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Acoustical effect of back woods
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=51779		 Page 2 of 2
Author:  Bri [ Sat Apr 06, 2019 6:58 pm ]
Post subject:  Re: Acoustical effect of back woods
Alan Carruth wrote:
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.


The question for me is, can we, as guitar builders manipulate these “alternative woods” and recreate/ equal/improve the tones/sounds of the revered BRW?
This article seems to indicate this is possible. I know that unless lightning strikes I won’t be buying any BRW.
This has been one of the more interesting threads as of late, thanks Trevor!
Author:  bftobin [ Sat Apr 06, 2019 7:00 pm ]
Post subject:  Re: Acoustical effect of back woods
I have to laugh. I remember how many builders back in the '80's and '90's said IRW was so inferior to BRW that
they would stop making guitars if BRW was no longer available.
Author:  Conor_Searl [ Sat Apr 06, 2019 7:10 pm ]
Post subject:  Re: Acoustical effect of back woods
Alan Carruth wrote:
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".


Interesting. Do you think that means then that perceived differences in tone woods are potentially more amplified coming off an assembly line of a mass produced brand than they would in the hands of an experienced builder? That idea makes sense to me, big brands need consistency when dealing with their much higher volumes, so they execute their plan as close to the same way as they can each time. Each part of the guitar building process is potentially in a different pair of hands. And each step is executed within a pre-ordained set of boundaries, regardless of the unique characteristics of the individual pieces. Whereas the smaller builder has the luxury of mitigating or highlighting the uniqueness of each piece of wood as they see fit, working in response to and with what they have in their hands at any given moment, guiding the entire process to a desired end point.
Author:  Alan Carruth [ Sun Apr 07, 2019 3:31 pm ]
Post subject:  Re: Acoustical effect of back woods
Bri asked:
"The question for me is, can we, as guitar builders manipulate these “alternative woods” and recreate/ equal/improve the tones/sounds of the revered BRW?"

In 'blind' tests, almost certainly. It's already well known that people listen with their eyes, hearing what they expect to hear. I've been testing the mechanical/acoustic properties of 'alternative' woods for a long time, and some, such as Osage Orange, can be so close to BRW that getting 'that sound' in a blind test should be easy. Of course, traditionalists will never accept that truth.

Conor_Searl asked:
"Do you think that means then that perceived differences in tone woods are potentially more amplified coming off an assembly line of a mass produced brand than they would in the hands of an experienced builder? "

Yes. I certainly think this is true of top woods, and is probably true of B&S woods as well. The back does, of course, have much less influence on the timbre of the instrument than the top. Note, too, that all species of wood show a lot of variability in their properties, and that there's a lot of overlap between species as a result. Thus you'd expect overlap in the tone.
Author:  Trevor Gore [ Mon Apr 08, 2019 7:11 am ]
Post subject:  Re: Acoustical effect of back woods
One can get very picky about the way these sorts of experiments are performed, but I'll try to stay away from that. However, trying to identify differences in sound due to the back woods when the T(1,1)1's and T(1,1)2's range over a semi-tone on non-live back instruments (no T(1,1)3's apparent, Fig 1A) doesn't give you much of a chance.

How the back and sides are treated can make a huge difference to the way a guitar sounds. Live vs. non-live backs, mass loaded sides etc. are ample proof of that. But what wood you use, much less so, UNLESS you systematically rely on the average species properties rather than build technique to effect the differences.

What you hear when a guitar is played are the modal resonances, defined by their center frequencies, amplitudes and bandwidth. If you can measure the mechanical properties of the wood (density, Young's modulus, damping) and use the right, well documented techniques, you can match the important modal resonances of guitars made of different woods pretty closely. That's what builders are doing (whether they realize it or not) when "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". So a wide range of woods can be made to sound alike, which means, of course, that players can't pick the difference, and guitar builders have a much greater range of woods at their disposal. I know that I can't pick wood species on my (modally tuned) guitars. All we need to do now is stop the factories from perpetuating the species myths and get them to promote some of the more sustainable alternatives. :D
Author:  jfmckenna [ Mon Apr 08, 2019 9:13 am ]
Post subject:  Re: Acoustical effect of back woods
Can I get an Amen!
Author:  SnowManSnow [ Thu Apr 11, 2019 7:36 am ]
Post subject:  Re: Acoustical effect of back woods
I’m probably they “least” of the builders here, however I have a thought.

I wonder is it actually that the woods don’t really make a difference, or that when folks play them they dampen the differences out?

I mean if someone were to play 3 different guitars with 3 different soundboards, but lay all over / dampen the thing to death they would likely all sound close to the same too. That’s what most do to the back of the instrument.

I have always attempted to make very lively backs, but once they are hugged to death it makes little difference.





Sent from my iPhone using Tapatalk
Author:  Eric Reid [ Thu Apr 11, 2019 8:46 pm ]
Post subject:  Re: Acoustical effect of back woods
Trevor Gore wrote:
What you hear when a guitar is played are the modal resonances, defined by their center frequencies, amplitudes and bandwidth. :D


That's the problem that I have with this study. The early pages establish that the guitars have very different modal resonances, and yet, in the A-B tests, the players can't distinguish between them (or some can, some can't, and the results are lost in the statistical noise). If what you are saying is true, why weren't the differences in modal resonances revealed in the A-B tests? To me, that suggests a problem with the tests--the judges, or more likely, the environment. Which begs the question: under these constraints, what can be heard? That might be a good starting point.
Author:  Trevor Gore [ Fri Apr 12, 2019 12:42 am ]
Post subject:  Re: Acoustical effect of back woods
Peter Coombe and others make a related point over here.

Whilst I agree with the basic thesis (back and sides woods don't make as much difference as you might think, but build technique can) about the only thing that people can agree on is that it is almost impossible to do such tests in a way that everyone will agree is valid.
Author:  Ernie Kleinman [ Fri Apr 12, 2019 6:06 am ]
Post subject:  Re: Acoustical effect of back woods
Sounds , like it is very difficult to get a consensus Trev,
Author:  Alan Carruth [ Mon Apr 15, 2019 4:05 pm ]
Post subject:  Re: Acoustical effect of back woods
Eroic Ried noted:
"The early pages establish that the guitars have very different modal resonances, and yet, in the A-B tests, the players can't distinguish between them..."

In his 1996 thesis Wright noted that altering the pitches of low-order resonances in his computer model only changed the timbre of notes that were very near a resonance. If you moved the 'main air' pitch from G# to F#, people who listened to the sounds the model generated would not generally hear them as 'different', unless one or the other of those notes was 'played'. In that case, they'd pick up the difference in those notes. Of course, that was not a 'real' guitar, but it's about the only way you can really isolate some of these variables.

IMO the complexity of the sound of the guitar is one of the main reasons we love it, but it also makes it really hard to know how some things work.
Author:  johnparchem [ Mon Apr 15, 2019 6:41 pm ]
Post subject:  Re: Acoustical effect of back woods
I held off giving my own from my hind side comments on blind listening tests mainly because of where I am pulling them from. Here goes ... Part of the context for my point is that humans are not like a microphone and a computer, we do not hear reality rather we have learned through both evolution but also our childhood, to process through a relatively slow low bandwidth organic connection between our ears and our brain pretty high fidelity sound. It seems like part of that ability is that we construct the high fidelity sound in our brains from the limited information we get. (this is part of my limited understanding after a drink enabled conversation with a neuroscientist studying that interface.)

Also context - What we can hear as an adult is a learned skill we mostly picked up in our childhood. As we grow the body prunes many neurons and we lose some of our innate abilities to hear. I ran into this learning Thai as an adult. What sounds like the same word to me can be 4 to six different Thai words. For the native speaker those individual words sounds as different as night and day. So much so that as I learned Thai a small mispronunciation for example a mid sound vs a high sound on the same english vowel was hard for a native speaker to understand even in context unless they were exposed to what english speakers do to their language

Going to the first point in terms of distinguishing an instrument we probably first hear Guitar - then Classical, electric and steel string acoustic - then in each of those groups people probably hear the player way more than the guitars - next might come bracing patterns (i.e. x brace vs ladder) and so on. I think the farther one goes down the tree I laid out away from guitar the ability to get a positive result in the blind test goes down. We do not know as one of the complaints against the study was that they had no control to test for a positive outcome. The tester did no work to distinguish what level of difference would provide a positive outcome for the test.

There may be tests with positive outcomes. Maybe a tune played on one guitar vs another would get a longer average listening time if posted on youtube or itunes. Remember the switch to CDs or MP3 it might have also been hard in a blind test to tell the difference yet there was a different in how people felt about the music over the long term.

All in all I am with Peter Coombe on anzlf that without a control it is hard to tell what this test shows. The best they can say is the test did not demonstrate that there is a disquirnishable difference.
Author:  jlarkin99 [ Tue Apr 16, 2019 7:50 am ]
Post subject:  Re: Acoustical effect of back woods
An experiment that we can all do easily:
Take a guitar--any guitar--and play it (full chords, scales, etc.) held away from your body. Then hold it tight to your chest and repeat. I have done this with four guitars, including two Fyldes built by Roger Bucknall, who built the guitars used in the study, and the results are pretty much the same. I can hear a difference, but the difference is tiny, much much less than the difference between the guitars, and small enough that I doubt I could recognize the difference if there was a time interval between the two trials. Three of the guitars in question are in the OM/OOO/GC size range (a Fylde Alexander, a Santa Cruz OM, and an Larivee OOO, all three sitka over EIR), and the differences between them are great enough that I am pretty sure I could tell which was which guitar was which in a blind test.

As for build style of the Fyldes used for the tests, Bucknall builds with pretty traditional "live" back and sides, with non-laminated sides, standard kerfed linings and typical ladder-braced backs. The necks are mortise & tenon bolt-on, and tops are x-braced with one major innovation--he is known for a fairly heavy A-shaped brace between the sound hole and the neck.
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