HONG KONG: When the Hong Kong Repertory Theatre returned The Impossible Trial to the Xiqu Centre Grand Theatre for a 30-performance run last October, it marked the musical’s third staging since 2019—and its most ambitious sonic realisation yet. Sound designers Jeffrey Yue and Ha Yan-pui revisited their immersive audio concept with renewed intent, evolving lessons from the 2022 production into a far more deeply integrated L-ISA experience, shaped in close collaboration with L-Acoustics application engineers and tuned precisely to the venue’s challenging acoustics.

The three-hour musical brings together a 21-member cast and a 12-piece live ensemble performing on traditional Chinese pipa, strings, winds, keyboards and drums, with director Fong Chun Kit’s theatrical vision and composer Leon Ko’s richly layered score demanding an audio design capable of supporting narrative subtlety as much as scale. For the 2025 production, Yue and Ha invited Chung Wah Khiew and Daniel Lee from L-Acoustics APAC to join at an early design stage, a move Yue describes as transformative. “We realized that to take the next step from our 2022 production, we needed deeper collaboration with the L-Acoustics team,” he explains, noting that the technical support enabled the team to push system design and creative ambition significantly further within a tight production schedule.

One of the key challenges carried over from the earlier run was slapback echo from the venue’s rear wall, particularly affecting the circle level. Between productions, WestK introduced additional acoustic treatment using curtains and absorbing materials, while the sound team expanded the delay system from two A10 enclosures to five A10 Wide enclosures deployed as L-ISA spatial fill for the circle, dramatically improving spatial coherence. “In our previous production, the main system needed to throw farther into the space, which excited the room considerably,” Ha reflects. “This year, the expanded delay system, combined with the venue’s acoustic improvements, made a dramatic difference in controlling those reflections.”

Rather than treating immersive audio as a constant effect, Yue and Ha used spatialisation selectively to serve the story. Distinct sonic identities were created for individual characters, particularly important when a single performer embodied multiple roles such as the Lord of the Netherworld, The Narrator and various Judges. “When he performs as the narrator, we position his voice more localised on either downstage ends to create an intimate storytelling feel,” Ha explains. “When he plays other characters, we adjust the spatial characteristics—sometimes narrower, sometimes spreading the image wider—to create a different presence for each role.” A ghost character’s vocal was treated with dynamic spatial movement, reverb and delay circulating through the 360-degree system, while the emotional finale employed expansive chorus reverb across the full surround field for maximum impact.

Musically, Ko eliminated conventional sound effects in favour of effects generated organically by the live ensemble, such as rhythmic door knocks performed by musicians and spatially circulated around the hall. This approach created a cohesive sonic texture that preserved narrative clarity while reinforcing the musical language of the score. With material ranging from pop ballads and jazz numbers to rock-driven passages, the mix required constant adaptation. “The score is incredibly layered and textured, which gave us significant scope in crafting the mix,” Yue notes. “Sometimes the enhancement was very detailed, sometimes subtle, but always in service of the story.”

The L-ISA Sound Spaces and trim functions proved critical in addressing the theatre’s intimate geometry, where the first three audience rows sit directly adjacent to the orchestra pit. For those seats, acoustic spill from the musicians necessitated a very different balance than for listeners seated further back. Object-based mixing and zone-specific trims allowed the team to deliver appropriate localisation and balance throughout the auditorium, with up to 56 mono objects feeding the main spatial mix. “The level of care required for each sound in an immersive audio mix for musical theatre is considerably greater than traditional approaches,” Yue observes.

The technical framework was underpinned by a clearly defined collaborative workflow. FOH engineer Kiki Yu, who has been with the production since 2019 and also serves as assistant musical director, worked closely with Ha on the immersive mix, while Yue focused on system management, Soundvision design, networking and L-ISA configuration. Ha’s two decades of experience working with Ko informed a methodical, storytelling-first approach. “We wanted to use L-ISA to deliver and enhance a storytelling-focused sound design,” she says, moving away from conventional pop-style treatment.

System design support was provided by Rightway Audio Consultants, with additional tuning by Chung Wah Khiew, while RAC Hong Kong and Showbros supplemented WestK’s in-house inventory to realise an L-ISA Hyperreal Immersive configuration. The scene system comprised five hangs of one A15 Focus and two A15 Wide each, with two centre-flown hangs of KS21 subwoofers, complemented by extensive front-fill, deck-fill, surround and delay systems built around 5XT, Syva, X8 and A10 Wide enclosures.

Following a China tour using pre-recorded music, the cast returned to Hong Kong for two weeks of live orchestra rehearsals ahead of the month-long run, with a tightly scheduled ten-day technical build and rehearsal period. The production generated strong audience response and significant social media attention throughout its run. Reflecting on the journey, Yue emphasises that immersive audio in musical theatre demands a fundamentally different mindset. “It’s not simply about having more speakers; it’s about how thoughtfully you use them,” he says, a sentiment echoed by Ha, who notes that immersive audio in live theatre delivers a level of dynamism and dimensionality that recorded media cannot replicate. Together, The Impossible Trial stands as a compelling case study in how careful collaboration, acoustic understanding and measured application of immersive technology can elevate musical storytelling to new emotional depth.