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Acoustical effect of back woods
http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10101&t=51779		 Page 1 of 2
Author:  Trevor Gore [ Thu Apr 04, 2019 3:38 pm ]
Post subject:  Acoustical effect of back woods
According to the Journal of the Acoustical Society of America (of which esteemed body I am a member) one of the most downloaded articles from the last year published in The Journal of the Acoustical Society of America is this one: “Effect of back wood choice on the perceived quality of steel-string acoustic guitars” (Samuele Carcagno, RogerBucknall, JimWoodhouse, Claudia Fritz and Christopher J.Plack). Some fairly famous names there.

https://asa.scitation.org/doi/pdf/10.11 ... ?class=pdf

This article has been made free to read, download, and share for a limited time (apparently).

After 16 pages of intense analysis their conclusion is:

“The results of our study indicate that steel-string acoustic guitars with backs and sides built using traditionally prized, expensive, and rare woods are not rated substantially higher by guitarists than guitars with backs and sides built using cheaper and more readily available woods. The poor ability of guitarists to discriminate under blinded conditions between guitars with backs and sides made of different woods suggest that back wood has only a marginal impact on the sound of an acoustic guitar”.
Author:  violinvic [ Thu Apr 04, 2019 3:50 pm ]
Post subject:  Re: Acoutical effect of back woods
Reaffirms my suspicions and opinion. I built a dread with white oak back and sides with a sitka top. I was real happy and surprised at the result. The owner loves it.
Author:  Alan Carruth [ Thu Apr 04, 2019 3:57 pm ]
Post subject:  Re: Acoutical effect of back woods
Why am I not surprised? I built my first 'almost matched' pair of classical guitars back in the '90s, with spruce tops and B&S of red oak and BRW, and found very little difference in the sound. When I published the article in the CAS Journal in '96 I attributed the differences to differences in the mass and damping of the backs, but the more I think about it the more I wonder if a pair of BRW ones would have been any more closely matched.
Author:  Tim Mullin [ Thu Apr 04, 2019 5:56 pm ]
Post subject:  Re: Acoustical effect of back woods
I remember reading that article when it first came out. A wonderful piece of work involving the amazing Claudia Fritz and her team. Some may remember work she did on player and listener discrimination of violins. Really interesting stuff. And, as a scientist working my whole life in statistics, I noted with great interest that they utilized Bayesian stats — not for the faint of heart, and not found in your average stats package, but ideally suited for experiments of this nature. Really first-class work! Sets a higher bar.


Sent from my iPad using Tapatalk
Author:  jfmckenna [ Thu Apr 04, 2019 7:58 pm ]
Post subject:  Re: Acoustical effect of back woods
One of the first things I remember reading when I started making guitars many years ago was about Torres's paper mache guitar. That stuck with me. And interestingly that's how long ago this argument has been brought up and yet still the buying public doesn't 'buy' it. At the same time in the back of my head I cannot help to think that, it's got to do something? It's more about the engineering properties of the chosen wood or even better how the engineer engineers them. To get one back to behave like another all you have to do is alter the thickness to get the same properties. Does wood species really mater? The argument continues...
Author:  Conor_Searl [ Thu Apr 04, 2019 8:29 pm ]
Post subject:  Re: Acoustical effect of back woods
A bit of a complementary tangent, are D-18's and D-28's constructed differently other than back and side wood? Because I can hear a difference between those guitars.
Author:  TimAllen [ Thu Apr 04, 2019 10:48 pm ]
Post subject:  Re: Acoustical effect of back woods
These studies do not prove that no one can hear a difference between guitars made with different B & S woods.

There was an interesting piece in NY Times in which their wine critic discusses the meaning of studies that, in blind taste tests, show that many people don't prefer more expensive wine, or prefer the less-expensive wine that they are used to drinking. I think some of his points are pertinent to this discussion. https://www.nytimes.com/2018/07/16/dini ... itics.html

Experienced guitar builders often express the view that backs and sides color the sound, and that this is a variable that builders can use to make a small but audible difference. In my observation the reason customers pay premium prices for guitars built of certain woods has less to do with sound and more to do with the appearance and connotations of particular woods.
Author:  Luthier1975 [ Fri Apr 05, 2019 6:58 am ]
Post subject:  Re: Acoustical effect of back woods
https://www.gaieroguitars.com/the-heret ... erie-woods

Interesting article by John Calkin about this.
Author:  Greg Maxwell [ Fri Apr 05, 2019 7:29 am ]
Post subject:  Re: Acoustical effect of back woods
TimAllen wrote:
These studies do not prove that no one can hear a difference between guitars made with different B & S woods.


It doesn't claim to prove that. What it does rather conclusively argue is that back and side species are not nearly as important to tone and voice as most people think they are.
Author:  jfmckenna [ Fri Apr 05, 2019 7:57 am ]
Post subject:  Re: Acoustical effect of back woods
Luthier1975 wrote:
https://www.gaieroguitars.com/the-heretics-guide-to-alternative-lutherie-woods

Interesting article by John Calkin about this.


Good article and a nice list of alternate woods to use too.
Author:  Pat Foster [ Fri Apr 05, 2019 10:07 am ]
Post subject:  Re: Acoustical effect of back woods
Conor_Searl wrote:
A bit of a complementary tangent, are D-18's and D-28's constructed differently other than back and side wood? Because I can hear a difference between those guitars.


I agree, especially with old dreads. 28s MIGHT have a slightly higher cosmetic grade of spruce in the top. If I recall, there's no structural difference.

Besides the B & S woods, D-28s have ebony bridges and fretboards; on D18s, they're East Indian rosewood, which is considerably lighter. Bridge weight alone can make a difference. There's also a difference in damping between ebony and EIR. I don't have hard data, but I'd venture a guess that a D-18 weighs less than a D-28. That can also influence sound.
Author:  jfmckenna [ Fri Apr 05, 2019 10:12 am ]
Post subject:  Re: Acoustical effect of back woods
The problem is that two 'identical' d-28's will sound different from each other as will any given two D-18's.
Author:  Conor_Searl [ Fri Apr 05, 2019 11:15 am ]
Post subject:  Re: Acoustical effect of back woods
jfmckenna wrote:
The problem is that two 'identical' d-28's will sound different from each other as will any given two D-18's.


Sure, I get that every guitar is going to be different to some degree. But would you not agree that there is a general tonal thing you can put your finger on that is consistent when comparing a mahogany guitar with a similarly constructed rosewood one?

I see now that this article isn't trying to argue that there is no difference between tonewoods, just that the obvious, traditional, and expensive options aren't categorically "better" than the alternatives.
Author:  jfmckenna [ Fri Apr 05, 2019 1:04 pm ]
Post subject:  Re: Acoustical effect of back woods
Honestly? No. I don't think I would be able to tell the difference between a rosewood or a mahogany guitar in a blind test. I would be able to use words to describe what I hear is in the difference between the two of them but that's about it. I'm only on my 65th guitar now so I am no expert by any means. And I have mostly used so called alternative woods. Those include Walnut, White oak, Maple, Cherry but then some exotics too like Bubinga, Imbuya, Pau Amarello (Yellowheart) and some others I can't remember. I've also built from Mahogany and EIR too. In fact I heeded the advice when I first started building in the early 90's to use cheap easily obtainable wood till you get your skills up. I've always wanted to build with BRW but didn't want to waste it either. After 25 years right now I am finally building my first BRW guitars, so I'll let ya know what I think ;)

But in all this time with my limited experience building, and having been doing repairs and seen lots of other guitars, I can conclude nothing for myself in regards to tonewoods for back and sides. And even tops generally speaking. I see it as this, a Sitka top might be a lot stiffer then a WRC one but if I test them out to the same spec which yields the same deflection and Youngs Modulus then I can expect them to behave in a very similar way once braced up and glued to complete a sound box.

I don't think in a blind test I'd be able to hear cedar vs spruce either, nevermind the differences between spruce species.
Author:  Conor_Searl [ Fri Apr 05, 2019 1:32 pm ]
Post subject:  Re: Acoustical effect of back woods
jfmckenna wrote:
Honestly? No. I don't think I would be able to tell the difference between a rosewood or a mahogany guitar in a blind test. I would be able to use words to describe what I hear is in the difference between the two of them but that's about it. I'm only on my 65th guitar now so I am no expert by any means. And I have mostly used so called alternative woods. Those include Walnut, White oak, Maple, Cherry but then some exotics too like Bubinga, Imbuya, Pau Amarello (Yellowheart) and some others I can't remember. I've also built from Mahogany and EIR too. In fact I heeded the advice when I first started building in the early 90's to use cheap easily obtainable wood till you get your skills up. I've always wanted to build with BRW but didn't want to waste it either. After 25 years right now I am finally building my first BRW guitars, so I'll let ya know what I think ;)

But in all this time with my limited experience building, and having been doing repairs and seen lots of other guitars, I can conclude nothing for myself in regards to tonewoods for back and sides. And even tops generally speaking. I see it as this, a Sitka top might be a lot stiffer then a WRC one but if I test them out to the same spec which yields the same deflection and Youngs Modulus then I can expect them to behave in a very similar way once braced up and glued to complete a sound box.

I don't think in a blind test I'd be able to hear cedar vs spruce either, nevermind the differences between spruce species.


That's super interesting. I haven't even built one acoustic guitar yet, so I humbly submit my limited experience with guitars to the collective wisdom here. The only reason I even chimed in on this post is that the more I learn about guitar making, the more interested I am in challenging my assumptions, and trying to find out what is fact and measurable, and what is psychological. The amount that back and sides wood plays into the end result is one of those things I always assumed was a given as being a pretty big part of the equation, to read that maybe it wasn't as big a deal as the common understanding says it is made me curious.
Author:  jfmckenna [ Fri Apr 05, 2019 1:39 pm ]
Post subject:  Re: Acoustical effect of back woods
Conor_Searl wrote:
jfmckenna wrote:
Honestly? No. I don't think I would be able to tell the difference between a rosewood or a mahogany guitar in a blind test. I would be able to use words to describe what I hear is in the difference between the two of them but that's about it. I'm only on my 65th guitar now so I am no expert by any means. And I have mostly used so called alternative woods. Those include Walnut, White oak, Maple, Cherry but then some exotics too like Bubinga, Imbuya, Pau Amarello (Yellowheart) and some others I can't remember. I've also built from Mahogany and EIR too. In fact I heeded the advice when I first started building in the early 90's to use cheap easily obtainable wood till you get your skills up. I've always wanted to build with BRW but didn't want to waste it either. After 25 years right now I am finally building my first BRW guitars, so I'll let ya know what I think ;)

But in all this time with my limited experience building, and having been doing repairs and seen lots of other guitars, I can conclude nothing for myself in regards to tonewoods for back and sides. And even tops generally speaking. I see it as this, a Sitka top might be a lot stiffer then a WRC one but if I test them out to the same spec which yields the same deflection and Youngs Modulus then I can expect them to behave in a very similar way once braced up and glued to complete a sound box.

I don't think in a blind test I'd be able to hear cedar vs spruce either, nevermind the differences between spruce species.


That's super interesting. I haven't even built one acoustic guitar yet, so I humbly submit my limited experience with guitars to the collective wisdom here. The only reason I even chimed in on this post is that the more I learn about guitar making, the more interested I am in challenging my assumptions, and trying to find out what is fact and measurable, and what is psychological. The amount that back and sides wood plays into the end result is one of those things I always assumed was a given as being a pretty big part of the equation, to read that maybe it wasn't as big a deal as the common understanding says it is made me curious.


But still, in the back of my head I think to myself, It's got to do something!!!

I just was reading a thread over at the AGF. It was a post from Bruce Sexaur in regards to using mahogany from 'The Tree.' He went on to say that before he ever used this wood he would have argued that any Honduran Mahogany guitar could be made to sound like one from The Tree. But since his experience using THe Tree wood he's come full circle round to saying that the the wood itself has a huge impact on the sound of the guitar.

I'm certainly not one to argue with Bruce.

But my hunch is that 'The Tree' due to it's curly quilted nature, which essentially is runout, might have engineering properties that give it sound rather then species properties.

I think Trevor probably seeded this question and is waiting back as we all discuss it and is due back anytime to share his knowledge :D I hope so anyway.
Author:  meddlingfool [ Fri Apr 05, 2019 3:23 pm ]
Post subject:  Re: Acoustical effect of back woods
What I take from that summary is not so much that back and sides don't make a difference to the sound (they do), but that the prized woods are not necessarily better than other less celebrated woods that also make good guitars. Lucky for me.

I also wonder how much different building styles can enhance/negate the influence of the back and sides.

It's my loose feeling that the b/s influence the sound by wicking off certain frequencies differently via damping, which is what gives them their particular tap tones. Like why mahogany will generally have far less ring and sustain than rosewood does.

If you build in the modern ethos with super stiff heavy double sides and massive linings in an effort to prevent energy from leaving the top, it makes sense to me that the b/s will have less opportunity to lend their influence than on a more traditional guitar with thin sides and light, triangular basswood linings, where a lot more energy can transfer into the side/back.

So a pair of dreads from Modern Man Inc. may well have less audible differentiation than a d18 and a d28. But that's just a loose philosophical pontification:)
Author:  Mark Mc [ Fri Apr 05, 2019 4:46 pm ]
Post subject:  Re: Acoustical effect of back woods
Conor_Searl wrote:
A bit of a complementary tangent, are D-18's and D-28's constructed differently other than back and side wood? Because I can hear a difference between those guitars.


Connor, have you actually tested your ability to discriminate these two guitars in a blinded manner? Or are you asserting this because when you have a D28 in your lap you find yourself saying "yep, sounds like rosewood" - which might be entirely an artefact of other cues.

In the studies that Professor Gore has set us for homework there is a part called the ABX experiment. 31 experienced guitarists were given two guitars (A and B) to play in quick succession- about a minute for each. They were blinded to the look, smell and other cues of the identity of the timbers. After playing A and B they were then given one of those guitars back again (guitar X) and simply asked to identify if it was A or B that they were playing now. They weren't asked to identify the timber, or which is best - just whether they can even tell the difference. This experiment involved guitars made of Brazilian rosewood, sapele or walnut. The results were not statistically different from a coin-toss.
Author:  Conor_Searl [ Sat Apr 06, 2019 1:22 am ]
Post subject:  Re: Acoustical effect of back woods
Mark Mc wrote:
Connor, have you actually tested your ability to discriminate these two guitars in a blinded manner? Or are you asserting this because when you have a D28 in your lap you find yourself saying "yep, sounds like rosewood" - which might be entirely an artefact of other cues.


Blinded manner, like what is described in the article? No. However I'm fairly confident I could tell you which one was which, and I'm sure I'm not unique in this. My personal guitar is a newer D-18. And over the last 15 or so years as my tastes as a player have developed I find I'm constantly drawn to the mahogany guitars in the room. Whether its a J-45, 000-18, or the D-18 I settled on. The same is true of Taylor's I've played, and Larrivee's too. (And I realize this list of guitars is in no way an impressive, exhaustive, or broad example of what is available.) Whatever the grossly generalized qualities mahogany brings to an instrument are, all other things being equal they are what I seem to like the most. And as subjective as personal taste may be, I feel I've come to be able to recognize at least some of those qualities.

But I realize now this tangent is a total red herring when it comes to what the article was trying to communicate, (sorry for hi-jacking). As some people have mentioned, it doesn't say that people can't tell the difference between different tonewoods, just that monetary/esteem value doesn't necessarily correlate to what ends up in a players hands, and really as consumers (that's the best I can claim for myself at this point) I should do my best when considering a new instrument to lay my prejudices aside.

I know I'm a sucker for the "mojo" of things, and fall in love with the idea of certain guitars because whatever hero of the moment played guitar X on whatever famous recording, or in some picture. Which is really as I mentioned earlier why I chimed in on this thread in the first place, I'm trying to get rid of the voodoo element, or at least call a spade a spade when it comes to interacting with guitars.
Author:  Woodie G [ Sat Apr 06, 2019 6:35 am ]
Post subject:  Re: Acoustical effect of back woods
In his book, Beaten, Seared, and Sauced: On Becoming a Chef at the Culinary Institute of America, Jonathan Dixon writes about a class in which the science of taste is explored, and specifically about the impact of the order in which things are tasted on that tasting experience. In other words, the act of employing our senses in sampling a range of similar things has an impact on our perception of those things.

I've experienced this artifact of order of presentation in scotch whisky and bourbon whiskey tastings as well, with the first sample closed and lacking in interesting flavors, and the final sample complex, with interesting and complementary flavors...and not coincidentally, exactly the same bottle as the first sample.

To the subject study, I was encouraged by the effort to randomize the order of presentation, but I have to wonder if an additional set of trials in which the order of presentation was fixed within runs would have shown more in the way of a consistent ranking, with that ranking influenced by the specific presentation order?
Author:  Clay S. [ Sat Apr 06, 2019 9:31 am ]
Post subject:  Re: Acoustical effect of back woods
Perhaps they should have listened to a bit of white noise between guitars to "cleanse their palate"? bliss
Author:  Clay S. [ Sat Apr 06, 2019 12:23 pm ]
Post subject:  Re: Acoustical effect of back woods
And on another note, when I first saw the title I was wondering what Acoustical effects they were talking about when playing guitar in the back woods. I guess I'm too much of a country boy. laughing6-hehe
Author:  J De Rocher [ Sat Apr 06, 2019 2:13 pm ]
Post subject:  Re: Acoustical effect of back woods
If a rosewood guitar and a mahogany guitar fall over in the woods, do they make different sounds?
Author:  meddlingfool [ Sat Apr 06, 2019 5:01 pm ]
Post subject:  Re: Acoustical effect of back woods
Yes. The rosewood one has more overtones, just ask the deer.
Author:  Alan Carruth [ Sat Apr 06, 2019 6:35 pm ]
Post subject:  Re: Acoustical effect of back woods
I have not finished reading the entire article, but I think the crux of the case is addressed on p 3538: "The guitar maker, by treating each back in the way that his experience suggested was best, has to a very large extent compensated for any physical differences between the types of wood".

On p. 3535:
"It is important to emphasize that this is a strength, not a weakness, of the study. To ask 'do guitars sound different if different back woods are used with identical thickness?" is not an interesting research question, because no professional instrument maker would ever do this."

In other words, what the study shows is not that 'back and side woods do not have an effect on the sound', but that it's possible to minimize this effect, although probably not to eliminate it. Or that's what it looks like to me.
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