dual tuning frequency

[Relic1Golf]

this is a strange question but is a dual tuning frequency subwoofer (a la HSU vtf/SVS pb12) possible without using a DSP or active EQ?

 

[AllenB]

You should, through simulating be able to find a box volume that can give you a range of useful responses by varying/blocking off ports.

 

[weltersys]

this is a strange question but is a dual tuning frequency subwoofer (a la HSU vtf/SVS pb12) possible without using a DSP or active EQ?

The SVS pb12 simply uses foam plugs to seal ports (three ports gives three tuning options plus sealed), plugging ports results in lower tuning (and more port compression ).
Since the box remains the same size, the lower tunings reduce bass level in the Fb (box tuning) range, so some LF boost is required to flatten response. That said, depending on your room, the additional LF gain may not be desired.

Generally a steep high pass filter is inserted just below Fb to keep excursion under control, so the HP would be dependent on the tuning chosen.