Try 3. First one went to Anthony, only. Second one (for which I am abased) didn't have a word of my reply in it. <hangs head>
The lutehole is a port-tuning device for miked acoustic guitars. Guitars generally have a resonance which matches neatly with the pitch of the A string. If you mike the guitar (in almost any way you can think of) and put that sound into the same hall with the guitar, feedback from the hall's speakers to the body of the guitar excites the resonance, peaking notes in the area of the open A string, the A string vibrates (or a fifth-fretted E string or harmonically-related notes) and feedback ensues. I wouldn't characterize it as screaming, myself, it's more of a bull-moose-in-heat effect, which goes on and on until it has either eaten up all the energy available and becomes a steady tone, or is damped, one way or another. The lutehole changes the hole's port resonance. This may also mitigate the airmass resonance behind that port. In engineering terms, it increases the impedance between the body resonance and the air, and luteholes are probably intended to be a physical filter centered at A=110. The same effect can be gotten by notching the sound board for the guitar's channel/s at 110Hz and balancing the depth of the notch (in my church, it takes about -12dB!). Either way, the feedback is a byproduct of the sound system, the speakers and their placement, the hall's shape and absorptive character (which changes with the number and placement of bodies, preferrably warm ones), the guitar's body size, enclosed air mass and hole size. As for changing the characteristic of the guitar to improve it's outdoor use without amplification? I wouldn't give it much chance. As a notch filter, it is removing A string intensity. Without the sound system and/or hall to resonate and increase the effect, the guitar does a fair job as it stands, but arbitrarily notching 110Hz (with unspecified other acoustic affects which a good sound guy can adjust for, if there's amplification) for unplugged performances is probably a Bad Thing(tm). ray To get on or off this list see list information at http://www.cs.dartmouth.edu/~wbc/lute-admin/index.html
