Numerical modelling of supra-aural headphones

• Main Author: Kelly, Liam
• Published: University of Salford 2010
• Subjects: 621.382
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.525889

Headphone design is facilitated by modelling and has traditionally been carried out using lumped parameters, which are efficient but limited to low frequencies. In this investigation a wave based approach is taken using finite elements to introduce a headphone modelling tool which has the capability to predict high frequency harmonic components in the acoustic field. The development of these increased bandwidth headphone modelling capabilities is carried out over 3 discrete design phases involving 2D axisymmetric and 3D models with the key components being the porous cushion, the headphone driver and the geometric profile of the pinna. The cushion is represented using a well established 6 parameter porous material model as an equivalent fluid which is a convenient approach for a finite element implementation. Characterisation of porous materials using such an approach generally involves an expensive and time consuming measurement regime; this investigation has shown that multi-dimensional optimisation gives an adequate representation without need for this. Simulations using the finite element model headphone model are compared against measurements taken on a HATS mannequin and show good agreement up to 10 kHz, a significant improvement in bandwidth over previous publications. An investigative survey was carried out using these software tools of various headphone dimensional parameters, including a representation of pinna variation which, significantly, shows wide variations in frequency responses at high frequency. If used as an indication of inter-subject variation it suggests the ability to model accurately to a high frequency may only have limited benefits for headphones intended for many different wearers.