On the linewidth of the ultrasonic Larsen effect in a reverberant body

Richard L. Weaver, Oleg I. Lobkis

Research output: Contribution to journalArticlepeer-review


A simple ultrasonic feedback circuit is applied to a high-Q elastic body. At sufficient gain, an ultrasonic howl - or Larsen effect, ensues. It is a pure tone with an extraordinarily narrow spectrum. Theoretical estimates are constructed that predict linewidths proportional to the ratio between the spectral power density of the background noise and the intensity of the howl. In these experiments, this is of the order of nano-Hz and is unmeasurable. By augmenting the absorption and adding noise, the width is brought into a measurable regime, and the theory's prediction of a wider line is confirmed. It is speculated and demonstrated that these narrow lines permit high precision measurements of tiny changes in structures.

Original languageEnglish (US)
Pages (from-to)102-109
Number of pages8
JournalJournal of the Acoustical Society of America
Issue number1
StatePublished - 2006

ASJC Scopus subject areas

  • Arts and Humanities (miscellaneous)
  • Acoustics and Ultrasonics


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