From an audio point of view, two things define home theater: surround sound and subwoofers. Until relatively recently, only one of them could be installed inside a home's walls without risking long-term structural damage or, in the case of multifamily dwelling units, annoying the neighbors.

Sustained high sound pressure levels (SPL) in the lowest reproducible low-frequency range, between 20 Hz and 40 Hz, has been shown to literally tear the house down, starting with protruding nail heads and ultimately cracking and tearing drywall. And even at non-destructive SPLs, a subwoofer's connection to a wall could add unwanted resonances (read: distortion) to the low frequencies. So most of us know the subwoofer as that great-sounding, squat intrusion that annoys dogs and interior decorators alike but makes action movies and the Palladium channel things to look forward to.

On the floor was always the best location for the subwoofer because it offered the best possibilities for isolating it from the rest of the house. Low frequencies also have a natural advantage in terms of speaker placement: the lower the frequency, the less directional the sound is, so subs could be placed in corners or behind certain types of objects, as long there was sufficient space for the frequency to fully unwind. For instance, an 80-Hz wave needs about 14 feet.

The Sub: Part of the House

But subwoofers create another impression: a sense of impermanence, of being in the house but not being part of it, which reduces the potential for builders to benefit from making it part of a home theater of whole-house audio system. The flexibility to make subwoofers an in-wall or in-ceiling proposition puts that potential back on the table.

A new generation of in-wall subwoofers that have arrived in the last two years offer that potential. In fact, according to data from the Consumer Electronics Association, in-wall and flush-mounted subwoofers grew over 35 percent as a category from 2007 to 2008, with nearly 90,000 units being purchased last December alone.

Paradigm's RVC-12 uses a vibration-cancelling technique that allows it to be either wall- or ceiling-mounted. Within its enclosure, two 12-inch oval speakers are directly facing each other and firing in phase, which effectively cancels out wall vibrations. The speaker assembly is placed in a high-pressure, die-cast chassis to contain vibrations as SPL is increased. An interesting touch is the pleated, molded thermoplastic ring that suspends the speaker cones, allowing smaller speakers to move further and thus attain lower frequency reaches.