When and How to Juice Yamaha Hammers

I was just recently preparing Yamaha CFIIIS for Simone Dinnerstein and got a note from her that the 6th octave didn't have enough sustain. I'd like to outline what I did to address the issue.

First I Checked the Regulation…

I made sure that the let-off was close but not so close that it could block even in the slightest and potentially dampen the tone. Next, I checked the hammer fit to the strings. I blocked the hammer to the strings by pressing up on the jack at the tender joint and made sure that all of the strings were muted equally when plucked. I checked the key frame bedding to make sure it was solid. I even tightened the action screws on the rails and the brackets. Lastly, I seated the strings to the bridge and even massaged the strings with a spinet shank. Since none of these actions yielded a substantial result the next thing to do was to inspect the hammer.

It Could Be the Hammer Then…

I say "inspect" because if the timbre of the hammer is pleasing then something related to the mechanics of the hammer might be the issue. By squeezing the hammer in the upper shoulders and also in the lower half by the staple you can get a sense of tension in the felt. You can also get a sense of how much needling the set of hammers has seen. When I squeezed the lower area by the staple I could feel that it was soft. My suspicion was that the hammers in this octave were a bit weak and so the lower area was "needled up" to increase their tone. A side affect of that particular voicing technique is a loss of dynamic range and potentially some sustain as well.

The Juicy Part…

Since you can't add tension back to a hammer, the only left to do in this case is juice the area. The idea here is to reinforce the felt fibers. Imagine that the hardener is coating the felt fibers and stiffening them. That's how we can get some tone back. I'm going to use plastic (PMMA or "poly methyl methacrylate") and acetone. You'll want be sure that your mixture looks similar to skim milk.

I concluded earlier that the bottom half of the hammer is too soft so I'll juice the lower hammer area by the staple and not any higher than 3 and 9 o'clock. Notice that these hammers have a reinforcement from the factory. That can potentially limit how effective our juicing will be (It's worth mentioning that needling the reinforced area of a hammer also produces limited results).

In this case it was enough and the artist was satisfied with the results. The juicing in combination with voicing for evenness did the trick.