Geometry

I just wanted to put all my thoughts on decisions about geometry in one place, where people can criticize them. I don't have real dimensioned plans to work from, so I'm kind of winging it and using my own faulty judgment to decide what goes where.

Overall footprint

Unless you really know about acoustics (I sure don't), I think this just has to be guesswork. My project's proportions are stolen from a photograph of Yale's Domenico virginal, all I did was guess a scale that would make the keyboard come out about the right size, and give smallish overall dimensions (portability is one of my main goals). Making it deeper allows for more strings, or more space between the strings (how much space do your jacks need?). Making it wider allows for getting the bass strings closer to the length they'd be in a regular harpsichord, and/or puts more soundboard area on the outsides of the bridges.

Making the case taller or shorter probably has a very noticeable acoustic effect (I wouldn't know how to predict the perfect height, that would require actual knowledge of acoustics and I'm just a lowly computer programmer) but otherwise, it doesn't make much difference mechanically. As long as there's enough space for the jacks to work, and not so much that reasonably-sized jacks can't reach from the ends of the key levers up to the strings, it will work. It just might sound like crap.

String band

I think the lowest string in the bass makes a lot of the decisions. You have to have a rough idea where the right-hand bridge goes in the bass. Presumably it needs to be a few inches to the left of the wrestplank (since it needs to be out in the middle of a live piece of soundboard), and not too close to the front of the case (again, to stay on the live part of the soundboard), but to be more specific than that you have to actually know something about acoustics. Which as I might have mentioned, I don't.

But anyway once you pick where the lowest string crosses that right-hand bridge, all you have to do is choose the angle that the string goes to the left towards the other bridge. On the Domenico this angle appears to be about 5.5 degrees. There are two limiting factors when choosing it:

• The jack -- the jack for the lowest string must be far enough away from the front of the instrument to allow space for the entire length of its key lever, including the part after the balance pin. This is why the strings can't be quite horizontal (where would the key's pivot point be if the string were almost touching the keywell?), well not without a bunch of wasted empty soundboard between the string band and the keyboard (to allow for the part of the keylever after the pivot point).
• The keywell -- on virginals with a recessed keywell, the lowest string must avoid hitting the right-hand corner of the keywell where it intrudes into the soundboard. Actually you probably want to miss it by at least 1/8" or so, to allow for the vibration of the string.

All the other strings are parallel to the lowest bass string. The highest treble string's position is limited only by the spine, you don't want it to be so close to the spine that it's on a dead part of the soundboard. Once you've decided upon the highest and lowest strings, the rest just fill in evenly. To save space, a virginal is laid out a bit like a 2x8' harpsichord, with pairs of strings (only 1/10" to 1/8" apart, i.e. 2.5 to 3 mm, just far enough that they won't hit each other while vibrating) interspersed with pairs of jacks (facing in opposite directions, and in the case of Flemish style virginals, sharing a double-size register mortise). But unlike a 2x8' harpsichord, where the two jacks are for the same key (each on a different choir), these jacks are for two consecutive keys. You must choose the depth of the virginal to allow for the spacing between pairs of strings to be enough for the two jacks to fit (including their plectra of course).

Keyboard

There are several things to worry about with the keyboard:

• Left-right position of the entire keyboard -- decides roughly where the plucking point will be, so put it more towards the left to pluck close to the ends of the strings, towards the right to pluck nearer the centers of the strings
• Width of the key heads -- must be spaced the way the player likes
• Length of the key heads -- again, to suit the player's tastes, but probably shorter than a regular harpsichord since you don't want to intrude into the string band's space too much (or project too far out if it's a non-recessed keyboard)
• Width of key tails (under the jacks) -- usually decided by key spacing so that the key tails are spaced at 1/12 of an octave (i.e. 1/12 the width of seven natural key heads), with slightly diagonal cuts between levers to make this all work out (not quite as simple as it looks, no two cuts within the same octave are parallel). You might squeeze things a bit more if you have split sharp(s) in a short-octave bass.
• Position of the jacks along the key levers -- in a regular harpsichord they can go wherever you want (since the strings are in line with the key levers), but in a virginal the string band is almost horizontal so the jack must be placed next to the intersection of the key lever and the string it plays (as seen from above). The jack should of course be offset from the string by the length of the plectrum.
• Position of balance pins -- different for each key due to the diagonal jack rail, must be calculated to get the desired relationship between key dip and jack travel. In the bass, you must pick your numbers carefully to make sure that the balance pin is behind the name board, or as close as possible. You can use shorter balance pins and put them under the key top if you have to, but it still can't be too close to the front.

Bridges

The bridges basically go where they have go to. The gross decisions are made by the shape of the soundboard and the lateral position of the keyboard, then by placing the bridges carefully you can fine-tune the scale and the plucking point. The left-hand bridge (which goes to the left of and behind the jacks) is straight, or close to it, and is placed to get the plucking point you want. The right hand bridge curls tightly in the treble and then straightens out in the bass, attempting to approximate the proper wavelength-based relationship between the active lengths of the strings (i.e. trying to double in length for every octave you go down, but failing miserably in the bass, like any harpsichord).

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