Torrefied Tonewood

[David Stiles]

I have been looking to order some violin timber and came across a European supplier who offers torrefied tonewood, maybe maple & spruce, for guitars.

I have found a bit of discussion on ANZLF about benefits of torrefication but unless I'm reading it wrong, there does not seem to be a whole lot of interest in it. The normally conservative violin world seems to be a little more enthusiastic.

I am interested in your views on this. Most of the discussion is around torrefied spruce tops and I can see the benefit there. I was surprised that the European supplier I mentioned are doing torrefied backs, sides necks and even brace stock. Is this really going to really make for a better guitar?

[kiwigeo]

I'm sceptical.....

[Jonny]

From what I see it's getting used an awful lot across NA
Another thing that seems to be used in abundance is wide grained red spruce !

[Allen]

I've built a few ukes with a torrified Sitka soundboard. And have a tenor in progress right now.

The soundboard itself is harder and stiffer than regular Sitka stock from the same supplier. I like the honey color of it and it does smell nice. Earth shattering difference to the instrument......no. But I would say that there is certainly some difference.

[kiwigeo]

What about terrified tonewood?

[Steve.Toscano]

Ive had a few students source their own torrefied woods to use at my school - mostly soundboards.
Honestly, I haven't found there to be any tone advantages in the instruments made with these timbers.
So in my opinion, unless you like the aesthetics of, then dont bother.

[nkforster]

Having made about 50 or 60 or so instruments with torrefied sitka, I can tell you that it isn't stiffer having been through the torrification process. For the work I do, I find regular sitka too heavy and too stiff. So I don't use it.

Baking the wood in an oxygen free oven (torrification) makes the wood both weaker and lighter (lower mass) and more brittle. Being weaker and lighter you are dealing with a wood more like Western red cedar. But not as soft.

So, in use, I really like it, it sounds more open than the Italian spruce guitars I make, more complex than the WRC. Give it a try if you're interested.

[kiwigeo]

Has someone actually sat down and done some stiffness testing on wood pre and post Torrification?

[Steve.Toscano]

Having made about 50 or 60 or so instruments with torrefied sitka, I can tell you that it isn't stiffer having been through the torrification process. For the work I do, I find regular sitka too heavy and too stiff. So I don't use it.

Baking the wood in an oxygen free oven (torrification) makes the wood both weaker and lighter (lower mass) and more brittle. Being weaker and lighter you are dealing with a wood more like Western red cedar. But not as soft.

So, in use, I really like it, it sounds more open than the Italian spruce guitars I make, more complex than the WRC. Give it a try if you're interested.

Nigel, have you tried thinning down your regular sitka to get it to the same stiffness as the torrefied stuff, and then comparing mass?
From the pieces i've seen there wasn't any difference in mass when at the same stiffness (measured with my hands, not anything scientific ).

Has someone actually sat down and done some stiffness testing on wood pre and post Torrification?

I'd like to see the results.

[nkforster]

Trevor may have tested this scientifically, but I've not.

Whenever I've been handed "normal" sitka, I've handed it back. I found it too heavy, too stiff and rather dead. It usually looked nice, which helps, but I'm also rather interested in sound. On the few occasions, I used sitka for braces (when I worked for Sobell, and we cut up an old block he had) I really didn't like working with it.

I'm well aware thousands of decent guitars have been made with it and there is much variation, but I was never sufficiently interested in it for me to invest in it over European spruce, with which I am more than familiar. And whilst there are some really nice sitka guitars out there, I've never played one which encouraged me to make one. For whatever reason, it never connected with me.

And oddly, in over 30 years of making guitars, no one has ever asked me for sitka until I started using torrefied sitka. Now its my most common "upgrade." I find it particularly appropriate for older customers. As one chap pointed out, he was in his mid-70s, he was going to have to wait 18 months for his guitar and didn't fancy waiting for another 5 for the guitar to "open."

What interested me in torrefied sitka initially was the marketing blurb claiming it made guitars sound "vintage." I discuss this in the article and video in the link below.

https://www.nkforsterguitars.com/blog/t ... e-guitars/

What also interested me was the fact you could buy it and use it immediately. The European spruce I buy is dry, but I still tend to keep it around a long time before I put it to use. I'm currently using European stock I bought in the early 2000s. That represents quite an investment on my part. So I thought it would certainly be worth trying torrefied woods if they could be used much sooner. And they can. That would mean I wouldn't have to keep investing in as much stock if I liked the wood. And I really like it for certain types of instruments. I was further interested because (like in this thread) I was reading completely contradictory things about it. Some folk saying it was stiffer, others that it was weaker etc...

In the end, you try it or you don't. Then if you do, you like it or you don't.

I did, and I do! That doesn't mean others will get the same results as I do, as so many other aspects of how I work differ from conventional building. But the wood really works well for me.

[kiwigeo]

Thanks Nick..interesting reading.

[nkforster]

Thanks Nick..interesting reading.

Nigel

[kiwigeo]

Thanks Nick..interesting reading.

Nigel

Nigel sorry.....I look at your monicker "nkforster" and for some reason I subconsciously turn the "nk" into "nick".

Cheers Michael...er I mean Martin

[Trevor Gore]

Trevor may have tested this scientifically, but I've not.

No, I haven't done any objective tests.

[kiwigeo]

Trevor may have tested this scientifically, but I've not.

No, I haven't done any objective tests.

The results could be quite torrifying

[kiwigeo]

Wasn't this device trying to achieve the same end result as torrification?: https://www.tonerite.com/

[Dave M]

I don't really think it is going to make a guitar sound more like a Torres!

D

[lamanoditrento]

I've got a couple of sequentially cut torrified, non torrified SBs waiting for me to test out. If only I had more time in my days

[kiwigeo]

I don't really think it is going to make a guitar sound more like a Torres!

D

I dunno mate. I think Ive discovered the secret to making an instrument that sounds like a Torres. Presenting my new Antonio de Torres moustache kit. Wear this moustache while youre building and I guarantee your instruments will sound like Antonio's

torres2.jpg (7.96 KiB) Viewed 78176 times

istockphoto-160350753-612x612.jpg (25.62 KiB) Viewed 78176 times

[Dave M]

Love it. D

[DaveO]

Has someone actually sat down and done some stiffness testing on wood pre and post Torrification?

Oh, yes. This report, commissioned by Pacific Rim Tonewoods, compares the 4 extant techniques for thermal modification of Sitka. It examines changes in stiffness, density and damping. As with everything else, technique matters, and a mere label of “Torrefaction” does not suffice. The outcomes vary substantially, as you will read. I’m quite sure this is a reason for the diversity of opinions as well

This report is, to my knowledge, the most comprehensive report specific to guitar wood.

https://drive.google.com/file/d/14MGkz ... p=drivesdk

Cheers, Dave Olson

[kiwigeo]

Thanks Dave

[seeaxe]

I don't really think it is going to make a guitar sound more like a Torres!

D

I dunno mate. I think Ive discovered the secret to making an instrument that sounds like a Torres. Presenting my new Antonio de Torres moustache kit. Wear this moustache while youre building and I guarantee your instruments will sound like Antonio's

torres2.jpg
istockphoto-160350753-612x612.jpg

Pretty sure you've got his archtop mo there Martin.
If you take another look at the photo he is sporting his falcate shaped face fuzz. Obviously was on the cusp of upstaging Trevor buy didnt quite get there.

[GregHolmberg]

Here's another report on torrefied wood. This is by the International Thermowood Association in Finland, 2003.

While engineering tests of the ThermoWood method indicated increased resistance to humidity, they also showed a significant reduction in strength (ultimate breaking point), while stiffness (modulus of elasticity) remained the same or was slightly reduced. Although the reduction in strength can be controlled by reducing the temperature of the process, the manufacturer recommends not using its product for structural purposes. However, it is perhaps possible to compensate for this loss of strength in guitars by using carbon-fiber stiffeners in necks and increased bracing in tops.

Greg

[GregHolmberg]

Oh, yes. This report, commissioned by Pacific Rim Tonewoods, compares the 4 extant techniques for thermal modification of Sitka. It examines changes in stiffness, density and damping. As with everything else, technique matters, and a mere label of “Torrefaction” does not suffice. The outcomes vary substantially, as you will read. I’m quite sure this is a reason for the diversity of opinions as well

This report is, to my knowledge, the most comprehensive report specific to guitar wood.

https://drive.google.com/file/d/14MGkz ... p=drivesdk

Cheers, Dave Olson

Thanks to Dave and his employer Pacific Rim Tonewoods for sponsoring this report at the University for Eberswalde University for Sustainable Development, Germany. Here's the paper on ResearchGate. You can download it there for free.

I read the report, and while I'm not an engineer, it seemed pretty thorough. They used some very nice equipment (piezo-electric hammer?), tested Sitka samples from several thermal processes from different companies in Finland, Netherlands, Italy, and Germany (different times and temperatures), and measured 11 samples for each.

The quick summary is that the different processes produced very different results, some improving the wood for use as a soundboard, and some impairing it. The process that worked the best was the one from FirmoLin Technologies in the Netherlands, which raised the temperature to 170 C for 4 hours, with a total time of 25 hours including warm-up and cool-down. Other processes went to a similar temperature (160 to 180), but times varied. Some produced quite negative results for use in a guitar.

So one lesson here is that all processes are not the same. Some work for guitars, some don't.

A second lesson was that the changes were relatively small, whether positive or negative.

All processes produced lower densities. For example, a typical result was to reduce a sample of Sitka from 370 kg/m^3 to 347, a 6% reduction.

The longitudinal modulus of elasticity (Young's modulus, E) was either unchanged or reduced for most of the processes. The FirmoLin process did produce a 5% increase (from 11,000 to 11,600). Several processes produced an increase of about 7% in the radial E also.

Together the change in density (ρ) and elasticity (E) produced an increase in the sound radiation coefficient, R = SQRT(ρ/E^3), in all processes. The best was again the FirmoLin process, which increased R by 13%. I think a higher R means it should be louder.

Damping, like E, was a mixed bag, some processes improving it, some impairing it. FirmoLin reduced damping by 5%, but another process did better, reducing it by 9%. The other processes increased damping.

Interestingly, they did not measure if there was any effect on resistance to humidity, one of the primary claims by guitar making companies for Torrefied tops.

My take-away from this is that guitar makers should be very careful in choosing torrefied wood. Many processes do not improve the wood for our uses (maybe their products are meant for other purposes), and even the ones that might improve the guitar, improve it only a little bit, and might require changes in thickness and/or bracing.

The common idea that a torrefied top sounds "played in" or decades old, was not investigated. In fact, no guitars were built and evaluated subjectively. So I guess that remains an unknown.

Greg