The "Coupling Effect"...

Discussion in 'Tonefreaks' started by WineRedFreak, Oct 27, 2017.

  1. Mookakian

    Mookakian Senior Member

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    Damn science $ucking out the fun again :confused:
    Science can be fun... just have to let it :cool2:
     
  2. WineRedFreak

    WineRedFreak Member

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    '
    Science is neither fun nor is it not fun, it just is...

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    Last edited: Oct 30, 2017
  3. spitfire

    spitfire Senior Member

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    I'd also like us to get things back on track. The only thing I have disagreed with you on is whether the physical behavior is knowable. I agree that knowing the physical behavior doesn't, itself describe what is good or bad tone. I agree this subjective nature is elusive and is itself not within the scope of engineering. But the engineering principles of wave propagation, acoustic impedance etc. are all well established concepts that can be applied to this. While all of this is standard engineering, that does not mean it is trivial.

    For example, it might be relatively easy to create a lumped parameter model of the guitar body for use in evaluating how the strings behave. This is much simpler than determining how every part of the body itself vibrates.

    As for everything else you said in the post. You're spot on. It's not just plausible, there's no question damping will be frequency selective. Dampening some frequencies more than others. However, I believe the damping is relatively high for all frequency. So no frequency is actually enhanced in an absolute sense. But rather, just not attenuated as much as others. Regardless, the net affect is a coloration of the overall sound. Just rap your knuckle on the guitar body and it will have a distinct tone. Not a highly resonant peak like a bell, but still a distinct frequency range.

    A little side note, we really don't want our guitars to be highly frequency selective in their behavior. If they were, some notes would jump out (honk) more than others. This would be undesirable. However, I do seem to notice this with some guitars I have. However, it could very well be the room I'm in resonating rather than the guitar.

    And I agree completely, the question is whether you can hear differences in body constrution. Clearly some of these effects can be heard. They are most obvious in acoustic guitars. I have a friend with a maple acoustic guitar. It is noticeable bright. I think it is due to the maple since this is the obvious difference compared to most guitars with a spruce top. But one data point does not a trend make. Even if not due to the wood, it is very much brighter than a typical acoustic guitar. This difference has something to do with the body. So to me, it's a proven fact that the bodies affect the tone.

    Obviously solid body guitars are not as sensitive to the characteristics of the body. But this is almost certainly a matter of degrees. And common sense suggest there is likely some characteristic of an acoustic guitar that can be heard, that crosses into the threshold of inaudible for a typical solid body guitar. In engineering speak, how significant an effect is is called sensitivity. Simple how sensitive is X to a change in Y. And it's not uncommon for something to matter a lot sometimes, but not matter other times depending on what else is going on.

    I hope we're all good now. I don't think we need to agree to disagree as I think we really are pretty much in agreement.
     
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  4. moreles

    moreles Senior Member

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    Yes, the strings and the body are two non-identical vibrating systems and they do interact, to an extent and nature dependent on the guitar design. As you describe, it does help to remember that the pickup registers string movement that is in fact affected by the vibrations cycling back via the body at various contact points (as well as the affect that amplified sound may have on the string; feedback). This is why everything, from tenon length to nature of glue joints to density of wood to heft of neck to fingerboard material all count... to some degree. Everytime a vibration passes from one material to another, it changes. The speed of sound through different materials is different. And yes, some glues filter, even deaden sound; others, not so much. Some of these effects are minimal, or only potentially significant; others can loom large. Generally, luthiery is like cathedral building -- the system is super-complex, but the practitioners do not qualify and objectively measure and control all the relevant factors... rather, they experiment, adjust and try stuff and go with what seems to work. I like the latter approach -- somebody else can compile the data and come up with formulas.
     

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