The IB Enclosure.

This is what the 4 x 15" vertical array looked like from the enclosure side.
I think you will agree that it looked very impressive.
The IB enclosure is a large prism, triangular in elevation and has a volume of about 600 cu.ft or 17 cu. meters. This small room was once an open balcony in the gable end of our old house. After the Danish Storm of the Century in late 1999 I had closed off the gable end with large, double-glazed windows to make a pleasant sitting room with a view out over our garden.

My wife suggested this space for the IB enclosure since it avoided clambering into the roof space and cutting holes in the planked ceiling of the AV room. Luckily the space offered a suitable volume and very easy access from the listening room via the original French windows. (glazed double doors)

The basic concept of an IB subwoofer is very simple indeed. The large drivers (loudspeaker units) are fixed into a wall (the baffle) between two adjacent spaces. The listener sits in one space and the IB subwoofer enclosure is the entire space beyond the shared wall. The loft can also be used as the enclosure with the ceiling acting as the necessary baffle. Underfloor IBs are also popular using the listening room floor as the baffle and the crawl space (or cellar) as the enclosure.

The black box on the steel table in the image above is a Behringer Europower EP2500, dual mono, power amplifier. Providing 450 watts RMS per channel into 8 Ohms. (650 Watts RMS into 4 Ohms) Designed for professional musician's instrument amplification it offers remarkable output for mere pocket money in domestic hifi terms. It closely matches the power requirements of my IB subwoofer. Its incredibly noisy original cooling fan has been replaced with a much quieter one! This is a popular and easy modification of these amps for domestic audio use.