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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

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
Overview
  • Intro
  • Quick Review of Key Concepts
  • Understanding Matters
  • Where You Stand May Matter More
  • Where it Goes Matters Too
introduction
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.
key concepts
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
key concepts1
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
understanding matters noise sources primary secondary
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
understanding the primary source s
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
the effects of multiple sources independent incoherent sources
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.

adding similar sources is location dependent
Adding Similar Sources is Location Dependent

Not! X +3 dBA

X’ +3 dBA

B

A

C

A

X dBA

X dBA

multiple source assesment
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)
where you stand matters
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?
where you stand matters1
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.
slide13

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

where it goes matters too noise paths
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
basic checklist
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
slide16

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

source control
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)
path contol
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)
receiver control
Receiver Control
  • Enclose the Operator (Shields, Booths, Control Rooms)
  • Limit Transient/Collateral Exposures