Banjo Physiology 101

An introduction to bluegrass banjo anatomy, health and upkeep

Overall Statement:

I had a boss once who often said that "a camel is a horse designed by a committee". If this is true, a banjo is a guitar designed by a committee. In the guitar, we have this nice, all wood, unitized construction, every piece glued neatly together into one efficient, light weight, sensible instrument. The banjo, on the hand, looks like what happens when snare drums are allowed to inter-marry with tennis rackets. Some components look like they belong on a furnace more than a musical instrument. Wood meets metal, pieces are bolted together, and the overall weight distribution is so unbalanced that you can drop the pitch of the instrument simply by pulling up on the neck. This quirky, anachronistic assemblage of wood, metal, calf skin, or plastic has come to be one of the - if not the most - unique American instrument, and produces a sound like no other musical instrument in the world. People tend to either love or hate the sound of the banjo. It produces strong reactions either way. While a softly played guitar might provide the gentle background sound to a nice evening out dining with a loved one, a banjo, in the same atmosphere, would almost certainly start a fight (if not a hoedown). When Hollywood needs the soundtrack to a car chase scene, especially involving anything country, or "hillbilly", it is almost certainly going to be a banjo. They are associated with missing teeth, overalls, retarded kids on front porches, inbreeding, moonshine stills, and just about anything seen as degenerate or "Southern". And yet, the sound of a well played banjo drifting through the trees on a summer afternoon at a bluegrass festival can, has, and probably always will, given me goosebumps.  What follows is a discussion of the elements that make up this instrument, how they fit together, their relative roles in producing the overall sound, and any conclusions that I have been able to draw based on my experience with the instrument that goes all the way back to a little kid in Illinois seeing Douglas Dillard play "Shady Grove" on the Andy Griffith show, and running out to buy his first banjo for 50 dollars almost the next day. I've been lost to this instrument ever since...

 

Tone Ring/Rim Component
 

There is no other single component of the banjo that effects the tone than the combination of tone ring and rim. Remember that we're principally concerned with the Mastertone style bluegrass 5 string banjo here, although what we'll talk about could relate to any tone ring banjo, really.

The Mastertone model banjo is centered around a relatively massive bronze tone ring fitted to a wood rim, either of multi-ply or block construction. The tone ring rests on the fitted rim with a head on top, just like that of a drum, and the entire assembly is tensioned by use of a hoop, brackets and a flange (more on those later).

Tone Rings

The tone ring is the single most controversial, perhaps confusing, and certainly controversial element of banjo construction. Tone rings can range in price from a hundred dollars or less to up to a thousand dollars and beyond, and yet little is understood as to the particular makeup of tone rings and how it applies to the overall sound of the banjo. Ostensibly, the sound produced by a banjo results from energy being transferred from the plucked string through the bridge, into the head, and somehow this reverberates in conjunction with the metal tone ring and wood rim, bounces of the resonator, and comes back out of the pot in the form of banjo sound. It is a strange, anachronistic process. By rights, it wouldn't seem like the tone ring would play much of a role at all save to merely support the head. Instead, it plays the largest role. There's some controversy in how this happens. Some contend that the sound is actually generated in the area between the top side of the rim and the hollow underside of the tone ring, stating that holes in the ring are necessary to release this. Which of course doesn't explain "no hole" tone rings, some of which are highly effective at generating banjo tone. My thinking is that this hole system - the bridge, head, tone ring and rim - are all under extreme tension. This tension "stores" energy in the system which is then released when the energy of the string strike is introduced. I have absolutely no basis in science of any kind to back this with, but I bet I'm at least warm.

Tone rings are generally made of bronze. Brass is used in some lower end models. Tone rings were originally added to wood rim banjos to increase the volume and "brightness" of the tone. The Gibson company standardized tone rings with the introduction of their Mastertone ring, a single cast piece of bronze nearly 3 pounds in weight. This has been the standard in bluegrass banjos for nearly a hundred years.

There is only one universal truth concerning banjo tone rings: That there is no universal truth concerning banjo tone rings. The sonic properties imparted to the sound of the banjo from the tone ring are little understood and highly speculative. Some inexpensive rings sound great in some banjos. Some expensive rings don't sound sound good in some banjos. Some identical (at least in that they came from the same production run) rings will sound noticeably different in the same banjo. Metallurgical studies, assays and the like have been performed on various tone rings, and they point to some pretty inconclusive results. Opinion appears to have at least as much to do with the perceived quality of a tone ring as any real science. After all, the test result - the resulting sound quality of the instrument - is as much individual perception; taste, prefernce, etc., as it is anything measurable. At times in my shop, I have had several tone rings of various manufacture hanging from shelves. It is possible to strike a row of these with a rubber mallet to produce a bell like tone, and have each ring sound noticeably different from the next. What this means, however, is equally ambivalent in that it's impossible to listen to this struck bell-like ring and know what sort of comparative tone it would produce in an assembled banjo anyway.

My favorite quotable person on the subject of tone rings is Pete Wernick, who has said that individual tastes and expectations play a larger role to any sort of measurable output. He has said (and I paraphrase widely) "what is the best hair color? What is the best religion?" We all expect different things when we play a banjo based on our own personal experiences and preferences.

One of the things about tone rings that has always puzzled me is that with few notable exceptions, most rings have no manufacture information on them. You can pull a tone ring out of a 70 year old Gibson banjo and hold it next to a tone ring manufactured last month, and they will, to all appearances, be indentical. I will lead you to draw your own conclusions based on this, but suffice it to say that there is more than enough room for chicanery in this important area of banjo construction. At the end of the day, as the pundits say, beauty is in the ear of the beholder. The best tone ring is the one you prefer.

 

Rims
 

Originally, banjos did not have tone rings. The rim was the ring, so to speak. And many banjo makers still follow this tradition. A wood rim banjo with no tone ring will produce what is usually described as a "woody" sound. To me, the sound is "poppier", with less snap and clarity than a tone ring banjo. Orville Gibson came up with the idea somewhere along the line to put a big old chunk of bell bronze on top of his rims, and set the standard for just about all modern day bluegrass banjos. The combination of metal on wood with a drum head stretched over the top produces the particular sound that most people seek in a bluegrass banjo. Rims are of either block or multi-ply construction. The chief role of the rim in this Mastertone style setup appears to be nothing more than simply supporting the tone ring, but the actual case is somewhat subtler. A banjo is an acoustic instrument. Energy is put into the system when you pluck a string, the string vibrates transferring this energy to the wooden bridge which in turn transmits it to the head which vibrates. The system that supports this head plays a very large role in how this energy is returned in the form of sound. The type of wood, density, grain orientation, amount of glue, tension stored in the wood, age of the wood, may all play roles in this sound. But, if you thought comparing tone rings was a soft science, it is almost mathematically accurate when compared to rim technology and how it impacts sound. Combine the two, and you have a group of little understood, unpredictable, almost mystical variables that can make for an excellent sound, or something that sounds like it's coming out of a bricked up well. The final guideline for selecting rims and rings is simply to try many combinations of the two. I have put the same tone ring on two different rims and had an almost identical result, and conversely put the same rim on two different rings and had widely varying results. I have used multiple rims of the same make on the same rim and had different results. The same for rings. Typically, maple was used, Eastern hard rock maple. Today, birch and even cherry are popular. Puzzled by all this, I asked Chuck Lee of Lee Banjos what he thought about all this, and his response was poetically simple: "Every one of my banjo sounds different." This says a whole lot about rims and rings.

Gibson once again set the standard in rims. A three ply maple laminate rim, although during the 60s and 70s, they made some black painted relatively thin rims of up to 9 laminate layers. Some of these banjos sound great, despite the multiple laminations.

 

String Weight
 
When I started in bluegrass in the late '60s, the prevailing thought was that you had to play medium gauge strings at least, if not heavies, to be a "serious" banjo player. The thinking was that light gauge strings weren't loud enough. I never understood this. Why take what is already far and away the loudest instrument in the bluegrass band and make it louder? Isn't the banjo already the source of enough angst when it comes to playing too loud? Over the years, I've come to have a more multi-dimensional view of string weight in how it impacts the overall sound.

Volume: It is true, to some degree, that playing heavier gauge strings produces a little more volume (amplitude is the real term for this. Volume is a measurement of size.) This factor is very secondary, though, to  other factors, discussed below. First, a general pseudo-scientific discussion of relative string gauge:

Physics: Lighter gauge strings have less mass. Heavier, more. Increased mass means a couple of things: 1) It takes more energy to make more mass vibrate. You have to impart more energy to the string to get an equal  amount of response. 2) The more mass in motion, however, the more energy is released in the form of increased amplitude. But mass isn't the only consideration. The thinner a string is, the less tension imparted at the tuner it takes to bring the string to a given pitch. This means a couple of things, too: 1) It will take less energy to move this lesser tension string. 2) Less energy will be transmitted to the sound board for a given pitch if the string is vibrated with the same amount of energy. What does all this mean in terms of sound? A lot of different things. To wit:

Clarity: While measurement of the degree of clarity of sound is entirely subjective, most would agree that a lesser tension string produces a "clearer" sound.

Sustain: This is not so well understood. Some believe that a heavier gauge string, having more mass, vibrated at a certain frequency should (according to Newton, anyway) tend to stay in motion longer than a lighter gauge string, producing more sustain. Others believe exactly the opposite, that a lighter gauge string, due perhaps to its lesser mass, is going to resound longer as their is less mass to move per given unit of energy input. My experience is that string gauge plays such a miniscule role in this regard when compared to the sound quality of the tone ring/rim combination, that it's almost dismissable.

Snap, Crackle, Pop: As they say in sports lingo, these are some of the "intangibles"; those qualities that are highly subjective and very hard to do science on. I was driving to a friend's a few weekends ago, a fairly long trip of about 5 hours, which gave me an opportunity to listen to a great two CD collection of bluegrass from Rounder. Hearing all these great bands recorded over the years on God-knows-how-many different banjos really lead me to the conclusion that there certainly is no one agree upon "good sound" from a banjo. To a fairly trained hear, the difference from one banjo to the next is profound. In describing the different sounds, I find myself somewhat surprisingly falling into wine connisseur terms. Some banjos are "growly", some "hollow and distant", some "brash" and "bright". But the sound I look for, my own personal choice, can best be described by terms used by the Kelloggs company when talking about their Rice Crispies. I look for "snap, crackle, and pop". I was exposed primarily to the playing of Douglas Dillard when I was young. Douglas has always played arch-top banjos which produce a sharper, thinner sound than a flat head, Scruggs style ring. I have always had far greater experience on any banjo in producing these qualities with light gauge strings. In my own experience, what you gain in bottom end and volume with heavier strings is not outweighed by what you lose in terms of brilliance, response and clarity with light strings. But, as mentioned before, this is based on the sound that I want to hear in a banjo.

 

String Height
String height is one of those double bind variables. You want it as low as you can for reasons of ease of play, least amount of tone distortion, and yet not so low that the string will buzz on adjacent frets. The higher the action, generally the louder the banjo, but this is only because you can strike the strings harder without string "buzz". The lower the action, the easier and "faster" the banjo plays. This is an area of great variation from one player to another based on preferences.

 

Head Tension

It may be perhaps apocryphal, but Earl Scruggs is said to have responded to the question "How tight do you run the head on your banjo?" with "I tighten it until it pops, then back off a half turn." There is a lot of soft science surrounding head tension, from head tension pressure gauges to "tap tuning" in which it is proposed that you tune your head to a given pitch. What can generally be said is that the tighter the head - to a degree - the sharper the tone response from a given note. The looser the head, the "bassier" or more hollow the sound. That's about as scientific as it gets, to me. I'm with Scruggs on this one. I tighten mine until I almost can't depress the head at all with a finger. In my experience, head tension is another one of those factors that is greatly outweighed by the quality of tone ring and rim. I find that people that mess around with their head tension are usually chasing problems that could better be attributed to tone ring problems. I have a great arch top banjo built around a 1984 Gibson Grenada tone ring that I haven't changed the head tension on since I built the banjo in 2004.

Unknown, Unexplored Factors

I remember learning about the resonant frequency of objects in some physics class somewhere along the line. This is best exemplified by singing in the shower. Have you ever noticed how, when crooning a tune in the rain closet, you hit a particular note, and it's like someone just plugged in a bass amp? The walls almost seem to shake. That's because they quite literally are. You have hit the resonant frequency of the shower stall. An object exposed to its resonant frequency will vibrate in sympathy with the sound. It follows, then, that any banjo will have its own resonant frequency. This will of course be changed when you change components like tone rings, bridges, anything that provides mass to the object. Even the neck will play a role in this, although the result is noticed in teh "pot" - the ring/rim assembly. The resonator plays a large role in this as well. Just take yours off sometime and listen to the difference in sound.

The Bridge

I think if I had to choose one simple change to make to a banjo that most impacts the resulting sound, it would be the bridge. When you think about it, all the energy that you impart into the banjo, all the energy that is then returned in the form of sound, must pass through this one tiny, narrow passage. Typically made of dense maple topped with even denser ebony, grain width, grain density, all the wood factors that would impact the rim construction are magnified ten fold in the bridge. It's a very inexpensive way to punch up almost any banjo. I'm always surprised at how frequently thousand plus dollar banjos will ship to a customer with a 3 dollar store shelf bridge.  Be cautious, though. There's little precise science in bridge building, and a lot of profiteering. It's one of those components of the banjo where each year, it seems, the new "perfect" bridge is invented and sold at about 50% more than last year's.

Neck Wood, Resonator Wood

There's a lot of talk about wood selection when it comes to rims. Necks and resonators, not so much. Typically, the wood selection for these over the years has been based more in cosmetic appearance than in how it impacts tone, although there are opinions about how the dense maple of a neck will resound differently than less dense mahogany. And really, this makes some sense. Remember our discussion about resonant frequency? It would stand to reason that the neck and resonator, both components of the total mass of the banjo, will play a role in determining the resonant frequency of the instrument.  How these woods impact the tone is not so much agreed upon. The only thing I will say on this is that the wood choice for the neck and resonator plays a vastly secondary role to the choice of wood in the rim. The analog to this in the acoustic guitar would be the difference in the choice of wood for the sound board (typically spruce) and the back, sides or neck (anything from mahogany to rosewood and beyond). While the back, sides and even the neck will change the tone in slight ways, the sound board is absolutely crucial to the guitar's sound.

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