Development of a Headphone Simulator : An Acoustical Test Rig for Simulating a Circum-aural or Supra-aural Earphone

Sammanfattning: This report was written as a part of the Master thesis conducted during the spring of 2017 at Zound Industries International AB and at the Department of Machine Design, School of Industrial Engineering and Management at the Royal Institute of Technology (KTH) in Stockholm. The timeline was 20 weeks of full time work. The purpose of the thesis work was to develop a device to evaluate the acoustical properties of an earphone. This device should be able to accurately simulate the internal volumes and leakages in an earphone. A research question to define the purpose was, “Can the frequency response of a headphone be simulated before manufacturing by using a physical Headphone simulator with variable parameters?”. The method used for the development process, was the so called Double Diamond Model. T he frame of reference presents different acoustic terms, sound measurement equipment and standardized types of earphones. The construction of an earphone is described and the mathematical models used in simulations when developing headphones are presented. The concept development phase of the project was a matter of first formulating requirements in collaboration with the acoustics and design departments. For example, The Headphone simulator should be equivalent to a circum-aural or supra-aural earphone. Then Problem Areas were formulated and explored, this to narrow down the points of interest before developing whole concepts. Concepts were generated, prototyped, regenerated and then evaluated using a Weighted decision matrix. The concept chosen was the Coaxial Concept. In the result chapter the development and manufacturing of the Coaxial Concept is shown. The development was done using first an Alpha prototype to test out the mechanism, then a Beta prototype to prove the concept using the correct materials and manufacturing methods. The Beta prototype was successfully run through some acoustical validations, this to prove that the performance was acceptable. Final improvements were done to the design and a fully CNC machined prototype was ordered. The results were then discussed using an economical, ecological and manufacturing perspective. Here the modularization and larger initial costs were discussed, this to reduce the ecological impact of the Headphone simulator. With the results presented, it was concluded that the Headphone simulator fulfills its purpose. However, further experimental tests are needed to see its full potential. Future work and recommendations are then presented. Here recommendations for drilling leakage paths are presented and the future work is how to improve the mechanical aspects of the Headphone simulator and the potential to develop a smaller version of the Headphone simulator.