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ME458 Lab 5 8/17/2000 page 1
ME458 Noise Control
Laboratory Exercise
Sound Power Measurement
Objective: Measure the sound power of a machine by two different methods and compare the results.
Background: The most widely used methods for determining sound power are based upon sound pressure measurements in known acoustical environments (either free field or diffuse field. Well-defined U.S. and international standards exist which specify these test procedures and are documented in your text.
Part 1 - In Free Field Above a Reflecting Plane Measure the overall sound power of the test object in the hemi-anechoic chamber using the procedure outlined in section 6.4 of Lord, Gatley and Evensen (ANSI standard S1.35-1979). Does the room meet the requirements listed in the text?
Measured Data:
ME458 Lab 5 8/17/2000 page 2
Part 2 - Substitution Method in Reverberation Chamber Measure the sound power of the same device as Part 1 in the reverberation chamber. Use the ILG source (the gray squirrel cage blower) as the reference sound source and take at least six measurements in the reverberant field at different locations in the room. How can you predict or measure where the reverberant field begins? The octave band power levels of the ILG source are listed on its nameplate. Determine the octave band power levels and the overall power level. Note: with this method you are essentially measuring the room absorption and empirically determining the relation between sound power and sound pressure. Does the room meet the requirements listed in the text?
Measured Data: Source SPL avg ILG
Summary of results: Test Method Sound Power Level (dB re 10-12^ watts) Free Field Substitution Method
Reporting Requirements: Submit a brief, concise lab report, including: cover page, list of instrumentation, calculation details, sources of error, conclusions, comments, answers to all questions
