Final answer:
The most relevant source for the study group preparing a report on the effects of mobile use on consumers' hearing is a university research paper about decibel limits of headphones and speakers.
Step-by-step explanation:
The most relevant source for the study group preparing a report on the effects of mobile use on consumers' hearing would be the university research paper about decibel limits of headphones and speakers. This source would provide information on the specific decibel levels that can cause hearing damage and the impact of mobile phone use on consumers' hearing health.