Ask those with experience in placing microphones for piano recording and the chances are you will hear of it being an art form rather than a reproducible technique. There is truth in that – as the variables are endless. On the other hand there are some tried and tested methods, or rather some useful guidelines, for placing various forms of cardioid phantom-powered condenser microphones.
Our experience with an upright piano is demonstrated in this Chopin and Bach link. We used three microphone pairs and selected a mix of each in the final editing. The open lid in an empty church was a bit heavy on the echo though.
For jazz groups and for gigs where instrument sound separation is required for later mastering, close ‘miking’ is essential – but might not be best for smoothness and ambience suited to quieter or classical music situations. Under those conditions, a pair of mics at a half to one meter distance (fully open lid) will give very decent results. However, if there risks to be people noise, then closer placement might still be necessary.
Here is a set-up which we used for a 2017 jazz group recording – a single pair of Neumann condenser microphones. Actually the sound was excellent; results here. Rules of thumb: place microphone pair above where the high and low strings cross – spread apart for better width pick-up – raise for more body.
A Swiss Radio (RTS/Espace 2) recording we attended at studio 15 in Lausanne – Enrico Pieranunzi trio – piano with 8 mics. (this blog update, 24Oct2017) :-
DPA’s “d:vote” microphone stereo kit for piano — Esteban Castro at Montreux and manufacturer’s image :-
At the AMR/Sud des Alpes concert room with the Grupetto :-
An in-piano microphone experience (2014): straight pair Audio Technica.