Small rehearsal rooms and recording studios demand carefully controlled acoustic conditions, typically defined by target values of acoustic strength and reverberation time. In the low-frequency range, however, sparse modal density leads to uneven frequency responses and non-diffuse reverberation. Conventional absorptive treatments are often narrow-band or space-consuming and may not sufficiently reduce the perceptual prominence of individual room modes.
This thesis investigates the use of Helmholtz resonators (HRs) for targeted low-frequency room mode manipulation in small spaces. Beyond their common interpretation as narrow-band absorbers, HRs exhibit widely tunable reflection properties, including frequency-dependent phase behavior that can influence modal distribution. Particular attention is given to the level-dependent response of HRs at sound pressure levels typical for room acoustics, with the aim of both characterizing nonlinear effects and exploring strategies to maintain or deliberately utilize them in practical designs.
The research integrates three complementary perspectives: resonator development, room-acoustic modeling, and perceptual assessment. First, the physical principles and level-dependent behavior of HRs are examined. Second, analytical and numerical studies explore their implementation in small rooms, including mode manipulation using HRs and hybrid simulation approaches. Third, an ABX listening test evaluates the minimum audible changes in low-frequency reverberation time for musical stimuli, focusing on relative mode damping rather than complete elimination of audible resonances.
By combining the above-mentioned perspectives, this work establishes a comprehensive framework for the application of Helmholtz resonators in small-room acoustics.