Yeah, I'm sure it was the combination; but since our original problem was the drummer's vocal mic feeding back (pulling down the 6.3k slider on a graphic EQ to -15 dB barely stopped it) and since the egg carton PDF shows high absorption at that range, I tend to "monday morning quarterback" the cause to (mainly) the egg cartons.
Actually, any urine-soaked second-hand mattress would have accomplished the same thing for that purpose, and I'm not using THOSE either :=) Steve