Splayed bridge legs For a good tonal response, string pressure needs to be directed to the centre or, even better, towards the outer edges of the bridge feet. It is fairly common for bridge legs to become splayed or over-widened on a cello with very rounded/pointed arching, and this leads to a deterioration in the cello’s tone. Bridge legs also tend to become splayed if a cello lying on its side is accidentally rolled over onto its bridge. Usually no structural damage occurs, particularly if the floor is carpeted, but the cello will sound dreadful because the bridge legs have spread sideways, putting pressure on the inside edge of the bridge feet and causing a temporary but major acoustical problem. If you can see air under the outsides of the bridge feet, they are definitely splayed and you’ll need some help to get the legs aligned again. In this case the luthier will squeeze the legs back towards each other until the bridge feet are in correct contact with the cello, which should ensure that the cello once more sounds like a desirable instrument, rather than the worst student cello you have ever heard.
Lost bridges. We are sometimes consulted by cellists whose instruments used to sound wonderful but have somehow lost their original quality. Even after visiting several different luthiers and having a series of changes made to their instrument, they are still unhappy. When we talk back through the history of such cellos, we frequently discover that the cello first stopped sounding good when the owner had to change the bridge because it was too low, was warped or broken. In some fortunate cases the owner has kept the old bridge, and it has been simple for us to copy the bridge and restore the original sound. Sadly though, it is common for owners to leave their old bridge with the luthier who has cut the replacement, which means that we have to start from first principles when determining what bridge design would best suit their cello. Always hang onto your old bridge as a reference, particularly if you were happy with the cello’s sound when it was on the instrument.
Bridge straightening In the days when all cellists used gut strings, players would routinely straighten their bridges almost every time a cello was tuned, due to the stretchiness of gut and its responsiveness to changes in temperature and humidity. Players knew their cello wouldn’t sound good unless the bridge was standing upright. However, our stable modern steel strings tend to stay in tune from one day to the next, so it is not necessary to straighten the bridge every time we tune a cello and many of us are no longer in the habit of straightening our bridges. However, the top of the bridge is affected by the movement of the strings over the string grooves, particularly if the pegs slip or if new strings are fitted to the cello. Failing to straighten the bridge can lead to the bridge becoming warped and it also causes deterioration in the tonal response of the cello due to the change in the bridge angle.
If a bridge is leaning back very slightly onto its ‘heels’, or leaning forward onto its ‘toes’, this is equivalent to a sound post adjustment and can change the sound of the cello significantly. The posture of the bridge should always remain upright so that the downward pressure is equal on both edges of the bridge feet – neither on ‘toes’ or ‘heels’, just comfortable. If you can see air/light at the back or front of the bridge feet, then your bridge definitely isn’t straight.
If you put new strings on a cello you will need to straighten the bridge as you tune the strings (first tune the string, straighten the bridge and then re-tune the string.) If it is difficult to straighten your bridge under full string tension, this indicates that you need to lubricate the string grooves on your bridge using either dried-out soap or graphite. It’s also advisable to lubricate string grooves when you change a string.
The effect of wood removal on bridge frequencies O.E. Rodgers and T.R. Masino University of Delaware. Newark. DE 19711. USA
Published in the Catgut Acoustical Society Journal Vol. 1. NO. 6 (Series III November 1990)
© Robin Aitchison & Sarah Mnatzaganian 2014
(an extended version of our bridge design article first published in 2006)
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