Hi,
JoshK is right and have very low bass output it will need a lot of box. Servos do work and a Rajacat is right as well. For me I would be more interested in making a bass augmenter that will blend with the speakers which is also very hard to do. The main problem is getting the right electronics made and this costs a lot. At this stage I would rather spend it on the speakers.
Thanks again,
Louis