Hi all and Happy New Year,
John Foy is the one doing the voicing on a Steinway D in North Carolina. It's not a teaching video. Just something I sent to a friend. Now that I see it's being picked up by others I'll add more info.
The technique utilizes a single wide angle needle on the crown might and might be best described as "Deep Sugaring". Sugar needling is usually done with multiple thin needles over the crown of the hammer at a shallow depth and is often used just before a concert to sweeten the tone. It does not last long. Deep Sugaring is a more vigorous technique and lasts a long time. Using a wide angle sharp needle point prevents the needle from going in deeply and killing the tone. The wide needle angle assures that the felt fibers at the surface are stretched apart vigorously making the felt quite a bit softer. The depth of the effect is easily controlled by the force of the blow with the voicing needle. The inclusive angle of the needle is 13 degrees and is a chart compass needle. 78 RPM needles also work. The method expands the pianissimo range without killing the fortissimo. It also creates purer unisons by cushioning the initial impact of the string against the hammer felt.
The method can work miracles on modern hammers that are pressed with a lot of heat. The heat irons the surface of the felt and makes it hard. This destroys pianissimo tone. My favorite quote for what we try to achieve in hammer felt is by Alfred Dolge in his book "Pianos and their Makers". Alfred Dolge is the Father of the Modern Piano Hammer (Post 1875)
“The art in hammer making has ever been to obtain a solid, firm foundation, graduating in softness and elasticity toward the top surface, which latter has to be silky and elastic in order to produce a mild, soft tone for pianissimo playing, but with sufficient resistance back of it to permit the hard blow of fortissimo playing.”
The Ball Peen hammer method might be described as a "Hammer Limbering" and the tool itself as a "Limbering Hammer". It is an adjunct to Deep Sugaring method, or as a stand alone method.
Merriam-Webster: Limber is an adjective which means - "Having a supple and resilient quality" It's also a verb which is to make something more limber.
The heat ironing that is on modern hammers (Post WWII) also reduces the resiliency and springiness of the wool felt fibers which is an essential quality for producing beautiful tone. The ball peening works to vigorously move the fibers to make them more limber. It simulates "Playing In" the voicing. Yamaha teaches a similar technique when needling which is to let the heel of the voicing tool hit hard against the surface of the hammer. This has the effect of opening the tone. One can see the effect by taking a strip of felt which is supple and flexible and ironing it to make it stiff and more dense. Working the felt by vigorously by hand, bending and flexing strip will restore the suppleness by restoring the limber of the fibers.
I first came upon the technique when I tried to kill the awful tone of a little short keyboard Caberet piano I had in a little room. The tone was loud with little mellow quality. I took the action out and laid it on the floor with a stick of wood under the hammer tails. I assailed the strike area of the hammers with the compass needle. This made a lot of holes in the hot pressed Hammers. Hitting the hammers with a very large and heavy pall peen hammer made the felt expand into the holes and the hammers actually looked like nothing had been done with them. The effect on the tone was astonishing and I do not use this adjective lightly. The tone now had the warm mellow sound of a a cold pressed hammer. When you laid into the keys the Forte tone came through with a pleasing power behind it. I did this about 5 years ago and the voicing is still beautiful.
The next time I used the technique was on a 9' c1903 Grotrian Steinweg in Alsace France. The piano had new hammers that were reproduced to be precisely shaped and constructed like the originals. Unfortunately the one difference was that heat was used in the pressing of the felt. The hammers in 1903 would have been cold pressed which maximizes resiliency of the felt. I tested with a couple of pokes of the compass needle on the crown of one hammer and I could tell that this was too much effect. So in this case I skipped needling and only used the Limbering Hammer. The effect was also astonishing and did not take much time to accomplish. The piano was transformed. Most recently I worked on a Pacific Rim grand with very harsh tone. This one took full needling and hammering and the effect was to make the tone lovely and warm. It took about 20 minutes.
Since then I have been teaching the technique in PTG conferences and it is clear that we have a new method to add to our tool kit. My friend and associate Boaz Kirschenbaum is marketing voicing tools for this method. Go to:http://vintagetonetoolco.bigcartel.com/products
Hope this helps,