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How Flooring Affects Acoustics in Home Theaters

Sam Cavitt breaks down the significant influence that flooring can have on the performance of a private theater.

The practice of designing private theaters involves many disciplines. In some cases, these disciplines can seem mundane when compared with more glamorous subjects like 3D audio formats and 4K video. The temptation is to gloss over these insignificant details. But, “God is in the details,” said one famous architect, and the opposite, “devil in the details” refers to those missed.

One such seemingly trivial item is the flooring of private theaters. We have a tendency to make certain assumptions and move on to bigger and better concerns, but one recent project brought the many ways the specification, installation, and execution of flooring in private theaters can have a significant influence on the final results.

A combination of wood and carpeted flooring in a recent private theater design

It all starts at the foundation level. Construction of the theater foundation will affect flooring choices all the way up to the finish and can impact the theater’s success. If the theater is going to be built on a raised foundation made of anything other than a grade or sub-grade slab, then you can expect structure-borne sound to plague the theater, inside and out. Thumping bass can resonate from the theater into the rest of the structure and the footfalls of even small people will carry from distant rooms, destroying those perfect moments from a favorite film’s soundtrack. Dealing with raised foundation conditions requires early planning, as there are no “magic bullets” to easily separate these structures. It takes all three quiet room techniques, (mass, deflection, and dimension) to effectively do the job. Sadly, on projects where the theater design is an afterthought, there is no way to mitigate the noise.

The foundation can affect flooring in other ways, as well. Often a theater has been designed with poured-in-place risers. It is rare that the video engineering, acoustical engineering–or any theater performance engineering, for that matter–has been considered to determine the configuration of said risers. This often results in the inability to include a decoupling material beneath the finish flooring, leaving potential for “flanking-path” sound to bypass wall and ceiling quiet-room assemblies. The design team is left choosing between awkward elevation transitions from areas outside the room or just giving up on mitigating flanking-path sound.

Comfort systems will also affect flooring in many ways. These systems have many variations. Hydronic (both heating and cooling), electric, integral, poured, and panelized are the most common. Poured and panelized systems will have a dimensional impact on finished flooring; electrical will have a smaller dimensional impact; and integral impacts flooring in a very different way. All the radiant systems other than integral can be modified to work with fully decoupled floor systems; however, advance planning will be required in order to do so, and it will add a difficulty factor in the execution. In short, the radiant systems must be located between the subfloor and finished floor. Thus the dimensional impact must be considered and the finished floor material verified to be compatible with the system of choice. For instance, the combined R-value of a carpet and pad will affect the efficacy of the radiant system. It is vital that these selections be checked against the particular system specs for best results. The integral system, where the radiant equipment is in the actual slab, will be rendered ineffective by any built-up platforms, so this must be taken into account.

What about the flooring outside the room? It is vital to verify the finish flooring–in fact, all flooring considerations including foundation construction, radiant systems, sub flooring, and finish flooring, of areas adjacent to the theater. If design specifications are being made to optimize the performance inside the theater, the effect at the transition has to be accounted for.

Many of our clients will assume that we expect the entire theater floor to be carpet. That is a fair assumption, but is not set in stone (pun unintended!). We do include a factor for a typical carpet and pad in our formulas for acoustical modeling, but not all carpets and pads are equal in their acoustical characteristics. One characteristic, however, is universal. Due to the thickness represented, carpeting absorbs no appreciable sound energy below 2kHz. It can, however, absorb significant sound energy above 2kHz. In fact, testing by the Carpet and Rug Institute shows a variance from 45 to 70 NRC in different combinations of carpet and pad. Since flooring represents a significant surface area of a theater, this variance can make an audible difference. An approach we have taken is to model specific flooring materials in their actual locations within the theater and quantify the frequency responses at the listening positions. This approach enables us to confidently assure our clients that their rooms will sound great and has also freed us to utilize various flooring materials where these would be acceptable acoustically.

Just like so many other elements of private theater design and engineering, what happens beneath our feet will either add to a successful effort or detract from what could have been. Which it will be depends on the attention given to this detail and the opportunity to address elements early enough to make a difference.