Acoustical properties of earplugs

Per Hiselius

Research output: ThesisDoctoral Thesis (compilation)


In this study an experimental setup for measurements of high impedance objects in ducts, yielding the acoustical Two-Port properties of the object, is applied to earplugs. A frequently used experimental setup for measuring objective acoustical properties of earplugs is that of artificial ears. Great effort is spent on duplicating the human ear. The acoustical properties of the earplug are thought to be given by the insertion loss. Such a setup, however, gives a ratio of the "response of a system" to that of "another system". The actual properties of the earplug are thereby embedded in a complicated artificial response. A novel approach, presented here, is to use a simple setup. Given the sound pressure level on both sides of the earplug for two sufficiently different termination impedances, the Two-Port properties can be assessed. First, a setup is used where the earplugs are fitted in a cylinder. Second, a setup based on molds of the ear canals of a real person is used. For six types of earplugs, the acoustical properties are assessed and numerically coupled to a model of the ear in order to predict the insertion loss. The predicted attenuation is compared to subjective (REAT) attenuation. In addition, experimental Two-Port data is used to model the acoustical behavior of three fundamentally different types of earplugs. It is shown that simple lumped models suffice to describe the acoustical behavior of the earplugs. Furthermore, it is shown that the measurement setup can be advantageously used to assess the acoustical properties of an arbitrary acoustical partition for a wide frequency range.
Original languageEnglish
Awarding Institution
  • Engineering Acoustics
  • Hammer, Per, Supervisor
Award date2005 Jan 21
ISBN (Print)91-628-6370-3
Publication statusPublished - 2005

Bibliographical note

Defence details

Date: 2005-01-21
Time: 13:15
Place: Lecture hall C at "V-huset", LTH, John Ericssons väg 1, Lund.

External reviewer(s)

Name: Poulsen, Torben
Title: Associate Professor
Affiliation: Örsted DTU, Denmark


Subject classification (UKÄ)

  • Fluid Mechanics and Acoustics


  • Maskinteknik
  • hydraulik
  • vakuumteknik
  • vibrationer
  • akustik
  • vibration and acoustic engineering
  • vacuum technology
  • hydraulics
  • Mechanical engineering
  • acoustic modelling
  • objective measurement
  • insertion loss
  • earplugs
  • HPE
  • HPD
  • hearing protectors
  • Two-Port
  • Four-Pole
  • attenuation
  • electro acoustics
  • acoustics


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