Sound Zone Control Robust To Sound Speed Change
Sankha Subhra Bhattacharjee, Jesper Rindom Jensen, Mads Græsbøll Christensen
TL;DR
This paper addresses SZC degradation caused by TH-induced changes in sound speed, which distort pre-measured IRs. It introduces SICER, a sinc interpolation-based IR correction that maps an IR at $c_{\textrm{old}}$ to a new IR at $c_{\textrm{new}}$ using $\beta = \frac{c_{\textrm{old}}}{c_{\textrm{new}}}$ and $ h'(m)=\frac{1}{\beta}\sum_{n=0}^{N-1} h(n)\mathrm{sinc}(\frac{m}{\beta}-n)$, preserving energy and avoiding discretization errors. This corrected IR is then fed into the VAST framework, yielding a SICER-corrected VAST filter $\bm{w}'$ that remains near-optimal under SPS changes. Simulations in a reverberant indoor room show significant improvements in acoustic contrast and reduced signal distortion compared with uncorrected IRs, for both SPS reductions and increases, illustrating practical robustness for real-world SZC deployments.
Abstract
Sound zone control (SZC) implemented using static optimal filters is significantly affected by various perturbations in the acoustic environment, an important one being the fluctuation in the speed of sound, which is in turn influenced by changes in temperature and humidity (TH). This issue arises because control algorithms typically use pre-recorded, static impulse responses (IRs) to design the optimal control filters. The IRs, however, may change with time due to TH changes, which renders the derived control filters to become non-optimal. To address this challenge, we propose a straightforward model called sinc interpolation-compression/expansion-resampling (SICER), which adjusts the IRs to account for both sound speed reduction and increase. Using the proposed technique, IRs measured at a certain TH can be corrected for any TH change and control filters can be re-derived without the need of re-measuring the new IRs (which is impractical when SZC is deployed). We integrate the proposed SICER IR correction method with the recently introduced variable span trade-off (VAST) framework for SZC, and propose a SICER-corrected VAST method that is resilient to sound speed variations. Simulation studies show that the proposed SICER-corrected VAST approach significantly improves acoustic contrast and reduces signal distortion in the presence of sound speed changes.