Relative Humidity?

[stuco]

 



Ok, Call me an idiot but I do not fully understand realative humidity.  I just got a digital hydrometer/ temp. gauge in the mail and turned it on and it said the temp was 75 and the rh is 34%.  So I take it upstairs where the air conditioner is broken and the temp is 80-85 during the day and the relative humidity reading was 50.  So here is my question, on the larrivee site it says that the rh shoud be 42-55 for optimal relative humidity.  Should you account for temperature say if it was 85 degrees what would be the appropriate relative humidity for the guitar?  Or if the temp were 60 degrees F what would be the appropriate rh?  Or should I always keep it at 42-45 rh no matter what the temp reading says?

[aboss]

My understanding is that RH is exactly what it implies... It is the humidity RELATIVE to the temperature. Therefore the reading you are getting on your RH gauge is showing the actual humitidy of the air compensated for the difference in temperature. So regardless of what the temperature reading is, the RH should be between 42 - 55 for your guitar. That said, you also want to take temperature into account, because excessive heat or cold can be bad for your guitar too... but thats a different matter. I hope this helps. (somebody let me know if i've said something wrong  :UND> ... this is how i understand it.)

aboss

[stuco]

 

Ok what would be a max and min temp to allow the guitar to thrive. Remember my guitar was made in Canada and is now in Georgia.  I is probably less than a month old so it is still settling.  I know the glue especially needs to settle.  Thanks for any more info on this topic. 

[aboss]

I honestly don't know the exact temperatures you should keep it between... but i follow a general rule. Don't expose your guitar to temperatures that would be comfortable for you personally. You wouldn't be comfortable sitting around and playing your guitar if it was freezing cold or extremely hot, so don't leave your guitar in those temperatures either. Its always served me well. If you find it too hot, your guitar probably does too.

[Steve]

We discussed this just awhile ago in this thread.

http://www.larriveeforum.com/smf/index.php?topic=12027.0

[Dale_I]

I'm going to place this here, since it was the first thread shown when searching "relative humidity". Sorry to drag up an old thread, but we'll all agree it's a seasonal topic... . I haven't read a concise post why relative humidity is, well, relative. So I thought I would try an explanation. Let me know if I'm wrong! I'll be ducking behind my keyboard...

Humidity is a measure of the amount of water vapor in the air. Relative humidity (RH) measures the amount of water vapor in the air in relation to the maximum amount of water vapor the air can hold.

The amount of water vapor a volume of air can hold will vary significantly:

Colder air is not able to hold as much water vapor as warmer air. Air at 41°F and almost saturated would contain about 0.2 g/m³. Heated to an indoor temperature of 73°F, if the absolute amount of water vapor remained ~0.2 grams/m³,the RH would only be ~33%.

Likewise, warm air can hold more water vapor than cooler air. Air on a hot humid 86°F day at 80%RH would hold ~0.8oz/m³ and cooling it down to 78° the RH would go over 100% and you would start condensing water on your walls and windows.

Relative Humidity is measured with a psychrometer in Depression. Depression is the difference between the actual temperature, called a dry bulb, and the temperature of the Wet Bulb, which measures a lower temperature when water is evaporated from its surface. A decrease in the humidity of the air brings an increase in the difference between dry- and wet-bulb temperatures called the wet-bulb depression.

Depression will reflect the percentage of water vapor in the air at that air temperature.

Think of a gallon of water, at 50% you would have a half gallon. But, if you started with 2 gallons, 50% would only be a gallon.

Temperature not the only factor:
A straight out calculation will not reflect the true humidity levels. The way we manipulate our environment also affects humidity. Most air conditioning systems will dehumidify and condense the water before entering your home. Without dehumidifying, you walls and ceiling would be soaked in the hot summer days. If you have a fired furnace in your home, there will be a loss of humidity as the furnace burns to warm the air. Doors opening closing, etc.

There is a component of atmospheric pressure as well. Atmospheric pressure is not easily manipulated, but It does shift the Wet Bulb Depression very slightly to the higher side. My elevation of 2000 ft only changes Depression less than 3% of the reading, not enough to worry about for non-sea level guitar players.

Guitars
As this relates to guitars, our goal is trying to maintain the same conditions as the environment our guitars are built in. At Larrivee I've confirmed that the long term wood storage and body building happens in an environment of 44% RH @ 22C°, which equates to 13.25°F Depression.

If you find the temperature you are at and look to where the 13.25 Depression line is, that will be the humidity you should attain at your location to be equal with the room when the guitar was built. If you were to simply believe that 44% RH is the same across the temperature range, you would be too dry for a safe range of relative humidity at anything over 78°F, even though hygrometer will read 44% RH. It is 44% RH @ 78°F, which is different than 44% RH @ 72°F.

I've attached a graph for you to see what your Relative Humidity should be at your temperature range and what is considered "safe" from the Care and Maintenance pdf on the Larrivee website...

Payment for reading until the end: 

[Rockysdad]

Ouch, my head hurts.                                                     

[Dale_I]

Yeah... me too. Wrapping your head around calculations that have several changing parameters... I still get confused. Easiest to go back to the gallon of water analogy.
Bucket= Air Temperature
Gallon= Relative Humidity

You need water every day. You only have a 1 gallon bucket. You order from the store by the percent and the store changes their bucket size every day. If the store bucket size is 1 gallon, you order 100%. If the store bucket is 2 Gallons, you order 50%. If the store bucket is 5 gallons, you order 20%. Same gallon, you just need to know the store bucket size to order the right amount.

Or, just look at the chart knowing that the target is paradise and the white zone is your playground...  

[bobsnuscruz]

I've lived near the California coast & SF Bay Area my whole life and have had 17 guitars (cheap to expensive), and pay NO attention to RH other than for the storage room under my stairs (60-70%, that's where the wine lives.)  I've had humidity problems effecting the action on two of these guitars, one made recently in Vietnam, one made in Japan in the early 1960s, both humid environments, both cheap guitars.  If you are comfortable, it's likely your guitar will be as well.  Don't worry, be playing.

[Dale_I]

Just like real estate... location, location, location. I used to live in Orange County near'ish the beach and never had a problem either. Pop a cork on a nice bold red and we'll talk...

Living in the inland Pacific Northwest currently is a different story. Manipulating the temps into indoor comfortableness takes a bite out of the natural humidity levels. Outside today is 48% RH @ 42°F, which is 7°F Depression... Inside 32% RH @ 70°F, which is 16+°F Depression... One way too high, the other too low. It's probably one of the reasons Larrivee relocated in a fair proximity to the Ocean. It's just easier to supply consistent humidity when you have a lot of water and you have to do a lot less with such consistently moderate temperatures.

And snow.... Not sure you guys have to deal with it much...  Texas appears to be experiencing what a normal winter for us is, but we have the infrastructure for it!

On the plus side... I don't need to de-humidify. So there's that to be thankful for.

[B0WIE]

I keep mine a bit on the dry side, purposely, because I think they sound better that way. But, I'm still very active in making sure the RH is consistent, I observe the instruments to make sure there's no warping, and I use whole room humidity. I suspect damage is most likely to come when a guitar quickly goes from being in the safe range to bone dry for a few days (such as when seasonal AC kicks on). Expansion and contraction is a killer.