They dothis by using the backward motion of the woofer into the cabinet to resonatethe air mass within the port. The function of ports on speakers and subwoofers is to producesound more efficiently in low frequencies than the drivers are able to. Hsu’s variable tuning subwoofers have been aroundfor years now, and for those not acquainted with the idea, here’s a briefexplanation. To begin discussion of its design, we will start withthe feature that most distinguishes it from many competing subs, namely thedual-port variable tuning.
It isdifficult to pin down the foremost feature of the VTF-2 mk5 since it is anevenly balanced design.
We have 1 HSU VTF-2 MK2 manual available for free PDF download: Manual Hsu VTF-2 MK2 Manual (12 pages). Manuals and User Guides for HSU VTF-2 MK2. The ‘VTF’ stands for ‘Variable Tuning Frequency’ and is Hsu’s line of ported subwoofers that use multiple ports that adjust the tuning point to the user’s preference. The VTF-2 has been a part of Hsu Research’s VTF subwoofer line for 17 years and has developed considerably in that time through a number of iterations. The reason for variable tuning is that all subwoofer designs, especially consumer-level subwoofers, involve tradeoffs in design. The VTF-2 MK5 succeeds down to a very deep 18 Hz with one port open (in maximum extension mode). Read our review of the $400 VTF-1 mk3 to see how we liked it.
Hsu's latest subwoofer, the VTF-1 mk3, is a little powerhouse with a 10' driver, 250 watt amplifier, and dual 3.5' diameter ports.