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Compensated Bridges

PostPosted: Mon Nov 13, 2017 12:37 pm
by Bob Gerard
I am wondering why some Mountain Dulcimer Fretboards are designed/cut for non-compensated Bridges (Bridge/Saddle) while others are not? It seems that other fretted instruments (Guitars, Ukes, Mandolins) are almost always compensated.
I am leaning toward 'floating bridges' to make this accommodation without making a permanently compensated bridge.
Your thoughts would be very much appreciated!

Re: Compensated Bridges

PostPosted: Mon Nov 13, 2017 7:29 pm
by GrantOlson
My guess is maybe a compensated bridge is hard. Compensation vs. floating are two different concepts. Compensation is where you adjust the intonation of each string relative to the others. A floating bridge allows you to move the bridge, which would change the intonation of every string. It is my opinion that a floating bridge is a good idea, the idea being that you can adjust it whenever it is needed, such as a sudden humidity change. (Though that's not good for the instrument anyway.)
Grant

Re: Compensated Bridges

PostPosted: Tue Nov 14, 2017 12:09 am
by dholeton
Bob
I think the string sizes, wound and unwound strings, fret size (height), and bridge/saddle height are factors. I used a tuner to check each fret on a dulcimer that I built and keep tuned DAA (28.5 inch VSL). All strings were perfect at the 7th fret. The .021 wound bass string was very close on all frets. The .014 middle string started going a few cents flat above the 10th fret. The .012 melody strings started going a cent or two flat at the eighth fret and progressively went more flat through the 17th fret.

I keep my McSpadden dulcimer tuned DAd (28.5 inch VSL) with .021 wound bass string, .012 middle string, and .012 melody strings. All strings are real close to the expected pitch at all frets.

My scheitholt has a 27 5/8 inch VSL and I keep the .012 melody strings tuned to G, the .014 middle string tuned to G, and the .021 wound bass tuned to C. It has 15 frets and all strings are real close to the expected pitch at all frets.

All three instruments have a 0 fret.

So, some possibilities might be the differences in the ages of the strings (I don't remember when I changed the strings on the DAA dulcimer but the McSpadden strings were replaced a couple of months ago and the scheitholt was completed in May). It's also possible the DAA dulcimer is lower at the bridge/saddle than the DAd dulcimer (or the melody and middle strings are lower than the bass at the bridge/saddle). Since I built the DAA dulcimer and I tried to use the fret spacing from the McSpadden dulcimer, I might have a fret placement error, but I'm thinking new strings or bridge/saddle height or distance adjustment might improve the DAA dulcimer above the 7th fret. I'll see what happens when I change strings.

Dave

Re: Compensated Bridges

PostPosted: Tue Nov 14, 2017 11:22 am
by Robin the Busker
Old dulcimers didn't need compensated bridges because only the melody string was fretted - the VSL of the drone strings makes not a jot of difference. From my experience most modern dulcimers don't need compensated bridges, just bridges set to the right VSL (a 1/4" or so longer than double the distance to the 12th fret, to allow for string stretch). If you can hear an issue then its the middle string in DAd that tends to be the 'problem' child, particularly if it is a thicker plain steel string than the melody strings. Most often, this string has a tendency to pull sharp more than the thinner melody strings when fretted higher up the fretboard. So a little compensation is often used to lengthen the VSL of the middle string slightly. The bass string often actually has the same core diameter as the melody strings and so tends to pull sharp at roughly the same rate.

If you set everything with an electronic tuner (tuning and compensation) - there's a good chance you'll still have chords that are 'out of tune'. And that's just the nature of any fretted instrument I'm afraid. You find that even on a dulcimer with perfect frets, perfect VSL intonation and perfect individual string compensation a player will 'tweek' the tuning to get the instrument sounding right for any particular tune or key they are playing.

Different players will want different intonations too. I use an equal temperament and sometimes compensated dulcimer to play from DAd but the same instrument drives me mad in DAA because the notes are not perfect (equal temperament is a compromise tuning NOT an accurate tuning).

So the bottom line is that you have to go with the best compromise you can get but don't think that because your electronic tuner tells you everything is in tune that it will actually sound in tune :lol:

Robin

Re: Compensated Bridges

PostPosted: Tue Nov 14, 2017 11:25 am
by strumelia
I've replied to this on the other site where you created the same discussion. 8) It's sometimes confusing to keep up with two threads with identical topics on two sites, especially when one is a member of both.

Re: Compensated Bridges

PostPosted: Tue Nov 14, 2017 2:23 pm
by Jon
Compensation depends on the planned tuning. A DAA tuning. requires that the D VSL be longer than the three A VSLs' This can be done (approximately) by using a 1/4 inch thick saddle and placing the contact point of the A strings at the front of the saddle and the D at the back. A Dad tuning requires teat the saddle rotated by ~2ยบ. I believe Richard Toughear did a pice o a mechanically compensated bridge. A search on compensated bridges turned up 181 listings-I didn't have time to go through them all.

Re: Compensated Bridges

PostPosted: Tue Nov 14, 2017 6:01 pm
by Bob Gerard
There has been so much information shared here (and on another dulcimer group site) and its great to get be able to learn from so many generous and talented folks on this subject.
Lots to take in and experiment with, and I really appreciate everyone's insights, knowledge and experiences. My personal preference is DDGd. I wonder how much more of an issue that is!