New clavichord project

My last clavichord project failed at the last moment, but not through lack of momentum. I got right to the point where I could play a full scale on it, but had to stop there, because I had learned enough from the project to realise that it would not work properly in the end.

The project I had envisioned was a clavichord built from very easily-sourced material: plywood. And the strings were made from high-tensile wire, using only one strand for the higher notes, and two or more for lower-frequency notes.

I didn’t actually expect to get as far as I did. My main intention with this project was to figure out exactly how clavichords work. This was a practice run.

Some mistakes learned from the last project:

  • The key tangent positions are crucial. If they’re off by even the slightest amount, you will miss the string or (even worse) the keys will overlap with each other.
  • When the strings are on, the tension created can warp the clavichord, making it bow in the middle, thus wrecking all your careful measurements and tunings.
  • It’s very hard to find explanations online about how /exactly/ sound-boxes work, such as how to make sure all notes sound equally loud, where to place ribs (if needed), the effects of the various measurements and materials.
  • Tuning is hard.

The new project will address these. I’m planning on building something which will address each of these problems, and also will allow me to test a few things I’m unsure of, and change things easily.

Firstly, the body will not be build as a solid rectangular block, as the last one was.

Instead, it will be built as a lightweight scaffold from metal rods bolted together. This allows me to easily re-arrange it if needed.

To stop the bowing, I will build a truss rod into the base, so if the strings cause the body to bend upwards, I can counter this by tightening the truss rod, pulling it back into shape.

To counter the tangent position problems, each key will be an adjustable three-part lever, which can be bent into shape, then “bolted” once it is correct.

Because the sound-box will probably be the hardest thing to get right, I have the idea of a removable box, so I can experiment with different materials and shapes. To make this possible, the bridge (which connects the strings to the sound-box) will be raise-able in its entirety, so the sound-box can be slipped out under it.

In a traditional “double-strung” clavichord, the string is looped around a tuning peg on the right side (next to the sound-box), pulled across the bridge, across the body, and looped around a pin, then back across the body, across the bridge, and looped to another tuning peg. I don’t really like the design of this, so will be changing it in mine.

In mine, each string will have a “ball end”, like a guitar string. the ball end hooks to the right end of the clavichord, and the string then is stretched over the bridge, across the body, then around a positioning pin and into a machine head. Machine heads are much easier to tune than tuning pins. This method also makes it easier to single-, double- or even triple-string different parts of the clavichord. In pianos, for example, the bass notes are single-strung using very heavy wire, and the treble notes are triple-strung using light wire.

I will also be adding a microphone and jack to mine, so the clavichord can be optionally amplified.

Some even more far-out ideas:

  • Add a touch screen and small computer (Raspberry Pi?) which can be used to display sheet music.
  • This could also be used to display a tuner, such as the awesome DaTuner Pro for Android.
  • And the most difficult: automatic tuning. A robot mechanism for turning the machine heads and picking/tapping the strings automatically to tune to Well-tempered, Pythagorean, Mean-tone, or any other tuning.

Well – that’s the plan! Now to watch some Red Dwarf and forget all about this madness…

clavichord fretting

My clavichord project stalled when I realised it was just not going to work the way I’d done it.

This is partly because I’d naively gone for the full un-fretted design in the beginning, then later realised this would put too much pressure on the cheap bodywork and cause it to implode.

Changing the design afterwards to a fretted design wasn’t going to work either, because of how the keys were laid out.

So, the new plan is to rebuild the keyboard on the current clavichord, and hopefully get the thing finished as a triple-fretted, single-strung design.

Now, to explain…

If you have one string per note, this is called “unfretted”. In this design, every string is only ever hit by only one key.

The usual way to design a clavichord is “double-strung”, this means that every note actually has two strings for it. This makes double-strung clavichords louder than single-strung clavichords, because the combination of the two strings’ waves tends to alternately strengthen and dampen what’s happening at the soundboard.

Back to fretting – consider a guitar. Despite only having six strings, a guitar can play many more than only six notes. This is accomplished by “fretting” the strings. When you play a “G” on an “E” string, what happens is that you are shortening the wavelength of the overall string (with the fret and your finger), causing it to play a different note (G) than it would play if it was unfretted (E).

With a clavichord, the very act of striking the string with the key (or “tangent”, as the striking edge is called) causes fretting. The strings are damped at the ends with cloth or felt so when the key is not touching the string, the string doesn’t vibrate.

When you design your keyboard to multi-fret the strings, you need to do some calculation – let’s say you have a note, C, which is struck on the strings 100cm (let’s say) from the bridge. If your fretting involves the C# hitting the same string, then that key’s tangent must hit the string at about 94.4cm.

This is quite a small distance between the two tangents (5.6 mm), meaning that if you decide to triple-fret all your notes, then the keys for the high notes will be very close together, and the lower notes will be further apart (lower notes have larger wavelengths, so the distance between semi-tone frets increases as well as you get lower).

That explains the following image (a double-strung, triple-fretted clavichord – click for a larger image):

Note that the keys are all squashed together on the right side where the high notes are, and the spaces gradually increase as you move further left.

Notice as well that at the extreme left, the increase in spacing stops and all the keys are together again.

The reason for this is that when the notes get too low, there’s simply no more room for multi-fretting, so instead, the lower notes are all one per string.

There’s one more point to make about the keys.

Let’s say you create a key, which has its tangent 25cm from the fulcrum (a clavichord key is a lever). When the key is pressed, the tangent arcs up and strikes the string. It is still 25cm from the fulcrum in a 3D sense, but when measuring x/y from a top-down view of the clavichord, if the string is 4cm above the tangent (with key at rest), then the tangent strikes the string about 22.5cm from the fulcrum.

This must be taken into account when you design where the strings will contact the bridge and the hitchpins, as getting this wrong will cause the tangents to miss. Yes, you could just place the tangents after doing the strings, but my goal here is to be as perfect as possible. (there’s also the added problem that the tangent’s top is a certain height (3cm, say) above the level of the fulcrum, but you get the picture)

I’ve explained some of the problems to do with designing a fretted keyboard and string layout. Now, I’m off to write a program to design one automatically!

what I’m up to

As usual, I’m behind on stuff.

I just submitted chapter 3 of my upcoming book “CMS Design with PHP and jQuery”, and chapter 4 was due to be complete and sent two days ago.

My clavichord project stalled when the cumulative number of mistakes made it incredibly unlikely I’ll complete it in a usable fashion.

In work, I’m behind on a pretty large online-store project, but in that case I’m okay with it – I wasn’t slacking; things are just very busy at the moment.

My piano playing has also stalled – I’ve been trying to learn The Heart Asks Its Pleasure First for the last month. I’m stuck on the final page, where the left hand is all over the place and the right has an intricate tune to play. Its all in my head, but I just can’t play it smoothly. Thinking of putting that on the back-burner and going onto Bach’s 2-part inventions instead.


Packt have asked me to review Expert PHP5 Tools. Looking forward to it. It’s got some stuff in it which I’ve read about but never tried. Including: UML design of applications, incorporating tests into subversion submissions, and automated documentation of source (among other things).

My piano teacher found an examiner who will be testing in Monaghan next month, so I’ll finally be able to get grade 2 out of the way. I’ve been practicing grade 2 and 3 tunes for months. Playing 6 tunes every day before I do anything else has been reducing th amount of time I have for the rest of my practice, so I’ll be glad to get this one passed as well.

I’m trying to push myself to get the current book finished as soon as possible. This is difficult as writing a CMS is a much more complex job than writing a cookbook of techniques. The chapter I just finished had 40 pages in it. By the 40th page of the previous book I was already into chapter 3. Chapter 2 wasn’t much smaller either!

When this book is finished, I’ll be starting a new one, on building a clavichord as cheaply as possible. Because I failed with the current one, but learned quite a lot from it, I feel I’ll get it right this time, and would like to document it as I go. There’s a lot of math involved in building a clavichord, and I think I may even get a good programming application out of it!

After that, I’m thinking of starting up contact juggling again, and completing the book, this time with videos.

When I get the time, I’d also like to get back into building robots. I think the gardening robot is a bit beyond me at the moment (involves some very complex AI), but I thought I’d try build a digger bot. You tell it what you want dug, where to put the debris, etc., and it gets to work.


List of things off the top of my head that I want to do:

  • write a book. already had a non-fiction book published, but I’d love to have an interesting an compelling original fiction idea to write about. I’m working on a second non-fiction book at the moment.
  • master a martial art. I have a green belt in Bujinkan Taijutsu (ninja stuff, to the layman), but that’s from ten years ago – found a Genbukan teacher only a few days ago so I’ll be starting that up soon (again, ninja stuff).
  • learn maths. A lot of the stuff I do involves guessing numbers or measuring. it’d be nice to be able to come up with formulas to generate optimal solutions.
  • learn electronics. what /is/ electricity? what’s the difference between voltage and amperage? who knows… I’d like to.
  • create a robot gardener. not just a remote-control lawn-mower. one that knows what to cut, what to destroy, that can prune bushes, till the earth, basically everything that a real gardener does.
  • rejuvenate, or download to a computer, whichever is possible first. science fiction, eh? you wait and see…
  • create an instrument. I’m just finishing off a clavichord at the moment. when that’s done, I think I’ll build another one, based on all the things I learned from the first. followed by a spinet, a harpsichord, a dulcimer, and who knows what else.
  • learn to play an instrument. I’m going for grades 2 and 3 in September for piano. I can play guitar pretty well, but would love to find a classical teacher.
  • write a computer game. I have an idea, based on Dungeon Keeper, for a massively multiplayer game. maybe I’ll do it through facebook…
  • write programs to:
    • take a photo of a sudoku puzzle and solve it. already wrote the solver.
    • take a photo of some sheet music and play it.
    • show some sheet music on screen, compare to what you’re playing on a MIDI keyboard, and mark your effort.
    • input all the songs you can play on guitar/keyboard. based on the lists of thousands of people, rate all these songs by difficulty, to let you know what you should be able to learn next.
    • input a job and your location. have other people near you auction themselves to do the job for you. or vice versa: input your location, and find all jobs within walking distance to you where you can do an odd job for some extra cash (nearly there:
    • takes a photo and recognises objects in it (partly done)
    • based on above, but can also be corrected and will learn from the corrections (also partly done)
  • stop being damned depressed all the time.

There’s probably a load of other stuff, but that’s all I’ve got at the moment!

clavichord progress: now with strings

I can understand now why these things go for so much money.

I’ve been working on this project for about two weeks and am just now getting a sound by pressing a key.

I’ve also learned a lot, which will be applied when I build the next one.

I originally planned to build a 49-key unfretted clavichord, but didn’t realise how difficult that was going to end up being.

One of the problems with this, is that because the strings are pulled diagonally across the board, hitting one string without hitting its neighbours is a very difficult thing.

This is easier to do if there are less strings.

So, after putting in all 49 hitchpins and drilling 49 holes for tuning pegs, I realised that there was no way I could do this unfretted without extreme precision, which my <€50 instrument was simply not capable of.

image showing 49 tuning pin holes, hitchpins, and the felted balance rail for the keyboard

So, I’ve strung the instrument with only 17 strings, each of which is used by 3 keys (yes, I know – one key will get a string all of its own).

17 strings crossing the bridge to 17 tuning pins

There’s another problem I’ve yet to overcome.

Because fretting involves hitting the same string at different points (the same as a guitar or violin), and I didn’t think far enough ahead, some of my tangents are going to have to hit their strings in positions above other keys…

Looking at other existing fretted keyboards, I now realise why the tangent positions are so staggered:

staggered tangents on a triple-fretted clavichord

I’ve just finished the sharp keys, and will be working on inserting all the tangents later today.

If I’m lucky, it may actually be playable by tonight.

clavichord keyboard and soundbox

Over the weekend, I cut out the keyboard for the clavichord and built the soundbox.

How a clavichord works is that you have strings which are strung between hitch pins and tuning pegs, with a bridge in between. The strings are damped at both ends by cloth called “listing”.

When a key is pressed, a “tangent” is banged up against the string, creating a standing wave between the tangent and the bridge. When the key is released, the tangent loses contact with the string and the wave is then damped.

As I’m building all of this as cheaply as possible, I don’t have proper material, so I’m very interested to see how well it sounds when finished.

I couldn’t find any proper wood to act as a soundboard, so used the side of an old computer case, cut to size. I’ve never heard of a metal soundboard in a clavichord – but then, I’ve also never heard of a plywood clavichord.

My friend Sean dropped over yesterday and gave me a roll of high-tensile wire – the sort of stuff that’s usually used in industry when strength is needed. The wire is made of 15-20 individual wires, each twined to create a single whole.

I haven’t got the tuning pegs created yet, but was able to test the sound of the clavichord by unwrapping a single strand from the wire, and running it from a hitch pin to a screwdriver in one of the tuning peg holes, and tightening it as much as possible by hand, then levering a small piece of plywood under the wire to act as a bridge on the soundboard.

Plucking the string made a clear tone, but hammering and holding the hammer against the string it didn’t make much of a sound. That’s kind of to be expected, though. After all, it’s been said that the clavichord is “the one instrument that can be played by a person on one side of a double-bed without disturbing someone in the other side”.

It will probably sound much better when I’ve made a proper bridge and got proper tangents running.

plywood clavichord project

My piano is going out of tune.

The local tuner says it can’t be tuned. but, seeing as he’s also the owner of the local piano shop, I really don’t think I can trust his word on that – especially as another tuner (in Dublin) laughed immediately when that was said to him.

I’m certain that I can tune the piano, but I’ve been told not to, by both the tuner in Dublin, and also by Bronwyn’s mum, who owns it – apparently the slightest mistake can be costly.

And so, I’m going to build my own keyboard, which I can tune if I want to.

Here’s a picture of the end-goal – a well-made clavichord:

To buy a ready-built clavichord would cost 8000 euro or higher. To get a kit version which you put together yourself would cost 3500 or higher.

I feel that’s a little bit high, so I’m trying to make a simple clavichord, where the materials cost 50 euro or less. I’m not counting the cost of the tools.

So far, the materials have cost less than 25 euro – a sheet of 22mm plywood, and some wood glue.

Today’s progress is that I have the basic shell of the thing created. It’s 100cm x 30cm in size, with internal walls of 10cm.

The keyboard will be four-octaves in length. 49 keys, from C two octaves below middle.

I’ll start cutting the keyboard out tomorrow. Hopefully I’ll be able to finish off all the woodwork by then.

Then it’s time to start thinking about the strings.