In-Wall Subwoofers: The Final Frontier of Built-In Audio

New ways to mount subs in walls and ceilings let builders add better bass (and value) without sacrificing space.

Source: DIGITAL HOME Online
Publication date: 2009-03-09

By Dan Daley

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.

Courtesy: Polk Audio Polk Audio's CSW155 in-wall sub Fits comfortably between standard 16-inch on-center studs.

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.

Jack Shafton, director sales and marketing at Paradigm, says a "stealth" sub has been a consistent request from builders and systems integrators. "It's a matter of both esthetics and square footage," he says. "The need for floor space is driving in-wall hi-fi, and the subwoofer is the final frontier of that trend."

Nashville custom home builder Michael Cronin agrees. He's been using NHT IW4 subs in both a current spec house project and in his own home. Cronin may have a bit more insight than the typical home builder. Through his company Cronin Acoustic Construction he also builds world-class music recording studios, and he feels that while in-wall subwoofers are a compromise in terms of sonic quality and quantity (of air moved), they make up for that by being invisible.

"Your partner may not want the house looking like Circuit City all the time," he says. "In-walls can be painted over and you can get decent performance out of them, as long as you isolate them properly."

Cronin uses Kinetics Noise Control's IsoMax sound isolation clips to secure the sub to the studs or joists to limit mechanical coupling, as well as adding two layers of 5/8ths-inch drywall to the rear of the enclosure. "The subs themselves aren't that expensive, but isolating them properly does incur additional cost," he says. "But it's worth it."

Al Baron is the product line manager for Polk Audio's new CSW line of in-wall subs, which range from $525 for the compact CSW 100 to $800 for the CSW 155. The line's 10-inch driver uses a neodymium motor structure to offset the unit's shallow depth. It's housed in a cast aluminum basket that is rigid and inert to suppress resonance.

Baron, who is also on the CEA's Multi-Room AV Council and the Builder Initiative between that the CEA's TechHome division and the NAHB, believes there remains a disconnect between builders and some home technology categories, particularly the "invisible" ones.

"We know from our surveys and other surveys that consumers want built-in audio, but we're also finding that to a large extent builders aren't aware of the consumer demand for the products," he says. "Invisibility equals cool, and it also represents significant profit potential to the builder because it's built in."

Low Frequencies in High Places

The ideal construction proposition for in-wall subs and speakers might be high-rise MDU residences, where floor space is at a higher premium. But it also presents the most challenges, thanks to numerous common walls between residential units.

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.

<i>Dan Daley is a frequent contributor to Hanley Wood's DIGITAL HOME Online.</i>