Page 1 of 2 12 LastLast
Results 1 to 25 of 39

Thread: Tonal difference between full contact or two-footed bridge

  1. #1

    Default Tonal difference between full contact or two-footed bridge

    My inexperienced intuition tells me a two footed could allow for richer overtones... More ways for the wood to wiggle. Anyone tried both on the same mando and noticed a significant difference?

  2. #2
    Registered User
    Join Date
    Sep 2002
    Location
    Northern California coast
    Posts
    2,038

    Default Re: Tonal difference between full contact or two-footed bridge

    First, on the experimental front: I made more than a dozen different bridges, fit them all to the same mandolin, and did accelerance spectra on each of them. Also did a "control" with the shaker on the mandolin top plate instead of on top of the bridge. All of the accelerance spectra looked pretty much the same, so I tried subtracting the "control" spectrum from each of the others. Found minor differences at most.

    Without making any major pronouncements, I'll just state how mandolins "wiggle". When you set the string in motion by picking, they don't do just any old motion. Rather, they vibrate in their own normal modes of motion. Normal modes of motion are how elastic objects vibrate. They don't do things that are not their normal modes of motion. The string vibrations stay in the strings. What they do is exert pulses of force on the bridge each time their amplitude passes through zero. The bridge pretty much transmits those pulses to the top plate unchanged, since it is in firm contact with it.

    Those pulses of force from the strings contain many frequency components. They in turn excite most or all of the normal modes of the top plate, and in turn of the rest of the instrument. The normal modes of the instrument body are different from those of the strings in that unlike the string modes, they are not harmonic. But they are similar in that like the strings, the body vibrates in its' normal modes of motion, and doesn't do any other motions. So, one big foot or two feet, the normal modes of the mandolin body are not gonna be any different. Also, the pulses of force are gonna be the same. If they go thorugh two feet instead of one, they will still be in phase. I'll leave the rest to you.

    http://www.Cohenmando.com/

  3. The Following 11 Users Say Thank You to Dave Cohen For This Useful Post:

    + Show/Hide list of the thanked


  4. #3
    Registered User fscotte's Avatar
    Join Date
    May 2010
    Location
    Zanesville, Ohio
    Posts
    2,490

    Default Re: Tonal difference between full contact or two-footed bridge

    If there is little to no difference between a one footer and a two footer, then there shouldn't be any reason to perfectly fit a bridge to the mandoln top, other than aesthetics. Leaving a little gap at the edge of the feet, or not getting the feet to make full contact near the center, etc... These little issues would have nil difference to tone.

    I say that to say this, I have no idea if there is a difference in tone between a one or two footer. And I have no idea if a perfectly fit bridge sounds better than a not so perfect fit bridge.

  5. #4
    Registered User
    Join Date
    Sep 2002
    Location
    Northern California coast
    Posts
    2,038

    Default Re: Tonal difference between full contact or two-footed bridge

    I don't think that one can necessarily equate 2-feet vs 1-foot with poor fit, unless the fit is really poor, and especially in the center. There are some potential problems I see with poor fit of the bridge foot/feet.

    One is "how poor is the fit?". If there is only a slight gap, especially at the outer edges (which is the most common poor fit), there is always the possibility of "chattering" of the bridge foot against the top plate. That is something entirely different from two well-fit feet.

    In principle, it doesn't matter where on a plate the exciting force is applied, except for one thing. It an exciting force is applied along the nodal line of a particular mode, that mode will be weak or absent, while all of the other modes will be excited normally. In practice, the force has to be applied exactly at the nodal line in order for the mode to be weak or absent. I have seen this while doing holography. Moved the magnet and coil off of the bridge saddle and onto the top plate in a few instances to excite a mode that wasn't happening. More recently, I have been exciting the instrument(s) remotely w/ a speaker, which removes the potential problem.

    In the bridge experiment mentioned in my first post, one of the bridges was a Gibson 2-footer. Some were my one-footer variations on the Gibson. Some were one-footers w/ a sliding wedge for adjustment - full contact all the way across, kinda like Jimmy D'Aquisto's later bridges. Two were one-piece two-footers supplied by Brian "Red" Henry. All were carefully fit to the mandolin top plate. Forgot to mention that in addition to only minor spectral differences observed, they all sounded like the same mandolin to me.

    http://www.Cohenmando.com/

  6. #5
    Registered User dustyamps's Avatar
    Join Date
    Jan 2011
    Location
    Springfield Missouri USA
    Posts
    300

    Default Re: Tonal difference between full contact or two-footed bridge

    Here is my direct comparison. I recently switched from a two foot bridge to a full contact bridge and used the same top section on both. Both bridges are similar in that I customize stock ebony adjustable bridges and shorten then to 4 1/4 inches long and sand the sides down so the bridge is about 5/16 inch thick, about the same as the original one piece Gibson bridge. The gap in the two footer is 1 inch. I fitted both to my mandolin. I can't hear a difference.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	016 (1024x768).jpg 
Views:	406 
Size:	316.4 KB 
ID:	119226   Click image for larger version. 

Name:	009 (1024x663).jpg 
Views:	398 
Size:	360.6 KB 
ID:	119228  

  7. #6
    Member
    Join Date
    Sep 2002
    Location
    Maryland
    Posts
    4,881

    Default Re: Tonal difference between full contact or two-footed bridge

    I think that some people want to hear a difference when they try things like this so in their minds there will be a difference, using electronic instruments will tell the true story...I had a bridge on one mandolin that wasn`t touching flush on the treble side so I removed it and refitted it so that it as perfect as I can get it and it did make a huge difference so an ill fitting bridge sound can be improved upon by making sure they fit flush all the way across, this was a two footed bridge base....I haven`t compared a one foot base....

    Willie

  8. #7
    Registered User fscotte's Avatar
    Join Date
    May 2010
    Location
    Zanesville, Ohio
    Posts
    2,490

    Default Re: Tonal difference between full contact or two-footed bridge

    Quote Originally Posted by Willie View Post
    I think that some people want to hear a difference when they try things like this so in their minds there will be a difference, using electronic instruments will tell the true story...I had a bridge on one mandolin that wasn`t touching flush on the treble side so I removed it and refitted it so that it as perfect as I can get it and it did make a huge difference so an ill fitting bridge sound can be improved upon by making sure they fit flush all the way across, this was a two footed bridge base....I haven`t compared a one foot base....

    Willie
    Perhaps people do, perhaps they don't. Depends on the quality of the ear. Some folks hear a difference in 44.1 Khz quality and some don't hear a thing compared to 96kHz samples. Digital analysis shows a difference, but people don't hear a diff sometimes.

    There may or may not be differences in bridges either. I'm not exactly sure if there is any technology that can fully analyze the differences either.

  9. #8
    I may be old but I'm ugly billhay4's Avatar
    Join Date
    Dec 2003
    Location
    Lakebay, Wa
    Posts
    4,162

    Default Re: Tonal difference between full contact or two-footed bridge

    In principle, it doesn't matter where on a plate the exciting force is applied, except for one thing. It {sic} an exciting force is applied along the nodal line of a particular mode, that mode will be weak or absent, while all of the other modes will be excited normally. In practice, the force has to be applied exactly at the nodal line in order for the mode to be weak or absent. I have seen this while doing holography. Moved the magnet and coil off of the bridge saddle and onto the top plate in a few instances to excite a mode that wasn't happening. More recently, I have been exciting the instrument(s) remotely w/ a speaker, which removes the potential problem.
    Would this suggest that a bridge with no gap would have a greater chance of applying force to an exact nodal line since more bridge is in contact with the top?
    Bill
    IM(NS)HO

  10. #9
    Registered User
    Join Date
    Sep 2002
    Location
    Northern California coast
    Posts
    2,038

    Default Re: Tonal difference between full contact or two-footed bridge

    Quote Originally Posted by billhay4 View Post
    Would this suggest that a bridge with no gap would have a greater chance of applying force to an exact nodal line since more bridge is in contact with the top?
    Bill
    The short theoretical answer is "It depends on where the nodes are." The short practical/empirical answer is "No."

    Regarding both answers: There are only two modes under 1 kHz with nodal lines that could be entirely under the bridge. One is the longitudinal rocking mode (aka (0,1) or T(1,2)). The other is the twisting mode (aka (1,1) or T(2,2)). Neither one of those are strong radiators in an ff-hole type mandolin. In doing holography, I have most often seen those nodal lines slightly displaced from the bridge location. In those cases, and even for those nodal lines in general, the answer to your question is definitely "No." In the rarer cases of those nodal lines being right under the bridge foot, what would help would be a wider or "fatter" bridge foot. However, there are tradeoffs to the wider foot, like too much mass, f'rinstance.

    I think the answer comes down to this: Do you like the looks of the two-foot bridge? If so, use it. Like the looks of the continuous bridge foot better? Then use that one."

    http://www.Cohenmando.com/

  11. #10
    Mandolin & Mandola maker
    Join Date
    Sep 2002
    Location
    Bega NSW, Australia
    Posts
    1,425

    Default Re: Tonal difference between full contact or two-footed bridge

    I have fooled around with bridges a fair bit, and participated with Red Henry when he was developing his one piece bridges. My experience is that I can't hear any difference between full contact and two foot bridges unless the gap in the middle is big. Small gaps don't seem to make much difference, but they do make fitting the bridge easier.

    A couple of things about bridges that do have me baffled as to an explanation. Mass of the bridge is important. Less mass and the mandolin will sound louder and brighter. So if I remove wood from the base of a Brekke bridge the mandolin sounds louder and more responsive. This is as you would expect since it removes about 20% of the mass. However, if I drill two holes in the saddle, this removes less than 2% of the mass of the bridge but there is quite a significant difference made to the sound, sometimes even more than taking wood off the base. I have repeated this many times and always get the same result. 2% is within the variation of the mass of the unmodified bridges, but they all sound the same. If the bridge does not flex as Dave says, I don't understand why such a small decrease in mass can have such a big effect.

    The other thing that also baffles me is - I once made two Brekke bridge saddles, one made from Indian Rosewood, the other made from Brazilian Rosewood. Absolutely identical saddles that weighed the same, and I used the same Ebony base. You would expect they would sound the same, or at least very similar since the mass is the same and bridge does not flex. Absolutely not. Massive difference in sound.

    Any ideas?
    Peter Coombe - mandolins, mandolas and guitars
    http://www.petercoombe.com

  12. #11
    Registered User
    Join Date
    Sep 2002
    Location
    Northern California coast
    Posts
    2,038

    Default Re: Tonal difference between full contact or two-footed bridge

    Quote Originally Posted by peter.coombe View Post
    I have fooled around with bridges a fair bit, and participated with Red Henry when he was developing his one piece bridges. My experience is that I can't hear any difference between full contact and two foot bridges unless the gap in the middle is big. Small gaps don't seem to make much difference, but they do make fitting the bridge easier.

    A couple of things about bridges that do have me baffled as to an explanation. Mass of the bridge is important. Less mass and the mandolin will sound louder and brighter. So if I remove wood from the base of a Brekke bridge the mandolin sounds louder and more responsive. This is as you would expect since it removes about 20% of the mass. However, if I drill two holes in the saddle, this removes less than 2% of the mass of the bridge but there is quite a significant difference made to the sound, sometimes even more than taking wood off the base. I have repeated this many times and always get the same result. 2% is within the variation of the mass of the unmodified bridges, but they all sound the same. If the bridge does not flex as Dave says, I don't understand why such a small decrease in mass can have such a big effect.

    The other thing that also baffles me is - I once made two Brekke bridge saddles, one made from Indian Rosewood, the other made from Brazilian Rosewood. Absolutely identical saddles that weighed the same, and I used the same Ebony base. You would expect they would sound the same, or at least very similar since the mass is the same and bridge does not flex. Absolutely not. Massive difference in sound.

    Any ideas?
    Did you take any sound spectra or accelerance spectra? Anything quantitative?

    The tall, thin, & light bridges of bowed string instruments do move, & especially so for the taller bridges of violas and cellos. That has been demonstrated, documented, and published long ago. In my measurements w/ mandolin bridges, I didn't see anything significant below 5 kHz. and I certainly haven't heard any massive differences. More like no differences at all. I would love to be wrong, to see/hear something measureable and repeatable.

    http://www.Cohenmando.com/

  13. #12
    Registered User
    Join Date
    Dec 2002
    Location
    Fairfax Co., Virginia
    Posts
    3,013

    Default Re: Tonal difference between full contact or two-footed bridge

    http://www.lafavre.us/tuning-marimba.htm

    I don't have time to get sucked into a rat hole right now, but there seems to be a great deal to a bridge!
    Stephen Perry

  14. #13
    Registered User
    Join Date
    Mar 2013
    Location
    Brooklyn, NY, USA
    Posts
    1,249

    Default Re: Tonal difference between full contact or two-footed bridge

    Doesn't the size and shape of a bridge dampen some of the modes of a top? I know if I push my finger on the top of my mandolin the sound changes.

  15. #14
    Resonate globally Pete Jenner's Avatar
    Join Date
    Oct 2011
    Location
    Mt Victoria, NSW, Australia
    Posts
    3,546
    Blog Entries
    1

    Default Re: Tonal difference between full contact or two-footed bridge

    Quote Originally Posted by Stephen Perry View Post
    I don't get the connection between the marimba and the mandolin bridge but it's good to see young Rossing's name cropping up in the cited references.
    The more I learn, the less I know.

    Peter Jenner
    Blackheathen

    Facebook

  16. #15
    Registered User
    Join Date
    Sep 2002
    Location
    Northern California coast
    Posts
    2,038

    Default Re: Tonal difference between full contact or two-footed bridge

    Quote Originally Posted by Pete Jenner View Post
    I don't get the connection between the marimba and the mandolin bridge but it's good to see young Rossing's name cropping up in the cited references.
    That's because there is no connection between marimba bars and string instrument bridges. Marimba bars are essentially simply supported beams, supported at the nodes for the first bending mode. They are also made from woods with very low internal damping, e.g., cocobolo, other rosewoods. Bending modes in violin bridges are vertical motions of something that approximates a beam clamped at both ends. Violin bridges are also very thin and very light - no more than a couple grams at most. Mandolin bridges weigh anywhere from about 5-6 grams at the lightest to over 16 grams.

    http://www.Cohenmando.com/

  17. #16
    Registered User
    Join Date
    Sep 2002
    Location
    Northern California coast
    Posts
    2,038

    Default Re: Tonal difference between full contact or two-footed bridge

    Quote Originally Posted by Nevin View Post
    Doesn't the size and shape of a bridge dampen some of the modes of a top? I know if I push my finger on the top of my mandolin the sound changes.
    When I started doing interferometry/holography with Tom Rossing (ca 1999), the bridges were on the instruments and the strings were tuned to standard pitch. We soon found that the strings needed to be damped, else they would steal energy from body modes that happened to occur at the open string frequencies. When I started workng with Thom Moore at Rollins (ca 2010), he suggested that the strings and bridge could simply be removed for simplicity's sake. I did modal analysis on one mandolin with the bridge on, strings at pitch and damped. Then removed the strings and bridge and repeated the modal analysis. There was literally no difference up to ~1.5 kHz, which is about as high in frequency as we usually bother to go in holography.

    Your finger is completely inelastic, or at least it is in the acoustical time domain. Bridges are not at all like fingers.

    http://www.Cohenmando.com

  18. The following members say thank you to Dave Cohen for this post:

    Nevin 

  19. #17
    Registered User sunburst's Avatar
    Join Date
    Nov 2003
    Location
    Kentucky
    Posts
    15,863

    Default Re: Tonal difference between full contact or two-footed bridge

    Quote Originally Posted by peter.coombe View Post
    ...one made from Indian Rosewood, the other made from Brazilian Rosewood. Absolutely identical saddles that weighed the same, and I used the same Ebony base. You would expect they would sound the same, or at least very similar since the mass is the same and bridge does not flex. Absolutely not. Massive difference in sound.

    Any ideas?
    Could that have to do with differences in internal damping in the two pieces of wood? Even that seems unlikely; that there could be enough difference between two pieces of rosewood to make the mandolin sound different.

  20. #18
    Registered User sgrexa's Avatar
    Join Date
    Nov 2002
    Location
    Haddon Heights, NJ
    Posts
    836

    Default Re: Tonal difference between full contact or two-footed bridge

    John Reischman has a full contact bridge on his Loar but it was not installed for better tone. I believe Todd Phillips made a full contact base as there was some top sink along the center seam. This spread the tension out along the entire length of the bridge footprint and solved the problem.

    Sean

  21. #19
    Registered User avaldes's Avatar
    Join Date
    Mar 2013
    Location
    Champaign County, IL
    Posts
    366

    Default Re: Tonal difference between full contact or two-footed bridge

    OK, not a builder, so please pardon what may appear to be ignorant questions.
    1. Many posts here refer to the importance of fitting the bridge base to a specific mandolin. If the actual area of contact is not important (two foot vs. continuous base), then why go to the trouble. Dave partially answered this with the chatter issue.
    2. No matter the base-to-mandolin fit, it seems that the strings can only transmit vibration through the two threaded posts (on a Loar style bridge). Isn't this a contact point that would benefit the sound if it could be improved?
    3. Bowl-backs have a wood bridge with a saddle made of (presumably synthetic) bone or ivory. Much less adjustable, but it would seem that it would transmit vibration better. Anyone make an adjustable bridge with the saddle portion of such a material?

  22. #20
    Registered User
    Join Date
    Sep 2002
    Location
    Northern California coast
    Posts
    2,038

    Default Re: Tonal difference between full contact or two-footed bridge

    Attached is a photo of a sampling of the bridges in the accelerance spectra experiment mentioned in my first post. Left, bottom to top: a Gibson adjustable in rosewood (started out as a two-footer, was sanded and fitted to become a one-footer), a Dave Cohen adjustable in ebony, and a Cohen adjustable in Indian rosewood w/ PEEK plastic posts and adj. nuts. Center: A red Henry one-piece (two footer) in maple, and another (same details) in ebony. Right, bottom to top: an "exploded" three-piece sliding wedge adjustable (A'la Jimmy D'Aquisto) in Macassar ebony, a similar 3-piece in cocobolo (rubber banded together), and two 3-piece adjustables in maple. The bridge masses in the photo vary from about 5.5 g to almost 12 g. The Red Henry bridges are two-footers; all others are one footers. There were a few others in the experiment, but the bridges in the photo are representative of the bridge types. All were carefully fitted to the same test mandolin.

    As I said in my first post (#2, above), I did not find any significant differences in the accelerance spectra for any of these bridges. I also added in a subsequent post that the mandolin sounded the same to me with all of the different bridges. It also sounded the same w/ all bridges to Jim Rae. He had hoped to see some spectral differences comparable to what he was seeing with banjo bridges. No such luck. Banjo bridges, like violin bridges, are way lighter than mandolin bridges. Also quite flexible, although in an orthogonal direction to that of violin bridges.

    Regarding Avaldes' points #2. & 3.: Strings do not transmit vibrations to top plates; they transmit force pulses through the bridge to the top plate. Force is simply related to accelerance (a = F/m) Once again, I did not observe any differences between the various bridges on a single mandolin.

    Regarding Avaldes' point #3: I made a thin, light saddle insert of cow bone for a bridge for a mandolin built for Mike Schroeder. He liked it. I couldn't tell any difference from the standard ebony saddle also made for that instrument.

    http://www.Cohenmando.com/
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	Differentbridges.JPG 
Views:	361 
Size:	59.8 KB 
ID:	119255  
    Last edited by Dave Cohen; May-15-2014 at 11:27am.

  23. The following members say thank you to Dave Cohen for this post:


  24. #21
    Registered User sunburst's Avatar
    Join Date
    Nov 2003
    Location
    Kentucky
    Posts
    15,863

    Default Re: Tonal difference between full contact or two-footed bridge

    Never mind, Dave was typing at the same time.

  25. #22
    Registered User sunburst's Avatar
    Join Date
    Nov 2003
    Location
    Kentucky
    Posts
    15,863

    Default Re: Tonal difference between full contact or two-footed bridge

    Oops. You'd think I'd get the hang of this eventually...

  26. The following members say thank you to sunburst for this post:


  27. #23
    formerly Philphool Phil Goodson's Avatar
    Join Date
    May 2006
    Location
    Statesville, NC
    Posts
    3,256

    Default Re: Tonal difference between full contact or two-footed bridge

    Dave,

    Am I correctly understanding what you are suggesting? Your post seems to imply that there is no obvious difference in sound produced by a mandolin regardless of whether its bridge has 1) one or two feet, 2) slight differences in mass, and (here is where I'm not certain of your implications) 3) differences in the material composition of the saddle.

    I don't really doubt points 1) and 2) very much, but my experience from having a mandolin with its ebony saddle reproduced in Tusk is that the two materials caused a great difference in the tone of the mandolin.

    I wonder if there are yet-to-be-measured parameters (e.g. forces produced by overtones or some such thing) that affect the tone of the produced sound and could cause the gap between our perceptions and documented physical measurements to date?
    ( e.g. Does Tusk absorb certain overtone frequencies more than others, and in a different pattern than ebony?) Just showing my ignorance here.

    Your thoughts?
    Phil

    “Sharps/Flats” “Accidentals”

  28. #24

    Default Re: Tonal difference between full contact or two-footed bridge

    I've really enjoyed reading the conversation sparked by my question... thanks for all of the thoughtful response.

    Dave, in your first post you said "So, one big foot or two feet, the normal modes of the mandolin body are not gonna be any different." That was essentially the crux of my question... I was assuming that the bridge is acting somewhat like a brace (at least in one direction), and so changing the "footprint" of the bridge might alter the modes of vibration in the top... e.g. open up more high-frequency modes...

    But it sounds like your careful experiments showed that if the modes are altered, it is not by enough to matter.
    Thanks for sharing your data.

  29. #25
    Registered User
    Join Date
    Sep 2002
    Location
    Northern California coast
    Posts
    2,038

    Default Re: Tonal difference between full contact or two-footed bridge

    Quote Originally Posted by Philphool View Post
    I don't really doubt points 1) and 2) very much, but my experience from having a mandolin with its ebony saddle reproduced in Tusk is that the two materials caused a great difference in the tone of the mandolin.

    I wonder if there are yet-to-be-measured parameters (e.g. forces produced by overtones or some such thing) that affect the tone of the produced sound and could cause the gap between our perceptions and documented physical measurements to date?
    ( e.g. Does Tusk absorb certain overtone frequencies more than others, and in a different pattern than ebony?) Just showing my ignorance here.

    Your thoughts?
    The likelihood that one material "absorbs" certain frquencies while another material doesn't absorb those frequencies is pretty small. Materials don't literally "absorb" motions of a certain frequency anyway. What would have to occur for a mode of vibration to be "drained' from a string or etc., is that the bridge from that material would have to be undergoing a motion at that frequency, or at least at a nearby frequency, so that there would be an exchange of energy. That I didn't observe any motions in any mandolin bridges below 5 kHz is not really surprising when you consider the dimensions and mass of mandolin bridges. If you calculate the lowest possible frequency for a normal mode of motion (e.g., approximated by a standing wave) based on the speed of sound in the bridge material and the dimensions of the bridge, it would most likely be at 10-20 kHz or above. In violin bridges, which are much, much thinner and more flexible than mandolin bridges, the well-known "bridge hill" resulting from the lowest freq. bridge motion occurs up around 2.5 kHz or higher, iirc. For something made like a mandolin bridge, that frequency would have to be several times that value, which is completely consistent with what I have measured.

    I don't expect anyone to believe anything I say here. What I have done, though, is make measurements which can be repeated, and either corroborated or falsified. All you have to do is get a shaker and repeat the measurements according to my description. I have also noted that those measurements are consistent both with my own anecdotal observations and with the mechanics of Newton, Hamilton, and LaGrange. On the other hand, you offer me one anecdotal observation which I cannot repeat under any circumstances, since you make no measurements of any kind. There is nothing I can do with that; I can neither verify it, nor falsify it.

    http://www.Cohenmando.com/

Tags for this Thread

Bookmarks

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •