Dumb first build question: Compensated bridges and scale lengths

[Sean Rush]

If I put on one of the bridges like on a regular acoustic, where do I put it?

I'm all fretted up for a 25.5 scale length, but where does that 25.5 mark lay? Logic tells me the inside edge of dead center, but I wanted to make sure.

[DeltaglowBoy]

measure 25.5 inches from where the strings first touch the nut.

or

12 3/4 inches from the 12 fret

 

[Sean Rush]

Maybe I should have clarified. I know I measure 25.5 from the nut, but when using a compensated bridge, where on the bridge should the 25.5 mark be, nothing I can find is very clear since it has a slant.

[Skeesix]

I measured a couple of my "real" guitars and it appears to be the longest string, i.e. the low E string.

Measure from the side of the nut closest to the first fret.

[ChickenboneJohn]

On a 25.5"  scale, that is the shortest distance your bridge should be placed at, ie the point at which the treble string goes over the saddle..in reality you'll need to add a little compensation to that...and a little more to the bass strings..hence the typical slanted or staggered saddles you'll see on 6 strings.

For a 25.5" the ACTUAL placement of the treble needs to be at 25.59" and the bass at 25.72" according to the StewMac fret position calculator. but bear in mind that's for a 6 string,  so your bass string on a 3 or 4 string probably won't need that much compensation, but it all does depend on the string gauges and the action.

Skeesix..either you are measuring wrong or both those guitars have been built wrongly!! The bass strings should usually be a little longer than double the "nut to 12th fret " distance. 

[Sean Rush]

Thanky. It's going to be a three string tuned either ADF# with the 5, 4, 3 strings or DF#A with the 4, 3, and 2. Probably the former. I guess I definitely need to decide that before putting the bridge on.

Can you link me to Stewart MacDonald's info about this?

[Skeesix]

CBJ,

Hmmm maybe my measuring tape is off a bit  or something as I was measuring a Fender and a Gibson. Now that I think further about it, when I've built guitars, I've made the treble E, the 25.5 or 24.75 and then the bass gets compensated longer like you said.

When building a three string CBG, I actually go by a tuner, so I don't know what the exact length is. First I put the bridge under the strings at 24.75 without gluing, and tune it up to pitch. Then I make the note fretted at the 12th fret, the same as the 12th fret harmonic. When those match up, then the string is compensated correctly.

Then I mark the position of the bridge and glue it on.

If you're using a one piece bridge, one of the strings (I think it's the middle one for a 3 string) may be slightly off, but overall it's going to sound way better than an uncompensated bridge.

[Ron "Oily" Sprague]

Sean,

http://www.stewmac.com/FretCalculator

[Rand Moore]

Hi Sean,

I always use a movable (aka "floating") bridge and then use my digital tuner to help me find the "optimal" tilt (compensation) for the bridge. To do this, first locate the bridge exactly to 25.5" (in your case) and perpendicular to all three strings. First we'll need adjust for optimal compensation on the first (thinnest) string. So, using the digital tuner, check the open string 1 note, and check the string again with the 12th fret stopped. It should be exactly the same note, just with an octave difference. Most likely these two notes won't be the same, so you will have to move the bridge (usually) out a few millimeters and re-tune the two strings again. Repeat this until you get the open string and octave (12th fret) tuned "spot on" to the same note (with an octave separation), Sometimes, you can't get it spot on, so try to average it out the best you can. Once you have found the optimal bridge location for string 1, mark the soundboard with a pencil where the treble side of the bridge should go. Then repeat the above procedure with string 2, trying to get the open string 2 and its octave (stopped at 12th fret) tuned to the same note (with an octave separation). Then with the third string repeat this process once again. Be sure to mark the bass side of the bridge on the sound board (in pencil). These pencil marks will help you relocate the bridge should it move on you. String tension should be enough to hold it in place most of the time, but maybe you have kids;-) Anyways, usually you will notice a slight slant to the bridge with the base string side a mm or two longer than the treble side. But as compared to six string guitars, the slant of the bridge on a 3-stringer will not as extreme because the string diameters are not that different. This process takes some practice, and I usually don't bother until a couple days after stringing up the guitar so the strings will have some time to settle in.

Because I build mostly stick dulcimers (aka strum sticks, strummers, pick'n sticks, etc.), I usually use the above process on diatonically fretted instruments where the octave is on fret 7 instead of fret 12 (some people call the octave "fret 8" and this occurs with folks who call fret "six and a half" (aka "fret 6.5") "fret 7"). Anyways, what I have noticed is that all I really need to do is to adjust compensation on string 1 since I usually just play strings 2 and 3 as drones (strummed open string). So, in my opinion, it's not really necessary to compensate strings 2 and 3 on a dulcimer (stick or mountain) unless you also play "up the neck" on strings 2 and 3. I don't play this way, so these days I usually just adjust for compensation on string 1. But on chromatic 4-stringers (and more strings), I do go ahead and try to compensate all strings for better intonation up and down the neck.

If my explanation is not clear, just ask me for a clarification.

-Rand.

[Troy]

hey guys, how would you measure a rod piezo installation if im placing it under the bridge, I'm concerned about drilling a hole in the box in the wrong location?

[Rand Moore]

The proper location for a rod piezo is under the base of the bridge (or in the saddle). So align the rod with the length of hardwood wood that you plan to use as your bridge and carve out a channel in the base (where the bridge will sit on the sound board) and tack the piezo in place with some hot glue. Other people build their bridges as a wooden saddle and a bone bridge, in which case the rod piezo would be placed in line with the groove in the saddle under the bone bridge. This will add some height to the bridge, so you may want to file or sand of the bone off the base of the saddle to compensate, You may also need to trim the rod piezo, especially if building a 3 or 4 string CBG. I assume you cut off the excess from the end of the piezo that does NOT have wires attached. I have not actually built with rod piezos, but they interest me and have read about them elsewhere on CBN and the Internet. You can uses CBN's search feature and search on "rod piezo" for more information. Or, Google it.

-Rand.

[Troy]

Thanks Rand