 Though the algorithm was good, the reference microphone was an unpredictable variable: it had practical placement problems. If it was near the audience, audience noise would skew the algorithm. If placed backstage, crew and equipment noises could be a factor. Thus, the Dugan Music System was not immediately developed into a product. Dugan studied the problem, researching alternative solutions. In 1975, Dugan filed a patent for the "Dugan Speech System", and in 1976 produced 60 copies of what he named the Dugan Model A. The automixer with serial number 1, a unit Dugan fabricated by hand, "was installed in the conference room of Bell Labs by Harvey Fletcher". Significantly, the external microphone reference of the Dugan Music System was replaced by a reference composed of the total signal received from all of the active microphones. Dugan described the process some three decades later:
