SashaB wrote: ↑Sat Feb 10, 2024 12:04 pm
timtam wrote: ↑Sat Feb 10, 2024 3:27 am
...
Good to see the exact references next time
I am a physicist, although in another area, but what can I say on the topic is the following:
When I play a good solid body guitar, I do feel with my belly how the body resonates. This is actually a bit controversial to the statement that minimal string vibrations flow to the body, and I do not need any device to prove it if I can just feel it.
At the same time I never really felt the neck to resonate as much, I would assume from my naive point of view that the truss rod could play a negative role here.
Turns out that being a physicist is not quite enough.
You'd also need to be a sensory neurophysiologist to make such judgments from what you feel, with the appropriate measurement objectivity (my professional area of scientific research just happens to span particular domains in the physical and human biological sciences that use many of the same techniques as the physicists, engineers, and other scientists doing guitar science work). The frequency response of your skin mechanoreceptors - the sense organs in your skin that you feel with - is not flat. In fact it's about as far from flat as you can get (it's also dependent on the skin surface area exposed to vibration). Skin mechanoreceptors are acutely sensitive only to a relatively narrow band of vibration frequencies. Outside that range, they are almost 'deaf' to vibration. So what you feel will tend to over-estimate vibrations at some frequencies, and ignore others.
Verrillo, R. T., & Bolanowski, S. J. (2008). Tactile responses to vibration. In D. Havelock, S. Kuwano, & M. Vorländer (Eds.), Handbook of Signal Processing in Acoustics (pp. 1185–1213). Springer.
https://doi.org/10.1007/978-0-387-30441-0_62
So while you say you don't
feel the neck vibrating as much as the body, you'd actually need to objectively measure the frequencies at which the two are vibrating; otherwise you're likely to mislead yourself. Vibration energy only flows from the strings to the guitar's structure at the frequencies for which the interface mechanical impedances (nut/frets/bridge) are low / admittance (conductance) is high - that is, at the structure's resonant modal frequencies. So even with sensitive measurements (like the accelerometry and laser vibrometry that have been used in guitar science research) , the vibration flows will only be high when the string is vibrating at those frequencies. When you feel the neck vibrating, it will typically feel as if it is vibrating a lot when some strings/notes are played, and much less for others. But it is impossible to objectively state, solely on the basis of those feelings, if you are feeling the variation due to differing resonant frequencies (eg less vibration when string vibrations do not match a neck modal frequency), or due to different mechanoreceptor sensitivity to the frequencies that are actually present in the neck. You need to measure the neck's vibrations to make those judgements. Pate's chart below shows those significant vibration flows from the strings to the neck at particular resonant frequencies corresponding to notes on particular frets (and their harmonics). The flows to the body via the bridge (top line) are almost invisible in comparison. Similar findings are consistent across the guitar science literature.
Paté, A., Le Carrou, J.-L., & Fabre, B. (2014). Predicting the decay time of solid body electric guitar tones. The Journal of the Acoustical Society of America, 135(5), 3045–3055.
www.researchgate.net/publication/262226 ... itar_tones
Within the sonically influential neck, the truss rod (mass tension stiffness) is indeed likely an influence. The physics of different truss rod designs have been studied to some extent, but likely variations
within a given design have not really been investigated. Perhaps because it is difficult to measure the truss rod in situ. The neck is obviously a long, thin, flexible, and
composite structure - neck wood, fretboard wood, headstock, frets, tuners, truss rod. There is at least some objective measurement evidence from real guitars that
all those elements can contribute to the neck's sonic performance. Studies tracking the evolution of modal frequencies as guitars are constructed have shown a range of
variation about the characteristic modal frequencies at each stage of construction. Exactly what elements of the neck are responsible for that variation has not been elucidated. It may be that variations in the neck wood are responsible, but it may also be that the exact truss rod tension/stiffness is important too. Resonant modal frequencies are nominally proportional to stiffness and inversely proportional to mass - so a stiffer truss rod would be expected to shift the resonant frequency upwards.
Paté, A., Le Carrou, J.-L., & Fabre, B. (2015). Modal parameter variability in industrial electric guitar making: Manufacturing process, wood variability, and lutherie decisions. Applied Acoustics, 96, 118–131.
https://sci-hub.hkvisa.net/10.1016/j.ap ... 015.03.023
Paté, A., Le Carrou, J.-L., Teissier, F., & Fabre, B. (2015). Evolution of the modal behaviour of nominally identical electric guitars during the making process. Acta Acustica United with Acustica, 101(3), 567–580.
https://www.researchgate.net/publicatio ... ng_Process
Objective measurements of a guitar's resonant modal frequencies are now used in
acoustic guitar building by those who take the (increasingly common) scientific approach (eg Trevor Gore, Giuliano Nicoletti); which is arguably the only way to consistently get results that accord with a particular sonic design objective. However they focus almost entirely on adjusting the 'thin plate' wood of the acoustic body, which drives those resonant frequencies in an acoustic guitar. In a solid-body electric, as I have indicated, the neck's modal frequencies are dominant. But even so, only one major (non-US) electric guitar manufacturer has routinely measured the neck in that way (notwithstanding a comical youtube video where a Fender CS salesman taps 'knowingly' on necks and bodies). The reason why no manufacturer/builder really measures the physics of the solid body during construction would seem to be simply that the science shows that properties of the solid body don't matter much.
I have not seen any objective evidence (guitar measurements or blinded listening tests) to support the Fender marketing dept's notions of how alder and ash are 'supposed' to sound. As I said earlier in the thread, they would appear to be simplistic conclusions drawn from the pre-scientific age of guitars. Although when you summarize their adjective soup it is actually hard to see where those supposed differences lie. One guitar scientist has referred to this marketing cynically as "you get more of everything !" ... regardless of the wood species.
https://www.fender.com/articles/behind- ... s-the-diff
And some reports suggest that
inside Fender the viewpoint is rather different (see link below). As I said earlier, Fender does not objectively measure any guitar physics - you don't need that to make good guitars ... especially if you build to 50-year old recipes that just 'work'. But you do need to measure to explain
how they work. So if you don't do that, you shouldn't be making fundamentally scientific assertions like the above which suggest that you do.
http://www.guitarattack.com/opinion/mythbusters.htm
Other reading:
Zollner, M. (2010). The Physics of E-Guitars: Vibration—Voltage—Sound wave—Timbre. 26th Tonmeistertagung – VDT International Convention, Leipzig, Germany.
https://citeseerx.ist.psu.edu/viewdoc/s ... 1.348.6822
Zollner, M. (2014). Physics of the Electric Guitar.
https://www.gitec-forum-eng.de/the-book/