As much as I dislike getting involved with this again, I find it necessary to correct certain inaccuracies about the A0-B0 matching process that have been posted here.
When we talk about A0-B0 matching, we are actually discussing the process of
exactly matching the vibration frequency of the entire neck assembly which includes the scroll, neck handle, machines, and of course the fingerboard with the A0 mode frequency. The goal is to have the entire instrument vibrate together in sync. If the A0 mode frequency is 71Hz, the B0 must be exactly 71Hz to match the A0. Using audible pitch such as the musical note "C" is far too inaccurate to be of any practical value for doublebass A0-B0 mode matching.
Adding weight to or subtracting weight from any part of the neck assembly will influence the vibrating mode frequency of the entire unit. Unlike the scroll and neck, the fingerboard is considered to be replaceable and is frequently modified by planning long after the instrument was completed by the maker. This makes it a very convenient place to add or subtract weight for the B0 mode frequency adjustment. However, when we do B0 adjustments, we are not doing it by changing the tap tone of the unsupported portion of the fingerboard, even though the tap tone pitch probably will change in the process. The tap tone of the fingerboard is the tap tone of the fingerboard - nothing more. Some makers do tune the fingerboard tap tone to a particular musical note, but this is
not B0 matching. If I were to swap out the tuning machines with a heavier or lighter set without touching the fingerboard, the B0 mode frequency will change up or down. However, the tap tone of the unsupported portion of the fingerboard would remain exactly the same as before.
The accepted method for finding the B0 resonance mode frequency is to use a high precision sine wave sound generator and a highly amplified speaker to set the neck assembly in motion. To find the B0 frequency, we slowly sweep through a frequency range of about 50 to 100 cycles per second (Hz). This is the range where A0 and B0 are usually are found. The B0 frequency is found when the neck vibrates at it's maximum amplitude. You can easily feel this with the tip of your fingers at the end of the scroll or the end of the fingerboard. In order to match the A0 mode frequency, we usually remove or add weight at the end of the fingerboard, but we could add or subtract weight from the scroll and accomplish the same thing.
[Added 9/19/07 by request]
Before the B0 mode frequency can be adjusted, the A0 mode frequency must be determined. This is the resonance frequency of the air that is contained within the body of the instrument and for all practical purposes can not be changed. For A0, the sine wave generator driven speaker is pointed at the back of the instrument and slowly swept through the 50-100Hz range. An inexpensive
Radio Shack ****OG Volume Meter is used with an extender to determine the maximum volume amplitude inside through one of the ff holes. If you were to plot the frequency and volume, you would find the A0 to be a very sharp peak. [End]
Because my 1997 paper on A0-B0 matching in basses was written for the Journal of a group of violin makers (The Michigan Violin Makers Assn), I may have made the assumption that the reader would have certain knowledge as a result of them making instruments. Someone who has not made instruments may misinterpret the meaning of certain things. The paper was checked for accuracy prior to publication by MVA Journal Editor David Brownell. David is also one of the co-authors of the Chuck Traeger book and a well known violin luthier. After publication, the paper was peer reviewed by the membership of MVA in a general meeting. In the decade since this paper was written, several freeware and shareware computer programs have become available that will substitute for the sine wave generator and greatly cut the cost of equipment needed to perform this process.
If anyone cares to read the entire paper, feel free to send me an email or PM requesting a copy of the paper. Please be sure to include an email address that can receive a 2.5 Mb document.