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
Dept. of Mech. Engineering
University of Kentucky 1

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

3. An Example
A source has a sound power level of 90 dB (re 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.
Dept. of Mech. Engineering
University of Kentucky 3

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

5. Two Vacuums Shopvac Bosch Dept. of Mech. Engineering 5
University of Kentucky 5

6. Bosch Vacuum Exhaust flows through foam Dept. of Mech. Engineering 6
University of Kentucky 6

7. Shopvac Vacuum
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University of Kentucky 7

8. Sound Power Exhaust Deflected Upward Dept. of Mech. Engineering 8
University of Kentucky 8

9. Time and Frequency Domains
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University of Kentucky 9

10. Sound Power Comparison – Bosch, All Sides
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University of Kentucky 10

11. Sound Power Comparison – Narrow Band
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University of Kentucky 11

12. Sound Power Comparison at Low Frequency
Low Frequency Tone
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University of Kentucky 12

13. Sound Power Comparison – 1/3 Octave
Dept. of Mech. Engineering
University of Kentucky 13

14. Sound Quality Bosch (original) Bosch (w/o foam) Shopvac
Bosch (w/o 1st peak)
Dept. of Mech. Engineering
University of Kentucky 14

15. 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.”
Dept. of Mech. Engineering
University of Kentucky 15

16. Foam Inside Bosch Vacuum
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University of Kentucky 16

17. Sound Absorption Coefficient
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University of Kentucky 17

18. Sound Absorption Coefficient of Foam
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University of Kentucky 18

19. Sound Intensity (Shopvac)
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University of Kentucky 19

20. Sound Intensity (Bosch)
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University of Kentucky 20

21. Sound Intensity (Bosch)
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University of Kentucky 21

22. 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
Dept. of Mech. Engineering
University of Kentucky 22