Say mounted in a 2" deep tube for the sake of simplicity, open ended. If you want to get more rediculous but better sound, metal cone full range drivers at this size often have better definition and bass detail but resonance peaks in the upper end but combine with a high efficiency ribbon tweeter for awesome dynamics, but you need a crossover. For simplicity we will say 1st order around 4k. And the two drivers mounted in a mild "V" shape words the ear, open part of the V around 4-5" with sound absorbing material covering every hard surface with the wide range driver closer to the rear and tweeter closer to the front if that makes sense. Example drivers:
Of course you can't power it off your iPod, need speaker terminals. Probably need a fair amount of equalization.