Sound Power Level:

# Sound Power Level:

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## Sound Power Level:

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##### Presentation Transcript

1. Amazing dB’s Sound Pressure Level: Sound Power Level: The main thing to remember is that 100 dB sound pressure level and 100 dB sound power level are completely different! To avoid confusion, use the reference values: 100 dB (re 20 Pa) sound pressure level 100 dB (re 1x10-12 W) sound power level 1

2. But they are related… S in m2 (no reflections) (Spherical source) r (Hemi-spherical source) S = cross-sectional area (duct) r 2

3. An Example A source has a sound power level of 90 dB (re 10-12 W). What is the sound pressure level at a distance of 10 m in (a) a free field, (b) in a hemispherical free field, and (c) in a duct of cross-sectional area 1 m2? a. b. c. 3

4. Numerical Acoustics Field Quantities p, u = sound pressure and particle velocity in the field. How do we determine these? un= velocity of surface in normal direction – must be known 4

5. Two Vacuums Shopvac Bosch 5

6. Bosch Vacuum Exhaust flows through foam 6

7. Sound Power Exhaust Deflected Upward 8

8. Sound Power Comparison at Low Frequency Low Frequency Tone 12

9. Sound Quality Bosch (original) Bosch (w/o foam) Shopvac Bosch (w/o 1st peak) 14

10. Sound Quality: Jury Test Note: Rate each vacuum on a scale from 1 to 10 where 1 is “very quiet” and 10 is “very loud.” 15

11. Summary • Absorption of foam in BOSCH significantly reduces sound power • Sound exhaust is better directed on BOSCH • Recommend altering design to reduce/shift first peak 22