I am certainly not a recording engineer or expert in this department, but I thought I’d post my results from a piano technicians perspective. I am also using more affordable microphones into an m-box protools setup.
Upright Piano Mic Techniques
I recently bought an inexpensive though well built used piano manufactured by Yamaha called an Eterna. I’ve been playing around with different mic techniques to capture the best quality of sound with this piano. I started off with a stereo pair of Behringer condenser mics. I pointed them diagonally away from each other using the included stereo mic adapter. I used a kick drum mic stand and perched it atop the piano with the lid down to ensure there was enough surface area for the mic stands base to find balance. If you are interested in recording your upright piano, get your piano technician to show you how to take off the front boards. I pointed the mics toward the place where the hammers strike the strings. One in the bass and one in the treble. You’ll get more attack sound there so it tends to be a brighter sound.
The sound was pleasant with a nice round top edge to it, however the noise floor was so high on the Behringer mics that I found the product unusable. The fuzz coming from the mics was as loud as the piano. This probably should have been expected considering the quality of the mics.
Next I decided to scrap the stereo sound and at least try and find a good mono mic position. I have a Rode NTK tube large diaphragm mic which I positioned in approximately the same place as the stereo pair had previously been. It captured much more of the nuances of my playing. Unfortunately it also captured too much mechanical action noise. The mics frequency response is maximized to meet the needs of capturing a complete vocal sound. The clicks from the action were probably the same frequencies as consonants in the human voice.
Thus, I took the bottom door off the piano and positioned the NTK underneath the keyboard action just to the right of the bass strings. This was to ensure the bass was not too over powering and to capture as much of the treble brightness as possible considering the mics position. The sound was much warmer and full though it lacked a certain clarity. It did pick up a touch of pedal noise though it wasn’t overly distracting.
I also have an older small diaphragm MXL mic kicking around. I had a listen to it just to make sure it had a usable noise floor, seeing that it is also an inexpensive mic. The noise floor was a lot quieter than the Behringers so I stuck it up above the keyboard action, pointing at the hammer strike point in the middle of the piano. I found the most usable sound from this mic formation. I got a gorgeous warmth and depth from the NTK below the keyboard and a nice rich and airy sound from the MXL above the keyboard. I panned the mic above the keyboard action 50% to the right and the NTK on the soundboard 50% to the left. A mixture of the two and I had captured the Eterna upright piano in a satisfactory way.