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Thread: Curious about bridge height, break angle and string gauge

  1. #26
    Registered User sunburst's Avatar
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    Default Re: Curious about bridge height, break angle and string gauge

    I think mass was mentioned somewhere in this thread, but I can't find the reference with a quick look-over of all the posts, so...
    Heavier strings have more mass than light strings, so even if you adjust the break-over angle at the bridge (by raising the bridge or lowering the tailpiece or whatever) so that the bridge pressure is the same with each set of strings, the mass of the strings is still different. Heavier strings require more energy to set in motion and heavier strings can potentially supply more energy to the instrument because of their greater vibrating mass. In other words, heavier strings are not "felt" the same as lighter strings by the mandolin even if the break-over angle is adjusted for the same bridge pressure. Furthermore, considering how little difference there is in the function of a mandolin with more or less bridge pressure (within reason), it seems to me that the difference in string mass is the greater change when going from light to heavy strings or vise versa.
    It is also important to consider that the pressure exerted on the bridge by the strings breaking over the bridge is a static load. The influence on the bridge made by the vibrating strings is dynamic and not too closely related to the static pressure of the strings. The two are often incorrectly assumed to be closely related.

  2. #27
    Registered User fscotte's Avatar
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    Default Re: Curious about bridge height, break angle and string gauge

    Quote Originally Posted by Larry Simonson View Post
    Here is an experiment to try. Measure how much the top deflects when brought up to pitch for the heavier strings and original break angle, then sample the tone, volume, sustain, harmonic content etc so you have a baseline reading(not easy, maybe not possible?) Now install the lighter strings and keep raising the bridge until you get the same deflection and then repeat the tone, volume etc. sampling and compare that to you baseline. Of course the action will get more manly but you may figure out if intrusive surgery would be worthwhile.

    If you do, this is an easy deflection jig to make which measures the top when the strings are detuned.

    Click image for larger version. 

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  4. #28
    Registered User Julian Morris's Avatar
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    Default Re: Curious about bridge height, break angle and string gauge

    Quote Originally Posted by fscotte View Post
    If you do, this is an easy deflection jig to make which measures the top when the strings are detuned.
    That, Sir, was cruel of you because now I really really want one of those but can't have one.

  5. #29
    Registered User fscotte's Avatar
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    Default Re: Curious about bridge height, break angle and string gauge

    Just 3 dial calipers from your favorite hardware store (harbor freight), 3 fish eye screws, and some scrap wood and a couple clamps.

    I also use them with my "macrostie style" deflection jig.

  6. #30
    Registered User Julian Morris's Avatar
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    Default Re: Curious about bridge height, break angle and string gauge

    Quote Originally Posted by fscotte View Post
    Just 3 dial calipers from your favorite hardware store (harbor freight), 3 fish eye screws, and some scrap wood and a couple clamps.

    I also use them with my "macrostie style" deflection jig.
    I AM tempted.

  7. #31
    Registered User Julian Morris's Avatar
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    Default Re: Curious about bridge height, break angle and string gauge

    The ongoing saga in my head about break angles and soundboard tension has taken me to ancient greece. Atached for anyone who wnats a brief but enrtertaining and informative read about why bows are pre-tensioned, see the attached extracts from Structures, or Why Things Don't Fall Down by J.E.Gordon.
    I think it must be so with the soundboard of a mandolin.
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  8. #32
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    Default Re: Curious about bridge height, break angle and string gauge

    Quote Originally Posted by jamandolin View Post
    The ongoing saga in my head about break angles and soundboard tension has taken me to ancient greece. Atached for anyone who wnats a brief but enrtertaining and informative read about why bows are pre-tensioned, see the attached extracts from Structures, or Why Things Don't Fall Down by J.E.Gordon.
    I think it must be so with the soundboard of a mandolin.
    You would be wrong. You make the all-too-common mistake of confusing statics with the dynamics involved in the production of sound by string instruments. A mandolin sitting on a stand "feels" the down force from the string tension on the breakover angle of the bridge., but does not make any sound. Sound is only produced when a string or strings is/are set on motion. There is very little motion at the bridge. The impedance at the bridge is very high, so essentially no motion is transmitted from string(s) to bridge to body. What does happen is that there are dynamical forces exerted on the bridge and in turn on the top plate each time the string(s) pass through zero amplitude. If you want a more current account of string instrument sound production, I suggest you look at the Fletcher & Rossing test, "The Physics of Musical Instruments", 2nd Ed., Springer, 1998

    http://www.Cohenmando.com

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    Registered User sunburst's Avatar
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    Default Re: Curious about bridge height, break angle and string gauge

    Quote Originally Posted by jamandolin View Post
    I think it must be so with the soundboard of a mandolin.
    I think not. Bows and mandolins tops do entirely different things.

  10. #34
    Registered User Julian Morris's Avatar
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    Default Re: Curious about bridge height, break angle and string gauge

    Quote Originally Posted by sunburst View Post
    I think not. Bows and mandolins tops do entirely different things.
    The point I was trying to get across is that, like a bow, the soundboard is pre-stressed. This ensures that the vibrational energy is not wasted in getting the soundboard up to operational stress or 'sweetspot'. A bow is in static stress when strung but not in use. It is in dynamic stress. I am not confusing the two. The nandolin on the stand is in static stress and when plucked is in dynamic stress. The bow is in tensional stress and the mandolin in compressional stress but that makes no difference to the principle. Stress is stress.

    The Siminoff site seems to back all this up. A break angle of zero would result in no string pluck energy being transmitted to the soundboard. A break angle of 45 degrees would topple the bridge, and if it didn't it would collapse the mandolin. Somewhere in between is an ideal pre-stressed state for th soundboard, around which it cna vibrate with relatively small amplitude and maximum efficiency.

  11. #35
    Registered User sunburst's Avatar
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    Default Re: Curious about bridge height, break angle and string gauge

    We don't know what the ideal "pre-stressed state" for a mandolin top is, and there may well not be one. Perhaps, as some believe, a mandolin top would function best with no bridge pressure at all, only a secure physical coupling. If we understand the basics of normal plate modes of motion, we can see what the mandolin top does when it is making sound, and it is not being bent and released like a bow is when it is doing it's job. The back of a mandolin is involved in sound production to an extent near that of the top, yet there is no bridge pressure there at all, so why is there "string pluck energy" at work there?
    The dynamics of a mandolin top (and back) can be put into motion by sound in a room whether the instrument is strung up or not. We can feel that if we hold the instrument in a room with sound loud enough to get the instrument moving. No bridge pressure is required for that, and in fact no string tension is required for that. That shows that the top and back can be set in motion in the absence of bridge pressure.
    We're not shooting arrows with mandolin tops, nor are we making music with bows. Both can be done (shooting arrows with mandolins and playing tunes on bows), but it's fairly easy to demonstrate that each is significantly better at what it is intended to do. The bow/mandolin top is not a very good analogy when it comes to the dynamics of the systems.

  12. #36
    Registered User fscotte's Avatar
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    Default Re: Curious about bridge height, break angle and string gauge

    jamandolin, you remind me of myself. Check my older posts. I'm a tinkerer and a thinker. I too thought if x+y=z, then z-y=x, or thereabouts. I even thought of a mandolin top as a bow.

    As Sunburst mentioned, the ideal mandolin sound is when the instrument achieves ideal coupling. You can achieve a good tone with a stiff mandolin as long as the plates and air resonance couple well. You can also achieve a good tone if the plates are loose, as long as they all couple well, and every stiffness in between. Pay close attention to the Sunburst's analogy of holding the mandolin up in a room without strings with sound pressure. The mandolin will likely "howl" at the moon like Loar himself came down to bless it. No string pressure at all. That should give an indication of how the sound is produced.

    Your mandolin may very well sound better with less bridge pressure, or it may sound worse. But don't attribute any improved tone to the change in break angle, or lessening bridge pressure. If you do that, you'll have the wrong idea about what makes a good mandolin, which will only lead to continued despair.

  13. #37
    Registered User Julian Morris's Avatar
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    Default Re: Curious about bridge height, break angle and string gauge

    Quote Originally Posted by Dave Cohen View Post
    If you want a more current account of string instrument sound production, I suggest you look at the Fletcher & Rossing test, "The Physics of Musical Instruments", 2nd Ed., Springer, 1998http://www.Cohenmando.com
    It looks to be a great book but I can't afford it just now (c.75)

  14. #38
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    Default Re: Curious about bridge height, break angle and string gauge

    Quote Originally Posted by jamandolin View Post
    It looks to be a great book but I can't afford it just now (c.75)
    Have you ever heard of such a thing as a library?

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    Registered User Julian Morris's Avatar
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    Default Re: Curious about bridge height, break angle and string gauge

    Quote Originally Posted by Dave Cohen View Post
    Have you ever heard of such a thing as a library?
    I am new to Mandolin cafe, and people have already been very gnerous with time and advice. It is not in my interests at all to be argumentative with people. It is with some trepidation therefore that I have to speculate that you are either rude or just very unfortunately blunt with your remarks. I woud like to err on the safe side and assume it is only the latter. In your first posting you told me that i was wrong and that I was confusing dynamic and static forces (whic I wasn't). Of course I have heard of libraries! What point are you trying to make? Don't you think I would already have checked my nearest libraries, then on drawing a blank looked at Amazon, eBay etc and researched suitable alternative texts that might be available locally or for lower prices?

    I may not have much knowledge yet of mandolin physics, but I'm not stupid. Sigh...........

  16. #40
    Registered User fscotte's Avatar
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    Default Re: Curious about bridge height, break angle and string gauge

    I'll tell ya this much, if it has anything to do with making adjustments to the bridge and tailpiece, neck angle, overall break angle, it's already been done. There is certainly nothing new under the sun in those regards. The mandolin makes good sound by good coupling, as mentioned previously. There isn't any easy way or shortcut around it. If the whole thing doesn't couple well there's little that can be done to improve it. A good coupling mandolin sounds good, has good sustain, is easy and supple to play, and plays itself.. Almost.

  17. #41
    Registered User Julian Morris's Avatar
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    Default Re: Curious about bridge height, break angle and string gauge

    Quote Originally Posted by fscotte View Post
    I'll tell ya this much, if it has anything to do with making adjustments to the bridge and tailpiece, neck angle, overall break angle, it's already been done. There is certainly nothing new under the sun in those regards. The mandolin makes good sound by good coupling, as mentioned previously. There isn't any easy way or shortcut around it. If the whole thing doesn't couple well there's little that can be done to improve it. A good coupling mandolin sounds good, has good sustain, is easy and supple to play, and plays itself.. Almost.
    I thank you for your sugestions and encouragement. I just want to relieve any unnecessary pressure on the soundboard. I will tweak tone accordingly, if I can or have to. I will carry with me the notion of 'coupling'.

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    Default Re: Curious about bridge height, break angle and string gauge

    Remember lighter strings may put less stress on the top, but i find i can have lower action with heavier strings as they don't vibrate or wobble shall we say because of the difference in tension. So while with no action change lighter strings may seem to play easier, you can lower the bridge more with heavier strings, have better action, more mass to drive the top, play very easy and break less strings while playing. I have one mandolin with a very low break angle and low bridge, sounds great have another with much more break angle and a taller bridge both are set up about the same action wise and both sound great. One is and oval hole one is an ff hole. So the comparison of the two sounds can't be compared, but both do sound very good with very different bridge heights and break action. I have other mandolins and comparison in sound between a low neck angle and a higher neck angle seems to make no difference to me in sound, well there is always a difference, but in quality of sound both are very good. A hundred Gibsons from the same year will sound very different even tho they are made similarly.
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  20. #43
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    Default Re: Curious about bridge height, break angle and string gauge

    Quote Originally Posted by pops1 View Post
    Remember lighter strings may put less stress on the top, but i find i can have lower action with heavier strings as they don't vibrate or wobble shall we say because of the difference in tension. So while with no action change lighter strings may seem to play easier, you can lower the bridge more with heavier strings, have better action, more mass to drive the top, play very easy and break less strings while playing.
    I'm still mucking about with figures here. What I have managed to show is vaguely interesting. To keep the stress on the soundboard the same when you move from light to heavy strings, you would have to reduce the break angle in proportion to the inverse of the diffference in the weight of strings. Thus for example going from a 34 G to a 39 G at weights of 0.000223 lb/ft to 0.000275 lb/ft, a break angle of say 15 degrees for the lighter string would need to be changed to 15 x (0.000223/0.000275) degrees = 12 degrees.

    Proof available on request if anyone is really interested.

    But I suppose what is confusing here is that the obvious way to change the break angle is to lower the action but what I am really talking about is raising the tailpiece and keeping the action the same.

    Fair enough, action is dependent on not getting buzz from excessive amplitude of vibration. So I see what you say, heavier strings for the same picking input have lower amplitude of vibration but may be returning a similar sound volume. Hmm...

  21. #44
    Oscar Stern s11141827's Avatar
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    Default Re: Curious about bridge height, break angle and string gauge

    This String Calculator always implies that Lighter Gauge & Lower Tension strings break less easily than the Thicker ones do, & that's because less stress = less prone to failure:https://wahiduddin.net/calc/calc_gui..._from_size.htm I compensate for the lower tension strings by extending the instrument's scale length by a few extra inches so instead of a 13 inch scale length it's now a 15 13/16 in scale length strung w/ ultra lights in Standard GDAE Pitch.

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    Default Re: Curious about bridge height, break angle and string gauge

    Blimey.

  23. #46
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    Default Re: Curious about bridge height, break angle and string gauge

    For anyone interested in calculating the relationship between all of the geometric variables and forces discussed here, my (now very old) neck geometry calculator is still online.

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  25. #47
    Oscar Stern s11141827's Avatar
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    Default Re: Curious about bridge height, break angle and string gauge

    A Higher break angle and lighter strings will produce a brighter sound.

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    Default Re: Curious about bridge height, break angle and string gauge

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  27. #49
    Adrian Minarovic
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    Default Re: Curious about bridge height, break angle and string gauge

    Lots of old BS and hearsay got repeated in this thread. I didn't read the old posts but that old article especially part about composite bows is pure BS.
    Adrian

  28. #50

    Default Re: Curious about bridge height, break angle and string gauge

    A ' composite bow ' is is a laminated type of archery weapon.

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