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Thread: The greater the neck angle the taller the bridge.

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    Registered User pefjr's Avatar
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    Default The greater the neck angle the taller the bridge.

    I am curious after reading this thread Single foot Loar-style bridge how the neck angle effects sound. Can we hear from some builders? Thanks in advance.
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    I may be old but I'm ugly billhay4's Avatar
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    Default Re: The greater the neck angle the taller the bridge.

    I can't say precisely about sound, but it does affect the downward pressure of the strings on the top. The higher the bridge, the sharper the strings break over the bridge and the greater downward pressure they exert.
    Bill

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    Default Re: The greater the neck angle the taller the bridge.

    Jimmy Gaudreau used to have a '25 Gibson Fern that he played for years that had the neck angle shimmed up by 1/8" to increase the break angle and response.
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    Registered User fscotte's Avatar
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    Default Re: The greater the neck angle the taller the bridge.

    I think a stiffer top would need a greater down pressure at the bridge, and vice versa. But neck angle isn't going to change, so all you can do is raise or lower the bridge, which has its own separate issues in relation to playability.

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    Registered User sunburst's Avatar
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    Default Re: The greater the neck angle the taller the bridge.

    The pressure on the top from the strings breaking over the bridge is a static pressure. In other words, the strings are just lying there in the bridge slots, unmoving, and the tension on the strings presses the bridge down against the top. The forces on the bridge that make sounds are the dynamic forces from the moving strings, and they are the same regardless of static downward pressure, so more break-over angle does not necessarily increase response or loudness or anything else sound-related. Too much pressure on the bridge may even "choke" the top, or dampen top movement in response to plucking the strings.
    There is a "school of thought" that says less downward pressure is better, and that just enough to keep the bridge in position is optimal for sound.
    I assume that there is an optimal downward pressure for each instrument and each player and listener, and no absolutes can be stated.

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    Registered User pefjr's Avatar
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    Default Re: The greater the neck angle the taller the bridge.

    I was thinking about the difference in the height of the bridge. The distance from the sound board to the strings. Does the neck angle mean less/more volume with a higher angle or maybe that is tap tuned? I have no idea, I just know some mandolins have a higher angle than others. I happen to have one that is high, it might be right at the critical point of being too high, and it has superior tone and volume. I know there are many factors to tone, but is neck angle another one in the magic formula?
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    Registered User Mando-Mauler's Avatar
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    Default Re: The greater the neck angle the taller the bridge.

    John Duffy always rejigged his mandolin necks so they had a greater height above the top-plate at the bridge. He maintained it increased volume and made things "stiffer". In one interview, he said that was one of Gibson's main faults...the neck angle was too low.I forget where I read it, but it's out there somewhere.But remember, this mando God belted a mandolin harder than anyone else on Earth.Years ago, Roger Buckmaster (first class maker) and myself, being of inquisitive nature, designed & built a strengthened top F5 with a REALLY sharp neck angle. It put so much pressure on the strings it used to snap the vertical metal tuning posts on the bridge...ended up we had to stick a Gibson guitar bridge on because the posts were thick enough to withstand the pressure. We messed around with this thing for about 25 years & got some weird sounds out of it; some people liked it some of it , other folks ran away screaming. After all those years of rejigging, adding & subtracting things & finally decreasing the neck angle, it plays and sounds beautifully. Only one moral here - don't go overboard. From memory, which is a bit fragile now, the best angle is up or down from a base 17 degrees. What does Steve Gilchrist use?

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    Registered User sunburst's Avatar
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    Default Re: The greater the neck angle the taller the bridge.

    Quote Originally Posted by pefjr View Post
    I was thinking about the difference in the height of the bridge. The distance from the sound board to the strings.
    Yes, but depending on other aspects of construction the string break-over angle can be different with the same bridge height. In other words, a higher or lower bridge on the same mandolin might make some difference in the sound (though the mass of the bridge is more likely to make a difference) but one mandolin with a 5/8" bridge might have the same break-over angle as another with a 7/8" bridge, so bridge height is not a good indicator of anything. Same thing with neck angle. If the neck overstand is different and/or if the arch height is different, different neck angles result in different string break-over angles on different mandolins.

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    Default Re: The greater the neck angle the taller the bridge.

    As a single element in total construction, neck angle is not as critical as numerous other issues. That being said, if the neck angle is too much... or too little... it will be detrimental to tone and volume. There is a pretty wide range that seems to be very workable. The most important issue is to not get it too high or too low. Each instrument responds differently to so many things that it really is the total build and not one single issue that is important. I think the shape and size of the bridge can have more effect than the normal neck angles we see.

    If the neck angle is so low the bridge cannot function properly, then it is probably too low. If it is so high that it is hard to keep the bridge in place, then it is likely too high.
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    Certified! Bernie Daniel's Avatar
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    Default Re: The greater the neck angle the taller the bridge.

    Quote Originally Posted by Big Joe View Post
    As a single element in total construction, neck angle is not as critical as numerous other issues. That being said, if the neck angle is too much... or too little... it will be detrimental to tone and volume. There is a pretty wide range that seems to be very workable. The most important issue is to not get it too high or too low. Each instrument responds differently to so many things that it really is the total build and not one single issue that is important. I think the shape and size of the bridge can have more effect than the normal neck angles we see.

    If the neck angle is so low the bridge cannot function properly, then it is probably too low. If it is so high that it is hard to keep the bridge in place, then it is likely too high.
    Not totally on topic but how do you accurately measure the break angle? I've thought about doing it just so I could make a precise estimation of the down pressure vector on the top plate.

    But its an awkward thing to do -- not being able to slip a protractor through the bridge for example. Best I have been able to do is measure the bridge height and then measure the string height two inches on either side of the bridge. I then use those those measurements to draw a simulation of the angle on paper to measure. But that estimate is not too accurate because the top plate is not flat.
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    Registered User sunburst's Avatar
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    Default Re: The greater the neck angle the taller the bridge.

    Quote Originally Posted by Bernie Daniel View Post
    ...how do you accurately measure the break angle?
    I would use a bevel gauge, set it to match the strings over the bridge and then measure the angle of the gauge.

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    Default Re: The greater the neck angle the taller the bridge.

    Quote Originally Posted by sunburst View Post
    I would use a bevel gauge, set it to match the strings over the bridge and then measure the angle of the gauge.
    Of course! Thanks!

    Sad to think I hadn't thought of that myself!
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    Default Re: The greater the neck angle the taller the bridge.

    Back to Johb Duffey, ....When he built his first "Duck" he said he increased the neck angle over what Gibson was using, I forget exactly to what degree he said he did that but as Mando-Maker stated, John believed that it made the mandolin sound louder and better...He also tried different things with the points by having some filled in and some not....I don`t know if he ever said what he finally decided to do with all of that info when he built the second "duck", I don`t believe #2 sounded exactly like #1 though and it wasn`t exactly the same shape, some variation in size and arch of the top....

    Willie

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    Default Re: The greater the neck angle the taller the bridge.

    I had an early Duff where the neck angle was cocked way back, bridge was sky high. Don't really remember how it sounded.

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    Formerly F5JOURNL Darryl Wolfe's Avatar
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    Default Re: The greater the neck angle the taller the bridge.

    My observations: All else being equal, extreme neck angle and bridge height equal stiff, super heavy guage string feel. Most likely equivalent to what I think John posted as being "bound up"
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    Registered User Chris Baird's Avatar
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    Default Re: The greater the neck angle the taller the bridge.

    Neck angle can affect the string's breakover angle at the bridge, which can affect the downward force on the top. The amount of downward force affects the modal frequencies of the instrument and their relationship to one another. This can be easily seen with an FFT program and various degrees of "tuned-up"... If one does a "bonk test" with just enough string tension to hold the bridge on, and then further bonks tests while incrementally tuning the instrument up, you will see that varying downward tension affects the modes.

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    Default Re: The greater the neck angle the taller the bridge.

    Well I Know Duffeys' early F-7 conversion has "IT" and I'd put that mando up against anything out there..It has all the Great things we all look for in a mandolin..And it has the steep neck angle,I believe 1 inch from the top of the mandolin to the top of the bridge..

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    Default Re: The greater the neck angle the taller the bridge.

    Duffey was always tinkering around with his mandolin and most of the time I saw it and heard it it sounded different each time but always sounded good, I am talking about his F-12 conversion, he did play an F-7 earlier but as far as I know that was not his
    so I don`t know if did any conversions on it or not....When we are talking about a high bridge with a neck angle being raised the strings can still be close to the fret board but Duffey liked them even high with the steep neck angle... and it surely didn`t kill his mandolin....Or maybe it did because I never heard it as a stock mandolin....

    Willie

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    Default Re: The greater the neck angle the taller the bridge.

    Chris:

    For an elastic system, the initial force does not affect the model properties of the system. The model properties are totally based on the properties of the instrument and not to the load you apply. So are you saying an instrument behaves non-linearly (P-delta affects) while remaining elastic?

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    Registered User Chris Baird's Avatar
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    Default Re: The greater the neck angle the taller the bridge.

    Arigato,

    I'm not sure what causes the effect I described, however, it can easily be tested as I've said. Try it and see. The forces that the string tension exerts throughout the mandolin affect the modes. The modes of a mandolin with bridge and strings on, but with only the slightest string tension, are significantly different from the same mandolin fully tensioned (tuned up). I assume the combinations of relatively extreme tensions, compressions, and torsions affect the stiffness of the woods??? I don't know.

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    Default Re: The greater the neck angle the taller the bridge.

    I haven't observed what Chris is describing. Early on in Tom Rossing's lab, I did see the (1,0) or sideways rocking mode split right at 440 Hz. After a little puzzling about that, followed by a forehead slap, I realized that the undamped open A strings were stealing energy from the sideways rocking mode, thanks to the overlap in frequency and the non-negligible mass of the strings. Damped the strings after that w/ a piece of foam between the strings and the fingerboard. Never saw that effect again, even though I did all my interferometry w/ the strings at pitch.

    More recently, I was doing some interferometry in Thom Moore's lab at Rollins. He wondered out loud about the possible perturbations from the strings. After running through the modes, I removed the strings and did the interferometry again. Within error, the modes were the same and their modal frequencies were nearly the same with no strings as they were with strings at pitch. That is, they were up to about 1.5 kHz. At higher frequencies like that, things started to look a bit different. The main events for plucked string instruments are all well below that, though. So I agree w/ Arigato; the normal modes are s'pozed to be the normal modes, regardless of how you excite them, and that is what I have seen. If Chris is looking at audio spectra (his "bonk testing"), he is seeing a whole lotta stuff besides the body modes all scrambled together. Can't really be sure from audio spectra which peaks correspond to normal mode peaks. I have even had trouble with that despite the hindsight of having just done the interferometry.

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    Registered User Chris Baird's Avatar
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    Default Re: The greater the neck angle the taller the bridge.

    I actually use an accelerometer and a small pcb force transducer hammer to gather frequency response functions. I'll post some data when I string up the next batch of mandolins. I also damp the strings. I'm pretty sure I'm just measuring modes and not audio junk.

    I've found really large differences between a mandolin sans bridge and strings vs. fully strung and tuned up. Which I find predictable considering the strings and bridge add considerable weight, if nothing else, to the equation.

    Anyway, as I've said, I'll post my data when I finish the next batch.

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    Default Re: The greater the neck angle the taller the bridge.

    I should know better than to post amongst these big dogs, but string tension, weight and response is something I have spent alot of time putting my attention on. I have a guitar that strung up to pitch is nothing to write home about. If you tune it a half-step down, it is better, but still nothing exceptional. If you tune it down a full-step and increase the string gauges very slightly (to adjust the tension and feel) you start to get that kind of flat-top sound that makes one turn their head. Same guitar, different circumstances.
    My mandolin has a full 1" distance from bridge-top to soundboard, necessitating the use of a Tall-Boy bridge and again I use slightly heavier than standard gauges on it. I am not going to brag on my mandolin, but let's just say not only will I be heard in any acoustic situation, but it will also sound sweet as well. I tried to use some of those same .011.5" E strings that I use on my brother's MK mandolin, and all it did was bind it up, shut it down, whatever you want to call that phenomenon when there is too much tension to let the instrument speak loudly and clearly. I don't have a specific point to make, other than that I know from direct experience that there is definitely something to finding the particular tension/action where an individual instrument sounds optimal, even if it involves increasing or decreasing the overall string tension and this will not always be found at "pitch'" or by using "standard" measurements for the neck angle, bridge height, etc.
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    Registered User pefjr's Avatar
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    Default Re: The greater the neck angle the taller the bridge.

    Quote Originally Posted by Fretbear View Post
    I should know better than to post amongst these big dogs, but string tension, weight and response is something I have spent alot of time putting my attention on. I have a guitar that strung up to pitch is nothing to write home about. If you tune it a half-step down, it is better, but still nothing exceptional. If you tune it down a full-step and increase the string gauges very slightly (to adjust the tension and feel) you start to get that kind of flat-top sound that makes one turn their head. Same guitar, different circumstances.
    My mandolin has a full 1" distance from bridge-top to soundboard, necessitating the use of a Tall-Boy bridge and again I use slightly heavier than standard gauges on it. I am not going to brag on my mandolin, but let's just say not only will I be heard in any acoustic situation, but it will also sound sweet as well. I tried to use some of those same .011.5" E strings that I use on my brother's MK mandolin, and all it did was bind it up, shut it down, whatever you want to call that phenomenon when there is too much tension to let the instrument speak loudly and clearly. I don't have a specific point to make, other than that I know from direct experience that there is definitely something to finding the particular tension/action where an individual instrument sounds optimal, even if it involves increasing or decreasing the overall string tension and this will not always be found at "pitch'" or by using "standard" measurements for the neck angle, bridge height, etc.
    Interesting. I had a Martin Guitar for 20 years and thought it sounded great. My son put on a heavier string gauge than I had ever had on it, just before I put it up for sale. I sold it recently to a Hawaiian, but before he bought it, he tried it out and he tuned it to what he called 'slack tuning'. Open 'G' I think. That guitar put out a beautiful sound I had never heard before. Too late to back out, I was already committed to sell it.
    I have the world in a jug, and the stopper in my hand.

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    Default Re: The greater the neck angle the taller the bridge.

    Rossing and I put some accelerance spectra in our 2003 paper inAcoustical Science & Technology, and we identified some of the spectral peaks w/ body mode peak frequencies. We had the benefit of hindsight from just having done the interferometry and knowing the modal frequencies, and even there, it was difficult. With accelerometry, you don't observe the air modes (even though they are there), but there is still a lot of stuff to deal with. I'm assuming that your accelerance spectra are OK, but I think you may be over interpreting your data, trying to say things that you can't really say. Even with interferometry, it is difficult to do the interpretation. There is lots of frequency overlap between the various modes, mode mixing, etc. All of the modes have different bandwidths, Q values, etc., and there is lots of difference between individual mandolins. Even mandolins that look very much alike and were built very similarly can have surprisingly different modal frequencies and Q values for each of the modes.

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