Are archtops as prone to top cracks due to dehydration as acoustic guitars?

[Burstbucker]

Lately I have gotten with the program and bought a few hygrometers and guitar humidifiers for my acoustic guitars.

I'm assuming that an archtop might be as prone to top cracks as much as flat tops if conditions get too dry? I went out and bought one of those Grover dampit tubes and after soaking it, then wringing it out, I just drop it into one of the F-holes of my Ibanez SS300 and will keep an eye on it.

Summer is right around the corner here in Atlantic Canada, we usually get loads of humidity during a 3-month period, so I should be able to relax during those three or four months but according to my new room hygrometer, things are a lot dryer in my basement music room right now than I would have imagined with relative humidity around 31%.

So I'm busy humidifying my three acoustic guitars and now my Ibanez archtop as well, I was just wondering if an electric archtop guitar with a solid spruce top, (which is what my SS300 is) is as tempermental as a solid spruce top on a flat top acoustic. I'm guessing that I should be minding the R.H. to be safe but what do you fellahs do with your solid top archtops?

[DanielleOM]

Regardless of the guitar type, I suggest you watch the humidity levels. Last year a luthier pointed out to me that every time you fretboard expands and contracts, your frets can also move and not necessarily end up in exactly the same place. A lot of fret jobs are required as a result of humidity changes and not fret wear.

I quit using the those in case humidifiers myself for home use. I think if you are not careful you can over humidify with those. I found it best to keep all my guitars in one small room, get a room humidifier, and a good humidity gauge.

I have seen archtops where the tops have cracked.

[fws6]

Yes definately !

[rlrhett]

Mine don't!


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[deacon Mark]

Arch tops are less prone to cracks than flat tops but they happen. Nothing wrong with proper humidity but I have seen those gadgets get guitars wet and drip water when not used correct. More important is how often the guitar is in and out of the climate. Playing gigs daily going around traveling takes more toll. Playing a gig in July outside then bring guitar inside a/c room is a big change.

i personally do no not use any of those humidifiers but some of my guitars are really not taken out except to play at the house. My Hollenbeck sees the most travel and after 24 years it is very stable. I have never adjusted the truss rod since I got it from Bill those years ago.

I do find though my most frequent repair I do is flattop cracks usually on each side of bridge running length wise. The drying and movement will cause stress cracks. Arch tops do not do this different animal. They tend to crack around the f holes below and above.

Also change strings even if not playing guitar much they start to lose flexibility and can actually increase stress.

[ptchristopher3]

Also change strings even if not playing guitar much they start to lose flexibility and can actually increase stress.

Huh? How does an aged string (assuming that there is an actual increase in hardness) "increase stress"?

[Danny W.]

Fixed by Gibson under warranty, doing fine nine years later.

Danny W.

[deacon Mark]

Huh? How does an aged string (assuming that there is an actual increase in hardness) "increase stress"?

The strings do not get harder they lose ability to flex and can result in greater tension on neck over time, but not always. Think this, you put new strings on a guitar they stretch into a steady state. Then over time they really are at yield. Corrosion and movement of the guitar happen but the strings lose ability to respond like when they were new.

Guitars are made of wood some are more stable than others just because of they way they are built. I have seen plywood Gibson guitars like 175 and similar start collapsing over the bridge. Some are like tanks and never move. My 1949 D'angelico has a truss rod but in the 32 years I have had it, it has never been used. I have not adjusted the action at the bridge in over 15 years maybe more. I remains 5/64 an 4/64 it gets played 2 hours or so a week. I keep .12-.53 strings on it change them every few months i
am easy on strings.

My friend has an Epi 1946 or so Broadway but it moves with the seasons. Raise action in winter as wood dries and lower in summer as it expands. I think it does more because neck and end blocks are smaller and no binding on f hole. I also think tailpiece is less stable than others those frequensators prone to
movement. If that sounds bad nothing worse than a featherweight flattop they can be a nightmare.

[Stevebol]

Archtop tops sink. A good old Dampit helps;

Amazon.com: The Original Dampit Cello Humidifier: Musical Instruments

[Donnie]

It never hurts to humidify; I have humidifiers in ALL my instrument cases. My own thoughts are to humidify once a month and wipe down every instrument I play with a slightly damp soft cloth after as well. I've invested too much money not too and after seeing some cracks, top warps, separations and neck problems, spend the $7.00 or $8.00 on humidifiers just makes since.

[ptchristopher3]

The strings do not get harder they lose ability to flex and can result in greater tension on neck over time, but not always. Think this, you put new strings on a guitar they stretch into a steady state. Then over time they really are at yield. Corrosion and movement of the guitar happen but the strings lose ability to respond like when they were new.

Some metals lose their "ability to flex" by work hardening.

No this does not at all result in greater tension on the neck over time. Not always, not ever.

You seem to colloquially suggest that elasticity along the length of the string diminishes and that this results in greater static tension on the neck. This greater static tension does not happen.


It is remotely possible that older strings could have greater inharmonicity (which is an artifact of stiffness) but I have never heard any practical artifact like this.

In my opinion and experience there is no practical (or in principle) change whatsoever to the static tension on a neck by the strings as they "age".

Chris

[deacon Mark]

Some metals lose their "ability to flex" by work hardening.

No this does not at all result in greater tension on the neck over time. Not always, not ever.

You seem to colloquially suggest that elasticity along the length of the string diminishes and that this results in greater static tension on the neck. This greater static tension does not happen.


It is remotely possible that older strings could have greater inharmonicity (which is an artifact of stiffness) but I have never heard any practical artifact like this.

In my opinion and experience there is no practical (or in principle) change whatsoever to the static tension on a neck by the strings as they "age".

Chris

I completely disagree with you and you certainly have not been around the guitars and the guitar makers I have been around. But we just disagree friendly though for sure.

[JSanta]

I completely disagree with you and you certainly have not been around the guitars and the guitar makers I have been around. But we just disagree friendly though for sure.

I will respectfully disagree with you as ptchristopher3 (and in his other incarnations on this board) has shown himself to be one of the most knowledgeable people with regards to guitars, physics, and mechanics I’ve ever encountered. He lives and breathes guitars at a professional level, and his experience around guitars probably is worth that of many lifetimes of others on this board and many others.

[ptchristopher3]

Just for fun I suggest that we consider what could possibly happen as a string settles in or even "ages".

1. The string could conceivably stretch. This would result in an infinitesimally narrower diameter.

2. The string could conceivably lose some elasticity (the earlier proposed "lose their ability to flex")

Now assuming for fun that both of these things happen AND assuming that each has a measurable effect,...

- a narrower diameter would result in LOWER tension on the string and thus the neck at a given pitch.

and,

- a stiffer string would vibrate at a slightly higher frequency over a given scale length also resulting in a LOWER tension when tuned to a given pitch.

Now in my opinion neither of these things happen to any practical extent. But fun to note that each would result in lower overall tension, not higher.

Chris

[ptchristopher3]

Oh, to clarify my addled opinion above:

I feel that strings do indeed stretch, but that this does not result in any measurable or practical change in diameter. It has to be there, but to a remarkably small extent.

It seems overwhelmingly likely that the steel will lose some elasticity, but again with no measurable or practical effect on a guitar (which is a real mess all in all).

And of course both effects would result in lower tension, not higher.

In my opinion.

[Ol' Fret]

The specification of music wire as used for piano or guitar strings covers two types of round, cold-drawn, high and uniform tensile spring quality wire: ASTM A 228 / A 228M-16 (http://c.ymcdn.com/sites/www.casmi-s...tion_for_S.pdf )

Drawing-process parameters such as reduction (deformation) ratio and drawing velocity influence the tensile properties of low-carbon steel-wire materials (yield stress, ultimate tensile strength, fatigue life, and elongation at rupture).

Extension and compression springs (our guitar strings), when held or cycled under load, are subjected to stress relaxation, which creates a loss of load carrying capability or available deflection. The modulus of elasticity in tension and shear, and the tensile and fatigue strength, vary as a function of physical and chemical composition (grain size, alloy type), cold works (residual stress, heat stressing), operating environment (corrosion, temperature, etc.), and to the stress a given spring material is under.

Though there are many factors that contribute to significantly extending a commercial spring's service-life (at increasing the cost), metallurgists say that, regardless of how much time, effort and money is spent to insure long life, it is nearly impossible to guarantee that there will be no failures in a given production lot of springs.



To come back to the OP's question: solid top (hollowbody) archtop guitars are less prone to top cracks due to their ingenious arched construction. Wood always remains hygroscopic. As the RH drops, it loses bound water until there's a new equilibrium moisture content (EMC) - and vice versa. In higher RH environments the arch will be on the higher side, in lower RH environments the arch gets lower. Of course, the wood movements are limited to a certain extent. The top of a flat top (or slightly domed top) guitar has comparably less range of movement left to cope with the wood's responding to changes in atmospheric humidity.
Less important: there's also a relation between the top thickness and the chance of cracking: generally, carved archtop guitars feature thicker plates than flat tops.

Stringed wooden instruments are the more subject to cracks the bigger the plates have to be. Fine cello makers have some tricks "to extend" the room of movement even on the archtop construction. They try to work less hot hide glue around the critical areas at the lower bouts. So if the moisture content is going to jeopardize the maximal movements of the wood, the plate can come loose at these "predetermined breaking points". Needless to say that it is much easier to reglue the loosened plate edge than to splint an ugly open crack. Unfortunately, most guitars don't allow to employ this trick due to their life span limiting construction with fancy looking plastic or wooden bindings.

[ptchristopher3]

Hi Ol Fret,

Great post, thanks.

Chris