Sound post tension...

Discussion in 'Setup & Repair [DB]' started by dhergert, Nov 20, 2018.

  1. dhergert

    dhergert Gold Supporting Member

    Jan 17, 2018
    Blue Zone, California
    I've recently had an eye-opening experience with the sound post in my Alcoa and wanted to hear if this is at all useful or practical for "normal" wooden double basses...

    First, there are some points about my Alcoa that should be mentioned:

    1) A typical stock Alcoa body is welded together and the top and back are not likely to separate from the ribs.
    2) My Alcoa has had a custom welded-patch repair to the top under the bridge area.
    3) My Alcoa has had a hinged trap-door installed in the driver side C to facilitate repairs and other customization. This trap door has allowed me to do some experimental and prototype sound post work.
    4) I've created and successfully installed a platform-topped sound post to provide more distributed support for the top repairs under both feet of the bridge.
    5) This platform-topped sound post is adjustable for length in 6 discrete locations and in one general location.
    6) Up to this point I have been using low tension strings on this bass (Innovation SilverSlaps E and A under SBW Deluxe G and D)

    A couple of weeks ago I increased the tension of this adjustable sound post by increasing its overall length by probably about 1.5mm. The goal was to reduce some subtle rattles that I was hearing while playing pizz at what was then the instrument's top volume. While 1.5mm isn't much, it did make the sound post significantly tighter.

    This has resulted in the desired elimination of the rattles. It has also noticeably increased volume and note clarity and it has reduced overtones, enough so that I'm no longer concerned about changing to higher tension strings in order to produce greater volume. Since making this change, I've played this bass in groups where I previously couldn't hear my bass acoustically, and now I can hear it very well, so I'm very pleased with this sound post change...

    I'd really like to hear thoughts about this:

    For a "normal" wooden double bass, is it (1) safe and (2) helpful to increase sound post tension when trying to achieve higher volume with low tension strings?
    Last edited: Nov 20, 2018
    Povl Carstensen likes this.
  2. wathaet


    May 27, 2007
    I think a general rule is hard to define, but I can tell you what my Pellacani and Hill do.
    The Hill actually sounds bigger with a looser post, but response and clarity is better with 1-2mm more length. It is louder where it matters in orchestra with a loose post, but maybe a bit more high end with a longer post.
    My Pellacani had too short a post by far and seemed only to like super low tension like genssler or tuned down solo. Once it was normalized it got bigger sounding, lost the scratch on the D string and sounds great with heavy strings all of a sudden. To be a bit unhelpful, it also seems different with each type of string. The variables drive me nuts!

    As for safe, I did it on a rather expensive 250 year old bass, but I am a bit nuts.
    Povl Carstensen and dhergert like this.
  3. dhergert

    dhergert Gold Supporting Member

    Jan 17, 2018
    Blue Zone, California
    Thank you Wathaet...

    Regarding that difference with each set of strings, my guess from seeing this sudden change with my bass is that maybe each bass has an optimal total tension of the strings combined with the tension of the sound post... And that perhaps the effect of these variables is something that is only becoming known as people start using adjustable sound posts more and more. Or maybe it's only visible to people like yourself and others here, who have been around a whole lot of double basses in the process of hearing, playing and maintaining them.

    And of course there is the weather changing now too -- while my aluminum bass isn't prone to humidity changes, it is prone to metal contraction and expansion due to temperature changes, so there might also be something going on there.

    These are very interesting beasts, double basses.
    wathaet likes this.
  4. BobKay

    BobKay Supporting Member

    Nov 5, 2012
    Estero, Florida; USA
    My recent experience is just the opposite of yours. Within the last two months I had sound post adjustments on both my hybrid and full ply. In both cases the soundpost was too long, probably because it was fitted in a drier climate and I live in SW Florida. On the hybrid I also changed from Spiro mittels to EP weichs. More volume, bigger sound. Maybe the top was being choked by the too-long posts. So I can’t confirm your results.
    dhergert likes this.
  5. Of all the possible “fiddlin” that can be done in a proper set up and maintenance on a doghouse, sound post placement and adjustment seems to me the most alchemical in both tone improvement and the actual process!
    dhergert likes this.
  6. dhergert

    dhergert Gold Supporting Member

    Jan 17, 2018
    Blue Zone, California
    I agree, different results, however your experiences may support my theory... That each bass has an ideal combination tension made up of both the string tension and the sound post tension -- and of course that is assuming the sound post is in the right location.

    Alchemy, yes. With multiple variables that are going to be different with every bass, it has to be very much like magic. And while adjustments may be excellent, perfection may never be verifiable.

    Wouldn't life be boring if there wasn't any mystery?
  7. james condino

    james condino Spruce dork Supporting Member Commercial User

    Sep 30, 2007
    asheville, nc
    Trap doors / access panels are wonderful in that someone like yourself can make these kinds of experiments to change both the position and tension ten different times within about 20 minutes, removing the alchemy, and then make a rational decision on their own. All basses should have access panels of some kind instead of having to play the #$%&*ING ship in a bottle game every time you need or are curious about a 30 second sounpost adjustment or a 15 minute repair instead of taking the whole top off!!!!!!!!!
  8. dhergert

    dhergert Gold Supporting Member

    Jan 17, 2018
    Blue Zone, California
    James, thank you for chiming in here. I totally agree!
  9. Gamba model fresh off the bench Feb/2020. Fully carved, sitka top, Italian black poplar back and sides. 42-3/8" mensure (turned out longer than I hoped). Heavy bass at 23.6lbs is 2.2lbs heavier than my Romanian flatback with C-extension. The center of the top table is 9mm, edges are about 4mm. Well arched.

    The sitch: I'm an orchestra/chamber/solo player. I've been experimenting on this new bass with my string box: belcanto, super flexible. permanent, evah P weich, S42 weich, S42 mitt, Jargar med, flex deluxe, Polychrome, passione med, flex 92. The last three sets (with S42 mitt E) being the most promising. Currently on my old flexocor 92 med set with old spirocore S42 mitt E. Overall, this bass seems bright and tight, I'd like more bottom, and better arco response for pianissimo. Has a great top end arco. A-string, both open and thumb harmonic, is wolfy. D-string F# thru Bb can be wobbly. Jazz pizz on this bass is plenty growly/sustainy with these strings.

    Given the above sitch, what do you guys think about this current SP placement (image below)? Previously, the SP was 5mm up norther and set in tighter more east, so I moved it here as shown. The pencil lines mirror the bass bar. It's tension is loose because I set it in with the G string not quite slack. What kind of tone, feel, and response would you expect? It didn't magically pop open the sound, maybe helped only a little. I want to know how far I can push it? And in which directions/tensions for more bottom and better arco response?

    I'm thinking try it south another 5mm (27mm)? But not sure about east/west?

  10. Well I just fit a new SP in this more south-western location below. Right away, the A is way more wolfy and the D and G strings seemed to get dimmer. The E is about the same.
  11. Greg Clinkingbeard

    Greg Clinkingbeard Commercial User

    Apr 4, 2005
    Kansas City area
    Black Dog Bass Works
    Only you know what sound and response you prefer. I am cautious about moving it too far from the bridge foot because it may compromise the top, unless the top is overly thick. No more than a diameter south and never outside the foot, east to west.
    DoubleMIDI and Michael Drost like this.
  12. The first spot is sbout where my sound post is. Which as hoped gave a deeper, softer sound/feel than before, when it was closer to the center (I shortened it 2 mms). The second placement seems almost too far from the bridge, even to my taste. But what works, works.
  13. Matthias Hacker

    Matthias Hacker

    Apr 8, 2018
    I´d follow this advise. Usually the east-west placement follows exactly the bass bar. I´d put it there and not worry about that any more.

    My experience: you´d better worry about a proper tension (length), a good fit, and straight placement between top and back. As a rough orientation for a proper tension, take a look at the treble side f-hole when the strings are tuned.

    What is marked here as "obere F-Klappe" should be in line with the surrounding table, or just a tad (0,5-1mm whatever that is in inch) below. With a lineal or even a pencil on the table you can make that perfectly visible. Know what I mean?

    Good luck!
  14. Greg Clinkingbeard

    Greg Clinkingbeard Commercial User

    Apr 4, 2005
    Kansas City area
    Black Dog Bass Works
    On a new bass (or one which hasn’t had too short of a post) it’s good practice to have the upper wing flush or slightly higher than the surrounding plate before any string tension is applied. Under tension, it may drop 1-2mm.
    Michael Drost likes this.
  15. AGCurry

    AGCurry Supporting Member

    Jun 29, 2005
    St. Louis
    A soundpost does not have "tension" - I think "pressure" would be a better word, as in "the pressure applied to the top and back." Just sayin'...
    james condino likes this.
  16. Thanks for all your inputs! I too am concerned about spot #2 being too far south, but I think it's good to experiment with extremes so you can see what the tonal adjustment possibilities are with each instrument. I already know that this bass is brittle and hard when the SP is directly under the foot. That's where it was when I took the bass home.

    The fit of the SP ends is my best work so far -- I've done several school bass SP's over the years.

    Pro tip: Use your phone camera (set on close-up "flowers" mode and flash) slipped into the ff's to get a picture of both sides of the top end of the SP. I do have a mirror, but I like the images better because it's clearer and you can zoom into the fit. You can also shoot a close-up the bottom of the SP from the bass-side ff-hole. DON'T drop your phone into the ff's. I've sandwiched a ribbon tether in between the phone's body and outer case.

    Deflection of the upper eye of the treble ff is about 1.5mm. I've never paid any attention to the ff-hole deflections until now.

    So, I let it settle over night (at the 2nd location), and have been playing the bass a while this morning with more objective ears and feel of senses (using arco solo, orchestral excerpts, and jazz pizz).

    As far as SP tightness, or pressure goes, I think it's "typical" -- my strings were slack and the SP popped off the spike of my setter tool. I did tap it slightly to perfection.
    1. It's a bit wolfier than it was with spot #1. The whole bass seems more resonant. I'm not happy with the wolf parade on this instrument.
    2. Feels looser, more responsive to the bow.
    3. Pianissimo is noticeably better/easier.
    4. The tone is less brittle sounding, though not sure that it sounds any fuller, just less edge.
    5. Yes, the G&D seemed dimmer last night, but I think what I was noticing is that the edge is less now.
    6. Still has decent projection and dynamics.
    So I think I've learned that I can coax a better response and tone quality out of this bass, but it is extremely wolfy. I don't think any SP adjustments will help much with this -- right??

    HOWEVER, the SP placement is not ideal/safe. Being certainly too far south. Before I shorten it anymore, my next move is northward next to spot #1, and see what happens -- keeping an eye on the ff-hole eye deflection.

    Since this is a SP tightness/tension/pressure thread. I'll also play with tightness in this spot #3 and let you know what the affects are. I might even convince myself to get an adjustable SP.
  17. Update. Spot #3 shown below sounds and feels pretty good.
    • After setting the SP in I gently cinched it in eastward maybe by 1mm. So I'll call this my "medium tight" setting. I can make it "looser" by tapping it westward a couple mm's especially if I employ slight G-string tension. I think I can make it a skosh tighter as well. The thing is that the position against both plates will also change. But this thread really is about just the tightness aspect of soundpost adjustment. It's unclear as to which aspect is more affective once you get the SP in the vicinity of the sweet spot. position or tightness?
    • The extreme wolfiness from spot #2 is much more manageable now. Not sure if the tightness or position were the biggest factor. The SP was set in loose for spot #2 AND in the original spot #1.
    • Tonally sounds less edgy than spot #1 both pizz and arco, which I was going for. The top end dynamics and harmonics are good.
    • Arco pianissimo response seems better now. At least I feel more inspired to want to play this instrument now.
    Any comments or suggestions for coaxing more arco response and a darker tone quality?
    IMG_20201125_090408014.jpg IMG_20201125_090408014.jpg
    Povl Carstensen likes this.
  18. Matthias Hacker

    Matthias Hacker

    Apr 8, 2018
    I´m a happy user of an adjustable soundpost. This might fit your needs Stefan if you like to experiment. A perfect fitted and placed regular spruce sound post might be even better, but for me the adjustable one has some crucial advantages.
    - no need of fitting it to top and back, no matter how it is placed. While it stays in place you can adjust the lenght.
    - my bass reacts a lot to humidity. I don´t need bridge adjusters anymore, I just keep the the upper wing flush of the treble f-hole inline with the surrounding plate or a tad below, this sounds best for me.

    You can perfectly fit a regular spruce sp, but as soon as you tune up the strings, the angle of the top will alter. Changes in humidity will also effect the angle of the top.

    There are so many variables with this sp thing that one might get a bit crazy. But actually I only adjust the length (tension or pressure) due to humidity changes as described above. And north or south is very interesting. I recently put on a set of lighter strings and was missing some power. So I pushed the sp a bit north, and that seemed to be a very good idea. It´s amazing how this affects the feel of the instrument, the strings seems to be a bit stiffer, the sound is a more focused.

    Some instruments seem to be picky with soundposts, others don´t react that much on it. The Upright bass still is an amazing kind of dynamic system with a lot of variables effecting each other. Or not ;)
    Povl Carstensen likes this.
  19. Hey Matthias, which adjustable SP are you using?
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  20. Matthias Hacker

    Matthias Hacker

    Apr 8, 2018
    Hi Stefan, I´m using a so called "Klangzauberstab" made by the german luthier Diastrad Downloads von uns für Sie - click Flyer Strada Varia Klangzauberstab.

    Because there has been some confusion in the past I need to make clear that I don´t have any relation to this luthier and I cannot compare this product to competitors.
  21. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

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