 D'Appolito initially configured his design using a 3rd order (18 dB/oct or 60 dB/dec) crossover, D'Appolito has since amended this original recommendation in favor of 4th order topology.However, this does not impart any significant effect on the MTM design's unique characteristics.There are speakers where the tweeter appears below the larger driver and though electrically it is identical to the MT configuration, it is customarily denoted as "TM".