This article first appeared in the Piano Technicians Journal December 2002

Dampers: Peace and Quiet at Last

For many technicians, dampers and their operation often represent the finale frontier of piano technology, full of mystery and no small measure of frustration. This first article will deal with grand pianos. This subject can in no way be exhausted within the scope of one article, let alone several.  But I hope this will help you in identifying potential problems and their solutions.

Let us begin with a complete understanding, from a musical perspective, of what a pianist really needs from the dampers and damper mechanism. Obviously dampers are meant to dampen the sound. One particular definition of dampen I find most appropriate is “to diminish progressively in vibration or oscillation.”  (Webster’s New Collegiate Dictionary, well at least it was new back in 1979). While a pianist certainly expects the damper to stop the sound, it doesn’t have to be instantaneous, with no degree of progressiveness.  There has to be the ability to stop the sound completely within a fraction of a second and the ability to gradually diminish the sound at a rate faster than the normal rate of decay.  This ability must be present and consistent from note to note in the keys as well as in the damper pedal.  Also the activation the underlever has to be late enough in the key stroke to be unnoticed by the pianist.  Everything which interferes with this criterion can be considered dysfunctional. 

To understand how to accomplish these goals, let’s start at the top.  I don’t think it really matters which brand of felt you use.  This by no means implies they are all the same, far from it, but rather they all can be made to work equally well, you have to match your techniques to the materials you use.  Some may disagree with these generalizations, but use them as a starting point for your own work with damper felt.  It has been my experience the felt from Steinway & Sons is quite stiff, while Yamaha felt is more of a medium density, Pianotek felt is a slightly less dense felt and Laoureux from Schaff is a softer felt. Each type of felt will present its own characteristics and problems, my personal preference is either of the middle density felts.

I have often found three and sometimes four short damper felts will work better in the bass and tenor than two long felts.  When three felts are used I have not found a consistent benefit in putting the third felt on the front or back side of the damper head.  The addition of felt will impact the damper weight, adding about ½ gram per piece.  I usually use felt pieces of about ¾” in length.  Care must be taken with the placement of the additional felt as with each piece of felt the opportunity for alignment error increases and nothing will make a damper ineffective faster than misaligned felt.

I have found David Stanwood’s work in action metrology most helpful in understanding and dealing with weight and its impact on performance, I would like to suggest one further extension.  The weight of the dampers has a great impact on their efficiency.  I will usually start the #1 damper head around 15 grams, 17 grams on 7’+ pianos.  This usually entails adding about 1 -2 grams of weight for which I use leaded solder.  I follow a curve similar to Stanwood’s though somewhat steeper.  You will need to add as much as 6 - 7 grams to the cut down dampers from the “Y” in the bass/tenor break.  (Any wonder why they often don’t work no matter what you do to them?)  I use underlever leads I have removed from deceased underlevers. The effect of doing this is a reduced dependence on damper springs.  On smaller pianos they are completely unnecessary and on larger pianos they are needed only on the bottom dozen or so notes.  Springs can weaken with age, break, come out of their groves, develop all sorts of friction problems in their grooves, not to mention be a real pain to effectively regulate so I count this as a nice benefit, well worth the effort.

For the damper/string contact to work efficiently several elements need to be in place.  The felt needs to have contact with the string throughout its entire length. Sometimes with trichords this can be a problem.  First cut the trichord down its center into two wedges of felt instead of one “W” shape.  If this does solve the entire problem, treading some silk butt flange chord through the felt will often open the felt sufficiently to get contact.  I use Yamaha’s. 

In addition to having contact along the edges of the damper, the strings need to be level. If one string hangs a little beneath its neighbors it will be virtually impossible to ever completely dampen it.  Level all the strings and retune the piano.  On some rare occasions dead level strings may not dampen properly because of unevenness in the damper felt. You often cannot correct this without replacing the felt.  In this case, a careful compromise between the string level for the hammer and for the damper may be called for.

On the bichords and especially the trichords the felt cannot extent much more than a strings diameter below the wire.  Any more than this and the damper will not clear the wire when the key is played or when the pedal is lifted.  Needless to say this would steal a lot of sound from a piano and can make tuning very difficult. Trim the felt so that the felt stops just below the string.

In regards the question of backing, I think it is much like the choice of felt, if you are doing everything else right, it doesn’t matter that much.  I haven’t used backed felt in at least 12 years.  Backing is much like the decision on angles, whether to match the angle of the head, or just cut it at a 90’ angle in the felt, it maybe more personal taste and cosmetic than functional.  I know there is considerable disagreement on this point.  All I can say is my unbacked dampers work and backed dampers work, so what is the difference?  Performance is all that matters.

Underneath the head and felt we find the bane of damper work, the wire and those pesky bends.  This first series of bends has four functions.  First it has to set the head parallel over the strings. The second function is to place both front and back ends of the damper evenly on the strings.  If only one end is resting on the string you will usually hear some long lasting harmonics.  Lift the damper slowly, if one side lifts first, correct it by gently bending the head down on that end.  The third function is to center the damper over the string from side to side.  There should be an equal amount of felt on either side of the damper.  The last bend should send the wire straight down the damper guide rail toward the first bend in the lower portion of the wire.  All of this must be accomplished while remaining far enough from the strings on either side so as to not vibrate against them with a hard blow. 

To add to the difficulties, the bends under the guide rails may impact the function of the bends above the rail.  These bends must allow the damper wire to travel in a vertical path while coming out of the center of the underlever head hole. The wire should be able to slide into this hole without binding or leaning to one side or the other.  Essentially, the head should be able to wobble freely with the wire inside the hole and the set screw loose.  If it does not wobble, the wire has a bend/alignment problem somewhere and with practice you can figure where based on how the wire fits in the hole.  As far as the location of the bends, when I have a choice I will divide the wire into thirds, but I have not found it really matters to the damper, but in the interest of a professional looking job and the ease of present and future work, a consistent pattern helps.

As the wire passes through the damper guide rail it should be clean and shiny, 4/0 steel wool works fine. The bushing should be free enough for the wire to pass through with an absolute minimum of friction, yet snug enough the damper doesn’t wobble when the key picks it up.  Loose guide rail bushings will cause the damper to land inconsistently on the strings, making refined damper work impossible. Overly snug bushings must be eased enough to allow free movement of the damper wires.  Any guide rail which needs to be eased more than twice probably has too much felt and without rebushing will need easing regularly.  It is beyond the scope of this article to deal with rebushing damper guide rails but suffice it to say it is not that difficult or time consuming.  It will take almost as much time in disassembly and reassemble the dampers as to do the actual work.

When the set screw in the underlever head is tightened it can cause the damper to twist. Simply grab the wire with a pair of pliers and gently twist the damper to its desired location. The dampers may appear to set squarely on the strings but slowly lift the damper and check if there is any twisting motion or if the felt comes off one side first.

The underlever is an often over looked yet very critical element in the efficient operation of the dampers.  Obviously all the center pins should be free, but just as important the lever must travel at 90’ to the damper tray. Traveling the underlevers requires at the very least the loosening of the upstop rail.  If the damper flange is accessible, travel them in the same manner you would hammer flanges, adding paper on the side of the travel.  If the flanges are inaccessible, as is the case many times, you will have to accommodate the poor travel with less than ideal wire bends.  Sometimes it is easier to remove the underlever system entirely and regulate the flanges out of the piano if there are significant travel problems.

The resting angle of the underlever can have a significant impact on the efficiency of the entire mechanism. The angle changes the weight effect on the damper.  The higher the front of the underlever the greater weight the damper will “feel”.  Conversely, the lower the angle the less weight.  A two lead Renner underlever, measured parallel to the scale, weighed 11.0 grams. At an angle commonly found in Steinway & Sons short arm system the weight dropped to 10.0, almost a 10% drop.  It may not sound like much but it does have an impact, and needs to be compensated for with the addition of more weight or spring tension.  At times it can be helpful to increase the thickness of the keyend felt to allow for a higher underlever rest height. (Always check the condition of the keyend felt as this can wreck havoc on damper timing and you may find insufficient lift for the felt to clear the strings.)

Damper timing can be set with any gage available from the supply houses or something easily made yourself.  It is necessary to determine the height of the bottom of the underlever so it will be picked up about ½ to 2/3 through the key travel.  Any lower and the pianist will feel the significant increase in weight as the underlever is picked up and higher, the damper will not clear the strings sufficiently. The proper time should be as late as possible and still get sufficient damper clearance yet high enough the string is not silenced the instant the key begins to come up.

Once the timing has been set, the damper tray timing needs to be set.  Sometimes, (ironically usually on lower end pianos) there are mini-capstans for each note and the tray timing can be quickly and easily set.  Otherwise shimming late lifting underlevers with packing tape will work just fine. (Adhesive tape is needed here, unlike hammer flanges where the paper can be held in place by the flange.)  And just in case we haven’t guilded the lily enough, you can shim the sostenuto tabs so that all the dampers will lift equally.

Since every manufacture has their own ideas as to what constitutes efficient trapwork, the best we can do here is to make some generalizations.  There have been articles in the Journal about retrofitting free piston type mechanisms (Steinway & Sons) to a fixed piston type.  This  procedure can go a long way to eliminating the many trapwork problems by addressing the tremendous friction which develops as the pistons move through the key bed.  I would leave it to these articles to get into the specifics.  In addition to the retrofit, the most important step to making the damper mechanism work better is replace all felt and leather.  After only 30 years of steady use, much of the leather will be badly worn and inevitably mounds of crude (graphite) will have built up around the various parts.  All the leather and felt should be replaced, in addition polish all metal parts, (removing tarnish and burrs,) and burnish any direct wood contact areas.

And finally a word about trap work springs.  Many times I have been able to remove one spring when there were two originally without any problems with the working of the trapwork.  Many pianists appreciate not having to stand on the pedal to get it to work.  I always leave the spring with the pianist in case they later change their mind so it can be put back in.

The best way to isolate problems in a system as complex as the damper mechanism is to start at either end, isolating a part at a time to determine if it is functioning properly.  My hope is to have given some idea as to what “functioning properly” means.

In no way have all the potential problem areas been covered here, additional areas could include voicing damper felt, damper guide rail rebushing, underlever rebuilding, (new or old parts), trapwork regulation, just to mention a few.

Andrew Remillard