Sharp Strings in the morning?

[MandoJimbo]

Put a little Flatiron A up after practice at night, Check the tuning and it's great... get up in the morning and everything is sharp... I notice it more with light Elixors.. but it happens with all the strings i've used.. One would think it would go flat? Curious if anyone understands the physics? http://www.mandolincafe.net/iB_html/non-cgi/emoticons/rock.gif

[John Flynn]

Tuning is a dynamic balance between the tension on the strings, the neck and the top. Change one and the others change. Changes in tuning overnight are likely due to fluctuations in some combination of temp and humidity. Especially with forced air heating, both can change a lot this time of year. Forced air heating really sucks the humidity out of the air and can cause the temp to fluctuate up and down a few degrees in pretty quickly cycles as the thermostat cycles on and off.

[J. Mark Lane]

I would think the tuning going sharp would indicate an increase, rather than a decrease, in relative humidity. If the rh rises, then there will be more water in the air, and the top will be able to take on more water. As it takes on more water, it swells. As it swells, tension on the strings is increased. Thus, tuning goes sharp.

Rh could increase due to a rise in temperature. Warmer air can hold less water. (That's why it "feels" more humid when it gets warm...the air doesn't "hold" the water as much, so you feel the water "in the air" because it is "leaving" the air.) So, given a fixed amount of water in the air, the rh might be 40% at 68 degrees. But if the temp rises to 78, then the rh might increase to 60%. Given that example, the change in rh would be enough to have an effect on the instrument.

As Johnny said, forced hot air heating does have the countering effect of forcing dry air into the space. So all of the factors effecting rh have to be considered in any given environment.

I would get myself a good indoor-outdoor hygrometer. Radio Snack sells decent ones. Set it up in the room where you keep your instruments, run the outdoor line through a window or something (don't break the line, I've done this). And monitor it.

I keep all my instruments in a room that is carefully controlled -- warm air humidification in winter, AC and dehumidification in summer -- to try to maintain an rh of between 35-50. Even then, I recognize that an instrument has to be tuned basically every time you play it, and especially after sitting overnite. I will play scales for five minutes to "warm up" the instrument, then tune it.

Mark

[Eugene]

Humidity is a big player in maintaining the health of a soundbox, but I think it's less of a player regarding morning pitch than has been supposed. #In spite of artificially heating our living spaces, it's typically colder in the morning than at the height of the afternoon. #Metal strings will contract slightly in the cold, increasing their relative tension and thus their pitch. #The expansion/contraction of metal under changing temperature is much more rapid than the hygrometric expansion and contraction of wood under changing humidity.

[J. Mark Lane]

Eugene... Is that really true, that metal will contract in cold faster than wood will expand in increased heat? Do the strings really contract and expand faster than the thin spruce (unfinished on one side) of a mandolin top?

It does make sense that this could be the real culprit, at least in a house that does, in fact, get colder overnite. In our house, we have the heat set so it comes on early in the morning, and so (hopefully) it's nice and toasty in the early morning. But it's hard for me to be an example, because my instruments are in a much more consistent environment than the rest of the house.

If the strings were "contracting" rapidly due to decreased temps, I guess they would "snap back" quickly, too. And if you tuned down in the morning to compensate, you would have to tune back up very soon after playing the thing at all. Right?

Mark

[Tom C]

Little things make a big difference. After I re-string, I tune up to pitch.
Once I clip them, I need to re-tune.

[aaronbrill]

I've noticed the same thing. #My mando almost always goes sharp if sitting around not being played. #My banjos almost always go flat, same with the guitar.

Aaron

[Eugene]

Eugene... Is that really true, that metal will contract in cold faster than wood will expand in increased heat?

I don't know, but I don't think wood is particularly prone to expansion/contraction because of temperature; it certainly is because of humidity. #The process of absorption of moisture by wood cells and resultant expansion of the material certainly is slower than density changes because of temperature, which are immediate. #Expansion and contraction of wood because of changing humidity is a function of semi-saturation/dessication in coming to an equilibrium with ambient humidity. #I doubt it takes a great long time in a very thin panel of spruce, but it certainly isn't immediate like changes in density as the temperature of a material changes.

If it's a matter of strings going sharp over time independent of temperature or humidity, there is an altogether different explanation. #If you're like me in tuning, you always take a string a bit flat and bring it back up to pitch. #Thanks to friction, tension is transferred unevenly from the tuners, over the nut, and to the vibrating string. #Some tension will be stored in the string above the nut. #As tension above the nut relaxes over time, it draws the vibrating string length a little sharp. #This is most obvious after the instrument is out of your hands for a number of hours. #Reducing friction over the nut--e.g., by using a low friction nut material like graphite, lubricating nut slots with graphite, making sure nut slots are clean of imperfections, putting strings in line over the nut as in snakeheads, etc.--will more directly transfer the work of the tuners to the vibrating string length and diminish this effect.

[Eugene]

...And the banjos go flat because the tuner is less able to maintain its position against tension than a geared mandolin tuner.

[JGWoods]

I would think the tuning going sharp would indicate an increase, rather than a decrease, in relative humidity. #If the rh rises, then there will be more water in the air, and the top will be able to take on more water. #As it takes on more water, it swells. #As it swells, tension on the strings is increased. #Thus, tuning goes sharp. #

Rh could increase due to a rise in temperature. #Warmer air can hold less water. #(That's why it "feels" more humid when it gets warm...the air doesn't "hold" the water as much, so you feel the water "in the air" because it is "leaving" the air.) #So, given a fixed amount of water in the air, the rh might be 40% at 68 degrees. #But if the temp rises to 78, then the rh might increase to 60%. #Given that example, the change in rh would be enough to have an effect on the instrument. #

As Johnny said, forced hot air heating does have the countering effect of forcing dry air into the space. #So all of the factors effecting rh have to be considered in any given environment. #

I would get myself a good indoor-outdoor hygrometer. #Radio Snack sells decent ones. #Set it up in the room where you keep your instruments, run the outdoor line through a window or something (don't break the line, I've done this). #And monitor it. #

I keep all my instruments in a room that is carefully controlled -- warm air humidification in winter, AC and dehumidification in summer -- to try to maintain an rh of between 35-50. #Even then, I recognize that an instrument has to be tuned basically every time you play it, and especially after sitting overnite. #I will play scales for five minutes to "warm up" the instrument, then tune it.

Mark
Relative humidity is just that- relative to temperature

The warmer air is the more moisture it can hold- that's why dew falls on the lawn in cool air- it precipitates out at the lower temperature.

an rh of 50% means different amount of water in the air depending on the temp of the room - so the rh will go up if the room cools off- even though the moisture in the air is the same.

You can find it all on
a Psychrometric Chart (http://www.taftan.com/thermodynamics/PSYCHART.HTM), though they are difficult to interpret.

Agreed - a good goal is rh of 30-50% at normal room temps of 68-70. If you run the house cooler then keep the rh higher.

best.
jgwoods

[J. Mark Lane]

Yeah, you know, you're right. I got it backwards on the temp/rh thing. I don't know what's wrong with me. I think I'm getting senile. Sheesh. Anyway, thanks for correcting that.

I wonder if the implication is that the lower temps of an early morning or overnight house caused the effect I was trying to describe. That is, lower temps, same amount of moisture in the air, higher rh, swelling of wood...?

Mark

[amowry]

I'm not sure that it's true to say that you should keep your RH higher if your house is cooler. We're interested in controlling RH rather than absolute humidity, because RH is what controls the amount of moisture exchange between the wood and air. I might be wrong, this is just the way I see it.

[JGWoods]

Moisture exchange- yes indeed that is probably what you are trying to keep right,and something I know nothing about vs the little I know about rh and dewpoints etc.

I work in a factory where we have to keep moisture out of the air to make product and I have done ventilation work there to try and satisfy the demand for dry air so I know a bit about that, but the point at which the moisture exchange takes place would involve knowing things about wood and how the moistrue is trapped in it that I do now know.

If you want to be able to calculate things easily this calculator will do it for you (http://www.engineeringtoolbox.com/8_240qframed.html)
input the room temp in the F db box, and set the lower box to %rh and you can get outputs in parts per million of water, water vapor, grains of water per pound, etc. which goes a way towards understanding rh and how much water is in the air next to the instrument

You can move all the values around to see what rh you need at what temp to keep a constant amount of moisture available.

Borrowing ideas from Taylor Guitars, pay close attention to the weight of your instruments to see if they are drying out. It seems that all of the repair work they get is from improper moisture content causing cracks or sinking tops, and that gettiing the moisture content, and weight of the instrument, back to what is was originally fixes a lot of problems- not cracks I guess.

best
jgwoods

[Michael Lewis]

The water that effects the wood is the Moisture Content, which is the moisture or water that is physically in the wood. This does not really change with the surrounding temperature, as does the relative humidity (in the air).

[8ch(pl)]

Lots of us turn the heat down at night, I have an automatic thermostat that is prorammed to do it for me. The air is cooler, like from 68F to probably 60F, which causes the metal in the strings to contract. The humidity will also go up as the air is not heated, causing the swelling of the wood. Bingo, the instrument will go sharp.

[Martin Jonas]

an rh of 50% #means different amount of water in the air depending on the temp of the room - so the rh will go up if the room cools off- even though the moisture in the air is the same.
Absolutely right, but it's a bit complicated how this relates to moisture absorption by wooden instruments. #The moisture content of the wood is in equilibrium with the relative humidity of the air, not the absolute humidity. #Let's assume that the wood has a moisture content of, say, 20% (fugure plucked out of the air) and at that moisture is in equilibrium with air at, say, 60% RH (again plucked out of the air). #That means that in a room with higher than 60% RH, the wood will absorb moisture form the air and in a room with lower than 60% moisture, it will give off moisture to the air and dry out. #The equilibrium changes somewhat with temperature, but only relatively slowly. #Thus, a mandolin in a cool room at a higher RH will take up mositure and in a warm room at lower RH will dry out, even though the warmer room may well have a higher absolute humidity than the cooler room.

It's a fairly complex interaction of variables, and for a full assessment, you would really need an ERH curve (showing the inter-relations between moisture content, RH and temperature) for the specific wood in your mandolin. #Keeping an constant RH is probably a good approximation, though.

Martin
(Your friendly neighbourhood physicist)

[JGWoods]

"...Keeping an constant RH is probably a good approximation, though.

Martin
(Your friendly neighbourhood physicist)"
Yes indeed- because room temp probably doesn't fluctuate much- 5-7 degress for most well contructed houses I would guess, and then it aveages over time to be unimportant.

Altitude is another factor as thin air holds less water so a 50% rh in Denver is a lesser amount of moisture in the air than a 50% rh in New Orleans carries.

So...If I was in Denver I'd probably want to keep close to 50% rh rather than the 35% which might be fine in NOLA

best
jgwoods

[amowry]

jgwoods- I'd have to disagree, even if the temp. range was greater than 5-7 degrees, I believe you'd still want to control RH rather than absolute humidity. Similarly, RH means the same thing independent of your elevation. I'd stick with 35% (for example) whether I was in Denver or New Orleans, even though the absolute humidity might be different in each place for a given RH.

[JGWoods]

I might have to disagree with me too, I'm past the limit of stuff I am familiar with. I know that rh is relative and that fact is mostly ignored to the detriment of the process one is trying to control, be it keeping an instrument properly humidified or an optical filter from absorbing moistrue in its coating.

I have a whole house humdifier and a humidity gauge that reads about 30-35% in winter and 50% in Summer, and no cracks in a dozen instruments, no caved in tops either so I am "in control"....I hope http://www.mandolincafe.net/iB_html/non-cgi/emoticons/laugh.gif

best
jgwoods

[Martin Jonas]

I think Andrew got that right (if one ignores the complication that the equilibrium of the wood shifts a bit with temperature). Sorry, JG, I'd aim for the same RH in Denver as in New Orleans.

Martin

[Pete Martin]

I have observed where my mandos are sharp the next day, not always just in the morning either. I have also observed that I have to keep tuning my mandos higher when I play them during the day.

Here is my idea (I have not a clue if it is accurate). http://www.mandolincafe.net/iB_html/non-cgi/emoticons/rock.gif Could it be that the mandolin being such a small instrument where so much of the instrument is right next to out bodiy, that it gets warmed up by our body temperature the more we play it, then cools down when we put it down? Would this account for the flat - sharp observation?

[Pete Martin]

Replace "out bodiy" with "our body" in the previous post. Sorry 'bout that.

[Eugene]

Could it be that the mandolin being such a small instrument where so much of the instrument is right next to [our body], that it gets warmed up by our body temperature the more we play it, then cools down when we put it down? #Would this account for the flat - sharp observation?
I really don't think that's it. I really think that much of what you're observing, petimar, has more to do with uneven distribution of tension over the nut.

[Moose]

Not to get "off-course" here, but from 30+ years of pickin' n' grin'n..., try working a stage - all nite - with a large fan OR a very active AC blowin' 'cross the stage..!!http://www.mandolincafe.net/iB_html/non-cgi/emoticons/rock.gif### - Have a few libations, fagetaboutit!!## - make the nite - collect money - ride outta' town(the Jesse James method)... http://www.mandolincafe.net/iB_html/non-cgi/emoticons/mandosmiley.gif http://www.mandolincafe.net/iB_html/non-cgi/emoticons/tounge.gif

[jbrwky]

Right Moose. And I think if it was strictly environmental I would see occasions when it went flat overnight too. But it doesn't. It is always sharp after not playing awhile. Interesting.

[PhilGE]

Ahem, ahem.... My Theory... Strings are thin before playing, thick while playing, then thin out after playing. ( http://www.mandolincafe.net/iB_html/non-cgi/emoticons/wink.gif for Mony Python Fans)

Okay, so I just had a bit of a brainstorm. It's not like you tune the instrument and then lay it down and don't play it. You tune up before playing, tune it while you play. Why do you need to tune while you play? Maybe that's because

1) the strings get slapped around by the pick (vibrate - and slip a bit at tuner)
2) the strings absorb energy fom the pick - not all of it can be transferred to the top of the instrument
3) this then means the strings warm up and lengthen a tiny bit.
4) put the instrument down for awhile and they cool down and shrink.

IF this is true, then the idea of an instrument "opening up" or "warming up" after playing can be explained similarly, except we're literally talking abou the top "warming up" from the energy transfer of string vibration through the bridge to the top. Not all the energy imparted from the strings through the bridge can be transferred into vibration, so the top absorbs some energy and warms up.

It's My Theory... and that's all it is. http://www.mandolincafe.net/iB_html/non-cgi/emoticons/smile.gif

-Phil (not a physicist)