Its sound and piano action!
The fact remains that the acoustic piano remains the first preference for a lot of pianists because of its authentic and rich sounds.
The most expensive pianos will produce the richest of sounds and will have the best piano action.
The word piano is derived from the word pianoforte, which simply means "soft and loud". Basically it refers to the pianos ability to produce sound at different dynamic levels.
An accomplished player can use this ability of the instrument, along with the use of pedals, to deliver an awesome performance.
The only reason for people to opt for a digital piano as opposed to an acoustic one would be the additional costs and efforts associated with maintaining the instrument.
You will need to get your Piano tuned regularly... at least every six months.
Grand Pianos, on the other hand, may not be a viable option for many because of its cost and the space needed to keep it.

Acoustic Pianos come in two types – Grand Pianos and Upright Pianos.
All the Upright Pianos are of the same size but a Grand Piano can come in varying sizes (width) depending on whether you want a Grand or a Baby Grand piano.
These are wider in size because the strings (which produces the sounds) are parallel to the ground and they move away from the keyboard. This makes the Grand Piano, a larger instrument.
A concert Grand will be around 3 meters in width (away from the keyboard).
Since the strings are parallel to the ground, the sound produced travel upwards and spreads throughout the room creating a better sound.
Ideally, a Grand Piano will need a room with higher ceilings for better resonance. That’s the reason you will find most Grand Pianos kept in halls and bigger rooms.
Most manufacturers even make smaller Grand pianos, normally referred to as the "baby grand" pianos. These pianos are around 1.5 meters wide and are used for domestic purposes.
Piano lovers who just do not want to settle for anything less, can consider Baby Grand Pianos.
These are much less wider compared to Grand Pianos as the stings are placed vertically i.e. parallel to the walls.
They have been designed to save on space and are comparatively easier to move around.
You need to make sure that you do not keep your upright piano very close to the wall. This will ensure that the sound resonates properly giving a better sound.
Piano lovers, not inclined towards digital pianos, and for whom, cost and space are important considerations, can consider going in for upright pianos.
You can read more on types of pianos here...

Discuss the various acoustic piano brands, their offerings and comparisons.
Click on the link below to read user experiences of the various acoustic piano brands, and their offerings. These were posted by visitors to this page.
Grand Piano Guide 




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