Most harpsichords and similar instruments use a single curved piece of hardwood for the bridge. This works pretty well. Usually, the builder just calculates the correct lengths for all the C notes on the soundboard, forces the bridge to pass through those points during the shaping process, and then the rest of the points on the exponential curve just kind of end up more or less where they should be, using the "curve fitting" of the bent wood itself. It's not deadly accurate of course, but probably close enough, I've never heard of anyone asserting that the notes in between the measured points ended up noticeably wrong, on any real instrument. (The only obvious problem would be if they were too long, because then the strings would break when brought up to pitch; other than that, errors in position would only lead to very subtle changes in tone quality.) Another probably-insignificant-in-practice issue with the curved bridge, is that when there are pairs of strings per-note, one of the two ends up being slightly longer than the other. Again, as long as nothing wanders over the safe maximum length, there is no real problem here -- though in this case, I have heard some people assert that they can hear the difference caused by the different lengths. This would be very hard to pin down, because another factor probably has a larger effect on the tone in most instruments, which is the plucking position on each string: this is nearly always different for the two strings in a pair. Having a difference in tone is not necessarily a bad thing, of course, as long as all the tones blend together well. Many times, the two strings of a pair can be turned off and on separately, allowing the player to get different tones for different parts of the music. Thus, some might argue that maximum tonal contrast, not minimum, is the right aim.
In addition to setting the correct lengths for the strings and coupling their vibrations into the soundboard, the conventional curved bridge has some other secondary effects, which may or may not be important. For one thing, it leads to a relatively large amount of coupling between strings of different notes. On traditional harpsichords, most of the notes will be damped (forced silent) at any given time; but on my pandalon, it will be possible to lift all the dampers at once, thus allowing strings to vibrate sympathetically with each other. A one-piece bridge would probably enhance this effect. Also, it's important to recognize that the one-piece curved bridge provides a tremendous amount of straightening and stiffening guidance, to the soundboard.
But I'm not using a curved bridge. Instead, I am using small individual blocks of wood, one for each pair of strings. Thus, there will not be as much coupling between notes. And the stiffness of the soundboard will have to be maintained entirely through other means (I have fitted some braces, we'll see if it's enough).
Each block carries two nails, which provide the string terminations. Well, actually (I'll have to post a link here when I find it), someone did a study and it turns out that the slight difference in length between the horizontal-plane termination of the string, provided by the nail, and the vertical-plane termination, provided by the point behind the nail where the string rests on the wood of the bridge (the "peak"), is quite critical to the tone. Larger separations between the bridge peak and the nail, lead to softer attack, longer sustain, and less fundamental in the harmonic structure. Of course there's a sweet spot, certainly less than 1 cm, which varies due to innumerable factors. Out of a hat, I picked a distance of around 0.25 cm, as much because that's where I could best drill the holes as out of any tonal concerns; but I could have made the distance smaller, close to zero, and after reading this paper I chose not to do that. One thing I could do with my monochord, is experiment with other distances, but I am so far satisfied with the tone quality I'm getting.
Of course, my bridge design looked really good on paper, in theory; but once I started building the monochord, I could see just how narrow the bridge pieces would really be. 1/2", to be exact. 1/2" wide sections of 3/4" quarter-round oak molding. So, they look like tall quarter-slices of lemons, standing on their cut edges. The tallness has always been a concern to me: would the sideways force of the strings, which make a 15-degree turn at the nails and then proceed to the hitching point, put too much torque on these pieces? So far, answer seems to be no, the Titebond is amazingly strong when a good glue joint is attained. However, the other factor which the narrowness brings in, which I somehow didn't forsee despite its obviousness in retrospect, is that I've pretty well done everything I can to make these blocks as likely to split as possible. Two long nails, side by side, penetrating almost all the way through a narrow slice of molding, right near one of its faces. If it were't hardwood, there wouldn't be a chance in the world of this working. But now I see how poor oak is, as a choice for this. I should be using something with a very dense and "closed" grain: I think maple might qualify better. Of course I drilled pilot holes, but they are significantly smaller than the nail diameters, both because that's the available choice I had, but also because I want the nails to be very tightly gripped by the wood, I don't want them coming loose with vibrations and humidity changes, etc.; so I am expecting to significantly compress the wood fibers as I tap in the nails. But how not to split the wood? Well, I have revised my order of events, in processing these bridge pieces. I was originally going to cut them up first, and then hammer in the nails. Now, I plan to hammer in all the nails while it's still a single strip of molding, and then dice-up the pieces. Even so, they might split after some time, being under constant strain from the fiber compression near the nails. So, I am planning to "size" the side faces of the blocks with glue, during the operation where I also glue the blocks to the soundboard. If this fails, well, I guess I'll try maple or some other variety of wood, next. I might also try impregnating the wood with polyethylene glycol ("PEG"), which my woodworking reference suggests is a good treatment for making small wood parts like this more stable and easy to machine.
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