Case Studies

Case Study - Webber Roundbody Guitar

This a guitar setup on a high-quality handmade guitar built by David Webber, of North Vancouver BC.  I was not in as much of a rush to work on this guitar, because its intonation was much better than the most guitars.  The guitar has a beautiful, full and balanced sound.

The guitar was originally set up for medium strings; the new setup is with Martin light/medium strings: .0125–.055, exactly between lights and mediums.

I made all of the pitch measurements using the Seventh String Tuner.

The bridge saddle is .122 thick (just under 1/8”).  The strings rested on a ridge along the edge of the saddle, in a straight line, with no individual string compensation.

As I have mentioned, on acoustic guitars we tend to play a lot at the lower end of the fretboard, so nut compensation is far more important than saddle compensation.  But, we often tend to cut too much slack for bridge saddle intonation.  Accomplished players deserve better; good players are doing high leads; swing players are doing full closed chords typically up to the 10^th fret or higher, etc.

At this time, I decided to do the full meal deal on the saddle.  As I do not have the means to cut a wider groove in the bridge (without destroying the guitar) I decided to make a new bridge saddle of the same thickness as the original, and add material to accommodate the intonation needs, similar to adding shelf material to the nut.  It's a shelf-saddle!

A problem with the original bridge saddle was that the 1^st and 3^rd strings were overcompensated (they played flat by 4 cents and 8 cents, respectively, at the 14^th fret) so material needed to be added to the new saddle, toward the nut.  Another problem was that the 4^th, 5^th and 6^th strings were under-compensated (played sharp by 3, 5.5, and 13.5 cents, respectively).  There was plenty of material to compensate the 4^th and 5^th strings, but the 6^th string needed to be faceted close to the back edge of the saddle.  I added a piece of bone to the saddle to provide a smooth curve for the 6^th string to follow, from the bridge pin up over the saddle, rather than a ski-jump with an abrupt edge.

It's important to notice that, in this case, the need for more bridge saddle thickness was not caused by compensation comparing fret 14 to fret 2, instead of open, or by compensating the nut.  The nut compensation actually reduced the amount of adjustment needed at the saddle for the 1st, 3rd, and 6th strings!

The nut was originally positioned forward of the standard calculated position, sufficiently to compensate the 2^nd and 5^th strings pretty well.  That left the 6^th string somewhat under-compensated, and the 1^st, 3^rd, and 4^th strings slightly over-compensated. 

Compensation was accomplished, using the original nut, by adding a partial shelf for the 6^th string, and faceting back at the 1^st, 3^rd, and 4^th strings.

Doing this guitar setup was tedious, but the result was well worth it! The guitar really sings!

Most readers looking at these photos, and comparing them to their own acoustic guitars, will probably be amazed at how much compensation is needed to really achieve equal temperament!  While almost all guitars show some amount of compensation measures, I think, especially for acoustic guitars, the usual standards are insufficient for serious players, and should be raised.

Case Study - Roberto Acha Geronimo Classical Guitar

This guitar was built by Roberto for a contest in Paracho; it won third place.  Lightly braced and slightly arched, it has a gorgeous, pleasing sound - and it's quite loud!  It has Paloescrito sides and back, with Canadian cedar top.  

It sounds really great with the compensated nut.  It was built with the nut slightly forward of design position, so the nut needed to be faceted back about .020" (.5mm) at the 4th, and just a bit at the 5th.  I was also able to improve the intonation at the bridge saddle; I was able to facet the original saddle, and still have enough height. Action at the nut is .013" - .018; at the 12 th fret is .120 - .114"

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