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  #16  
Old 03-01-2021, 05:02 PM
yaharadelta yaharadelta is offline
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I'd agree that that my guitars sound better when things are on the dryer side of 45-50% humidity. In my experience I'd buy into the theory that a drier top is less dense and more resonant. My guitar room is usually around 45% in the winter using a room humidifier. It usually happens in the Fall before I crank up the humidifier, that levels drops to around 35% for a few days (before I find filters etc.) and my guitars sound great, very resonant and crisp.
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  #17  
Old 03-02-2021, 09:28 AM
Alan Carruth Alan Carruth is offline
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Thanks for the link Kevin H.

Most such studies are undertaken by engineering students who are learning to use tools like finite element analysis and modal analysis that they will use later in working with 'real' stuff like bridges and aircraft. Often the department head or their advisor is interested in musical instrument acoustics, and the students are 'slave labor' (willingly, often enough). Now that the tools are becoming ubiquitous there is a lot more such work going on, which relives us fanatics from some of the labor.
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  #18  
Old 03-02-2021, 09:40 AM
llew llew is offline
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Mine sound better when the RH is under 45%.
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  #19  
Old 03-02-2021, 09:47 AM
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Quote:
Originally Posted by imc2111 View Post
It is well known that HIGH humidity can make most guitars sound like they have socks stuck in the soundhole; muffled, lifeless and uninspiring. As someone that lives in a high humidity area, I know this too well.

But what about the other end of the spectrum, low humidity? Does it impact tone when it gets too low?
Hi imc-etc

We live in low humidity country. When it's 30-35% my guitars sound their best.

Above 45% they increase the 'stuffed with socks' phase noticeably, and it's worse at 50-60%.

My guitars live at between 38-42%. Sometimes in the driest parts of winter, they live in their cases because we cannot sustain the humidity in the house above 30%.




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  #20  
Old 03-02-2021, 10:46 AM
J Patrick J Patrick is offline
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...I live in Oregon where we have a wet side of the state and a dry side of the state....I have owned homes and lived on both sides for years so I have observed the effects each side of the state have had on my guitars multiple times....they definitely sound better to my ears when they are on the dry side...but it’s not a huge difference because I always keep my finer guitars in their cases to protect them from any sudden or prolonged changes in temperature and humidity....

...I do find the 35 to 40 percent RH can make a lightly built guitar more resonant and responsive than 50 to 60% RH....but the tone is pretty much the same...
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  #21  
Old 03-02-2021, 03:39 PM
varve varve is offline
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As Mr. Carruth stated with his usual eloquence and thoroughness, it isn't the moisture content per se that impacts tone, but rather the impact of the top's moisture content on the physical properties of the wood, chiefly stiffness (Young's Modulus) and damping (internal friction).

As such, your own guitar is an elegant demonstration device of the importance of these properties. There is a broad agreement, in this post and elsewhere, that low RH regimes (35 - 45% of so) improve tone, provided the instrument's structure remains stable (of course). Or, as the late Bill Collings told me in the one conversation I was lucky to have with him: "Guitars always sound best just before they crack!" .

It turns out, this is predictable and demonstrable with long standing data. One of the leading tonewood researchers in the world, IMO, is E. Obataya, late of Kyoto University. Decades ago, he produced research on the effect of moisture content on stiffness and damping , encompassed in the following graph:

https://www.flickr.com/photos/188914...posted-public/

The horizontal axis represents equilbrium moisture content, which is a direct reflection of the relative humidity, after a period of equilibration. At room temperature, 40% RH yields a moisture content in Sitka of about 7-8% (wood nerds can consult Bruce Hoadley's excellent book Understanding Wood). At this MC%, stiffness is at a maximum (the open squares), and damping is at a mimimum (filled squares). At higher RH, thus higher moisture content, stiffness decreases and damping skyrockets, resulting in an instrument that sounds like it has "socks stuffed in the soundhole" (great description of the muted tone that arises in guitars built with highly damped Sitka).

Cheers, Dave Olson

Last edited by varve; 03-02-2021 at 03:50 PM.
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  #22  
Old 03-02-2021, 05:43 PM
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Pura Vida Pura Vida is offline
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That's really good, helpful info. Thanks to Alan, Dave, and others.
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  #23  
Old 03-02-2021, 09:16 PM
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Quote:
Originally Posted by varve View Post
...At higher RH, thus higher moisture content, stiffness decreases and damping skyrockets, resulting in an instrument that sounds like it has "socks stuffed in the soundhole" (great description of the muted tone that arises in guitars built with highly damped Sitka)...
Interesting! Is that data for spruce? I'm curious if that behavior is broadly applicable to other woods used for tops.
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  #24  
Old 03-02-2021, 10:30 PM
Dustinfurlow Dustinfurlow is offline
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I had a conversation with a fairly reputable steel-string builder awhile back who says he keeps the shop around 35% at all times, I was pretty amazed to hear that. I thought maybe 40-50% at all times but I guess as previously stated: more moisture = less stiffness.
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  #25  
Old 03-02-2021, 11:16 PM
donlyn donlyn is offline
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Does low humidity affect tone?

The answer is of course, yes.

Surprise. No surprise.

The real quesrion is 'how much and is it enough to be heard?'.

It's in the ears of the listener, which is about as inexact as it gets.

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  #26  
Old 03-03-2021, 08:09 AM
varve varve is offline
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Quote:
Originally Posted by KevinH View Post
Interesting! Is that data for spruce? I'm curious if that behavior is broadly applicable to other woods used for tops.
It is certainly applicable to the softwoods - spruce, cedar, etc. At our lab, in Washington state, we expend a certain amount of energy keeping the RH at 45%. Otherwise, the properties skew predictably.

The real point, tho, is that even after controlling for moisture content, there is a great deal of intrinsic variability in the properties of density, stiffness and damping from one piece to another. And this variability leads to predictable differences in tonal quality from one guitar to another, given a particular design and build.

The differences we see in the tone of a single guitar at different moisture regimes is simply an elegant proof of that concept.

Damping seems to be particularly important, with marked differences in tone over a relatively small range - the range that is effected by household variations in relative humidity. Guitars built with low damping top wood tend to have preferred tone on blinded tests, at least for the parlor and Grand Auditorium designs we have studied. This paragraph summarizes the last three years of work on two continents. Published work is in progress now

Cheers, Dave Olson
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  #27  
Old 03-03-2021, 09:55 AM
Alan Carruth Alan Carruth is offline
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"Damping seems to be particularly important,"

That makes sense.

In my latest 'matched pair' experiment the two instruments had spectra that were indistinguishable below ~1000 Hz, but in 'blind' tests everybody could tell them apart easily. There were small random differences in the output in the high range, particularly between 2k-4k Hz, where normal hearing is particularly acute, and those must have been what people picked up on. These could be linked in at least some cases to changes in high order mode shapes due to small variations in wood structure, such as 'knot shadows' or local changes in the degree of quarter.

Damping normally dissipates energy at a certain rate per cycle of oscillation. A common measure of damping is the 'Q-value' or 'quality factor', which is the proportion of energy dissipated per cycle: a Q of 100 means that 1% of the energy is 'lost' for every cycle. That would cut the energy in half after about 72 cycles (more or less). At 100 Hz it would take .72 seconds, but at 1000 Hz only .072 seconds, so damping 'eats' highs fast.

It seems to me that the intrinsic damping of the wood itself sets an upper limit on how much damping the structure will have. It's distressingly easy to build in more damping, via things like poor glue lines and bad design, but tricky to cut it down to the minimum of what the wood does. That's one of the differences between 'average' and 'good' guitars, IMO.

I'll note that there is some question about whether damping in wood is a 'constant'; the same at all frequencies. I suspect it's not, and that the way it varies could be fairly complex, but it's hard to sort out. Haines, in his study of violin tone wood, could not say for certain whether the damping changes he measured were intrinsic, or just artifacts of his test method. And so it goes.
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  #28  
Old 03-03-2021, 10:34 AM
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Quote:
Originally Posted by Alan Carruth View Post
...In my latest 'matched pair' experiment the two instruments had spectra that were indistinguishable below ~1000 Hz, but in 'blind' tests everybody could tell them apart easily...
Hi Alan. When you say the spectra were indistinguishable, are you referring to the frequency spectrum or the spectrogram? I'm wondering if there may have been differences related to damping, or something else that shows up in the spectrogram, that they were picking up on.
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  #29  
Old 03-03-2021, 10:46 AM
Don W Don W is offline
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40-45 is best for my guitar tone. High humidity makes them sound "thumpy"
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  #30  
Old 03-03-2021, 07:47 PM
Alan Carruth Alan Carruth is offline
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I was referring to a frequency spectrum from an impulse test. I've been using those for a long time, and set up a small 'semi-anechoic closet' for the purpose. Its not perfect, but at least it's always the same, so the results are quite reproducible.

In this case they were 'matched' as closely as I could make them. The tops were cut back to back from the same old split spruce billet, and the backs and sides were 'sisters' sawed from the same plank. Ditto the necks and bridges. The fingerboards were as similar as I could get: with Macassar ebony from a supplier I could not specify sister cuts, but they could well have been by appearance, and they weighed the same. All the dimensions were controlled as well as possible, weights of components were held to close tolerances (a gram or so in most cases, iirc), and the 'free' plate resonant mode frequencies and shapes were also matched. A student pointed out that the biggest visible difference was in the hand-cut headstock inlays; one owl leaned more 'left' and the other 'right'.

I will say that those two guitars were about as similar in sound as they could be. Neither was 'better' than the other, as would be expected if there were damping differences, for example. They were just 'different'.

Last edited by Alan Carruth; 03-03-2021 at 07:58 PM.
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