kept other manufacturers from exploring this is unclear, but popular reception of this design seems uniformally positive within online communities.

The most ambitious, and by far the most expensive action, is Yamaha’s full repetition actions now equipping their N/NU series of digital pianos. Rather than simulating an acoustic action, it simply is an acoustic action, complete with full reptition, whippens etc. For a digital piano with 88 keys, this is the ultimate, however it comes with a price tag more consistent with an acoustic.  They are fully regulating, nearly 100% authentic actions. From a technical stand point, it’s hard to find fault anywhere. The high price point will keep this out of reach for most customers unfortunately; they match or exceed the price of their acoustic equivalents.