Jason Sloan, vice president of sales for Sonance, says the size and depth of MDU walls vary widely, and many utilize two-inch metal strips for drywall support rather than the 2-by-4 wooden studs found in most single-family homes. Furthermore, some condo associations forbid the installation of any speakers in walls.

However, says Sloan, the higher up one goes in altitude, the more opportunities there are for in-wall audio. "Upper floors tend to have penthouses with no common walls with a neighboring unit, and upper floors also tend to see more multiple-unit purchases by the same buyer, which eliminates having a common wall with a neighbor," he says.

Developers have also been swayed to allow in-wall audio if they can be convinced that the right type of MDF enclosure around the subwoofer can contain vibrations. One of Sonance's subs, the BPS-1, is specifically designed for ceiling installation, using a two-chambered, fourth-order bandpass enclosure that routes the sound through flexible ducting.

Sloan agrees that builders in general are not up to speed when it comes to the range of products for the in-wall subwoofer category. "Ninety-five percent know about in-wall speakers, but I'd say less than twenty percent know you can put a subwoofer in the wall," he says. "The growth in this category is being mainly by the systems integrators and to a lesser extent by home buyers."

Carl Kennedy, vice president of sales for JL Audio, cautions that placement of an in-wall sub is critical not just for keeping low frequencies from disturbing neighbors, suggesting the builder or the systems integrator check with an acoustical consultant to avoid nulls (dead spots) and compression areas (bass build-ups) to assure optimum performance. JL Audio plans to ship a new sub product later this year, the Fathom IWS, which it displayed at the Consumer Electronics Show in January. The product will include equalization software and a new mounting technology, Kennedy says.

And builder, buyers, and installers can expect even more options in the future. The in-wall sub puts the finishing touches on the invisible sound system concept. And like any built-in, it offers builders and buyers alike a value-add that doesn't take up an inch of floor space.

Dan Daley is a frequent contributor to Hanley Wood's DIGITAL HOME Online.