There are different types of voicing. Deep needling is pretty much a permanent change. Shallow needling wont last nearly as long, a lot depends on how much you are playing. Adding lacquer is also relatively permanent. Hammer filing and shaping will need to be redone regularly based on use and expectation. There are many different voicing techniques for different outcomes, so deep needling and hammer hardeners may or may not be appropriate. Your ear will also adjust to the ideosyncracies of your instrument as the voicing goes.
If you are playing Liszt and Rachmaninoff at a high level for 1 -2 hours a day, the voicing wont last as long as if you are playing Bach and Mozart. It also, as BDB pointed out, really depends on your taste.
Keith D Kerman
Bluthner, Mason & Hamlin, Steingraeber, Irmler, Breitmann, Stanwood Precision Touch Design, Rebuilds www.pianocraft.net
Thank you for the thoughtful reply.
I believe the voicing work done last summer was shallow needling and reshaping of the hammers. As I said, the results were very good, just not permanent.
Also, I want the piano to sound and play perfectly. All the time. (Even though I don't). My expectations may not be reasonable given the myriad of factors involved.