Perhaps the size of the listening room has something to do with the limitation of sound frequency. Assume that sound travels at 1223km/hour at sea level. Then if my conversion table is correct, sound travels at 1,114 feet/second. The sound frequency that we are debating here is 40 cycles per second. The wavelength of sound at 40 cycles per second is about 28 feet. That means that it would take a 28 foot room to fully develop sound at 40 cycles per second. I think that this is size limitation of most listening rooms. Larger rooms will develop lower frequencies of sound. If you want to fully develop sound at 35 cycles per second, you will need a 32 foot room. If you want to fully develop sound at 30 cycles per second, you will need a 37 foot room. If you want to fully develop 25 cycles per second, you will need a 45 foot room, etc., etc. In conclusion, why are we torturing ourselves trying to get speakers of lower frequencies, when we should be considering getting LARGER ROOMS. Let's go for broke, if want to develop a one cycle per second sound wave, you will need a 1114 foot room!!!