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JANUARY 22, 2018    

Bass Bars
By James N. McKean

     It happens at every violin shop. A musician appears, worried about a buzzing sound that has suddenly materialized. The instrument isn’t open, the tailpiece and chin rest are solid; there’s nothing on the outside to point to as the culprit. The violin maker examines the violin, tapping it here and there, checking the usual suspects often linked to an elusive rattle. The unspoken worry that has been plaguing the owner can be held back no longer; like a patient watching a doctor reading a chart, the worst fear arises. “Is it the bass bar?” Is it my ticker, doc? The bass bar is one of the instrument’s vital organs: out of sight, not really understood, taken for granted until things go wrong – and then the object of unreasoning fear.
     The bass bar serves two purposes that might seem contradictory. It reinforces the top, making it more rigid, and helps distribute the vibrations emanating from the bridge when you play. The violin top has somewhere in the range of 40 pounds of pressure exerted on it through the feet of the bridge. Spruce, the wood used for the top, has one of the best strength-to-weight ratios of any natural material. Even so, at its thickest point the violin top measures less than 3 mm (the cello top, in spite of its vastly larger area and greater pressure exerted by the strings, is not much thicker – not even reaching 5 mm). Forty pounds is much more than one-sixteenth of an inch of spruce could withstand on its own, regardless of its stellar strength ratio. Of course, the top could be left thick enough to resist the pressure of the strings – a good half-inch might do it – but then the violin would, with a lot of forcing, put out about as much sound as a practice violin with a mute on it. The making of a violin is a balancing act: there is a very narrow range between leaving enough wood for the instrument to last and too much wood for it to vibrate freely.
     The reinforcement the top needs is inside the violin, under each leg of the bridge. If you look in the treble soundhole, you will see the soundpost, a small dowel of spruce wedged between the top and the back. Look in the upper eye of the other f-hole and you will see the side of the bass bar. When you play your instrument, the bass bar acts like a spring under the bass leg of the bridge as it rocks back and forth, adding more vibration to the natural resonance of the body of the instrument. Because most of the sound produced by the lower strings comes from the vibration of the top plate, it is of the utmost importance that the bar be properly positioned and shaped. It has to be right before the body is closed up, for once the top is on, the bar is completely inaccessible.

The new bassbar is glued in place and clamped

 

The bassbar distributes the vibrations of the top while also supporting it. The proper shape of the new bar is determined by flexing the top as the bar is being trimmed.


 

 

     Faced with the prospect of fitting a new bar – perhaps the sound of the lower end has lost its punch, or the top is sinking more than it should, indicating that the old bar is played out – the violin repairer has not much to go on beyond experience and a good pair of ears. All he or she can do is measure the placement of the old bass bar and then have the musician play the instrument. Keeping that sound in mind when the top is off, the repairer can then deduce what needs to be done differently to make a better sound. In spite of the bass bar’s importance, and the amount of attention and care that goes into its placement, fitting, and shaping, there are few specifications to go by, and they are no more than general guidelines that must be tailored to the individual instrument and player. It’s a good example of why violin making is as much an art as a craft. Every maker has his or her own approach – one that comes down, essentially, to intuition.
     The bar itself is fashioned from a piece of spruce, preferably split (rather than sawn) from the billet to assure the straightest possible grain and therefore the most strength in the finished product. It is then fitted, by plane and knife, so that it conforms exactly to the contours of the top. This can be a tricky undertaking, for the interior surface of the top of an older instrument is, more often than not, quite irregular. To make the fitting even more difficult, the bar is sprung in with tension – which means that, when fitting it, a gap of a few millimeters is left at each end. The result is that when the bar is glued in, it raises the top slightly – so that when the instrument is strung up, the top will settle back down under the pressure of the bridge to the shape in which it was cut. Every violin maker has his or her own opinion of how much tension is necessary and how it should be distributed. In any case, the spring has to be distributed so evenly that the maker can close his eyes and roll the bar – that is, rock it from end to end – without feeling the slightest irregularity. It must fit perfectly, for the top is very flexible and will deform if necessary to match an imperfectly set bar. Shaping the new bassbar with a small thumb plane. When do you need a new bass bar? That’s not easy to say. The sound might have “gone off” – lost its cushion or bite, particularly on the lower end. But that could mean no more than a soundpost adjustment, or something as mundane as new strings or rehairing your bow. Try all these first. A sinking of the top is another clue, but again, this is hard to determine. All tops sink; it is very unusual to find an instrument, even one almost new, that has not dropped on the bass bar side. However, it’s as much a matter of how the top has sunk as how much. The key here is the shape of the top in the area of the bass soundhole. If the upper wing is sunken in, and the lower wing lifted up above the level of the top, then there is a good chance that the bar is not doing its job.

Shaping the new bassbar with a small thumb plane.

 

The bassbar also serves to distribute the vibrations of the strings and bridge. As the new bar is being shaped, the top is tapped to see how it resonates.

 

Fitting a new bassbar.


 

     The other indication of a bass bar that needs replacing is a bulging of the arch of the top, at the upper curve of the bass f-hole. The areas of the top at the upper and lower arcs of the f-hole are known as the hinges, for they are where most of the movement of the top takes place. The top is left extra thick in these areas with this in mind. While they’re supposed to move, it’s the bass bar that keeps the movement from deforming the top on the bass side. If the arch has bulged at the upper arc, the bar is not providing enough support for the top to return to its natural shape as it flexes. Cracks can develop along the bass bar – from accidents, a poorly fit bar, or a weak top. They create another problem entirely, for the repair of a bass bar crack is a major undertaking. It requires removing the top, taking out the old bar, and then fitting a new one over reinforcements.
     As for that perennial worry about the bass bar – relax. In more than 20 years of buzz-hunting, I’ve never found the bass bar to be the cause. In fact, in all that time I’ve only found one loose bar – and that instrument, ironically, didn’t even have a buzz (and luckily it still didn’t after I replaced the bar). The bass bar, like the heart, may play a vital role, some of it mysterious; but it is not the source of all strength, nor the cause of all trouble.


The finished bassbar, shaped and sanded.


     James N. McKean has been making, restoring, and dealing in fine violins in New York City since 1977, when he graduated from The Violinmaking School of America. His articles regularly appear in Strings Magazine, for which he is a Corresponding Editor. He has served in a number of positions on the Board of the American Federation of Violin and Bow Makers, including President.

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