Deep low frequency extension is a common goal for a subwoofer and small box volumes are also considered desirable.

Two incremental improvements over the exponential horn include slightly better support for low frequency extension and a somewhat broader high-frequency coverage pattern.

They came with special extenders used to widen the mouths of the horns and take advantage of the theater walls to further increase low frequency extension.

As the efficiency is proportional to Fs, small improvements in low frequency extension with the same driver and box volume will result in very significant reductions in efficiency.

For example, if a speaker is optimized for performance in a 40 liter enclosure, one iso-group of the same speakers can achieve the same low frequency extension and overall response characteristics in a 20 liter enclosure.

Six rotary woofers are installed as part of an immersive Niagara Falls attraction known as Niagara's Fury, located in the Table Rock House, to provide low frequency extension down to less than a single Hertz, to emulate those waves created by the falls.