I don't know; there's been some stuff in the Journal recently on high Bl drivers but nothing in relation to horns. This hasn't been that big an issue for horns until fairly recently, as even in the theatrical realm their haven't been many horn loaded subs, and above 80 Hz the problem seldom occurs, due to the lowered excursion requirements. I more or less stumbled on it when I started experimenting with high impedance subs, and only then with high power(over 100 watts)inputs at 60 Hz and lower.