ProfileKarl Eilers has worked as an electronics engineer for nearly 50 years with an emphasis on pro audio. His varied experience includes sound for a Billy Graham crusade and design and construction of the audio system at the Valleyfair! theme park near Minneapolis. He also accompanies silent films on the theater organ and has appeared twice on the Prairie Home Companion radio show. Eilers has written several articles on speech intelligibility and lectures on commercial audio and 70-volt speaker systems. He is the publisher and principal author of the study guides for the ETA Electronics Modules 1-5 certifications and one of the authors of a new Systems Level handbook, due out soon.