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Ned Milburn -> RE: fan bracing (May 6 2013 16:56:03)
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In reply to J.Shelton and Anders:
Re: Cedar stiffness - Experiencing the woods in their raw form (ie: before building) will tell you all you need to know. Cut similar sizes and grain orientation of cedar and several different spruces, then flex them. There should be enough difference to get an accurate assessment of their relative stiffnesses. I have worked with or handled red spruce, sitka, Englemann, European (which is a broad term) and Lutz spruce, as well as Canadian western red cedar and Eastern Canadian Hemlock. It is pretty clear in which order the stiffnesses occur. Also interesting is to flex both with the grain and across the grain, since different species have different balances. (Ie: the Englemann I have worked with tends to be stiff with the grain but less stiff than other spruces perpendicular to the grain.) Several builders have used weights and rulers to measure the stiffness (deflection) of wood as they build guitars.
Re: Cedar softness - Similar to the above, working with the woods will tell many answers. I would be surprised if most people who have worked with red cedar and a variety of spruces would experience anything other than cedar being softer than spruces. Englemann spruce is the softest spruce I have experienced so far, but it still has a lot more resistance to impact than cedar. Try your fingernail on some off-cuts.
Re: Speed of sound - Although I have seen speeds of sound posted on the internet, this in itself is not enough to base a conclusion upon. However, the consistency of the few figures I have seen showing cedar has a slower speed of sound than most spruces, coupled with my own knowledge and experience of music and the basics of physical sound propagation gives me enough support to believe that cedar is indeed a slower conductor of sound than (most) spruces.
Specifically, in general, sound travels quicker through dense objects than less dense objects. Also, in general, sponge-like and softer substances conduct sound more slowly than solid harder objects. Similar to a hanging-ball-bearing "perpetual motion" executive desk toy, the molecules bump directly into adjacent molecules. If the molecules are tightly packed, there is less loss of energy before they bump into the next molecule. Take the same desk toy analogy and rather than the hanging ball bearings being right next to one another, move them a centimetre apart, and it will take more time for the final ball bearing to be moved than if they were tightly packed. This is why water, for example, conducts sound much more efficiently than air, and sound waves through water can travel further than through air. (Even on foggy days, sound travels further through air than on dry days, because there are more molecules in suspension to be affected by the sound wave.)
Also, I fall back here to my experience of playing jazz guitar (I studied jazz guitar during my university music degree and after playing regularly in Montreal). Many modern jazz guitarists use a small amount of delay on their sound. This delay (could be anywhere from 10 to 100 milliseconds or more) smooths out the attack of the note by blending another attack shortly after the initial attack, but at a lesser volume. Hence, instead of having one loud attack that begins to decay immediately, we effectively lengthen the initial attack of the note. The sound created is often described as "warm" or "mellow". Cedar, interestingly enough, when compared to spruce, is often described as "warmer" or "mellower", and "less bright" and lacking a bit of punch, power, or projection. These are general comparative descriptors, but are so ubiquitous as to be indicative of a true existing characteristic of the woods themselves, rather than any subjective psychoacoustic perceptions. (Understand that I know quite well it is possible with modifying thicknesses and bracing patterns to have a cedar topped guitar that does not fit the general description of a "cedar" sound, but these are rare, and tend to also exhibit some characteristics of the "cedar" tone.)
After putting a lot of thought into cedar versus spruce and over 15 years after having first been introduced to the differences in sound, a plausible reasoning came to me in a flash of insight. Similar to the jazz guitar, with a slower (slightly, ever so slightly) propagation of sound through a cedar topped instrument, the attack that is sharp and clearly delineated in a spruce guitar is more "mellow" in a cedar guitar due to the slightly slower sound propagation that spreads its attack over a slightly longer time. I like to keep in mind, also, that the guitar is a unique type of percussion instrument (physical strike creates sound which immediately begins to decay). The guitar's sound generally comes from the "release" of a string, even though it appears as though the string is being "struck". This is why I state a "unique" percussion instrument. So, due to its percussive nature with strong attack and immediate decay, the attack of the note and its immediacy of translation to airborne sound takes much greater precedence than an instrument with sustained note ability (ie: a violin). Hence, the small difference of extra time taken for sound to propagate through a cedar topped instrument can very plausibly explain the difference in sound of the two wood types. There is more to it (the difference between cedar and spruces' sounds) than this, however, since we get into measurements of stiffness and elasticity (stiffness being how hard it is to deflect a solid object from its natural form, and elasticity including the speed and strength at which the deflected object is able to return to its rest position).
As an aside, it is very easy to derive direct empirical evidence of several of wood's properties by doing one's own experiments. Shortly after I purchased my first bandsaw, I practised resawing with some spruce 2x4's I had left over from house renovations. From the exact same 4 inch length of spruce, I cut several 3 mm pieces, of which most were not 100% quarter sawn, but one piece was. At this point in my development and knowledge gathering, I wondered why top builders preferred well-quartered wood. The answer was apparent immediately due to the superb stiffness of the 100% quartered cut, versus the soft "flompy" nature of the non-quartered wood. The softness increased as the cut went further from quarter. I still keep these wood pieces to show to my clients as an introduction to showing them about the properties of wood and the reasons why only top quality wood can produce the highest quality guitars.
Presently, I am building 2 "twin" classical guitars - exact same cut of wood for sides, back, neck, linings, and braces, but the tops are Lutz and Englemann spruces. I am about 1/2 way through the French polishing, but even once the wood-work was finished I could tell that both instruments, while producing nearly exact same pitches in similar areas (tap tones), expressed a different quality in their sustain and quality of sound, with the Englemann being the one that misses a little bit of sustain, power and clarity. (This is a subtle difference that requires a sensitive ear to detect, but I expect that many who participate in this forum would be able to hear the difference.) Remember what I stated above that Englemann tends to be less stiff across the grain (90 degrees to the grain). It is logical that this lower stiffness is a factor in the slightly different tones between these two spruces.
FWIW - Here is a link with some interesting figures. It is the quickest one I was able to find, and while I do not by any means take it as gospel, the comparative figures are interesting and of the softwoods I have worked with that are included, the figures are comparatively as I would expect from my experience handling these woods.
http://uk.answers.yahoo.com/question/index?qid=20081102053004AAGPJj9
I have a link to a local university physics researcher who might be interesting for me to contact in efforts to conduct some tests on woods that I have at hand to get some better measurable readings on certain woods' speeds of sound. If I ever do this, I'll try to remember to post some findings.
Cheers!
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