A banjo’s tone ring filters out some tones from the string and head, allowing others to come through. It’s kind of like an equalizer.
The banjo’s strings are the main energetic drivers of the instrument. Their sound is amplified by the head. The head’s ability to amplify the string’s energy is a question of efficiency. A loose head can act kind of like a shock absorber. The looseness of the head absorbs energy instead of converting it into vibration and sound. Low head tension results in loose coupling to the rim. A banjo with a loose head will sound kind of dumpy, muted, and often produces undesirable overtones.
A tight banjo head results in firm coupling to the rim and uses the string’s energy efficiently. The whole sound generating system that is the string-head-rim assembly has less slack in it when the head has high tension. There are fewer opportunities for energy to slip away in a firmly coupled system.
Equalizing Banjo Tone
A tone ring sits between the rim and the head. Tone rings may be made from wood or metal. Wooden tone rings are often a different species of wood than the main part of the rim, chosen for particular tonal qualities, and glued to the top edge of the rim. Brass is a common choice of material for metal tone rings.
Not all banjos have tone rings. Some banjo rims have a simple rounded edge on the side of the rim that meets the head. Other “no-tone-ring” banjos have a “bearing edge”, rounded on the outside and routed at 45 degrees on the inside, creating a sharp edge that the head sits on. Bearing edge banjos often sound crisper than those with the rounded edge (assuming equal head tension). Using a different species of wood for the tone ring is a way to draw out particular tones from the banjo’s head and strings.
It is possible to subtract certain tones, overtones, or frequencies by adding more components to the banjo’s rim . It’s kind of like an equalizer. It may be helpful to think of each component of an instrument as having a subtractive effect (says Paul Reed Smith). The additional mass and density of the tone ring material is worth considering. The shape of the tone ring’s edge at the point where it meets the head has an impact too.
Metal tone rings provide a way to filter the tone generated by the strings and the head. There are many different kinds of tone rings each of which has its own unique way of modifying the interface between the head and the rim. I’ll touch on just a few of them here.
Rolled Brass Tone Ring
I like this type of tone ring very much. It has a great old-time sound and may be my favorite. Rolled brass is about as plain as a metal tone ring gets. It is a piece of 1/4 inch or 5/16 round brass rod rolled into a ring that matches the outside circumference of the rim. This type of tone ring sits on top of the banjo’s rim. The head holds it in place. The plain rolled brass tone ring is easy to plan for and implement. This is the easiest metal tone ring to make in the small shop.
Little Wonder Tone Ring
The Little Wonder is very similar to the plain brass ring. It is perhaps a bit louder and brighter with some set ups. It uses a sleeve that wraps over the brass ring and continues over the outside edge of the rim a 1/4 inch or so. The sleeve needs a snug fit with the rim. Fitting the sleeve to the rim may require a bit of additional work with the lathe or perhaps the router. The idea is to make the sleeve flush with the outside of the rim. The sleeve provides an additional way to keep the tone ring in place.
Whyte Lady Tone Ring
The Whyte Lady offers a bright clear tone with a good bit of volume. It is similar to the Little Wonder in that it features a brass ring trapped by a sleeve. The Whyte Lady incorporates the use of scalloped ring underneath the round brass ring. The scalloped ring sits on a ledge routed into the top edge of the rim. Like the Little Wonder, the sleeve wraps down over the whole assembly and onto the rim. The photo below shows the scalloped portion of the tone ring.
Tubaphone Tone Ring
The Tubaphone is one of loudest and brightest of the tone rings commonly found in open back banjos. Like the Little Wonder and Whyte Lady tone rings, it has a brass rod trapped by a sleeve. The rod one sits on top of a hollow tube with holes drilled into it. The lathe (or possibly the router) work for the tuba-phone is similar to the Whyte lady.
