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Brüel & Kjær Sound & Vibration Measurement A/S.

Copyright © 2009. All Rights Reserved.

Advanced Measurement Techniques

FFT & Sound Intensity

www.bksv.com

Brüel & Kjær Sound & Vibration Measurement A/S.

Copyright © 2009. All Rights Reserved.

2250 FFT Narrowband Zooming Frequency Analyzer Application BZ7230

Getting the details.

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FFT

•The Fast Fourier Transform (FFT) is an important tool for environmental acoustic assessment.

•Frequency content of an industrial or transportation source can be used for:•The detection of tonality

•The design of abatement e.g. barriers

•Many sound level meters, e.g. Type 2238, are capable of octave and 1/3 octave acquisition. Advanced sound level meters, e.g. Type 2250, Type 2260, are capable of calculating the FFT of a source.

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L[dB]

LA [dB(A)]LB [dB(B)]LC [dB(C)]LD [dB(D)]LLin. [dB]

Frequency[Hz]

1/1 Octave

1/3 Octave

FFT

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Brüel & Kjær Sound & Vibration Measurement A/S.

Copyright © 2009. All Rights Reserved.

Handheld Vibration Measurement

withModel 2250

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Why Make a Frequency Analysis?

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Frequency Spectrum or Overall Level

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“Real World” Vibration Levels

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2250 FFT offers incredible performance

Up to 6400 Line FFT! Which means…

You cover the complete 0-20KHz audible frequency span with high frequency resolution ~ 3 Hz

Providing the real benefit of simplifying the measurement process.

AND… coupled with zoom analysis you an unprecedented resolution in ahand held analyzer – 1/64 Hz (0.015625Hz)

Providing the real benefit of seeing the details like never before.

You can select from 100 to 6400 lines of analysis in a binary sequence (100, 200, 400, 800, 1600, 3200, 6400)

Because there are lots of times you don’t need all that data!

The Type 2250 FFT lets you pick the transform size to match the job!

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Note: 2KHz Span 1600 Line FFT with expanded display

Zooming has never been more fun!

Touch and drag, select zoom and go!– The Type 2250 will automatically select the next wider frequency span.

– Un-zoom by clicking the X axis option

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Tools to Help you with Frequency Analysis

A-weighting of Spectrum

Overall A-weighted Values, Too!

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Auto-peak finder

Corrected Frequency

Compare with Reference

Tools to Help you with Frequency Analysis

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Type 2250 FFT gives you only good vibrations

Finally, an easy to use vibration meter.

– The BZ7230 application gives you vibration measurement capability to any Type 2250 (just add an accelerometer) and display results as Acceleration, Velocity or Displacement – in SI or US/UK units

– Broadband dB re 10-6 m/sec

Total Value, too

Limit Level

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Other things you should know…

1-2-5 frequency span sequence – industry standard.

Don’t forget the Sound Recording Option

RPM can be measured as a parameter – Use the Trigger input – full function tacho setup

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BZ5503 Utility Program

Preview, Search &

Sort Measurements

Open and work with

measurements

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Do More with BZ5503

Export data to other useful programs

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Type 2250 FFT for Production Test

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Type 2250 FFT for Production Test

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Type 2250 FFT for Production Test

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Outline specification for Tolerance bands

Tolerance windows are specified by an upper and lower limit and an upper and lower frequency range

Tolerance windows can be specified graphically

Up to 10 tolerance windows available

Tolerance windows can have overlapping frequency ranges

Each Tolerance window can be named

The combined pass/fail should be available as a voltage output from the instrument

Limitless number of tolerance window definitions, e.g. one for each device and device variant to be tested.

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2250 FFT - tolerance window operation

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2250 H 001 to consists of

2250 body only (no mic and preamp) with preamp cap

Power supply

Leather cover for meter

BZ 7230 FFT application license

BZ 5503

USB cable

5 Stylii

Options for inclusion to basic system configuration

Suitable Accelerometer for intended application

BZ 7226 signal recording (and SD card)

Vibration Meter model of 2250 – Pending

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2250 & 2270 Standard Development Kit

GO

USB Interface

NO GO

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2250 & 2270 Standard Development Kit

GO

USB Interface

NO GO

Sample control program

• Vast library of commands offering total control of 2250• Used with Visual Basic, C++, C # or any program environ.• Data can be used with statistical batch applications, databases ..

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Sound intensity• Many regulatory agencies and modeling procedures require the use of Sound Power

data for a source.

• Sound Intensity of a measurement technique allows for the determination of the sound power in the field.

• Sound intensity can determine sound power:• Non-standard survey (indication)

• According to standard (ISO 9614-1 and ISO 9614-2)

• Data gathering for modeling

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Sound IntensityA sound intensity measurement system should consist of:

• Sound Intensity probe:• 2 closely phase matched microphones

• Preamplifiers with tight phase matching

• Low noise cables

• Signal Conditioning:• Power supply for microphones

• Appropriate high/low pass filters• High pass filters must have good phase matching!

• Analyzer:• Minimum of 2 channels

• Ability to calculate sound intensity directly

• Meets appropriate acoustics standards

• Real time is an advantage

• Sound Intensity Calibrator:• Can verify SPL, particle velocity, and PRI index of system

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Sound intensityBruel & Kjaer 2260E System

•3595 Intensity probe• Includes 4197 phase matched microphones

•2260 Type 1 Sound Level Meter• 1/1 & 1/3 octave analysis

•BZ7205 Intensity Software• Intensity option for 2260

Benefits

• Highly portable

• Mapping and Sound Power calculations done in the meter

• World’s first and only handheld intensity analyzer

• Upgradeable

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Case: Radio studio

Measure level in control room (L1)

Scan each segment of partition (LI)

See results (RI = L1 - 6 - LI )

L1 Measure sound intensity for each segment

Scanning pattern

Procedure:

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Case: Results

R’ is for PressureRI is for Intensity

Sound Reduction Index for total partition ...

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10

20

30

40

50

60

70

100 200 400 800 1.6k 3.15k Hz

dB

R'

RI

RIw = 54dB

R'w = 53dB

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Case: Results

R’ is for PressureRI is for Intensity

Sound Reduction Index for total partition ...

... and for each segment0

10

20

30

40

50

60

70

100 200 400 800 1.6k 3.15k Hz

dB

R'

RI

RIw = 54dB

R'w = 53dB

69 63

59 58

Window

76

69 74

76 94

76

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Case: Conclusions

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10

20

30

40

50

60

70

100 200 400 800 1.6k 3.15k Hz

dB

R'

RI

RIw = 54dB

R'w = 53dB

Poor total result Should be 10-15 dB higher Same for Pressure and Intensity

Sound Reduction Index for total partition

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Case: Conclusions

0

10

20

30

40

50

60

70

100 200 400 800 1.6k 3.15k Hz

dB

R'

RI

RIw = 54dB

R'w = 53dB

69 63

59 58

Window

76

69 74

76 94

76

Intensity tells that

Poor total result Should be 10-15 dB higher Same for Pressure and Intensity

Window is OK ............................... Leak in one corner Cause: cable entry ...............................................

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Summing up

Pressure gives quick total result

but no trouble shooting

Intensity pinpoints problems

and is now affordable and practical

with 2260 Investigator

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Acoustic leak detection

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Acoustic leak detectionNumber Map: 4x4 or 8x 8 grids

Contour Map:

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Acoustic leak detection

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58

46

6553

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Thank you for your attention

Any questions?