leemysliwiec - Posted - 07/22/2011:  15:09:04

That is my question. What is the logic of a compensated bridge.  What is being compensated????  Isn't the 12th fret exactly 1/2 the distance from the nut to the bridge??? Why are some bridges curved.  Doesn't that mess up the distance?   Really, my bridge is straight.  Why would I need to "compensate" with another type bridge?   

uncle.fogey - Posted - 07/22/2011:  15:39:04

I just posted this on another thread, but I'll post it again - I don't use a compensated bridge, but I use a "moon bridge".

Here's the logic of it:

banjos are funny instruments because they use a movable bridge and use very light strings. On classical guitars, using gut or nylon strings, the bridge saddle is almost straight because nylon strings have very little stiffness compared to steel strings.  The bridge saddle on a steel-strung guitar is cocked at an angle because of the difference in relative stiffnesses of the strings.  Violinists and fretless players care nothing about this because they have no frets and do it all with their ear.



Why is this?

No doubt I will be corrected by various physicists, but I'll try to explain it as best I can.



String stiffness is the key.



The physics of vibrating strings is such that:



(1) a string stretched between two points will ALWAYS ring at the octave by chiming a harmonic at the center of its length (12th fret on a banjo) This is a physical law and cannot change.



(2) THEORETICALLY, a string should also ring at the octave if it's FRETTED at the center of its length, but the STIFFNESS of the string interferes with this for some reason I don't understand, and the stiffer the string, the sharper the fretted note will be compared to the harmonic (true) note.



(3) the stiffest string on a banjo is almost always the third string - the thickest plain steel string, hence the third string is the most problematic one. and is always sharp if you have a straight bridge going straight across the head perpendicular to the strings.



(4) stretching the string by pushing it down hard against the fret exacerbates this problem by making it even sharper.



(5) In the old days (Earl, Ralph, Sonny) everyone used straight bridges and they would cock them towards the 5th string (nobody but Bill Keith fretted the 5th string), which mitigated the problem just as it does in a guitar bridge.  These guys learned to deal with this and I never got upset because I thought Earl’s 3rd string was sharp - with BK music, the notes are fast coming and every note on the 3rd string is surrounded by others  on other strings.



ENTER the electronic tuner.  All of a sudden, you didn’t have to listen to the instrument any more, but you turned the tuning peg and watched the digital thingy.  Well, folks, it ain’t going to work on every string, and God forbid, you get it tuned and capo up.



(6) you can compensate for this by building a bridge (or a silly nut)  that makes the centerpoint of each string different, to compensate for the difference in stiffness, hence the term “compensated”.  

Nowadays, there are people out there building VERY NICE bridges that do that, and they will work as long as you don’t change string gauges too much.  If you are nervous about different strings not matching the readouts on the digital tuner, I would recommend one of those.  An excellent builder of them has made comments on this thread



Another alternative is what’s called a “moon bridge”, which doesn’t attempt to make every string exactly right so that you can tune it up and never have to correct it,  but is another step beyond the age of the classic players and helps solve the problem by getting the 1st and 3rd strings into good relative intonation.  The arc can be changed according to how far you want to go with it and what your string gauges are:

It's complicated - hope this helps.

Ken

leemysliwiec - Posted - 07/22/2011:  15:44:34

That helps a LOT.   Explains why banjos never seem to be in tune!!!   I'm looking forward to other comments, but I don't see how others can be better than yours.  LEE

BDCA - Posted - 07/22/2011:  16:30:44

Playing Irish tenor creates an even bigger compensation issue because we use a .012 to as high as.044 over 4 strings.  We compensate by angling the bridge, closer on the treble side. The angle can be fairly extreme...

Cya!

Bob

steve davis - Posted - 07/22/2011:  17:17:18

A good compensated bridge,placed correctly,achieves fretted and capoed notes all over the neck that are closer to 0 on a tuner.



This is a subtle thing that adds up to closer chord harmonies.Closer harmony,like in singing,will make goosebumps happen on your shoulders and neck and there is a full bodied vibrance to the sweetness of the "near 0 on the tuner" combination.



This phenomenon actually adds a tiny bit of enhancement in the vibrations of the neck and resonator,imo.Of course,I can only speak for my bridges.

I'd be happy to send you one of my compensated bridges,Lee.

No obligation...just to try it out and see what it does.You can just mail it back to me afterwards.

Straight bridges work fine,too because our ears don't demand that all notes be nearer 0 on a tuner.But,there are benefitsin compensators like not needing to retune the main 4 strings when capoing.

Edited by - steve davis on 07/22/2011 17:28:24

trapdoor2 - Posted - 07/22/2011:  17:24:46

Another way of looking at it is via "stretch" (which relates to stiffness...the whole instrument is a system, everything affects everything else).

Compensation deals with two types of stretch:

1. Travel stretch: When you move the string from its basic open state to a fretted state, you stretch the string slightly as you press it down to the fret. This is commonly "compensated" at the bridge. Action height, string mass, stiffness, etc. all can change the level of compensation required. As the third string has the most mass and the highest stiffness...yup, it gets the most compensation at the bridge.

2. Fretting stretch: you do not hold the string perfectly onto the fret...you must press the string between the frets and add some pressure to keep it from buzzing...this further stretches the string. This stretch is typically compensated at the nut (although many instruments do not compensate there). On the banjo, the 2nd string is the one that is most affected by this. Stelling banjos (and some others) routinely use this.

Because the banjo produces a note which decays very quickly, it isn't exactly known for "perfect pitch". Electric guitars, with their nearly infinite sustain, need to be very closely compensated in order to keep the sound clean and pitch-perfect. You'll find most electrics have finely adjustable bridges.

Here's a good article on it: pjguitar.com/website/forums/ar...tion.html

steve davis - Posted - 07/22/2011:  17:31:07

My bridges are designed as if they had the electric guitar's adjustable saddle.

I always wanted one of those,I guess.

Edited by - steve davis on 07/22/2011 17:32:01

Bart Veerman - Posted - 07/22/2011:  19:22:54

Great replies to the "what." The why though - most modern banjos do not have an intonation problem but some do and compensated bridges are capable of fixing this problem if you have it. Keep in mind that generically compensated bridges seldom do the job 100% as intonation problems are always unique for each banjo and custom compensation is the way to go.

Bart.

uncle.fogey - Posted - 07/23/2011:  06:24:29

I agree with Bart.  All banjos are not created equal, and I recall a "brand name" entry level one I played at a music store a year ago that I could NOT get to play in tune despite a lot of fiddling with the bridge.

I have a bunch of banjos that I play every day and I don't have any intonation problems that require special compensation.  The generally fast note patterns and fast decay of the banjo make it hard to dwell on any single note for very long, PLUS experienced players will know their instrument and know if they have to watch out for some note in some song.  Most orchestral brass musicians know how to adjust their instrument so they can fix problems with their lip - if you think that banjos have intonation problems, try a tuba.  Orchestral string players deliberately go EVER so slightly sharp on certain notes, which they refer to as "brilliance". A slightly sharp note can add a little zing to some lines, whereas a flat note is just that - flat.

Back to Bart's excellent observation that it has to be done "custom" or individually based on the instrument and strings used, there's a Finnish custom electric guitar builder named Juha Roukangas, who makes pricey guitars with every fret compensated individually by a computerized method he has developed.  If you look at the instruments in this picture, which serves as a graphic representation of compensation, you will see that (1) they are not the same, (2) the amount of compensation changes and diminishes as you go up the fretboard  (3) they both have zero frets.  Too bad we can't see the bridge in the picture.

marshh - Posted - 07/23/2011:  07:26:19

marshh - Posted - 07/23/2011:  07:39:46

Recommend you google "just tuning" and "equal temperament". There is a lot to it, but once you understand it, you'll understand the basic physics that underlie dissonance in a fretted instrument and why some banjos use a compensated bridge (Stelling uses a compensated nut.)





It's a bit involved, but if you have a instrument tuned in "just" tuning to one key and the frets set accordingly, say in "C", it will play basically true all the way up the neck and for all notes, but if you try playing the instrument in another key you will have notable dissonance. Modern instruments "fudge" the physics and use "equal temperamant". This results in a fretted instrument that is "almost" true in all tunings, but a bit off in some cases (i.e. the dreaded 3rd string).

 

Edited by - marshh on 07/23/2011 07:50:12

uncle.fogey - Posted - 07/23/2011:  07:48:45

That's very true, and why violin players and fretless banjo players don't have the problems created by frets.  The equivalent in a brass instrument would be a trombone.

marshh - Posted - 07/23/2011:  07:54:54

Right on, Uncle F,  I was reading an article the other day that claimed most modern  fretless instrument players actually plays in tempered tuning.  It's what their ears are used to hearing, and sounds better with other modern instruments.

Richard Dress - Posted - 07/23/2011:  09:39:32

A lot of good info above but one element seems to be missing from the discussion, and that missing element is weight or mass of the bridge.  Generally speaking, more mass results in loss of tone/volume.  All the discussion has been on the upside of compensating a bridge and none on the downside.  

I used a moon bridge on both my raised head and flat head for thirty years (but I dropped them immediately as soon as the banjos fixed themselves and so I have changed back to a standard straight bridge).  The moon bridge designer told me he had to go for the best intonation with the smallest weight penalty.  Given these guidelines, the computer gave the moon shape as the solution.

In every real world problem there is a tradeoff.  Always look at the downside, if you can.  Are you losing tone/volume?  Does it matter to you?  Most of the old-timers stuck with their old bridges because they already had learned to compensate with their fingers and they didn't like the mass penalty of bridge compensation.  Bad news for Randy Stockwell's advertising efforts but that's life in the business world.

Which is best for you?  Everyone's preference is different, every bridge is different, and every banjo is different.  What works on one banjo probably sounds bad on the next banjo.  You have to experiment with Steve, Bart, and Randy's bridges and figure it out.  There is no other way, really, other than blind luck.  

With these modern computer-cut fingerboards the need for compensation has decreased.

rudy - Posted - 07/23/2011:  09:54:23

quote:

---

Originally posted by Bart Veerman



Great replies to the "what." The why though - most modern banjos do not have an intonation problem but some do and compensated bridges are capable of fixing this problem if you have it. Keep in mind that generically compensated bridges seldom do the job 100% as intonation problems are always unique for each banjo and custom compensation is the way to go.

Bart.

---

 Very elegantly stated, Bart.

Hat's off to the other posters here who all have very succinct and valuable comments regarding compensation, bridge mass, and equal temperament.  This topic serves as an excellent counter-point to the other current "compensation" topic,  "Does a capo affect intonation?"   All good reading.

Edited by - rudy on 07/23/2011 09:57:08

leemysliwiec - Posted - 07/23/2011:  11:19:52

Thanks, everyone.. I really appreciate the information given.  The question has been answered thoroughly....unless there is more info coming in.    The willingness for  members of the Hangout to share their knowledge and insights never ceases to amaze me.  

uncle.fogey - Posted - 07/23/2011:  13:01:13

quote:

---

Originally posted by Richard Dress

A lot of good info above but one element seems to be missing from the discussion, and that missing element is weight or mass of the bridge.  Generally speaking, more mass results in loss of tone/volume.  All the discussion has been on the upside of compensating a bridge and none on the downside.  

I used a moon bridge on both my raised head and flat head for thirty years (but I dropped them immediately as soon as the banjos fixed themselves and so I have changed back to a standard straight bridge).  The moon bridge designer told me he had to go for the best intonation with the smallest weight penalty.  Given these guidelines, the computer gave the moon shape as the solution.

In every real world problem there is a tradeoff.  Always look at the downside, if you can.  Are you losing tone/volume?  Does it matter to you?  Most of the old-timers stuck with their old bridges because they already had learned to compensate with their fingers and they didn't like the mass penalty of bridge compensation.  Bad news for Randy Stockwell's advertising efforts but that's life in the business world.

Which is best for you?  Everyone's preference is different, every bridge is different, and every banjo is different.  What works on one banjo probably sounds bad on the next banjo.  You have to experiment with Steve, Bart, and Randy's bridges and figure it out.  There is no other way, really, other than blind luck.  

With these modern computer-cut fingerboards the need for compensation has decreased.

---

I've heard this about moon bridges weighing a lot before, and I just don't get it. Is there someone out there who makes really heavy moon bridges?  I make moon bridges and they weigh exactly the same amount and regular straight bridges.  I can make them weigh as much or as little as I like.  There's absolutely no difference except that straight bridges are straight and moon bridges are curved.  Same thickness, same weight, same wood etc etc.

oldwoodchuckb - Posted - 07/23/2011:  13:13:04

Uncle fogey,

Absolutely agreed. The only "overweight" compensated bridges I've ever seen are the "Shubb/Grover Compensated" which are rather rough hewn. Moon Bridges are extremely efficient and pared down to the minimum to do the job. In fact I prefer the heavy Grover as it imparts a much darker sound than the Moons which sound like compensated versions of straight bridges to me.

I think someone has been reading too much banjo theory and has not spent any time trying things out for himself.

Edited by - oldwoodchuckb on 07/23/2011 13:17:27

Richard Dress - Posted - 07/23/2011:  15:18:55

The original Stockwell Moonbridge, I believe, came in two or three heights and light, medium, heavy weights.  That would give nine different weights.

The MB is curved along several axes to reduce weight, it's not a straight piece that has been bent.  Hey, OWC, I write banjo theory, I don't read it.  All I am doing is passing along what the inventor said about compensation/mass.  I didn't read it, I talked to him.  Just accept it, don't complain.

steve davis - Posted - 07/24/2011:  07:33:50

I've been curious about compensated banjo bridges ever since I noticed adjustable saddles on electric guitars.I'd look at a set up guitar and see that the strings were set at different lengths and wonder why my banjo bridge was straight across.
I soon realized that a mechanism like that attached to a banjo would destroy the acoustic tone with all that mass.

I've never approached the making of a compensated bridge from a desire to fix individual intonation problems in some banjos.

I was just curious about why electric guitars set their saddles crooked and wanted some way to do something like that for banjos.

I needed a jig or tool of some sort to let me change the string lengths and that turned out to simply be a 5/8 tall block of wood set where the bridge would normally be.
By drawing 5 lines spaced at 1 11/16 across the top of the little block,I had the string spacing for each string.

With lined block in place of a bridge and all 5 strings attached,I needed a way to control each string's location of contact on the line on the block...something moveable.
A paperclip would've worked,but I have a few pounds of "hog rings" that are used as fasteners in lobster trap construction,so I used one of those.By hooking the clip under a string I could slide the string's point of contact along its corresponding line on the block by sliding the hog ring along that line,changing the length of the string.

I have been setting the location of my bridges by comparing 12th fret fretted and harmonic notes for many years,so I went right to that procedure for locating each string's location on its line on the block.
I started with the 1st string and,with hog ring hooked between the string and block and in the middle of line 1 I tuned the string to pitch and checked the 12th fret F&H notes against themselves.
I found its fretted note to be sharp to the harmonic and slid the hog ring a bit toward the tailpiece,retuned the open note and compared at 12,again.

When the fretted/harmonic comparison both read 0 on the tuner,I made a mark where the hog ring contacted the block line.
Going through the same procedure for all the strings produced the pattern that I use for my bridges.

The banjo I used as a benchmark is my Jimmy Cox built tb2 conversion.
There is absolutely nothing wrong with construction of this Cox neck or the way it is attached to this pot.The frets are exactly where they are supposed to be and the scale length is the same as most any 5 string bluegrass banjo on the planet.
The only thing I wanted to deal with was the fine tuning of the straight bridge.
I figured this would be as good a banjo as I could get to design from.

This has never been about fixing some kind of construction anomally or problem.
It's also not about making 0 perfect notes everywhere on the neck,though it comes darn close to achieving that.

I just wanted to see how the banjo would perform if I could get all the notes zeroed at the 12th fret.
I was pleasantly surprised to find a few benefits such as:

No need to retune strings 1 thru 4 when capoing
Most fretted notes all over the neck to be 0 on the tuner.
The feel of the relationship of the notes in a given chord when those notes are in closer harmony with each other.Very powerful phenomenon,this closer harmony.

This isn't about builders not making well intonated banjos.It's only about the difference between my design and a straight bridge.

It's also not about putting down banjos with straight bridges.Those banjos work and sound good,too,but they can need to be adjusted at times where my doesn't.

I'm just naturally curious about stuff like this and feel driven to explore and figure stuff out.

Once I plotted the 5 string locations it became obvious that I had a new problem.The traditional placement of the 3 feet wouldn't be stable with the forward string load.
I remember thinking,"If I could turn those feet a little to counteract the load...maybe concentric with the pot would do it,so I carved one that way and it stood up fine.

uncle.fogey - Posted - 07/24/2011:  12:30:01

quote:

---

Originally posted by oldwoodchuckb

Uncle fogey,

Absolutely agreed. The only "overweight" compensated bridges I've ever seen are the "Shubb/Grover Compensated" which are rather rough hewn. Moon Bridges are extremely efficient and pared down to the minimum to do the job. In fact I prefer the heavy Grover as it imparts a much darker sound than the Moons which sound like compensated versions of straight bridges to me.

I think someone has been reading too much banjo theory and has not spent any time trying things out for himself.

---

Thanks for clarifying that, Tony.  I've heard that before, and wondered what it was about.  I have seen those Grover bridges that go back-and-forth as if they have hiccups. I once thought they were a "kit" meant to be filed down. I also agree with your idea that a slightly heavier bridge is "darker".  Darker is not a bad thing, especially on really snappy banjos - I used to err on the side of too light, and now if I'm wrong, it's on the side of too heavy, but the red maple retainss all the complexity.

I am now using a slightly heavier moon bridge than I normally make on my old archtop Granada, which tends to be very bright and cutting with lighter bridges, and the heavier bridge seems to make the sound of that banjo darker and better to my ear without taking anything away - it ADDS something, I think.

Also, I think making a slightly heavier bridge (3 grams M/L) from maple is different than making a lighter bridge from walnut or cherry - they mellow the sound for sure, but you give something up.  With a maple bridge that's a little heavier, you get more.

If you ever want a heavier than normal moon bridge, let me know.

Ken

steve davis - Posted - 07/24/2011:  12:37:38

When I make my compensated bridge for clawhammer players,they like a 2.7 gram maple/ebony.

oldwoodchuckb - Posted - 07/24/2011:  12:58:40

Just accept it? Accept It ? Sorry Richard but your BS to reality ratio says I can't accept anything you say that isn't on the cover of Banjo Theory Magazine. I can tell you don't read any banjo theory along with a lot of other stuff. And your attempts to double down whenever someone hits you with a fact is simply classic Internet BS Theory. You reached the PH&D (Piled Higher & Deeper) level quite some time ago.

Edited by - oldwoodchuckb on 07/24/2011 13:11:01