Bass reflex ports produce noise at high sound-pressure levels due to turbulence and vortex shedding. Flared ports can reduce port noise compared to straight ports, but the optimal flare rate in ports has remained an unsolved problem. This work demonstrates that there is in fact an optimal amount of flare, and it proposes a design method based on acoustic Finite Element simulations to efficiently predict the optimal flare rate for given port dimensions. Optimality of the flare rate is confirmed with noise and compression measurements as well as double-blind listening tests. At onset of unwanted port noise, optimally flared ports can be played 1 to 3 dB louder than slightly under-flared or over-flared ports, and 10 to 16 dB louder than straight ports.
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https://aes2.org/publications/elibrary-page/?id=20683
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