Electrolux EHP Training Basics

noise measurement

EHP Training Centre 2004

Wilhelm Nießen

2

Sound

Sound is produced by bodies that vibrate.The vibration causes changes in the air pressure.The waves generated this way produce a sound.

µbar

3

Frequency and Wavelength

The range of the human speech

amounts to approximately

300 - 3,000 cycles per second (Hz)

The audio range of humans (young

and healthy) is with approximately

20 - 20,000 cycles per second (Hz)

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Comparison of Audio Ranges

Chicken 125 – 2 000 Hz

Humans 20 – 20 000 Hz

Dog 60 - 45 000 Hz

Cat 45 - 65 000 Hz

Bat 2 000 – 110 000 Hz

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Speed of Sound / Noise Levels

Speed of sound:Air 334 m/sWater 1400 m/sSteel 5000 m/sTypical noise levels:Calm room 25-35 dB APopulated area 35-50 dB ATrade area 50-65 dB A

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Sound and Noise

Airborne sound covers mechanical oscillations of air, 16 – 20,000 Hz, from tones, sounds and noises.

Tone = Sinusoidal change of air pressure

Sound = Mixture of individual tones

Noise = Unwanted tones and noises

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Noise

Large volumeis not always the causefor disturbing noises

Noise = Unwanted tones and noises

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Practice 1

Now we want to do some measurements.

Measuring instrument “testo”

Measuring instrument“Voltcraft”

1. Room noises

2. Appliance “a”

3. Appliance “b”

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Measuring Table

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Sense of hearing

The ear collects the airborne sound waves and leads it over the auditory canal to the ear drum. The received hearing impulses are converted to electrical nerve impulses and passed on tothe brain.

0

The auditory sensation is very complex, psychologically due to the attitude towards the sound event and physiologically individually very different.

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Characteristic of Human Hearing

The human hearing is not equally sensitive for all frequencies. At the same sound pressure, tones <300 and >5000 Hz are more felt less loud than tones within the range 1000 to 3000Hz.

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Measurements

Frequency

Each doublingof the distance tothe sound source

reduces the volume by 6 decibels.

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Sound Level dB (decibels)

The (A) valuation is approximately the frequency response of the human hearing. Noise valuations in work areas,or traffic noise, are measured in dB (A). In (B) and (C) valuations, the frequencies up to 1000 cycles per second are more strongly considered.

Sound level measurements are made over valuation filters.Valuated sound levels are marked by the suffix (A), (B) or (C).

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Actual Sound Measurements

Noise Measuring

0

10

20

30

40

50

60

70

.2khz 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 3.5 4 5 6 7 8

dB

Testo dB (a) Voltcraft dB (A) Voltcraft dB (C)

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Sound Measuring

Keep minimum distances.

Align microphone to the source of sound.

For further reference refer to the operating instructions!

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Practice 2

Now we make it correctly!

Measuring instrument “testo”

Measuring instrument“Voltcraft”

1. Room noises

2. Appliance “a”

3. Appliance “b”

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Addition of Sound Levels

Sample:

level 1 = 82 dBlevel 2 = 85 dBdifference = 3 dBcorrection from diagram of 1.7 dB total levels = 85 dB + 1.7 dBresult = 86.7 dB

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Subtraction of Sound Levels

Sample:

total noise = 60 dBbackground noise = 53 dBdifference = 7 dBcorrection from diagram = 1 dBequipment noise = 60 dB – 1 dBresult 59 dB

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Noise Lab

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Objective / Subjective Noise Test

Mean Value: 3.2

0

0.5

1

1.5

2

2.5

Notaudible

2 Average 4 Veryloud

subjective volume (5 persons)

Mean Value: 2.6

00.5

11.5

22.5

33.5

Notaudible

2 Average 4 Very loud

29.5 dB A

subjective disturbance (5 persons)

Electrolux EHP Training

Basic inGeräuschmesstechnik

EHP Training Centre 2004

Wilhelm Nießen