Qualities of Spruce

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Kim Strode
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Qualities of Spruce

Post by Kim Strode » Sat Jan 25, 2020 2:04 pm

I would like to pick your collective brains. I have a number of spruce sets of different varieties which I have acquired over the years. Some came from Martin and others through a forum group buy. Could you please advise which sets would best suit Classic Guitars and which sets suit Steel String, or other acoustic properties?

1. Sitka Spruce AA
2. Marked as Swiss Spruce
3. Lutz Spruce (High Mountain Tonewoods)
4. ADI Red Spruce (Group Buy)
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Re: Qualities of Spruce

Post by kpcart » Sat Jan 25, 2020 3:15 pm

all will work for classical, but you need to judge the wood on its tap tone and stiffness weight, not on its name or origin.

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Re: Qualities of Spruce

Post by Allen » Sat Jan 25, 2020 6:38 pm

All work well for either steel or nylon strings. But for my money on a classical my first pick would be Swiss Spruce or Lutz.
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Re: Qualities of Spruce

Post by kiwigeo » Sat Jan 25, 2020 9:55 pm

Saw your PM Kim but have been flat out with a new house build of late so didn't get around to replying to the PM.... sorry mate.

My thoughts - I've used Lutz and Englemann on classicals with good results. I think I even used Sitka once on a classical and that sounded ok.
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Re: Qualities of Spruce

Post by Dave M » Sun Jan 26, 2020 3:58 am

From all my reading the message I hear from the people who actually know about this stuff is that the particular species, be it spruce or otherwise is not really important.

What makes a good top is the highest stiffness (Youngs modulus) and the lowest density. Good values of these will enable one to make a low mass top which will be more responsive than a heavier one.

Alan Caruth has shown that stiffness tends to be proportional to density, within a certain tolerance, for all types of spruce, but that within any particular species - or indeed within any group of boards there is great variation of these properties and it is only by measuring the properties can you select the boards likely to make the best guitar.

Now again as I understand it this is true for both types of guitar. The different overall strength of the soundboard required for these two types is determined by the thickness and the bracing applied. Clearly much lighter for the classical.

The other quality that comes into play may be the softness or otherwise of the material. Cedar is notoriously easily damaged so may not be appropriate for a steel string which you may expect to be handled a bit more roughly than a classical.

Sorry if I'm teaching about the sucking of eggs... and I realise I have not really answered the question, but I think testing your store of boards for their material properties is a good place to start.

Good luck Dave M
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Re: Qualities of Spruce

Post by ozziebluesman » Sun Jan 26, 2020 12:08 pm

Hi Kim,

Adi is traditionally the stiffest of spruce but as you well know no two pieces of wood are the same. Adi is used for guitars where you want some headroom in your sound like in Bluegrass music where you need a guitar with volume. The Adi top can also be very sweet fingerpicked.

Sitka is used as an allrounder and I have played many Sitka topped steel string and classicals while working in the retail music industry and some sounded real good. Again I have used very floppy and very stiff Sitka tops, braced them accordingly and both guitars sounded good but different.

Lutz I have used in a few steel string builds and I like it the best of all. I have a classical build on the go with a Lutz top so in the future I can comment on it's tone.

The majority of my builds have been AA tops bought through the forum and I think they are great value tops. Some AAA and Master Grade tops are very expensive and not necessary unless you are wanting to provide a discerning commission buyer with the best material available.

I have used Engelmann tops AA from Graham Hein and they made great guitars.

A cedar topped parlour I built is a sweet fingerpicking tone.

Good luck and have fun experimenting

Cheers

Alan
"Play to express, not to impress"

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Re: Qualities of Spruce

Post by DaveO » Mon Jan 27, 2020 3:23 pm

It is true that spruce has a wide variability in its physical properties. Two important ones mentioned already are Modulus of Elasticity (a measure of intrinsic stiffness) and density. I have measured thousands of pieces for some consulting I do for a tonewood supplier. Enclosed is a graph of a few hundred of those measurements, representing three common topwood spruce s- Red, Sitka, and Lutz (a naturally occuring hybrid of Sitka and Engelmann spruce). MOE on the longitudinal axis (along the grain) is found on the vertical axis, and density along the horizontal.

The red dots clustered in the upper right represent Red spruce (aka Adirondack) - a classic tonewood that grows along the Atlantic interior of North America. Red/Adi is typically the "densest and stiffest" of the species, but as you can see there is a lot of variability. In this case, the samples shown are a mix of trees from the southern end of the range (wood graciously supplied by the Hampton Brothers of the Carolinas) and the northern end of the range (from Canadian supplier Boucher, who also supplies Martin with their Adi). It turns out, there are no significant differences when comparing the properties from the geographic extremes of the range, which surprised me. There is the highest degree of variability with Adi in stiffness to density ratio, compared with the other two.

Sitka is represented in blue, and shows a large variability in density, with an interesting significant drop off in stiffness at the lower end of its density range. I see this trend in other data sets as well - if you have ever noticed your low density Sitka having a palpable floppiness, you are not imagining things.

Lutz (in green) is interesting for several reasons. First, it is found in a relatively constrained geographic region in Central British Columbia, but there is a predictable and known degree of genetic variabilty within that population, formed from thousands of years and dozens of generations of genetic crossing (ref.Dr. Jill Hamilton, a forest geneticist from U of B.C. and the true world's expert) However, there does seem to be a certain "hybrid vigor"* when it comes to tonewood properties, in that Lutz tends to be fairly consistently "above average" when it comes to stiffness to density ratio. In this graph, this is represented by the fact that most of the pieces are above the regression line for the whole data set. Secondly, Lutz tends to maintain its high stiffness to density ratio at lower densities, unlike pure Sitka.

So, if you are looking for a low density, stiff piece of wood for, say, a classical build, you could do well to reach for a set of Lutz. Better still, though, is to measure these properties yourself, by a variety of means (including those found in Trevor and Gerard's books). When you do, you too will see that these species substantially overlap in their properties.

Cheers,
Dave Olson
Bellingham WA

* for any biologists out there, I am aware that I misused the term hybrid vigor. My apologies, and I look forward to your letters :)
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Re: Qualities of Spruce

Post by Dave M » Tue Jan 28, 2020 2:45 am

Dave that is a fascinating and important data set. It shows the variability very clearly. Those samples of Sitka are very offputing!
This should be more widely publicised.
As you say it would seem that Lutz is a clear winner for instruments.

Since you are in the trade you presumably have a sound method for distinguishing between the species. I have always felt that this is pretty difficult for us at the end of the supply chain, and without impugning our suppliers I suspect we don't always get the timber as it is labelled. Any thoughts on how we may do this?

Thanks for showing us this Dave M
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Re: Qualities of Spruce

Post by Dave M » Tue Jan 28, 2020 6:55 am

You do not talk about Engelmann. Do you have any data on that variation of the spruce family?
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Re: Qualities of Spruce

Post by DaveO » Tue Jan 28, 2020 3:46 pm

from Dave M:

"Since you are in the trade you presumably have a sound method for distinguishing between the species. I have always felt that this is pretty difficult for us at the end of the supply chain, and without impugning our suppliers I suspect we don't always get the timber as it is labelled. Any thoughts on how we may do this?

Thanks for showing us this Dave M"

Thanks for this message, Dave! One of the best methods I've seen is found in the Gore/Gilet books, which reference free shareware, using resonance techniques to derive Young's Modulus and density of a given piece of wood. This, along with Trevor's methods for determing panel thickness gives you a step by step method for determing the optimal use for the wood you have. This frees one from the obligation of finding the "perfect" piece of tonewood.

Your point is well taken, though. Indeed, our research to date demonstrates what is often suggested - there are important physical properties that can't be seen, and must be measured, if we are to grow beyond the curious grading schemes that rely upon integer multiples of "A" , but tell us nothing about the sonic potential of a given top. Stay tuned, this may change :)

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Re: Qualities of Spruce

Post by blackalex1952 » Tue Jan 28, 2020 6:16 pm

Wouldn't end grain structural assessment using a low magnification pocket microscope be a good way to identify the different species? Or do all the spuces exhibit a similar end grain structure?

Of course working out the Young's modulus would be the next step for builders.
Cheers! Ross
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Re: Qualities of Spruce

Post by DaveO » Wed Jan 29, 2020 9:42 am

blackalex1952 wrote:
Tue Jan 28, 2020 6:16 pm
Wouldn't end grain structural assessment using a low magnification pocket microscope be a good way to identify the different species? Or do all the spuces exhibit a similar end grain structure?

Of course working out the Young's modulus would be the next step for builders.
Cheers! Ross
The degree of silking is the best way to visually estimate radial stiffness at a given density, and is a useful index when comparing this property among the western N.Am spruces - Sitka, Engelmann, Lutz, and White. Red/ Adirondack spruce is genetically distinct, separated by 2 million years of glaciation from its western cousins, and has intrinsically shorter medullary rays even when the board is rift sawn, with perfect vertical grain.

However, as with every other property, visual and otherwise, there is so much overlap that it can’t be used to distinguish between the species, per your question on identification. I personally have to see a twig and a cone to tell one species from the other. With the Lutz hybrid, that’s often not enough. We’ve gone so far as to use genetic markers, (single nucleotide polymorphisms) in an individual tree’s genome—strenuous fieldwork which also involves bears, mosquitoes and spectacular scenery in the BC interior :)

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Re: Qualities of Spruce

Post by hepikohetaniwha » Wed Jan 29, 2020 8:18 pm

That’s a fantastic graph Dave! Thanks very much. It would be also very interesting to plot the stiffness to weight ratio against n.

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Re: Qualities of Spruce

Post by Trevor Gore » Thu Jan 30, 2020 9:06 am

Thanks for posting that DaveO. I have a similar chart with a tighter spread, which just indicates that a lot of selection has gone into the wood before I measure it (so not a random sample). Also, the regression line is lower down the page in my results, indicating lower measured Elong values. I presume your measurements were taken using ultrasonic methods rather than resonance methods?

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Re: Qualities of Spruce

Post by kpcart » Thu Jan 30, 2020 11:26 pm

A couple thing about spruces:
The trees supply about 60% of the worlds oxygen.

most European spruces (Swiss, Norway,German, Carpathian, Frech, Italian etc) are all the same tree (Picea Abies).
Bosnian/Serbian Spruce common in violin making is a different European spruce (Picea omorika)

The American spruces:
Sitka spruce (Picea sitchensis) is reported to be one of the heaviest spruces, but ive got sets of sitka with less weight than European spruce. One of Australia's first classical makers Andries De Jager used Sitka at a time when other makers at the time were only using European Spruce.

Lutz Spruce (Picea × lutzii) is a naturally occurring hydbrid of sitka and white spruce (Picea glauca).

Engelmann Spruce (Picea engelmannii) seems almost axactly the same to me as European spruce from the few sets I purchased in USA. It tends to be the cleanest looking, great white colour.

Adirondack red spruce (Picea rubens) tends to grow in lower mountains and has wider growth rings, but you can find super fine grain ones too. I find this wood to vary the most of the spruces in tap tone and stiffness, and also look. all that will be from its growth habit. I have a great torrefied (baked) light weight set that I look forward to using.

other American spruces like white spruce and black spruce (Picea mariana), blue spruce/Colorado spruce ( Picea Pungens) are not commonly cut for instrument making.

Japanese Yezo Spruce (Picea jezoensis) is impossible to get unless you work at Yamaha, they are using it for their highest models now (previously it was for lower end models, and European spruce used for higher end). It is very similar to Sitka Spruce.

the best individual piece of spruce I have owned that I saved for a special flamenco negra was Caucasian spruce (Picea Orientalis)

To me, I think master grade (as close to perfect quarter sawn does make a difference, both in looks and I find cut like that, it is more consistent set to set as having great stiffness and great tap tone. 2A often varies a lot from the same sequentially cut log in tap tone.

The closest woods I have come across to spruce are (I actually have these) are Western Hemlock (Tsuga heterophylla) - north American, looks very similar to spruce timber, Western White pine (Pinus monticola) - looks just like sitka spruce but with heaps of resin pockets (pitch), Subalpine Fir (Abies lasiocarpa) from north America (probably other firs I haven't held in my hands). Also I have had a few sets of random wood that have matched spruce in stiffness and tap tone, they are Bunya pine (a couple lightweight very well quartered sets), and surprisingly a master grade set of Mediterranean Cypress with tight grain, which I cant wait to use, hopefully this year, lovely smell too. oh and Californian Incence Cedar, looks just like Western Red cedar, but far far stiffer, almost impossible to find though.

Torrefied spruce looks promising to me from what I have owned, touched.

I don't believe in a general consensus for describing a "sound" each spruce will make. you can make a great guitar from a perfectly quarter sawn European spruce, or a great guitar from a heavy dull taptone Red Spruce. all spruce is GOOD ENOUGH, but then you have to know how to apply it, and if you don't know how to tune a guitar, (ie to get the body resonance you want and to get the back to resonate to the top at a certain interval, then a mastergrade set might in theory give a better result) At the end of the day, Spruce is the best overall wood for guitar soundboards, they make guitarry sounding guitars with brightness, clarity, great bass.

The more you spend time around tone wood, you can tell almost instantly if a piece of wood is good, you hold it in you hands, feel the weight, the flex and most importantly do something that isn't taught in most guitar making courses LISTEN TO THE WOOD, tap tone can be understood quite quickly the more time you spend tapping on guitars and on tonewood.

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Re: Qualities of Spruce

Post by Dave M » Fri Jan 31, 2020 3:35 am

Well kpcart I thought I had come across most of the Spruces but you've given me another on in omorica!

Thanks for sharing your experience with the various timbers. Dave M
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Re: Qualities of Spruce

Post by DaveO » Mon Feb 03, 2020 6:01 am

Trevor Gore wrote:
Thu Jan 30, 2020 9:06 am
Thanks for posting that DaveO. I have a similar chart with a tighter spread, which just indicates that a lot of selection has gone into the wood before I measure it (so not a random sample). Also, the regression line is lower down the page in my results, indicating lower measured Elong values. I presume your measurements were taken using ultrasonic methods rather than resonance methods?
Thanks for the reply, Trevor! It is indeed a resonance test, the BING software out of the CIRAD Forest products laboratory in Montpelier France. We were interested in the natural range of variability of the various spruces, and so no sorting was done beyond the typical rejection of structural defect (knots, grain angle, etc) by the respective mills.

For this test, we sampled bracewood stock, (450 mm longitudinal (long), 19 mm tangential (thick), and 60 mm radial (wide). I consider this to be a representative sample of a representative sample, just dipping a cup into the river of tonewood that flows out of the mill. Overall production of such bracewood stock exceeds a million linear feet per annum, and we have measured a random sample of about 1600 of those pieces, reported on several hundred as here, along with the red spruce from a couple of well known eastern N.Am suppliers. The wood was conditioned in the lab for a minimum of three months, averaging 45 % RH. Oven dry testing on three samples for each species constrained the equilibrium moisture content to 8.2 - 9.6 %. Quick aside on EMC, I could have tested each piece , but I have yet to find a meter with adequate accuracy, pinned or pinless, so we went with a sample of the gold standard oven dry testing. (Plenty of controversial statements in the last sentence, folks -- and I welcome constructive feedback, ie accompanied with referenced sources! )

I have pondered, in a cursory way, the observable differences between techniques. Ultrasound methods for determining velocity thru a sample, of course, do produce a result that is predictably higher than the various resonance methods. Resonant methods based on beam theory should yield roughly similar results, one to the other, as the formula mathematically scales to the conformation of the sample. But I have noticed slightly (non significantly) higher E long results comparing thin bracewood to wider soundboard stock, when comparing population with a simple t-test.

We may be able to compare apples to apples soon, however. We are currently sampling four Sitka logs to determine whether we can make an early determination of mean physical properties of the entire log by sampling wood at compass points around a basal round, the goal being to shunt logs to their appropriate bins at an earlier stage of processing than what we are doing now (randomly sampling the finished boards). Part of that will involve splitting the wide (220 mm) soundboard blanks into three bracewood pieces, and comparing the mean of those pieces to the wider board. If the mean values match the single soundboard measurement, then Hallelujah. If we see a predictable difference between bracewood and soundboard wood from the same piece, we will be able to create an index to compare the two. If there is a random difference....well, that's science - and a trip back to the drawing board :)

Cheers, Dave Olson

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Trevor Gore
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Re: Qualities of Spruce

Post by Trevor Gore » Mon Feb 03, 2020 9:52 am

Thanks, DaveO.
DaveO wrote:
Mon Feb 03, 2020 6:01 am
...But I have noticed slightly (non significantly) higher E long results comparing thin bracewood to wider soundboard stock, when comparing population with a simple t-test.
My charts are from data made up primarily of sound board samples planed to ~ 4mm thick and measured for the elastic constants using resonance methods. I think there is a tendency for thin wood to measure a little less stiff than thicker wood which I suspect is due to long grain run-out and the shorter fibre length involved, which matters more on thin samples.

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Re: Qualities of Spruce

Post by GregHolmberg » Mon Dec 04, 2023 12:03 pm

I don't have data on the spread within a species, or even within Spruces, but I used the averages from wood-database.com to chart about 200 species, both softwood and hardwood. And there is a pretty good fit to a trendline relating density and stiffness. And an even better fit relating density and the sound radiation coefficient, R = SQRT(E/ρ^3), where E is the stiffness (flexural modulus) and ρ is the density.

These species go from Balsa at 150 kg/m^3 to Black Ironwood at 1355. E is in GPa.

E = 0.015 * ρ + 2.06, with a fit (R^2) of 0.70.

R = 8202 * ρ^-1.1, with a fit of 0.94.

It's interesting how tightly clustered the R values are on the red line. R is very predictable from density.
Screenshot 2023-12-03 4.49.26 PM.png

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