On the same power, for loudness, if two sealed (Xcon) 18's have an F3 & FC of 43HZ and 2 ported 15" BTLs are tuned @ 35hz, the 18's are -12db @ 33hz & -24db @ 23hz and the 15's are -12db @ 30hz & -24db @ 25hz, not much of a difference on the low end so would the +158 sqin of cone area make up for 18's not being ported? What happends above F3 for both?