Official Luthiers Forum!

Here in the midwestern US it's our annual crack season where lots of acoustic guitars that are not kept humidified will crack and need repair.

One of the very best ways to avoid cracks and having to visit us if you are not skilled in repair is to humidify your instruments.

I've written much on RH and hygrometers on this forum and others over the years and previous threads are available for those interested in searching for same.

My annual ritual at my house it to get out the psychro-dyne and run several tests comparing the wet/dry bulb results to what the hygrometers indicate and then either adjust the hygrometers or annotate on them the error rate.

Some back ground: I've yet to test a digital hygrometer that is accurate and as such even when they are accurate when new the electro-chemical reaction that digitals depend on also breaks down over time and the hygrometers drift often a great deal. We've also tested digitals that may read pretty close in a certain range, say 40 - 50 but may be 10% or more off above 50% or below 40%.

Conclusion - digitals are junk.... YMMV.

A word about the standard that we use. A Psychro-dyne is simply an implementation of the wet bulb test which can be done also with two thermometers or a sling psychrometer. In our experience any wet bulb test done correctly will be WAY more accurate than any hygrometer that we might purchase sands the multi thousand dollar offerings.

I'm going to post some rather poor pics, forgive me please my Photoshop is not working so they are not edited and off an IPhone.

You will see on some of the crappy digitals that I annotate the error rate. I've crossed off last year's error rate and replaced it with what the tests provided me with this AM. Both digitals have brand new batteries as well.

Interestingly enough a little $8 mechanical hygrometer that I picked up last year just to check it out is again, just like last year, the winner for accuracy. Go figure... So if you are looking for an accurate hygrometer the mechanical one pictured is currently recommended for the budget crowd. When you are inclined to spend more the Abbeon Cals are excellent and my standard for my home. My Abbeon was about 3% off this morning and I adjusted it to be calibrated and that will get me though the year.

For new builders maintaining a proper RH range is so very key to acoustic guitar building, important for electrics as well, that it should be job one when outfitting a shop. Ignore RH requirements and you will be building time bombs in terms of instruments that will not hold up well with RH swings in the future.

It's important, an understatement.

Hopefully my reminder and some of the information here will be useful to our OLF pals.

Hey Hesh,

I can't open the pics for some reason, can you tell me what brand/model that little mechanical one is? Curious to try one.

Thanks,
Greg

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Gwaltney Guitars

Yep, hide glue and cauls at the ready!

My experience is that my $20 cigar humidor digital hygrometers run about 8-10% low when the Psychro-dyne indicates 45% RH, and the built-in readout on my humidifier is slightly high. I used to keep the shop at 50-55% all winter based on the digitals. With the Psychro-dyne I am now saving a lot of $$ on replacement filters. And I got the like-new Psychro on eBay for next to nothing.

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It will probably be alright.

Sure Greg, it's a BestAir and I got mine at an Internet reseller who sells humidifier wicks. I think it was only 7 - 8 dollars and it seems to work great.

PS: It has not drifted at all in a years time when my Abbeon drifted about 3% this year.

It's nice when things work out to our advantage! We have three of the psychro-dynes two from University of Michigan property disposition and one from eBay and none of them cost more than $30 IIRC.

Greg it's interesting that you rated the Caliber hygrometers 8 - 10% low when mine was 9% low this morning! As such we are having exactly the same experience with ours as you are with yours.

Thank you!!

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Gwaltney Guitars

Thanks for the reminder bud. It is time for a hygrometer upgrade for me.

So, being a hobby builder,
I don't sell my guitars.
I do like to build them,
but don't want to set up a controlled building/storing wood environment.
What I do is do important glue ups at between 40 to 50 %,
with a questionable hygrometer.
If I didn't do that, I couldn't build at all.
Good advise, Hesh,
for builders that don't want call backs!
I did have humidity issues with a couple of tops that sunk down at the bridge,
but the kind folks here on the olf told me it was humidity issues.
Thanks!

Thanks! I just ordered ordered one for $7. Shipping was $7 from Amazon.
Dan

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wah
Wah-wah-wah-wah
Wah

It's not all that often that the worm really turns for us.... and a solution that is not expensive out performs some much more expensive alternatives.... The BestAir hygrometers although not sexy technology or expensive do seem to be pretty accurate.

Next we should talk about guitar humidifiers and we like the Oasis case and guitar humidifiers and sell lots of them too. What I like the most about the Oasis over the alternatives is the visual indicator that it needs to be recharged. It shrivels up giving the impression at a glance that it needs attention.

I also like the technology where the gel suspends the moisture in a gel state making leaking pretty darn near impossible. Good product!

At Heshtone Global Headquarters here I've already deployed three of the four humidifiers that I use and now I feel like Adam Sandler in the Water Boy.... Every morning I get up and start schlepping water... and when I get home in the evenings the cycle repeats too....

I try to keep my home at 45% all winter long and can do that but it's some work to do and a bit pricey as well. Put in an order for humidifier wicks, chemicals, etc. a month ago and this winter will cost me about $200 to keep everyone feeling comfortable humidifier wise.... I have VERY hard water so a furnace humidifier will surely calcify and crud all up in short order.

At least the RH that our instruments prefer is also perfect for we human bags of mostly water (Veger on Star Trek...).

I recommend all new builders to use your first soundboard offcuts to make one of these

One long grain strip and one cross grain strip glued together, sanded until flexible, and one end attached to some kind of base. Best to glue it up when humidity is around 50%, so it has the most swing either direction. Mine is about 3/4" wide, 7" long, and thickness tapers 1.5mm at the base to 1mm at the tip. The long grain side is a bit thinner than the cross grain side, because long grain is stiffer, and because the cross grain expanding/contracting is what generates the stress to move it, so having more of that gives more movement.

The numbers on mine are not accurate, though the paper itself is still good as a visual reference for how close it is to either edge. I tried to calibrate it from the digital, but kept being wrong. The wood one responds more slowly, plus has the hysteresis effect of wood, where going from dry to wet will read lower than going from wet to dry. But that's all good when you're using it to measure wood, because everything else in your shop should be in a similar condition to the hygrometer, whereas with an exact numeric reading you have to compensate for those wood behaviors.

It takes time to observe the behavior of your wood hygrometer, but after a couple years you can just glance from across the room and see if it's good bracing weather. Get a numeric one of some sort too for use early on (mine is from David Burgess http://www.burgessviolins.com/products.html), but in the long run the wood one is great.