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The idea that cedar soundboards are ‘open’ almost from the start whereas spruce takes some time to achieve ‘openness’ is interesting and something I’ve heard many times over, not only for SS but also for CL. Does anyone know why this is? What is going on internally in the spruce that is different from cedar as it ages?

Joe

Perhaps the original post has been edited, but I believe Joe is asking about the opening period of the two, not the tonal characteristics.

Joe, I only built with redwood and lutz spruce up to this point. My experience was that the redwood took about an hour of playing time to lose its bash tinny sound, and the lutz took about a day of solid playing (perhaps 5-10 hours of playing time, not just time under tension).

Thanks Filippo. I get that there can be a difference in tone character and nuance between the two and that bracing, thickness, etc. will play a part in this. But I’m not sure you’ve explained why cedar soundboards are more open from the start whereas spruce soundboards take time to open up and fully develop their characteristic sound.

James, yes that’s more to the point of my question. I’m just wondering why this is.

Joe

I'm not sure anyone can claim to know the answer to this question but if so I'd love to know my self.

I will probably P.O. some people here but I believe there is a profound difference in a spruce top versus a cedar top. I have played hundreds of classical guitars and flamenco guitars , some built by famous makers and I can say without a doubt that the spruce top guitars do change in qualities of volume and tone & most importantly overtones whereas most of the cedar top guitars remain constant over time. A famous friend of mine who is a professional flamenco guitarist and educator has even said that he has heard a spruce top open up in the middle of a piece. I do not think it is a simple matter of bracing or humidity control. There are many intangible elements to guitar construction that are not fully understood in spite of all of the computer aided tools that are available. If you ask any luthier that has made many guitars, I think they would agree. It is also interesting to note that the use of spruce in spain was started because of a shortage of cedar during wars, and I think that shortage actually advanced the art form of luthery...

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John Nowicki

This is timely because I just closed the box on a cedar top guitar and while voicing the top (tap voicing), I was amazed at how it sounded open and full from the beginning. I did much less carving on the braces than I do on a Spruce top and it's about .120" in thickness as opposed to the usual .105" - .115" I usually end up with on Spruce tops..

I'm with Joe in wondering what the physical properties (cell structure, density, specific gravity, etc.) are in Ceadr vs. Spruce that cause this.

Sorry, this is obviously not an answer...

Chuck

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"To live a creative life, we must lose our fear of being wrong"
- Joseph Chilton Pearce

First: the whole topic of 'playing in' or 'opening up' is at least a bit controversial in the larger guitar world. Most luthiers agree that it happens, but many players remain unconvinced and even hostile to the notion.

We can measure changes in the way the guitar responds after it's been played for a while, and these tend to correlate well with people's subjective judgements about how the sound changes. We just don't know _why_ they change.

It's interesting to me that the woods that are felt to have short play-in times, Western red cedar, and Redwood, also tend to be prone to cracking along the grain. It makes me wonder if Doug fir, which is also splitty, has a short play-in time. If it does, maybe there's some connection. I've got some nice wide quartered Doug fir, too: rats, there's another 'science fair project'.

OTOH, I have to say that the cedar topped classical I got from George Bowden in Majorca many years ago took about three years of hard playing to fully break in. 'Generally' does not mean 'always'. I'll also note that, despite living a fairly tough life, it has no top cracks.

I know I've read one explanation before although I cannot attest to it's accuracy or validity. The explanation I was given was that as a spruce top ages over time, the sap crystalizes more and then it fractures from the vibrations as the top is being played. A cedar top on the other hand does not have nearly as much sap and thus sound is fairly mature right out of the gate. As the spruce top ages over time, the sap supposedly continues to fracture until it reaches maturity. Of course this is all theory and would be hard to test, however I have some great equipment where I work that would allow examination at the molecular level. On a side note, I have access to laser equipment that can map the vibration of a guitar top in 3 dimensions with extreme accuracy (the equipment is used to test high speed vibrations in an aircraft). If anybody has any ideas how this could be useful in taking the Chladni tests to an entirely new level, please let me know.

Cheers!

John

John,

Wow very interesting!


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FWIW the very best classical guitar I have ever built has a cedar top. I think it's more of a preference in tone more then anything when deciding what top to have. For lack of any better luthier words to describe tone, this guitar sounds woody, earthy, breathy and just for a little flavor, chocolaty.

I typically notice a change in the tone of a guitar within the first two weeks. Maybe this is the strings maturing maybe a combination of both. But I've built guitars that when first stringing up was kind of disappointed only to be redeemed after two weeks. So that's not sap content, it's something else. Maybe it's a placebo who knows.

Add another year on that and it truly has matured.

I'm not at all qualified to make pronouncements on the physics of sound - I just find it to be a thought provoking subject. I'd appreciate reactions from those more qualified to do so (Alan, others...)

Here's a hypothesis: Long "Breaking in" time tends to be associated with those tonewoods that are (tend to be - I know, every piece of wood is different) denser (Adirondack, for example), measured in mass per volume (I use grams per cubic inch). I accept that it can be a controversial subject (is there a subject in luthiery that DOESN'T cause some dissenting opinion among passionate lutheirs?? )

Cedar is almost always less dense than luthier-grade spruce. (and frequently, Adirondack is denser than Sitka and Engleman). So the density of the wood seems to correlate with length of time needed to "open up". It seems logical to me that at least some of this break in time, is the guitar accepting the tension of the strings, bending a bit in places perhaps very, very subtlely, and taking up the slack in tension between the cellular bonds between the glue and the wood, within the wood, etc. Once the guitar's been under tension for some time, aided by the vibration of playing, it becomes a more efficient instrument for transferring sound waves. If a top is denser, it tends to be stiffer (Alan, I think you have data to support this) and thus takes longer for the process to reach the point at which there is no more "give" in the wood. (Or at least the point at which the continued reaction to the stress has been slowed to a very large degree - the flex in the top, reacting to the string tension, has reached a point getting close to equlibrium.)

Does this make sense? Thanks.

Corkey, that makes a lot of sense! Do you think those materials are more dense because of a higher sap content? Also, what happens at that point of equilibrium to finally 'open up' the guitar?

It's interesting that for almost all of the softwoods I've tested (with one exception: Eastern hemlock) there's a linear relationship between density and Young's modulus along the grain. Something like 2/3 of the samples I've measured fall within 10% of the same line. What this means is that any two tops with the same density will tend to have the same stiffness at a given thickness, no matter what the species. This seems to be a reflection of the fact that all softwoods have much the same microscopic structure.

The stiffness comes mostly from fibers of cellulose, which are glued together with a mix of lignin 'glue' and hemicellulose 'filler'. About 50% of the structural weight of wood is cellulose, with the rest being about equal parts of lignin and hemicellulose. I'm not sure where resins come into all of this: from what I've read they don't contribute to the strength, though.

We know that the hemicellulose tends to break down over time into H2O and CO2, and dissappear. As it does the wood loses some density and stiffness, but the density loss is higher, so the stiffness to weight ratio of a piece of wood tends to rise over time. This is a very slow loss: iirc something like 1%/decade.

Hemicellulose is an amorphous material, and as it dissappears the crystaline/amorphous ratio of the wood would change. I know that resins tend to dry out with age, but I have to wonder if the loss of hemicellulose is at least part of the 'crystalization' people talk about.

My understanding is that hemicellulose is the part of the wood that absorb moisture from the air; as it breaks down wood takes up less moisture and becomes more stable. High humidity tends to make wood less stiff as well, so maybe over time the stiffness stays more constant.

One hypothesis that I've seen suggests that playing tends to break the hemicellulose down faster, by heating the wood slightly in areas that are bending. It occurs to me that spruce, in particular, becomes more opaque as it ages: the hemicellulose breakdown leaves voids, which act like the air spaces in a snow bank, reflecting light and making what would be a transparent medium opaque. Perhaps this could be measured in a piece of wood that gets vibrated, as a check on this hypothesis.

Another idea is that shearing forces in the wood cause microfractures in the lignin, and allow the wood to move more easily. This could help explain the idea that unplyed instruments 'revert' to a less-played-in state. Lignin is a thermoplastic, and many such materials will 'heal' over time when fractured. Think about hard candies that stick together. Again, this should be testable, perhaps by running shear fracture experiments. It would help to have access to an electron microscope, too.

At any rate, it makes a lot of sense that heavily built structures would take longer to loosen up than more lightly built ones. A dense Red spruce top will be alot stiffer and stronger at a given thickness than a less dense Engelmann one, and I'd expect the REd to play in more slowly, if only for that reason.

I have a Red spruce top and a Western red cedar top that have exactly the same density, and the young;s modulus along and across the grain matches perfectly. What's different is the 'damping factor': the cedar top rings a lot longer when you tap it. They're going to make an interesting 'matched pair' when I get around to it, and maybe we can look at the playing in behavior then.

John:
We need to talk...

Alan, your post was (as always) quite interesting - it brings up a related question: I've read about some folks that will 'bake' their top wood in the kitchen oven; I've never understood why that is done, but perhaps 'boiling off' some of the sap will hasten some of the changes that you've talked about. Just curious to know if you think that would be related.

Steve

If what Alan postulates about a woods propensity for splitting to correlate to break-in time I wonder if conversely Port Orford Cedar would take the longest to break-in as it is the most split resistant. Alan, another science project. The amount of sap in any given species is interesting also. So many variables.

Link

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Cut to size.....Beat to fit.....Paint to match.

I wonder if baking tops, a la Collings and Taylor, is a way of cooking off some of, and possibly 'cauterizing', the hemicellulose. The initial impetus seems to have been to stablize the wood, and shrink it as far as possible, so that it won't crack later. I am not sure how well it works.

Some violin makers like to 'stew' wood: soak it in hot water for days or more. This is also supposed to eliminate some of the hemicellulose.

I'll note in connection with the hemicellulose model of 'playing in' that new instruments made of old wood still sound new, and need to be played in.

There's lots we don't know...

Alan,

Thanks for educating us on the cellular structure of tonewoods - as usual an enlightening and very interesting contribution. You've discussed the impact on the stiffness and density of the given top as the hemicellulose breaks down. What do you suppose happens to the "damping factor"? e.g. if your equally dense and stiff cedar and spruce tops were to be tested 50 years after you built similar guitars with them, do you have any hypotheses of the ringing tone that these two will produce? Do you suppose that the spruce will have more/less sustain than the cedar? Do you suppose that wood, like wine, can be "past it's prime"?

We've got lots of examples of well-aged red spruce guitars, legendary pre-war Martins, etc. - are there comparable examples of red cedar guitars that were made many years ago?