which exact svs cylinder sub will match up perfectly with a svs pb12-nsd i currently own?

one pb12-nsd is not quite enough for me and i don't have room for two pb12-nsds....

thanks

You best match should be a 20-39 Pci. The tuning should be close.

can't you stack the two PB12NSD's?

otherwise, the PCi 20-39 (I think) can be retuned to match the tuning of the PB12NSD [email SVS (Ed M) for this option]