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  1. #1

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    Greets on the board,

    I'm worried about my archtops re humidity and would love to know what the experts think.

    I recently got a hygrometer and keep it in the case of my Crockett JC1, the finest guitar I own.

    It reads 62% today (in the damp Atlantic climate of the UK) and I've read here and there that this is way too wet.

    I've heard I should try to stay in the 45-60 zone.

    Is this correct info and should I be using silica sachets (or something else) to achieve this?

    Thanks ahead

    Sun B

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    The Jazz Guitar Chord Dictionary
     
  3. #2

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    Quote Originally Posted by sunbambino View Post
    Greets on the board,

    I'm worried about my archtops re humidity and would love to know what the experts think.
    If you want some first-hand information on carved tops and humidity I think a good violin shop would be able to help because they deal with humidity issues all of the time.

    As for me... one of the beautiful things about a "plywood" Jazz box is it has more resistance to humidity swings. But it's a trade-off. I tend to go for durability rather than what a fine quality instrument provides however, I do have a viola that's very nice and it is well protected as far as in-house atmospherics. The only sure way up that I have found to keep the viola in such good condition is to keep my household humidity at 50-55% and never take it anywhere.

    So I would think a lot of people who go in and out of different climatized areas and outdoors etc... They tend to buy stuff that is somewhat impervious to humidity changes.

    Conga players might play natural skin heads but some of the conga players that I know use synthetic heads and they never have to tune and retune and slack and do all the required procedures to a membrane that you would normally have to do.

    My local guitar shop down the road has a an acoustic guitar room that is kept at a constant 45% humidity. Searches indicate that 45-55% is considered ideal, but 40-60% is generally acceptable
    Last edited by geogio; 08-18-2019 at 01:09 PM.

  4. #3

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    First thing you should do is get your hygrometer checked or calibrated, they can be (quite) inaccurate. There are various ways of doing this - the best (in my view) is comparing it with a sling psychrometer. Given the cost of your guitar they are a comparatively small investment. Otherwise your 62% reading is fairly meaningless, apart from being a baseline to indicate changes.
    There are various salt (silica gel) solutions you can put in your case, which are probably the easiest way of keeping things as you wish.

  5. #4
    AFAIK my digital hygrometer does not need calibration (according to the manufacturer, ThermPro)

    62% is with silica gel in the case 24/7

  6. #5

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    My take on the issue with humidity is this : there is nary "too much" but beware of "too low" - when wood shrinks in a dry climate there is imminent danger. I doubt that in a 50-70% humidity environment your guitar will suffer in any major way. Think of all the instruments in Japan, West Africa, Florida, you name it - it's humid as hell there and I have yet not heard any horror stories of guitars falling apart ....

  7. #6

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    Taylor guitars recommends 50% relative humidity, as ideal. So 47% - 53% is probably OK.

    HVAC should help manage indoor humidity. If temperatures are too mild for HVAC you can use those mobile de-humidifiers that roll on wheels. You simply put them in a closet when done. They can be noisy but you can cycle them on and off. One unit usually handles one room just fine as long as the room isn't too large, in which case you'll need two.

  8. #7
    Been looking at mean humidity figures for S England and it looks like 62 isn't that high.

    gitman, you say 50-70 is acceptable, that's calmed me down a bit. ;-))

    geogio, cheerz for all the good info

    I might look into HVAC but it seems ike overkill.

    I actually think my silica is maybe saturated and I need to get me a new batch.

    When I take the hygrometer out of the case it actually goes down to 58-60

    Has to be my silica packs are finished and are doing more harm than good

  9. #8

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    There is no specific ideal humidity for wood in general. (But wait...)

    There is no particular acceptable range around this non-existent ideal. (But wait...)

    Wood swells and shrinks based on moisture content.

    This moisture content will stabilize when wood is stored at a given temperature and relative humidity.

    The duration of storage needed is based on the starting moisture content, the target moisture content, the wood species, the wood dimensions, the storage conditions for air circulation, and probably some things I forget.

    If wood is (or is not) kiln-dried, this has no practical effect on its eventual moisture content when later stored for sufficient time to reach a moisture content consistent with the temperature and relative humidity of the storage conditions.

    EDIT: There is nothing particularly right or wrong about kiln-dried wood for musical instruments. There are good arguments for and against kiln-drying. Humorously, they are sometimes the same argument.

    The moisture content of air at a given relative humidity (RH) changes based on temperature. This is the ‘relative’ part.

    So saying only the RH and not the temperature can be relatively meaningless unless we all agree that we mean “sort of at room temperature”.

    **********************

    next post —->
    Last edited by ptchristopher3; 08-19-2019 at 08:18 AM. Reason: Minimum waste, maximum joy

  10. #9

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    Wood swells and shrinks on all three axes, but to FAR different extents along these axes.

    Looking at a guitar with a quarter-sawn spruce top:

    The radial axis is from the center of the tree to the bark, or across the top of the guitar.

    The tangential axis is perpendicular to the radial axis and also parallel to the ground, or through the thickness of the top of the guitar.

    The longitudinal axis is from the ground to the sky, or roughly parallel to the guitar strings.

    Wood swells and shrinks far more on the radial and tangential axes than the longitudinal - so much that the wood industry ignores the longitudinal axis when considering dimensional stability. But on a guitar neck, the difference between the minuscule changes along the longitudinal axis of an ebony FB and maple neck (for example) can make for seasonal changes in neck relief.

    But for purposes of cracked spruce tops, we can ignore the tiny changes along the longitudinal axis of the top and the bent sides of the body.

    **********************

    Now on to the actual guitar... next post —->

  11. #10

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    In principle:

    If your guitar is built from wood that had truly been stored at a consistent temperature and RH, and the guitar was built under those same conditions, then the best conditions for the completed guitar would be the condions under which the wood was stored and the guitar was built.

    One specific example as to why:

    Look at the bottom of the guitar, near the tailpiece on an archtop, where the spruce top meets the maple sides. The radial axis of the spruce (subject to VERY large dimensional changes based on moisture content) is parallel to the longitudinal axis of the lower section of the bent sides of the body (subject to almost no dimensional change).

    So if we glue these together at 22 degrees C and 50% RH, we have now married the fates of radial axis of the spruce to the longitudinal axis of the maple.

    Now drop the RH to 20% at 22 degrees C and the moisture content plummets over a week or so. The spruce tries to shrink along the radial axis but is held under tension by the unyielding longitudinal axis of the maple. This tension can be relieved somewhat by a crack opening in the spruce. It happens.

    Sometimes it does not happen.

    Now if we raise the RH to 85% at 22 deg. C the spruce tries to swell along the radial axis, still thwarted by the longitudinal axis of the maple. The top is now under compression along the radial axis. Damage from compression can and does happen, but to a far less extent, and far less frequently than damage from tension.

    next —->
    Last edited by ptchristopher3; 08-19-2019 at 09:00 AM. Reason: Spelling mistakes and huge geometrical description errror

  12. #11

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    If a given guitar maker (for example) were to say:

    1. We store wood at 50% RH +/- 5%. And 22 deg. C +/- 1 deg.

    2. We build under those same conditions.

    3. Keep your guitar at 45 to 55% RH at “room temperature” and you will be fine.

    Now this would all make sense.

    But to turn that into broad statements about wood and guitar storage requires a great deal of assumptions and faith.

    Based purely upon experience and the concepts involved, it seems very reasonable to say that moderate levels of moisture content are likely best, and that the margin for error is often far greater on the wet side than the dry side.

    Saying anything more specific, or debating small details, seems unhelpful unless you knew the exact conditions under which the wood was stored and the guitar was built.

    all in my opinion.

    And note that I have only considered the wood. Finish checking also can happen as a result of dimensional changes in the wood - and conditions that are challenge for the finish. The classic is freezing a guitar and checking the lacquer all over the guitar. But you can also get more local damage and checking in the spots that we all have seen. Consider the intersection of different wood types and different axis orientations, and all these checks make sense.

    Chris

  13. #12

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    Hi Paul.

  14. #13

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    Chris, awesome posts as always !

    Thank you for taking this time, that was some real education !

  15. #14

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    And for laughs:

    If one lived in drizzly wet conditions and your guitar lived happily at 75% RH and 18 deg. F for years, should you rush to get it to “50% RH” because of interweb opinion?

    There is an argument that wood that has been under compression for so long (as the spruce top on this guitar has been along the radial axis) then the resins and fibers have taken on a “set” under these conditions and could crack if restored to the lower moisture content of the guitars manufacture.

    Wood is a matrix of resin and fiber. The fibers can and do move relative to each other over time if stressed. This can happen with no resulting cracks. At such a point, the conditions under which this has happened will likely be the most beneficial for use and storage if you want to avoid cracks.

    Oh and...

    This all ignores the idea that one might prefer the sound of a given guitar at a given moisture content. I have never really noticed a sound change based on moisture content, but have definitely noticed changes in the amplitude of a resonant peak (wolf notes, etc.) based on seasonal changes in RH. So presumably a more sensitive player may notice this as a tone difference.

    what a fun mess.

  16. #15

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    Quote Originally Posted by ptchristopher3 View Post
    And for laughs:

    This all ignores the idea that one might prefer the sound of a given guitar at a given moisture content. I have never really noticed a sound change based on moisture content, but have definitely noticed changes in the amplitude of a resonant peak (wolf notes, etc.) based on seasonal changes in RH. So presumably a more sensitive player may notice this as a tone difference.

    what a fun mess.
    ...Uh-oh - - could this be heading to the dreaded 'laminated spruce vs laminated maple' discussion, with moisture content added to the mix ?

    Gulp.

  17. #16

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    Hi Dennis,

    Things both real and imagined seem fair game.

    My view is just that I can objectively, demonstrably find a difference - seemingly based on moisture content - in the resonant peak of some few (but far from all) substantially acoustic instruments.

    I can absolutely not hear any actual “tone” difference, but it seems possible that some people may hear a real or imagined tone difference.

    Maybe this could be due to a mass difference via the added water in the wood, maybe there is a different level of hysteresis in wetter wood, maybe we wear sweaters in the winter and this affects some frequencies slightly just below our ears.

    *******

    Part of the added stability of a typical laminate top is that there are wood layers with a longitudinal axis orientation both up and down the top, as well as across it.

    Funny enough, many laminate veneers and layers are made by stripping wood off the surface of a cylinder (like a log is a cylinder). This results in the radial axis now being through the thickness of the laminate. It is how you can get a 17” wide maple top layer of a laminate from a nine-inch diameter maple log.

  18. #17

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    Quote Originally Posted by Dennis D View Post
    ...Uh-oh - - could this be heading to the dreaded 'laminated spruce vs laminated maple' discussion, with moisture content added to the mix ?

    Gulp.
    Oh, and then there are maple laminates with a spruce veneer (Benedetto Bravo), and maple laminates with a poplar center, and likely other mixes as well.

  19. #18

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    Quote Originally Posted by ptchristopher3 View Post
    Oh, and then there are maple laminates with a spruce veneer (Benedetto Bravo), and maple laminates with a poplar center, and likely other mixes as well.
    " and then the finishes and the glue - - water soluble / low voc vs - - -".......

    On we go.....

  20. #19

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    I have never tried a water soluble finish on any sort of fine woodwork.

    I understand that fine furniture makers first spray water to ‘raise the grain”, then do a final sand with the idea that the wood will then not overly react to the water soluble finish.

    It may work very well, but I am a nitrocellulose lacquer person and it has yet to kill me, completely.

    I even once tried to set a swept up pile of lacquer overspray dust on fire (since it is reputed to be explosively combustible.). It burned about as well as I think used bubblegum would.

    I stopped worrying about overspray dust.

    *******

    Back to moisture (sounds like a romance novel):

    I am sure that moisture content affects sound more than many of the imaginary things like Les Paul headstock angles. I am surprised it has never come up in discussion.