The AV industry has been chasing immersive audio for a while, and now, at long last, it’s starting to have its moment in the spotlight. The problem has long been that, in designing an entertainment space—immersive or otherwise—acoustic, spatial, and aesthetic considerations come into play. This has long made it hard for residential integrators to determine the most crucial aspects of designing and assessing a system’s overall performance.

Then, in September 2023, CEDIA and the Consumer Technology Association published CEDIA/CTA-RP22: Immersive Audio Design Recommended Practice. This guide outlines criteria for achieving high-performance levels in immersive home audio systems, and its principles also apply to Hi-Fi setups.

RP22, therefore, serves as a valuable tool, addressing the many considerations involved in creating an optimal audio experience. Among its key recommendations: Use digital signal processing (DSP) to optimize performance.

This comes right as homeowners, who may have upgraded their home entertainment systems during the pandemic are now enhancing the experience with cinema-quality, spatial technology for a more lifelike, three-dimensional sound.

Last year, by some estimates, nearly three quarters of installed home theaters–including multipurpose entertainment spaces–featured immersive audio systems, prompting a genuine demand in the market.

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What Do You Need to Focus On When Creating Immersive Audio?

RP22’s performance objectives are grouped into three main categories of spatial resolution, dynamic range, and timbre, and within these categories are additional parameters that contribute to the overall quality of an immersive audio system, including frequency response below a room’s transition frequency, seat-to-seat consistency (including consistency of bass response), in-room bass extension, total SPL (sound pressure level) capability of the LFE (low-frequency effects) channel, and several others.

The standard also emphasizes bass frequency response and seat-to-seat bass variation as two areas that require special attention. These areas are particularly challenging due to standing waves and resonances, which can create variations in bass response of 20 dB or more and impact the immersive experience. Managing the interplay between bass speakers and a room is essential for improving overall performance.

The emphasis on achieving good bass is pretty important as research shows that 30 percent of a listener’s experience is attributed to bass performance.

For that reason, the, when optimizing a system for immersive audio, the first step is to invest in hardware with strong dynamic range (power handling, distortion, dynamic range, linearity), bass extension, and dispersion. RP22 also emphasizes the importance of consistent speaker characteristics for optimal spatial performance and timbre.

But while specifying identical speakers can theoretically improve results, real-life constraints normally prevent using the same model for front, center, and surrounds, let alone ceiling speakers. What’s more, variations in early reflections and speaker placement inevitably degrade performance.

Optimizing Bass Response and Surround Sound for Immersive Audio

To address these challenges, RP22 recognizes the benefits of DSP-based precision audio calibration solutions with “rephasing” or “retiming” capabilities, as these provide a solution for achieving target response curves across different speakers, thereby enhancing spatial resolution and timbre.

An integrator could achieve good spatial resolution and timbre without DSP, but it could require additional spending on speakers, acoustic treatments, and installation labor. Moreover, the physical space for these additions may be limited, especially when designing an immersive audio system.

For instance, integrators can reduce bass variations using multiple bass-capable speakers, including multiple subwoofers, which can improve bass response in the preferred listening position by exciting room modes differently. RP22 suggests various subwoofer arrangements to yield more consistent bass but notes that optimal placement can only be determined through experimentation, which can be time consuming.

Optimizing bass response at just one seat in a room is also difficult and time-consuming without measurement-based optimization, as bass performance varies significantly between different listening positions. Near a back wall, for example, there’s typically exaggerated, boomy bass response, while at other positions there may not be enough bass.

How to Use Audio Calibration to Achieve Better Bass Performance

Digital precision audio calibration schemes aimed at evening out bass response and seat-to-seat variations provide another remedy regardless of subwoofer placement. To control bass in several seats with multiple subwoofers, an advanced, measurement-based co-optimization of the subwoofers is often the only practical way.

Here’s how key bass-related performance parameters can be improved using audio calibration technologies:

Frequency response below a room’s transition frequency: Room correction software optimizes each speaker’s frequency response toward a user-defined target curve. For multi-subwoofer, immersive audio systems, however, single-channel optimization does not guarantee the summed bass response reaches the target. In such cases, bass control software helps achieve the intended target. From there, a solution like Dirac Live Active Room Treatment can improve results further through optimization of the wave propagation in the room.

Seat-to-seat consistency below a room’s transition frequency: Single-speaker immersive audio optimization via room correction systems can’t improve seat-to-seat variations. Rather, they improve average response (or the response at a selected position) while seat-to-seat variations remain. Solutions like Dirac Live Bass Control and Dirac Live Active Room Treatment can possibly reduce the seat-to-seat variance by optimizing the combined output of several speakers.

In-room bass extension: Traditionally, bass extension is defined by speaker characteristics. We would not generally advise using single-channel optimization or EQ to extend the low end. However, if the homeowner doesn’t plan to listen at the loudest levels, room correction software can yield a certain bass extension without increasing the risk of distortion. Speaker placement near walls can usually improve bass extension, though at the expense of boomier, less tight bass. But by combining room correction with near-wall speaker placements, integrators can achieve both low-frequency extension and tight bass.

Total SPL capability of LFE channel: Both Dirac Live Bass Control and Dirac Live Active Room Treatment offer options that combine multiple speakers (subwoofers and/or full ranges) to ensure that the SPL over the entire LFE frequency region is maximized and that all speakers sum constructively across the LFE frequency range.

Additional Optimization: DSP solutions with audio calibration can help address other RP22 performance parameters, such as avoiding null points of low order standing waves. And they can improve on many non-bass-related performance criteria, like inter-speaker polarity coherence and the level of early reflections relative to direct sound for improved immersive audio and stereo performance.

Ultimately, as integrators begin installing more immersive audio systems, they should follow RP22 recommendations to get the best results.

Lars-Johan Brännmark is chief scientist for Dirac.

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