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Different Woods and their Natural Resonances

Discussion in 'Luthier's Corner' started by Free Tibet, Sep 27, 2005.


  1. Free Tibet

    Free Tibet Guest

    Sep 20, 2005
    Florida
    I am curious if there has been any research on the subject of different woods and their natural frequency responses. Is why I ask is because I am interested in having a sub-contra bass guitar created for me. At the moment, many of the extended range basses I have seen out there are carved from some type of maple. If anyone has any links or personal experience with different types of woods and where they sing the sweetest, I'd love to hear from you.
     
  2. Free Tibet

    Free Tibet Guest

    Sep 20, 2005
    Florida
    Maybe in the General Bass Guitar section there might be some more info.
     
  3. mahrous

    mahrous

    Aug 13, 2005
    Egypt
    there are no acknowledged studies of wood characteristics as they appear in hundreds and thousands of different species.

    Rosewood appears in at least a dozen of different areas with different characterstics etc etc.
     
  4. Free Tibet

    Free Tibet Guest

    Sep 20, 2005
    Florida
    I was aware of the fact that each specific species, and likely phenotype of their offspring, would have different characterics. However, I wasn't looking for anything that specific.

    I am more intereted in sampling a range or ballpark of common species used in instrument construction. I could limit this search even further to a sample of woods offered by the Wood Gallery, taking into consideration each separate block would have varying results depending on where they were grown, soil content, elevation, rainfall, termpurate, humidity, how they were harvested and preserved, etc.

    A wood that we could get nit-picky with would be lyptus, for example, because from what I've learned it is a specific few phenotypes and they tend to grow it in climates which are very similar, but I'm not interested in a discussion on that level.

    Again, THANKS!
     
  5. FBB Custom

    FBB Custom TalkBass Pro Commercial User

    Jan 26, 2002
    Maryland
    Owner: FBB Bass Works
    Are you implying that you might be interested in actually doing the study, or are hunting for someone who has done it?

    Personally, I would love to see some science done here. I don't know how you measure and compare frequency response of woods, but I think some of the touchy-feely speculation on the sound of wood could be laid to rest if it were done right.
     
  6. Free Tibet

    Free Tibet Guest

    Sep 20, 2005
    Florida
    Like yourself, I don't know the specific way of going about this. Off the top of my head, there are a couple ideas that are very cloudy. One is:

    You could have a bunch of different woods in a sound-proof room, all the exact same dimensions.
    Then take an instrument that could induce vibrations from 0~20khz onto them, and have some sort of other instrument recording the amount of resonance, and interpreting them in wave form.

    Extremely elementary I agree, but I am not particularly learned in the field.
     
  7. Kelly Coyle

    Kelly Coyle Supporting Member

    Nov 16, 2004
    Mankato, MN
    The first thing you'd have to do is establish through an analysis of variance that the differences between species were greater than the differences between individual examples of a single species. I bet it varies so much by piece that anything past really gross gereralizations will fail. A lot of builders listen for a specific "tap" from wood, and they will go through dozens of pieces of the "same" wood until they find the one they like. On the other hand, masonite makes a fine bass.
     
  8. Tim__x

    Tim__x

    Aug 13, 2002
    Alberta, Canada
    The question is flawed, an object's resonance is determined not only by material properties, but also by the object's dimensions. Except for molecular resonances (on the order of 10^10 hz) wood has no natural frequency of resonance.

    There may be more resonances caused by the heterogenous nature of wood, but those are most likely very low Q and so undetectable.
     
  9. Scott French

    Scott French Dude Supporting Member

    May 12, 2004
    Grass Valley, CA
    I agree with Tim. Take a piece of wood 2" thick, hold it at a node and thunk it. It goes *dink dink dink*. Take that piece, book match it, and process it down to 2 pieces .75" thick. Hold one at a node and thunk it. It goes *donk donk donk* (lower).

    From what I've heard Brian Burns has done a lot of research about wood and frequency response. I remember seeing some photos of acoustic tops with nodes plotted on them that I think he was responsible for.
     
  10. nateo

    nateo Schubie Fan #1

    Mar 2, 2003
    Ottawa, Ontario
    A neat trick for acoustic tops is to clamp them at the edges (much like how they'd be secured on the instrument), cover them with iron filings (or some other very visible small grained material) and vibrate them. As they vibrate the iron filings will move towards the stationary parts of the top, giving you a great view of the nodal lines. I heard of a luthier who used this to figure out where to put the braces on his acoustic tops.

    Not that it really applies to much, I just thought it was neat.

    -Nate
     
  11. Suburban

    Suburban

    Jan 15, 2001
    lower mid Sweden
    Not only dimensions, but also shape, as we are talking rather complex volumes with all the carving of a bass body.

    Bottom line being, that there is no scientific resonance per speices, only per specific block.
    You can get hints, though, from the stiffness and hardness numbers (ranges) that can be found in some wood construction handbooks. I bet Pilotjones has a few links to share - I seem to have lost mine... :scowl:
     
  12. FBB Custom

    FBB Custom TalkBass Pro Commercial User

    Jan 26, 2002
    Maryland
    Owner: FBB Bass Works
    Okay, but is there a range within a species?

    I understand that resonance is specific to size/mass/shape, but if you were to fix the size and shape of the samples, then you could compare the responses within species and across species.

    Lord knows I don't have the money/time/equipment to do it, but an experiment could be designed that would be more informative than the stuff you see on web sites in regards to woods and tone. We're interested in comparing the natural resonances between and within species, all other things (size, shape, etc) held constant.

    If I could point to a table and say "see, not much difference between honduras mahogany and african mahogany" that might save me some time. ;)
     
  13. nateo

    nateo Schubie Fan #1

    Mar 2, 2003
    Ottawa, Ontario
    That's a pretty great bit of data, but interpretation is going to be the trick here. It just occured to me that if you have a bass that resonates at, say, 400 Hz then you're going to loose that part of your signal since the energy will be absorbed by the instrument rather than being transmitted to the amp. Ideally I figure you'd want a bass with a rediculously high resonant frequency so minimize the losses, which would mean a perfect bass would be infinitely stiff. Odd how that keeps coming up.

    However, this does give some strength to the wood / tone argument. Obviously different pieces of wood will absorb different frequencies, but wether or not it's possible to use that to "tune" the tone of your instrument is still up in the air. Unfortunately these resonant frequencies will be much different once you reach the instrument's final shape, but I assume the trend will stay the same (i.e. according to the data a Beefwood neck will always have a lower resonant frequency than a Black Wattle neck of the same dimensions).

    Now someone just has to do a quantitative analysis of how these resonant frequencies effect the output of an instrument.

    Sure is neat stuff to think about, though.

    -Nate
     
  14. pilotjones

    pilotjones Supporting Member

    Nov 8, 2001
    US-NY-NYC
    That Noyce site is very interesting, in that it gives an idea of how, comparatively, different woods in the same size and shape sample will have relatively higher or lower pitched resonances. This is useful information. It does not say how much energy at resonance is absorbed versus reflected/transmitted, which could be implied by a decay measurement, given a regulated constant input impact. And even then, this would not give information on this type of response at frequencies other than the resonant frequency. So it does not give an idea of frequency response. As one poster suggested, to get a frequency response, you'd have to attach some type of driver, and do a sweep and analyze it.

    The frequency of resonance is related to the ratio of density to stiffness. As Suburban has pointed out in the past.

    The original post asks about how various woods will affect the frequency response of an instrument. This question is about twenty times more complex than the questions that can be answered with the Noyce site info alone. Entering into the analysis would be (among other considerations):
    - size and shape (mass distribution) of the instrument
    - frequency response of the woods (not known, as stated above)
    - how the instrument's frequency response lines up with the string-generated frequencies for any given note.
    - construction methods of the joint, etc.
     
  15. pilotjones

    pilotjones Supporting Member

    Nov 8, 2001
    US-NY-NYC
    Actually, at the resonant frequency, the vibration is enhanced rather than diminished.
     
  16. Tim__x

    Tim__x

    Aug 13, 2002
    Alberta, Canada
    Quite right. By dimensions I was not reffering to the dimensions of the smallest rectangular prism that would contain the object, but rather to the absolute dimensions that completely define an objects shape.
     
  17. I was this-><-close to doing this exact experiment with my son as a science project a couple of years ago (I'm a physicist turned geologist). We may do it still.

    The fundamental resonant frequency depends entirely on the vibrating volume, so it is completely independent of the wood's physical properties. All the "action" you're talking about is frequency response superimposed on the resonance. So the way to start the study is with different woods of identical dimensions.

    In lutherie, the main vibrations that strings impart to the body+neck are transverse (the way we normally think of strings vibrating) and compressional (parallel to the strings). With solid bodies, the body and neck woods act essentially as frequency filters, their different properties will dampen different frequencies.

    So the way to do this is much the same as the way engineers measure the frequency response of speakers. You use either pink or white noise, or a 20-20kHz chirp, to vibrate the body (in some way) and measure the vibrations of the body (in some way), then compare.
     
  18. pilotjones

    pilotjones Supporting Member

    Nov 8, 2001
    US-NY-NYC
    Not quite. Unless I'm misunderstanding you. It depends on both the material volume, and its properties, as your following suggestion to try different woods implies.
    I would say they are primarily perpendicular to the fretboard, secondarily parallel to the fretboard, and tertiarily axial to the neck.
    I would say that it's a little more complex than that. The neck in particular can not only dampen, but can be made to resonate, reinforcing particular frequencies.
    Something like this?
    http://www.unibw-muenchen.de/campus/LRT/I04/hauptdoc.html