The Buzz Feiten System certified installers do partial nut compensation by moving the nut forward by a specified amount, and then using one of their patented Feiten pitch offsets to tune the open strings. Then they set the saddle intonation (also using the BTFS pitch offsets).
Moving the nut forward consists in either trimming the end of the fretboard, or using a Feiten-manufactured shelfnut. The distance that the nut is moved forward is specific to each of the different guitar types, and for each, there is a corresponding tuning offset chart, and usually an alternative chart, which will produce a slightly different character of sound, or which works better for different chord structures.
It appears to me that the amount of offset is based on about what is needed for the largest unwound string (for the type of guitar) to be in tune. The shelf nut is straight across, apparently with no provision for intonating individual strings. Instead, the prescribed tuning offsets are applied.
My understanding is that the offsets serve, at least in part, to make up for the strings not being compensated individually at the nut. The Feiten offsets also are used to "sweeten" by making third intervals less sharp, particularly between the third and second string.
The Feiten system requires moving the saddle intonation back a slight amount. This can be problematic, because acoustic guitar saddles are quite thin, hopefully about .125", but often .010 or even less – usually not quite enough to accommodate accurate intonation of all the strings. Because of that, the Feiten literature speaks of sometimes needing to fill and re-route the saddle slot on acoustic guitars. That could be expensive. (Wouldn’t it be much easier to widen the slot and install a wider saddle?) (However, if you have understood the basic lessons of this site, you will know that the saddle is best set independently of the open strings and nut.)
Electric guitars with locking nut also present a problem. They are difficult to move, some more than others.
Although you can tune a guitar with the Feiten system manually, you would normally use a tuner with the built-in Feiten tuning mode.
Some manufacturers are incorporating the Feiten System in new guitars. The reasons are that they would like to capitalize on the heavily advertised Feiten name, and that, after changing the nut and saddle positioning, there is no additional per-unit manufacturing cost, other than the Feiten license fee.
Earvana Nut System
Earvana offers a nut with an adjustable top. The bottom piece fits into the original nut slot and is filed/sanded until its top is level with the fretboard. The thin top piece contains precut grooves (or not) and is attached by two screws to the bottom piece. You can adjust it by loosening the screws and sliding it forward or backward.
There are also one-piece Earvana nuts, block-shaped, with tiny bore holes for the offsets (they look like bore holes, but they are probably molded or CNC’ed, whatever).
The principle seems OK, but the offsets don’t make sense to me, being dissimilar to the offsets that I and others have found for nut compensation for equal temperament. (Offsets for string 2 and 3 seem much exaggerated, and 5 and 6 are receding, instead of increasing. Also way too much compensation on the wound 3rd on an acoustic guitar.)
There seems to be some conflicting information on their site. on the Earvana Technology page, The tuning chart shows almost perfect equal temperament, yet in the text below the chart, they are at least strongly implying that they are using "stretch tuning" similar to pianos.
Earvana recommends expert installation, but, from what I see on the web, these nuts are often being sold to players without providing much direction for adjusting the saddle in relation to the compensated nut. In instructions and demo videos, they say to adjust the saddle intonation, using the open string (or 12th fret harmonic) as reference, before applying the Earvana nut. It doesn't make much sense to use a reference that the Earvana nut is about to change!
There are complaints that the plastic adjustable nut tops wear out. Some complain that the strings buzz on the plastic nut tops, but that might be because the installer didn't file the string slots at enough of an angle.
The Earvana nuts do seem to be quite popular, though, and they get good reviews (on Harmony Central, for instance). Both Earvana and Feiten benefit from the fact that alternatives are not well known.
Available to fit an assortment of fretboard radii, this oversized bone blank will have a shelf already cut to fit your guitar's fretboard radius. Compensation offsets can be adjusted to any guitar by filing the shelf back the needed amount for each string! Available in bleached or unbleached bone. See a one-piece nut blank fitted and installed on a guitar. Go here for more information and to Order Shelf Nuts. If you have further questions, Please contact me for more information.
Monte Allums sells a very inexpensive kit of nut extenders, of assorted materials, to slide in front of your original nut, effectively moving the nut forward. He also offers a set of tuning offsets that he claims are the best available - "better than Feiten’s".
It's very important that you measure your guitar's intonation between the open strings and the second fret before deciding to try something like this. The nut may already be in a forward position, in which case, a further move would most likely make your intonation worse. (This would be the case if any of the lighter-cored strings are already overcompensated (fret 2 flat compared to open))
Another thing to consider is that, if you just slide something in front of your existing nut, your action will be higher. In order to correct the action back to optimal height, you would need to file slots in the eNut (which, I believe, is explained in the eNut instructions). You would also need to file the slots deeper in the original nut, so that the strings descend toward the tuning machines - this makes the process somewhat irreversible. Bottom line - these items can be a real inexpensive time-saver and enable you to improve intonation, but you need to know what you're doing enough to make the needed refinements.
If you want to compensate the nut for each string separately, you can accomplish that with the included bone eNut. This could be a very low cost do-it-your-selfer’s delight.
Luthier Dennis Hook, Rancho Murietta, Ca, will custom build a truly compensated nut for your guitar!
Be sure to see his video
Greg Byers, of Willits, Ca, a renowned builder of superb classical guitars. Mr Byers provides some interesting information on nut compensation and saddle compensation on his website.
He suggests the use of a test fretboard setup, and an elaborate method of measuring and plotting all, or many, of the notes on the fretboard. The measurements can be processed statistically to calculate the offsets needed for all the strings, both at the saddle and at the nut, after moving the nut forward 1 mm (.039"). Mr Beyers effectively moves the nut forward, and facets the nut offsets back for compensation at each string. (His site provides a closeup photo of his saddle, but, unfortunately, not the nut.)
Byers has provided his compensation offset measurements, which can be used by luthiers and builders working with classical guitars.
His research work is exemplary. That amount of effort can be justified by someone building many guitars, however, a similar result can be produced with much less effort. My information, and Stephen Delft's, advise setting the saddle based on measurements at fret 2 and 12 or 14, and then set the nut for opens in tune with lower frets. This is a much easier way to approximately accomplish what Byers did, and it is probably more than adequate for most players. On the other hand, I think it is absolutely worthwhile to sample what's going on with the other fretted notes after having set up in this way. Also, as I have described elsewhere, you should intone best where you play the most.