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In the spirit of TECHNOLOGY?

Discussion in 'Basses [DB]' started by 400$Bass, May 1, 2009.

  1. 400$Bass


    Jan 18, 2009
    Central Indiana
    How does a Bass actually make it's sound. Without really being told this is what I kind of assumed just studying mine Bass.

    1. when you pluck or arco the string it vibrates.
    2. this vibrating string conducts the vibration to the bridge.
    3. the bridge carries the vibration to the SOUND POST?
    4. the soundpost carries the vibration to the instruments back
    5. the vibration is then transferred to the entire bass hence making a tone sound which omits out of the sound holes.

    Now this is just conjecture on my part. I would like to be advised by folk on this forum as to what produces the sound of a bass. For the most part is is all mechanical isn't it?

    Please respond.
  2. uprightben


    Nov 3, 2006
    Boone, NC
    My concept of how violin family instruments (including bass) amplify the sound produced by the string is different from above.

    The string drives the bridge, which interacts with the body in several different ways at the same time. The sound posts does two things: it creates a pivot point for the bridge to rock back and forth, pumping the bass side, and it couples the front and back acoustically so that both plates produce sound. Since the bridge is pumping the bass side of the top, the bass bar transfers that pumping motion along it's length. Aside from this pivot/pump motion of the bridge, the bridge is also moving in every direction at the same time, causing the top and the back to vibrate in ways too numerous and complex for me to be able to describe. All of the other parts of the instrument resonate as well (neck, end pin, etc.), making subtle contributions to timbre.

    I don't think that the sound comes primarily from the ff holes. Sound waves of equal energy are produced by the front and back (or inside and outside) of each plate. That means that full strength sound waves are comming off the outside of the instrument, while the sound waves being produced inside of the instrument have to bounce around until they get squeezed through the ffs. That is why I think that the biggest part of the sound comes directly off the front and back, and the amount of sound comming out of the ffs is less, but still very significant.

    Interesting thread, I hope people who are more knowedgeable than me correct and contribute to it.
  3. Ben you are right.

    The sound coming from the ff holes is mainly the lowest resonance that the bass produces. The flexibility of the two plates and sides make a contribution to this also. The front plate has bending motion that puts out a lot of sound in the low end as well as many in the mid and higher region as you said. Since the back is coupled to the front through the post, it can prevent or change the motion of the top vibration.

    Each bass has a set of resonances that create its unique voice. Better (higher priced) old basses have a series of equally spaced resonances in the low region that create a sound that is smooth which we associate with good sound.

    The bridge filters the sound of the strings and allows a bunch of resonances to go through to the top plate in the mid/high region. This creates a kind of "formant" that also shapes the vowel sound or voice of the bass.

    Things that are desirable in a bass are IMO:
    Low resonance of the lowest top plate sound.
    Resonance of the air in the body that is lower than but close to the lowest top plate sound.
    Evenly spaced resonances in both amplitude and frequency in the low/mid frequency region.
    A well tuned bridge.
  4. ctregan


    Jun 25, 2007
    Syracuse N.Y.
    How do you tune a bridge?
  5. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Just FYI, a ported speaker is a good analogy to how the ff holes produce sound.
  6. Matthew Tucker

    Matthew Tucker Commercial User

    Aug 21, 2002
    Sydney, Australia
    Owner: Bresque Basses, Sydney Basses and Cellos
    I don't think the sound post "transfers" much vibration to the back at all. maybe a bit of HF. I believe that the back vibrates in sympathy with everything else, depending on how stiff you build it and the ribs.

    I like to thing of sound production using the theory of relativity. Instead of thinking about a vibrating string moving in relation to the body, I imagine the vibrating string as the fixed part, then imagine what has to move to make the sound. Its a bit of a weird concept, but it helps my thinking, I think!

    Then I imagine the body as made of rubber, think what happens to the string. flub. then imagine the body made of concrete. ping. Somewhere between those extremes is a beautiful sound.
  7. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    I think that in reality, the behavior of a bass can't be described as a step-by-step process. The energy doesn't just go in one end and out the other. Rather, any two neighboring parts are influencing one another. After all, the strings don't just "know" when to stop vibrating at the end of a note.
  8. Bass


    Nov 10, 2003
  10. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    If that's true, then a bow shouldn't work.
  11. from what I understand, the soundpost is not meant to 'transfer' sound/vibration from the top plate to the back plate. The ribs play an important role in sound vibration transfer. The sound post serves as a means of 'tuning' the top and back plates, which is why a bass can resonate differently or develop/cancel wolf notes depending on the sound post position.
    flat back basses can't really have their back tuned in the same manner as a round back because the post is set on a horizontal beam called the 'sound bar' instead of directly on the back plate.
    I think the way the post tunes the plates is sort like creating a 'node' or a spot of lesser resonance, so vibrations are sort of rippling around the post position.
    The bass bar distributes sound/vibration along the length of the top. It functions in the same way structurally, loading the weight of the strings via the bridge across the top plate.
    Correct me if I'm wrong, but this is what has been explained to me.
  12. Nice misllustration but I think not. An activated string moves mostly sideways on the bridge top - makes no difference which way it starts, in less than 1/40 of a second it will be going the other way.

    The sideways movement translates to pressure or relief on the bridge "E" side foot because the sound post stabilizes the "G" side foot which acts as a pivot. String movement toward the treb side raises the bass bar (by easing some string down-pressure), string movement toward the bass side presses the bbar down. Of course the top follows the bbar movement creating sound waves. This cycle happens 42 times per second on low E.

    "Pressure to the base bar is released ... " Seems rather backwards.

    BTW Traeger referenced an experiment that proved that the sound post carried very little vibration to the back. It is there to support and fix the position of the bridge "G" side foot.
  13. arnoldschnitzer

    arnoldschnitzer AES Fine Instruments

    Feb 16, 2002
    Brewster, NY, USA
    The effect that Bass has illustrated above is real. I noticed it first when trying to play a left-handed bass right-handed. It only applies to pizzicato. Try it...
  14. Pentabass


    Dec 11, 2007

    No, the string does not not vibrate. They 'jerk'. They pull together, let go, and swing back and forth. They gyrate. Momentum changes into tension, back and forth. Some of that energy (initially generated by your finger or the bow) is transferred to the rest of the instrument system:

    Please observe: BOTH ends of the string interact with the rest of the instrument: The Bridge AND the NUT. It is tempting to think only of the bridge, but remember that (on the open string) the same energy is going into the nut, the neck assembly.

    With all due respect, you demonstrate mono-causal thinking: A one-dimential chain of cause and effect. I think, it is a more complex system, that means, it is more than a summary of it's parts.

    Searching for relations in, and manipulating this system, in the pursuit of beautiful tone... that defines for me the realm of our respected luthiers. I believe they will never get bored, because always there will be another surprise, like ... which way do you pluck your string?
  15. Yes. In my experience the bass bar is the most effective part in terms of spreading the sound around and shooting it out of the F's. (as Ben says). As you can imagine, it vibrates and actually "flutters". Much like a Rutter on a boat, the fluttering can get pretty intense....pizz or arco. Obviously more intense with arco. IMO.
    Most folks give credit to the bar in terms of strengthening the plates which, of course, is true....but the effect it delivers in terms of sound projection is a biggy.

    Another top quality Photo-Shop illustration from Bass....thanks, man.
  16. Hi Craig,

    Make it normal looking and it will be tuned correctly. But the biggest bugaboo is not thinning it enough from heart to top.
  17. Matthew Tucker

    Matthew Tucker Commercial User

    Aug 21, 2002
    Sydney, Australia
    Owner: Bresque Basses, Sydney Basses and Cellos
    Or thinning it too much from heart to top ... how do I know this? :)
  18. Jake deVilliers

    Jake deVilliers Commercial User

    May 24, 2006
    Crescent Beach, BC
    Owner of The Bass Spa, String Repairman at Long & McQuade Vancouver
    Did you mean 'propeller' Paul? I've never seen a fluttering rudder! :)
  19. Hey leave Paul alone, there are no boats in Colorado!
  20. Here are Double Bass facts:

    1. The whole bass body resonates at about 40 hz (open E) like a mirimba bar. But does not omit sound since it is 2D.

    2. The neck resonates at about 60 Hz (between open A and D) but does not omit sound.

    3. The air inside the body resonates about the same frequency as the neck and is the main contributor to the fundamental of the note. Yet this fundamental is always quieter than the second or third partial. Louder fundamental is perceived as fuller. Lack of fundamental contribution is also perceived as harsh.

    4. The top plate resonates at its lowest in a pattern that flexes with bass bar side up and sound post side down and visa versa. This is about open G.

    5. Just Above open G, and close to the top plate resonance in #4, the whole body corpus resonates in a couple patterns.

    6. The bridge has 3 distinct frequencies where it flexes in response to string vibration. These vibrations cause the bass to vibrate and create sound. The lowest bridge flexing is where the area above the heart flexes to and fro at about 650 hz (around the fundamental of a violin E string!)

    It is possible to find these resonances by changing the pitch of an open string while feeling the movement of the top plate, neck or feeling for air coming out of the ff hole.

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