I've had this question awhile now and it seems that everywhere I go the pianos are not to the exact same matching tune. On one piano the middle C could be 261.63 Hz and than on the other it would be 262 Hz. Is it because of manual tuners or is it something else?
SIDE NOTE: All weather conditions were the same and both pianos were tuned on the same day.
Interesting question. The comments of the original poster imply these are quality pianos tuned by the same piano technician.
There are a number of reasons I can think of:
Pianos respond differently to temperature change. If the stage lights were turned off shortly after tuning, for example, they may have changed in different amounts. Or perhaps one is under stage lights and the other is not, or some similar effect? This can throw some notes off significantly, though a pianist may not notice if the overall pitch changes but the piano stays relatively in tune with itself.
Basstickler and Carl hint at the issue of false beating, which can cause a note to have an energy spectrum instead of a single, pure note. Tuning devices may distill it to a single displayed frequency but not fully explain what is going on. Tunelab has a real time spectrum analyzer and can make that clear. These notes tend to have a distinctive timbre. The effect may be that the "correct" frequency is a matter of judgement.
Replaced individual strings can give the same effect as described above, if they are not well matched in a bi/tri-chord on replacement.
Scale design is different across brands and models. The inharmonicity inherent in the design does not play a large factor in the midrange, but it can have an effect on the technician's choice of stretch, which can.
Not every technician tunes equal temperament, for both good and trivial reasons, depending. The approximately 2.45c difference in the cited example is well within the variance of different temperaments, see Jason Kantor
Even a technician attempting equal temperament will produce different tunings when applying the same techniques to different pianos. Pianos are just different, and give different strengths of partials, have varying friction points, different pin in block feel, etc., all of which can contribute to slight differences.
Tuning software (if the tuning was not done aurally) generally requires the taking of samples from the piano in order to build a tuning curve according to the software's internal model. If on one piano the sample was taken incorrectly (technician error), or was fooled (device in an audio standing wave null, or false beating) then its curve will be incorrect, possibly explaining the difference.
I agree 2.45c is likely not noticeable, though it could be, if combined with other errors in an accumulating fashion. I don't know if that's your situation. But in the end, are the performers and audience happy with the way it sounds?
The meticulously maintained grand pianos at major performance halls are certainly tuned accurately. As are the pianos of individuals who are careful to keep their instruments in top condition.
Unfortunately, a great number of pianos are not kept well. A lot of school and home pianos take a beating and are only serviced when they get unplayable. For these pianos, tuning is a battle. It's not like a guitar where you have just a few strings and you can simply dial them in to their correct frequencies. Pianos have way too many strings and various concessions have to get made to make the instrument sound in tune with itself. On an abused piano, it may be a difficult enough task to do this; trying to also get it all the way up to concert pitch may be too difficult to be worth it. If the piano is only going to be used as a solo instrument (common in the home), why does it matter if A=435 instead of A=440?
Not to mention that A=440 isn't even a universal standard.
I have built a few guitars in my time and I can tell you that even using Wood cut from the same block /from the same tree will give you a different sounding instrument. Material density and condition would be a factor, environmental conditions would be a factor. ( temperature humidity Etc.) even what the instrument is sitting upon could make a difference/ the room's acoustics. (I.e. a wooden floor) Since most people cannot afford an electronic tuning device to tune pianos I would suspect it was probably due to the 'human factor'. and if you can hear the difference in frequency that is that minuteyou need to get a job as a locksmith cracking safes. LOL
