BRUEL & KJAER 2240 User manual

Technical
Documentation
Integrating-averaging
Sound Level Meter Type 2240
Instruction Manual
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English BE 1694 – 12
Cover_BE169412.fm Page 1 Wednesday, March 7, 2007 1:06 PM

BE 1694−12 March 2007
Integrating-averaging
Sound Level Meter Type 2240
Instruction Manual

Copyright ©2004 – 2007 Brüel & Kjær Sound & Vibration Measurement A/S
All rights reserved. No part of this publication may be reproduced or distributed in any form, or by any means,
without prior written consent from Brüel & Kjær Sound & Vibration Measurement A/S, Nærum, Denmark
Safety Considerations
This apparatus has been designed and tested in accordance with IEC 61010 – 1 and EN 61010 – 1 Safety Require-
ments for Electrical Equipment for Measurement, Control and Laboratory Use. This manual contains infor-
mation and warnings which must be followed to ensure safe operation and to retain the apparatus in safe condition.
Special note should be made of the following:
Safety Symbols
The apparatus will be marked with this symbol when it is important that you refer to the associated warning
statements given in the manual.
Protective Earth Terminal Hazardous Voltage
Explosion Hazard
The equipment is not designed to be used in potentially explosive environments. It should not be operated in the
presence of flammable liquids or gases.
Warnings
• Switch off all power to equipment before connecting or disconnecting their digital interface. Failure to do so
could damage the equipment.
• Whenever it is likely that the correct function or operating safety of the apparatus has been impaired, it must
be made inoperative and be secured against unintended operation.
• Any adjustment, maintenance and repair of the open apparatus under voltage must be avoided as far as possible
and, if unavoidable, must be carried out only by trained service personnel.

Table of Contents
CHAPTER 1
Introduction.......................................................................................................................................... 1
1.1 About This Manual..................................................................................................................................... 1
1.2 Topics Covered in User Guide BE 1695 and Non-applicable Topics ........................................................ 2
CHAPTER 2
Hardware Setup ................................................................................................................................... 5
2.1 Measuring at Low Static Pressure............................................................................................................. 5
2.2 Frequency Weightings............................................................................................................................... 5
2.3 Measured Quantities ................................................................................................................................. 7
CHAPTER 3
Conformance Testing........................................................................................................................ 11
3.1 Introduction.............................................................................................................................................. 11
3.2 Selecting C-weighting.............................................................................................................................. 11
3.3 Mounting for Acoustical Tests ................................................................................................................. 11
3.4 Mounting for Mechanical Vibrations Tests............................................................................................... 11
3.5 Electrical Substitute for Microphones ...................................................................................................... 11
3.6 EMC Test Procedures ............................................................................................................................. 12
CHAPTER 4
Specifications .................................................................................................................................... 15
4.1 Specifications .......................................................................................................................................... 15
4.2 Standards ................................................................................................................................................ 15
4.3 Reference Environmental Conditions ...................................................................................................... 15
4.4 Reference Conditions for Acoustic Calibration ........................................................................................ 15
4.5 Microphone.............................................................................................................................................. 16
4.6 Frequency Response .............................................................................................................................. 16
4.7 Directional Response .............................................................................................................................. 17
4.8 Self-generated Noise............................................................................................................................... 17
4.9 Measuring Range .................................................................................................................................... 18
4.10 Detectors ................................................................................................................................................. 20
4.11 Influence from the Operating Environment.............................................................................................. 21
4.12 Electrical Input to Type 2240 ................................................................................................................... 21
4.13 Electrical Output from Type 2240 ............................................................................................................ 21
4.14 Power Supply .......................................................................................................................................... 22
4.15 Warm-up Time......................................................................................................................................... 22
4.16 CE-mark and C-Tick mark Compliance ................................................................................................... 22
APPENDIX A
Tables ................................................................................................................................................. 23
A.1 Electrical Frequency Responses ............................................................................................................. 23
A.2 Free-field Frequency Response .............................................................................................................. 25
A.3 Diffuse-field Frequency Response .......................................................................................................... 27
APPENDIX B
Indexes ............................................................................................................................................... 29
B.1 Indexes .................................................................................................................................................... 29
B.2 Standard Cross-indexes .......................................................................................................................... 29
B.3 Irrelevant Topics ...................................................................................................................................... 36
INDEX ........................................................................................................................................................................... 37

1
Chapter 1
Introduction
1.1 About This Manual
This Instruction Manual supplements User Guide BE 1695 – 11. This manual and the User Guide together
comprise the full documentation of Type 2240 as required by IEC 61672 – 1, as well as the earlier
standards IEC 60651 and IEC 60804.
The User Guide provides all the information necessary for operating Type 2240, descriptions of the
measured quantities, and general advice as to proper measurement practices. The User Guide also
contains the technical specifications that are most likely to be of practical use when making standard
sound-level measurements. This information is not repeated in this manual, except for the specifications,
which are given in full here. In the event of any unintended inconsistency between the User Guide and
the Instruction Manual, this manual takes precedence.

Integrating-averaging Sound Level Meter Type 2240 – Instruction Manual2
1.2 Topics Covered in User Guide BE 1695 and Non-applicable Topics
The table below lists the documentation requirements from IEC 61672 – 1 that are fully covered in the
User Guide and therefore, as a rule, not repeated in this manual. The table also lists the requirements
that are not applicable to Type 2240. For the sake of brevity, the corresponding requirements listed in
section 9.2 of IEC 61672 – 1 (which partly sums up documentation requirements) are not repeated here
as they are already covered by reference to previous sections of the standard.
Table 1.1 Section in
IEC 61672–1 Gloss Chapter in BE 1695
5.1.4 Configuration and normal mode of operation Chapter 2
5.1.6 Appropriate procedures for use Chapter 4
5.1.6 Model of microphone Chapters 2 and 7
5.1.7 Mounting of microphone Chapter 2
5.1.7 Microphone extension device Not applicable.
Preamplifier, and hence the
microphone, cannot be
detached
5.1.8 Computer software Not applicable
5.1.12 Level range control and selection of optimum level
range
Chapter 4
5.1.14 “Hold feature” and clearance Chapter 2
5.1.17 Multi-channel instruments Not applicable
5.2.1 Recommended sound calibrator model Chapter 4
5.2.3 Calibration procedure Chapter 4
Note: The reference is to
the acoustical calibration
procedure. The electrical
calibration described is, as
stated in the User Guide,
not the relevant procedure
in this context
5.2.7 Recommend calibrator or actuator for periodic
testing
No such recommendation
5.4.12 Optional frequency responses No such responses
5.5.11 Display less than linear operating range Not applicable
5.10.1 Operation and interpretation of overload indication Chapter 4
5.11.1 Operation and interpretation of under-range
indication
Chapter 4
5.14 User-selectable thresholds Not applicable
5.15.2 Indication of measured quantity Chapter 2
5.15.3 Display device Chapter 4
Note: The quasi-analogue
bar graph does not display
a measured quality in the
sense of IEC 61672 – 1. It is
for guidance only

CHAPTER 1
Introduction 3
5.15.4 Other quantities displayed Chapter 4
5.15.7 and 5.16.1 Digital output Not applicable
5.17.1 Display of elapsed time and preset time Chapter 4
Preset time not applicable
5.17.2 Minimum and maximum averaging times Chapter 4
5.17.1 Time-of-day Not applicable
5.17.2 Minimum and maximum averaging times Chapter 4
5.20.3 Type of internal batteries and life time Chapters 2 and 7
5.20.4 Integration time longer than battery life time Not applicable
5.20.5 External power supply Not applicable
7.1 Correction for extension devices Not applicable
7.2 and 7.3 Effects of optional accessories No accessories
recommended
7.4 Use of bandpass filters Not applicable
7.5 Effect of auxilliary devices Not applicable
9.2.3 b) Sufficient power supply Chapter 4
9.2.5 b) Sounds from reference direction, sounds with
random incidence, minimising influence of
instrument and observer
Chapter 4
9.2.5 e) Settling time Chapter 7
9.2.2 g) Applicable display update rates Chapter 7
9.2.2 k) Specification of non-standardised quantities Not applicable – no such
quantities
9.2.7 a) Components to be kept in environmentally
controlled enclosure
Not applicable
5.18.2 Radio frequency emission Not applicable
9.3 n) Radio frequency emission of cables and devices Not applicable

Integrating-averaging Sound Level Meter Type 2240 – Instruction Manual4

5
Chapter 2
Hardware Setup
2.1 Measuring at Low Static Pressure
The frequency response of the microphone depends on the static pressure. Using a Sound Level Calibrator
to adjust the sensitivity of a sound level meter at the calibration check frequency provides no information
on the influence of static pressure on frequency response. Conformance to the specified standards
ensures that the system measures within the standards’ tolerances, in the range of 85 kPa to 108 kPa.
Data for the frequency response as a function of static pressure for Microphone Type 4188 can be
found in Microphone Handbook BA 5105.
At the calibration check frequency, both the microphones and the recommended Brüel & Kjær Sound
Level Calibrator Type 4231 are rather insensitive to static pressure variations below 0.001 dB/kPa.
2.2 Frequency Weightings
The A and C frequency weightings conform to requirements in IEC 60651 and IEC 61672 – 1 standards.
Table 2.1 states the design-goal frequency responses for the frequency weightings according to
IEC 61672 – 1. They are stated for the complete instrument including the microphone. For the A and C
frequency weightings, these design goals are equivalent to the ones specified in IEC 60651. The
corresponding tolerance limits can be found in the standards.

Integrating-averaging Sound Level Meter Type 2240 – Instruction Manual6
Table 2.1
Frequency weight-
ings according to
IEC 61672 – 1,
Table 2
Nominal Frequency
(Hz)
Exact Frequency
(6 digits)
(Hz)
Frequency Weightings
(1 decimal)
(dB)
AC
10 10 –70.4 –14.3
12.5
16
20
12.5893
15.8489
19.9526
–63.4
–56.7
–50.5
–11.2
–8.5
–6.2
25
31.5
40
25.1189
31.6228
39.8107
–44.7
–39.4
–34.6
–4.4
–3.0
–2.0
50
63
80
50.1187
63.0957
79.4328
–30.2
–26.2
–22.5
–1.3
–0.8
–0.5
100
125
160
100.000
125.893
158.489
–19.1
–16.1
–13.4
–0.3
–0.2
–0.1
200
250
315
199.526
251.189
316.228
–10.9
–8.6
–6.6
0.0
0.0
0.0
400
500
630
398.107
501.187
630.957
–4.8
–3.2
–1.9
0.0
0.0
0.0
800
1000
1250
794.328
1000.00
1258.93
–0.8
0.0
+0.6
0.0
0.0
0.0
1600
2000
2500
1584.89
1995.26
2511.89
+1.0
+1.2
+1.3
–0.1
–0.2
–0.3
3150
4000
5000
3162.28
3981.07
5011.87
+1.2
+1.0
+0.5
–0.5
–0.8
–1.3
6300
8000
10000
6309.57
7943.28
10000.0
–0.1
–1.1
–2.5
–2.0
–3.0
–4.4
12500
16000
20000
12589.3
15848.9
19952.6
–4.3
–6.6
–9.3
–6.2
–8.5
–11.2

CHAPTER 2
Hardware Setup 7
2.3 Measured Quantities
The measured quantities are also described in the User Guide in practical terms. For completeness, the
formal definitions of the relevant quantities are given here.
2.3.1 Overload
For Running Measurements, the Overload indication is displayed for as long as the overload
condition exists or for a period of 1 s, whichever is the greater. Overload is indicated at full-scale
+0.3 dB. An overload deteected during a timed measurement is latched and displayed with the relevant
parameters until these are cleared by initiating a new measurement.
2.3.2 Under-Range
For Running Measurements, the Under-range indication is displayed for as long as the under-
range condition exists or 1 s, whichever is the greater. Under-range is indicated at scale lower limit
–0.5 dB.
2.3.3 F Time-weighted Sound Level
The time-weighted sound level, Lxy(t), is defined as twenty times the logarithm to base ten of the ratio
of a given root-mean-square sound pressure to the reference sound pressure, root-mean-square sound
pressure being obtained with a frequency weighting, x, and standard time weighting, y, where:
• x is A for A-weighted, C for C-weighted
• y is always F for Fast-weighted using a 0.125 s time constant
The time-weighted sound level is a continuous function of time and is expressed in decibels (dB).
Lxy(t) is not displayed, but is the base for LxyInst(Tn)and LxyMax(T).
In symbols, frequency-weighted and time-weighted sound level, Lxy(t), at any instant of time, t, is
represented by:
where:
•τ is the exponential time constant in seconds for time weighting F
•ξis a dummy variable of time integration from some time in the past, as indicated by –∞ for the lower
limit of the integral, to the time of observation, t
•px(ξ) is the xfrequency-weighted instantaneous sound pressure
•p0is the reference sound pressure, equal to 20 μPa
2.3.4 Instantaneous Time-weighted Sound Level
The instantaneous time-weighted sound level, LxyInst(Tn), is defined as the time-weighted sound level,
Lxy(t), sampled at t=T
nwhere:
•xis A for A-weighted, C for C-weighted (available for test purposes only)
•yis F for Fast-weighted
•Tn=t0+n·Δt
•t0is some starting time;
•nis an incrementing integer
•Δtis the display update interval
The instantaneous time-weighted sound level is, in other words, updated every Δtseconds, and
expressed in decibels (dB).
Lxy t() 20lg 1 τ⁄()px
2
–∞
t
∫ξ()e–tξ–()τ⁄dξp0
⁄[dB]=

Integrating-averaging Sound Level Meter Type 2240 – Instruction Manual8
2.3.5 Peak Sound Level
The peak sound level, Lxpk(Tn), is defined as twenty times the logarithm to the base ten of the ratio of
the greatest absolute instantaneous sound pressure, px(t), during a time interval starting at t= Tnand
ending at t =T
n+Δt, to the reference sound pressure, p0, instantaneous sound pressure being obtained
with a frequency weighting, x, where:
•xis C for C-weighted
•px(t) is the xfrequency-weighted instantaneous sound pressure
•p0is the reference sound pressure, equal to 20 μPa
•Tn=t0+ n·Δt
•t0is some starting time
•nis an incrementing integer
•Δtis the display update interval, equal to 1 second
The peak sound level is, in other words, updated every 1 second and expressed in decibels (dB).
2.3.6 Timed Broadband Measurements
These measurements are only executed when Measurement Start is activated and are stopped when
Measurement Stop is activated. The time interval between start and stop is the Elapsed Time. During
the measurement time interval, intermediate results are displayed as if the measurements were stopped
at the time of the display update. When the measurements are stopped, the set of results, including
Latched Overload, is called Current Measurement and is held until a new set of measurements are
started. At this time, all the results included in Current Measurement are automatically reset before the
new measurements are started.
2.3.7 Maximum Time-weighted Sound Level
The maximum, time-weighted sound level, LxyMax(T), is defined as the greatest time-weighted sound
level, Lxy(t), within a time interval starting at t=T and ending at t=T+Δtwhere:
•xis A for A-weighted, C for C-weighted
•yis F for Fast-weighted, S for Slow-weighted or I for Impulse-weighted
•Tis the start time of the measurement
•Δtis the measuring period, indicated as Elapsed Time
The maximum time-weighted sound level is expressed in decibels (dB).
2.3.8 Equivalent Continuous Sound Level
The equivalent continuous sound level (also called time-average sound level), Lxeq(T), is defined as
twenty times the logarithm to the base ten of the ratio of a root-mean-square sound pressure during a
time interval to the reference sound pressure, sound pressure being obtained with a frequency weighting,
x. The time interval starts at t = T and ends at t=T+Δtwhere:
•xis A for A-weighted, C for C-weighted
•Tis the start time of the measurement
•Δtis the averaging time interval, indicated as Elapsed Time
The equivalent, continuous sound level is expressed in decibels (dB).
In symbols, equivalent continuous sound level, Lxeq(T), is given by:
Lxeq T() 20lg 1 Δt⁄() px
2
T
TΔt+
∫ξ()dξp0
⁄[dB]=

CHAPTER 2
Hardware Setup 9
where:
•ξ is a dummy variable of time integration over the averaging time interval
•px(ξ) is the xfrequency-weighted instantaneous sound pressure
•p0is the reference sound pressure, equal to 20 μPa
2.3.9 Maximum Peak Sound Level
The maximum peak sound level, LxpkMax(T), is defined as the greatest peak sound level, Lxpk(t),
within a time interval starting at t= T and ending at t=T+Δtwhere:
•xis A for A-weighted, C for C-weighted
•Tis the start time of the measurement
•Δtis the measuring period, indicated as Elapsed Time
The maximum peak sound level is expressed in decibels (dB).

Integrating-averaging Sound Level Meter Type 2240 – Instruction Manual10

11
Chapter 3
Conformance Testing
3.1 Introduction
This chapter contains the information needed to conduct conformance testing according to the specified
standards.
3.2 Selecting C-weighting
Normally, Sound Level Meter Type 2240 measures LAF, LAFmax, LAeq and LCpeak, but for testing
purposes it is possible to replace the A-weighting with C-weighting, so that LCF, LCFmax, LCeq and
LCpeak are measured.
To do this, press and hold the Sound Level Range key for more than 10 seconds – the display now
shows C-weighted parameters. Repeating this action returns the instrument to its normal mode.
3.3 Mounting for Acoustical Tests
For acoustical tests, it is important that the test rig for mounting the microphone to be tested is
designed to minimise the influence of reflections to a level that is comparatively smaller than the test
parameter's maximum Expanded Uncertainties of Measurement. This has to be demonstrated with a
good, known laboratory microphone.
During acoustic tests, the sound level meter must be placed in a reflection-free room. According to
good practice in acoustic laboratories, the sound level meter must be placed in a way that eliminates
any surrounding influence.
3.4 Mounting for Mechanical Vibrations Tests
Type 2240 should be mounted on the shaker with a suitable holder so that the vibration is applied in a
direction perpendicular to the plane of the microphone diaphragm.
3.5 Electrical Substitute for Microphones
To obtain a BNC type electrical input, replace the microphone with a WA-0302 – A 12 pF fitted with a
UA-0245 adaptor.
All electrical inputs can be short-circuited when needed for testing.

Integrating-averaging Sound Level Meter Type 2240 – Instruction Manual12
3.6 EMC Test Procedures
3.6.1 Signal Source for Immunity Test
The acoustic signal, which is used during the Immunity test, is applied to the microphone through a
½″plastic hose (a normal water hose) from a source outside the test room. In this way, the acoustic
source is not affected by the RF field. The source can be a normal entertainment earphone.
Fig.3.1
Connecting the
microphone to the
signal source for
immunity testing
To prevent the acoustic source from being affected by acoustic noise in the surroundings, the following
method can be used:
Insert an acoustic attenuator in the hose close to the microphone, so that the sound pressure within the
greater part of the hose is held far above the surrounding sound level. The acoustic attenuator can
easily be made from a short piece of metal tubing with an outer diameter of ½ ″. Squeeze a piece of
paper tissue into the tube, and compress it until the desired attenuation is obtained. Up to 40 – 60 dB of
acoustic attenuation can be obtained.
3.6.2 Reference Orientation
Fig.3.2
Reference
orientation relative
to RF emitter/
receiver
3.6.3 Testing EMC According to IEC 60804
The exponential, time-averaged detectors in Sound Level Meter Type 2240 are digital and their results
calculated based on the same samples used for calculating the linear averaged detectors.
Therefore, the LxFInst measurement values will be equal to short Lxeq values when measuring steady
signal levels.
For this reason, measurements of LxFInst must be used during testing for Immunity to RF signals
when testing according to both IEC 60651 and IEC 60804. That is, only one test has to be carried out
and no special operating mode, giving a short-duration Lxeq measurement, is provided.
Microphone assembly
(wind screen removed)
Water hose
50dB SPL inside
Acoustic
attenuator
Compacted
paper tissue
Water hose to
acoustic source
>90dB SPL inside
040132
040253
Type 2240

CHAPTER 3
Conformance Testing 13
Emission
See “Testing EMC According to IEC 60804” above.
Immunity as Sound Level Meter
The highest Susceptibility (Susceptibility = 1/Immunity) to radio-frequency fields, is achieved when set
up as shown in Fig.3.3.
Fig.3.3
Setup for highest
susceptibility to
radio-frequency
fields
AntennaAntenna
040134

Integrating-averaging Sound Level Meter Type 2240 – Instruction Manual14

15
Chapter 4
Specifications
4.1 Specifications
Unless specifically noted otherwise, specifications are given as typical data under Reference
Environmental Conditions.
4.2 Standards
Type 2240 conforms to the following International Standards and Classes/Types/Groups:
•IEC 60651 (1979) plus Amendment 1 (1993 – 02) and Amendment 2 (2000 – 10), Type 1, Group X
•IEC 60804 (2000 – 10), Type 1, Group X
•IEC 61672 - 1 (2002 – 05), Class 1, Group X
•DIN 45657 (1997 – 07)
•ANSI S1.4 – 1983 (R 1997) Type S1
•ANSI S1.43 – 1997, Type 1
In the text elsewhere in this manual, references to these standards are shortened to the standard’s name
but are to be understood as the full text above.
The International IEC Standards are adopted as European standards by CENELEC. When this happens,
the letters IEC are replaced with EN and the number is retained. Type 2240 also conforms to these EN
Standards.
4.3 Reference Environmental Conditions
Air Temperature: 23°C
Static Pressure: 101.325 kPa
Relative Humidity: 50%
4.4 Reference Conditions for Acoustic Calibration
Reference Range: 60 – 140 dB
Reference Sound Pressure Level: 94.00 dB re 20 μPa
Reference Frequency: 1 kHz