Tuesday, September 28, 2010

How Does One Set Up A Bridge? How Does One Replace Strings?

Have you ever noticed that your Dixie sounds out of tune as you play it on higher frets? You can fix that by adjusting the intonation of the instrument. Here's how.

Two different types of bridges.
As you probably know, the bridge is the device at the opposite end of the strings from the tuning pegs and the nut.

There are several things that affect the tuning of strings:
  • The length of the string (from nut to bridge).
  • The tension on the string.
  • The diameter of the string.
  • The tension on the banjolele's head.
  • The material the string is made with.
  • The weather (temperature, humidity, maybe barometric pressure).
Shorter strings vibrate faster than longer strings. Tighter strings vibrate faster than looser strings. Smaller diameter strings vibrate faster than larger diameter strings. Warmer strings vibrate faster then cooler strings. Humidity and barometric pressure can affect ears as well as the speed of travel of sound waves.

Faster vibration = higher pitch. Slower vibration = lower pitch.

You decide the diameter of your strings when you purchase them.

You control the tension of your strings by adjusting the tuning pegs and the banjolele's head tension.

You control the length of your strings by adjusting the bridge. But what is proper adjustment?

The rule I follow is that the strings should be in tune when played open and when played at an octave higher (the 12th fret).Doing whatever is required to get both in tune is called "adjusting the intonation."
  1. Using your ear or a tuning device, tune one of the strings to proper pitch by adjusting the tuning peg for that string.
  2. Play the same string while pressing the 12th fret.
  3. If the 12th fret tuning is flat (lower than the proper pitch), you need to shorten the distance from the 12th fret to the bridge. If the 12th fret tuning is sharp (higher than the proper pitch), you need to lengthen the distance from the 12th fret to the bridge.

    • The only way to do this is by moving the bridge. Yes, this will affect the open tuning of the string, but we'll take care of that as we go along.
    • To state the obvious, moving the bridge toward the 12th fret will shorten that distance (raise the pitch). Moving the bridge away from the 12th fret will lengthen that distance (lower the pitch).
    • How much should you adjust the bridge? If you're just learning this technique, start by getting the exact pitch at the 12th fret.
  4. Now check the pitch of the open string. It will probably need some adjustment using the tuning pegs.
  5. Recheck the tuning at the 12th fret and make any adjustments necessary.
  6. Recheck the open tuning and adjust.
  7. Get used to doing steps 5 and 6. You may end up doing that a lot on all four strings.
  8. Complete steps 1-7 for all four strings.
  9. Recheck the open and 12th fret tunings of all the strings. Tweak any that require it.
  10. You may find that the bridge ends up at an angle -- that's OK and happens a lot in my experience. If you look at the Dixie in the photo at the top of the blog, you'll see that bridge is at an angle.
  11. Notice that the tuning of an individual string can affect the tuning of all the other strings. You may have to meet a happy medium with your final setting so that the strings are as close to correct as possible.
  12. Over time, you'll learn how to make quicker adjustments by "almost" correcting the 12th fret tuning so that a proper open tuning will bring the 12th fret to perfect tuning.
"So," you say, "I'll put a pencil mark so I always know where to set the bridge." In a perfect world, this would work. The problem is that all strings are not created equal (even if you always buy the same set). Very minor variations in string diameter and string material (gut, nylon, steel, whatever) will affect the 12th fret tuning.

Many stringed instruments have individual string adjustments for intonation, so there's no need to move the bridge. These are usually devices that move each individual string slot of the bridge.

Restringing --

While I'm at it, let me share with you one way to avoid string slippage when re-stringing with either nylon or steel strings.

First, make sure that you have enough string to fit the instrument :-) This will let you know how much extra you have to work with.

Replace one string at a time. Keep the old strings in place and leave them as tuned. This keeps the bridge in place and proper tension on everything while you're replacing each string.

On one end of the string, do a surgeon's knot by forming a loop and passing the end of the string through the loop 2-3 times. Larger diameter strings will easily get by with two passes through. This knotted end of the string becomes the tail end.

Three times is probably overkill for this gauge string.
Since this string is nylon, it would make it easier to tighten the knot by wetting it. If you do that, make sure to dry it off good before putting it on the instrument.

The tightened surgeon's knot.
You only need to hand tighten the knot. If you trim the "tail" of the string at the top of the photo above, make sure not to trim it so much that it will slip back through the knot. By the way, I ended up only using two passes through for this knot.

The knot goes below the tail piece -- string up through the hole/slot.
In the photo above, I'm replacing metal strings with black nylon strings. The metal strings came with the Dixie when I bought it. The pencil bridge marks you see will do me no good for setting proper intonation. The nylon strings will most certainly change that setting.

This knot will tighten more when you tune the string. This will require that you keep tuning the string until the knot is as tight as it is going to get.

Feed the string through the hole in the tuning peg.
Notice that I've not removed all of the strings -- just the one I'm presently replacing. This helps me to remember the rule that "strings wind around the tuning peg from the center of the instrument to the side." The center is where the "X" in Dixie is, between strings two and three. So, the strings closest to you in the photo above (strings three and four) wrap around the tuning peg from the X (inside) toward you or the outside.

String numbering -- what's with that? String 1 is the string toward your feet when you're playing. To really confuse things, that same string is also called the top string. This sounds like a perfect "who's on first" scenario :-) The way to remember it is that usually the highest pitched string is string number 1, and # 1 is always on top. Also, string 1 is usually the highest pitched string, making it the top pitch.

So, string 1 is also called the top string, but it's on the bottom when you're playing the instrument.

String 4 is also called the bottom string, but it's on the top when you're playing the instrument.

What if you wind the string the wrong way? It might make the inner strings (2 and 3) rub against the tuning pegs of the outer strings (1 and 4). That may cause unwanted vibration/noise. Otherwise, the instrument would still work.

If you do wind a string the wrong way, just loosen it and restring it the proper way.

Put the string through the peg hole twice to form the loop you see.
It doesn't matter which way you put the loop above, but this one little thing will limit string slippage a lot.

How much string does one need to leave loose between the tuning peg and the tail piece so we have some string to wind around the tuning peg?

I use two to three fingers at the 12th fret.
 Before I tighten the loop, I make sure there's enough string to go around the tuning peg at least twice. For all but the thickest strings, I find that two fingers is enough. While I'm raising the string two fingers at the 12th fret, I pull on the loop at the peg until the string is fairly tight against my fingers.

Pull the loop tight.
Try to keep the loop tight as you tighten the string. Also, keep the string relatively tight between the tuning peg and the bridge so it wraps snugly around the tuning peg.

This is a view of another 4th string I'm replacing.
Notice that the string is wound tightly around the peg.

Tune the string. It will quickly go out of tune because of knot tightening and stretching. No problem. That's normal. It may take several hours (or even days) before it stays in tune.

Most important! Be extremely careful trimming the string's extra "tail" at either end of the string. It's easy to accidentally cut the string itself. If you do cut the string and it is too short to use as cut, it may still be usable if you read up on knots to re-attach the two pieces back together.

I hope this information is helpful in some way.

2 comments:

  1. thank you. I haven'y been able to find much n the subject. Do have any tips on drum tension?

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  2. The best thing I can say is be careful applying the tension, especially on an older head. Better to have a loose head than a busted one.

    Remember that the type and gauge strings you have can make a real difference in the sound you're getting from your Dixie. Order several different brands and find the one that makes your Dixie sound the best it can the way it's set up right now. If you're still not satisfied or if you're sure that the head is too loose -- it isn't holding the bridge up enough to keep strings from buzzing, it's easy to press it down with very little pressure, etc. -- go slow in tightening.

    If you're familiar with changing a car tire, you know that you don't tighten it by going from one nut to the next.

    Tighten no more than 1/8 of a turn each time. The head tension nuts have 24 turns per inch. So you're tightening the head down by 1/8 of 1/24 inches with this 1/8 turn. That works out to 1/192 of an inch. Doesn't sound like much, but it can make a real difference depending upon the already existing tension on the head.

    Before you start the process, tune your Dixie and record yourself strumming it with various strum pressure and various chords. It doesn't have to be musically correct -- just do something you can play again later.

    I'm assuming that this is a head that has been under tension for a while and it's not very or totally loose.

    Now loosen your strings so there's little to no pressure on the head (bridge).

    Start with one of the nuts next to the neck/body connection. 1/8 turn.

    Now tighten the nut directly across the body from it. 1/8 turn.

    Now go to the 2d nut from that one in a clockwise direction. Tighten 1/8 turn.

    Next is the nut directly across from that one. 1/8 turn.

    Now go clockwise to the next nut (just one removed at this point). 1/8 turn.

    Go to the one directly opposite that one. 1/8 turn.

    Go clockwise to the second nut from there. 1/8 turn.

    Go to the nut directly across from it. 1/8 turn.

    That's all 8 of them.

    Tune and play. Compare the sound with your recording.

    If you hear a desired difference but don't think it's enough, take the above steps once again.

    If you hear no difference (and the head's not obviously loose), I'd leave well enough alone.

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