THE AIR CHAMBER
Banjo Setup File #3
Note: This information is valid only for banjos with resonators.
In his recently released book, How to Set Up the Best Sounding Banjo, Roger Siminoff discusses tuning the air chamber. The air chamber is the complete rim and resonator setup with the head. In other words, it is the enclosed space defined by the head, rim and resonator. In other instruements, such as guitars, mandolins, violins, etc., there is an optimum pitch for the air that is enclosed by the body of the instrument. It stands to reason that the same would be true of banjos.
While I agree with Roger that the air chamber of a banjo has an optimum pitch, I do not agree that it should fall within a limited pitch range. Roger and I disagree on a number of points on banjo construction and adjustment.* One of these is in tuning the head, another is tuning the air chamber. Roger feels that all flathead banjos with a one-piece flange should be tuned to a particular pitch, and that all archtop banjos with a one-piece flange should be tuned to a different specific pitch. This does not take into account the differences in the tone rings, the rim densities, etc. In the section on tuning the head, I discuss the facnt that this pitch may vary greatly from one instrument to another. When we adjust the head tension, we are looking for the resonant frequency of the head and rim assembly. This may vary depending on the tone ring, the rim and some other factors.
If it is true that different tone ring and rim combinations will have different resonant frequencies, then it stands to reason that the different air chambers will also have different resonant frequencies. My method for tuning the air chamber is similar to Roger's. It is done by changing the depth of the chamber.
Remove the resonator screws and place the instrument in the case. The strings should be off the instrument for this procedure. You will need several 1/32 inch thick shims about 1/4 inch by 1 inch to do this work.Tap the head of the instrument in several places and take note of how responsive the sound is. Place a shim between each of the resonator brackets and the resonator and repeat the procedure. (If your resonator flange brackets do not extend all the way to the resonator, place the shims under the resonator flange itself.) As you approach the optimum air chamber depth, the sound will become more responsive. When the sound begins to become less responsive, remove one shim from underneath each resonator flange bracket. Make note of how thick the stack of shims that was necessary to achieve the correct distance is.
You have three choices at this point. If your banjo has short resonator flange brackets, which do not extend to the resonator itself, you can purchase the proper long brackets, and bend them to the proper angle to place the resonator into the proper relationship with the resonator flange. If you already have the long brackets you can bend them downwards to make the air chamber deeper. Or you can glue the shims (or their equivalent) to the underside of the resonator flange brackets, which will give you the proper chamber depth for your instrument.
*Note: this does not mean that I think that Roger is all wet, a raving loony or anything else like that. If you adjust your banjo the way he tells you to in his book, you will very likely end up with a good sounding banjo. Many people prefer my method. One thing about my method. You can't beat the price.
Go back to Banjo Setup
Go back to My Music
©2006 Bill Palmer. All rights reserved. For permission to republish contact Bill Palmer. The opinions expressed on this page are strictly Bill Palmer's. Mastertone, Stelling and the other brand and model names are the property of the manufacturers and other people who own them.