Box Tuning

[paradigm]

Given optimun enclosure parameters
Vb=1 cu.ft
Fb=30Hz
F3=35Hz
Lv=10 inches

Will decreasing the port Lv have the same effect on Fb and F3 as if you had decreased only the volume Vb.

In other words, if I decrease the optimum volume to ??? cu.ft and obtain a new Fb=40Hz and F3=50Hz, is it possible to get these same new parameters by just shortening the length of the vent and keep the optimum volume?

[Jeff B.]

> Given optimun enclosure parameters
> Vb=1 cu.ft
> Fb=30Hz
> F3=35Hz
> Lv=10 inches

> Will decreasing the port Lv have the same
> effect on Fb and F3 as if you had decreased
> only the volume Vb.

> In other words, if I decrease the optimum
> volume to ??? cu.ft and obtain a new Fb=40Hz
> and F3=50Hz, is it possible to get these
> same new parameters by just shortening the
> length of the vent and keep the optimum
> volume?

No, it is not. You may be able to reduce the port length and raise the tuning, and even change the F3 to the same frequency as the smaller box, but the shape of the knee at the roll-off will be different, so techincally it is not the same response. These are called "alignments" and for a given woofer they are a specific combination of cabinet volume and tuning.