The "Coupling Effect"...

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

  1. WineRedFreak

    WineRedFreak Member

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    Tonewood: To be or not to be, that is the question...

    I believe there is a phenomenon that I (a mere commoner) will perilously refer to as the "coupling effect".

    As it pertains to the Laws of Physics, the ultimate question isn't whether this quirk of nature does or does not exist (I think it most certainly does) but rather: To what degree does it affect anything or everything?

    I happen to believe there is a profound effect, but that's just me...

    Hence:

    The strings are attached to the guitar (obviously); At one end they go over the nut and are anchored to the tuning posts, at the other end they are either attached to the bridge/tailpiece itself or anchored directly to the body.

    Anyway, as the strings vibrate, this vibration resonates through the body. In turn, these resonant frequencies are transferred back to the strings and the resulting fundamental frequencies, along with many complex overtones, are ultimately captured by the pickups.

    So, yes, the pickups are just picking up the string vibrations, but the overtones born from being coupled to the body are all part of what makes a particular guitar sound like it does - and I just so happen to believe that this transfer of energy contributes to what we call the instrument's "timbre".

    Need proof of this transfer? Place your ear against the back of the neck whilst strumming.

    The pickups themselves are also "coupled" to the guitar, since they are attached to it (either directly or indirectly), thus picking up some of these resonant frequencies, although probably to a much smaller degree.

    Some pickups are apt to be more sensitive to this than others. Tapping on them (and the body) with your pick (amp cranked) should provide an idea of how much.

    This effect can also be applied to amplifiers - while sitting on a stage floor for instance - where they can be "coupled" to the stage, in turn affecting their perceived tone (bass amps in particular).

    Of course, the only way to truly demonstrate this phenomenon (or lack there of) is to have the strings and pickups suspended in mid-air with neither of them coupled to anything and listen to how that sounds going though an amplifier...

    IMG_4100.JPG

    ...then instantaneously transfer everything over to an appropriate guitar assembly - using some sort of Star Trek level of technology of course - so we can compare the two sounds in real time!

    Anyway, should anyone decide to take on this noble challenge, be sure to Youtube it using your smartphone so we can all witness the amazing results...

    ...ok, now all you "nay-sayers" can trash me if you wish...



    '
     
    Last edited: Oct 28, 2017
  2. ARandall

    ARandall Senior Member

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    A point - the first goldtop was redesigned as the strings were passing under the tailpiece not over (supposedly as requested). It was awkward to play and there were no easy palm muting.

    Your test would require an alternate reality where physics is different....which would probably render the results useless in this universe. But the theory of physics is enough to confirm what you say without a specific test.
     
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  3. WineRedFreak

    WineRedFreak Member

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    There are accounts that allude to both its physical and sonic deficiencies, but your point is well taken.

    I once played an original 1952 Gibson Goldtop Les Paul and can at least verify that it wasn't an especially great sounding guitar, which doesn't necessarily prove my case but doesn't exactly lend support to the contrary either.

    Anyway, I decided to delete this portion of my pseudo-dissertation to avoid any ongoing controversy...

    '
     
    Last edited: Oct 27, 2017
  4. Thumpalumpacus

    Thumpalumpacus Senior Member

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    Trapeze tailpieces do just fine getting acoustic archtops to resonate well.
     
  5. WineRedFreak

    WineRedFreak Member

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    Like I mentioned above, I decided to delete this portion of my article to avoid a never ending debate and hopefully stay on topic...

    '
     
    Last edited: Oct 27, 2017
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  6. Thumpalumpacus

    Thumpalumpacus Senior Member

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    Sorry, that post wasn't visible when I was writing my reply. No harm, no foul intended.
     
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  7. spitfire

    spitfire Senior Member

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    There certainly is a "coupling" between the strings and the rest of the guitar and the structure of the guitar is known to affect the sound. Les Paul noted this very early on with his experiments with electric guitars. As you initially mentioned there is debate over tone wood. But I think that debate is not whether the guitar neck/body affects the guitar, it clearly does. Rather, whether specific species of wood have constantly different characteristics.

    A nit picky point I would like to make though, is this coupling DOES NOT produce overtones. The body/neck etc will NOT create any frequencies that are not already in the strings to begin with. These frequencies are created by exciting the string via plucking. The strings and to a much, much lesser extent the rest of the guitar function as a filter exaggerating or dampening specific frequencies. The string dominates this due to its very specific resonance.
     
  8. WineRedFreak

    WineRedFreak Member

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    It would seem rather "unlikely" that the strings and the rest of the guitar would vibrate identically, so, whether the body and/or neck's mass dampens the string's vibration or otherwise affects the way the strings oscillate, it would seem "likely" that it's altered in some way nonetheless and, if that alteration is captured by the pickups, then in my mind that is the timbre...

    So, IF it's determined that there is some degree of interaction between the strings and the body/neck, the crux of the debate is whether it's noticeably significant or of a "much, much lesser" significance.

    I believe that it's at least a relevant consideration.

    Unfortunately it's virtually impossible to prove unless NASA scientists are involved and they're probably far too busy trying to figure out how to colonize Mars I suppose...


    '
     
  9. Mookakian

    Mookakian Senior Member

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    I Recommend trying a Pine tele and then an Alder tele... the difference is pretty dramatic.

    Im a believer wether its the wood vibrating or the way the wood makesnthe strings vibrate or both and more, there is most certainly abdifference in materials used for the body and neck, the pinocaster is a monster in its own league, desired by few but big difference to the standard
     
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  10. spitfire

    spitfire Senior Member

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    There most certainly is an interaction. It's basically physics 101. No need for NASA. The strings and guitar form a system. The string is highly resonant (high Q factor).

    The strings have low mass relative to the guitar body et al. So the strings move over a much greater distance and I believe with proportionally higher velocity. The body etc., being so massive essentially doesn't move at all. This is the basis for more sustain from more massive (heavy) guitars.

    But that doesn't mean the body doesn't matter, but it doesn't matter nearly as much as the strings.

    As I said, the entire system functions as a filter. The strings providing a well defined resonance and the picking or plucking exciting the string at both its fundemental frequency and its harmonics (overtones).

    Everything else is just filtering these frequencies (like a very complex EQ) and it is this filtering that contributes the specific character (timbre) to the sound.

    My earlier point was simply the guitar body does not create any overtones. Though it may dampen or enhance those created by the action of plucking the string.

    Since its the plucking of the string that actually creates the overtones, this is what explains the concept of "tone in the fingers". Anyone with even a little experience has heard for themselves the huge difference the choice of pick makes and of course player technique. That is the ultimate source of the signal. Everything else in the guitar is just inhancing or reducing the frequencies in that sound.

    And of course how it shapes that is extremely important. So many parts of this are within the guitar as well as the many external contributors through the amp and including the room itself.
     
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  11. ARandall

    ARandall Senior Member

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    Your point about the body is important......but maybe the body/structure is more important than at first glance.
    The high mass creates a strong momentum effect. Get that vibrating and it tends to have a much longer sustain tail than the string would do if not attached to something so beefy. Also there is a lot of potential energy already in the system before plucking the string......so this is an aspect that a lot of people do not consider.

    On the string side, not only does the string move through a bigger arc, but it is moving through air which has a high damping co-efficient to compound the effect. It also has a high area for its mass. So the mass of the body is a really important counter to the potential losses of the string
    So the 'mass to surface area' ratio of the body really helps to hold energy in the system much longer than it would compared to say the strings stretched on a metal frame.
     
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  12. spitfire

    spitfire Senior Member

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    Most of the energy stays within the string itself. As one part of the string deflects in one direction, another part deflects in the other (standing wave). Therefore conserving momentum within the string.

    Ideally it would be a standing wave and no energy would transmit to the guitar body at all. I would agree that most of the energy is lost in the string itself. As you say air resistance would be one of those losses. As would the heating of the string caused by bending it back and forth. I suspect significant loses near the fret and saddle, as this points are not perfect knife edges and the string will make periodic contact beyond the primary contact point causing friction loses. Of course the string will impart energy as sound directly to the air.

    The fact that the loses are mostly in the string, isn't becasue the body is so good at retaining energy. It's because very little of the energy gets into the guitar body at all. In fact compared to the string, the guitar body has much more damping. Pluck a string and you can easily hear it ring for 5-10 seconds. Similarly, tap on a tuning fork. It rings (sustains) for a long time. This indicates low damping (good at holding energy). Tap on a solid body guitar and it doesn't ring or sustain to any significant degree, this indicates it is poor at retaining energy.

    The ideal body for sustain, not musical qualities, would be perfectly rigid. Being perfectly rigid it would not deflect and therefore could not dissipate or dampen energy within it. But this doesn't lead to desirable properties. As I mentioned before, I believe Les Paul did experiments early on using a very rigid "body". I think it may have been a piece of railway rail or similar. Thinking this would be ideal for sustain, but realized it lacked character. So again, I believe the body matters. But this is due to it's frequency selective dampening, rather than some energy storage ability of the body.

    As I said before, it is obvious the guitar body moves very little as being in contact with our fleshy bodies has no significant impact on the tone, at least for solid body guitars.
     
  13. WineRedFreak

    WineRedFreak Member

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    I do agree that MOST of the energy stays with the string, but there's also absolutely no question that SOME of it transfers to the body and neck (thus the ear against the neck analysis).

    The unknowable question is how everything interacts and how that potentially affects the string vibration. After all, since there's absolutely no doubt that a transfer of energy is taking place - from the string to the body then back to the string again - it would be folly to assume that one does not somehow affect the other in some conceivable way.

    While I agree that the strings will still have the same fundamental tones regardless of what body/neck materials are used, it also makes some sense that the overall interactions can cause subtle nuances that give each instrument their own unique character - sometimes that's not easily quantified since it's based so much on something as extremely subjective as sound.

    So it appears that any hypothesis would be dependent on both perception and common sense as well as pure science, thus the eternal debate goes on...

    '
     
    Last edited: Oct 28, 2017
  14. ARandall

    ARandall Senior Member

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    Most of the energy does remain in the string of course. But the body is like a coiled spring....in that it is helping to provide the 'opposite reaction'. A degree of the ability of the string to maintain its loudness initially is in the nature of the body NOT being totally rigid.

    So in effect if you were to have a totally rigid body then you would be relying wholly on the physics of the string movement - so maybe a louder initial sound. But a tendency due to the mass, surface area and damping properties of the surrounding air to drop away quickly.

    Adding in a greater mass of a 'pliable but stiff' body/neck means that there is a greater quotient of initial energy involved in vibrating the body (which already has potential energy stored in resisting the strings don't forget) but then as a whole has less losses over time due to external transference.

    Of course string part of the equation loses energy quickly, but this is bolstered continually to equilibrium with energy from the lower loss body/neck section. This energy of course is filtered by the natural way that the wood/metal and other components that those materials impart.
     
    Last edited: Oct 28, 2017
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  15. spitfire

    spitfire Senior Member

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    I generally agree with what you said. Especially concerning the fact that there is ultimately a combination of science (physics) and perception. The science can define the physical behavior, likely very accurately, and this is valuable in replicating the behavior. Whether these characteristics are good or bad comes down to perception.

    The string dominates the behavior, but since the body is not an ideal rigid body, there is an interaction. This, as we would all agree, is indisputable. If the body had no effect, than solid body, hollow body and acoustic guitars would all sound the same. And clearly they do not.

    I will argue the with your statement "The unknowable question is how everything interacts and how that potentially affects the string vibration." This is all very knowable. It's pretty standard engineering. While analyzing a guitar at this level doesn't have any obvious commercial benefits, and therefore is not likely to get much attention, I wouldn't be surprised to find that some senior engineering projects or maybe even masters thesis have been done on the subject.

    So I suggest you resist the urge to treat this like unknowable black magic because you are unfamiliar with the formal physics or engineering concepts. Analysis of vibrating mechanically systems, and the very similar electronic systems, are being done constantly by engineers. There's a very well established knowledge base that this subject falls squarely into.
     
  16. spitfire

    spitfire Senior Member

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    Simple not true. The body pretty much behaves as a lumped mass with a lot of damping. To a small degree it has some elasticity, but this could hardly be characterized as "a coiled spring".

    The mass and damping dominate. Again, rap a knuckle on a solid body guitar and the sound does not sustain at all.

    No, quite the opposite is true. The body does nothing to help continue the sustain (ignoring feedback from the amp). The string will vibrate the longest if the body were an ideal rigid structure. Energy is not somehow stored up within the body and then returned later to help the string continue to vibrate.



    "pliable but stiff", these are opposing characteristics. Pliable means not stiff as well as plastic (bends and doesn't bend back).

    "quotient of initial energy" What exactly is that? It's not a an engineering or physics term I've ever seen.

    The body has no mechanical potential energy in it to resist the string or do anything else.


    No the string does not lose energy quickly. It is the primary part of the system that retains energy for a long period of time. There's nothing the body is going to do that doesn't reduce sustain (absorb energy) of the string.

    It's very similar to striking a tuning fork. Anything you can touch that tuning fork to will dampen that tuning fork MORE quickly. To be sure I'm not talking about touching it to a system designed to actively amplify the mechanical vibrations. This again would be similar to playing loudly and having the loud amp feedback to the guitar body and help sustain the note. That of course happens, and I believe would be another mechanism where the body characteristic affect the tone. But, again, that's not what we are talking about.
     
  17. efstop

    efstop Senior Member

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    A string has next to no mass but vibrates for a period of time. A guitar body has thousands of times more mass but vibrates for a much smaller period of time. IMDO (in my drunken opinion) the body is mainly a damper, and due to its mass, its composition makes nearly zero difference to its damping characteristics. Putting your ear to the back proves that a body makes a somewhat decent, unamplified speaker, but playing that way will just make your neck hurt.

    We can spend years debating this or just buy what sounds good, and accept that tone and sustain are mythical, unexplainable features of our chosen instrument.

    I now return you to your thread and I will return to my hoppy beverage.
     
  18. WineRedFreak

    WineRedFreak Member

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    ''
    Sometimes it's easy to confuse facts with theory. I freely admit that my belief is only a theory although I feel my theory has some degree of validity. Rightly or wrongly I interpret what you believe as a declaration of indisputable fact...

    By "unknowable" I mean that there are certain things that just can't be absolutely known for sure. I know I'm not absolutely sure and if anyone were to claim to be so sure as to be indisputable then I have no choice but to voice my overwhelming skepticism.

    Even if someone claimed they were 90% sure I'd still have a hard time believing them.

    And even at 90%... well that still leaves 10% that's not known, which is no small amount...

    As for "Standard engineering"? Practically everything that has been done in developing stringed musical instruments has been through the process of empirical methodology (based on, concerned with, or verifiable by observation or experience rather than theory or pure logic), so, while I'm not doubting the phenomenon can be measured, I still think it would be impossible to get a true consensus on how a particular "tone" is "perceived", since everyone perceives things differently... thus it is "unknowable"...

    '
    Please, do entertain us with your vast knowledge of all vibrating and electromagnetic things in the infinite universe - things that the brightest minds in the world still can't fully explain btw...

    While there are no doubt countless studies on vibrating bodies, I can't help but think that, as it applies to something as subjective as "tone", you may be able to observe the vibration(s) but that doesn't in itself tell you how it sounds.

    The so-called "magic" is in finding "meaning" in something that otherwise has no meaning. Trying to measure music in scientific terms is utterly ridiculous - as it would be with any form of art. All I was attempting to do was to provide one "possible" explanation that melds the two worlds.

    Anyway, I think I've been fairly clear that my hypothesis is not only based on already established knowledge but also on things that can't be measured, such as "good" or "bad" tone.

    After all, since we've already dragged science into it, MOST of science is based on observation and one should be careful not to let their vision be obscured by some urge to sling petty innuendo...


    '
     
    Last edited: Oct 30, 2017
  19. spitfire

    spitfire Senior Member

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    I'm not slinging petty innuendo. You claimed the process of how the string and body interact is unknowable. It is not. And to extrapolate that since there are still unknowns in the infinite universe, therefore there are unknowns in this (and apparently every other physical system) is silly. Essentially stating because we don't know everything, we cannot know anything.

    As I said, I agreed with you that understanding the physics doesn't equal an understanding of the subjective nature of tone. I don't necessary agree that this is ultimately unknowable. Brain science may one day allow us to understand subjective preferences. But I agree that this is unknown today.

    This is the statement you made. Nothing about the subjective or perceived quality. And this is not true.

    "The unknowable question is how everything interacts and how that potentially affects the string vibration."

    As far as the fact that most musical instruments were developed without applying engineering is a pointless argument. Just becasue engineering and physics can be used to describe the behavior of something, doesn't mean those principles were needed or used in the design. We haven't been discussing how existing instruments were designed. And I certainly never claimed guitars had to be engineered. We've been discussing how the string interacts with the guitar body. And ultimately this can be analyzed and described using engineering principles.

    The bulk of everything we have discussed we agree on. Simply put, the string interacts with the guitar body and therefore the guitar body has an effect on tone. I took issue with you stating that the physical behavior is unknowable, as if this were somehow out of reach of human understanding.

    I quick Google search brings up many references to the science of stringed musical instruments. Here's just one example. Essentially a book on the subject. I have not read through this, but I bring this up to show that there is much specific knowledge about this subject. And there is much more general physical and engineering knowledge underlying that.

    http://logosfoundation.org/kursus/The Science of String Instruments.pdf
     
  20. WineRedFreak

    WineRedFreak Member

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    First of all, I'd like to make it perfectly clear that I am sincerely attempting to find some common ground here and I am not purposely trying to contradict anything you've said, but I would like to further clarify my views before ultimately seeking some kind of resolution to our awkward quagmire.

    In other words; I'm not trying to convert you in any way, but would like to make sure there's no confusion on what I'm trying to say either and I'm hoping you'll read the entire post before drawing any conclusions...

    ~~~~~~~~~~~~~~~~~~~~

    Ok, even if I were to concede that all this is "knowable", it'd still seem somewhat peculiar to think that a string vibration would be so unquestionably predictable that one could accurately describe its interaction with the body's mass as a simplistic, easily definable phenomenon (and I'm absolutely NOT claiming you said anything of the sort on this).

    However, it does seem reasonably possible (to me) that the results of these complex interactions may vary and, if this is the case, I'd say that would imply a chance that it's either discernible or indiscernible.

    Furthermore, if in fact the body has a dampening effect, as previously discussed, it also seems reasonably "plausible" that the interactions aren't affecting every frequency or overtone exactly the same.

    Thus, if certain frequencies or overtones are being dampened more than others then, in effect, other frequencies or overtones would (by default) be accentuated - or they could otherwise be emphasized or deemphasized (resonant frequencies).

    If any of this is at least "plausible" then, to me, there's only one relevant question: "Is there enough of an effect to hear an audible difference?".

    I could be wrong (and I often am), but you seem to be implying that it's either "implausible" or "not enough" while I empirically deduce that it "is plausible" and "is enough", so - if we are indeed stuck in that proverbial stalemate - there's obviously nothing more to say on the subject that will change each other's mind.

    Therefore (if I'm reading the situation correctly), can we at least agree to disagree?


    '
     
    Last edited: Oct 31, 2017
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