In Person Only at the Boston Park Plaza

11 – Acoustic Isolation
Nicolas Jobert (Alma Consulting)

Tuesday, November 14, 2023
2:00 PM – 6:00 PM (EST USA) – Part 1

This tutorial aims at providing the attendees with a sound basis for efficiently addressing structural vibrations originating from acoustic pressure fluctuations, namely : airborne vibrations.

While the field of structure-borne-sound is relatively well covered, the converse is not true. One obvious reason is that airborne vibrations can usually be ignored, unless sound pressure level are considerable, or if admissible vibrations amplitudes are very small.

In the first case, typical of aerospace launchers or power generation industry, detailed simulations are conducted and further validated via testing. or, when configurations are similar enough for project-to-project deviations to be remain minimal, they can be handled via design-by-rule procedures. For particularly demanding precision engineering tasks however, the allowable levels can be extremely small, while geometries and mechanical configurations are be highly diverse, ranging from slender (vibration immune) supports to large (vibration prone) enclosures.

Overall, for the precision engineer, there is a need for recognizing situations where acoustic induced vibrations are indeed significant, and in such situations, how to best control them. And the end of the tutorial, it is expected that the attendees should be equipped with clear notions about how acoustics waves might disturb a given system, how to quantify their contribution and when required, what are the technical options for mitigating the problem at hand.

  1. Basic Notions
    • Sound Pressure Level / Acoustic Intensity vector
    • Sound Pressure Field : making sense of time-wise and space-wise patterns.
    • Sound in ducts and enclosures .
  2. Orders of Magnitudes, rules of thumb, simplified approaches
    ◦ estimating loads
    ◦ estimating compliance : taking advantage of randomness in time and space domains:
    ◦ numerical application using spreadsheet : joint acceptance integral method
  3. Sources identification and ranking
    ◦ Principles
    ◦ Sensors and their limits
    ◦ Application with microphones (live!)
  4. Mitigation techniques
    ◦ source modifications
    ◦ propagation path modifications (filters / insulation)
  5. Illustrations using real-world test-cases
    ◦ Pressure shell
    ◦ Sample stage

Intended audience : This is a beginning to intermediate level course, with material ranging from basic to complex, to provide both an overview and references for further study. The intended audience is graduates, postgraduate engineers/physicists, plus industry technical staff having a first experience in systems for which vibration-induced disturbances are relevant, and aiming at strengthening their insight so as to reduce guesswork for future projects.

After graduating in 1996 from the Ecole Centrale Marseille, where he studied Mechanical Engineering and specialized in Noise and Vibrations, Nicolas Jobert has been active in a range of consulting companies providing services for industry, civil engineering companies and numerous research centers.