Yes that is correct, growlers.
If you go over to Jeff's forum, he replied to someones answer to the possibility of using growlers in an HT setup.
Jeff mentioned that he will experiment to find out the capabilities of multiple growlers in a room, he's anticipating those numbers.
Im very intrested on the performance of four captivators. He has mentioned several times....that for him that is the "ultimate setp"
I for one would like to see some numbers and frequency response of the captivator. I know its not the end all be all of the performance of this sub, just like to get a rough idea.
I have seen the youtube video of 6 growlers and 2 triple8 filling a gymnasium with sound, kids grabbing their chests. I believe that maybe Jeff is referring to the same feeling if you were to place 4 captivators in a room.