Vented Box Alignment

There are many software freely available over the internet that one can use to tune a vented box. The one featured here is WinISD, an excellent program by LinearTeam.

Optimized Alignment

With the T/S parameters generated by LMS, WinISD recommends a Box of 23 Liters tuned to 46Hz. F3 is at 45Hz (Figure 5 - Green Curve). This is an attractive proposal. 23L is manageable and 45Hz is respectable, especially from a 23L enclosure.

Ordinarily, I would have settled for this but in this instance, I decided to tune it to suit my listening room. With only 22x18 ft, bass can be overpowering due to room node excitation.

Preferred Alignment

Figure 5 (Yellow Curve) is my preferred alignment. This tuning results in a System Q of 0.6. Note that it has a higher F3 (50Hz) but a gentler rolloff. The result will be slightly softer bass passages but with better transients. An added bonus is a slight reduction in box size, from 23L to 18L.

(Figure 5) Box Plot of Vifa PL18WO09 by WinISD

Actual Fb

An impedance sweep is now done with the PL18 mounted onto a 18 Liters box. Internally, all walls are lined with 1 inch mineral fiber to reduce standing waves.

Figure 6 is the result of this sweep. The lowest point of the valley is at about 42Hz, where the Helmholtz Resonator is most active. This was accomplished with a port with a diameter of 1.5 inches and length of 3 inches - dimensions suggested in simulation.

With the box correctly tuned, we can now proceed to find the actual acoustic response of the PL18 loaded in a 18L vented box.

(Figure 6) Impedance Sweep of Vifa PL18WO09 in Vented Box
Box Volume = 18L
Fb= 42Hz

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