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Tuning Violin Family Bridges:
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...Author IsaakVigdorchek in his violin making book (The Acoustical Systems of Violins of Stradivarius and other Cremona Makers, Page 143) noted that Stradivari shaped his bridges so that the top section of the bridge related to the acoustics of the top plate of the instrument just as the bottom cross bar section was shaped to relate to the acoustics of the back plate.
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Examining this particular string; tap the top surface of the bridge next to the place where the string touches it and immediately after, tap the top plate just in front of the bridge listening for the fundamental tap tone. Unless I am mistaken, you will discover that there is an exact agreement between these tap tones. Now examine the relationships for the other lesser sound quality strings, and you will discover that they do not have the same tap tone agreement with the top plate (tapped just in front of the bridge).
...The time to do this bridge tuning when fitting a new bridge is after the feet and top arching of the bridge and carving is almost completed. As the front surface (toward the fingerboard) of the bridge is thinned and shaped, constantly tap the top and front surfaces until the front and top fundamental tap tones of the bridge surface (above the waist kidneys) matches the top plate tap just in front of the bridge position. Then sand/scrape down the front surface of the lower horizontal bar section of the bridge to match the back plate tap tone. If you wish, you can then adjust the area toward the bass bar side bridge foot to match the top plate, as this may enrich the lower toned strings.
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...The top area of the bridge should match the fundamental tap tone of the top plate tapped just in front of the bridge (that is, the lowest pitched major response of the tap tone sound spectrum) while the bottom bar area of the bridge should match that of the back plate. In addition, you might want to experiment by lowering the tap tone of the bass bar foot side of the bridge to the frequency of the top plate as this does seem to enrich the low notes--this insight is thanks to Pierre Liebre of the Bahamas.
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...Proof of the importance of this acoustical agreement is best observed by plucking across the center of the open strings of violin family instruments. When doing this, occasionally one hears a particular string that is unusually full and rich.
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Figure Four
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..The tap tone of both the top edge and front upper surface of the bridge should match the tap tone of the top plate just in front of the bridge.
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Scrape this red area on the front side of the bridge to lower the tap tone here to match the tap plate to enrich the G and D strings.
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