Piano World Home Page Forums Our Most Popular Forums Piano Forum Sound with the una corda pedal depressed

Prout, Sanfrancisco and Mark Polishook are on the right track.

Many contemporary piano makers are using hammers so wide and with such dense felt that the shift pedal cannot be set to reliably clear one string and not have the hammers hit the next higher note. (This is one of the reasons I state that some modern piano makers do not know what they are doing. They actually do not understand how the piano is supposed to function as a musical instrument.)

The dense felt issue causes a "twang" when the edge of the hammer is still striking the third string and is set into a much more horizontal vibration that brings the string into contact with the side of the hammer ever so slightly.

These makers must set the shift so the hammers only move far enough to strike the hammer on the less grooved surface. This is only a "half-shift" position. A properly regulated shift pedal offers half-shift and full-shift for two tone color differences. But if the hammers are wrong, you are stuck with the half-shift only.

But as Mark noted, a full shift brings a complicationg issue with using the damper pedal. Since on full shift all the struck unisons vibrating contain one string 180 degrees out of phase, when you slowly release the damp pedal as the string begin to contact the dampers an "oinking" sound is produced. This is because you have "twice" as many hits between the strings and the felts. If the piano has the softest damper felts possible this is greatly reduced. Old M&H's had felt like this and slow damper release with full shift was very forgiving. But those felts are easily damaged by careless tuners and others. Pianists must in general avoid slow damper pedal release with full shift.

Multiple unison strings can "communicate" with each other when they vibrate. This "communication" is usually refered to as coupling in the physics world. Because they are linked via a moveable structure, (the bridge), the motion of one affects the motion of the other. They will try to link up and move together when the forces they carry are strong enough. This is why properly trained tone regulators go to great pains to get the hammer striking all unison strings at the same instant. This puts the unison strings in the same phase when the hammer strikes. When the unisons are precisely phased the piano sounds warmer, richer, fuller, has more sustain, (Too our musical ears when in fact it is less, but this is another story) and tunes better.

A full shift clear of one string takes advantage of the change in coupling between the three strings at the bridge. The unstruck string doesn't start to vibrate until the first half wave from the two struck strings reaches the bridge. (Well the longitudinal mode has already arrived so some bridge motion is imparted but we are going to ignore that here). The unstruck string starts moving in the opposite direction to the struck strings. (This is referred to in physics as 180 degrees phase difference.) The 180 degree out of phase string "robs" some of the hammer impact from the struck strings and this reduces the perceived impact sound. After hammer strike, the unstruck string now vibrating along with the two struck strings reduces the rate of unison coupling and this extends the decay envelope.

I would guess that in the first way the sound mostly just gets softer but the tonal quality doesn't change that much. In the second way, I would guess that not only does the tone get softer but the timbre changes a lot more since the strings are striking the less compressed felt in the hammer.

1. It's possible to adjust the UC so that the hammer contacts two strings in the deep grooves(meaning the grooves caused by playing without the UC) but this is usually not done.

2. The usual set up is to have either two or three strings hit the part of the hammer felt that has not compacted as much as the deep grooves.

rying to summarize some of the simpler parts of what has been said, would each of the following be true or false(again I'm just talking about the trichords to keep things simple):

1. It's possible to adjust the UC so that the hammer contacts two strings in the deep grooves(meaning the grooves caused by playing without the UC) but this is usually not done.
2. The usual set up is to have either two or three strings hit the part of the hammer felt that has not compacted as much as the deep grooves.

[...]Horowitz using all three pedals [...] hiking boot you can work both straight on.

Somehow, the image of Horowitz in hiking boots ....

Cheers!

I've seen a YouTube of Horowitz using all three pedals in various combinations (including all 3 at once!). He of course was wearing thin dress shoes so to activate the uc and sostenuto in combinations he rotated his left heal outward with the toe on the sostenuto and ball of his foot on the uc. He then would rock his foot back and forth, looked real uncomfortable. With a wider light hiking boot you can work both straight on.