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Locating the Correct Bridge Position.

If your banjo is perfectly tuned but plays out of tune when fretted, that’s a sign that the bridge is incorrectly positioned. Don't panic!Here's a tip to locate the sweet spot for the bridge from Wendy Holman of Fingerstyle that's practical and precise. You'll need an electronic tuner and to know how to make a harmonic note.

The Laws of Acoustics Rule, OK? Locating the Correct Bridge Position.

OK, hands up all those pickers who have neat little pencil marks round the ends of their bridges?  As we all know, the bridge shifts with every change in pressure because it sits on a flexible membrane - the skin, or head.  This factor encourages us to change a set of strings one at a time to keep the bridge in that sacred sweet spot.  But what happens if we change the type of bridge?  What about when the head needs to be changed or we strip down the banjo for a 100,000km service?  That sweet spot that keeps the banjo in perfect intonation changes or is no longer visible. 

The new owner of a rather nice banjo wasn't happy with the sound and brought it to me for a tweak.  It had a moon bridge which the previous owner had outlined in red ink!  That was unfortunate as the bridge that gave the best sound for this banjo turned out to be a Snuffy Smith Compensator. 

We tried 3 different bridges of varying thicknesses and lengths.  The owner was surprised that no complicated measurements from nut to bridge to 12th fret were needed at any stage.  Here's how we did it.

1. Detune the strings approximately equally* until there's still a 'note' possible but the strings are soft and wobbly.  (*This ensures the pressure on the head is equal.)
2. Banjo flat across your knee, slip the new bridge into position between the present bridge and the fingerboard.
3. Holding the old bridge firmly at each end, tip it backwards towards the tailpiece until it falls over and the new bridge takes the string strain.
4. Holding the new bridge firmly at each end, slide it into the same spot as the old one.  If the head is the white, frosted type, try to lift as you ease the bridge to avoid marking the head. Sit the bridge upright and sight down from the tailpiece to align the 1st and 5th strings with the fingerboard binding.  (Don't want to go through the following only to find the bridge is wildly to one side!)
5. Tune up the strings until you can hear clear notes and it's roughly in tune to a chord - I say this as it's best to NOT tune all the way up.  The bridge needs very fine adjustment which is difficult if the strings are up to full tension.

Now the clever bit.  If you don't have a good ear for tuning, you'll need an electronic tuner.


6. On the 1st string, sound a harmonic right over the 12th fret metal.  Immediately compare that with the fretted note at the 12th.  If the fretted note is higher than the harmonic the bridge needs to be moved a tad towards the tailpiece.  If it's flat of the harmonic, shift the bridge towards the fingerboard.  We're talking bees-whiskers here, not centimetres!  Use both hands to steady the bridge and 'lift' a little against the string pressure. 
7. Repeat the harmonic/fretted comparison.  When it's correct for the 1st string, do the same for the 4th string.
8. If the bridge was shifted either way for the 4th string, re-do the 1st string. 
   NOTE:  the 3rd string, G, is an unreliable string to use for bridge placement.  It's almost always going to be a tad sharp - that's an anomaly to do with the formula for the fret spacings.  Bridge-makers have tried to solve this by producing compensator bridges which give a tad more length to the G string. 
9. When you're satisfied, recheck the bridge alignment.  Thinner bridges are surprisingly flexible - see any wiggles?
10. If all is well, tune the banjo up to pitch and play a few chords up the neck.  Should sound perfect. 

After you've used this method you'll be confident about bridge placement when replacing a head or stripping and cleaning.  Changing bridges will hold no fears.  Bridges have varying qualities that affect the sound of your banjo.  Experimenting with bridges can be an enlightening experience, tweaking the tonal qualities and sustain to suit your playing preference and style.  And you'll never need pencil marks again!

This method works for 2 reasons...  harmonics at the 12th fret locate the precise half-way point between nut and bridge.  Secondly, the shorter the string, the higher the pitch.  The laws of acoustics rule, OK?  We alter the length of the string by moving the bridge.  If the fretted note is sharp compared to the harmonic, that means the distance between the 12th fret and the bridge is too short - the string should be lengthened to match the mathmatically 'perfect' harmonic.