Pros and cons of equipping Harmonic Acoustic Pneumatic Sources (HAPS) with quarter wave tube: analytical model versus experimental validation

Pneumatic acoustic sources enable high Sound Pressure Levels (SPL). Harmonic Acoustic Pneumatic Sources (HAPS), utilizing airflow modulation to create precise acoustic pressure fields with controlled amplitude and phase, emerge as solutions for active harmonic-noise control at high SPLs. While theoretically capable of generating pure tones, HAPS appear to be non-linear sources with significant harmonic distortion in practice. Additionally, the mass airflow consumption of this source could be a drawback in certain applications. The aims of this study is to evaluate the advantages of a Quarter-Wave Tube (QWT) located at the HAPS output. A numerical analytical linear model has been developed to compute the radiated acoustic pressure and consumed mass air flow, according to the QWT and HAPS characteristics. For the cases of HAPS equipped with various QWT, this presentation will compare experimental results with the analytical model. This aims to highlight the advantages, including increased SPL of the radiated fundamental, reduced fundamental/harmonic distortion over a wide frequency range, and decreased airflow consumption. The disadvantage is related to the space required by the QWT because its diameters must be greater than the HAPS output. Whatever, this study demonstrate that HAPS can be improved when equipped with a dedicated exhaust.