The drawing above shows an initial sketch of a 2 x 15" horn. The actual horn varied slightly from this. The rear volumes behind the drive units were adjusted with blocks of polystyrene based on listening tests and crude measurements. The recently calculated response below is a bit of a cheat because I haven't got the drive unit parameters so I used those of a drive unit that I thought would be similar to the originals. The graph is based on two cabinets stacked on the floor.