1. The coupled air between the two drivers adds to the moving mass of the system and thus results in a less than optimal coupling between the drivers. Remember that the idea is to get these two subwoofers to act as one driver, and by adding a springy mass between them this ideal is somewhat compromised. Some might find that this leads to a beneficial lowering of the system Q (when the volume indicated in blue in the picture is sealed) but more often than not this effect is undesireable as it makes response predictions more difficult.
2. The coupling chamber negates one of the primary benefits of isoloading--small enclosure size. By the time we account for the displacement of this coupling tunnel in determining the gross volume of the blue chamber, the enclosure starts to approach the volume required by a single conventionally mounted driver.
3. Since the drivers are both firing in the same direction, there we do not reap the benefit of cancelled driver non-linearities as we would with a design implementing a push-pull configuration.
4. The driver whose magnet structure is housed in the coupling tunnel is in a highly unfavorable cooling environment and will be subject to power compression at lower levels. Basically, the drivers will be more or less equal performers at first, but as things start to heat up and the impedance of the front driver rises due to rising voice coil temperatures, the drivers start to fight each other to some degree rather than complement one another. This results in increasingly non-linear behavior with possible unpleasant audible side effects (e.g. sloppy transient behavior).

In essense, this configuration is more of a cosmetic "oh neat-o" design more than anything else, and we recommend that it not be used, especially for high-powered applications where the thermal power handling of the drivers would be called into question.

Copyright 2001-2003  Peter Ferlow