Googe E:
Alembics actually have three angles:
1) The 'neck angle' you mention (or 'draft angle'
term that Mica used) is a construction method
used to raise the string height at the bridge
2) ... so that the angle where the strings cross
from the bridge to the tailpiece is greater.
This tends to give greater sustain by creating
more 'downforce' (to use a racing term) on the
bridge. The separate tailpiece (and the brass
sustain block in some models) boosts sustain as
well.
3) The 'third' angle is the headstock pitched down
from the plane of the fingerboard. Again, this
makes more 'downforce' on the nut, adding
sustain. It also simplifies restringing as
this allows the builder to eliminate the string
trees used on Fender-style instruments. The
tree arrangement can't possibly deliver a
uniform loading to the nut. GOTOH has even
begun building staggered-height tuning keys to
attempt to compensate for this.
These construction methods are neither cheap or common in most basses. If you set out to build the very best, they are, however, the ONLY methods you would use.
Combine this with the laminated necks and slab ebony fingerboards, it's no wonder The BigRedBass seems to sustain forever, even at low volume.
I am continually delighted by the insight manifested in the construction of my bass.
Joey Wilson