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This is quite a common question that I’ve been asked over the years. My usual response is “not much” because in reality, there isn’t much of a difference. My Yamaha U3 and U1 pianos are reconditioned to the same standards regardless of whether they are from the 70s or 80s, so they are all put back in the same condition. In terms of the sound of the pianos, I have found them to be very much similar and when there are differences in sound from one piano to the next it doesn’t seem to the case that age is the relevant factor. You can have three Yamaha U3s or U1s from 1983 sat in a row and one will sound bright, the other will sound mellow and the other will be somewhere inbetween.
So I don’t treat age as a significant factor when trying to make general rules about pianos of a certain age.
HOWEVER, having said, I do often find that a 1980s piano will often have slightly (only slightly) clearer tone in the bottom 2 octaves. Some people like this extra clarity whereas others prefer a softer, mellower tone in the bass.
There are 2 main factors which affect the tone of a Yamaha U3 or U1 and none of them relate to whether the piano was made in the 1970s or 1980s. The first factor is the voicing of the hammers. It is possible to treat hammer felt in such a way that it produces a bright, medium or mellow tone. This is useful if you are worried that the piano may be too powerful for your home because you can “tone it down” a touch.
The other factor affecting the tone is the soundboard. I suppose cheap, modern pianos will have quite predictable tone as they are now made with sheets of plywood instead of solid spruce wood as is found in top end pianos such as the U3 and U1. Solid spruce soundboards have their own unique character due to the fact that no 2 pieces of wood are the same. The soundboard’s job is to amplify the vibrations of the strings and in doing so it will add it’s own character into the mix. Therefore, 3 identical Yamaha U3 pr U1 pianos will all have slightly different tonal characterists and that includes whether the piano is bright, medium or mellow.
In conclusion, try not to worry too much about the age of the piano. If you like a fraction of extra clarity then you might like an 80s U3 or U1. If you like a slightly softer sound then you might find that a 70s U3 or U1 is more suited to you.
If you have any further questions about any of this or if you’d like to pop by to visit my pianos please email me at firstname.lastname@example.org