Compensating Bridge

Guest · Post by **Guest** » 5 May 2003 3:15 pm

Guitar players are familiar with compensating bridges, where the bridge is either angled or strings are individually adjustable to provide accurate tuning at all frets. I never understood the physics of why this was needed, but it seems to be an established fact.

I figured that compensating bridges didn't exist on steel guitars just because it was probably to difficult to do, not because it wasn't a good idea. But now I see that Excel steel guitars do provide a changer where the position of each finger can be adjusted forward or backward to compensate for string width. This seems like genius to me, can anybody confirm that what I'm seeing is correct?

C Dixon · Post by **C Dixon** » 5 May 2003 4:56 pm

I own an Excel PSG and I am not aware of a compensating bridge. Could it be you are mistaking the way this changer works with a compensating bridge?

IE, the Excel and the Anapeg has a changer that does not change pitch by bending the string back and forth. Rather it stretches and relaxes the string in an almost straight line.

Incidently, the reason regular guitars often have a bridge that is adjustable is to counteract the tendency of a string or strings to increase in pitch as the string is pushed down on the fret board. This is not the case on a steel since the bar is straight. And under most circumstances, exerts even pressure on all (picked) strings. Thus no need to compensate the bridge.

carl

Guest · Post by **Guest** » 5 May 2003 5:06 pm

Carl, I believe you may be right about my misunderstanding what I saw. Could you tell me more about how the Excel changer works? It sounds totally different from other changers.

Donny Hinson · Post by **Donny Hinson** » 5 May 2003 6:17 pm

Basically, it works just like Carl said. When a string is raised, it gets stretched by moving the bridge (instead of just "rolling the bridge). Same thing (in reverse) when a string is lowered, the bridge doesn't "roll", but it moves closer to the nut, relaxing the string. Ergo, any time a change is made, the string length (as well as the tension) changes. On most other pedal steels, the string length is a constant, and only the tension changes. I think the jury is still out as to whether it's a better system, or not. Logic would indicate that the changing string lengths might cause a problem as far as chordal intonation. Too few players here have one to get enough data to form a conclusion.

Guest · Post by **Guest** » 5 May 2003 6:47 pm

Thanks, Donny. Now I understand. It seems that the steel has a "dynamic scale".

My guess is that the change in the length of the string is small enough not to be very noticable, but I wonder what the advantages of such a system are?

C Dixon · Post by **C Dixon** » 5 May 2003 8:20 pm

A bit more on the saga.

I was sooooo very concerned about intonation problems on this type of changer, that I became a real bore (I imagine) with Tom Brumley and Bill Stafford over it; BEFORE I would place an order for one. Note: Tom bought the Anapeg and Bill bought the Excel. Both have this basic type of changer.

I talked to each of them at length about it. They both said over and over they could NOT hear any intonation errors. When I considered that both these players are among the greats; and have ears to die for; I was 95% convinced. But I still had Bill do some experiments for me over the phone just to see if there could be ANY intonation measured using harmonics. Such was NOT the case.

After I received my guitar, I was still somewhat worried. But so far after 3 yrs, whatever intonation problems there might be, I simply cannot hear it. And since things like cabinet drop and hysterisis drives me nuts, I do believe I WOULD hear it, IF there was any. But I don't.

As I have thought about it many times, there might be a legitimate reason for it. It could be that as a string is pulled (or loosened), it just might need some compensation to actually aid in intonation.

IF this is true, the changer moving instead of pivoting would accomplish this compensation automatically; and explain why neither Bill, Tom or any one that I know of (including me) has heard any intonation problems on these unique PSG's.

But the cherry on the Christmas pie is the fact that because these changers do NOT bend the string back and forth (to change pitch), they simply do NOT break strings. And that is a big plus in my book.

Praise Jesus,

carl

Stephen Gambrell · Post by **Stephen Gambrell** » 5 May 2003 9:47 pm

Brother Carl, the reason a 6-string guitar has a compensating bridge(or nut)is because of the different diameters of the strings, NOT because the strings are being depressed to the fingerboard. Judging from the low action I've seen on some guitars, the weight of a steel bar depresses the string much more than a finger. And if the depression of a string WERE the reason for the adjustable intonation, wouldn't the guitar need to be tuned at each fret, rather than open? And would the intonation be set up differently than it is?(The twelfth fret harmonic vs. the 12th fret fretted note?)

Guest · Post by **Guest** » 6 May 2003 3:35 am

Just so you all know, here's the picture that caught my interest:

from the site www.fuzzypsg.com

Sure looks like each finger can be individually adjusted for compensation. Carl, I sure apprecate your comments. I guess the folks at excel really know what they are doing. Looks like a really excellent steel guitar.

Jim Smith · Post by **Jim Smith** » 6 May 2003 5:08 am

Stephen, that picture is of the keyless tuner at the nut end, not the bridge.

The arms you see that are at different lengths are the tuners themselves. Just above them are the roller nuts, which are fixed.

Guest · Post by **Guest** » 6 May 2003 5:49 am

ha ha ha! yep, I sure know my steel guitars! Well, I never have seen a keyless in person. In the meantime, I also saw this picture of what appears to be a 16th century steel guitar.

Anybody have any experience with these?

David Doggett · Post by **David Doggett** » 6 May 2003 5:59 am

Stephen, seems like you and Carl are both right (Carl is almost always right I have found). Because of their different diameters the wound and unwound strings on a guitar will travel different distances to reach the fret board when fretted. Also, the wound strings stretch more and change pitch less (that's why a wound 6th string requires more bell crank travel on a pedal steel). The compensation at the saddle helps correct for these string differences.

On the Anapeg and Excel, maybe tuning the pedal and knee stops takes care of the pitch changes caused by the moving bridge. It's hard to imagine how this stays constant all up and down the neck, but if it works, it works. Carl, how does everything else play with yours?

David Mason · Post by **David Mason** » 6 May 2003 6:02 am

There's an Excel over on ebay at a pretty good price right now, I just don't have a spare $1600 lying around this week.

John Kavanagh · Post by **John Kavanagh** » 6 May 2003 6:07 am

The instrument in question would appear to be an 11-course Baroque lute, which are usually tuned Cc Dd Ee Ff Gg AA dd ff aa d' f', though there are some variations. I've only played a 10-course Rennaisance lute, and I own one with 8 course. For some reason I've never tried it with a bar. Might not work well on low-tension gut strings, but the d minor tuning would be interesting.

It looks keyless because the peghead is angled back at almost 90°, either to increase tension at the string break or to
save a little space in those crowded minstrel's galleries... [This message was edited by John Kavanagh on 14 May 2003 at 10:25 AM.]

David L. Donald · Post by **David L. Donald** » 6 May 2003 6:46 am

I was handed a similar lute at a Renaisance festival to play with. I jammed ancient muqisque for about an hour with a recorder and Nickleharp.
As weird a combination as I have ever played with except dijerido, uprightbass, maracas and clarinet.

Very nice instruments, wish I had one. Some where between a guitar and a mandolin, and yet very different. Never tried a slide on it, but it could be interesting.

But nothing close to a compensating bridge.
Except that on some the frets are gut and movable to create intonation differences at every note if you want.[This message was edited by David L. Donald on 06 May 2003 at 07:48 AM.]

Guest · Post by **Guest** » 6 May 2003 6:48 am

But, can you play Steel Guitar Rag on it?

ed packard · Post by **ed packard** » 6 May 2003 7:26 am

RE staggered bridges on standard guitars, ..ask two luthiers and get three answers as to why. the nut end is usually grooved so as to make the distance from the bottom of the string to the fret approximately a constant value, .. on good instruments the frets are so low and constant that they are a non issue, ..so much for deflection differences. On the old jazz arch tops (pre amplifiers) the strings were up a good bit from the fret board so as not to buzz when attacked "with great vigor" by a tortoise shell pick, hence some conpensation for deflection induced pitch change was desireable. More modern reasons are given as related to the "beat" issue that is associated with getting the 3rds etc in tune, ..when you tune for an open C chord, you are out in an open E chord.

On the PSG: The previous problem exists when you tune beats out using one string as a root reference and then use another string as the root of the chord. This is not noticable if the two root strings are related as a root and 5th, but just use the 3rd as a root string and be prepared to be annoyed. In as much as the E9 and C6 don't have G# and E rooted chords played in the open position with no bar motion, or as harmonics, this is not usually a noticed problem for the beats out pickers.

On a 24&1/4" scale, the distance from the nut to the 1st fret is 1.354". This is a one halftone step. One cent of this would be (averaged) 0.0135", two cents would be 0.0270", three cents would be 0.0405" etc..So harmonic locations with a soft finger would not be noticably affected by as much as 0.100 or more inches of string length difference. These values per cent are half at the 12th fret, and one fourth at the the 24th fret, ..you my friends, are just not that accurate in you bar placement except by ear adjustment and slow music.

The basic difference in string length with the Excel and Anapeg changers are tuned out as you tune each change with the changer activated. If you played with the last little bit of string length (very short string length) the effect would be more of a problem because the ratios of length between the strings would be greater, ..such is not the case as most players don't get into the strings third octave (last quarter of the string). Chord style playing is more sensitive to the length, and tuning issues than the two string styles. Slow is more sensitive than the "gatling gun" style.

C Dixon · Post by **C Dixon** » 6 May 2003 1:50 pm

"Brother Carl, the reason a 6-string guitar has a compensating bridge(or nut)is because of the different diameters of the strings, NOT because the strings are being depressed to the fingerboard

We will respecfully disagree brother

The poster is correct concerning the picture of the Excel keyless. That is the nut end of the Excel SuperB model. Mine is not like this. Here is why. I never cared for the chopped off look of keyless PSG's. So I had mitsuo make the guitar JUST as long as a keyed guitar.

Together, he and I came up with a nice keyless head design that is quite esthetically appealing (IMO). IE, it looks great and leaves a nice "surround" area for my picks and bar.

Incidently I just receieved my old keyless head back from Mitsuo. He made me a new one that incorporates his proprietary "counterforce" mod to eliminate cabinet drop. I will be putting it on a bit later. I can't wait.

"There's an Excel over on ebay at a pretty good price right now, I just don't have a spare $1600 lying around this week."

That is not a SuperB model. That is his older model that incorporates the standard type changer.

"On the Anapeg and Excel, maybe tuning the pedal and knee stops takes care of the pitch changes caused by the moving bridge. It's hard to imagine how this stays constant all up and down the neck, but if it works, it works. Carl, how does everything else play with yours?"

Well to my ears, and the ears of Tom Brumley and Bill Stafford to name just 3, it does stay constant. I do NOT have an authoritative answer as to how or why. Just know that I cannot hear one semblance of intonation problem ANYwhere on the neck. Maybe someday, someone will tell us why this is.

Finally, with the exception of string rattle, EVERYthing else plays fine. Of course, as I said in another thread, I have struck out on four different brand new PSG's when it comes to the strings NOT being flat at the nut rollers. It has turned into my NUMBER 1 pet peave when it comes to our beloved instrument.

I gotsa danged mad over it, I told my wife,

"The second thing I'm gonna do when I become presidink of thie hyar yuuuu nited states; is to make it a fedral law against any manufacturer building a petal steel git' tar that has string rattle at the first few frets!!"

God bless you all,

carl

Donny Hinson · Post by **Donny Hinson** » 6 May 2003 4:05 pm

But I still had Bill do some experiments for me over the phone just to see if there could be ANY intonation measured using harmonics. Such was NOT the case.

If they were "open string" harmonics, you wouldn't notice any intonation problems created by differing string lengths. Remember, open string harmonics are governed by the open string note, and not the string length. A 12th fret harmonic is the "open note", just an octave higher. As an example, a 12th fret "E" harmonic on a 22" scale guitar would be identical to a 12th fret "E" harmonic on a 24" scale guitar. Big difference in string length, but the notes would still be the same.

As to why you don't notice any intonation problems with this type of changer, look at it this way. The bar is merely a mobile "nut", able to move up and down the neck. The additional (or reduced) string length of any given string is exactly the same, regardless of where the bar is placed.

However, there is one circumstance where I believe you would notice an "intonation problem" with this type of changer, and that is if you were playing behind the bar! On rare occasions, this is done as a special effect. To see if I am right, tune several pedaled strings JI (beatless), and then place the bar at the 12th fret. Now, playing behind the bar should show a definite intonation problem, due to the fact that the string length behind the bar will be different (for some strings) that the string length in front of the bar.

This doesn't turn out to be a big deal, though. As far as I know, only one hit song ("Tippy-Toeing", by The Hardin Trio) used this effect.

C Dixon · Post by **C Dixon** » 6 May 2003 5:38 pm

You CAN indeed use harmonics to determine an intonation problem on a PSG.

Here is why. IF the scale with NO pulls is exactly 25 and 1/2" (which mine is), then you should have a pure harmonic exactly at 12 and 3/4". NOW if you engage lets say the A pedal and the changer moves so that the string's length is exactly 25 and 5/8", THEN the harmonic should be NO longer at 13 and 5/8". But more to the right of 12 and 5/8".

As Bill and I found out, the harmonic did NOT seem to shift. I do NOT know why. All I know is, I can hear a cabinet drop soo slight as to be barely detectable, yet I have never knowingly heard any intonation problems on this guitar. Which I am thankful for since it would negate the incredible value of this unique changer.

carl

Guest · Post by **Guest** » 6 May 2003 6:46 pm

Carl, just how much does the changer move in a raise or lower? Can it be measured? It probably doesn't change the scale to any significant exent, am I right?

ed packard · Post by **ed packard** » 7 May 2003 7:02 am

CD: Your assumed numbers re 12th fret harmonics make your case but; the assumption is that to get the 12th fret harmonics (yes, that is plural), you must "block" exactly at one half of the string length, ..not so. First you r finger is not infinitely thin, ..second the string is a resonant member with a high Q, hence it will respond to "in the vicinity" excitations. Using my little finger, I can get an very acceptable "harmonic" sound 1/4" either side of the 12th fret (25" scale here). This allows for a large difference in string length and still get the sound.

What happens when you block at half the string length is that you kill (or substantially reduce) the first harmonic (fundamental) of the open string. You also kill (or substantially reduce) all the odd harmonics in the string because they also had a maxima of excursion at the half string length. The odd harmonics are left to ring out, and the evens begin to sneak back in as the vibration decreases. To get the most out of the 12th fret (half string length) harmonic(s) pluck (excite) the string at the 24th fret(quarter string length).

Measurement of the amount of Anapeg/Excel string length change may be difficult as one cannot see exactly where the string contacts the moving member as it moves. The same may be said for the rotary changer, ..we really don't know where the string touches the round top of the finger, ..a constant tangency point is "assumed". The larger the finger top diameter, the less accurate the knowledge.

Donny Hinson · Post by **Donny Hinson** » 7 May 2003 7:17 am

I meant no disrespect to Carl, he is a very knowledgeable fellow,

and what he say is true, in theory. However, as Ed pointed out, a harmonic "chime" will yeild the same note even if your finger placement isn't "perfect". (It's no where near as critical as bar placement.)

As for myself, I get a very acceptable 12th fret harmonic...even if my finger placement is off by 1/2 fret either way.

Bobby Lee · Post by **Bobby Lee** » 7 May 2003 10:00 am

Carl, just how much does the changer move in a raise or lower? Can it be measured? It probably doesn't change the scale to any significant exent, am I right?

I suspect that you're correct, Stephen. Recently I had to set up the bridge on my Variax guitar. I was surprised by how much the pitch of each string changed with very small adjustments to the bridge.

In theory, the scale length is changing, but in practice the amount that it changes is very small. On the guitar, a slight turn of the adjustment screw raises the pitch a full step or more, but the 12 fret note only changes by a cent or two.

------------------
<img align=right src="http://b0b.com/b0b.gif" width="64" height="64">Bobby Lee - email: quasar@b0b.com - gigs - CDs
Sierra Session 12 (E9), Williams 400X (Emaj9, D6), Sierra Olympic 12 (C6add9), Sierra Laptop 8 (D13), Fender Stringmaster (E13, A6),
Roland Handsonic, Line 6 Variax

Stephen Gambrell · Post by **Stephen Gambrell** » 7 May 2003 11:43 am

This is beginning to turn into one of those "tuning" things, isn't it. Here's a question: Can ANY fretted(or fingered, or barred) stringed instrument play a chord in tune, and then, WITHOUT RETUNING, change chords, and remain in tune? Single note lines
don't count, of course, since they're at the mercy of our ears. I've never seen a guitar that can do it, and I doubt I ever will.

C Dixon · Post by **C Dixon** » 7 May 2003 12:24 pm

"quote:
--------------------------------------------------------------------------------
Carl, just how much does the changer move in a raise or lower? Can it be measured? It probably doesn't change the scale to any significant exent, am I right?
--------------------------------------------------------------------------------"

high G# to A; about an 1/8"

high E to F#; a little more than an 1/8"

D# to C#; just under 3/16"

high E (4th string) E to C#; about 3/16"

All the rest that I can think of are less than the above. Since I no longer pull the first sting to a G# (I will later), I imagine it would have the longest travel, not sure.

carl