Dave Wilson talks about the importance of dynamic range and especially dynamic contrast in speaker design. I believe these two criteria can be combined and is consistent with what is typically referred to as the transient response of a speaker, especially a mid-woofer and woofer. In this regard, a transmission-line design like the one used by PMC generally has an advantage over sealed and bass reflex (ported) designs.

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System 1: McIntosh MC302, MA6600 w/T2, MCD500, Denon DP-72L w/Grado Reference Platinum 1
PMC OB1i, Vienna Acoustics Concert Grand
System 2: McIntosh MA6500, MCD205, MR85, bel canto Dac, MacBook Pro w/AE
McIntosh LS320 - PS112, Klipsch Heresy III