Contents
1 Information
1.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2
2

2 Summary4

3 Frequency domain analysis
3.1 Frequency response . . . . . . . . . . . . . . . . . . . .
3.2 Relative level compensation . . . . . . . . . . . . . . . .
3.3 Low frequency extension . . . . . . . . . . . . . . . . .
3.4 Peaks and notches . . . . . . . . . . . . . . . . . . . . .

6
6
9
9
10

4 Time domain analysis
4.1 Time of Flight . . . . . . . . . . . . . . . . . . . . . . . .
4.2 All early reflections . . . . . . . . . . . . . . . . . . . . .
4.3 Early vs late sound . . . . . . . . . . . . . . . . . . . . .

14
14
15
17

5 Time-Frequency domain analysis
5.1 Reverberation time . . . . . . . . . . . . . . . . . . . . .
5.2 Waterfall . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.3 Wavelet . . . . . . . . . . . . . . . . . . . . . . . . . . .

20
20
21
25

6 ITU-R BS1116 compliance
6.1 Operational room response curve . . . . . . . . . . . . .
6.2 Strongest early reflection . . . . . . . . . . . . . . . . .
6.3 Reverberation time . . . . . . . . . . . . . . . . . . . . .
6.4 Summary of compliance . . . . . . . . . . . . . . . . . .

26
26
27
27
28

7 Glossary and Acronyms
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

29
29

1

Chapter 1
Information
The following tables show information collected from Genelec GLM
software and the AutoCal 2 room calibration algorithm.
GLM setup nameGroup nameGroup description
Room dimensions (LxWxH)(m/ft)
Room volume (m3 / ft3 )Measurement date (local time)
Report created
GRADE version
Microphone serial number

Seamer 8331B 7370 16.3.22.sam
Room Report Cal
8351B + 7370 A
Height 1.28
Distance 1.1m
3.40 x 2.20 x 2.40 / 11.2 x 7.2 x 7.9
18 / 600
2022-4-29 17:13:52
2022-05-16 13:56:32
2022-05-16
202722

Table 1.1: Measurement information.

Name

Serial number

Sub 7370A
Left 8351B
Right 8351B

7370AP71001184
8351BM71004417
8351BM71004418

Firmwareversion1106919 1.10.8.4408
1149357 1.20.0.4668
1149365 1.20.0.4668
UID

Calibrationgroup ID
0
0
0

Table 1.2: Monitor and subwoofer information.

1.1

Scope

This room acoustic report analyses the measurements taken by GLM’s
AutoCal calibration system. We hope this document can help you understand and improve your monitoring room acoustics and the placement of your monitors where necessary, for the purpose of professional monitoring. The metrics have been selected to present the most
relevant information for loudspeaker systems that are used for highprecision audio monitoring work: reliable frequency response, good
imaging and accurate delivery of the envelopment within the recorded
audio.
In professional monitoring, the aim is a neutral frequency responseat the listening position. As variations in the listening level will affect2

the way we hear sounds, this level must be taken into account. Because exposure to high sound levels can affect your hearing, we recommend avoiding the regular use of sound levels that can harm theauditory system. This means keeping the daily and weekly soundexposure below 80 dB (LEX,8h) - see the EU Noise at Work Directive 2003/10/EC (http://data.europa.eu/eli/dir/2003/10) and EBU R128
(https://tech.ebu.ch/loudness).
While there may well be some simple improvements that you canmake yourself, you should also find the depth of information in thisreport useful when discussing your room with acoustic treatment suppliers, acousticians and studio designers.

3Chapter 2
Summary

Monitor nameOperational room
response (%)

Early reflectionlevel (dB)

Early vs latesound ratio (dB)

T60 flatness,
inside window (%)

Deepest notch
below 300 Hz(dB)

Your monitoring system performance is summarised on this page. The
table shows all the monitors and subwoofers in your system, along withan overall analysis of their characteristics.
The system performance is colour coded. The green colour indicates excellent performance. When the colour is yellow, your system performance is good, but you may want to consider improvements
where possible. When the colour is red, your system may not have
optimal performance and improvements may significantly enhance thequality of your monitoring system.

Left 8351B
Right 8351B

100
100

-10.4
-14.6

8.8
8.3

66
66

-5.8
-13.6

Table 2.1: Summary of results, colour coded to indicate excellent/good/problematic performance.
The Operational room response (%), Early reflection level (dB),
Early vs late sound ratio (dB) of your monitoring system and room
are showing excellent performance. This provides good audibility of
acoustic details.
The T60 flatness, inside window (%), Deepest notch below 300 Hz(dB) of your monitoring system and room are showing good performance. However, there are certain areas where some improvements
could increase the accuracy of your system even further. These areindicated in yellow.

4

Operational room
response (%)

Early reflectionlevel (dB)

Early vs latesound ratio (dB)

T60 flatness,
inside window (%)

Deepest notch
below 300 Hz
(dB)

> 90
90 to 80
< 80

< -10
-10 to -3> -3>3
3 to 0<0> 80
80 to 50
< 50

> -10
-10 to -20< -20

Table 2.2: Summary of the colour thresholds used in Table 2.1.

5

Chapter 3
Frequency domain analysis
The room compensations applied by GLM AutoCal reduce the soundcolouration caused by the room, improve the similarity between themonitors in the room, and can increase the monitoring system’s low
frequency extension. If a subwoofer is used, GLM AutoCal sets the optimal crossover frequency in the room and aligns the subwoofer phase.

3.1

Frequency response

This section shows you the frequency responses with AccuSmoothsmoothing applied. AccuSmoothing gives you good visibility of details
at low frequencies so you can detect room resonance related effects,
and also provides an accurate presentation of mid and high frequency
response so you can understand how neutral or coloured the audio isin these frequencies. Each monitor is shown separately.

Magnitude (dB)20
correction
measuredcalibrated

10

0

−10

−20
10

100
Frequency (Hz)Figure 3.1: Sub 7370A frequency response.

6

20
correction
measuredcalibrated

Magnitude (dB)

15
10
5
0
−5
−10
−15
10

100

1k
Frequency (Hz)10k

Figure 3.2: Left 8351B frequency response.

20
correction
measuredcalibrated

Magnitude (dB)

15
10
5
0
−5
−10
−15
10

100

1k
Frequency (Hz)Figure 3.3: Right 8351B frequency response.

7

10kIn order to provide the maximum detail in the measurement data,
the following AccuSmoothed comparison of all the monitors in yoursystem shows the similarity between the monitors. When the curves
overlap, the monitors in your system can deliver accurate imaging.
15
Left 8351B
Right 8351B

Magnitude (dB)

10
5
0
−5
−10
−15
10

100

1k
Frequency (Hz)10k

Figure 3.4: Frequency responses for monitors. AccuSmoothed.
One-octave smoothing of the frequency responses enables you to understand the general sound colour balance. When this curve is flat, theoverall sound is balanced and does not tend to emphasise certain frequency areas over others. You can also see how similar the monitors
are in terms of the general sound colour balance.
15
Left 8351B
Right 8351B

Magnitude (dB)

10
5
0
−5
−10
−15
10

100

1k
Frequency (Hz)10k

Figure 3.5: Frequency responses for monitors. One octave smoothing.

8

15
Sub 7370A

Magnitude (dB)

10
5
0
−5
−10
−15
10

100
Frequency (Hz)Figure 3.6: Filtered frequency responses for subwoofers. 1/12 octavesmoothing.

3.2

Relative level compensation

The relative level compensation calculates the mean output level within
the frequency range 0.5 - 3 kHz, and finds the compensations needed
to set the same SPL for all monitors at the listening location. The
subwoofer level is calculated in the frequency range 30 - 80 Hz, and isthen set at the same level as the monitors. In this way, the level-related
stereo imaging can work with the best accuracy.
Speaker nameSub 7370A
Left 8351B
Right 8351B

Level compensation
(dB)
0.0
-0.3
-0.1

Level offset after
calibration (dB)
0.0
0.0
0.0

Table 3.1: Relative level compensation of speakers.

3.3

Low frequency extension

The -6 dB point at low frequency is related to the practical bass extension of your monitoring system and room, and how much the room
acoustics either support or limit the bass output range.
At -6 dB the monitor outputs half of the average pressure in the
mid-band frequencies. When the measured -6 dB point moves downin frequency compared to the anechoic measurement of your monitor,
you gain in low frequency extension in your room. Monitor locations
can have a significant effect here.

9Speaker nameModel

Sub 7370A
Left 8351B
Right 8351B

7370A
8351B
8351B

Measured -6
dB point
(Hz)
11.9
24.6
24.6

Anechoic -6
dB point
(Hz)
19.0
32.0
32.0

Gain in low
frequency
extension (Hz)
7.1
7.4
7.4

Table 3.2: Low cutoff -6 dB point.
Subwoofer nameSub 7370A

Model
7370A

Measured -6 dB point (Hz)132.0

Table 3.3: High cutoff -6 dB point for subwoofers.

3.4

Peaks and notches

This section shows you where you have the most influential narrow
band colourations, before calibration. These are shown for each monitor separately.
Comments related to the following monitors: Right 8351B. We
are observing a wide loss of sound level (also called a dip) below 200
Hz.
This typically causes the feeling that the system bass response islacking or poor.
• A dip can be caused by an acoustic reflection from the nearest
wall, typically behind a monitor. To remove this problem, try moving the monitor closer to the wall. Doing so will move cancellation frequencies up to a value where the monitor mainly radiates
audio in the forward direction, so the effect of the back wall is
minimised.
• Alternatively, move the monitors far away from the walls. This reduces the level of reflected audio, and makes the acoustic effectless detectable. For this approach, the monitors should be morethan 1.1 metres (4 ft) from the nearest wall. Refer to Genelec
Monitor Setup Guide for more details. https://www.genelec.com/
monitor-placement• You can also consider moving your listening position. This canhelp if the acoustic problem is only audible at a certain locationin the room. When the dip is caused by audio reflecting off theside walls, you can reduce the level of reflection by adding absorption or diffusion materials on the reflecting surfaces. Notethat recalibration of the monitors should be performed whenever
the monitors or the listening position have been moved.
• A sufficiently thick absorbing layer is needed for lower frequencies, where the audio wavelength is long. When the dips arecaused by reflections from the ceiling and floor, moving the monitor locations up or down may help.
• A very effective absorbing method for specific frequencies only is
the Helmholtz resonator absorber. More information is available
in the Genelec Monitor Setup guide: https://www.genelec.com/
monitor-placement

10Comments related to the following subwoofers: Sub 7370A. We
are observing a wide loss of sound level (also called a dip) below 100
Hz.
This typically causes the feeling that the subwoofer output is lacking
or poor.
• The nearest-wall reflections are a typical cause of such problems.
Try moving the subwoofer closer to the nearest wall.
• Consider rotating the subwoofer so that the driver faces the wall,as this is even more effective in removing the effects of the nearest wall cancellation. Note that recalibration should be performed
after moving subwoofers. When you do this, leave about 10 cm(4 in) of space between the subwoofer and the wall.
• The acoustic reflections from the side walls in the room can also
cause this problem. To fix this, try moving the subwoofer closer
to the side wall or towards a corner.

Magnitude (dB)

20

10

0

−10

−20
10

100
Frequency (Hz)Figure 3.7: Sub 7370A peaks and notches (before calibration).

Peak
Centre frequency
number
(Hz)
1
16.9
2
53.0
Dip number
1
72.8
2
98.8

Gain
(dB)
11.2
7.2

Qualityfactor
3.03
3.55

-16.5
-21.4

13.7
17.2

Table 3.4: Sub 7370A peaks and notches (before calibration).

11

Magnitude (dB)

20

10

0

−10

−20
10

100

1k
Frequency (Hz)10k

Figure 3.8: Left 8351B peaks and notches (before calibration).

Peak
Centre frequency
number
(Hz)
1
34.3
2
52.2
3
90.5
4
538.3
Dip number
1
43.2
2
115.8
3
212.9
4
297.1

Gain
(dB)
4.5
13.9
6.3
3.9

Qualityfactor
3.75
8.62
5.34
2.76

-5.8
-4.7
-7.2
-6.2

8.6
5.4
9.9
11.5

Table 3.5: Left 8351B peaks and notches (before calibration).

Magnitude (dB)

20

10

0

−10

−20
10

100

1k
Frequency (Hz)10k

Figure 3.9: Right 8351B peaks and notches (before calibration).

12

Peak
Centre frequency
number
(Hz)
1
34.3
2
52.2
3
161.6
4
420.7
5
807.7
Dip number
1
43.2
2
114.2
3
198.0
4
669.0

Gain
(dB)
4.4
14.5
6.3
4.8
3.8

Qualityfactor
3.75
8.62
5.91
5.74
4.85

-6.5
-13.6
-9.7
-3.0

8.7
13.9
11.5
4.6

Table 3.6: Right 8351B peaks and notches (before calibration).

13

Chapter 4Time domain analysis
4.1

Time of Flight

Differences in the times of flight (TOF) for audio between monitors indicate that they are at different distances from the listening location, orthat the electronic delay alignment is not perfect.
About 1 ms of delay difference completely displaces the centre image in a stereo system to the nearest monitor.
Time alignments should show close to zero differences in order for
all sound images to appear at the correct locations.
The time differences are also expressed as distances using the
speed of sound in the air. This shows how much the monitor should
move towards or away from the listener to remove the delay difference.
Time of flight is calculated using a filtered impulse response. The
impulse response is bandpass filtered from 1 to 8 kHz.

Magnitude (dB)

−15
−20
−25

Left 8351B
Right 8351B

−30
−35
−40
0

5

10
Time (ms)15

20

Figure 4.1: Bandpass filtered impulse responses of monitors, before
time of flight compensation.

Monitor nameLeft 8351B
Right 8351B

ToF
compensation
(ms)
0.0
0.0

Table 4.1: Time of Flight.

14

Magnitude (dB)

−15
−20
−25

Left 8351B
Right 8351B

−30
−35
−40
0

5

10
Time (ms)15

20

Figure 4.2: Bandpass filtered impulse responses of monitors, after
time of flight compensation.

Magnitude (dB)

−45
−50
−55
Sub 7370A

−60
−65
−70
−75
−20

0

20
Time (ms)40

60

Figure 4.3: Lowpass-filtered impulse response envelopes of subwoofers.

4.2

All early reflections

Early reflections are the reflections of the sound arriving at your ears
shortly (less than 15 ms) after the direct sound. Early reflections colour
the audio and move the locations of sound images in your mix. For
this reason, early reflections should be kept low. This section shows
all significant room reflections in the acoustically sensitive midrange
frequencies (1-8 kHz). Direct sound is scaled to 0 dB level. You can
immediately see the level of reflections relative to the direct sound.
Reflections higher than -15 dB are shown in the tables.
A -15 dB reflection causes a 1.4 dB ripple in the audio signal.
The ripple is a frequency dependent variation in the sound level which
colours the audio, causing sound colour inaccuracy.
The frequency response graph also indicates the lowest frequencyof the acoustic cancellation that can result with each reflection. In reality the cancellations can also happen at higher frequencies, and canbe more complicated since the reflections can interact with each other.
The level of early reflections in your room is low and meets the requirements for high precision monitoring.
15

Magnitude (dB)

0

←1

−10

−20

−30

−40

0

5

10

15
Time (ms)

20

25

30

Figure 4.4: Left 8351B early reflections.

Reflection Gain
number(dBFS)

Time
(ms)

1

1.7

-10.4

Time indistance (cm/ in)
57 / 22.6

Frequencyof first dip
(Hz)
296.3

Comb filteringripple (dB)
2.3

Table 4.2: Left 8351B. Peaks in impulse response.

20

Magnitude (dB)

Measured
1: 297.1 Hz

10

0

−10

−20
10

100

1k
Frequency (Hz)10k

Figure 4.5: Left 8351B. Response and lowest cancellation frequency
resulting from early reflection.

16

Magnitude (dB)

0

−10
←1
−20

−30

−40

0

5

10

15
Time (ms)

20

25

30

Figure 4.6: Right 8351B early reflections.

Reflection Gain
number(dBFS)

Time
(ms)

1

1.7

-14.6

Time indistance (cm/ in)
59 / 23.1

Frequencyof first dip
(Hz)
289.2

Comb filteringripple (dB)
1.5

Table 4.3: Right 8351B. Peaks in impulse response.

20

Magnitude (dB)

Measured
1: 288.6 Hz

10

0

−10

−20
10

100

1k
Frequency (Hz)10k

Figure 4.7: Right 8351B. Response and lowest cancellation frequency
resulting from early reflection.

4.3

Early vs late sound

The Early vs. late sound plot shows the level of sound after the AutoCal
optimisation. The ’Full’ curve represents the sound level of the complete room response and contains the contributions of the ’Early’ and’Late’ components. The ’Early’ curve shows the sound level contributedby the sound in the room during the first 20 ms after the direct sound.
During this time, sound travels a distance of 6.8 m (22 ft) in the room.
The ’Late’ curve shows the level contributed by the sound in the room
after the initial 20 ms, until the reverberation has died out. ’Late’ level17

describes the significance of the reverberation. All responses are 1/3rd
octave smoothed.
The early vs. late sound shows the significance of the reverberation in determining the total sound colour. When the Late sound is low,
more than 3 dB below the Full level, it is unlikely that the late energy
will dominate your experience of sound colour. When the late energy
level is high, close to the Full level, then the room reverberation dominates the sound colour you hear in the room. This is typical at low
frequencies (below 500 Hz) where reverberation time is often significant, and sound takes longer to decay. At higher frequencies in a highquality listening room, the Early sound should remain higher than the
Late sound.
For subwoofers, the early part is the level in the first 20 ms after the
peak in the impulse response envelope, and the late part is the level
after this point. The maximum impulse response is detected in theimpulse response envelope after a 120 Hz lowpass filter. The delayof a subwoofer is usually much higher than that of a monitor since
the subwoofer is reproducing a very narrow frequency band at a low
frequency.
Full
Early (<20ms)
Late (>20ms)

Magnitude (dB)

10

0

−10

−20

−30
10

100
Frequency (Hz)Figure 4.8: Sub 7370A. Full, early and late frequency response.

Full
Early (<20ms)
Late (>20ms)

Magnitude (dB)

10

0

−10

−20

−30
10

100

1k
Frequency (Hz)10k

Figure 4.9: Left 8351B. Full, early and late frequency response.

18

Full
Early (<20ms)
Late (>20ms)

Magnitude (dB)

10

0

−10

−20

−30
10

100

1k
Frequency (Hz)10k

Figure 4.10: Right 8351B. Full, early and late frequency response.

Monitor nameLeft 8351B
Right 8351B

Early vs late sound ratio, 100
Hz - 10 kHz mean (dB)
8.8
8.3

Table 4.4: Early vs late sound ratio.

19Chapter 5
Time-Frequency domain
analysis
5.1

Reverberation time

Reverberation time (RT60) is analysed by looking at the decay time
T60 of one-octave bandwidths. RT60 is the mean of the nine bands
having centre frequencies from 63 Hz to 16 kHz. The T60 decay timein a listening room should be similar across all frequencies and besuitably low. Then, all details in the audio are audible in a balanced
way. The most critical are the midrange of frequencies.
0.8
66 % inside window

Time (s)

0.6

0.4

0.2

0
10

100

1k
Frequency (Hz)10k

Figure 5.1: Mean decay time T60 of all monitors, after calibration.
One-octave bandwidth.

Monitor name
Mean of all monitors
Left 8351B
Right 8351B

RT60 (s)
0.21
0.22
0.20

T60 min (s)
0.10
0.10
0.11

T60 max (s)
0.60
0.61
0.60

Table 5.1: Reverberation time RT60.

20

0.8
Left 8351B
Right 8351B

Time (s)

0.6

0.4

0.2

0
10

100

1k
Frequency (Hz)10k

Figure 5.2: Decay time T60, after calibration.

5.2

Waterfall

Waterfall is good for spotting room resonances. Waterfall analysis
shows you the decay time of audio at different frequencies.
The decay time shows how fast sound disappears after the loudspeaker has stopped playing.
Room resonances (room modes) can cause certain notes to ‘ring’
for a long time in a room. In a typical room, bass notes can resonate
for up to half a second. At high frequencies you can experience ‘flutter’echo between two parallel hard surfaces. This is the annoying ’ping’that you can hear after you clap your hands, for example.
Flutter echo and room mode resonances both lengthen the decayof sound in a room, and are visible in a waterfall plot. You can see
the frequency of a resonance and how slow it decays relative to otherfrequencies.
Prominent room resonances are detected in the decay at 60 ms
after the end of the audio signal. This method may not detect all theroom resonances, but all the resonances are visible in the waterfall
plot. The decay times of the prominent resonances are calculated.
When the prominent resonance decay times are much longer than the
typical decay time of other frequencies, the slowly decaying room resonances can mask other audio, and reduce the ability to hear details
in the audio correctly.
The nearly horizontal sections at later time values in the detectedresonance decay curves are not usually indications of acoustic delay,
but indicate the noise level in the room.

21

Waterfall (Fourier) − 0.167 oct sm − win left 5 & right 500 ms

Magnitude (dB)

20

0

−20

−40
0
Time (ms)100

500 10Frequency (Hz)Figure 5.3: Sub 7370A. Waterfall.

Decay of room resonances

Magnitude (dB)010.6 Hz, T60 1.06 s
15.2 Hz, T60 0.65 s
25.3 Hz, T60 0.95 s
51.4 Hz, T60 0.52 s

−10
−20
−30
−40
−50
−60

0

100

200

300

400

500

Time (ms)Figure 5.4: Sub 7370A. Decay of detected resonances.

Waterfall (Fourier) − 0.167 oct sm − win left 5 & right 500 ms

Magnitude (dB)

20

0

−20

−40
0
Time (ms)
500 101k100Frequency (Hz)Figure 5.5: Left 8351B. Waterfall.

22

10k

Decay of room resonances

Magnitude (dB)052.2 Hz, T60 0.52 s

−10
−20
−30
−40
−50
−60

0

100

200

300

400

500

Time (ms)Figure 5.6: Left 8351B. Decay of detected resonances.

Waterfall (Fourier) − 0.167 oct sm − win left 5 & right 500 ms

Magnitude (dB)

20

0

−20

−40
0
Time (ms)
500 10

10k

1k

100
Frequency (Hz)Figure 5.7: Right 8351B. Waterfall.

Decay of room resonances

Magnitude (dB)052.2 Hz, T60 0.52 s

−10
−20
−30
−40
−50
−60

0

100

200

300

400

Time (ms)Figure 5.8: Right 8351B. Decay of detected resonances.

23

500

10

20

30

40 50 60 70 80 100
Frequency (Hz)

200

300

Figure 5.9: Colourmap for resonances.

Speaker nameSub 7370A

Left 8351B

Right 8351B

Unit
Freq (Hz)Gain (dB)
Decay time T60 (s)Freq (Hz)Gain (dB)
Decay time T60 (s)Freq (Hz)Gain (dB)
Decay time T60 (s)

Mode
1
10.6
-4.0
1.06
52.2
6.7
0.52
52.2
7.9
0.52

Mode
2
15.2
10.9
0.65

Mode
3
25.3
-1.8
0.95

Table 5.2: Room modes - all monitors and subwoofers.

24

Mode
4
51.4
-1.8
0.52

5.3

WaveletWavelet is good for spotting reflections. The wavelet analysis shows
the decay of sound after the loudspeaker has stopped playing. This
helps you understand how well the sound is controlled acoustically at
different frequencies.
Early reflection problems can be seen using the wavelet analysis.
Compared to the waterfall plot, the wavelet plot has excellent timeand frequency resolution. This means you can see when the soundlevel peaks, and at what frequency, after the loudspeaker has stopped
playing audio in the room.
Wavelet − 3 sine cycles −15

Time (ms)

−5
−10

10

−15
5

−20
−25

0
100

1k
Frequency (Hz)

10k

−30

Figure 5.10: Left 8351B. Wavelet.

Wavelet − 3 sine cycles −15

Time (ms)

−5
−10

10

−15
5

−20
−25

0
100

1k
Frequency (Hz)10k

Figure 5.11: Right 8351B. Wavelet.

25

−30

Chapter 6
ITU-R BS1116 compliance
ITU-R BS.1116 is a quality recommendation for broadcasting services
describing high precision audio listening conditions, for monitoring applications such as recording studios, post-production and audio editing.
This section of the report compares your monitoring setup measurements and calibration results to the ITU-R BS.1116 recommendation. If your results are close to the recommendation, then your monitoring setup will have excellent precision for details in audio, enablinghigh quality audio engineering work.
You can freely download the full text of the ITU-R BS.1116 recommendation at https://www.itu.int/rec/R-REC-BS.1116/en

6.1

Operational room response curve

The frequency response at the listening location is called the Operational Room Response. To hear uncoloured audio, the Operational
Room Response should show the same level across frequencies. The
green limits indicate deviations that are usually safe and do not causesignificant colourations.
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Left 8351B − 100 % compliance
Right 8351B − 100 % compliance

Magnitude (dB)

15
10
5
0
−5
−10
−15
10

100

1k
Frequency (Hz)Figure 6.1: Operational room response curve.

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10k

6.2

Strongest early reflection

The ITU-R limit for early reflections is -10 dB relative to the direct soundlevel produced by the monitor. In theory, a -10 dB reflection causes a
comb filtering effect that results in a 2.4 dB ripple (inaccuracy of soundcolour) in the audio signal.

Magnitude (dB)0←−10.4 dB, 1.7 ms

−10

−20

−30
Left 8351B
reflection limit

−40

0

2

4

6

8
Time (ms)

10

12

14

16

Figure 6.2: Early reflections. 1-8 kHz band. Level is relative to direct
sound level.

Magnitude (dB)0−10←−14.6 dB, 1.7 ms−20−30
Right 8351B
reflection limit

−40

0

2

4

6

8
Time (ms)

10

12

14

16

Figure 6.3: Early reflections. 1-8 kHz band. Level is relative to direct
sound level.

6.3

Reverberation time

The recommended reverberation time depends on the volume of yourroom (Table 6.1). The room volume is calculated using the hard wallsof your room. Please note that these walls may be hidden behind alayer of absorbent material, making the acoustic volume larger thanthe visible volume inside the room.

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V (m3 )

30

60

100

300

600

1000

V (ft3 )

1100

2100

3500

10600

21200

35300

T60 (s)

0.17

0.21

0.25

0.36

0.45

0.54

Table 6.1: Room volume V and decay time T60.
0.8
Left 8351B
Right 8351B

Time (s)

0.6

0.4

0.2

0
10

100

1k
Frequency (Hz)10k

Figure 6.4: Decay time T60, after calibration. Target decay time Tm =0.14 s (based on calculated room volume).

6.4

Summary of compliance

Monitor name

Model

Operationalroom response,
inside limits (%)

Left 8351B
Right 8351B

8351B
8351B

100
100

Early
reflections,
number ofproblem peaks
00Table 6.2: ITU-R BS1116 compliance summary.

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Reverberation
time RT60,
inside limits
(%)
65
75

Chapter 7
Glossary and Acronyms
Glossary
AccuSmooth AccuSmooth is a smoothing-in-frequency method applied by Genelec to provide maximum detail to acoustic measurements. This is a variable-width smoothing. The frequency
range of the smoothing is 1/12th per octave below 250 Hz, and1/6th per octave above 250 Hz. The AccuSmoothing applied tofrequency response plots increases the visibility of the acoustically relevant details in the system frequency responses.
GLM Genelec Loudspeaker Manager (GLM) is a software app thatruns on Windows or Mac computers. It issues management commands to all Genelec Smart Active Monitors for volume, mutes,
solos, EQ, and offers automatic system calibration in a room.
This includes individual monitor equalisation, and time and levelalignment for more than 80 loudspeakers and subwoofers.
impulse response The impulse response of a system is the outputof the system when presented with a short input signal called an
impulse. The impulse response is the reaction of any system toa change, and it describes that reaction as a function of time.
The impulse response of a room can be used to analyse earlyreflections of audio in the room. The impulse response can also
be analysed further to understand how the room changes thelevel of audio, its timing and phase.
loudspeaker Can be a monitor or subwoofer. Commonly shortenedto ‘speaker’.
monitor A loudspeaker for audio monitoring purposes. Can produce
full audible bandwidth from 20 Hz to 20 kHz. Usually there issome low frequency limitation.
one-octave smoothing One-octave smoothing applies a smoothingin-frequency from half an octave below to half an octave above
a given frequency, and assigns the mean of the pressure in thisrange to this frequency. This is useful for revealing wideband
level variations. This can clearly display the general tonal balance of a monitoring system.
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reflection Room walls and objects, such as furniture, reflect audio.
Sound reflections can occur at any frequency and can colour thefrequency response, making recording and mixing decisions difficult or inaccurate. The ratio of direct to reflective sound energy
is important to know. The lower the reflection relative to direct
sound, the smaller the influence the reflection has.
RT60 Reverberation time of a room. This is the time it takes for soundto decay by 60 dB.
subwoofer Loudspeaker which produces low frequencies only. Low
frequency content can be ‘bass managed’ from monitors to subwoofers, reducing the LF workload of the monitors. This can increase maximum system SPL and reduce distortion in the monitors. Typical subwoofer bandwidth is 20 Hz to 120 Hz.
T60 Narrow-band decay time in a room. This is the time it takes forsound to decay by 60 dB within the given frequency range. In aroom, T60 should be similar in low, mid, and high frequencies toprevent the room decay interfering with the sound colour balance.

30