forgot to mention, such PB12-ISD2 was original called PB2-ISD in 3 yrs ago [2004].
then probably in about 2 yrs ago [2005], it has a new name: PB12-ISD2. 12 means driver size, ISD is driver type, 2 means twin drivers.
upgraded to newest NSD drivers in 2006. so it's PB12-NSD2 now.
