... Once the bridge is properly sized and fitted to your instrument...(or on existing instruments in good playing condition), it is time to take a survey of the currect adjustment of the bridge to its' instrument:
... According to Russian violin Maker Isaak Vigdorchik, the bridge should be adjusted so that the top area of the bridge (under the strings) is even in tone and matching the frequency of the top plate under the bridge feet (or just in front of the bridge).
... Additionally, the bottom area (the wood bar that goes full width just above the bridge feet) should be adjusted to match the frequency of the center of the back plate. {ideally, our violin plates should be tuned to give an over-all even tone, although usually this is not the case}
...As a final step, lower the tap tone of the bass bar side of this bottom area to match the top plate with smooth tap tone transisitions between the two frequencies.(see photo below).
... If the above goal is reached, you will discover that each string, when plucked, will give a rich, wonderful, melodic, ringing tone; rather than a somewhat displeasing or uninspiring tone. As you get near your ideal bridge adjustment, some of the strings will begin to sound superior; then you know that the bridge support frequency at the string contact is correct, so now just adjust the remaining strings (areas of the bridge under the strings) to match these.
... Once the bridge is adjusted to be in harmony with the instrument, it should remain in proper relation from then on, enhancing your playing and audience listening enjoyment.
...We will be using an ordinary wooden pencil as our tapping tool. (Try to pick one out with a low toned ring when it struck against a hard object, a dull sound rather than a bright ringing tone... this will make our job of listening much easier.)
... Tap against the face of the bridge next to each string in turn listening to the tone (please do not 'talk to youself' in your mind, as this will interfere with your getting good results).
...Next pluck each string and listen to see if any sound especially pleasing.
...Next, tap the top of the plate just in front of the bridge with the eraser end of the pencil (or the same wood end (unsharpened of course) as you used above.
...Mentally compare the tones. Our goal is to adjust the bridge so the bridge taps all match the 'top-of-the-plate' tap tone.
Gently tapping the top plate for comparison...
To review this important concept:
...This top area should be all even in tap tone and should be the same as a tap on the top plate, as pictured, just above.
...This area of the bass bar side should be tuned to the top plate frequency also.
...This tip makes a significant improvement and is thanks to Pierre Leiba.
...This portion of the bottom 'bar' should be all even in tap tone and should be the same as the tap tone on the center of the back plate.
...This matching of tap tones is done in several steps, and naturally should progress in a certain order.
...First, do this step only after all sizing of the bridge have been accomplished... this is to be the final work done to the bridge for many years (we hope). {See the companion article on shaping the bridge and do those steps first.}
...Do a tap survey and determine what the two major areas are currently at compared to their respective violin plates. I will explain the fine adjustment by giving examples of various situations and how to adjust.
These two taps should match.
Example One: The entire bridge is too low in tone...
Notice the curve of the bottom of the bridge. Usually this is just a flat shape of slight arc on new bridges. ...As an approximation, it should be shaped to parallel the top curve of your top plate. Filing and sanding more to a higher arch shape will increase the tone of the entire bridge. As you work this shape, be sure that most of the wood removal is in the center and tapers out to the feet in a smooth curve. Work evenly and continually check progress by comparing with the the two plates. Our goal here is to slightly be too high in all areas of the two main areas, shown in photo 'AA' above.
... It is probably a good idea to tune the bottom cross bar (above bridge feet) first { to match the tap of the back plate} before tackling the upper areas. (See photo 'AA')
... Assuming that the bottom 'bar' is now slightly too high, it is carefully reduced to match the back by sanding on the front surface (toward fingerboard) with a small sanding stick. [the old fashioned sandpaper nail file boards (of wood) work well here]. work carefully as small changes make big differences. When the front-of-the-bridge, across the bottom, tap tone matches the back plate tap tone, we then reduce the frequency on the side toward the 'G' string to match the top plate with a smooth transition between the two tones (see yellow area on photo above).
...The back surface (toward tail piece)is left perfectly flat(this is the side with the stamped label). All the changes will be to the front face. Notice that there should be a smooth tapering of the thickness on the other (front) side, beginning with the lower cross bar (which is now in tune and not to be altered anymore) and moving up in an arc to the top 1/16" width at the string surface.
...Tap all over and continue adjusting until the top area is lowered just to the tap tone of the top plate (which is our reference here), with smooth transitions between the areas.
...Now let us suppose that all is well except the area circled in blue, which is too low in tap tone. The solution to this problem is to evenly sand (or file) the top part of the side 'kidney' (preserving a good shape), which will raise the tone of just that string, until it matches the tap tone of the top violin plate just in front of the bridge. {The same applies to the other side of the bridge; only one side is shown for clarity.}
...One additional method to raise the tap tone of the top of the bridge is to evenly sand the side of the bridge, from the kidney shape upward. This will raise the tap tone of the strings on that side of the bridge.
... Eventually you should be able to adjust the bridge tone so that each string has a full and rich tone. You can check this on a strung up and tuned instrument by tapping the top of the bridge beside each string . All the strings should have the same tap tone (which matches the top plate just in front of the bridge. If any strings are different, check by the plucked string tones to determine which ones are closest to matching the top plate and adjust the others to match the tap tone of the best sounding string. This acts as a good double check for accuracy.
...When you discover one string that has a 'heavenly' rich sound when plucked (in the center of its length); that becomes your reference for adjusting the bridge for the other strings to match its tap tone next to that string on the top of the bridge. You will be amazed at how much change in tap tone (and string sound quality) can be made with only a slight amount of material removal from the bridge!
...When this stage is completed, your bridge should be in perfect adjustment for your violin for many years of playing pleasure.

by David Langsather (c) 2007