I've been working on and off with the Trasuntino for the past two months, trying to get a handle on the troublesome repetition in the tenor and bass regions. What stymies me is that the jacks work perfectly well in the upper two-thirds of the instrument, yet they become troublesome about an octave below middle c'. No harpsichord will repeat perfectly right down to the bottom of the keyboard, but my problem areas are much too high up for me to feel completely comfortable playing the instrument.
After soliciting suggestions from the harpsichord list, I learned something very interesting that pertains to my difficulties. In a nutshell, the longer a string is, the thicker it must be in order to maintain a reasonable amplitude of vibration. "Reasonable" in this case means an amplitude that is not difficult to damp out when the jack comes back down. If the amplitude can't be controlled, repetition will be compromised.
The list experts reviewed my stringing schedule and a consensus developed that the schedule was too light in the lower regions by at least one, if not two, gauges. Several suggestions were offered that advised me to end with gauge #1 in the lowest regions (0.020"). One maker said that anything less than this would behave like a "loose clothesline". Since heavier wire must be under greater tension to reach the correct pitch, the resulting increase in stiffness means the wire won't flap around as much when vibrating.
Part of my stringing problems stemmed from a slight misunderstanding of mine regarding how stringing by numeric progression works. The original instruments on which this was practiced had keyboards extending up to d''', and starting higher by those extra two notes would allow heavier gauges to be used by the time one reached E in the bass. The Trasuntino only goes up to c''', which means I finished with gauge #3. I should have started with 9 strings of #9, and not 10, in order to get the correct results.
The new schedule has the crossover points between gauges occurring on higher notes than the current schedule. In adjusting the stringing to conform to the new schedule, there will be minor changes in the alto and treble, while the lower part of the instrument will require extensive restringing.
The changes higher up are so minor that I decided not to bother with them: besides, this isn't the problem area. So I applied the new schedule only from c' downwards. Because the crossovers occur higher up in this region, I was able to recycle a lot of existing wire by removing strings and tuning pins together, shortening each string slightly, and reinstalling it about a fourth higher. By reusing wire, I saved myself the trouble of depleting my wire supply, and also gained the advantage of using wire that has already stretched out over many months and developed its tone.
From F# downwards, new wire in gauges #2 and #1 was required. Since the numeric progression rule dictates that 2 wires of #2 and 1 of #1 are called for, there wouldn't be enough to reach C unless I wanted to use even thicker gauges , and excessively thick wire has its own problems (it can sound dull or otherwise strange). So I bent the rule by using 3 of #2 and 4 of #1. The short-octave note GG/BB was left unaltered, as it was originally strung quite heavily (.022" red brass).
I tried this schedule out on the front 8' at the beginning of October, and found that the stiffer wire did indeed improve repetition noticeably, without completely curing the problem. I decided to give the new wire several weeks to settle down and develop its tone.
Now, at the end of October, I've concluded the new wire sounds good, so I'll keep the changed schedule. Recently I've been revoicing the plectra in the restrung region, as they are not so well matched to the new wire. My sense of the register as a whole is that my initial voicing back in August was too heavy, so I went ahead and thinned all the quills in the entire register. With a lighter touch, the repetition has improved even more, to the point that I think the problem is almost cured. Next, I'll do the same to the back 8'.
Amplitude and string vibration have a more crucial effect on the playability of a harpsichord than I initially suspected. Originally I thought that, provided the scale was correct for the intended pitch level, one could string a harpsichord with purely sonic considerations in mind, but I now see that the mechanical reliability of the action is impacted by the string schedule too.
Friday, October 30, 2009
Thursday, September 10, 2009
Debugging phase
Construction of the harpsichord is essentially done. Only the music desk remains to be made at some point.
The harpsichord has been playing since the end of August. I'm now in a kind of debugging phase in which I play the instrument and track down things that need improvement. So far I have
The harpsichord has been playing since the end of August. I'm now in a kind of debugging phase in which I play the instrument and track down things that need improvement. So far I have
- increased the depth of touch about 1/32" by substituting a thinner cloth for one of the two layers under the jackrail
- shimmed up the keys with more punchings at the balance pin to help increase the depth of touch
- moved both of my gap spacers which, despite my best efforts, had not been located exactly under the strings and were slightly rubbing the nearest jacks
- tweaked the off positions of the registers to make sure the plectra cleanly miss the strings
- glued little cloth squares between the registers so they don't touch themselves or the edges of the gap
- done a little remedial voicing to quills that feel stiffer or sound louder than their neighbours
The main outstanding issue to be resolved is the troublesome repetition of notes in the bass. In this region the amplitude of the plucked strings is large. Damping can be problematic as a result, and the tongue is often flung backwards quite energetically when the jack descends and the plectrum touches the string. So I am experimenting with damper shapes, stiffer springs and various other factors in an effort to resolve this problem.
Monday, August 31, 2009
Dampers
Dampers are installed after the preliminary voicing, as it is easier to see the quills without them.
Dampers come in the form of a strip of felt about 1 cm wide and several feet long. A portion is pushed into the damper kerf of the jack and cut off from the back, leaving the damper a bit long. To determine the correct length, the damper is trimmed from the front while the register is in the off position (i.e. further from the string). If the damper sits on the string in this position, it will also work in the on position (closer to the string).
It's important that the dampers not be excessively long in the off position; otherwise, when the register is turned on, the damper may reach past its own string and damp a neighbouring one. This also means the register's off position cannot have the plectra too far away from the strings, otherwise by the time the register reaches the on position, the dampers may be too close to a neighbouring string.
I'm using so-called flag dampers, which are more or less square in shape and flat along the bottom edge. These dampers allow the jacks to hang slightly from the strings, which makes transposing the keyboard easy. If the jacks actually sat on the keys, the resulting weight and friction might interfere with transposition.
The bottom edge of these dampers should be just slightly above the tip of the plectrum. This little bit of slack keeps the action reliable during changes of humidity.
Dampers come in the form of a strip of felt about 1 cm wide and several feet long. A portion is pushed into the damper kerf of the jack and cut off from the back, leaving the damper a bit long. To determine the correct length, the damper is trimmed from the front while the register is in the off position (i.e. further from the string). If the damper sits on the string in this position, it will also work in the on position (closer to the string).
It's important that the dampers not be excessively long in the off position; otherwise, when the register is turned on, the damper may reach past its own string and damp a neighbouring one. This also means the register's off position cannot have the plectra too far away from the strings, otherwise by the time the register reaches the on position, the dampers may be too close to a neighbouring string.
I'm using so-called flag dampers, which are more or less square in shape and flat along the bottom edge. These dampers allow the jacks to hang slightly from the strings, which makes transposing the keyboard easy. If the jacks actually sat on the keys, the resulting weight and friction might interfere with transposition.
The bottom edge of these dampers should be just slightly above the tip of the plectrum. This little bit of slack keeps the action reliable during changes of humidity.
Voicing
Voicing, in the context of harpsichord-making, refers to the cutting of plectra (also known as quills) in a manner that draws forth a musically enjoyable sound from the instrument and feels controllable to the performer's fingers.
The same term is also used to describe the adjustment of organ pipes after manufacture. Unlike organ voicing, however, the voicing of harpsichord plectra cannot fundamentally transform the sound of the instrument. The tone is largely determined by various construction factors and the stringing materials, not by how plectra are cut. Volume and touch can be affected, along with the degree of shrillness, but not much more.
Historically, raven and goose feathers were the preferred materials for quill. Today, real quills are still used by some makers, while many others use Delrin or Celcon plectra. Both of these are hard, slippery plastics that have a long working life. They don't sound exactly like real quill, though they can get close if worked on by a knowledgeable voicer.
The process begins with ghosting, or setting the silences. Jacks are placed into all register slots, black delrin plectra are installed into all tongues, and the side-to-side position of the register is adjusted until the tongues are about 5 mm from the strings. The plectra are then trimmed from the tip until they just brush the strings when the jack is raised, without actually plucking in the normal manner, though in the bass they are allowed to weakly pluck the strings to adjust for the wire thickness. This process yields a consistent plectrum length of around 5 mm. As each quill is trimmed, the tip (as viewed from the side) is given a chisel-shaped profile to assist the backward tilt of the tongue when the jack descends.
Next, the register is advanced forward so that the plectra project past the strings by about one string diameter. This is the correct "on" position. The correct "off" position is set slightly behind the position at which the plectra ghost the strings.
With the register turned on, the tongue springs in each jack are adjusted so that the tongue tilts back as the jack descends. The severest test is to let the jack down extremely slowly: if the plectrum doesn't get hung up on the string, then the jack will work properly in every playing scenario. If the spring is too firm, stopping the tongue from tilting adequately, the tongue spring is bent back slightly and tested until the jack descends reliably.
Voicing can now begin. The intention is to produce plectra that pluck the strings consistently but not so strongly that the tone is harsh. To the fingers, the plectrum should be neither too firm nor too weak. A gradation in touch from bass to treble is required. The bass needs stronger quills because the string feels like it stretches somewhat before it gets plucked, due to the deeper plucking point in this region. In the treble, the short strings and close plucking point makes things feel stiff, so a weaker quill is needed.
This process can be expedited by using quills of differing thicknesses. Before ghosting, I experimented with 8 different quill thicknesses, discovering where it helped to change from one thickness to the next. I erred on the heavy side, since of course a heavy quill can be thinned to maker it weaker, but nothing can be done to strengthen a weak quill. Ultimately I used 6 different thicknesses, changing approximately every tritone to a thinner quill.
Voicing requires controlled cuts on the sides, arrises and underside of the quill, all of which thin the quill and reduce its stiffness. When done sensitively, the resistance of the quill as it raises the string seems to yield slightly just before the pluck, which I find feels quite controllable to my fingers.
The customary tools for voicing are shown below:
A set of wire cutters helps to trim excessively long plectra from the back. The hemostat acts like a set of pliers for installing and removing quills. Either a #11 scalpel blade (shown above) or a #11 Xacto knife blade are used for cutting the plectra. A voicing block—in this case the hard end-grain surface of an ebony block—acts as a little cutting board.
Once both registers received their preliminary voicing—a lengthy process that took two days of on and off work—the jack end screws were adjusted to locate the plectra a consistent distance below the strings. I first unscrewed each screw considerably, lengthening each jack to the point that the plectrum was actually above the string even with the jack fully lowered. Then I screwed back in until the plectrum just barely slipped under the string. At this point, I gave the rear row of jacks (the "back 8") 3 more half-turns, and the front row (the "front 8") 6 more half-turns. This difference separates the plucking instant between the two rows so that, if they are both turned on and played together, they won't pluck at exactly the same time. Otherwise the touch would be extremely heavy.
With these preliminaries out of the way, the instrument was played for several days and any discrepancies were corrected by replacing plectra, shaving down plectra, or adjusting the jack end screws further. These screws should not be cranked around much once they are set, but sometimes one or two more half-turns make a positive difference.
The same term is also used to describe the adjustment of organ pipes after manufacture. Unlike organ voicing, however, the voicing of harpsichord plectra cannot fundamentally transform the sound of the instrument. The tone is largely determined by various construction factors and the stringing materials, not by how plectra are cut. Volume and touch can be affected, along with the degree of shrillness, but not much more.
Historically, raven and goose feathers were the preferred materials for quill. Today, real quills are still used by some makers, while many others use Delrin or Celcon plectra. Both of these are hard, slippery plastics that have a long working life. They don't sound exactly like real quill, though they can get close if worked on by a knowledgeable voicer.
The process begins with ghosting, or setting the silences. Jacks are placed into all register slots, black delrin plectra are installed into all tongues, and the side-to-side position of the register is adjusted until the tongues are about 5 mm from the strings. The plectra are then trimmed from the tip until they just brush the strings when the jack is raised, without actually plucking in the normal manner, though in the bass they are allowed to weakly pluck the strings to adjust for the wire thickness. This process yields a consistent plectrum length of around 5 mm. As each quill is trimmed, the tip (as viewed from the side) is given a chisel-shaped profile to assist the backward tilt of the tongue when the jack descends.
Next, the register is advanced forward so that the plectra project past the strings by about one string diameter. This is the correct "on" position. The correct "off" position is set slightly behind the position at which the plectra ghost the strings.
With the register turned on, the tongue springs in each jack are adjusted so that the tongue tilts back as the jack descends. The severest test is to let the jack down extremely slowly: if the plectrum doesn't get hung up on the string, then the jack will work properly in every playing scenario. If the spring is too firm, stopping the tongue from tilting adequately, the tongue spring is bent back slightly and tested until the jack descends reliably.
Voicing can now begin. The intention is to produce plectra that pluck the strings consistently but not so strongly that the tone is harsh. To the fingers, the plectrum should be neither too firm nor too weak. A gradation in touch from bass to treble is required. The bass needs stronger quills because the string feels like it stretches somewhat before it gets plucked, due to the deeper plucking point in this region. In the treble, the short strings and close plucking point makes things feel stiff, so a weaker quill is needed.
This process can be expedited by using quills of differing thicknesses. Before ghosting, I experimented with 8 different quill thicknesses, discovering where it helped to change from one thickness to the next. I erred on the heavy side, since of course a heavy quill can be thinned to maker it weaker, but nothing can be done to strengthen a weak quill. Ultimately I used 6 different thicknesses, changing approximately every tritone to a thinner quill.
Voicing requires controlled cuts on the sides, arrises and underside of the quill, all of which thin the quill and reduce its stiffness. When done sensitively, the resistance of the quill as it raises the string seems to yield slightly just before the pluck, which I find feels quite controllable to my fingers.
The customary tools for voicing are shown below:
A set of wire cutters helps to trim excessively long plectra from the back. The hemostat acts like a set of pliers for installing and removing quills. Either a #11 scalpel blade (shown above) or a #11 Xacto knife blade are used for cutting the plectra. A voicing block—in this case the hard end-grain surface of an ebony block—acts as a little cutting board.
Once both registers received their preliminary voicing—a lengthy process that took two days of on and off work—the jack end screws were adjusted to locate the plectra a consistent distance below the strings. I first unscrewed each screw considerably, lengthening each jack to the point that the plectrum was actually above the string even with the jack fully lowered. Then I screwed back in until the plectrum just barely slipped under the string. At this point, I gave the rear row of jacks (the "back 8") 3 more half-turns, and the front row (the "front 8") 6 more half-turns. This difference separates the plucking instant between the two rows so that, if they are both turned on and played together, they won't pluck at exactly the same time. Otherwise the touch would be extremely heavy.
With these preliminaries out of the way, the instrument was played for several days and any discrepancies were corrected by replacing plectra, shaving down plectra, or adjusting the jack end screws further. These screws should not be cranked around much once they are set, but sometimes one or two more half-turns make a positive difference.
Keyboard hold-downs
As the keyboard was designed to transpose, the key frame must stop slightly short of the lower bellyrail to allow side-to-side motion. This means there's a bit of front-to-back slop when the keyboard is in place. In addition, the light weight of the keyboard means it might not stay still if the instrument is ever moved, which often involves flipping it onto its spine.
I made two hold-downs that attach to the baseboard inside the keywell, just behind the front rail of the key frame where the head stop cloth is stapled down. Here's one of them:
It's basically a scrap block and a mirror support clip used to attach mirror glass to walls. When the keyboard is in place, the mirror clip ensures the key frame is kept fully forward. It overlaps the rear edge of the front rail, holding the keyboard down:
The block can pivot out of the way if the rear screw is loosened. This releases the keyboard and allows it to be removed.
I made two hold-downs that attach to the baseboard inside the keywell, just behind the front rail of the key frame where the head stop cloth is stapled down. Here's one of them:
It's basically a scrap block and a mirror support clip used to attach mirror glass to walls. When the keyboard is in place, the mirror clip ensures the key frame is kept fully forward. It overlaps the rear edge of the front rail, holding the keyboard down:
The block can pivot out of the way if the rear screw is loosened. This releases the keyboard and allows it to be removed.
Jackrail supports installed
Both jackrail supports were glued down after the finish was applied to the case. Where the supports were to go, the gluing surface was protected with masking tape, as I felt it would be easier to varnish without the supports getting in the way. So here's what the spine side support looks like glued down and with the jackrail in place:
Case finish applied
I've been busy working on the harpsichord this past month, but remiss in updating this blog. Quite a bit of work has been done: in fact, the harpsichord is practically finished.
The exterior of the case, and all remaining interior portions, were finished with two coats of paste varnish. After drying, each coat was buffed lightly with a finishing pad (a kind of steel wool substitute) to smooth and level it.
The exterior of the case, and all remaining interior portions, were finished with two coats of paste varnish. After drying, each coat was buffed lightly with a finishing pad (a kind of steel wool substitute) to smooth and level it.
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