Depends a lot, too, on how much you are able and willing to spend. There's also the other driver(s), crossover and cabinet. Also to consider is whether you have any preferences for size and technology (sealed, ported, transmission line, or horn-loaded enclosures), sensitivity, which influences what amplification is appropriate (the range seems to be from perhaps 86 to 100 dB/w/m), frequency response ("monitor" or "full range" -3 dB @ 20-30). There's also the possibility of using used/vintage components (Altec, Tannoy, JBL, etc.) or using very expensive new components like TAD---although the four previous are all high sensitivity (efficiency) drivers that require ported or horn-loaded enclosurres. . . .Having said that, I have a pair of 15" two-way Altecs in the original sealed enclosures and they manage 94 dB. . .Have a lot of fun, whatever you get and whatever you build and keep us posted! Regards, Dr_joe.