QUICK GUIDEHOW TO TEST...

the Acoustics in Meeting Rooms

This document provides a practical guide on how to commission meeting rooms.

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Index
Introduction

3

Ambient Noise Measurements

3— Instruments you need3

— How to measure Ambient Noise

3

Measuring Noise Curves

6— Instruments you need6

— How to measure Noise Curves

6

Reverberation Time RT60 Measurements

9— Instruments you need9

— How to measure RT60

9Speech Intelligibility STI Measurements

14— Instruments you need14— How to measure STI

14

The Instruments you need18

Appendix A

19

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How to test the Acoustics in Meeting Rooms

QUICK GUIDEIntroduction
The acoustic characteristics of a meeting room can have a significant impact on the success ofmeetings. If, for example, the room surfaces create too many reflections of acoustic sound, or evenabsorb too well, the spoken word is at risk of not being understood.
Also, if there is too much ambient noise in the room (air-conditioners), or too much outside environmental noise entering the room (traffic noise), the full potential of the room may not be realized.
Further, the quality and setup of the audio equipment, such as microphones and loudspeakers, cantoo have a negative effect.
Fortunately there are objective measurements that can be carried out to quantify that a meetingroom is fit-for-purpose.

Ambient Noise Measurements
Ambient (background) noise should not interfere with the purpose of the room,
e.g. the noise of an office air-conditioning system and consistent noise of traffic
outside the building should not interfere with video conference calls or conversations.

INSTRUMENTS YOU NEED
Measure with the XL2 Analyzer.

XL2 Analyzer

HOW TO MEASURE AMBIENT NOISE
An unoccupied room can be measured to produce a single LAeq broadband value and a 1/1 octave
spectrum of the ambient noise.

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1. Setup XL2— Choose SLMeter.
— Press the Page key to switch to the spectral display.
— Select LZeq, 1/1 octave resolution, and low Range 20 120.

2. Verify Background Noise— Ensure that the level of background noise in the room istypical for the room when it is unoccupied i.e. nobody
should be talking and no extraordinary sounds during themeasurements

3. Measure— Press the START/STOP button to start.
— Measure for 30 seconds.
— Press the START/STOP button to stop.
— The result is saved in the internal memory.

4. View Spectral Results— The XL2 shows the ambient noise spectrum.

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5. View Broadband Result— Switch to SLMeter 123 for the broadband result.
— The LAeq result is the average ambient noise level during
the measurement period.

6. Connect to a PC
— The results of your measurement are stored on the SD
Card of the XL2. To access the data, connect your XL2
via USB cable to a PC, as a Mass Storage Device.

7. Access the Files— The results are stored as tab-delimited, plain text files inthe /Projects/MyProject directory.
Files named “_123 ..” contain broadband values and files
named “_RTA ..” contain the spectral results.

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Measuring Noise Curves
Noise curves are a common way to specify ambient (background) noise in unoccupied buildings and spaces. They provide a single value that represents thecomplete spectrum of measured ambient noise.

INSTRUMENTS YOU NEED
Measure with the XL2 Analyzer.

XL2 Analyzer

HOW TO MEASURE NOISE CURVES
In the XL2 with the “Spectral Limit” Option installed, all standardized methods for measuring Noise
Curves are available.
It is recommended to perform a measurement at all typical positions that may be occupied in a room.
If a single value is required, extend the total measuring time (10 points need 10 x 30 seconds = 300seconds), measure each point for 30 seconds, and press the PAUSE button between measuringpoints.

1. Verify Instrument Configuration— Power up the XL2.
— Check that you have the Spectral Limits option installed

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2. Select Measurement Function— Choose Noise Curves from the Main Menu

3. Select Noise Curve Type— Choose the noise curve typeThe default is NC-2008. Some projects
may require another noise curve type selection; kindly verify your project requirements.

4. Verify Background Noise— Ensure that the level of background noise in the room istypical for the room when it is unoccupied i.e. nobody
should be talking and no extraordinary sounds during themeasurements.

5. Start Measurement— Press the START button

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6. Measuring— The XL2 measures the ambient noise, displays the spectral curve, calculates the NC value, and saves each resultin the internal memory.

Each measurement takes 30 seconds.

7. Connect to a PC
— The results of your measurements are stored on the SD
Card of the XL2. To access the data, connect your XL2
via USB cable to a PC, as a Mass Storage Device.

8. Access the Files— The results are stored as tab-delimited, plain text files in
the /Projects/MyProject directory

Further reading:— Noise curve measurements with the XL2
https://www.nti-audio.com/Portals/0/data/en/NTi-Audio-AppNote-XL2-Noise-Curves.pdf— About noise curve measurements
https://www.nti-audio.com/noise-curves

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Reverberation Time RT60 Measurements
Reverberation is one of the most signiicant acoustic properties of a room.

INSTRUMENTS YOU NEEDMeasure with the XL2 Acoustic Anaylzer.
As a sound source, connect the PA3 Power Amplifier (with built-in noise generator) to the DS3 Dodecahedron Speaker.

XL2 Analyzer

PA3 / DS3HOW TO MEASURE RT60
RT60 values vary at different positions within a room. Therefore, the measurement microphone isplaced at each measurement position and an average reading taken across the space being measured.
For large rooms, measurements are also taken with the loudspeaker in other positions. The loudspeaker and microphone positions should be asymmetrical and more than 1 m from the walls. Themicrophone should be placed at ear height.

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1. Select Measurement Function— On the XL2 select RT60

2. SET Background Noise Floor— With a quiet room, press SET to measure the room noisefloor

Now wear hearing protection!

3. Adjust the Source Level— On the PA3, play “EQ Pink” noise and adjust the level ...

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QUICK GUIDE... until the black bars on the XL2 reach above the levelmarkers indicated by the grey bars.
Turn the PA3 Signal OFF.

4. Measurement— Press the START button on the XL2.
— Turn the PA3 Signal ON.

5. Toggle Sound Source— Every 3 seconds, toggle the sound source on and thenoff.
— Do this 3 times.

6. Trigger Measurement Cycle— An RT60 measurement is triggered every time the soundsource is switched off, as indicated by the tick marks

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7. How Many Measurements?
— After 3 measurements, the reverberation time and themeasurement uncertainty is displayed for each frequency
band on the results page (press the Page button). Continue measuring until you have an acceptably-low measurement uncertainty in the lowest frequency band thatis relevant for you.

8. Stop Measurement— Press the STOP button.
— To see the results, press the Page button

9. Repeat— Move the microphone to the next appropriate position
and measure again

10. Connect to a PC
— The results of your measurements are stored on the SD
Card of the XL2. To access the data, connect your XL2
via USB cable to a PC, as a Mass Storage Device.

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11. Access the Files— The results are stored as tab-delimited, plain text files inthe /Projects/MyProject directory

12. Make the Report— Drop the *.xl2 files (or the contents of the entire folder)
into the XL2 Room Acoustics Reporter software

Further information:— XL2 Room Acoustics Reporter
https://my.nti-audio.com/support/xl2/download/XL2-Room-Acoustics-Reporter.zip— VIDEO: How to measure RT60
https://youtu.be/D2j4UknWzTc— Recommendations during RT60 measurements
See section “Appendix A: Tips on Measuring RT60”— About RT60 measurements
https://www.nti-audio.com/rt60

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Speech Intelligibility STI Measurements
STIPA (Speech Transmission Index for Public Address) is the most acknowledged standardized
method for measuring the intelligibility of a spoken message. STIPA provides a single STI (SpeechTransmission Index) value between 0 (unintelligible) and 1 (excellent intelligibility).

INSTRUMENTS YOU NEED
Measure with the XL2 Acoustic Analyzer.
As a sound source, use the TalkBox acoustic signal generator.

XL2 Analyzer

TalkBox

HOW TO MEASURE STI
STI values may vary at different listening positions within a room. The values may depend also on
the position of the speaker. Therefore, the TalkBox is placed at each appropriate speaking position.
Then the measurement microphone is placed at each appropriate listening position and an averagereading taken across the space being measured.

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1. Verify Instruments Configuration— Power up the XL2.
— Check that you have the STIPA option installed.

2. Position the TalkBox— Place the TalkBox at a typical speaking position.

3. Position the Microphone— Place the microphone at a typical listening position.

4. Select Measurement Function— On the XL2 select STIPA.

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5. Verify Background Noise— Ensure that the level of background noise in the room
is typical for the room when it is occupied i.e. nobody
should be talking and no extraordinary sounds during themeasurements.

6. Play the STIPA Signal— On the TalkBox, select the STIPA signal (signal number1) and switch the Output Mode to loudspeaker to play
the signal

7. Start— Press the START button

8. Measuring— The XL2 measures the STI value, and saves the result inits internal memory

Each measurement takes 15 seconds.

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9. Repeat— Move the microphone and/or the TalkBox to the next appropriate position/s and measure again.

10. Connect to a PC
— The results of your measurements are stored on the SD
Card of the XL2. To access the data, connect your XL2
via USB cable to a PC, as a Mass Storage Device.

11. Access the Files— The results are stored as tab-delimited, plain text files inthe /Projects/MyProject directory12. Make the Report— Add the *.txt files to the NTi Audio STI Reportwww.nti-audio.com

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Further information:— NTi Audio STI Reporthttps://my.nti-audio.com/support/xl2/download/NTi-Audio-STI-Report.zip— About STI measurements
https://www.nti-audio.com/sti

The Instruments You NeedXL2 MEASUREMENT KIT FOR MEETING ROOM ACOUSTICS
including— XL2 Acoustic Analyzer— Spectral Limits Option for XL2— Speech Intelligibility Option for XL2— XL2 System Case
— M2230 Measurement Microphone— ASD Microphone Cable for XL2— PA3 Power Amplifier with built-in noise generator— DS3 Dodecahedron Speaker— Speaker Stand for DS3— TalkBox Acoustic Generator

Optional as required:

CLASS 1 SOUND CALIBRATOR— for microphone calibration to actual environmental conditions

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QUICK GUIDEAppendix ATips on Measuring RT60

Use ear protection during the RT60 measurements.
The pink noise used to generate the signal for the RT60 measurement must be at least 35dB above
the noise floor in each frequency band.
Within each cyclic RT60 measurement it is necessary to saturate the room with as much sound energy as possible within each frequency band. This “saturation” occurs when a sound is played fora continuous period and that sound has “had enough time to reflect on all possible surfaces”. The
RT60 value for the room is a good indication of the time required for this saturation to occur. Thusfor toggling the pink noise we choose a cycle time of at least the RT60 value of the room.
After the pink noise is turned off, the XL2 starts to measure the reverberation time in each frequency
band. If the background noise is sporadic, this may interfere with the reading, giving you either anincorrect RT60 value or no value at all.
To overcome this, either reduce the sporadic nature of the background noise (make sure nobody istalking in the room during measurements and measure when there is less traffic noise from outside)or measure many RT60 cycles and delete the outlying cycles.

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