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Engineering Noise Control Getting Started with Just a Sound Level Meter

Engineering Noise Control Getting Started with Just a Sound Level Meter. Keith M. Groth, CIH, CSP IHI Environmental March 7, 2012 Salt Lake City AIHA Local Chapter. Overview. Intro Quick Review of Key Concepts Understanding Matters Where You Stand May Matter More

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Engineering Noise Control Getting Started with Just a Sound Level Meter

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  1. Engineering Noise Control Getting Started with Just a Sound Level Meter Keith M. Groth, CIH, CSP IHI Environmental March 7, 2012 Salt Lake City AIHA Local Chapter

  2. Overview • Intro • Quick Review of Key Concepts • Understanding Matters • Where You Stand May Matter More • Where it Goes Matters Too

  3. Introduction • The Intent is Start the Process of Moving Beyond Ending Noise Assessments With, “For Noise Exposure Above 90 dBA OSHA Required Feasible Engineering Controls” • The Intent is Not Provide a Course in Acoustics Engineering.

  4. Key Concepts • Classical Approach is Employ Noise Control at: Source=>Path=>Receiver • Sources: A Primary Source is Rarely Without Secondary Sources • Source Types: Vibrating Surfaces, Compression, Combination • Path: Contiguous volume of lowest sound energy resistance between source and receiver. Usually “Paths” – One Usually Dominates for Each Source • Receiver: Fixed, Mobile, Task

  5. Key Concepts • Frequency Content Is Usually Important • Can Help Identify Source of Concern (Primary or Secondary) • Determines Effective Noise Control Options • Noise Can Be Highly Directional • ROI and Doubling are Directly Related

  6. Understanding MattersNoise Sources (Primary & Secondary) • Primary Noise Source • Can Be Multi-Component • Motor, Articulating Members • Cabinet, Mounts • Independent Versus Dependent • Secondary Sources • Structure Borne • Reverberant Noise • Can Be a Significant Distance From Primary

  7. Understanding The Primary Source(s) • What is Producing the Noise? • Vibration • Rotating Source • Turbulent Fluid/Vibrating Surface • Compression • Rapid Air Movement/Change • Blade Passage Frequency • Overpressure/Blast • Evaluate Source SPL (Flat & A) & Octave Band

  8. The Effects of Multiple SourcesIndependent (Incoherent) Sources To add together more than 2 noise sources; start with the two largest. Combine the two largest and then third next. Keeping going until dB difference is greater than 10. About 10 dB is the most you will ever add to the highest reading.

  9. Adding Similar Sources is Location Dependent Not! X +3 dBA X’ +3 dBA B A C A X dBA X dBA

  10. Multiple Source Assesment • Measure Overall Noise at the Receiver(s) (A-Weighted, Octave Band or 1/3 Octave Band) • If Possible, Evaluate Sources Independently • Identify and Rank Order Sources (Usually Based on dBA)

  11. Where You Stand Matters • Is Relative Source/Receiver Position Dynamic? • Which Noise Field is the Receiver In? • What Are the Noise Paths? • Are there Flanking Paths?

  12. Where You Stand Matters • Near Field: Instantaneous pressure and velocity are not in phase. Normally occurs close to surface of radiating device. • Far Field: Instantaneous pressure and velocity are in phase. Typically starts far from source for low frequency and closer to source for high frequency. • Reverberant Field: Measured sound levels are dominated by reflected noise. Sound level is nearly constant with distance.

  13. Reverberant or Direct Source Near Field Far Field Conceptual Depiction of Noise “Master Equation” Sound Pressure Level Reverberant Field Direct Field Critical Distance Free Field Log r

  14. Where it Goes Matters TooNoise Paths • Direct Noise (Air-Borne) Normally Found By Inspection, If Necessary Use Sub-Paths • Reverberant Noise Measure To Find It, Location, Can Occupy Lower Frequencies • Flanking Paths Can be Hard To Find, Noise Intensity a Factor • Structure-Borne • Typically Borne by Rigid Members, Frequency Usually Different From the Source

  15. Basic Checklist • Define The Problem • Qualitatively Identify Source(s), Path(s), Receivers(s) • Free Body Diagram • Evaluate and Rank the Sources • Give Consideration to All Possible Controls • Select Combination of Controls for Budget • Apply Controls and Evaluate Results

  16. Notional Free Body Diagram Receiver V R Flanking Path V Reverb Field R R V R R Receiver R V= Vibration Source R=Radiating Source

  17. Source Control • Normally Will Provide the Most Benefit if Feasible • Lower Excitation Forces • Alter Structure to Change Response to Input Forces (Isolation, Dampening) • Modification is most Practical in Design (Newer Model or Retrofit Available)

  18. Path Contol • Eliminate Path Start (Move Source, Move Receiver) • Alter Path to Reduce/Eliminate Energy Transfer to Receiver (Barriers/Walls, Enclosures) • Eliminated Secondary Sources By Path Elimination (Acoustical Treatment)

  19. Receiver Control • Enclose the Operator (Shields, Booths, Control Rooms) • Limit Transient/Collateral Exposures

  20. DISCUSSION/QUESTION?

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