There's an interesting post on PW about Steinway's "accelerated action", which has been a marketable selling point for their NY instruments for many years, compared with the Renner action Hamburg uses. Steinway has recently unified production from both factories to use the Renner action and has since phased out the NY accelerated action. Apparently, this was done due to artist preference. Ed Foote gave some great insights:
Greetings,
A common misconception about the "Accelerated" action was that the acceleration was referring to repetition speed. It was not. It refers to the half-round fulcrum under the key, which changes the action ratio (in theory) as the key is depressed, thus, accelerating the hammer's speed towards the string. In practice, this would work if the balance rail pin was slightly offcenter in the half-round so that the fulcrum would effectively move proximally during the stroke. Many of these actions appear to have the hole in the center of the fulcrum, so any accelerating of the action's ratio is minimal at best.
The the other half of the accelerated patent called for the key leads to be placed as close to the balance rail as possible, but I did not see that being practiced on the production line, so who knows.
The Hamburg pianos were far more consistent than the New York ones, and their factory prep, as well as adherence to the design of the actions and pianos was far closer than the Astoria pianos.
The modern piano actions, either Hamburg, New York, Kawai, or Yamaha can all, if properly regulated, repeat faster than a human can move (near 14 times per second), so when pianists say this or that piano is faster, it is usually due to how they are adjusted, not how they are designed.
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I'm having a NY Steinway D rebuilt, and now I'm curious if it'll be rebuilt with the accelerated action or without it. If there are any rebuilders here yet, have you ever rebuilt a NY Steinway with a Hamburg-like Renner action? How were the results?