From Banjo Newsletter, 2003
This month we're going to explore the topic of banjo bridges. We will look into their function, learn some tips to help choose a good bridge, and enter the world of smoke & mirrors. We will even give the experts reason to go back to school.
The choice of a bridge is a major point that you as the musician have complete control over. Its contribution to the overall sound of your banjo cannot be understated. Hopefully the information presented here will help prepare you to choose a bridge that suits your needs.
The bridge is the point where all energy from the plucked strings enters the banjo to be amplified and become music. Because of its relative minute size you may likely understand why small details can have profound effects on its ability to transmit string energy. By its nature it acts as a filter, enhancing some frequencies and suppressing others. This can be both positive or negative depending on many variables, not the least of which is what sound you like from your banjo.
Important factors that control how any bridge will sound include what materials its made of, its design or shape, its dimensions (weight, height, and thickness), and its density.
I want to concentrate on mostly dimensions and density in this discussion.
Hard rock maple is the wood of choice for most but not all bridges. It has gained this acceptance because its natural properties produce the sound we have come to accept as "banjo music." It is also strong enough to resist the stress of string tension.
A key feature of maple is its hardness/density. It allows a crisp, clear sound with a minimum of "damping." Damping is the effect of "coloring" the sound by absorbing certain frequencies. Excessive damping will produce a tone that is "muddy," lacking in clarity, and unbalanced. Maple has the ability to produce the crisp ringing trebles while at the same time it transmits those deep bass notes that every good banjo has in abundance.
That being said, there is still great diversity of characteristics within each tree and even each board. Some bridges will produce a great sound for you while others wont. We will now explore some of the reasons for this.
The following guidelines and recommendations are generalizations, and do not assume the vast variety of possibilities available when set up specs. are changed. So....all other things being equal....
A bridge that is thinner and/or lighter in weight will tend produce more power and volume. It will allow your banjo to produce a bright tone stronger in the treble ranges. This kind of bridge is a good choice for anyone needing more power to be heard in a group situation. Also, anyone needing to brighten the tone of banjo with a dark or "muddy" sound should consider this feature.
A bridge that is thicker and/or heavier will enhance the bass response and depth of tone from your banjo. It will also tend to reduce the overall volume in many cases.
This is the kind of bridge to look for to reduce the harshness of an overly bright banjo. And obviously this is a characteristic to explore to improve the proper balance of tones in any banjo requiring more mid and bottom end range of tone.
It should be noted that drawing out a balanced, clear tone from your banjo that is strong in mid and bass response is a much more difficult task than simply making a banjo louder or improving the treble. The search for a full rich sound can turn into a quest and involves every aspect of banjo set up of which bridge selection is just one point. It is my advice to approach the heavier bridges in a conservative manner. Some banjos will show significant change in sound with as little as 0.2 grams change in bridge weight. It's very easy to pass up the improvement in sound and go straight to a "muddy" tone. Without getting too technical, it must also be mentioned that weight distribution within the bridge also effects its performance. In other words, a bridge with thick, heavy feet will sound different than a bridge the same weight with a thick heavy top.
Most bluegrass banjos will have a 5/8 inch tall bridge. This has come to represent the "standard" in bridge height. It is tall enough to exert enough string pressure on the head to produce the power and full tone demanded by players.
A bridge lower than this is really not suitable for bluegrass instruments. Taller options do exist and bridges of 21/32 and 11/16 are very common.
The primary reason for using a taller bridge is to increase the power, and improve the tone of your banjo.Here again, the exact effect on tone will depend on other aspects of the total set up.
One word of advice. Although a very slight raise in string height over the fingerboard can assist in executing pull-offs, there is no good reason to have excessively high string action over the fretboard. The power and performance benefits of using a higher bridge are focused on the height of strings off the banjo head by increasing string tension on the head. If you do change from a 5/8 inch to a 11/16 inch bridge or higher, you should plan on having the heel of your neck recut to return your string height to its original setting and playability.
At this point you may be feeling a bit overwhelmed with information. If so, this is for you.
Here is a very simple test everyone can do. I learned this trick over 20 years ago. Many banjo technicians and bridge makers use this exact technique to test and select a good bridge. Again, as in adjusting your banjo head, it involves simply listening.
Assuming you are selecting a bridge from a group, take each bridge and drop it on to a solid surface such as a table or counter top. Listen to the sound the bridge makes when it hits the table. Listening carefully, you will notice that each produces a different sound. Regardless of the sound you want from your banjo, the response you are looking for can best be described as a clear and distinct "click". The bridges to avoid are the ones that make a dull lifeless "thud" when dropped. This is directly related to damping and the density of the bridge material.
There is no real relationship between a bridge that "clicks" being strong in treble sound and one that "thuds" being good for bass. What you are experiencing is that the "thud" bridges are lower in density and the clarity is being absorbed (damped) into the bridge itself. This characteristic will show itself in the sound produced by a banjo with this bridge, where the sound will be more "muddy" and unbalanced. I tend to use this technique not really to find a good bridge as much as I use it to eliminate the obviously bad ones. Then ,from the group of "clicking" bridges, I can go ahead and select thick/thin or heavy/light according to my needs.
My apologies to the music stores who will be accosted by customers bouncing bridges off the counter tops!
Now we will enter the world of mystery and misinformation. I consider the counting of grain lives in a banjo bridge to judge its performance to be a major point of misinformation in the banjo world. I find it astonishing that in spite of the fact that even acoustic guitar builders learned almost 15 years ago that this point when choosing spruce had no real bearing by itself on the performance of a guitar, banjo players seem to cling to this myth. I know people who swear by a certain number of grain lines per inch being the secret to "the sound." Unfortunately there seems to be those who swear that the magic number is "as many lines as possible." Some that insist the number is between "5 to 7" and those that promote "3 - 4." If you consider this inconsistency with the fact that no one has an answer when one of these bridges doesn't produce "the sound" and you have solid grounds to be skeptical. I often see that instead of questioning, people choose to invoke the "banjo gremlins" as responsible.
There are many things that contribute to a bridges potential sound. Grain lines do figure into the question, but by no means can they be seen as a point that stands by itself as showing good or bad in a bridge. Weight and density are much more consistent indicators to judge by.
What was the point that shook the acoustic community 15 years ago and caused a reassessment of standards in the selection of spruce for guitar tops.
The term is "grain run-out" and it is now common knowledge in all aspects of acoustic building except banjos. Violin makers have known of this for 100's of years.
Grain run out is the invisible flaw that will ruin a piece of wood for any use where its strength or acoustic properties are important. It is truly invisible. The most perfectly quarter sawn (grain lines laying 90 ° to the cut faces) guitar top, or banjo bridge can be structurally weak and acoustically, trash. Natural run-out occurs when a tree twists as it grow, a not uncommon condition. When a board is cut from this tree, the wood fiber chains that normally run the entire length of the piece, (the wood between the grain lines), will enter and exit on the sides & faces of the wood, due to a straight piece being taken out of twisted stock. This wood is obviously weak due to the short fibers, and this also means sound does not travel through the piece consistently for the same reason.
Acoustic guitar tops made from this kind of wood will be weak and very inconsistent acoustically. And so will banjo bridges. This is one of the reasons for the inconsistent sound coming from numerous bridges that are all made from visually beautiful wood. This also contributes to the "thud" we talked about. On a banjo bridge specifically, this means that the fibers that should run the length of the bridge (and carry sound waves) may be as short as a fraction of an inch due to the thin width of a bridge.
The only guaranteed method of guarding against this problem is the method used by violin makers for hundreds of years. You must split not saw one face of the wood from which you will cut the bridges. If there us any run out, the split will follow this and give you a clear sign.
This is an introduction to a very complex subject, one that musicians need not understand, but builders and repairmen need to be educated about.
This has been a peek into the science and technology of the banjo bridge. There is much more to touch on. I will explore this in future columns. Topics like alternate (non maple) woods, and non traditional designs deserve attention and have a wealth of new sounds to offer the banjo player.
Until next time...........
Scott Zimmerman - 9-9-03