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Hybrid bass stability?

Discussion in 'Luthier's Corner [DB]' started by bassmanbrent, Dec 4, 2018.

  1. Hey all! This may seem like an obvious question for some, but lately I've been wondering if hybrid basses are actual more resistant to season movement than fully carved ones... The top is still a different material than the back and ribs, so different parts of the bass are still absorbing and releasing moisture at different rates... Anyone willing to take the time to explain the science behind all this? Thanks in advance!

    PS. I'm asking mainly because I take my hybrid bass to any outdoor or touring gigs and have always assumed there was less risk of cracking/damage than there would be for my carved bass. Now I'm not so sure...
  2. damonsmith


    May 10, 2006
    Quincy, MA
    I have the same feeling. The back should at least move less, also a new bass is probably less prone to cracking.
  3. Eric Hochberg

    Eric Hochberg

    Jul 7, 2004
    From what I understand, plywood moves less than solid wood when humidity changes. So the stress of the solid top sitting on the relatively stable ply sides and back may be less, and the chance of cracking lower. Of course, the hide glue join should release, too, under stress before cracking occurs.

    A new bass with well seasoned wood and proper % of hide glue should avoid cracking too, within reason.
    bassmanbrent likes this.
  4. statsc

    statsc Supporting Member

    Apr 23, 2010
    Burlington, VT
    I think the age of the wood also has something to do with it. My 1850’s carved bass moves a lot less than my 2017 laminate.
  5. A new bass is less prone to cracking when made from properly seasoned wood that is acclimated to the environment which the bass eventually habitats.

    Spruce is soft. Maple is hard. During humidity swings the hard maple back and ribs want to move but the soft spruce top doesn’t. Something has to give — either a seam or the top along the grain.
  6. Makes sense. Thanks! So not to flog a dead horse, but I'm assuming the laminate used for the back and sides is maple or something nearly as hard as maple but, because of the cross grain orientation of the plys, it is more dimensionally stable than solid maple? Did I get that right?
    KUNGfuSHERIFF likes this.
  7. Chris Fitzgerald

    Chris Fitzgerald Student of Life Staff Member Administrator

    Oct 19, 2000
    Louisville, KY
    I don't know the answer, but I've been playing a hybrid for over a decade and it's the most stable bass in terms of tuning that I've ever played - even moreso than my ply of the same make.
  8. Thanks for sharing your knowledge, everyone! One final question... So is spruce more dimensionally stable than maple? Seems like that's what people are saying here... I would have thought the opposite. I guess I just assumed that something hard (maple) would expand and contract less than something soft (spruce)...
  9. I've been using a Shen SB-180 hybrid the past 4 years and have had to do very little repair work to it. I have one small seam that pops once a year (usually either during the end of spring or start of summer) on the corner of the upper left side bout where the back meets the rib. It's a super easy and cheap fix for my luthier. Usually done in a day or two. Overall it's been a very stable instrument for me. It does get a but fussy when the weather and especially the humidity levels change but it mostly effects the action. Rarely the sound.
  10. houblon


    Apr 4, 2009
    New Jersey
    You can check yourself here: The Shrinkulator – WoodBin
    For example Sugar Maple has a radial shrinkage factor of 4.8% (worst case)
    Engelmann Spruce has 3.8%. Bigleaf Maple has 3.7%. Answer is: it depends.
    As an example, an Engelmann Spruce top of say 30in width would shrink about 0.66in if your relative humidity drops from 90% to 20%. This is assuming quarter sawn.

    Some good reading is "Bruce Hoadley: Understanding Wood".

    The worst situation should be where you have a cross-grain situation, which is at bottom of the bass. But since it is a "circle" and the biggest expansion happens at the widest diameter of the top, could it simply push the sides apart? Do seams typically open up at the lower portion?

    s0707 likes this.
  11. s0707


    Jun 17, 2015
    I was thinking that most of the back and sides should be soft maple (i.e. bigleaf, red, etc) because it tends to have more flame than hard/sugar maple; just my guess.

    Sharing some thoughts...

    Yes, definitely the problem with solid-wood instruments (or any solid-wood big object, i.e. boxes, tables) is that expansion/contraction varies with the grain of the wood -- greatest=tangentially (are solid backs and sides mainly slab-sawn?), middle-of-the-road=radially (a quarter-sawn DB top), and least=axially (vertically in a standing tree, vertical direction in DB top, back, and rib circumference), and the instrument has joints/seams with differing grain directions. If wood expanded/contracted the same in all grain directions it wouldn't be a problem.

    Theoretically plywood with its cross-grain plys expands/contracts the same in all dimensions (though some say it warps or twists), and there's not much mention of its shrinkage properties, probably expands/contracts much less compared to solid wood. In a hybrid DB you're combining plywood behavior with the usual solid-wood top behavior, so I am still careful with/watchful of relative humidity...

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