HOW SOUND POSTS WORK ON THE DOUBLE BASS
This article comes from Barrie Kolstein and was originally published in the Winter 2000 edition of Bass World (Vol. XXIV №2). Join the ISB to get this great magazine and gain access to over 50 years of great content like this!
As the climate changes from the warm summer months to the cooler fall and winter seasons, preventative maintenance for the double bass becomes essential, particularly with issues concerning its set-up.
My first topic, in what will be a continuing series, concerns the purpose, function and proper set-up of the sound post.
HOW A SOUNDPOST WORKS
Tonally and functionally, the sound post is one of the most important devices on the bass. It optimizes the instrument’s tonal qualities (i.e. sound), as well as protecting the structural stability and integrity of the instrument.
Technically, the sound post conveys lateral vibrations that enter the top table of the bass (via the string vibration, through the bridge, fingerboard, neck, tailpiece, end block, etc.) and travel to the back table, which allows overtones to develop.
These vibrations are then literally pumped out of the bass by the back table, in much the same fashion that a speaker cone projects sound out. The sound post acts as a controlling device for these vibrations by limiting the overtones and eliminating the potential for mass wolf tones, which would potentially cancel out massive ranges of the bass.
STRUCTURAL DEVICE
In addition, the sound post serves as a structural device, supporting the G string side top of the instrument. (Structurally, the bass bar supports the E-string side, and also provides limited support to the G-string side.) But the proper fit and placement of the sound post really protects the structural integrity of the top. The correct placement of the sound post is a procedure that I feel should be accomplished by a qualified repairman, at the very least, annually.
Aspects that should be considered are the fit of the post, the position of the post and the material utilized for a particular instrument’s sound post. These aspects can greatly affect the tonal and structural qualities of the bass in either very positive or adverse ways.
KNOWLEDGE IS POWER
Even though I strongly advocate the adjustment of sound posts to be accomplished by a qualified repairman, I do feel that a player’s knowledge of the correct placement for the sound post is useful information.
In the “textbook” position, ideally the sound post is positioned centered behind the G-string foot of the bridge, approximately 12 to 14mm or 1/2″ to 3/4″ away from the backside of the bridge, favoring the tailpiece.
In general, the more that you move the sound post toward the tailpiece and away from the back of the bridge, the more a darker, open quality of sound will be obtained. However, in this position a less well defined quality can result.
WHY?
Because the post has a less controlling effect upon the primary vibration passing through the bridge into the top and then on through the post and ribs to the back table.
Conversely, the closer the fit of the post to the backside of the bridge, the brighter and more pointed the sound will be. But each bass reacts slightly differently to sound post adjustments.
All of this works in theory, but each instrument is different, as are the tastes of players and those doing their adjustments.
DARK-SOUNDING INSTRUMENTS
Another important consideration is the type of wood utilized for the sound post itself. For an extremely dark sounding instrument, lacking point and definition, I will likely choose a higher density piece of spruce (that “taps” tones of a higher pitch), perhaps use a slightly smaller diameter, and place the post in a somewhat tighter position to the backside of the bridge. This will likely obtain a more pointed tone that will enhance the existing dark qualities of the bass and produce better definition and point.
BRIGHT-SOUNDING INSTRUMENTS
For an instrument with a bright, high tension or lacking depth of sound, the opposite basically occurs. I would choose a softer density material for the post, with a lower tap tone pitch, wider grained and a bit thicker in diameter (perhaps 20 to 22 mm) and position it a bit further away from the backside of the bridge. This would likely enhance the depth and warmth of the bass, but maintain the point to its sound.
FITTING THE SOUND POST
In my opinion, the fitting of the sound post is the most difficult part of the procedure, requiring the experience of an individual who has cut thousands of sound posts for all designs of basses, so that it has become second nature. The difficulty in fitting comes from the fact that it is considered a “blind” fit. The repairperson is not able to see the two interior surfaces (of the top and back
tables) to which the post is fit.
SO HOW IS IT DONE?
Through long term experience of fitting posts to contours of similarly designed basses, or from having a long term relationship with the instrument about to be adjusted.
Clearly, the experience of the individual who is doing the sound post adjustments and his familiarity with your instrument (or instruments of similar quality to yours) may have a marked affect upon the tonal qualities of your instrument. The post is first fit (carved for length and shape) as accurately as possible to both interior surfaces. After that, it is soaked in hot water for about 30 seconds, to soften the density of the end grain. This produces “forgiveness” in the wood of the post, allowing it to more accurately fit any slight voids or inaccuracies in the top or back table surfaces.
EXPANSION AND CONTRACTION
Structurally, most instruments are in constant transition, with top and back rising and contracting due to the climatic and environmental changing conditions. In general, most tops and back will rise in the summer or warmer climate and contract in the colder climatic
conditions.
Unfortunately, the sound post itself stays consistent in length and does not adjust to these changes of the bass. In the summer, with the expansion of the top and back, the post will likely loosen. Usually, I do not feel that this is a major concern, structurally or tonally, unless the change is extreme. The tonal qualities may be affected, but this is more likely because the tension of the strings on the bridge will end up compressing the top of the bass to meet the shorter
sound post.
In extreme cases, this could possibly distort the top, causing some sinkage in the sound post area of the table. This scenario is not common and should not be of major concern.
The contraction of the top due to the cold climatic conditions, however, is a much more serious problem. When the top and back contract, the sound post becomes tightly fit into the instrument. Inevitably, adverse tonal effects are felt, usually in the form of a tightening of sound of the bass, and if there are wolf tones or difficult registers of a bass, these problems will be greatly magnified.
POTENTIAL STRUCTURAL PROBLEMS
Of even greater concern are the negative structural effects that may occur. At the very minimum, the soft top table will usually suffer some form of gouging from the overly tight sound post, and in extreme cases (such as an instrument that is subjected to some form of trauma, like an impact), the bass may suffer a crack in either the top table, back table or both. This is something that needs to be avoided at all extremes!
Sound post crack repairs are extensive, expensive, and even if accomplished in an expert manner, they will depreciate the value of an instrument. The key here is preventive maintenance performed
by a qualified repairperson!
ABOUT THE AUTHOR
Barrie Kolstein has completed well over one hundred instruments (Violin, Viola, Cello and Bass Violins) utilized by renowned players including Jeffrey Turner, Pittsburgh Symphony; Robert Gladstone, Detroit Symphony; James Van Demark, Professor of Double Bass Eastman School of Music and world famous soloist; Charles Urbont, Metropolitan Opera; James Clute, Minnesota Symphony Orchestra; David Sheets, Baltimore Symphony Orchestra; Lou Norton, New York Philharmonic; Caitlyn Kamanga, Hong Kong Philharmonic;, Scott Haig, Assistant Principal Bassist, Cleveland Orchestra; Hienrich Joachim, renowned soloist and former member of the New York Philharmonic; Lew Norton, New York Philharmonic; Barbara Yendell, and the Hong Kong Philharmonic.
