Having owned Dynaco A25's (the first commercial aperiodic-tuned speaker AFAIK), I've often wondered why aperiodic loading didn't catch on more. I've heard of the North Creek and Omega examples but I think North Creek is gone and the Omega aperiodics are long discontinued. Chief benefit of this approach is a relatively flat impedance curve, making for an easy amp load. Curious why Omega stopped using it, as their speakers are popular among users of low-power amps which stand to benefit.