Veröffentlichungen und Präsentationen

Determining an optimal port profile for a vented loudspeaker is still an unsolved problem. Studies that measured distortion content suggest a gently flared port is best, while subjective listening tests suggest that more aggressive flare rates are optimal at low to moderate levels, but at higher levels the gentler flare rates perform better. Recent advances in nonlinear loudspeaker control can be used to implement limiters based on port output, such that ports remain below turbulence cutoff. This work aims to extend subjective listening tests and correlate them with objective measurements as well as simulations in COMSOL Multiphysics^® simulation software.

This work aims to correlate subjective listening tests and objective measurements in anechoic chambers with linear acoustic Finite Element simulations. We hypothesize that the optimal port profile can be designed with linear acoustic simulations, as long as the port vent can be operated below turbulence levels. Under the assumption of linear flow, the optimal port profile generates a minimal amount of shear in the air inside the port, because with minimal shear, the port will stay laminar for the highest possible volume velocity, and thus the highest possible SPL.

We have 3D printed 9 different port profiles and tested them in our anechoic chamber. The ports have all been designed to tune to the same frequency of 40 Hz inside a test box, which is driven by two 10" subwoofers. Three different test signals are recorded at different levels for all ports in the test box. The recordings are then used with high quality headphones to conduct the subjective measurements.

The port profiles were all simulated using the Acoustics Module in COMSOL Multiphysics^® to determine the appropriate tuning frequency. The two drivers are simulated as Lumped Parameters using equivalent electric circuits in the AC/DC Module. The optimization Module was used to determine the optimal port profile with the minimal amount of shear in the air inside the port. Additionally, Model Methods were used to facilitate the automation of the optimization setup. This allowed for simplified execution of different optimization runs with different objectives, while automatically updating the design parameters.

The novel contribution of this paper to the audio community is the systematic correlation of subjective measurements, objective measurements of noise and distortion, with predictions that can be made with linear Finite Element simulations in conjunction with numerical optimization. It shows that optimal port geometries can be designed without the need to perform expensive and complicated fully turbulent CFD analyses.