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.
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.
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.
5) Box Plot of Vifa PL18WO09 by WinISD
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.
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.
the box correctly tuned, we can now proceed to find the actual
acoustic response of the PL18 loaded in a 18L vented box.
6) Impedance Sweep of Vifa PL18WO09 in Vented Box
Box Volume = 18L