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.

I bought a small little used Yamaha made piano about 6 months ago. The Eterna ER-10 is a well built, inexpensive piano which was manufactured in Japan in the 90′s. The previous owners hadn’t had the piano tuned in over 10 years. The piano was a quarter tone flat, which isn’t that terrible considering the fact it hadn’t been tuned in such a long time. Once I got the piano in my house I proceeded to give the piano a pitch raise. It is often recommended to let the piano sit and accustom to the new humidity level for a couple days before tuning. The piano, which was a quarter tone flat, was enough out of tune that it wasn’t going to make much of a difference whether I tuned it immediately or whether I waited. Besides, a pitch raise is merely a rough tuning to get the piano up to an approximate pitch of A=440Hz. I gave the piano the pitch raise and then let it sit for a couple days.

I gave the piano a good solid tuning a few days later which lasted about a month. Certain unisons began to go out and the overall pitch had fallen a couple of cents in that month. A cent is 1/100^th of a semitone which on the whole wouldn’t be that noticeable to the average ear, while the unisons being out would be noticeable. I put another solid tuning on the piano which lasted another month before the summer humidity began to kick in and the piano’s pitch moved sharp, as well, unisons had audibly gone out of tune with themselves, though there were fewer then the previous time. I proceeded to tune the piano again, this time leaving the piano a couple cents sharp. I did this knowing that come fall, the piano will move back down to proper pitch.

The audible sign of tuning instability is unisons going out of tune. On each treble note there are three strings. When they go out of tune with each other you will notice a sometimes audible whine or warble. The unisons on my piano have been stable since that last tuning and it has been longer then a month. When a piano hasn’t been tuned in a number of years, the piano loses it’s tuning stability. The wooden soundboard and bridge become accustomed to the tension exerted by the strings which may be flat by a quarter tone or more. When they are forced back up to their proper tension being A=440Hz a resulting instability is created. The wood is fighting the new tension as well as the steel string. When I do a pitch raise on a piano, I leave the piano perfectly tuned, though in the coming weeks the piano will try to adjust to its new tension and unisons will undoubtedly go out.

Conclusion:

A piano which has had its tuning neglected over a number of years may take 3-5 tunings to regain its tuning stability. Keep your piano tuned regularly at least once a year and you will enjoy a tuning that is more stable and lasts longer.