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Installation Profile: THX at Home

Aug 1, 2008 12:00 PM, By Dan Daley

Quality-assurance specifications dictate a budget built for acoustics.

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“To meet the low-frequency specifications of THX and get the bass coherently in between the seats, we found that more and smaller subs did the job better than the fewer 18in. subs we modeled,” Rosenbaum says. “This was a great example of how a less expensive solution was able to achieve the THX specification, allowing us to allocate more of the budget to the acoustics of the room. I've been in theaters where larger and much more costly subs didn't perform as well in their space as these do.”

Isolation was challenging. The theater could not be mechanically decoupled from the home's concrete slab, and the owners wanted the entrance to the theater at the same level as the anteroom. To serve both purposes, the design included a one-step riser for the first row and a two-step for the second with variably tuned Helmholz resonators beneath each of them.

The THX specification called for a Noise Criterion (NC) level of 30 — the theater, as measured in THX's certification process, came in at NC 17. It could have gone even lower if the situation had allowed for a spring ceiling like those found in many commercial THX theaters. “We're heavily protected across the spectrum from noise from below and from the sides and from the HVAC system,” Rosenbaum says. “But if someone is walking in high heels in the kitchen [above the theater], you might hear it. It's one of the compromises of residential THX.”


Equipment choices for THX on a residential scale are circumscribed — although Rosenbaum says that helped the process in a way, removing the temptation to pursue “trophy” gear.

“There's a whole suite of performance constraints and performance benchmarks along the audio chain that have to be met, and THX requires using equipment certified by them to achieve it,” Rosenbaum says. This includes a difference in volume of less than +/-3dB between seats and the ability of the space to handle 105dB without distortion. “That's why the isolation was so important. It had to achieve the same level of volume as a commercial theater.”

Among the systems that met THX certification standards and were appropriate for this residential install were the Triad loudspeakers, the Lexicon MC-8B DSP digital controller, Ashly Audio ne24.24M matrix processor, and QSC Audio DCA Cinema amplifiers.

This equipment was installed in a rack next to the home's whole-house audio and home-automation systems in a separate control room, allowing for easier integration with other functions of the house. Existing motion sensors from the security system and feedback from the lighting system, through the home's Crestron CNX-PVID8X3 video-distribution system, enable an integrated alert and monitoring system. When motion is detected, the alert system shows output of the proper camera on either the touchpanel or the screen. The lighting system is used to make sure the camera has adequate light. If the screen is chosen for alert monitoring, the movie or TV show is automatically paused. (When just the owners are using the theater, interruptions triggered by the security and monitoring systems will automatically pause the show. There is also a guest mode that lets the movie continue to play and the alert simply lighting up the Crestron TPS-15 touchpanel controller with the appropriate indications.)

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