Smart material wolf note eliminators
Wolf notes are unwanted modulated sounds that can occur in string instruments, violoncellos in particular. The elimination of these wolf notes is a well-known challenge for violin makers. Some mechanical wolf note eliminators have become popular and are used by many cellists and violin makers to reduce the problem. These conventional solutions are usually based on the physical principles of tuned mass dampers or simple rubber dampers. Generally, these wolf note eliminators are able to eliminate the wolf notes. Unfortunately, they affect the whole cello sound even if no wolf note occurs. Another drawback is their sensitivity to environmental conditions, such as the ambient temperature or the humidity. An interdisciplinary approach, combining the experiences and methods of musicians, instrument makers, and engineers in the use of so-called smart materials has allowed the development of active and semi-active solutions to eliminate wolf notes with negligible effects to the whole cello sound while being independent of environmental influences. An active and a semi-active smart material wolf note eliminator, and the corresponding development challenges are presented. Both systems work with a piezo ceramic patch actuator, which must be applied to the surface of the cello body. The semi-active approach is based on resonant shunt damping while the active approach is implemented by means of a triggered velocity feedback controller. Effects of both systems on the wolf notes and the cello sound, compared to those of conventional mechanical dampers, are pointed out, and a complete wolf note elimination using the active system is presented.