Based on a reply I got once, what does it mean for a headphone to "fatigue" your head? Is it similar to heat/sweat around and inside your ears? If so, do all headphones do this? Which headphones do not? The clamp on my Philips set is broken, so I think I'll be looking around for some non-fatiging, isolating, quality sounding headphones. The reply to a post I got once specified Grado SR-40's (if I remember correctly) but I can't find a place to sample them. Who sells them (namely in Boston)?.