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  #16  
Old 02-18-2019, 10:39 AM
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Simon Fay Simon Fay is offline
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There is no debate about the effectiveness of using salt tests for calibration purposes. It's hard science.

As some individuals have mentioned, there is a lot more to calibration. You ideally want to data points to make a calibration - but we aren't in a lab and don't care about how the hygrometer responds at higher or low RH ranges. The Potassium Carbonate salt test is more than sufficient for our purposes here.

The amount of salt and water doesn't matter - just make certain the solution is saturated and make sure to use a container that has a good seal and make sure you give that environment enough time to reach an equilibrium RH before you take your readings. As I mentioned, I will make a pictorial on this in the near future.
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  #17  
Old 02-18-2019, 11:04 AM
menhir menhir is offline
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I don't bother with calibration, mostly trusting to the majority opinion of my hygrometers.

I have four...
Two little cheapo mechanical ones, a battery powered digital one in my guitar room and a digital one built into the large pedestal humidifier on the first floor.

They all pretty much agree, close enough that I have confidence in keeping the guitars in their comfort range between 40 and 60%.

The least accurate sensor, not included in the count above, is the one in my Vornado Evap. It works well as a humidifier, but I usually turn it off and on based on the other hygrometer readings. It doesn't have a readout, but doesn't turn off and on reliably based on it's settings.
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Old 02-18-2019, 01:02 PM
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Another way of checking the calibration is direct measurement of the ambient and dewpoint temperatures. All you need is an accurate thermometer, a thin wall glass, some water, and a little ice.
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  #19  
Old 02-18-2019, 01:37 PM
Bernieman Bernieman is offline
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Quote:
Originally Posted by ljguitar View Post

(...) First of all, we only need to know the guitar is between 35-45% to be safe, and a $11 to $14 hygrometer from Amazon wil let you know that. (...)
What should I consider as ideal for guitars ? I was reading the other day that people at Santa Cruz Guitars would keep a 49% rate in the plant all the time I think...I was thinking 45 % to 55% would be okay, but as you say 35-45%, it makes me wonder if it isn't a bit too much humidity after all ?
I wonder what is the danger zone : I got an hygrometer I bought several years ago working recently, and it has been between 42 and 58% since I checked it out regularly...The clock works fine, the alarm-clock rings, the temperature seems to be okay, but i've read in the thread that hygrometers need to be calibrated regularly, so I woory a bit, in case it could be wrong...
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  #20  
Old 02-18-2019, 03:46 PM
charles Tauber charles Tauber is offline
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Originally Posted by Bernieman View Post
What should I consider as ideal for guitars ? I was reading the other day that people at Santa Cruz Guitars would keep a 49% rate in the plant all the time I think...I was thinking 45 % to 55% would be okay, but as you say 35-45%, it makes me wonder if it isn't a bit too much humidity after all ?
It isn't complicated.

The guitar was made at 49%. The ideal is to keep it at all times at a constant 49%. Catch is, this isn't practical for most guitar owners to keep their guitars at a single RH all of the time. That's where practicality enters into it.

As the ambient relative humidity drops, guitars - and other wooden objects - lose moisture and shrink. If the stresses in the wood due to shrinkage are sufficiently high, beyond the strength of the wood itself, the wood will crack to relieve the stresses. The exact amount of shrinkage that will cause a piece of wood to crack depends upon a variety of factors: at no one value will all pieces of wood crack. So, it is a game of chance: the lower the RH, the greater the shrinkage, the greater the chances of cracking. The further your instrument is below the 49% at which it was assembled, the greater the chances of it cracking.

So what is the minimum desired RH? That depends upon how much trouble/cost you want to go to to maintain the humidity, how much chance you are willing to take (i.e. how far you are willing to let the RH drop below the ideal) and the circumstances of your environment.

If you maintain your guitar at 49%, the chances of it cracking are very small. At 40% the chances of cracking are increased. At 35%, they chances are even higher. At 20%, and below, you can expect it to crack and are lucky if it does not. You chose the balance - for you - between probability of cracking and the amount of time, money and effort you want to put into maintaining the ideal RH.

At the other end of the spectrum, higher than the ideal humidity, unless you maintain your guitar at near 100% humidity for long periods of time, you aren't likely to see much permanent damage to the wood - mold and mildew are possible. There are, however, two undesirable consequences of higher humidity that are not damaging.

The first is that the instrument swells. As it does so, the top, in particular, arches more. As it does so, it takes the bridge and saddle with it, increasing the string height over the fingerboard. This makes the guitar physically difficult to play. Some counter this by using a lower saddle, particularly during higher humidity months (e.g. summer).

The second is that many report instruments to sound deadened at elevated humidity levels, like the guitar is stuffed with socks.

These two things, practically, govern the upper limit of RH that most are willing to stand: sound and playability. Again, that is at the discretion of the individual player. Many have found that above 55 or 60% these negative things begin to become noticeable.

In conclusion, many are comfortable in balancing the risks of cracking by keeping humidity levels above 35 to 40%. Many are willing to accept humidity levels of 55 to 60% before experiencing changes in tone or changes in playability.
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  #21  
Old 02-18-2019, 05:07 PM
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Try to keep the relative humidity between 35% and 55%. Dry is much worse than wet because the guitar can crack.

As mentioned before, the Caliber IV hygrometer will be plenty accurate enough for a guitarist to monitor their environment. I highly recommend getting this particular hygrometer and just buy a new one every few years.
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  #22  
Old 02-18-2019, 05:09 PM
Bernieman Bernieman is offline
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I do get 56 or 57% a lot these days, and I don't know what to think of my hygrometer, theoretically new as I never used it until a week or so ago, but that came with a battery wrapped in a plastic sheet, stuck in it's compartiment and that I couldn't get out when I tried to use the thing...User's manual was written so small I couldn't read it (shop too far away, then I moved, forgot about it for several years...).
Managed to get it going recently thanks to tutorials on the web...But does it work properly ? Don't know if it could be adjusted, probably not (€23 here - €9,50 on the web ! -, bad shop I guess...), so maybe it could be 65% humidity or 34% at the other end - I got 42% at the very beginning - considering it could be 8% wrong at the most...
I've been using wet clothes near the heater during the cold seasons, and I want to keep my guitars alive even if I have to pay for it...
Good guitars stay in their cases when unplayed, some others do not have a hardshell, and a couple remain ready to be used with not even a soft case...Might as well know what is okay to do, what's not.

So thanks very much Charles for your answer : seems like things should be okay so far, but I do get some frets rather sharp on the edges (nothing drastic it seems) so I need to be careful. I'd like to compare my hygrometer's results with some other(s). It's an HCT-1 Thermometer Indoor Digital LCD Hygrometer, so I'll keep reading this thread and maybe visit a friend who'd have some reliable device if I can...
Thanks again,

Bernie
And thanks too Simon, since you have posted while I was writing...
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Last edited by Bernieman; 02-18-2019 at 05:21 PM.
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  #23  
Old 02-18-2019, 05:26 PM
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Quote:
Originally Posted by Bernieman View Post
What should I consider as ideal for guitars ? I was reading the other day that people at Santa Cruz Guitars would keep a 49% rate in the plant all the time I think...I was thinking 45 % to 55% would be okay, but as you say 35-45%, it makes me wonder if it isn't a bit too much humidity after all ?
I wonder what is the danger zone : I got an hygrometer I bought several years ago working recently, and it has been between 42 and 58% since I checked it out regularly...The clock works fine, the alarm-clock rings, the temperature seems to be okay, but i've read in the thread that hygrometers need to be calibrated regularly, so I woory a bit, in case it could be wrong...
Hi B-man

There has been good advice here in the thread - Charles Tauber's is very good advice. Unless you buy a really expensive hygrometer, you cannot calibrate it. Most are not adjustable.

But that kind of precision, while good for protecting museum quality relics, is certainly NOT necessary for our day-to-day-playing instruments. And it's worth noting cracks in guitars happen for other reasons than being dry.

I live in a dry climate (often single digit humidity in the winter) and I maintain 40% in the room the guitars are hanging on the wall in. Not because it is the absolute safest number, but because it's perfectly safe for my guitars (has been for over 40 years) and they sound a whole lot better at 40% than at 55%.

I imagine (on paper) 55% would be a notch or two safer than 40%, but I've never experienced issues at 40% and we've lived here for 42 years without a crack. But I've also not allowed my guitars to dry out.

And they sound SO MUCH BETTER it's a risk I've lived with. My guitar never sound so BAD as they do when we travel back East (USA) during humid weather. I suffer (they don't).

At home, my guitars hang in the living room (my playing area) and it stays at between 40-45%, though in really dry weather the humidity has dipped to 30% at which point they go into cases and I raise it back up to 40% till the dry spell passes.

For me it's not as big a deal as it seems to be for many people. I guess when you are 70 years old and have played for more than 55 years, either you are willing to be a risk taker, or you realize some things are not as big of a deal as some people make them out to be.

I have a friend who knows and works on his cars, and he changes the oil in ALL his vehicles (and filters) every 1500 miles. His engines are likely technically than mine (which are changed when the manufacturer says they should be). But it's a risk I'm willing to take. I use good quality synthetic oil and go 7,500 miles between changes.



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  #24  
Old 02-18-2019, 05:47 PM
Shuksan Shuksan is offline
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Originally Posted by ljguitar View Post
Hi B-man
Unless you buy a really expensive hygrometer, you cannot calibrate it. Most are not adjustable.
A hygrometer doesn't have to be adjustable to calibrate it in practice. If you determine that the display on a digital hygrometer reads 47% in a potassium carbonate test instead of 43% as it should, for example, then you know to subtract 4% from the display readings for RH values in the range that's important for guitars. That is essentially what happens when you adjust an adjustable hygrometer so that it displays the correct value. Write "-4%" on a piece of tape and stick it on the non-adjustable hygrometer as a reminder and it's calibrated.

Last edited by Shuksan; 02-18-2019 at 09:00 PM.
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  #25  
Old 02-19-2019, 04:26 PM
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Quote:
Originally Posted by Shuksan View Post
A hygrometer doesn't have to be adjustable to calibrate it in practice. If you determine that the display on a digital hygrometer reads 47% in a potassium carbonate test instead of 43% as it should, for example, then you know to subtract 4% from the display readings for RH values in the range that's important for guitars. That is essentially what happens when you adjust an adjustable hygrometer so that it displays the correct value. Write "-4%" on a piece of tape and stick it on the non-adjustable hygrometer as a reminder and it's calibrated.
No, that is not calibration, which requires more than one data point and adjustment to match all the data points.

It is plenty good enough for practical purposes.
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  #26  
Old 02-19-2019, 05:19 PM
Shuksan Shuksan is offline
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Originally Posted by Rodger Knox View Post
No, that is not calibration, which requires more than one data point and adjustment to match all the data points.

It is plenty good enough for practical purposes.
I think this may be veering into semantics . There is such a thing as one-point or single-point calibration. If you look up methods for calibrating analog hygrometers, a standard method is to wrap the hygrometer in a damp cloth or paper towel and after 30 minutes check to see if it reads 95%. If it does not, you adjust the screw on the back so that the indicator reads 95%. An example of single-point calibration. Alternatively, salt tests are recommended. Again, single-point calibration but to a different RH value. Calibration to 95% obviously assumes that the hygrometer's response to RH is linear over its range, which it may not be. If it's not, calibrating to 95% may result in inaccurate readings in the 45% range. Which is why doing a single-point calibration with potassium carbonate at 43% makes send for guitar owners and builders.
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  #27  
Old 02-22-2019, 12:51 PM
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Quote:
Originally Posted by Shuksan View Post
I think this may be veering into semantics . There is such a thing as one-point or single-point calibration. If you look up methods for calibrating analog hygrometers, a standard method is to wrap the hygrometer in a damp cloth or paper towel and after 30 minutes check to see if it reads 95%. If it does not, you adjust the screw on the back so that the indicator reads 95%. An example of single-point calibration. Alternatively, salt tests are recommended. Again, single-point calibration but to a different RH value. Calibration to 95% obviously assumes that the hygrometer's response to RH is linear over its range, which it may not be. If it's not, calibrating to 95% may result in inaccurate readings in the 45% range. Which is why doing a single-point calibration with potassium carbonate at 43% makes send for guitar owners and builders.
Agreed! 910
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