What’s the Difference Between an Acoustic and a Digital Piano?

ACOUSTIC PIANOS

Overview

These pianos produce sound when felt hammers (mallets), triggered by pressing keys, strike metal strings.  The resulting string vibrations are “amplified” by a large, thin sheet of wood called a soundboard.  Essentially, the soundboard is a wooden speaker. 

Each key on a piano is linked to:

  1. A single, metal wrapped “bass” string.
  2. A pair of strings
  3. Three strings.

String groupings 2 and 3 are referred to as unisons, because they are typically tuned to have the same pitch or sound.

Acoustic Piano Types

There are two types of acoustic pianos. A grand has a soundboard and cabinet that’s parallel to the floor.  The most common grands range in horizontal length from five to over nine feet. 

A vertical‘s soundboard and cabinet stand upright, hence the generic name “upright” given to these pianos. 

Strictly speaking, an upright is the tallest class of vertical piano produced today, approximately 49″-52″ inches in height.  Moving downward in size, studios are ~45″-48″ and consoles are ~”40″-44″.  Spinets (~33″-36″), which have a very poor tone, are also difficult to tune properly.  As a result, they are no longer produced.

Insider Tips: Under no circumstances should you purchase a spinet piano or accept a free one for your child’s musical study.  The minimum size vertical you should buy, which has respectable tone quality and the key response to the touch of the fingers, is a Studio.

Internal Functionality of an Acoustic Piano

The keys of an acoustic piano are linked to the hammers with an elaborate mechanism known as the action

Grand Piano Action Diagram

In a grand piano, the keys are about two times longer than they appear externally; the remaining portions are inside the piano.  When considered as a whole, the two portions are referred to as keysticks.

Specifically, they act like seesaws whose leverage is transferred via the action to the hammers.   In a grand piano, the hammers move up towards the horizontal strings for each key/note.  In a vertical piano, they move forward towards the upright strings.

An important feature of an acoustic piano action is the escapement.  This is the point where the hammer, being pushed by a wooden post in the action called a jack, flies free of the jack and immediately strikes the strings linked to a key/note.  At medium volume levels/downward key speeds and below, the escapement point occurs prior to the key hitting bottom.  In particular, if it’s moved very slowly, you can sense a bump in your fingertip, which is the feeling associated with the hammer releasing from the jack inside the action.

When playing loudly, which requires moving the keys downward very quickly, they can hit bottom before the hammers strike the strings.

An acoustic piano also has dampers, which are blocks of wood with felt bottoms.  When a key is in its resting position (not held down), dampers touch the string/s for the associated note.  When the key is pressed, its damper rises, allowing strings to vibrate when struck by the hammer.  When the key is released, the damper falls back down onto the strings, silencing their sound. 

Pressing down the damper pedal of an acoustic piano—the one on the far right—raises all the dampers at once.  As a result, notes played one after another sustain without being held by the fingers.  This allows notes linked to widely spaced keys to overlap, producing harmony..

Use of the damper pedal also enhances the piano’s tone, making it rich and airy.  The resulting effect is often called “pedal resonance” or “pedal wash“.  This occurs because there are no dampers resting on any of the strings.  In turn, strings not struck by hammers vibrate along with strings for notes that are played.  This phenomenon is called sympathetic vibration.  

At one time, the damper pedal was called the “loud pedal” because the volume of the piano increases when it is pressed down. This term is rarely used today.

Acoustic grand pianos also have an “una corda” pedal, which is the leftmost of the three pedals.  It moves the entire set of hammers and action parts a small distance to the right. As a result, you can actually see the keyboard moving in that direction. In turn, the hammers strike:

  1. Two strings of three-string groups
  2. One string of two-string groups
  3. Single strings off center

Since the portion of the hammer felts striking the strings is fresher (less compacted) than normal, the tone is mellower. Since the portion of the hammer felts striking the strings is fresher (less compacted) than normal, the tone is mellower. In addition, striking fewer strings or striking them off center reduces the volume of notes.  This explains use of the colloquial term “soft pedal“.

In a vertical piano, the leftmost pedal usually moves the hammers closer to the strings. As a result, the volume is lower, but the tone change is not as dramatic as heard on a grand piano.

DIGITAL PIANOS

Overview

These pianos consist of a piano keyboard, pedals, a “computer”, amplifier and speakers. 

The computer contains recordings of acoustic piano notes (samples), or synthesizes notes electronically as they are played (Roland’s term for this is modeling).  Either is triggered when keys are pressed and played through the speakers.  

Since a digital piano doesn’t have strings or a primary soundboard, the damper pedal effect is synthesized electronically.  As a result, it lacks depth and realism..

Advances in Digital Piano Technology and Performance

Formerly, major drawbacks of digital pianos were their fake sound and relatively crude actions.  In particular, the keys were plastic with a hinge at the far end. Thus, their key leverage feel and control were grossly inferior to that of an acoustic piano.

Nowadays, digital pianos, such as the Casio PX-870 (our top entry-level recommendation), have a surprisingly realistic sound. 

In addition, some have wooden, weighted keys, triple key-speed sensors for better touch response in terms of volume changes, escapement simulators, etc. In many cases, the inherent digital piano key leverage problem has been compensated for with advanced features, making it much less noticeable. In the best cases, where all these improvements are implemented, you can barely tell that you’re playing a digital vs. an acoustic.

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