Tuneable saddles for nut intonation

[that_sustain]

Playing along to something, I decided to drop the nut down..since the neck had bowed forward a little.  I noticed after retuning(bridge was still in pitch) the lower notes had improved in intonation while still playing along to the same music.  It'd be great to have the option of leaving the nut height where it was (and) having the lower notes as in tune as I've described(tried to). Would intonation saddles make such a thing possible?

[edwin]

I think what's going on is that when the nut was at a higher level, you were increasing the tension on the strings as you pressed them to the fingerboard because of the string to fingerboard distance down at the nut. By lowering the nut, you end up with less increase in tension because of the decreased distance traveled.
 
I've never heard of an adjustable nut with respect to scale length, but I think the Buzz Feiten system does involve a compensating nut that might be addressing something like this issue.

[adriaan]

There is a company that uses a Compensated Nut - but Edwin is probably right about what was happening.

[that_sustain]

I'll never mod my bass, just wondering if it already existed.  Facts and link appreciated...

[dfung60]

As Edwin suggested, what you're hearing is what the Buzz Feiten system is about.  When you press down the string, you're stretching it by the amount of relief that's dialed into the neck, which makes the fretted notes a tiny bit sharp.
 
Part of the Feiten system is that the nut is moved closer to the bridge than expected.  Doing this should be an overall improvement in intonation for fretted strings.
 
But this makes the open strings out of tune relative to the fretted ones.  So the other part of the Feiten system is modified tuning that compensates for the nut position.  
 
The last part of Feiten is how the intonation is set since everything is slightly adjusted.  I don't know what's involved here.
 
These adjustments are tiny, something like 2-4 cents or hundredths of a semitone, so most people wouldn't notice them while playing, but if you use an electronic tuner, you're probably tuning your open strings closer than that already.
 
The amount of nut shift toward the bride is tiny - you can hear even the small adjustment in nut height in the tuning.
 
David Fung

[that_sustain]

Thanks guys. I'm still wondering if string trees on specific spots of the peghead change intotion of the lower notes..or, if that even matters.  I didn't know nut height affected intonation.
 
I think I was in inventer's mood when I wrote this one.  lol

[edwin]

String trees or any other interaction with the strings on the outside of the nut or bridge will have absolutely no effect on intonation. It's all about nut to bridge length and then what happens to the tension when the string is pressed to the fingerboard. That's it! There are arguments made that it can affect tension, but I remain skeptical. However, it can affect how well the strings stay in the saddle and nut slots.