FV18 has three port openings. With two (three) ports open, the max extension is 12hz (16hz). In the following is the frequency response when extension filter is set to 12hz and low damping for 2 port operation.

Fig 1.0 - FV18 Frequency response chart with line-in 12hz low damping and two ports open

Fig 1.1 - FV18 Frequency and phase response chart with line-in 12hz low damping and two ports open

Figure 1.1 has the phase response added. FV18 also has a rumble filter with -6db @10hz. This is suitable for playing opening scene in movie Edge of Tomorrow and 3 port operation to control cone excursion in the subsonic range. Fig 1.2 shows the frequency response of this rumble filter.

Fig 1.2 - FV18 Frequency response of the selectable rumble filter

To summarize, two port operation gives deeper extension and the recommended setting is 12hz low damping with optional rumble filter on. Three port operation gives more output and the recommended setting is 14hz mid damping with rumble filter ON.

Integration

One important aspect of getting a correct integration is phase alignment. We have written a guide on how to achieve a phase aligned subwoofer. More