Abstract: To address the limited space available for secondary sources of active noise control systems in the vehicle cabins, a sparse regularization method incorporating L1-norm constraints is proposed. This method explicitly accounts for structural constraints imposed by the cabin on candidate speaker positions, numbers, and combinations, thereby improving the noise reduction performance. A numerical model of the vehicle cabin is established. The finite element method (FEM) is employed to compute the acoustic transfer functions (ATFs) from secondary sources inside the cabin to the head locations of the driver and front passenger seats. Based on these numerically computed ATFs, the optimal placement of secondary sources is determined by minimizing a cost function using the CVX optimization toolbox, combined with a partition-based optimization strategy. The results show that, under an equivalent control configuration, the optimized speaker positions yield superior noise suppression at error sensor locations—specifically at the head positions of the driver and front passenger—compared to the original placements. In the frequency range of 20–140 Hz, the overall sound pressure level (SPL) is reduced by more than 10 dB; the optimal combination (speakers at positions 6, 12, 18, and 24) achieves a 11.1 dB reduction. In the 150–500 Hz range, the overall SPL is reduced by approximately 1 dB, with the optimal combination yielding a 1.0 dB reduction. This method addresses secondary source placement optimization in the non-free-field, acoustically complex environment of vehicle cabins, offering a practical and engineering-feasible analysis method for active noise control system design in automotive applications.