Czech Metrology Institute  
Okružní 31, 638 00  Brno  
 
 
1. ------IND- 2018 0577 CZ - EN- ------ 20181224 --- --- PROJET 
Executive summary for the EC (not part of this legislation)  
‘Sound -measuring instruments of classes 1 and 2, bandwidth filters, measurement microphones’ may 
be placed on the market and put into use in the Czech Republic as specified measuring instruments  
pursuant to Act No  505/1990 on metrology, as amended. Pursuan t to this act, the specified measuring 
instruments are measuring instruments in the List of Specified Measuring Device Types (Decree 
No 345/2002) and specified (by the manufacturer/importer) for measurement important for the 
protection of public interests in the following areas: consumer protection; contractual relations; 
stipulation of sanctions, fees, tariffs and duties; health protection; environmental protection; 
occupational safety or protection of other public interests protected by separate legislati on. This is 
therefore a similar purpose to that which is used to identify stipulated products – non-automatic 
measuring and weighing instruments pursuant to Directives  2014/31/EU and 2014/32/EU. The 
requirements of this General Measure do not apply to meas uring instruments not placed on the market 
in the Czech Republic for the above purposes, identified by Act No  505/1990 on metrology.  
The purpose of this notified legislation is to lay down metrological and technical requirements for these 
specified measuri ng instruments. This legislation also stipulates tests for type approval and verification 
of specified measuring instruments of this type.  
(End of executive summary)  
 
Author: Mgr. Tomáš Hendrych  
Telephone: 545  555 414 
 
 
P U B L I C  N O T I C E 
 
As the aut hority with substantive and territorial jurisdiction in the matter of laying down metrological 
and technical requirements for specified measuring instruments and stipulating the testing methods for 
type approval and verification of specified measuring inst ruments pursuant to §  14(1) of Act 
No 505/1990, on metrology, as amended (hereinafter the ‘Metrology Act’), and in accordance with the 
provisions of §  172 et seq. of Act No  500/2004, the Code of Administrative Procedure (hereinafter the 
‘CAP’), the Czech M etrology Institute (hereinafter the ‘CMI’) commenced ex officio proceedings on 
2 March 2016 pursuant to §  46 of the CAP, and, based on supporting documents, issues the following:  
 General Measure No  0111 -OOP -C087 -18 
2 I. 
D R A F T  G E N E R A L  M  E A S U R E 
number: 0111 -OOP -C087 -18 
laying down the metrological and technical requirements for legally controlled measuring 
instruments, including testing methods for verification of the following legally controlled 
measuring instruments:  
‘Sound -measuring instruments of classes 1 and 2, bandwidth filters, measurement microphones’  
 
This General Measure introduces electroacoustic operating requirements for the following types of 
sound -measuring instruments:  
 conventional sound level meters which exponentially measure time -weighted sound pressure 
levels; 
 integrating -averaging sound level meters which measure the equivalent sound pressure levels;  
 integrating sound level meters which measure sound exposure levels;  
 intensity sound level meters which measure acoustic energy or intensity in a sound field;  
 measurement condenser microphones, single or in pairs, or microphone fields;  
 octave and third -octave filters (as well as software filters and analysers).  
An individual sound level meter must ensure any or all types of measurement. All sound level meters 
specified in this Measure must be equipped with frequency function A. They may also be equipped with 
additional octave and third -octave filters. However, they must always be capable of working with 
measurement microphones which have properties pursuant to th e technical conditions specified in this 
Measure.  
1 Basic definitions  
For the purposes of this General Measure, the terms and definitions according to VIM and VIML1, 
ČSN  IEC 50(801)2 shall apply.  
2.1 Operating conditions  
2.1.1  Operating conditions for use  of the measuring instrument  
The operating conditions for sound measurement instruments shall be specified by the manufacturer for 
the particular type of measuring instrument. If not specified, the following requirements shall apply to 
class  1 sound level meters:  
 the ambient operating temperature range must be at least −10  °C to +50  °C; 
 the relative air humidity limits must be at least 30  % to 70  %; 
 atmospheric pressure must at least be within the limits 85  kPa to 108  kPa. 
                                                      
1 TNI 01 0115 International Vocabulary of Metrology – Basic and General Concepts and Associated Terms 
(VIM) and International Vocabulary  of Terms in Legal Metrology (VIML) are part of the technical 
harmonisation compendium ‘Terminology in the Area of Metrology’, which is publicly accessible at 
www.unmz.cz.  
2 ČSN  IEC 50(801) International Electrotechnical Vocabulary – Chapter  801: Acoustics  and electroacoustics  General Measure No  0111 -OOP -C087 -18 
3 2.1.2  Reference operating conditio ns 
The reference ambient conditions are:  
 air temperature 23  °C; 
 static pressure 101.325  kPa; 
 relative air humidity 50  %. 
2.1.3  Temperature stabilisation period  
The times needed for temperature stabilisation of the measuring instrument must be clearly indic ated on 
the measuring instrument and stated in the manufacturer’s documentation.  
3 Technical requirements  
3.1 General technical requirements  
3.1.1 This Measure specifies two operating categories of sound level meters, class  1 and class  2. An 
additional cla ss 0 having the lowest permissible error values is established for filters.  
3.1.2 Sound level meters (except intensity meters) must have specified frequency characteristics for 
sound impacting the microphone in a single main direction in a free sound field  or in random directions.  
3.1.3 Sound level meters are intended for measuring sounds within the range of human hearing, but if 
ultrasound is present within the audible sound, then the frequency function AU may be used. If the sound 
level meter is equipped  with a frequency function AU, the measurement result will be measured as a 
sound pressure level AU. The nominal characteristics of the frequency function AU and associated 
maximum permissible error values are in the frequency range of 10  Hz to 20  kHz in a ccordance with 
the nominal characteristics and maximum permissible error values specified in Table  3 of this Measure 
for frequency function A. Sound pressure level measurement with an AU weighting function is also the 
sound pressure level measurement with an A weighting function.  
3.1.4 This Measure applies to the design of a sound level meter within the specified range. A sound level 
meter may be an individual manual instrument with a connected microphone (or multiple microphones) 
and a built -in display dev ice. A sound level meter may be made up of separate components located in 
one or more units and may be capable of displaying multiple levels of an acoustic signal. Sound level 
meters may include extensive processing of an analogue or digital signal, be it individually or in 
combination with multiple analogue or digital outputs. Sound level meter components may include 
multi -purpose computers, data loggers, printers and other devices which constitute an essential 
component of the complete instrument.  
3.1.5 Sound level meters may be designed for use with an operator present (or without, using remote 
control), or for automatic or continuous measurement of sound pressure levels without an operator 
present. The technical requirements specified in this Measure fo r response to sound waves apply to 
sound fields without an operator present.  
3.2 Technical requirements for measurement microphones  
3.2.1 The body diameter of measurement microphones must be:  
 for a 1" microphone: (23.77  ± 0.05)  mm; 
 for a 1/2" microphone: ( 13.20  ± 0.05)  mm; 
 for a 1/4" microphone: (7.00  ± 0.05)  mm; 
 for a 1/8" microphone: (3.50  ± 0.05)  mm. General Measure No  0111 -OOP -C087 -18 
4 Microphones must have a screw -on protective screen so that an electrostatic actuator (which must be 
specified and supplied by the manufacturer) can still be  placed on the microphone. In case of a design 
with a fixed screen, this screen must be galvanically separated into two parts and structurally prepared 
so that the front part of the screen can still be used as an electrostatic actuator. The technical param eters 
of this actuator as well as the external actuator must be specified in the operating instructions.  
3.2.2 A measurement microphone must be removable from the sound level meter so that it can be tested 
separately. It must be marked with a type and seri al number. This also applies to microphone systems 
(such as an intensity sensor).  
3.2.3  Every measurement microphone must include the following information, which must be in printed 
form or in a known electronic format (readily readable):  
 manufacturer’s na me, microphone type, serial number, year of manufacture;  
 characteristics of use (for the free field, angle of incidence, pressure microphone, intensity probe);  
 nominal microphone size (its diameter specified in millimetres and in fractions of an inch);  
 specifications for the microphone insert threads and microphone cover screen;  
 microphone sensitivity measured in an open circuit (specified in mV/Pa and in dB  re 1V/Pa) at 
reference conditions as well as with specified measurement uncertainty;  
 magnitude of co ndenser microphone’s polarisation voltage (in V);  
 resonance frequency (in kHz or Hz);  
 frequency characteristics in tolerance field of ±2  dB; 
 maximum permissible SPL value (sound pressure level) which may be applied to the microphone 
at 3 % signal distortio n (in dB re 20 µPa);  
 microphone’s internal noise (specified in dB(A));  
 microphone’s electrical capacity (in pF);  
 equivalent volume (in mm3); 
 types of pre -amplifiers which the microphone can work with;  
 types of usable acoustic calibrators with essential data needed to verify or calibrate the 
microphone (such as correction for standard pistonphones), while the type of acoustic calibrator 
must be capable of calibration itself;  
 influence of static pressure on the microphone’s sensitivity level (in dB/hP) at 250 Hz; 
 influence of air humidity on the microphone’s sensitivity level (in dB/%RH) at 250  Hz; 
 influence of temperature on the microphone’s sensitivity level (in dB/degree Celsius) at 250  Hz; 
 influence of the magnetic field with an intensity of 80  A/m at a  frequency of 50  Hz (in  dB re 
20 µPa);  
 influence of axial vibration 1  m/s2 (in dB per 20  µPa);  
 estimated long -term stability value at specified temperature (time/dB);  
 type of electrical actuator for measuring frequency characteristics and applied electric al voltage 
(in V);  
 graph of frequency characteristics for excitation via electrical actuator;  
 graphs of frequency characteristics in a free field for various angles of acoustic wave incidence;  
 correction of actuator frequency characteristics for a free fie ld (for entire usable frequency range);  
 for intensity microphones, information must be specified for proper functioning and measurement 
via intensity probe, including the verification or calibration process.  General Measure No  0111 -OOP -C087 -18 
5 3.3 Technical requirements for filters  
3.3.1 Amb ient reference conditions  
The reference conditions for the surrounding area which apply to hardware filters include an ambient 
air temperature of 20  °C, relative air humidity of 65  % and atmospheric pressure of 101.3  kPa. 
3.3.2  General  
The electrical prope rties and frequency characteristics specified in this Measure for octave and fractional 
octave filters apply under the reference ambient conditions pursuant to Article  3.3.1. As long as the 
resulting instrument meets all applicable requirements of this Mea sure, any desired filter design can be 
used, be it as a base ten system or a base two system. The technical requirements specified in this 
Measure also apply to software filters which are used as basic or supplementary equipment in sound 
level meters.  
3.3.3 Nominal mean band frequencies  
Octave and fractional octave filters must be identified or marked with the nominal mean band 
frequencies which are suitable rounded values of exact mean frequency bands. The exact and nominal 
mean frequency bands for octave  and third -octave filters are specified in the following Table  1. 
Table  1 – Mean frequency band for octave and third -octave filters in sound frequency range  
Value  
X Base ten exact fm 
(10x/10)(1 000) Hz Base two exact 
fm 
(2x/3)(1 000) Hz Nominal mean 
frequency  
Hz  Third octave  Octave  
−16 
−15 
−14 25.119  
31.623  
39.811  24.803  
31.250†  
39.373  25 
31.5 
40 ° 
° 
° ° 
−13 
−12 
−11 50.119  
63.096  
79.433  49.373  
62.500†  
78.745  50 
63 
80 ° 
° 
° ° 
−10 
−9 
−8 100.00  
125.89  
158.49  99.913  
125.00†  
157.49  100 
125 
160 ° 
° 
° ° 
−7 
−6 
−5 199.53  
251.19  
316.23  198.43  
250.00†  
314.98  200 
250 
315 ° 
° 
° ° 
−4 
−3 
−2 398.11  
501.19  
630.96  396.85  
500.00†  
629.96  400 
500 
630 ° 
° 
° ° 
−1 
0 
1 794.33  
1 000.0†  
1 258.9  793.70  
1 000.0†  
1 259.9  800 
1 000 
1 250 ° 
° 
° ° 
2 
3 
4 1 584.9  
1 995.3  
2 511.9  1 587.4  
2 000.0†  
2 519.8  1 600 
2 000 
2 500 ° 
° 
° ° General Measure No  0111 -OOP -C087 -18 
6 5 
6 
7 3 162.3  
3 981.1  
5 011.9  3 174.8  
4 000.0†  
5 039.7  3 150 
4 000 
5 000 ° 
° 
° ° 
8 
9 
10 6 309.6  
7 943.3  
10 000†  6 349.7  
8 000.0†  
10 079 6 300 
8 000 
10,000  ° 
° 
° ° 
11 
12 
13 12 589 
15 849 
19 653 12 699 
16 000†  
20 159 12 500 
16 000 
20 000 ° 
° 
° ° 
NOTE The exact mean frequency bands (except for the exact values marked with a †) are calculated to five 
decimal places from the equation  
fm =(G(2x+1)/(2b) ) fr (1) 
in which x is an arbitrary whole number, positive, negative, or zero and fr is the reference frequency 1  000 Hz. 
 
3.3.4 Reference attenuation  
With all filters, the manufacturer must specify the reference attenuation in the permeable band, which 
must be identical fo r all filters from the set of filters.  
3.3.5 Relative attenuation measurement  
3.3.5.1 The relative attenuation at the reference range must be tested with the same three filters with 
which the linearity was measured.  
3.3.5.2 The relative attenuation measur ement is conducted as a measurement of the response to 
sinusoidal signals with a constant amplitude of various frequencies. The level of the signals must be (1 
± 0.1)  dB below the specified upper limit of the linearity range.  
3.3.5.3 The standardised frequ ency of the test sinusoidal signal Ωk = fk / fm must be determined in each 
filter with the mean frequency fm according to the relation:  
Ωk = 1 + [( G1/(2b) − 1) ( Rk- 1)] / ( G1/2 − 1) (2) 
where:  G  ........   is the octave ratio of the frequencies;  
 b  .........   reciprocal of the numerical designation of the bandwidth;  
 Rk  .......  frequency parameter defined in Table  2; 
 K  ........   whole number in a range of 0 to 7.  
 
The index of standardised frequencies during the test must be expanded according to the relation:  
Ωk = 1/Ω-k  (3) 
in which Ωk and Ω-k have the same relative attenuation acceptance limits.  
The technical requirements specified in this chapter constitute the abbreviated general requirements 
specified in the applicable standard.  
In the case of octave filters, Ωk = Rk. General Measure No  0111 -OOP -C087 -18 
7 Table  2 – Relative attenuation limits for octave filters  
Index  
k Frequency  
parameter  Minimum; maximum relative attenuation acceptance limits  
dB 
Rk Class  1 Class  2 
0 G°=1 −0.4; +0.4  -0.6; +0.6  
1 G1/8 -0.4; +0.5  -0.6; +0.7  
2 G1/4 -0.4; +0.7  -0.6; +0.9  
3 G3/8 -0.4; +1.4  -0.65; +1.7  
4 G +16.6; + +15.6; + 
5 G2 +40.5; + +39.5; + 
6 G3 +60; + +54; + 
7 G4 +70; + +60; + 
 
3.3.5.4 Figure  1 shows the limits of the minimum and maximum relative attenuation of the octave filter. 
The figure also shows discontinuous changes in the minimum and maximum relative attenuation at the 
limit frequencies of the band and the linear change in the limits of relative attenuation between 
normalised frequencies with the fraction  points specified in Table  2. 
 
General Measure No  0111 -OOP -C087 -18 
8 Poměrný utlum, ∆λ, dB  Relative attenuation, ∆λ, dB  
Minimální mez  Minimum limit  
Maximální mez  Maximum limit  
Normalised frequency (logarithmic scale)  
Figure  1 – Maximum and minimum relative attenuation limits for class  1 octave filters  
3.3.6 Integrated filter characteristics  
3.3.6.1 Integrated filter characteristic ∆ B: in decibels, must be determined for the bandpass filter 
according to the equation:  
∆B = 10 log (Be/Br) (4) 
where:  Be  .......  is the normalised effective bandwidth;  
 Br  ........   normalised reference bandwidth determined from equation (5) for the same mean band 
frequency:  
 Br = (f2 − f2) / fm = [G +1/(2 b) − G −1/(2b)]  (5) 
3.3.6.2 For an arbitrary filter, the normalised effective bandwidth with exact mean band frequency fm 
represented by the equation:  




 




fB
mfA
efdfm
01,0
10
 (6) 
3.3.6.3 The integrated filter characteristic must not exceed ±0.4  dB for any bandpass filter integrated 
into the instrument for class  1 instruments or ±0.6  dB for class  2 instruments.  
3.3.7 Pre -filters for interference  
The manufacturer must prepend interference filters to a device with digital filters or sampled data filters 
in either analogue or digital form  as needed. Pre -filters for interference must minimise interference 
between the input signal and the sampling process, which could create disruptive frequency components 
in the input signal and cause the filter’s relative attenuation frequency characterist ics to exceed the 
maximum value of the permissible minimum limits specified in Table  2. 
3.3.8 Operation in real time  
The manufacturer must numerically mark bandwidths and corresponding frequency ranges in which the 
output signal level in the response to th e sinusoidal input signal with constant amplitude, whose 
frequency logarithm changes at a constant speed, is the theoretical level of the output signal for class  1 
instruments with an accuracy of ±0.3  dB for class  2 instruments with an accuracy of ±0.5  dB.  
3.3.9 Linearity range  
3.3.9.1 At each accessible measurement range and for all bandwidths of a filter for flat frequency 
characteristics, if integrated, it holds true that errors in the amplitude characteristic linearity must not 
exceed the following in the linearity range:  
±0.4 dB in linearity ranges of at least 50  dB for class  1 filters;  
±0.5 dB in linearity ranges of at least 40  dB for class  2 filters.  
3.3.9.2  Overlapping of measurement ranges (if there are more than one) must be conducted so that the  
linearity range overlaps by at least 40  dB for class  1 filters and by at least 30  dB for class  2 filters.  General Measure No  0111 -OOP -C087 -18 
9 3.3.9.3 In case of filters with more than one measurement range, the permissible tapering of the linearity 
range is on the most sensitive measurement  range, assuming that the range is not a reference range.  
3.3.9.4 In filters which have a display as an inseparable component or if the filter’s output is transmitted 
to an external display or other device with a greater range than the linearity range, the  manufacturer 
must specify the amplitude characteristic linearity tolerances, which are complied with outside of the 
linearity range.  
3.3.10 Flat frequency characteristics  
The manufacturer must specify the range of frequencies in which the relative attenua tion is in an 
accuracy range of ±0.4  dB and ±0.6  dB with respect to the relative attenuation at the reference frequency 
for instruments of class  1 and class  2, respectively. In measurements of the relative attenuation of flat 
frequency characteristics, the  reference attenuation is the same as with measurements of the relative 
attenuation of a bandpass filter if the instrument is equipped with a frequency -independent transmission 
range (i.e. flat frequency characteristics).  
3.3.11 Total of output signals  
The difference between  
a) the input signal level minus the reference attenuation and  
b) the level of the sum of average values of the squares of the output signals from various filters with 
a specified bandwidth  
must not exceed  
+1.0 dB; −2.0  dB (class  1 instru ments) and  
+2.0 dB; –4.0 dB (class  2 instruments)  
for a sinusoidal input signal of a random frequency between two sequential mean frequencies of an 
octave or fractional octave band.  
3.3.12 Maximum input signal  
The manufacturer must specify the maximum ef fective voltage value of the input sinusoidal signal at 
which all filters integrated into the instrument at each measurement range meet the requirements of this 
Measure.  
3.3.13 Terminating impedance  
If relevant, the manufacturer must specify the input and output terminating impedance necessary to 
ensure proper operation of the instrument.  
3.3.14 Sensitivity to various environments  
3.3.14.1 Ambient temperature  
At the nominal mean band frequency, the relative attenuation of a random filter integrated into th e device 
must not deviate from the relative attenuation at the same frequency under reference ambient conditions 
by more than ±0.4  dB for class  1 instruments and ±0.6  dB for class  2 instruments in an ambient 
temperature range of at least 0  °C to +50  °C. 
3.3.14.2  Relative air humidity  
The relative humidity range and corresponding air temperature at which the device may continuously 
operate must be established by the manufacturer and specified in the user manual. After 24  hours of 
exposure to a damp atmospher e with a relative humidity of 75  % and an ambient temperature of +40  °C 
and without condensation on the internal components of the test device, the relative attenuation at the 
nominal mean band frequency of a random filter integrated into the device must n ot deviate from the General Measure No  0111 -OOP -C087 -18 
10 relative attenuation at the same frequency under reference ambient conditions by more than ±0.15  dB 
for class  0 instruments and ±0.3  dB for class  1 instruments and ±0.5  dB for class  2 instruments.  
3.3.15 Power supply check  
For instruments which are powered by a battery or rechargeable battery, the manufacturer must ensure 
a suitable means of checking the power supply which, at the moment of the check, must have sufficient 
capacity to operate the instrument in accordance with all  requirements of this Measure.  
3.4 Technical requirements for sound level meters  
3.4.1 General  
3.4.1.1 A regular digital sound level meter is made up of a microphone, pre -amplifier, signal processing 
device (filters, amplifier, attenuator), A/D converter, processor, indication unit, memory, D/A converter, 
power supply unit and control elements – this is generally a combination of microphone, signal processor 
and display device. Sound level meters must be capable of either indicating measured values directly  on 
the display or store the measurement results into a memory and then display them on a device specified 
by the manufacturer.  
3.4.1.2  The operating requirements specified in this chapter apply under reference ambient conditions 
specified in Part  2.1.2.  
3.4.1.3 A sound level meter which is specified as a class 1 sound level meter in the user manual must 
meet all binding requirements for class  1 which are specified in this Measure. A sound level meter which 
does not meet all requirements for class  1 (but me ets the remaining requirements for class  2) must be 
allocated to class  2. A class  2 sound level meter may have certain properties of a class  1 meter, but if 
some of the properties only meet the requirements for class  2, then the instrument is a class  2 sou nd 
level meter. The sound level meter may be specified as a class  1 instrument in one configuration and as 
a class  2 instrument in another configuration (for example, with a different microphone or pre -
amplifier).  
3.4.1.4 The configuration for a complete s ound level meter and its normal operating mode must be 
specified in the user manual. If appropriate, the sound level meter configuration includes a wind 
protection cover and other devices which are installed around the microphone as an inseparable 
componen t in normal operating mode.  
3.4.1.5 For specifying high -frequency emissions and immunity to high -frequency fields, sound level 
meters are divided into the three following groups:  
 group X: individual instruments which encompass a sound pressure level measur ement device in 
accordance with this Measure and for which a power supply from an internal battery is specified 
in normal operating mode, not requiring external connection with an additional instrument for 
measuring sound pressure levels;  
 group Y: individu al instruments which encompass a sound pressure level measurement device in 
accordance with this Measure and for which a connection to the public electrical grid is specified 
in normal operating mode, not requiring external connection with an additional in strument for 
measuring sound pressure levels;  
 group Z: individual instruments which encompass a sound pressure level measurement device in 
accordance with this Measure requiring two or more components of a device which forms a basic 
part of the sound level  meter to be connected together in normal operating mode. Individual 
components may be powered by internal batteries or the public electrical grid.  
3.4.1.6 If necessary, the user manual must specify how the microphone is to be fastened in order to meet 
the requirements for directional characteristics and frequency weighting. A microphone stand or cable 
may be necessary to meet the requirements. In such case, the user manual must specify that the sound General Measure No  0111 -OOP -C087 -18 
11 level meter only meets the applicable requirements for d irectional characteristics and frequency 
weighting if the specified devices are installed. This primarily pertains to sound level meters composed 
of a microphone with a pre -amplifier connected to other instruments by a cable.  
3.4.1.7 The minimum possibilit y of a conventional sound level meter is to indicate sound pressure level 
A with time characteristic F. An integrating -averaging sound level meter must at least provide a means 
of indicating the equivalent of sound pressure level A. An integrating sound le vel meter must at least 
provide a means of indicating sound exposure level A. Sound level meters may include any or all design 
models for which operating requirements are specified in this Measure. The sound level meter must 
meet the applicable operating r equirements for these design models according to which they were built.  
3.4.1.8 A sound level meter which has more than one measurement range must be equipped with a 
suitable range switch. The measurement range(s) must be described in the user manual with the nominal 
sound pressure level at a frequency of 1  kHz. The function of measurement range switches must be 
described in the user manual together with recommendations for selecting the optimum measurement 
range to display the measurement results for sound  pressure level or sound exposure level.  
3.4.1.9 The user manual must also specify the reference sound pressure level, reference measurement 
range and reference orientation. The user manual must specify the reference direction for each type of 
microphone i ntended for use with the sound level meter; the position of the reference point microphone 
must also be specified. The reference sound pressure level is 94  dB. Alternatively, a reference sound 
pressure level of 74  dB, 84  dB, 104  dB, 114  dB or 124  dB may be  specified. A sound pressure level of 
94 dB closely corresponds to the effective acoustic pressure value of 1  Pa. 
3.4.1.10 Frequency function A must be included in every sound level meter. Sound level meters in 
compliance with the maximum permissible error s for class  1 must have a frequency function C at least 
for the purposes of type tests. Sound level meters which measure sound pressure level C in intermittent 
sounds must also measure sound pressure level C in continuous sounds, at least for type -testing 
purposes. Frequency function ZERO (weighting function Z) is selectable. The user manual must 
describe all available frequency weighting functions. The sound level meter may be equipped with 
octave or third -octave filters. Analogue filters may be connected to a measurement chain as a self -
standing instrument or may be part of a sound level meter. Digital filters may be special programmes 
according to which the processor processes digital sound (in digital sound level meters).  
3.4.1.11 A sound level meter may  have more than one display device, whereas the connection of a direct, 
alternating or digital output on its own is not deemed to be a display device.  
3.4.1.12  It must be possible to transmit electrical signals to the input of the sound level meter in orde r 
to ensure that the sound level meter’s parameters are in accordance with the requirements of this 
Measure. These signals should be equivalent to signals from the microphone. The user manual for each 
respective type of microphone must specify the nominal impedance and valid tolerance of the electrical 
properties of the device or means with which the signals can be transmitted to the sound level meter’s 
electrical input. Electrical properties include the resistance and reactance component of electrical 
impe dance at the output of the device. The nominal impedance value must be specified for a frequency 
of 1 kHz.  
3.4.1.13  The user manual must also specify the maximum sound pressure level at the microphone’s 
location and the maximum peak -to-peak voltage which c an be connected to an electrical input without 
damaging the sound level meter.  
3.4.1.14 If the sound level meter is to be capable of measuring the maximum time -weighted sound 
pressure level and the peak sound pressure level C, a ‘hold’ function must be ava ilable while measuring 
these quantities. The user manual must also describe the operation of a device with a ‘hold’ function 
and means of zeroing the display, which is blocked for this function.  General Measure No  0111 -OOP -C087 -18 
12 3.4.1.15 A computer software program may be an inseparable part of a sound level meter. The user 
manual must specify a unique identification of all such programs, including location in the directory 
structure of the computer being used, or must note that certain ot her programs which could interfere 
with the proper operation of the sound level meter may not be used at the same time.  
3.4.1.16 The operating requirements specified in this Measure apply (where applicable) to any time or 
frequency weighting working at th e same time and to any independent channel in a multi -channel sound 
level meter. The user manual must describe the properties and functions of each independent channel. 
Multi -channel sound level meters may have two or more microphone inputs.  
3.4.1.17 Once the initial time interval has elapsed after switching on a power supply and whose length 
must be specified in the manual and must not exceed 2  minutes, the sound level meter must reach a state 
of equilibrium and all requirements for the sound level meter’s  electroacoustic response as per this 
Measure must apply.  
3.4.2 Indicated levels and their settings  
3.4.2.1 The user manual must specify at least one type of acoustic (or electrostatic) calibrator for 
calibrating the sound level meter.  
3.4.2.2 A calibrator  of the same or more accurate class must be used for verifying or calibrating a sound 
level meter of a particular class.  
3.4.2.3 The procedure and indication for setting the sound pressure level displayed in the response to 
the application of an acoustic c alibrator must be specified in the user manual for the reference sound 
pressure level in the reference measurement range and for the calibration frequency. The result of the 
use of the indication setting procedure must be a sound pressure level or sound ex posure level which 
would be indicated in the response to plane progressive sinusoidal sound waves impacting from the 
reference direction or, as the case may be, in the response to sounds with an impact in a random direction. 
The procedure and indications f or settings must at least relate to the ambient conditions in the usable 
ranges which are specified in this Measure, including the reference ambient conditions. The settings 
must apply to all microphone types specified in the type -approval certificate with  which the sound level 
meter is used, and to all associated devices provided by the sound level meter manufacturer to fasten the 
microphone to the sound level meter.  
If the wind protection cover is type -approved as an inseparable component of the sound le vel meter, the 
user manual must contain information on corrections for the average effects of the wind protection cover 
on the microphone’s frequency characteristics.  
3.4.2.4 Information on corrections for deviation in the microphone’s mean frequency characteristics 
from stable frequency characteristics and average effects of reflections for the sound level meter’s cover 
and deflection around the microphone must be specified in the user manual for all types of microphones 
which are type -approved togeth er the sound level meter. Average effects of reflections and sound 
deflection relate to the sound pressure level at the microphone’s location and without a sound level meter 
present.  
In order for a sound level meter to meet the technical requirements of th is Measure with the wind 
protection cover installed around the microphone and without it, the information described above must 
be specified for both configurations. In the case of the configuration with the wind protection cover, the 
information must inclu de corrections for the average effects of the wind protection cover on the 
microphone’s frequency characteristics. If the wind protection cover is an inseparable part of the sound 
level meter in normal operating mode, the information on corrections for the  wind protection cover need 
only be specified for this configuration.  
Corrections for the microphone’s average frequency characteristics and average effects of reflections, 
deflections and a potential wind protection cover must apply to plane progressive s inusoidal sound 
waves impacting in the reference direction and under wind -free conditions. The information must 
include the associated values for expanded measurement uncertainties. The expanded measurement General Measure No  0111 -OOP -C087 -18 
13 uncertainties and basic information must be speci fied separately in the user manual in tabular form, 
whereas the correction for the microphone’s average frequency characteristics and average effects of 
reflections and deflection may be provided as two separate corrections or as one combined correction.  
3.4.2.5 The data required in Article  3.4.2.4 must be provided in the following formats:  
 for class  1 sound level meters, the information must be specified in tabular form in nominal third -
octave intervals from 63  Hz to 1  kHz and then in nominal intervals of one-twelfth of an octave at 
frequencies higher than 1  kHz up to at least 16  kHz;  
 for class  2 sound level meters, the information must be specified in tabular form in nominal third -
octave intervals from 63  Hz to at least 8  kHz;  
 corrections for average effec ts of the wind protection cover on frequency characteristics of the 
microphone must be specified in tabular form in nominal third -octave intervals from 1  kHz to 
16 kHz for class  1 sound level meters and from 1  kHz to 8  kHz for class  2 sound level meters.  
3.4.2.6 Deviations in measured effects of reflection, deflection and the wind protection cover (if any) 
on the frequency characteristics of the microphone from the effects specified in the user manual, 
expanded by the expanded measurement uncertainty, must not exceed two -thirds of the maximum 
permissible errors specified in Table  3. 
3.4.2.7 The user manual must specify data on the types of calibrators suitable for verification purposes. 
It must also specify data for their settings in order to obtain an equiv alent sound pressure level A which 
would be displayed under reference ambient conditions in the response to plane progressive sinusoidal 
sound waves impacting in the reference direction. These data for settings must apply to the sound 
pressure level A displayed in the response to sound pressure created by the acoustic calibrator or in the 
response to acoustic pressure simulated by the electrostatic calibrator.  
3.4.2.8 The data for settings must be provided for at least the frequencies of 125  Hz, 1  kHz and e ither 
4 kHz or 8  kHz and must apply to the specified combination of microphone, sound level meter and type 
of acoustic or electrostatic calibrator. The data for settings must be provided for all types of microphones 
or microphone -wind protection cover conf igurations for which it is determined that the sound level 
meter meets the requirements of this Measure. Deviations in the data for settings obtained by 
measurement from the data specified in the user manual must not exceed ± 0.4  dB or half of the size of 
the applicable data for the settings depending on which value is greater.  
3.4.3 Directional characteristics  
3.4.3.1 For the configuration of the sound level meter which is specified in the user manual for the 
normal operating mode, or for those parts of th e sound level meter which are located in the sound field, 
Table  3 specifies the requirements for directional characteristics which apply to plane progressive sound 
waves with an arbitrary angle of sound incidence in the specified ranges, including the refe rence 
direction. The nominal characteristics are equal to the response to sound from all directions of sound 
incidence at a random frequency.  
3.4.3.2 The requirements specified in Table  3 apply to any frequency in the specified ranges for any 
orientation o f the sound level meter or the applicable components around the reference direction.  
Table  3 – Maximum permissible errors in directional characteristics (including maximum 
permissible expanded measurement uncertainty)  
Frequency  
kHz Maximum absolute difference in displayed sound pressure levels for any two angles of 
sound incidence in a range of ± ϴ degrees with respect to the reference direction  
dB 
ϴ = 30° ϴ = 90°  ϴ = 150°  
Class  
1 2 1 2 1 2 General Measure No  0111 -OOP -C087 -18 
14 0.25 to 1  1.0 2.0 1.5 3.0 2.0 5.0 
> 1 to 2  1.0 2.0 2.0 4.0 4.0 7.0 
> 2 to 4  1.5 4.0 4.0 7.0 6.0 12.0 
> 4 to 8  2.5 6.0 7.0 12.0 10.0 16.0 
> 8 to 12.5  4.0 ... 10.0 ... 14.0 ... 
NOTE To demonstrate conformity with the specified limits, maximum absolute differences are expanded by the 
expanded measurement uncertainty in the sound pressure levels displayed.  
 
3.4.4 Frequency weighting function  
3.4.4.1 In the sound level meter configuration specified in the user manual for the normal operating 
mode , the frequency weighting function for the maximum permissible error specified in Table  4 applies 
to the response to plane progressive sound waves impacting the sound level meter in the reference 
direction or in a random direction, or potentially in the ca se of impact by means of the first and second.  
3.4.4.2 The frequency function values A, C and Z rounded to a tenth of a decibel and corresponding to 
the maximum permissible error for class  1 and class  2 sound level meters are specified in Table  4. The 
maximum permissible errors specified in Table  4 apply to the given operating class in all measurement 
ranges and after the setting described in Article  3.4.2 for responses to the acoustic calibrator at 
calibration frequency and under reference ambient conditi ons. 
3.4.4.3 The nominal value 0  dB with corresponding maximum permissible error ±1.1  dB for class  1 
sound level meters and ±1.4  dB for class  2 sound level meters is specified for all frequency weighting 
functions at frequency 1  kHz.  
3.4.4.4 At frequencies  between the sequential frequencies specified in Table  4, the frequency function 
C or A must be calculated from equations (7) or (8) and rounded to the tenth of a decibel. The maximum 
permissible errors are the greater of the values specified in Table  4 for two sequential frequencies.  
3.4.4.5 The deviation of the sound pressure level displayed from the sound pressure level which is at the 
microphone’s location without the sound level meter present, expanded by the expanded measurement 
uncertainty, must not exceed the maximum permissible error values at any frequency specified in 
Table  4. The sound pressure levels measured without the sound level meter present must be weighted 
with a valid frequency weighting function according to equations (7), (8) or (9).  
3.4.4.6 The frequency characteristics of the weighting function C is realised with the use of two fields 
at low frequency f1, two fields at high frequency f4 and two zeroes at 0  Hz. With these fields and zeroes, 
the response of the transmission power of the  weighting function C falls to fL = 101.5  Hz and 
fH = 103.9  Hz with respect to the response at the reference frequency f1 = 1 kHz by D2 = 1/2 
(approximately −3  dB). The frequency characteristics of the weighting function A are realised by 
supplementing the  frequency characteristics of the weighting function C by adding two linked high -
frequency first -order passes. The limit frequency for both high -frequency passes is given by 
fA = 102.45  Hz. 
3.4.4.7 The practical realisations of frequency functions C, A and Z specified in Table  4 may be derived 
as a frequency function from analytical expressions according to equations (7), (8), or (9).  General Measure No  0111 -OOP -C087 -18 
15 Table  4 – Frequency weighting functions and maximum permissible errors (including maximum 
permissible expanded measurement u ncertainty)  
Nominal 
frequency  
Hz Frequency weighting function* 
dB Maximum permissible errors (dB) 
Class  
A C Z 1 2 
10 -70.4 -14.3 0.0 +3.0; – +5.0; – 
12.5 
16 
20 −63.4 
−56.7 
−50.5 −11.2 
−8.5 
−6.2 0.0 
0.0 
0.0 +2.5; – 
+2; –4 
±2.0 +5.0; – 
+5.0; – 
±3.0 
25 
31.5 
40 −44.7 
−39.4 
−34.6 −4.4 
−3.0 
−2.0 0.0 
0.0 
0.0 +2.0; −1.5  
±1.5 
±1.0 ±3.0 
±3.0 
±2.0 
50 
63 
80 −30.2 
−26.2 
−22.5 −1.3 
−0.8 
−0.5 0.0 
0.0 
0.0 ±1.0 
±1.0 
±1.0 ±2.0 
±2.0 
±2.0 
100 
125 
160 −19.1 
−16.1 
−13.4 −0.3 
−0.2 
−0.1 0.0 
0.0 
0.0 ±1.0 
±1.0 
±1.0 ±1.5 
±1.5 
±1.5 
200 
250 
315 −10.9 
−8.6 
−6.6 0.0 
0.0 
0.0 0.0 
0.0 
0.0 ±1.0 
±1.0 
±1.0 ±1.5 
±1.5 
±1.5 
400 
500 
630 −4.8 
−3.2 
−1.9 0.0 
0.0 
0.0 0.0 
0.0 
0.0 ±1.0 
±1.0 
±1.0 ±1.5 
±1.5 
±1.5 
800 
1 000 
1 250 −0.8 
0 
+0.6 0.0 
0.0 
0.0 0.0 
0.0 
0.0 ±1.0 
±0.7 
±1.0 ±1.5 
±1.0 
±1.5 
1 600 
2 000 
2 500 +1.0 
+1.2 
+1.3 −0.1 
−0.2 
−0.3 0.0 
0.0 
0.0 ±1.0 
±1.0 
±1.0 ±2.0 
±2.0 
±2.5 
3 150 
4 000 
5 000 +1.2 
+1.0 
+0.5 −0.5 
−0.8 
−1.3 0.0 
0.0 
0.0 ±1.0 
±1.0 
±1.5 ±2.5 
±3.0 
±3.5 
6 300 
8 000 
10,000  −0.1 
−1.1 
−2.5 −2.0 
−3.0 
−4.4 0.0 
0.0 
0.0 +1.5; −2.0  
+1.5; −2.5  
+2.0; −3.0  ±4.5 
±5.0 
+5.0; – 
12 500 
16 000 
20 000 −4.3 
−6.6 
−9.3 −6.2 
−8.5 
−11.2 0.0 
0.0 
0.0 +2.0; −5.0  
+2.5; −16.0  
+3.0; – +5.0; – 
+5.0; – 
+5.0; – 
*Frequency functions C and F were calculated with equations (8) and (9) with frequency f calculated from the 
equation:  
f = (fr ) [100.1(n-30)], (7) 
 in which fr = 1 kHz and n is a natural number between 10 and 43. The results were rounded to the nearest tenth 
of a decibel.  General Measure No  0111 -OOP -C087 -18 
16  
3.4.4.8 At any frequency f in hertz, the weighting function C( f) in decibels must be calculated from the 
equation:  
C(𝑓)=20log[𝑓4 2 𝑓2
(𝑓2+𝑓1 2 )(𝑓2+𝑓4 2 )]−C1000 (8) 
Weighting function A( f) must be calculated from the equation:  
A(𝑓)=20log[𝑓4 2 𝑓2
(𝑓2+𝑓1 2)  (𝑓2+𝑓2 2   )1/2 (𝑓2+𝑓3 2   )1/2  (𝑓2+𝑓4 2 )  ]−A1000 (9) 
in which C 1 000 and A 1 000 are standardising constants in decibels representing the electrical gain needed 
for the frequency weighting functions to have a gain of zero decibels at 1  kHz.  
Weighting function  Z(f) must be calculated from the equation:  
Z(f) = 0  (10)  
3.4.4.9 The frequencies of fields f1 and f4 must be determined in units of Hz by solving a quadratic 
equation in which:  
 f1 = [{−b − (b2 − 4c)1/2}/2 ]1/2  (11) 
and  f4 = [{−b + (b2 − 4c)1/2}/2 ]1/2  (12) 
The constants b and c must be derived from the equations:  
 b = {1/(1  − D)}{fr 2 + ( fL2 fH2)/fr 2 − D(fL2 + fH2)} (13) 
and c = fL2 fH2  (14) 
3.4.4.10 At limit frequency fA specified in Article  3.4.4.6, the characteristic fields at frequencies f2 and 
f3, which are necessary to introduce the additional high -frequency  passes, must be determined in Hz 
according to the equations:  
 f2 = [{3 – (5)1/2}/2] fA  (15) 
and f3 = [{3 + (5)1/2}/2] fA  (16) 
NOTE The addition of the linked high -frequency passes to the frequency characteristics of weighting function C 
is equivalent to adding two zeroes at 0  Hz and fields at frequencies f2 and f3; see 3.4.4.6.  
3.4.4.11 The approximated values of frequencies f1 to f4 in equations (8) and (9) are:  
f1 = 20.60  Hz, f2 = 107.7  Hz, f3 =737.9  Hz and f4 = 12 194 Hz. 
The standardising constants C 1 000 and A 1 000 rounded to 0.001  dB are −0.062  dB and −2.000  dB, 
respectively.  
3.4.4.12 The user manual must specify the nominal  frequency characteristics and maximum permissible 
errors which are complied with around the nominal values, if the sound level meter is equipped with 
them. The maximum permissible errors must include the applicable maximum expanded measurement 
uncertainty  for the frequency weighting functions.  
3.4.4.13 The frequency weighting filter FLAT must have a transmission of 0  dB from less than 31.5  Hz 
to more than 8  kHz during acoustic excitation. For the applicable operating classes, the maximum 
permissible errors  at the individual frequencies around the nominal value must not be greater than those 
indicated in Table  4. Different maximum permissible errors may be specified for the excitation of the General Measure No  0111 -OOP -C087 -18 
17 sound level meter by acoustic and electrical input. However, these tolerances must include the applicable 
maximum permissible expanded measurement uncertainties.  
3.4.4.14 The differences in transmission between weighting filters C, Z or FLAT and the transmission 
values in the use of weighting filter A during excitation v ia sinusoidal electrical signal 1  kHz must not 
exceed ±0.4  dB. This requirement applies at reference sound pressure level in the reference 
measurement range. It does not apply to indications of peak sound pressure level C.  
3.4.5 Amplitude characteristic li nearity  
3.4.5.1 The measured signal level must be the linear function of the sound pressure level at the 
microphone’s location in the entire dynamic range. The amplitude characteristic linearity must apply to 
the measurement of time -weighted sound pressure  levels, equivalent sound pressure levels and sound 
exposure levels.  
3.4.5.2 The maximum permissible errors of the amplitude characteristic linearity apply to electrical 
signals supplied by the applicable device.  
3.4.5.3 The assumed signal level in any mea surement range and at any given frequency must be given 
by the starting point specified in the user manual in the reference measurement range plus the change in 
input signal level with respect to the input signal level which caused the starting point to be  displayed. 
The reference sound pressure level must be indicated at the starting point at the frequency of 1  kHz, 
where the tests to determine the amplitude characteristic linearity are initiated.  
3.4.5.4 The linearity range spread at the reference measurement range at a frequency of 1  kHz must be 
at least 60  dB. 
3.4.5.5 With class  1 sound level meters, the maximum permissible error of the amplitude characteristic 
linearity must not exceed ±1.1  dB, and ±1.4  dB for class  2 sound level meters.  
3.4.5.6  Deviations from the nominal values increased by the expanded measurement uncertainty for any 
change in the input signal level from 1  dB to 10  dB must not exceed ±0.6  dB in class  1 sound level 
meters and ±0.8  dB in class  2 sound level meters.  
3.4.5.7 The r equirements specified in the previous two articles apply to the entire dynamic range at any 
frequency in the sound level meter’s frequency range and to any frequency weighting function or 
frequency characteristic available.  
NOTE In principle, the requirem ents for the amplitude characteristic linearity error apply at minimum to any 
frequency from 16  Hz to 16  kHz in class  1 sound level meters and from 20  Hz to 8  kHz in class  2 sound level 
meters. If the amplitude characteristic linearity error is measured at  low frequencies, the assessment of the test 
results should explain the cause of the ripple which results during the measurement of the sinusoidal signals with 
time characteristic F. The ripple reaches approximately 0.2  dB at a frequency of 16  Hz. 
3.4.5.8 In sound level meters which measure the time -weighted sound pressure level, the linearity ranges 
at a frequency of 1  kHz must overlap by at least 30  dB in adjacent measurement ranges. If the sound 
level meter measures the equivalent sound pressure level or  sound exposure level, they must overlap by 
at least 40  dB. 
3.4.5.9 The user manual must specify the nominal sound pressure level A and, if available, the nominal 
sound pressure levels C and Z for each measurement range and for the lower and upper linearit y range 
limits at which the sound pressure level can be measured without a low signal level or overexcitation 
arising. The user manual must specify the linearity ranges at frequencies 31.5  Hz, 1  kHz, 4  kHz, 8  kHz 
and 12.5  kHz for class  1 sound level meters  and at 31.5  Hz, 1  kHz, 4  kHz and 8  kHz for class  2 sound 
level meters.  General Measure No  0111 -OOP -C087 -18 
18 3.4.5.10 The user manual must, at the frequencies specified in Article  3.4.5.9, specify the starting point 
initiating the tests for amplitude characteristic linearity errors in a specified measurement range.  
3.4.5.11 If certain sound level meters use display devic es with a range smaller than the linearity range, 
then the user manual must describe the means for testing the amplitude characteristic linearity error 
outside of the limits of the display range.  
3.4.6 Internally generated noise  
3.4.6.1 For the most sensit ive measurement ranges, the user manual must specify the sound pressure 
levels which would be indicated when the sound level meter is placed in a sound field with a sound 
pressure level of zero. Such sound pressure levels must correspond to the assumed max imum internally 
generated noise level for each type of microphone which is specified for use with the sound level meter.  
3.4.6.2 The user manual must specify the internally generated noise levels as time -weighted sound 
pressure levels or, as the case may b e, as equivalent sound pressure levels.  
3.4.6.3 If the microphone is substituted by an electrical input device and the input is terminated by the 
means specified in the user manual, then the noise generated must not exceed the level declared in the 
user ma nual.  
3.4.6.4 The sound pressure levels specified in the user manual for internally generated noise must be 
specified for all available weighting functions under reference ambient conditions.  
3.4.6.5 The user manual must describe the method of measuring l ow sound pressure levels while taking 
the internally generated noise into account.  
3.4.7 Time -weighted characteristics F and S  
3.4.7.1 For time characteristic F (fast), the nominal time constant is 0.125  s and for time characteristic 
S (slow), the constant  has a value of 1  s. The available time -weighted characteristics must be described 
in the user manual.  
3.4.7.2 The time constant of a decrease is determined by the response to a sudden interruption in a 
continuous sinusoidal electrical input signal with a frequency of 4  kHz. After the signal interruption, the 
speed of the decrease of the sound pressure level displayed increased by the expanded measurement 
uncertainty must be at least 25  dB/s at time characteristic F and between 3.4  dB/s and 5.3  dB/s at time  
characteristic S. This requirement applies to any measurement range.  
3.4.7.3 The deviation in the indication of sound pressure level A with time characteristic S and 
potentially of the installed equivalent sound pressure level A from the indication of the  sound pressure 
level with time characteristic F, increased by the expanded measurement uncertainty, must not exceed 
±0.3 dB at an input continuous sinusoidal electrical signal with a frequency of 1  kHz. This requirement 
applies to the reference sound pres sure level in the reference measurement range.  
3.4.8 Response to a tone impulse  
3.4.8.1 The specification for the sound pressure level measurement of a transitional signal is given in 
the form of tone impulses with a frequency of 4  kHz. The specification o f the impulse tone response 
applies to electrical input signals.  
3.4.8.2 The response to a tone impulse in the case of an individual tone impulse with a frequency of 
4 kHz for frequency function A and selectable frequency functions C and Z must be in confo rmity with 
the indications specified in the second column of Table  5 for a maximum sound pressure level with time 
characteristic F or S and in the third column for sound exposure levels. The deviation of the measured 
response to the tone impulse from the c orresponding reference response to a tone impulse, increased by General Measure No  0111 -OOP -C087 -18 
19 the expanded measurement uncertainty, must be within the maximum permissible error limits of the 
valid tolerances in the entire range of duration times of the tone impulse.  
3.4.8.3 For the ton e impulse durations between two consecutive tone impulse duration times specified 
in Table  5, the reference response to the tone impulse must be determined from the applicable equation 
(16) or (17). The maximum permissible errors correspond to the maximum permissible errors specified 
for the shorter of the tone impulse duration times.  
3.4.8.4 The reference responses to tone impulses and maximum permissible errors specified in Table  5 
also apply to integrating -averaging sound level meters which do not displa y the sound exposure level. 
In such instruments, the sound exposure level of a tone impulse must be converted. The averaging time 
T must correspond to the time displayed on the sound level meter and must include the tone impulse.  
Table  5 – Reference respon ses to a tone impulse with a frequency of 4  kHz and maximum 
permissible errors (including maximum permissible expanded measurement uncertainty)  
Tone impulse 
duration  
Tb 
ms Reference tone impulse response with a 
frequency of 4  Hz δ ref with respect to a 
continuous sound pressure level  
dB Maximum permissible errors  
dB 
Class  
LAF max − LA 
LCF max − LC 
a 
LZF max − LZ; R.(17)  LAE max − LA 
LCE max − LC 
a 
LZE − LZ; R.(18)  1 2 
1000  
500 
200 0.0 
−0.1 
–1.0 0.0 
−3.0 
–7.0 ±0.5 
±0.5 
±0.5 ±1.0 
±1.0 
±1.0 
100 
50 
20 –2.6 
−4.8 
–8.3 −10.0 
−13.0 
−17.0 ±1.0 
±1.0 
±1.0 ±1.0 
+1.0; −1.5  
+1.0; −2.0  
10 
5 
2 −11.1 
−14.1 
−18.0 −20.0 
−23.0 
−27.0 ±1.0 
±1.0 
+1.0; −1.5  +1.0; −2.0  
+1.0; −2.5  
+1.0; −2.5  
1 
0.5 
0.25 −21.0 
−24.0 
−27.0 −30.0 
−33.0 
−36.0 +1.0; −2.0  
+1.0; −2.5  
+1.0; −3.0  +1.0; −3.0  
+1.0; −4.0  
+1.5; −5.0  
 LAS max − LA 
LCS max − LC 
a 
LZS max − LZ; R.(17)   
1 000 
500 
200 −2.0 
−4.1 
−7.4  ±0.5 
±0.5 
±0.5 ±1.0 
±1.0 
±1.0 
100 
50 
20 −10.2 
−13.1 
−17.0  ±1.0 
±1.0 
+1.0; −1.5  ±1.0 
+1.0; −1.5  
+1.0; −2.0  
10 
5 
2 −20.0 
−23.0 
−27.0  +1.0;  −2.0 
+1.0; −2.5  
+1.0; −3.0  +1.0; −3.0  
+1.0; −4.0  
+1.0; −5.0  General Measure No  0111 -OOP -C087 -18 
20 NOTE 1 For the purposes of this measure, the reference response to the tone impulse with a frequency of 
4 kHz δref is determined for the maximum sound pressure level of conventional sound level meters with the help 
of the following approximation:  
                              𝛅𝒓𝒆𝒇 =10 lg (𝟏−𝒆−𝑻𝒃𝝉⁄)                        (19) 
where  
Tb is the specified tone impulse duration in seconds, such as from column  1 
τ is the standard exponential time constant specified in 3.4.7.1 and  
e is the basis of the natural logarithms.  
Equation  (19) applies to isolated tone impulses with a frequency of 4  kHz.  
 
NOTE 2 For the purposes of this measure, the reference response to a tone impulse with a frequency  of 4 kHz 
δref is determined for the maximum sound pressure level of integrating and integrating/averaging sound level 
meters with the help of the following approximation:  
δref = 10 lg(Tb/ T0) (20) 
where  
Tb is the specified tone impulse duration in seconds , 
T0 = 1 s is the reference sound exposure duration.  
NOTE 3 The reference responses to a tone impulse with a frequency of 4  kHz specified in Table  5 apply to 
frequency functions A, C and Z. The other frequency weighting functions may result in different re ference 
responses to the tone impulse.  
 
3.4.8.5 The reference responses to the tone impulse and corresponding maximum permissible error 
values apply to any tone impulse duration in the ranges specified in Table  5 and to in the reference 
measurement range in the entire range of continuous input signals. The range of continuous input signals 
with a frequency of 4  kHz from which the tone impulses are derived, extends from the input equivalent 
to an indication of 3  dB lower than the specified upper limit  of the linearity range downwards to the 
input equivalent to the indication of 10  dB higher than the specified lower limit. As soon as the response 
to the tone impulse can be monitored on the display device and an indication is produced which is at 
least 1 0 dB higher than the specified noise level created by the actual noise of the microphone and the 
electronic elements in the sound level meter, the responses to the tone impulse must be within the 
maximum permissible error limits.  
3.4.8.6 An overexcitation indication must not appear during any measurement of the response to a tone 
impulse in the range of the signal levels specified in Article  3.4.8.5.  
3.4.9 Response to repeated tone impulses  
3.4.9.1  The specification of the response to repeated tone impulses  applies to frequency function A and, 
if available, for frequency functions C and Z and to any succession of tone impulses with a frequency 
of 4 kHz, corresponding to amplitude and to duration. In the case of sound exposure levels, the deviation 
in the equ ivalent sound pressure level from the equivalent sound pressure level calculated for a 
succession of tone impulses increased by the expanded measurement uncertainty must be within the 
maximum permissible error limits specified in Table  5 for responses to t one impulses. These 
specifications apply to the reference measurement range for tone impulse duration times between 
0.25 ms and 1  s and an indication of 3  dB lower than the specified upper limit of the linearity range 
downwards to the input equivalent to t he indication of 10  dB higher than the specified lower limit.  
3.4.9.2 For any total measurement duration, the difference δ ref in decibels between the theoretical 
equivalent sound pressure level of a succession of N tone impulses derived from a continuous s inusoidal 
signal and equivalent sound pressure level corresponding to the sinusoidal signal is given by the 
equation:  
 General Measure No  0111 -OOP -C087 -18 
21 δref = 10 lg(NT b/Tm) (21) 
where  Tb ........   is the tone impulse duration (s);  
 Tm  .......  is the total duration of measurement (s).  
The corresponding continuous sinusoidal signal must be averaged over the entire duration of 
measurement.  
3.4.10 Overexcitation indication  
3.4.10.1 Every sound level meter must be equipped with an overexcitation indicator. An overexcitation 
indicator of th is kind must work in connection with any usable display device. The user manual must 
describe the function and interpretation of the overexcitation indication.  
3.4.10.2 Overexcitation at sound pressure levels above the upper limit of the linearity range mu st be 
displayed prior to exceeding the maximum permissible error limits for linear amplitude characteristics 
in continuous mode or prior to exceeding the maximum permissible errors for responses to tone 
impulses. This requirement applies to all measurement  ranges and at any frequency from 31.5  Hz to 
12.5 kHz for class  1 sound level meters or from 31.5  Hz to 8  kHz for class  2 sound level meters.  
3.4.10.3 The signals from the positive and negative half period derived from a continuous sinusoidal 
electrical si gnal must activate the overexcitation indicator. The response signals must begin and end at 
the zero transition points. With signals with a positive and negative half period, the difference between 
the input signal levels which first trigger an overexcitat ion indication, increased by the expanded 
measurement uncertainty, must not exceed 1.8  dB. 
3.4.10.4 The overexcitation indication must last for the duration of overexcitation or 1  s, depending on 
which is longer, if the sound level meter uses time characte ristics F or S to measure the sound pressure 
levels.  
3.4.10.5 The overexcitation indication must also appear if it is being measured and the condition for 
overexcitation is present. The overexcitation indication must remain blocked until the measurement 
results are zeroed. These requirements also apply to measurements of the maximum time -weighted 
sound pressure levels, peak sound pressure level C and other quantities which are calculated during the 
measurement interval or are displayed once it has elapsed.  
3.4.11 Low signal level indication  
3.4.11.1 If, during any measurement situation, it happens that the time -weighted sound pressure level, 
equivalent sound pressure level or sound exposure level is lower than the specified lower linearity range 
limit at the  given frequency, then a low signal level indication must be displayed before the maximum 
permissible error limit for the amplitude characteristic linearity error is exceeded. The low signal level 
indication must last at least as long as the low signal lev el appears, or 1  s, whichever is longer. The 
interpretation of the low signal level indication and the functioning of this indicator must be described 
in the user manual.  
3.4.11.2 The display of the low signal level indication at the most sensitive measure ment ranges need 
not be activated as long as the lower limit for the maximum permissible error of amplitude characteristic 
linearity is reached due to the internal noise of the microphone and electronic elements inside the sound 
level meter.  
3.4.12 Peak sound pressure level C  
3.4.12.1 If it is possible to display peak sound pressure levels C on any class  1 or 2 sound level meter, 
then the user manual must specify the nominal range of peak sound pressure levels C for each 
measurement range. The spread of t he peak level range at peak sound pressure levels C indications must General Measure No  0111 -OOP -C087 -18 
22 be at least 40  dB in at least the reference measurement range. Peak sound pressure levels C must be 
within the specified ranges indicated without the overexcitation condition being displa yed.  
3.4.12.2 Indications of peak sound pressure levels C must be specified in the form of a response to one 
period and to the positive and negative half periods of the electrical signals. Signals with one period and 
a half period must be derived from con tinuous sinusoidal electrical signals and must be supplied to the 
specified electrical input device. The entire periods and half periods must begin and end at the zero 
transition point.  
3.4.12.3 A deviation in the indication of the peak sound pressure leve l C (Lcpeak) minus the corresponding 
indication of the sound pressure level of a continuous signal ( Lc) from the corresponding difference 
specified in Table  6, increased by the expanded measurement uncertainty, must not exceed the 
maximum permissible error  limits specified in Table  6. 
Table  6 – Peak sound pressure levels C and tolerances (including maximum permissible 
expanded measurement uncertainty)  
Number of test signal 
periods  Test signal 
frequency  
Hz LCpeak − L C 
dB Maximum permissible errors  
dB 
Class  
1 2 
One 31.5 2.5 ±2.0 ±3.0 
500 3.5 ±1.0 ±2.0 
8 000 3.4 ±2.0 ±3.0 
Positive half period  500 2.4 ±1.0 ±2.0 
Negative half period  500 2.4 ±1.0 ±2.0 
 
3.4.13 Zeroing  
3.4.13.1 If the sound level meter can measure equivalent sound pressure levels,  sound exposure levels, 
maximum time -weighted sound pressure levels and peak sound pressure levels C, it must contain a 
device for zeroing the loaded data and resuming measurement.  
3.4.13.2 The use of the zeroing device must not cause false indications on the display device and from 
the loaded data.  
3.4.14 Measurement thresholds  
3.4.14.1 If the user of integrating -averaging sound level meters or integrating sound level meters can 
select the measurement thresholds, then their functioning and method of opera tion must be specified in 
the user manual at the measured equivalent sound pressure levels or sound exposure levels.  
3.4.15 Data display  
3.4.15.1 Sound level meters which display more than one measurement quantity must be equipped with 
a means of indicatin g the quantity which is being presently displayed.  
3.4.15.2 The acoustic quantity presently measured must be clearly marked on the display or by means 
of control elements. The indication must be displayed in the user manual and must contain the frequency 
and time weighting or, if applicable, the averaging time. The indication must be given using suitable 
symbols or abbreviations.  General Measure No  0111 -OOP -C087 -18 
23 3.4.15.3 The display device(s) must be described in the user manual and must enable measurement with 
a resolution of 0.1  dB within a display range of at least 60  dB. Sound level meters with an analogue 
display device may have a display range of 60  dB divided into two parts.  
3.4.15.4 If, in the case of digital display devices, the data are refreshed in the display at periodic in tervals, 
then the value of the quantity selected by the user at the moment the data are refreshed on the display 
must be indicated after each time the display is refreshed. Further quantities may be indicated at the time 
the data on the display are refresh ed, and if this is the case, must be explained in the user manual.  
3.4.15.5 If a digital indicator is used in the sound level meter, then the user manual must specify the 
speed of refreshing the data on the display and the conditions for when the first ind ication will be 
displayed after measurement has been initiated.  
3.4.15.6 For sound level meters which enable integrating and averaging, the user manual must specify 
the time it takes to display data after integration has ended.  
3.4.15.7 If the sound level meter is equipped with a digital output, the manual must specify the interface 
and data transfer format. If a computer is connected to the sound level meter, then the software enabling 
mutual communication must be specified, and the computer’s interface te chnical equipment must also 
be specified.  
3.4.15.8 Any alternative device for displaying signal levels which is type -approved constitutes an 
inseparable component of the sound level meter. Each such alternative device must be included among 
the components which must meet the operating requirements of this chapter and the associated 
requirements for ambient conditions specified above.  
3.4.16 Analogue or digital output  
3.4.16.1 If the sound level meter contains an analogue output, the user manual must descri be the 
characteristics of the output signals. The characteristics must include frequency weighting, output signal 
range, internal electrical impedance at the output and the recommended range of load impedances.  
3.4.16.2 If passive impedance (including zero  – i.e. short -circuit) is connected to the analogue output 
without accumulated electrical energy, this must not influence any ongoing measurement by more than 
0.2 dB. 
3.4.16.3 If the sound level meter does not have an analogue or digital output for purpose s of general 
application, an output must be integrated for testing the properties of a class  1 sound level meter. A 
class  2 sound level meter may be equipped with such an output. Changes in signal level at an analogue 
or digital output in response to chang es in sound pressure at the microphone or to changes in the 
electrical input signal must be identical within one decimal to the changes in signal level indicated on 
the display devices.  
3.4.17 Timing devices  
3.4.17.1 A class  1 sound level meter which indic ates an equivalent sound pressure level or sound 
exposure level must enable the display of the time elapsed at the end of the integration time or equivalent 
indication of the integration time interval. It may also have a function which allows the integrati on time 
interval to be set in advance. The time of day may also be displayed. The user manual must describe the 
procedure with which the integration time is set in advance and the procedure for setting the time of 
day. If a real -time clock is part of the s ound level meter, then the user manual must describe how to set 
it and must specify the nominal deviation of the displayed time for a period of 24  hours.  General Measure No  0111 -OOP -C087 -18 
24 3.4.17.2 The user manual must specify the minimum and maximum averaging and integration time 
during me asurement of equivalent sound pressure levels or sound exposure levels for signal levels within 
the range of the display device.  
3.4.18 High -frequency emissions and interference from the public electrical grid  
3.4.18.1 If the sound level meter requires the  use of cables in connecting its parts, then these cables must 
be specified in the user manual.  
3.4.19 Crosstalk  
3.4.19.1 If one input channel of the sound level meter is supplied with a continuous electrical signal 
with a level at the upper limit of the linearity range and the other input channels are terminated by the 
relevant electrical impedance (which must be specified in the user manual), then the crosstalk between 
the channels may reach a maximum of 70  dB in the difference between the measured level s. 
3.4.20 Software  
Software which is essential for the metrological properties must be identified and secured. Easy 
identification of software must be possible. Proof of every intervention must be available.  
3.4.20.1 If computer programs are part of the so und level meter, the type -approval certificate must 
specify their version and must also describe what hardware configuration (measuring device as well as 
evaluation and display device) they are intended for. The possibility of unauthorised tampering changi ng 
the software so that the sound level meter would measure and display incorrect values must be 
prevented.  
3.4.21  Power supply  
3.4.21.1 The sound level meter’s display must show an indication during operation that the power supply 
is sufficient to operate  the sound level meter according to the specifications of this Measure.  
3.4.21.2 In case of a change in supply voltage from the maximum to the minimum permissible value, 
the change in measured and displayed sound pressure level increased by the expanded m easurement 
uncertainty must not exceed ±0.3  dB in class  1 sound level meters and ±0.4  dB in class 2 sound level 
meters.  
3.4.21.3 The batteries or rechargeable batteries which are used to power the sound level meter must be 
specified in the user manual. Th e user manual must also specify the sound level meter’s time of operation 
under reference conditions which can be expected during the specified normal operating mode after 
fully charged batteries or rechargeable batteries have been installed.  
3.4.21.4 Battery-powered sound level meters which enable indication and processing of measured values 
for a time which exceeds the nominal service life of the batteries or rechargeable batteries must have the 
recommended means of operating the sound level meter from a n external power source described in 
their user manual.  
3.4.21.5 If the sound level meter can be powered from a public electrical grid of alternating frequency, 
the user manual must specify the nominal voltage and supply frequency, as well as the associated 
tolerance. If the sound level meter or parts thereof can be powered from a common DC voltage source, 
the user manual must specify the maximum current drawn, the supply voltage value and its permissible 
ripple and must determine which pole is con nected to the body of the sound level meter or to the earthing 
conductor of its inputs and outputs.  General Measure No  0111 -OOP -C087 -18 
25 3.5 Environmental criteria and electrostatic and high -frequency criteria  
3.5.1 General  
3.5.1.1 The sound level meter must meet all technical requirements sp ecified in Chapter  6 which apply 
to the use of the sound level meter under consideration.  
3.5.1.2 The user manual must specify the typical time interval which the sound level meter needs to 
stabilise after a change in ambient conditions. Any technical req uirement influencing the operating 
environment applies to a sound level meter which is switched on and set up for a typical method of 
measurement.  
3.5.1.3 The technical requirements with regard to the influence of fluctuations in static pressure, air 
temp erature and relative humidity apply to the sound pressure level indicated in the response to the use 
of an acoustic calibrator which operates at a frequency range of 125  Hz to 1  250 Hz. The influence of 
fluctuations in static pressure, air temperature and relative humidity on the sound pressure level created 
by the acoustic calibrator must be known.  
3.5.1.4 In accordance with these requirements, no testing may be done at combinations of air 
temperature and relative humidity which result in a condensation po int at temperatures higher than 
+39 °C and lower than −15  °C.  
The sound level meter must still maintain the required technical properties in cases where air humidity 
condensation occurs in a temperature range from −15  °C to +39  °C. 
3.5.2 Static pressure  
3.5.2.1 If the static pressure changes within a range of 85  kPa to 108  kPa, then the deviation of the 
displayed sound pressure level from the sound pressure level displayed at reference static pressure, 
increased by the expanded measurement uncertainty, mus t not exceed ±0.4  dB in class  1 sound level 
meters and ±0.7  dB in class  2 sound level meters.  
3.5.2.2 The maximum permissible value by which the measured and displayed quantity may change 
from the quantity measured and displayed at reference static pressur e, increased by the expanded 
measurement uncertainty, if the static pressure changes from 65  kPa to less than 85  kPa, is:  
±0.9 dB in class  1 sound level meters;  
±1.6 dB in class  2 sound level meters.  
3.5.3 Air temperature  
3.5.3.1 The influence of a fluctuation in air temperature at the measured signal level is specified in a 
temperature range of −10  °C to +50  °C for class  1 sound level meters and for temperatures of 0  °C to 
+40 °C for class  2 sound level meters. The temperature ranges apply to the en tire sound level meter.  
3.5.3.2 In components of the sound level meter (such as a computer) which the user manual designates 
as components only intended for use in areas with controlled ambient conditions (such as inside 
buildings), the temperature range m ay be limited to +5  °C to +35  °C. The limited temperature range 
does not apply to microphones with pre -amplifiers and connecting cables or microphones with 
integrated pre -amplifiers and A/D converters.  
3.5.3.3 The deviation in the sound pressure level disp layed at any temperature from the sound pressure 
level displayed at reference air temperature, increased by the expanded measurement uncertainty, must 
not exceed ±0.5  dB in class  1 sound level meters and ±1.0  dB in class  2 sound level meters. This 
requirem ent applies within the applicable air temperature ranges specified in Article  3.5.3.1 or 
Article  3.5.3.2 and to any relative humidity within a range specified in Article  3.5.4.  General Measure No  0111 -OOP -C087 -18 
26 3.5.3.4 The error in amplitude characteristic linearity at a frequency of 1  kHz in the specified linearity 
range of the reference measurement range must remain within the maximum permissible error limits 
specified in Article  3.4.5. This amplitude characteristic linearity specification applies to the air 
temperature ranges specified in Article  3.5.3.1 or Article  3.5.3.2 and to a relative humidity within a 
range of ±20  % with respect to reference air humidity.  
3.5.4 Air humidity  
3.5.4.1 The deviation in the sound pressure level displayed at any relative humidity from the sound 
pressure  level displayed at reference relative humidity, increased by the expanded measurement 
uncertainty, must not exceed ±0.5  dB in class  1 sound level meters and ±1.0  dB in class  2 sound level 
meters. This requirement applies within a relative humidity range f rom 25  % to 90  % at any air 
temperature and within the applicable ranges specified in Article  3.5.3.1 or in Articles  3.5.3.2 and 
3.5.1.4.  
3.5.5 Electrostatic discharge  
3.5.5.1 The sound level meter must function according to its intended purpose after being exposed to a 
contact electrostatic voltage discharge of up to ±4  kV and an air electrostatic voltage discharge of up to 
±8 kV. The electrostatic voltage polarity is in relati on to earthing.  
3.5.5.2 The exposure to electrostatic discharges specified in Article  3.5.5.1 must not cause any long -
term operational impairment or loss of function of the sound level meter. If specified in the user manual, 
the operation or function of t he sound level meter may be temporarily impaired or lost as a result of 
electrostatic discharge. The specified impairment of operation or loss of function must not include any 
change in operational status, change in configuration or destruction or loss of saved data.  
3.5.6 Magnetic fields caused by grid -frequency alternating current and high -frequency fields  
3.5.6.1 Exposure to a specified magnetic field of grid frequency and high -frequency fields must not 
cause any change in the operational status, configu ration, or saved data or impact it. This requirement 
applies to the entire sound level meter or associated component, or to a multi -channel sound level meter 
system and to any operating mode which is in accordance with normal operation. The user manual mus t 
specify the operating mode(s) of the sound level meter and any connecting component which has the 
highest sensitivity (lowest immunity) to magnetic fields of grid frequency and high -frequency fields.  
3.5.6.2 The specification of sensitivity to magnetic f ields of grid frequency must apply to exposure to a 
homogeneous alternating magnetic field with an effective intensity value of 80  A/m at frequencies of 
50 Hz and 60  Hz. The homogeneity of the magnetic field must be determined without the sound level 
meter  present.  
3.5.6.3 The specifications for exposure to electrical grid frequencies apply to the orientation of the sound 
level meter which is specified in the user manual so that it has the highest sensitivity (lowest immunity) 
to magnetic fields of grid fr equency.  
3.5.6.4 The specifications for sensitivity to high -frequency fields must apply to exposure in the range of 
carrier frequencies from 26  MHz to 1  GHz. The signal of the high -frequency field’s carrier frequency 
must be amplitude -modulated by a contin uous sinusoidal signal with a frequency of 1  kHz with a depth 
modulation of 80  %. If the carrier frequency signal is not modulated, the homogeneous electrical field 
must have an effective intensity value of 10  V/m without the sound level meter present.  
3.5.6.5 The sound level meter’s immunity to magnetic fields of grid frequency and high -frequency fields 
must be demonstrated by means of a sinusoidal sound signal with a frequency of 925  Hz acting upon 
the microphone. Without the action of the magnetic field of grid frequency and the high -frequency field, 
the source of sound must be set so that the sound level meter indicates sound pressure level A with time General Measure No  0111 -OOP -C087 -18 
27 characteristic F or equivalent sound pressure level A of 74  dB ± 1  dB. If the sound level meter has mor e 
than one measurement range, the sound pressure level must be displayed in a measurement range whose 
lower limit is as close as possible to, but not higher than, 70  dB. 
3.5.6.6 The deviation in the displayed sound pressure level from the sound pressure le vel displayed 
when not affected by the magnetic field of grid frequency or high -frequency field, increased by the 
expanded measurement uncertainty, must not exceed ±1.0  dB in class  1 sound level meters and ±2.0  dB 
in class  2 sound level meters.  
3.5.6.7 With sound level meters from group  Y or from group  Z with an AC power supply input and, if 
integrated, with its own power output, immunity to common high -frequency interference must be 
demonstrated in a frequency range from 0.15  MHz to 80  MHz. The high -freque ncy field must be 
amplitude -modulated by a sinusoidal signal with a frequency of 1  kHz with a depth modulation of 80  %. 
If the signal is not modulated and is emitted from a source with an output impedance of 150  Ω, the 
effective high -frequency voltage valu e must be 10  V. The immunity to rapid transients at the power 
source must apply to a signal which has a peak voltage of 2  kV and a repetition frequency of 5  kHz.  
3.5.6.8 With sound level meters from group  Z with signal or control inputs/outputs, the requi rements 
for immunity to interference from high -frequency fields in a frequency range from 0.15  MHz to 80  MHz 
apply to an effective unmodulated voltage value of 10  V. These requirements apply if there is any 
connecting cable longer than 3  m between parts of  the sound level meter. The requirements for immunity 
to rapid transients in the public electrical grid apply to the entire dynamic range at any frequency in the 
sound level meter’s frequency range and to a signal with a peak voltage of 2  kV and a repetiti on 
frequency of 5  kHz.  
3.5.6.9 The user manual must state that the sound level meter meets the specified technical requirements 
when exposed to high -frequency fields at a sound pressure level lower than 74  dB. In this case, the 
sound level meter must be in  compliance with the limits of the maximum permissible errors specified 
in Article  3.5.6.6 at sound pressure levels lower than 74  dB downwards toward the specified lower level. 
This requirement applies to all measurement ranges for all technical requiremen ts concerning the group 
of sound level meters. The lower level, specified in the user manual with a resolution of 1  dB, must 
apply to all operating modes of the sound level meter.  
3.6 Measures for the use of auxiliary devices  
3.6.1 The user manual must sp ecify details for all correctional measurement results conducted with 
optional microphone stands or cables installed between the microphone and microphone pre -amplifier 
or between microphone pre -amplifier and other components of the sound level meter which  the 
manufacturer provides.  
3.6.2 The user manual must specify the average effect of the optional accessories provided by the 
manufacturer of the sound level meter. The specifications must apply to all important characteristics of 
the sound level meter wh ich are influenced by the installation of accessories. The optional accessories 
include wind protection covers and rain protection devices which are installed around the microphone 
(stable outdoor microphones such as those for measuring aircraft noise). Sp ecifications under wind -free 
conditions must be provided for the typical effect of any kind of recommended wind protection cover 
on the microphone’s sensitivity, directional characteristics and frequency weighting.  
3.6.3 If optional accessories are install ed in the sound level meter, then the user manual must state 
whether or not doing so will put the sound level meter into a different class in terms of the technical 
requirements. If, after optional accessories have been installed, the sound level meter doe s not meet the 
technical requirements for the original operational class, the user manual must state whether the sound 
level meter will meet the technical requirements for a different class, or whether it will still not meet the 
requirements for either cla ss 1 or class  2. General Measure No  0111 -OOP -C087 -18 
28 3.6.4 The user manual must describe the means by which the sound level meter is to be used to measure 
filtered sound pressure levels or for spectral analysis, if its components include internal or external 
bandwidth filters.  
3.6.5 The user  manual must specify the details for connecting auxiliary devices supplied by the 
manufacturer of the sound level meter and any potential effects of such devices on the properties of the 
sound level meter. It must also specify auxiliary programs which may be used when saving and 
processing the measured values. The configuration of the computer (if used) must also be specified and 
a list must be provided of programs which may not be running on the computer at the same time as 
programs which constitute a part  of the sound level meter (e.g. due to disruption of the synchronisation 
of the data flow, disturbance of operations of a program which must be operating properly in order for 
data processing to be correct).  
3.7 User manual  
3.7.1 Every sound level meter or equivalent device which meets the technical requirements of this 
measure must be supplied together with a user manual.  
a) The user manual must contain all of the information required in Chapter  3. 
b) If the sound level meter is made up of several independent components, then a user manual must be 
available for such combination as constitutes a complete sound level meter. The user manual must 
describe all essential components and their influences on one another.  
c) The user manual must be available in print form i n one or more parts.  
3.7.2 The user manual must contain the following operating data relating to the sound level meter.  
3.7.2.1 General  
a) A description of the type of sound level meter; classification group X, Y or Z in terms of its sensitivity 
to high -frequency fields; and an indication of class  1 or class  2 in accordance with the technical 
requirements of this Measure. If relevant, a description of the sound level meter configurations which 
meet the technical requirements for class  1 and class  2. 
b) A descrip tion of the complete sound level meter and its configuration in normal operating mode, 
including any potential wind protection cover and associated devices. The description must contain 
the method of fastening the microphone, identifying the additional ele ments, and the procedure for 
installing the wind protection cover around the microphone. The additional elements include a 
microphone stand or cable which may be necessary for the sound level meter in question to meet the 
technical requirements of this Mea sure for the given operating class.  
c) The types of microphones with which a complete sound level meter meets the technical requirements 
in operating class  1 or class  2 in a free field, or, if applicable, in a field with random sound incidence.  
d) If a microphon e stand or cable is required, a declaration that the sound level meter meets the technical 
requirements for directional characteristics and frequency weighting, but only if the specific device 
or cable is installed.  
e) The properties and operation of each sep arate channel in the case of multi -channel sound level 
meters.  
3.7.2.2 Design properties  
a) A description of the acoustic quantities which the sound level meter is capable of measuring with the 
use of each display device, such as the time -weighted sound press ure level, equivalent sound pressure 
level and sound exposure level, be it separately or in combination, including an explanation of all 
abbreviations and symbols specified.  
b) Detailed descriptions of the function of the sound and frequency angle and the fun ction of relative 
frequency characteristics on sinusoidal plane waves for a sound level meter with a configuration in 
the normal operating mode, optionally in tabular form.  General Measure No  0111 -OOP -C087 -18 
29 c) A description of the frequency weighting functions which meet the technical require ments of this 
Measure and, if integrated, frequency characteristics of optional weighting functions Z and FLAT.  
d) A description of the time -weighting characteristics which are available.  
e) Measurement range identification by means of nominal sound pressure lev els A at a frequency of 
1 kHz.  
f) A description of the functioning of the measurement range switches.  
g) A description of all display devices, including operating modes and the applicable speeds of 
refreshing data on digital displays. If more than one display de vice is available, a declaration on 
which of these devices meets the technical requirements of this Measure and which devices are for 
other purposes.  
h) The dynamic range of sound pressure levels A which can be measured at 1  kHz in the applicable 
tolerance r ange.  
i) If integrated, the ranges of peak sound pressure levels C, which can be measured in each 
measurement range.  
j) Clear identification of all computer programs essential to the operation of the sound level meter and 
the procedure for installing and using them.  
k) Data on the nominal characteristics and tolerances which should be complied with for the quantities 
the sound level meter is able to indicate, but for which no operating requirements are specified in 
this Measure. The characteristics include selectab le frequency weighting functions.  
3.7.2.3  Power supply  
a) Recommendations on permissible types of batteries or rechargeable batteries and the nominal 
duration of continuous operation in normal operating mode under reference ambient conditions when 
fully charg ed batteries or rechargeable batteries are installed in sound level meters with internal 
power supply.  
b) A description of the indicator or method with which it is confirmed that the power is sufficient to 
operate the sound level meter in accordance with the technical requirements of this Measure.  
c) A description of the means of ensuring the operation of the sound level meter via an external power 
source in sound level meters powered by a battery, which are designed so as to enable sound pressure 
level measureme nts for a period of time exceeding the nominal service life of the batteries or 
rechargeable batteries.  
d) Declaration of the nominal voltage and frequency of power supply and permissible tolerances around 
the nominal values for sound level meters intended to  operate using the public electrical grid.  
3.7.2.4 Setting of indicated levels  
a) Identification of the types of acoustic calibrators which can be used to check and maintain the sound 
level meter’s precision of indication.  
b) Calibration control frequency.  
c) Contr ol procedure and data for setting the sound level meter’s indications. The procedure and data 
must apply to the reference sound pressure level in the reference measurement range and at the 
calibration control frequency.  
d) A combination of corrections for dev iations in the mean frequency characteristic of the microphone 
in a free field from the stable frequency characteristic and average effects of reflections from the 
instrument’s cover and deflections around the microphone under ambient conditions which are close 
to the reference ambient conditions at the frequencies and under the test conditions specified in 
Articles  3.4.2.4 and 3.4.2.5, for microphones of all types which are specified for use with a sound 
level meter. The information must also contain corre ctions of the average effects of the wind 
protection cover, if a wind protection cover is an inseparable part of the sound level meter’s 
configuration under normal operating mode or if it is specified that the sound level meter meets the 
technical requirem ents of this Measure with a wind protection cover placed around the microphone. 
The information may be specified in the form of separate data for the mean frequency characteristics General Measure No  0111 -OOP -C087 -18 
30 of the microphone in a free field and the average effects of sound reflecti on and deflection and of the 
wind protection cover.  
3.7.2.5 Sound level meter operation  
a) Reference direction.  
b) Procedures for measuring sounds which generally come from one main direction or a random angle 
of incidence, including recommendations for minimisi ng the influence of the cover on the instrument 
and of the operator, if present during the sound measuring.  
c) Recommendations for selecting the optimum measurement range when measuring the sound pressure 
level or sound exposure levels.  
d) Procedures for measuring in sound fields with low sound pressure levels at the most sensitive 
measurement ranges keeping in mind the influence of the instrument’s intrinsic noise.  
e) The time which must elapse from the instrument being turned on after reaching equilibrium w ith the 
surrounding environment before the sound level meter can be used to measure sound pressure levels.  
f) Time interval after completing measurement before the data is displayed for integrating -averaging 
and integrating sound level meters.  
g) Procedure for s etting the integration time before measuring and, if applicable, setting the time of day.  
h) The minimum and maximum integration time during measurement of equivalent sound pressure 
levels and sound exposure levels.  
i) Operation of the ‘hold’ function and means to release a blocked display.  
j) Operation of a zeroing device during measurement of equivalent sound pressure levels, sound 
exposure levels, maximum time -weighted sound pressure levels and selectable peak sound pressure 
levels C. Declaration on whether opera tion of the zeroing device interferes with the overexcitation 
indication. Nominal delay time between the operation of the zeroing device and the repeated 
initiation of measurement.  
k) Function and interpretation of the overexcitation indication and the low si gnal level indication and 
means of zeroing the indication.  
l) Operation and function of any measurement thresholds selectable by the user during measurement 
of equivalent sound pressure levels and sound exposure levels.  
m) Method of transferring or recording dig ital data onto an external recording or display device and 
identification of software and technical computer equipment for performing such tasks.  
n) Recommendations for the typical lengths and types of cables (such as shielded or unshielded) and 
description o f the properties of devices which are expected to be connected by cables in sound level 
meters allowing for connection of an interface or connector cables.  
o) Time -weighted, or, as the case may be, equivalent sound pressure levels corresponding to the highest  
internal noise level at the more sensitive measurement ranges under reference ambient conditions 
and for every accessible frequency -weighted function and frequency characteristic. The internal 
noise must correspond to the anticipated noise of the combinat ion of any specified type of 
microphone and other components of the sound level meter. In the case of an equivalent sound 
pressure level, the averaging time must be specified. The averaging time must be at least 30  s. 
p) The frequency weighting function, rang e of effective sinusoidal output signal voltage values, internal 
electrical impedance at the output and the recommended range of load impedances at the electrical 
outputs.  
3.7.2.6 Accessories  
a) Description of the average effects on important properties of th e sound level meter under wind -free 
conditions caused by the microphone being surrounded by the recommended wind protection cover, 
rain protection device or other accessories provided or recommended in the user manual. Declaration 
of the operating class wh ich the sound level meter meets after installation of such accessories, or General Measure No  0111 -OOP -C087 -18 
31 declaration that the sound level meter still does not meet the technical requirements for either class  1 
or class  2. 
b) Corrections which apply to measurement results, or procedure whi ch is to be used when positioning 
an optional microphone stand or cable between the microphone pre -amplifier and other components 
of the sound level meter.  
c) Information on the use of a sound level meter equipped with band filters.  
d) Information on connecting auxiliary devices provided by the manufacturer to the sound level meter 
and the effect of such auxiliary devices on the sound level meter’s properties.  
3.7.2.7 Influence of fluctuations in ambient conditions  
a) Identification of components of the sound level  meter only intended for operation in areas with 
controlled ambient conditions.  
b) Effects of electrostatic discharges on the sound level meter’s operation. Declaration on potential 
temporary impairment of operation or loss of function of the sound level mete r caused by exposure 
to electrostatic discharges. Declaration on preventative measures against damage caused by 
electrostatic discharges in sound level meters which require the user to access the instrument for 
maintenance reasons.  
c) Declaration on whether the sound level meter meets the basic specifications of this Measure on the 
required immunity to a magnetic field of grid frequency and to high -frequency fields. Optional 
declaration on sound pressure levels with time characteristic F or, if applicable, eq uivalent sound 
pressure levels lower than 74  dB in all applicable measurement ranges in which the sound level meter 
meets the technical requirements of this Measure during exposure to a magnetic field of grid 
frequency and to high -frequency fields. The inf ormation must contain the specific frequency of the 
magnetic field.  
3.7.3 The user manual must contain the following information for testing the applicable type of sound 
level meter:  
a) Reference sound pressure level.  
b) Reference measurement range.  
c) Microphone r eference point for the types of microphone specified for use with the sound level meter.  
d) Settings for obtaining sound pressure levels A equivalent to the response to plane sinusoidal sound 
waves impacting in the reference direction and at least at the freq uencies required for verification of 
the sound pressure level A displayed in the response to sound pressure created by the acoustic 
calibrator or in response to acoustic pressure simulated by the electrostatic calibrator. The type of 
acoustic or electrosta tic calibrator to which the information on settings applies must be identified.  
e) A table with the nominal sound pressure levels A at the lower and upper limits of the linearity ranges 
in each measurement range. The sound pressure levels must be specified in  tabular form at 
frequencies of 31.5  Hz, 1  kHz, 4  kHz, 8  kHz and 12.5  kHz for class  1 sound level meters and at 
31.5 Hz, 1  kHz, 4  kHz and 8  kHz for class  2 sound level meters.  
f) The starting point at which tests are initiated for the amplitude characteristic  linearity error in the 
reference measurement range at each frequency at which the frequency -weighted sound pressure 
levels are specified at the lower and upper limits of the linearity ranges. The reference sound pressure 
level must be the starting point f or the frequency of 1  kHz.  
g) A description of the nominal electrical characteristics and applicable tolerance of the input device or 
means to connect electrical signals to the electrical input device for each specified type of 
microphone.  
h) For each specified type of microphone with which the sound level meter meets the technical 
requirements, the applicable time -weighted and equivalent sound pressure levels corresponding to 
the maximum anticipated internal noise created if, in place of a microphone, a specifie d electrical 
input device is installed, which is terminated by the specified means, and a sound level meter is 
positioned in a sound field with a low sound pressure level. The sound pressure level must be General Measure No  0111 -OOP -C087 -18 
32 specified at the most sensitive measurement ranges and for each available frequency weighting and 
each available frequency characteristic.  
i) The maximum sound pressure level at the microphone’s location and the maximum peak -to-peak 
voltage at the electrical input device which the sound level meter, based on its design, is able to 
process for each specified type of microphone with which the sound level meter meets the technical 
requirements.  
j) The maximum and minimum voltages of the power source at which the sound level meter meets the 
technical requirements of this Measure.  
k) The recommended means for tests of amplitude characteristic linearity errors within the limits of the 
display range in the case of sound level meters equipped with a display device whose spread is tighter 
than the linearity range within any m easurement range.  
l) The typical time interval needed to stabilise after changes in ambient conditions.  
m) The effective intensity value of an unmodulated electrical field higher than 10  V/m at which the 
sound level meter meets the technical requirements of this  Measure, if it is built that way.  
n) Operating mode(s) of the sound level meter and any connecting parts which create the highest level 
of high -frequency emission in the specified measurement range. Description of the sound level 
meter’s configurations which  create the same or lower high -frequency emission.  
o) Operating mode(s) of the sound level meter and any kind of connecting part which has/have the 
highest sensitivity (lowest immunity) to magnetic fields of grid frequency and high -frequency fields 
and the corresponding reference orientation of the sound level meter in relation to the main direction 
of the field.  
4 Markings  
All of the information on the sound level meter must be indelible, irremovable and legible for the entire 
duration of use.  
4.1 Sound lev el meter markings  
Every sound level meter must be marked with at least the following information:  
a) manufacturer’s name or trademark;  
b) type of sound level meter;  
c) standard whose requirements the sound level meter meets;  
d) serial number and year of manufacture;  
e) operating class of the sound level meter;  
f) type-approval mark of the measuring instrument.  
4.2 Marking individual parts of the sound level meter  
If the sound level meter is made up of several separate parts, then, if feasible, each basic unit or 
component mu st be marked in the manner described in Article  4.1. 
4.3 Placement of the official mark  
Placement of official marks is stipulated in the type -approval certificate or other document or activity 
applied within the context of conformity assessment when placin g the device on the market and putting 
it into use.  
Official marks must be placed so that after their placement, the measuring instrument cannot be adjusted 
or components cannot be accessed, if forbidden in their case. Marks must be designed so that they c annot 
be removed without damaging or destroying them.  General Measure No  0111 -OOP -C087 -18 
33 5 Type approval of the measuring instrument  
5.1 General  
The sound level meter type -approval process includes the following activities:  
a) external inspection, including:  
 completeness of the required technical documentation;  
 conformity of the metrological and technical characteristics specified by the manufacturer in 
the documentation with the requirements of this Measure;  
 completeness and condition of the sound level meter pursuant to the specified te chnical 
documentation;  
 compatibility of the sound level meter’s software version with the version specified by the 
manufacturer;  
b) tests of the sound level meter’s resistance to mechanical influences;  
c) tests of resistance to environmental influences;  
d) tests of  influences of electrical properties;  
e) electromagnetic compatibility (EMC) tests;  
f) functional tests.  
5.2 Submission for testing  
5.1.1 At least three samples of the same type of sound level meter must be submitted for the type 
examination. The laboratory must  select a minimum of two samples for testing. At least one of these 
two samples must be fully tested pursuant to the established procedures specified in this Measure. The 
laboratory must decide whether the complete tests will also be conducted for the seco nd sample, or 
whether complete or limited testing will be sufficient for the type approval.  
5.1.2 A user manual must be submitted with the three sound level meters as well as all other parts or 
accessories which the user manual identifies as inseparable co mponents in normal operating mode. 
Examples of additional parts or accessories include microphone pre -amplifiers or microphone cables 
and peripheral devices.  
5.1.3 If the sound level meter manufacturer supplies devices which are to be connected to the soun d 
level meter with cables, then the devices and cables must be submitted together with the sound level 
meter.  
5.1.4 A calibrated acoustic calibrator of the type specified in the sound level meter’s user manual must 
be supplied with the sound level meter. T he user manual for the acoustic calibrator must also be 
available. The calibrator type must meet the technical requirements for the given class of acoustic 
calibrator.  
5.2 Sound level meter markings and specifications in user manual  
5.2.1  It must be verif ied whether the sound level meter is marked in accordance with the requirements 
specified in this Measure.  
5.2.2 Before any kind of tests are carried out, it must be verified whether the user manual contains all of 
the required information on the devices w hich are part of the sound level meter.  
5.2.3 If the sound level meter does not meet the requirements of 5.2.1 and 5.2.2, then no type tests may 
be conducted.  
5.2.4 After all tests have been completed, their results must be examined to ensure they are corr ect and 
none of the applicable limits specified in the user manual or technical specifications for the measuring 
instrument were exceeded.  General Measure No  0111 -OOP -C087 -18 
34 5.3 Mandatory equipment and general requirements  
5.3.1 No test specified in this Measure may be left out unless the sound level meter does not have the 
equipment which requires testing. If the design of a sound level meter which was type -approved is 
changed, and a new type approval is required, then it will be at the laboratory’s discretion whether it 
will be necessary to test again those electro acoustic  operating properties not affected by the change in 
design.  
5.3.2 It must be verified whether a time -weighting sound level meter is capable of displaying sound 
pressure level A with time -weighting F and, if such a conditi on arises, whether it is capable of indicating 
the condition outside the maximum value in the upper range (overexcitation) and, on the other hand, the 
condition of the lower signal level, i.e. the lowest value in the lower range.  
5.3.3 It must be verified whether an integrating -averaging sound level meter is capable of displaying the 
equivalent sound pressure level weighted by filter A and, if such a condition arises, whether it is capable 
of indicating the condition of overexcitation and the condition of t he lower signal level below the 
specified range.  
5.3.4 It must be verified whether an integrating sound level meter is capable of displaying sound 
exposure level A and, if such a condition arises, whether it is capable of indicating the condition of 
overex citation and the condition of the lower signal level.  
5.3.5 It must be verified whether all display devices of the sound level meter are capable of displaying 
the sound pressure level or sound exposure level with the required resolution. The display range must 
correspond to at least the minimum required range.  
5.3.6 If the sound level meter is capable of displaying the measured maximum sound pressure level or 
peak sound level (or both), it must be verified whether it is equipped with a ‘hold’ function.  
5.3.7 It must be verified whether a class  1 sound level meter is equipped with frequency weighting C.  
5.3.8 If the sound level meter is capable of indicating peak sound pressure level C Peak, it must be verified 
whether it is also capable of displaying time -weighted sound pressure level C or the equivalent sound 
pressure level C Leq as well.  
5.3.9 With sound level meters which are able to display more than one measurement quantity, it must 
be verified whether there is any clear means of ascertaining which quantit y is being displayed at the 
moment.  
5.3.10 Sound level meters having multiple measurement ranges must be verified to ascertain whether 
the overlapping of the measurement ranges is in accordance with the prescribed technical requirements.  
5.3.11 If the soun d level meter does not have the mandatory equipment specified in Articles  5.3.2 to 
5.3.10, then the sound level meter does not meet the technical requirements of this Measure and none of 
the type tests may be conducted.  
5.3.12 In all type tests, the config uration of the sound level meter or multi -channel sound level meter 
system must be in accordance with the specifications listed in the user manual for one or more normal 
operating modes, including the required accessories. The configuration must also inclu de the wind 
protection cover, if a wind protection cover is an inseparable part in normal operating mode or if it is 
specified in the user manual that the sound level meter meets the technical requirements of this Measure 
with a wind protection cover insta lled around the microphone. The type of wind protection cover must 
be identical to the type which is specified in the user manual for use with the sound level meter. All the 
sound level meter configurations must be tested which are defined in the user manu al as configurations 
meeting the requirements of this Measure.  
5.3.13 If the user manual states that the sound level meter meets the requirements of this Measure with 
the optional equipment installed, then it must also be tested in combination with the optional equipment 
installed in order to demonstrate conformity.  
5.3.14 If the sound level meter is equipped with an electrical output and the laboratory intends to use 
the electrical output instead of the display device, the laboratory must verify whether  changes to the General Measure No  0111 -OOP -C087 -18 
35 levels of acoustic or electrical input signals applied cause changes to the level of the signals on the 
display device and at the electrical output in accordance with the specifications specified in this Measure. 
This requirement applies to  each channel of a multi -channel system. If multiple outputs are available 
and the user manual specifies an output for testing, then this output is recommended for use in the type 
tests.  
5.3.15 The sound level meter must be powered by its preferred source in all tests.  
5.3.16  Before the power supply is switched on to conduct the test, it must be possible for the sound level 
meter to reach a state of equilibrium under the prevailing ambient conditions, i.e. to adapt to the 
temperature, pressure and humidity of the environment in which the sound level meter is to be tested.  
5.3.17  The tests for demonstrating conformity with the technical requirements on the effects of changes 
in ambient conditions are preferably to be carried out before the tests for demonstr ating conformity with 
the technical requirements for electro acoustic  operating properties.  
5.3.18 If the sound level meter has more than one channel for signal processing, the type tests must be 
carried out on each channel which uses an exclusive method of  signal processing. In the case of multi -
channel systems with the same functional equivalence on all channels, the number of channels which 
can be tested may, at the laboratory’s discretion, be lower than the total number of channels. With a 
multi -channel system, the number of channels should be determined in consideration of the milieu, in 
which there is an array of microphones which supply each input with a signal and in which the signals 
are processed by the same means on each channel. When selecting the  number of channels and the 
testing method, it is recommended to take into consideration the differences described in the user manual 
concerning the signal processing method integrated in various channels.  
NOTE If the sound level meter is a multi -channel device (such as a sound level meter with two or more separate 
signal inputs with non -parallel processing of digital data in time -sharing mode, but with a quasi -parallel display 
for the signals displayed), it is generally possible to test the same functiona lity of the channels either by setting the 
function of the channels for the same processing and indication on the display(s), or by enabling cyclical changing 
of the channels ’ functionality in the settings for a special test procedure whereby the display(s ) can be compared.  
5.3.19 Conformity with the technical requirements is demonstrated if both of the following criteria are 
met:  
a) the measured deviation from the nominal value does not exceed the applicable acceptance limit; and  
b) the corresponding measureme nt uncertainty does not exceed the corresponding maximum 
permissible measurement uncertainty specified in the technical requirements for sound level meters 
for the same probability of coverage of 95  %.  
These requirements include an example of evaluating c onformity with the help of these criteria.  
5.3.20 The laboratory must use instruments with valid calibrations for the applicable quantities. 
Depending on the requirement, the calibration must be tied to national standards.  
5.3.21 At least the following ele ments are included when calculating the actual measurement 
uncertainties in the applicable test:  
 Uncertainty attributed to the calibration of the individual components and devices used in carrying 
out tests, including the acoustic calibrator.  
 Uncertainty r esulting from small errors which may occur in the signals used.  
 Uncertainty resulting from environmental effects or corrections.  
 Uncertainties assigned to the resolution of the display device of the sound level meter being tested. 
With digital display devices which indicate the signal level with a resolution of 0.1  dB, the 
element of uncertainty should be assessed in such a manner that it has a rectangular distribution 
with a half -range of 0.05  dB. 
 The uncertainty attributed to the effects associated wi th the repeatability of the measurement 
results. If the laboratory is only required for an individual measurement, it is essential for the 
laboratory to determine an estimate of the random contribution to the overall uncertainty of General Measure No  0111 -OOP -C087 -18 
36 measurement. The estimat e should be determined from previous assessments of multiple 
measurements of the operating properties of similar sound level meters.  
 The uncertainty resulting from the deviation of the sound field in the free -field test facility from 
the ideal sound field.  
 The uncertainty assigned to the device used to fasten the sound level meter in the free -field test 
facility.  
 The uncertainty assigned to each correction made to the measurement data.  
5.3.22 If the measurement uncertainty exceeds the maximum permissible me asurement uncertainty, the 
test results may not be used to demonstrate conformity with the technical requirements and the type 
approval may not be granted.  
5.3.23 When carrying out type tests, the laboratory is required to make use of the recommendations 
specified in the user manual.  
5.4 Tests of the influence of the environment, electrostatic discharges and high -frequency 
fields  
5.4.1 General  
5.4.1.1 The indication of sound pressure level A at the calibration control frequency must be checked 
using an aco ustic calibrator specified in 5.1.4 before starting, but not during, the tests described in the 
articles of Chapter  5.4. If necessary, the sound level meter must be configured so that the required sound 
pressure level is indicated under reference ambient c onditions. In a multi -channel device, the 
corresponding indication must be checked in all channels selected for testing.  
5.4.1.2 The ambient conditions at the time the indication is checked must be recorded.  
5.4.1.3 The effect of the ambient conditions (air temperature, barometric pressure and relative humidity) 
at the sound pressure level created by the acoustic calibrator must be determined in accordance with the 
procedure specified in the user manual for the acoustic calibrator and with the data from its calibration. 
The effects must be assessed in terms of the sound pressure level created under reference conditions.  
5.4.1.4 An acoustic calibrator which creates a signal about a known sound pressure level in the sound 
level meter’s microphone must be us ed in the environmental influence tests. In the case of class  1 sound 
level meters, the acoustic calibrator must meet the technical requirements of the applicable standard for 
acoustic calibrators for either class  LS or class  1. In the case of class  2 soun d level meters, the acoustic 
calibrator must meet the technical requirements of the applicable standard for acoustic calibrators for 
either class  LS, class  1 or class  2. If the acoustic calibrator meets the requirements of the applicable 
operating class at  a nominal frequency of 1  kHz, then the environmental influence tests must be carried 
out at a nominal frequency of 1  Hz. The corrections for static pressure, air temperature and relative 
humidity on the sound pressure level created in the coupler of the acoustic calibrator in the range of 
ambient conditions specified for the tests must be known.  
NOTE The range of ambient conditions specified for type tests exceeds the range specified in the applicable standard 
for class  LS acoustic calibrators.  
5.4.1.5 The sound level meter must be configured so that a typical measurement of the time -weighted 
sound pressure level, equivalent sound exposure level or sound exposure level, takes place in the 
reference measurement range. The frequency weighting must be set to weighting function A.  
5.4.1.6 The time -weighted sound pressure levels, equivalent sound pressure levels or sound exposure 
levels indicated by the sound level meter in response to the signal from the acoustic calibrator must be 
recorded for every testing c ondition. If necessary, the equivalent sound pressure levels must be 
calculated in accordance with the technical requirements for sound level meters from the sound exposure 
level indication and the time elapsed. The averaging time in the case of equivalent  sound pressure levels 
and the integration time in the case of sound exposure levels must be recorded.  General Measure No  0111 -OOP -C087 -18 
37 5.4.2 Uncertainties in ambient test condition measurements  
When measuring static pressure, the actual measurement uncertainties must not exceed 0.2  kPa. When 
measuring air temperature and relative humidity, the actual expanded measurement uncertainties must 
not exceed 0.3  °C or 4  %, respectively. These measurement uncertainties must be determined for a 
coverage probability of 95  %. 
5.4.3 Influence of stat ic pressure  
5.4.3.1 During measurements of the influence of static pressure, the air temperature must be maintained 
within an accuracy of ±2.0  °C with respect to the reference air temperature. At reference static pressure, 
the relative humidity must be mai ntained with respect to the reference relative humidity with an accuracy 
of +20  % relative humidity to −10  % relative humidity.  
5.4.3.2 The relative humidity is specified at the reference static pressure. The relative humidity in this 
area changes with th e reduction or increase in static pressure in an enclosed area around the sound level 
meter. No corrections may be made to such an effect.  
5.4.3.3 The influence of static pressure must be tested at the reference static pressure and at seven other 
static pr essures. Before recording the indicated sound pressure level, the acoustic calibrator specified in 
5.4.1.4 and the sound level meter (or other important components) must be acclimatised for at least 10 
minutes for each static pressure. The acoustic calibra tor must remain connected to the microphone 
during the acclimatisation period during tests of the effect of static pressure. The sound level meter’s 
power supply may be continuously switched on or it may be switched on and switched off via remote 
control.  
5.4.3.4 The sound pressure levels must be measured twice at the nominal static pressures, which are 
distributed in approximate corresponding intervals between the lowest and highest static pressure 
specified in the applicable standard. The two static press ures measured must not differ by more than 
1 kPa under each nominal static pressure condition. One measurement sequence must begin at the lowest 
static pressure and continues by gradually increasing by each selected nominal pressure until the 
maximum is re ached. The other sequence must continue by reducing the pressure from the maximum 
across each of the selected nominal pressures until the minimum is reached. Only one indication must 
be recorded at the highest static pressure.  
5.4.3.5 At each static pressu re test condition, the measured deviations of the indicated sound pressure 
level from the sound pressure level indicated first at the reference static pressure must not exceed the 
applicable acceptance limits specified in the technical requirements for sou nd level meters.  
5.4.3.6 The indicated sound pressure levels must be corrected in terms of any difference between the 
sound pressure level generated by the acoustic calibrator under test conditions and the sound pressure 
level generated under reference amb ient conditions.  
5.4.4 Limits for air temperature, relative humidity and static pressure  
Unless specified otherwise, each test of the influence of air temperature and relative humidity, including 
the requirements for acclimatisation specified in 5.4.5, the  measured air temperature must not exceed 
±1.0 °C of the specified air temperature, the relative humidity must not exceed ±5  % of the specified 
relative humidity and the difference between the highest and lowest value of the prevailing static 
pressure must  not exceed 6.0  kPa.  
5.4.5 Requirements for acclimatisation in tests of the influence of air temperature and relative 
humidity.  
5.4.5.1 During the test of the influence of air temperature and relative humidity on the sound level meter, 
the acoustic calibr ator corresponding to the specifications pursuant to 5.4.1.4 and the sound level meter 
(or relevant component thereof) must be placed in a climatic chamber.  
5.4.5.2 The acoustic calibrator and sound level meter must be acclimatised for a period of at least  12 h 
under reference ambient conditions.  General Measure No  0111 -OOP -C087 -18 
38 5.4.5.3 Under all test conditions which are different from the reference ambient conditions, after the 
initial 12  h acclimatisation period has elapsed, additional acclimatisation of the acoustic calibrator and 
soun d level meter must be allowed for a period of at least 7  h, unless the laboratory has sufficient proof 
that a shorter acclimatisation period will suffice.  
5.4.5.4 In tests of the influence of air temperature and relative humidity, the acoustic calibrator a nd 
sound level meter with the fastened microphone disconnected and during the acclimatisation period, 
both instruments must be supplied with power in the ‘off’ position.  
5.4.5.5 Once the acclimatisation period has elapsed, the acoustic calibrator must be p laced on the sound 
level meter’s microphone and the power supply is switched on for both instruments.  
5.4.5.6 The laboratory may be equipped with equipment with which the acoustic calibrator is connected 
to the microphone on the sound level meter without i nfluence of temperature and relative humidity in a 
climatic test chamber. If such equipment is available, the sound pressure level may be recorded after the 
period of time specified in the user manual after the pressure in the microphone has equalised. If such 
equipment is not available, then an additional acclimatisation period must take place for at least 3  h 
before the test begins.  
5.4.6 Abbreviated test of the combined influence of air temperature and relative humidity  
5.4.6.1 In order to limit the time  and cost for verifying the influence of air temperature and relative 
humidity on the sound level meter’s operation, a set of abbreviated tests at the specified air temperature 
and relative humidity will have to be carried out first.  
5.4.6.2 The acceptance  limits for abbreviated tests of the influence of combined air temperature and 
relative humidity are narrower than the acceptance limits specified in the applicable standards. If the 
sound level meter meets the narrower acceptance limits under all specifie d test conditions, the sound 
level meter must be deemed to be an instrument which entirely meets the specifications listed in the 
technical requirements for sound level meters. After that, no additional tests will be required. If the 
sound level meter does  not meet the narrower acceptance limits in any of the specified test conditions, 
then additional tests described in 5.4.7 and 5.4.8 must be conducted to determine compliance with the 
technical requirements specified in this Measure.  
5.4.6.3 After completing the acclimatisation procedures described in 5.4.5, the sound pressure level 
indicated in the response to the action of an acoustic calibrator which meets the requirements specified 
in 5.4.1.4 must be recorded for the specific combination of air temperature and relative humidity. When 
setting the test conditions, it is necessary to prevent sudden changes in air temperature in the test 
chamber. One must proceed with caution so that changes in temperature in the climatic test chamber do 
not cause co ndensation. In order to make sure that the relative humidity remains within the specified 
range, it is important to monitor the relative humidity in the climatic test chamber every time the air 
temperature changes.  
NOTE The combinations of temperature and relative humidity specified in 5.4.6.4 and 5.4.6.5 were selected in 
consideration of the condensation points which may be reached in accessible climatic test facilities. The 
combinations also reflect the range of ambient conditions during common applicatio ns of class  1 and class  2 sound 
level meters.  
5.4.6.4 In the case of sound level meters in which all components can function in a wide range of air 
temperatures and relative humidity covered by the technical requirements specified in the technical 
requirem ents for sound level meters, the following test conditions are required:  
a) for class  1 sound level meters:  
 reference air temperature and reference relative humidity;  
 air temperature of −10  °C and relative humidity of 65  %; 
 air temperature of +5  °C and relati ve humidity of 25  %; 
 air temperature of +40  °C and relative humidity of 90  %;  
 air temperature of +50  °C and relative humidity of 50  %; General Measure No  0111 -OOP -C087 -18 
39 b) for class  2 sound level meters:  
 reference air temperature and reference relative humidity;  
 air temperature of +0  °C and relative humidity of 30  %; 
 air temperature of +40  °C and relative humidity of 90  %. 
5.4.6.5 For those parts of the sound level meter which, according to the user manual, are designed for 
operation in an area with controlled ambient conditions, the followin g ambient conditions are required:  
 reference air temperature and reference relative humidity;  
 air temperature of +5  °C and relative humidity of 25  %; 
 air temperature of +35  °C and relative humidity of 80  %. 
5.4.6.6 With sound level meters which are made up  of combinations of components, the abbreviated 
environmental influence tests must be carried out in three steps.  
In the 1st step , components which can function in a wide range of ambient conditions (such as 
microphone and pre -amplifier) and components whi ch only function when conditions are controlled 
(such as a computer) must show functionality under reference ambient conditions.  
In the 2nd step , components which can function in a wide range of ambient conditions must be shown 
to function in combinations of ambient conditions pursuant to 5.4.6.4 (four conditions for class  1 sound 
level meters or two conditions for class  2 sound level meters), while components which only function 
when conditions are controlled, remain as showing functioning under reference ambient conditions.  
In the 3rd step , components which only function when conditions are controlled must be shown to 
function under two combinations of ambient conditions pursuant to 5.4.6.5, while components which 
can function in a wide range of ambient co nditions remain as showing functioning under reference 
ambient conditions. If it is essential to ensure that the actual measurement uncertainty does not exceed 
the maximum permissible uncertainty, it is permissible to replace an acoustic signal from an aco ustic 
calibrator with an equivalent electrical signal when exposing the microphone to reference ambient 
conditions.  
The acclimatisation procedure specified in 5.4.5 must be complied with under each test condition. The 
indicated sound pressure levels must b e recorded.  
5.4.6.7 In all tests, the indicated sound pressure levels must be corrected in terms of any difference 
between the sound pressure level created by the acoustic calibrator under test conditions and the sound 
pressure level created under referenc e ambient conditions.  
5.4.6.8 In sound level meters which are not made up of independent components, as well as in each test 
condition, the absolute value of the maximum deviation of the indicated sound pressure level from the 
sound pressure level indicate d under reference air temperature and reference relative humidity must be 
determined. In those sound level meters which are made up of combinations of components, the sum of 
the absolute value of the maximum deviation of the sound pressure level ascertaine d pursuant to the 2nd 
step in 5.4.6.6 from the sound pressure level measured pursuant to the 1st step and the absolute value of 
the maximum deviation of sound pressure level ascertained in the 3rd step from the sound pressure level 
measured pursuant to the  1st step must be determined.  
5.4.6.9 Other than the above -mentioned tests of the influence of temperature and humidity on the sound 
level meter’s operation, a special test of the influence of increased temperature on amplitude 
characteristic linearity err ors described in 5.6.8.2 must also be conducted.  
5.4.6.10 The absolute values or sums of absolute values of the maximum deviations determined pursuant 
to 5.4.6.8 must not exceed the narrower acceptance limit of 0.7  dB in class  1 sound level meters and 
1.2 dB in class  2 sound level meters.  
5.4.7 Influence of air temperature  
5.4.7.1 If the sound level meter does not meet the requirements in the abbreviated tests pursuant to 5.4.6, 
the following tests of the influence of air temperature on the operation of the  sound level meter must be 
carried out. The specified relative humidity is the reference relative humidity. To make sure that the General Measure No  0111 -OOP -C087 -18 
40 relative humidity does not exceed the specified ranges, it is important to monitor the relative humidity 
in the climatic test chamber every time the air temperature changes. When setting the test conditions, it 
is necessary to prevent sudden changes in air temperature in the test chamber. One must proceed with 
caution so that changes in temperature in the climatic test chamber do  not cause condensation.  
5.4.7.2 In the case of sound level meters in which all components can function in a wide range of air 
temperatures defined in this Measure, the sound pressure levels indicated in the response to the action 
of an acoustic calibrator  which meets the requirements specified in 7.1.4 must be measured at five air 
temperatures, specifically:  
a) at reference air temperature;  
b) at the minimum valid air temperature specified in the technical requirements for sound level 
meters;  
c) at the maximum val id air temperature specified in the technical requirements for sound level 
meters;  
d) at a temperature of +15  °C; 
e) at a temperature of +30  °C. 
The acclimatisation procedures pursuant to 5.4.5 must be carried out at each test condition.  
5.4.7.3  With sound level  meters which are made up of combinations of components, the influence of air 
temperature must be tested in three steps.  
In the 1st step , all components must be exposed at the reference air temperature.  
In the 2nd step , components which can function in a wide range of ambient conditions must be shown 
to function:  
a) at the minimum valid air temperature specified in the technical requirements for sound level 
meters;  
b) at the maximum valid air temperature specified in the technical requirements for sound level 
meters; 
c) at a temperature of +15  °C; 
d) at a temperature of +30  °C, 
while components which only function when conditions are controlled remain exposed under the 
reference air temperature.  
In the 3rd step , components which only function when conditions are contro lled must be shown to 
function:  
a) at the minimum valid air temperature specified in the technical requirements for sound level 
meters;  
b) at the maximum valid air temperature specified in the technical requirements for sound level 
meters,  
while components which can function in a wide range of ambient conditions remain as showing 
functioning at reference air temperature.  
The acclimatisation procedure specified in 5.4.5 must be complied with under each test condition. The 
sound pressure levels indicated in th e response to the action of the acoustic calibrator must be recorded.  
5.4.7.4 The sound pressure levels must be corrected in terms of any difference between the sound 
pressure level created by the acoustic calibrator under test conditions and the sound pre ssure level 
created under reference ambient conditions.  
5.4.7.5 In sound level meters which are not made up of independent components, as well as in each test 
condition, the absolute value of the maximum deviation of indicated sound pressure level from the  sound 
pressure level indicated under the reference air temperature and the reference relative humidity must be 
determined. In those sound level meters which are made up of combinations of components, the sum of 
the absolute value of the maximum deviation of the sound pressure level ascertained in the 2nd step in General Measure No  0111 -OOP -C087 -18 
41 Article  5.4.7.3 from the sound pressure level measured pursuant to the 1st step and the absolute value 
of the maximum deviation of the sound pressure level ascertained in the 3rd step from the soun d pressure 
level measured pursuant to the 1st step must be determined.  
5.4.7.6 The absolute deviations and sums of absolute values of the maximum deviations determined in 
5.4.7.5 must not exceed the applicable acceptance limits specified in the technical r equirements for 
sound level meters.  
5.4.8 Influence of relative humidity  
5.4.8.1 If the sound level meter does not meet the requirements in the abbreviated tests pursuant to 5.4.6, 
the tests of the influence of relative humidity must be carried out.  
5.4.8. 2 During the tests of the influence of relative humidity, the deviation in static pressure from the 
specified static pressure must not exceed the limits specified in 5.4.4. The deviation in actual relative 
humidity from the required relative humidity speci fied in 5.4.8.3 and 5.4.8.4 must not exceed the limits 
specified in 5.4.4.  
5.4.8.3 In the case of sound level meters in which all components can function in a wide range of relative 
humidity defined in the applicable standard, the sound pressure levels indicated in the response to the 
action of an acoustic calibrator which meets the requirements specified in 5.4.1.4 must be measured at 
four combinations of relative humidity and air temperature. The test conditions are:  
 reference relative humidity at the reference air temperature;  
 minimum relative humidity at an air temperature of +40  °C; 
 maximum relative humidity at an air temperature of +40  °C; 
 relative humidity of 70  % at an air temperature of +40  °C. 
The acclimatisation procedure specified in 5.4.5 mus t be complied with under each test condition.  
5.4.8.4  With sound level meters which are made up of combinations of components, the influence of 
relative humidity must be tested in three steps.  
In the 1st step , all components must be shown to function at th e reference relative humidity at the 
reference air temperature.  
In the 2nd step , components which can function in a wide range of ambient conditions must be shown 
to function in an air temperature of +40  °C:  
a) at the minimum relative humidity specified in t he technical requirements for sound level meters;  
b) at the maximum relative humidity specified in the technical requirements for sound level meters;  
c) at relative humidity of 70  %, 
while components which only function when conditions are controlled remain at the reference relative 
humidity and the reference air temperature.  
In the 3rd step , components which only function when conditions are controlled must be shown as 
functioning in an air temperature of +35  °C: 
a) at the minimum relative humidity specified in th e technical requirements for sound level meters;  
b) at the maximum relative humidity specified in the technical requirements for sound level meters,  
while components which can function in a wide range of ambient conditions remain at the reference 
relative humidity and the reference air temperature.  
The acclimatisation procedure specified in 5.4.5 must be complied with under each test condition. The 
sound pressure levels indicated in the response to the action of the acoustic calibrator must be recorded.  
5.4.8.5 The sound pressure levels must be corrected in terms of any difference between the sound 
pressure level created by the acoustic calibrator under test conditions and the sound pressure level 
created under reference ambient conditions.  
5.4.8.6 In sound level meters which are not made up of independent components, as well as in each test 
condition, the absolute value of the maximum deviation of the indicated sound pressure level from the General Measure No  0111 -OOP -C087 -18 
42 sound pressure level indicated under the reference air temperature a nd the reference relative humidity 
must be determined. In those sound level meters which are made up of combinations of components, 
the sum of the absolute value of the maximum deviation of the sound pressure level ascertained in the 
2nd step in Article  5.4.8.4 from the sound pressure level measured pursuant to the 1st step and the 
absolute value of the maximum deviation of the sound pressure level ascertained in the 3rd step from 
the sound pressure level measured pursuant to the 1st step must be determined . 
5.4.8.7 The absolute deviations and sums of absolute values of the maximum deviations determined in 
5.4.8.6 must not exceed the applicable acceptance limits specified in the applicable standard.  
5.4.9 Influence of electrostatic discharges  
5.4.9.1 The sou nd level meter must be immune to the influence of electrostatic discharges.  
5.4.9.2 Tests with electrostatic discharges must be carried out with the sound level meter switched on 
and set so that it exhibits the lowest immunity to electrostatic discharge, a s determined in a preliminary 
test. If the sound level meter can be equipped with connecting components which, according to 
specifications in the user manual, are not required as part of the configuration in normal operating mode, 
then no cables may be con nected during the tests on electrostatic discharges. The sound level meter 
systems with two or more channels for signal processing must have at least two microphone systems 
installed.  
5.4.9.3 Discharges of electrostatic voltage must not be conducted at the  outlet of the connectors which 
are hidden beneath the surface of either the connector or the body of the sound level meter.  
5.4.9.4 Electrostatic  discharges of the maximum positive and maximum negative voltage specified in 
the applicable standard must be conducted ten times at the contacts and ten times through the air. The 
discharges must be conducted at any point on the sound level meter which the laboratory deems to be a 
suitable point. The range of points must be limited to those points which are acces sible during normal 
use. It must also encompass those points inside the sound level meter to which the user has access, unless 
the user manual prescribes preliminary measures to prevent damage from electrostatic discharges. It is 
necessary to proceed with caution so that the sound level meter being tested is free of any kind of effects 
of the discharge before the discharge is repeated.  
5.4.9.5 After the discharge, the sound level meter must return to the same operating status it was in 
before the discharge.  Any data saved on the sound level meter before the discharge must remain 
unchanged after the discharge. Unquantified changes in the sound level meter’s activity are permissible 
during the discharge.  
5.4.10 Effects of magnetic fields caused by a grid -frequ ency alternating current and high -
frequency fields  
5.4.10.1 Sound signal  
5.4.10.1.1 A sound signal which has the properties specified in the technical requirements for sound 
level meters must be set so as to create an indication of the equivalent sound pressure level A or sound 
pressure level A with time characteristic F 74  dB ±1  dB. In the case of equivalent sound pressure level 
indications, the averaging time must be recorded. If the sound level meter has more than one 
measurement range, the measuremen t range in which the lower sound pressure level limit is specified 
must be set as closely as possible, but not higher than 70  dB. If the sound level meter only indicates the 
sound exposure level, it is necessary to calculate the corresponding equivalent so und pressure level as 
specified in the technical requirements for sound level meters for the averaging time.  
5.4.10.1.2 The method of applying the sound signal to the microphone must not cause any mutual 
interference with the grid -frequency alternating cur rent caused by the acting magnetic field or high -
frequency field. The method of using the sound signal must not disrupt the normal operation of the 
sound level meter or affect the sound level meter’s sensitivity to magnetic fields caused by a grid -
frequenc y alternating current or to high -frequency fields.  General Measure No  0111 -OOP -C087 -18 
43 5.4.10.2 Tests of the influence of magnetic fields caused by a grid -frequency alternating current  
5.4.10.2.1 The sound level meter being tested must be oriented pursuant to the specifications listed in 
the user manual, in which it has the minimum resistance to magnetic fields caused by a grid -frequency 
alternating current. In the case of sound level meters in which a microphone must be connected via 
microphone cable in order to meet the specifications liste d in the technical requirements for sound level 
meters, the tests in a magnetic field caused by a grid -frequency alternating current must also include the 
microphone unit.  
5.4.10.2.2 In tests of the influence of a magnetic field caused by a grid -frequency alternating current, 
equipment must be used which is capable of creating an essentially homogeneous magnetic field with 
an effective intensity value of 80  A/m. The equipment must enable the complete sound level meter or 
relevant parts thereof marked in the  user manual to be located in the magnetic field. The frequency of 
the alternating magnetic field must be 50  Hz or 60  Hz. The measurement uncertainty of the intensity of 
the magnetic field must not exceed 8  A/m.  
5.4.10.2.3 Before the tests of the influence  of alternating magnetic fields are initiated, the sound signal 
described in 5.4.10.1.1 must be connected and the indicated sound pressure level must be recorded. After 
the sound level meter is placed in the alternating magnetic field, the sound pressure l evel must be 
recorded at the same acoustic signal at the microphone’s location in which it was used in the first test. 
The exposure period must be at least 10  s. The deviation of the indicated sound pressure level A from 
the sound pressure level A indicate d before placement in the magnetic field must be determined.  
NOTE The maximum permissible measurement uncertainty specified in the technical requirements for sound level 
meters does not include any contribution from the measurement uncertainty of the magne tic field ’s intensity.  
5.4.10.2.4 The deviations determined in 5.4.10.2.3 must not exceed the applicable acceptance limits 
specified in the technical requirements for sound level meters.  
5.4.10.3 Tests in a high -frequency field  
5.4.10.3.1 A sound level met er must be immune to the effect of high -frequency fields.  
5.4.10.3.2 If the sound level meter is equipped with any kind of connecting component which enables 
the connection of an interface cable and connector cables, then all tests of immunity to high -frequency 
poles must be conducted with the cables connected to all the connection components which are available. 
The lengths of the cables must be identical to the lengths of the cables recommended in the user manual. 
All cables must be left unconnected on th e other end. If the sound level meter manufacturer also supplies 
devices which are connected to the sound level meter via cable, the influence of the high -frequency field 
must be determined under the conditions in which all components are connected togethe r. 
5.4.10.3.3 The test of the influence of high -frequency fields must be carried out with the sound level 
meter set up in normal operating mode as specified in the user manual. In the case of sound level meters 
for which the specific orientation includes a  microphone connected by cable, the microphone must be 
placed above the centre of the sound level meter’s body at a height of approximately 250  mm. If the 
cable is longer than 250  mm, the cable must be wrapped around itself so as to form a figure eight. An  
even number of loops of the same length must be formed, in which all parts are secured together on both 
ends and in the centre. The reference orientation of the sound level meter specified in the user manual 
must be initially identical to the main axis of  the emitter of the high -frequency fields.  
5.4.10.3.4 If several connections can be made with the same connecting component, then the influence 
of the high -frequency fields must be tested in the configuration which is specified in the user manual as 
the co nfiguration which has the lowest immunity to high -frequency fields. Other configurations which 
are equally or more resistant to high -frequency fields may be specified in the user manual in the list of 
suitable configurations. As long as the configuration t ested fully meets the specifications listed in the 
technical requirements for sound level meters, other configurations may be specified without further 
testing.  General Measure No  0111 -OOP -C087 -18 
44 5.4.10.3.5 In sound level meters of group  Z, which are hand -held, the accessories typically hel d in the 
hand must be positioned around the sound level meter during tests of the influence of high -frequency 
fields.  
5.4.10.3.6 The effective intensity value of the electrical field (unmodulated) must meet the specification 
listed in the technical require ments for sound level meters. The carrier frequency of the modulated signal 
must change in increases of up to a maximum of 4  % in a range from 26  MHz to 500  MHz. At 
frequencies from 500  MHz to 1  GHz and at frequencies from 1.4  GHz to 2.7  GHz, the interval must be 
up to a maximum of 2  %. The effective intensity value of the electrical field must be within a range from 
0 % to +40  % of the nominal intensity of the electrical high -frequency field.  
NOTE An increase in frequency of 2  % or 4  % means that an additi onal signal frequency is higher than the previous 
signal frequency by a factor of 1.02 or 1.04, respectively. Increases in carrier frequency from 2  % to 4  % are 
deemed to be suitable increases.  
5.4.10.3.7 Before the tests of the influence of high -frequency  fields are initiated, the sound level meter 
must be exposed to the sound signal described in 5.4.10.1.1 and the indicated sound pressure level must 
be recorded. The indicated sound pressure level for the same sound signal must be recorded at the 
microphon e’s location at every carrier frequency, as described in the initial test. The equivalent sound 
pressure level (or sound exposure level) must be zeroed at the beginning of measurement at every carrier 
frequency. The measuring period must be at least 10  s with the high -frequency field present, as well as 
in its absence.  
5.4.10.3.8 The measured deviation in the indicated sound pressure level A from the sound pressure level 
A indicated before the high -frequency field was added must not exceed the applicable ac ceptance limits 
specified in the technical requirements for sound level meters.  
NOTE The maximum permissible measurement uncertainty specified in the technical requirements for sound level 
meters does not include any contribution from the measurement uncer tainty of the electrical field ’s intensity.  
5.4.10.3.9 Testing at the discrete frequencies specified in 5.4.10.3.6 does not exclude the requirement 
to meet the specifications listed in the technical requirements for sound level meters at all carrier 
freque ncies within the range specified in the technical requirements for sound level meters. If there are 
signs that the acceptance limits specified in the technical requirements for sound level meters pursuant 
to 5.4.10.3.6 could be exceeded at the carrier freq uencies between two sequential frequencies, then tests 
will have to be carried out at further carrier frequencies.  
5.4.10.3.10 If the user manual states that the sound level meter meets the specifications listed in the 
technical requirements for sound leve l meters at electrical field intensities higher than those specified in 
the technical requirements for sound level meters, then all tests of the influence of high -frequency fields 
must be repeated at the highest of these electrical field intensities.  
5.4.10.3.11 The tests pursuant to 5.4.10.3.6 to 5.4.10.3.10 must be repeated while maintaining the 
configuration described in 5.4.10.3.2 to 5.4.10.3.5 in order to measure the influence of high -frequency 
fields on at least one other plane. The other plane m ust be approximately perpendicular to the basic 
plane in the reference orientation while complying with the limits of the test fastening’s setting. The 
measured deviation in the indicated sound pressure level A from the sound pressure level A indicated 
before the high -frequency field was added must not exceed the acceptance limits specified in the 
technical requirements for sound level meters.  
5.4.10.3.12 While the high -frequency field is being applied, the sound level meter must remain 
functional and in th e same configuration as it was before it was exposed to the effect of the high -
frequency field.  
5.4.10.3.13 The user manual must state that the sound level meter meets the specifications listed in the 
technical requirements for sound level meters at sound pressure levels lower than 74  dB. In this case, 
additional tests of the influence of high -frequency fields must be carried out in each applicable 
measurement range. The additional test must be carried out at the lowest sound pressure level specified 
in the  user manual at which the specifications listed in the applicable standard are complied with. The General Measure No  0111 -OOP -C087 -18 
45 source of sound described in 5.4.10.1.1 and the sound signal described in 5.4.10.1.2 must be used in 
these additional tests.  
5.4.10.3.14 The measured deviatio n in the indicated sound pressure level A from the sound pressure 
level A indicated before the high -frequency field was added must not exceed the applicable acceptance 
limits specified in the technical requirements for sound level meters for every step of the signal level 
from the sound source.  
5.4.10.3.15 In the case of sound level meters from group  Y or group  Z, additional tests must be carried 
out which verify conformity with the specifications listed in the technical requirements for sound level 
meters for immunity to high -frequency interference at the AC inputs/outputs. The effective intensity 
value of the electrical field must not be lower than −0  % or higher than +40  % of the nominal intensity 
of the electrical high -frequency field.  
5.4.10.3.16 In th e case of sound level meters from group  Z, which use or for which connector cables 
longer than 3  m are specified, additional tests must be carried out in order to demonstrate conformity 
with the specifications listed in the technical requirements for sound  level meters for immunity of signals 
and control inputs/outputs to high -frequency interference. The AC voltage of the electrical grid must 
not be lower than −0  % or higher than +5  % of the nominal voltage.  
5.5 High -frequency emissions and interference fro m the public electrical grid  
5.5.1 The high -frequency field intensity emission levels in decibels are in relation to the reference value 
of 1 μV/m. The high -frequency emissions tests must be carried out with a switched -on sound level meter 
which is powered  from the preferred source and set in operating mode and in the measurement range in 
which the highest levels of high -frequency emissions are generated.  
5.5.2 All design elements and fastening components used to maintain the position of the sound level 
meter, including microphone and cable (if used), must have a negligible effect on the measuring of high -
frequency emissions from the sound level meter.  
5.5.3 The high -frequency emissions levels must be measured in the frequency ranges specified in the 
applica ble standard with the sound level meter set up in the specified reference orientation.In the case 
of sound level meters with which a specific configuration includes a microphone connected via cable, 
the microphone and cable must be arranged as described in  5.4.10.3.1. Multi -channel sound level meter 
systems must be equipped with microphones connected to the input of each channel.  
5.5.4 The high -frequency emissions levels must be measured on one other plane selected by the 
laboratory while maintaining the ar rangement (if applicable) of microphone and cable with respect to 
the body of the sound level meter as specified in 5.5.3. The other plane must be approximately 
perpendicular to the main plane in the reference orientation in the limits of the position of t he system 
used when measuring the high -frequency emissions level.  
5.5.5  If the sound level meter is equipped with any kind of connecting component which enables the 
connection of an interface cable or connector cables, then the high -frequency emissions lev els must be 
measured with the cables connected to all connection components which are available. The length of 
the cables must be the maximum length recommended in the user manual. All cables must be left 
unconnected on the other end. If the sound level me ter manufacturer also supplies devices which are 
connected to the sound level meter via cable, the influence of the high -frequency field must be 
determined under the condition in which all components are connected together.  
5.5.6  If several connections can  be made with the same connecting component, then the high -frequency 
emissions levels must be measured in the configuration which is specified in the user manual as the 
configuration which produces the highest level of high -frequency emissions. As long as the 
configuration tested fully complies with the limits specified in the technical requirements for sound level 
meters, other configurations with the same or lower high -frequency emissions levels may be specified 
in the form of a list in the user manual wi thout further testing.  
5.5.7 In the case of sound level meters from group  Y or group  Z, which are powered from the public 
electrical grid, a test of interference from emissions radiated by the public electrical grid must be carried General Measure No  0111 -OOP -C087 -18 
46 out. Unless a different measurement range is specified in the user manual, the sound level meter must 
be set to the reference measurement range during these tests.  
5.6 Electro acoustic  operating tests  
5.6.1 General  
5.6.1.1 The tests described in this chapter are conducted by mean s of acoustic or electrical signals 
pursuant to the specifications for each test. The operator may not be present in the sound field during 
tests with acoustic signals. Electrical signals of equivalent output from the microphone must be sent to 
the sound l evel meter by means of the input device which is specified in the user manual. It must be 
verified whether the difference between the changes in signal level indicated on the display device and 
the changes corresponding to the signal level at the electrica l output (if used) do not exceed the limit 
specified in the technical requirements for sound level meters.  
5.6.1.2 In tests with acoustic signals, the sound pressure level at the location of the sound level meter’s 
microphone must be measured by a calibrat ed laboratory reference microphone which meets the 
technical requirements specified in the applicable standard for measurement microphones. When 
determining the sound pressure level at the test frequency, the frequency characteristics of the reference 
microphone must be taken into consideration. With multi -channel sound level meter systems having 
identical microphone units and identical installation configurations, at least one microphone channel 
must be tested and any other microphone channels must be test ed based on the laboratory’s judgement. 
If the microphone units or installation configurations are not identical, then each different microphone 
channel must be tested.  
5.6.1.3 The stability of the sound pressure level between measurements with the laborat ory reference 
microphone and measurements with the sound level meter must be known either based on a previous 
assessment, or according to the measurement of the stability of the sound pressure level with a 
monitoring microphone during tests with acoustic s ignals.  
5.6.1.4 In tests with acoustic signals and measurements of internally generated noise, the ambient 
conditions must be within the following ranges for the duration of the test: static pressure of 97  kPa to 
103 kPa, air temperature of +20  °C to +26  °C and relative humidity of 40  % to 70  %. 
5.6.1.5 The deviation in frequency of the input signal from the specified frequency must not exceed 
±0.25  % of the specified frequency  
5.6.1.6 If the laboratory is situated in a way which makes it infeasible to the maintain static pressure 
within the range specified in 5.6.1.4, the laboratory may use the results of the tests conducted pursuant 
to 5.4.3 to determine the operation of the sound level meter under the reference static pressure. In this 
case, the actual me asurement uncertainty must include the additional elements of the valid corrections 
to offset the effects of differences between the prevailing static pressure and the reference static pressure.  
5.6.1.7 The ambient conditions at the time of the test must b e recorded.  
5.6.1.8 With respect to the properties of the applicable free -field facility and the applicable test method 
used, the contribution of the measurement uncertainty of the sound level meter’s acoustic response from 
the uncertainty caused by the so und field deviations in the facility from an ideal sound field without 
reflections must be assessed in the case of tests conducted in a free -field test facility.  
NOTE Practical considerations to measurements in free -field facilities are discussed in the ap plicable standard 
concerning determination of the sensitivity of operative reference microphones.  
5.6.2 Indication at calibration control frequency  
5.6.2.1 If an acoustic calibrator specified in 5.1.4 is used, the indication must be checked at the 
calibration control frequency before starting (but not during) the tests described in the various articles 
of Chapter  5.6. If necessary, the sound level meter must be set so that the required sound pressure level 
is indicated under reference ambient conditions.  General Measure No  0111 -OOP -C087 -18 
47 5.6.2.2 The settings at the calibration control frequency are verified if the difference between the setting 
during measurement and the corresponding setting  specified in the user manual does not exceed ±0.3  dB. 
5.6.2.3 The effect of the ambient conditions at the sound pressure level created by the acoustic calibrator 
must be determined in accordance with the procedure and data setting specified in the user ma nual for 
the acoustic calibrator and the data from its calibration. The effects must be determined in terms of the 
sound pressure level created under reference ambient conditions.  
5.6.3 Directional characteristics  
5.6.3.1 The sound level meter’s directiona l characteristics must be determined using plane progressive 
sinusoidal sound waves in a free -field test facility. All sound level meter configurations must be tested 
which are defined in the user manual as configurations which meet the requirements for di rectional 
characteristics specified in the technical requirements for sound level meters.  
5.6.3.2 The equivalent sound pressure levels or sound pressure levels with time characteristic F must be 
measured. If absolutely necessary, the equivalent sound press ure level must be calculated for any 
suitable integration time, as is specified in the technical requirements for sound level meters from the 
indicated sound exposure levels. Frequency weighting C or Z must be selected if available; otherwise, 
frequency we ighting A must be selected.  
5.6.3.3 In the case of sound level meters which are symmetrical around the main axis passing through 
the microphone connected to the sound level meter by an extension cable or other device, then the 
directional characteristics m ay be measured on any plane passing through the axis of symmetry. The 
sound pressure levels indicated on the display device or equivalent indication of sound pressure levels 
at the electrical output must be recorded with sounds impacting the microphone at the applicable range 
of angles in relation to the reference direction pursuant to the technical requirements for sound level 
meters. One of the angles of sound incidence must be in the reference direction.  
5.6.3.4 If an electrical output is integrated and used in the directional characteristic tests, preliminary 
tests must be carried out which determine how the frequency -weighted signal levels correspond to the 
voltages at the electrical output. With sound level meters without an electrical output, the dire ctional 
characteristic tests can be conducted on an acoustically and electrically equivalent device supplied by 
the sound level meter manufacturer which has exactly the same physical dimensions and shape, but is 
equipped with an electrical output.  
5.6.3.5 In the case of sound level meters, including wind protection cover and accessories, if they are 
part of the configuration in normal use, which are not symmetrical around the main axis passing through 
the microphone, or in which the microphone is not connec ted to the sound level meter by an extension 
cable or other device, the directional characteristics must be measured on two mutually perpendicular 
planes. Each plane comprises the main axis of the microphone. Each plane must be perpendicular to the 
surface  of the sound level meter which contains control elements and potentially a display device.  
5.6.3.6 The following test method must be used in case the user manual does not provide detailed 
information indicating that the directional characteristics of the complete sound level meter meet the 
technical requirements for sound level meters.  
 With class  1 and class  2 sound level meters, the frequency of the sound signal must be in the range 
of frequencies from 500  Hz to 2  kHz at third -octave intervals and then in  a range of frequencies 
higher than 2  kHz to 8  kHz at intervals of one -sixth of an octave.  
 With class  1 sound level meters, the frequency of the sound signal must be in the range of 
frequencies higher than 8  kHz to 12.5  kHz at intervals of one -twelfth of an octave.  
 The test frequencies at third -octave intervals, at intervals of one -sixth of an octave and at intervals 
of one -twelfth of an octave must be in accordance with the technical requirements for sound level 
meters.  
 The angle intervals at each test f requency must not exceed 10° during measurements of directional 
characteristics.  General Measure No  0111 -OOP -C087 -18 
48 5.6.3.7 If the user manual provides detailed tables of information on directional characteristics, including 
any potential directivity factors for random sound incidence, the directional characteristics must be 
measured on every plane of symmetry in the entire ran ge of angles of sound incidence specified in the 
technical requirements for sound level meters, albeit at intervals not exceeding 30°. It is necessary that 
the test signal frequency be:  
 in a range from 500  Hz to 12.5 kHz at third -octave intervals for clas s 1 sound level meters and  
 in a range from 500  Hz to 8  kHz at octave intervals for class  2 sound level meters.  
5.6.3.8 With sound level meters designed to measure sounds with a random direction of incidence, the 
measurement of the directional characterist ics must cover the range of angles of sound incidence up to 
±180° on each plane of symmetry in relation to the reference direction on each measurement plane.  
5.6.3.9 In measurements of directional characteristics at various angles of sound incidence, based  on 
movement of the sound level meter or of the source of sound, the axis of the microphone’s rotation 
symmetry and the main axis of the source of sound must remain on the same, principally horizontal, 
plane. Movement of the sound level meter on the horizo ntal plan is preferably made by rotating around 
the vertical axis passing through the reference point of the microphone. If the equivalent sound pressure 
level or sound exposure levels is being measured, it is necessary to ensure a stable indication for ev ery 
increase in angle by allowing a sufficiently long integration time.  
NOTE If the source of sound and the reference point of the microphone remain at fixed locations during the 
measurement of the directional characteristics, it will minimise the influenc e of slight fluctuations in the sound 
field in the testing room.  
5.6.3.10 An alternative test procedure consists of measuring the directional characteristics under 
conditions when the signal frequency from the sound source changes, but the given angle of s ound 
incidence is retained. The test is repeated for each angle of sound incidence. The sound pressure level 
at the location of the sound level meter’s microphone should stay the same at any angle of sound 
incidence at the given test frequency. The same si gnal from the sound source must be used for each 
angle of sound incidence at each test frequency.  
5.6.3.11 A constant signal level from the sound source must be maintained at any test frequency when 
the sound level meter is placed in positions with various  angles of sound incidence. In all tests, the sound 
pressure level at the microphone’s location with the sound source switched on must be at least 30  dB 
higher than the sound pressure level indicated when the sound source is switched off.  
5.6.3.12 On each measurement plane and at all applicable frequencies, the greatest absolute difference 
between the sound pressure levels at any two angles of sound incidence in each range of angles specified 
in the applicable standard must not exceed the applicable accepta nce limits specified in the technical 
requirements for sound level meters.  
5.6.3.13 If the user manual provides detailed data on directional characteristics and if the directional 
characteristics are measured in a limited number of angles of sound incidenc e and signal frequencies, 
then, other than the requirements specified in 5.6.3.12, the measured values of the maximum absolute 
differences between sound pressure levels must not exceed the corresponding nominal values of the 
maximum absolute differences in  sound pressure levels which are specified in the user manual.  
5.6.4 Frequency weighting tests via acoustic signals  
5.6.4.1 General  
5.6.4.1.1 The procedure described in Article  5.6.4.3 for verifying frequency weighting by means of tests 
in a free -field tes t facility assumes that the sound level meter does not have an electrical output and that 
the sound pressure level at the sound level meter’s location is first determined with the help of a 
calibrated laboratory reference microphone. If an electrical outpu t is available, it may be expedient to 
conduct measurements in reverse order, i.e. in that the sound level meter is first installed in the test 
facility and the sound source is set so that the applicable indication is on the sound level meter. The 
sound le vel meter is then removed and a laboratory reference microphone is placed at the location of the General Measure No  0111 -OOP -C087 -18 
49 sound level meter’s microphone in order to determine the corresponding sound pressure level in the free 
field 
5.6.4.1.2 If an electrical output is available an d used in tests, preliminary tests must be carried out to 
determine how the frequency -weighted signal levels indicated on the display device correspond to the 
voltage levels at the electrical output. There must be no attempt made to determine the amplitude  
characteristic linearity errors in any of the frequency weighting tests.  
5.6.4.1.3 At least one of the frequency weightings for which fulfilment criteria are specified in the 
technical requirements for sound level meters must be tested using sinusoidal ac oustic and electrical 
signals. Further frequency weightings which are integrated into the sound level meter and for which 
nominal values and acceptance limits are specified in the technical requirements for sound level meters 
or in the user manual must be tested with either acoustic or electrical signals. In tests of further frequency 
weightings via electrical signals, the test methods must include correction for the actual frequency 
characteristics of the microphone and the average effects of reflections f rom the body of the sound level 
meter and sound deflection around the microphone.  
5.6.4.1.4 The sound level meter must be set to measure the sound pressure level with the time 
characteristic F, if available; otherwise it must be set as per the equipment fo r measuring the equivalent 
sound pressure level or sound exposure levels. If absolutely necessary, the equivalent sound pressure 
level must be calculated from the results of measuring the sound exposure levels, pursuant to how it is 
specified in the applic able standard for any suitable integration time.  
5.6.4.1.5 If possible, all tests of frequency weightings and other frequency characteristics must be 
conducted in the sound level meter’s setting for reference measurement range. If the laboratory decides 
that the setting of the measurement range switch may affect compliance with the technical requirements 
for frequency weighting, additional tests must be carried out in further measurement ranges.  
5.6.4.1.6 If the sound level meter enables frequency weighting , tests with acoustic signals must be 
carried out with frequency weighting C or Z. If weighting function C or Z is not available, then frequency 
weighting A must be used for the tests. The tests with acoustic signals must be carried out with plane 
progress ive sound waves in a free -field test facility at frequencies higher than the lower limit frequency 
of the free -field test facility. The tests at frequencies lower than the lower limit frequency must be carried 
out by means of a comparative coupler.  
5.6.4.1 .7 In the case of a sound level meter configuration in which the specified reference direction is 
not in accordance with the microphone’s main axis of symmetry, the frequency weighting must be 
verified in the reference direction for the specified polar ang le around the main axis in at least three 
further positions on the conical surface created by rotating the reference direction around the 
microphone’s main axis.  
5.6.4.2 Correction for wind protection cover  
5.6.4.2.1 If a wind protection cover is required pursuant to 5.3.12 and the user manual states that the 
sound level meter meets the technical requirements of this Measure in both the configuration including 
the wind protection cover as well as in the configuration not including the wind protection cover,  the 
frequency weighting determined with the acoustic signals must be measured in the free -field test facility 
with the cover and without the wind protection cover of the specified model which is installed around 
the microphone. The differences between fre quency weightings are the measured corrections for the 
wind protection cover for sound impacting in the reference direction on the specified measurement plane 
passing through the microphone’s main axis. Data on the corrections and associated measurement 
uncertainties must be determined at each test frequency. The difference must be determined between the 
measured correction for the wind protection cover and the corresponding correction for the wind 
protection cover specified in the user manual.  
5.6.4.2.2 In  sound level meter configurations in which the specified reference direction is not in 
accordance with the microphone’s main axis of symmetry, the correction for the wind protection cover 
must be determined in the reference direction for the specified pola r angle around the main axis and in General Measure No  0111 -OOP -C087 -18 
50 at least three further positions on the conical surface created by rotating the reference direction around 
the microphone’s main axis.  
5.6.4.3 Free-field tests  
5.6.4.3.1 If frequency weighting C or Z is selected for free -field tests and for the purpose of comparing 
data needed to verify corrections in a free field, the tests must also be conducted with frequency 
weighting A, albeit only at test frequencies for which data on corrections in a free sound field are 
provided i n the user manual.  
5.6.4.3.2 In tests of class  1 and class  2 sound level meters, the frequency of the acoustic signal in the 
free-field test facility must be in the range from the lower limit frequency of the free -field test facility 
up to 2  kHz at third -octave intervals and, at frequencies higher than 2  kHz to 8  kHz, at intervals with a 
width of one -sixth of an octave. With class  1 sound level meters, the frequency of the acoustic signal 
must be in the range of frequencies higher than 8  kHz to 20  kHz at in tervals with a width of one -twelfth 
of an octave. An index of the required frequencies is specified in the technical requirements for sound 
level meters.  
5.6.4.3.3 If the user manual specifies tables with detailed data on frequency weighting, tests to veri fy 
the manufacturer’s data may be limited to third -octave intervals with class  1 sound level meters and to 
octave intervals in class  2 sound level meters.  
5.6.4.3.4 At all test frequencies, the sound pressure level at the location of the reference point of  the 
microphone on the sound level meter must be determined with the help of a laboratory reference 
microphone without the sound level meter present. The sound waves must arrive at the reference point 
of the laboratory reference from the direction in which  the microphone was calibrated. At any test 
frequency, the sound pressure level with the sound source switched on must be at least 30  dB higher 
than the sound pressure level with the sound source switched off.  
5.6.4.3.5 At each test frequency, the output f rom the sound source must be set so that a reference sound 
pressure level is generated at the selected location in the free -field test facility. If it is not possible to 
maintain the reference sound pressure level at any test frequency, then another sound pressure level may 
be used. The sound pressure levels and any corrections which were used must be recorded.  
5.6.4.3.6 The laboratory reference microphone must then be replaced with a sound level meter. The 
reference point of the microphone on the sound lev el meter must take the same position as the reference 
point of the reference microphone. The sounds must arrive at the microphone from the specified 
reference direction. At each test frequency, the signals from the sound source must be the same as they 
were in the tests with the laboratory reference microphone. The signal level indicated by the sound level 
meter must be recorded at each test frequency.  
5.6.4.3.7 At each test frequency, the frequency weighting must be calculated from the level of the 
frequen cy-weighted sound pressure indicated by the sound level meter minus the sound pressure level 
measured with the laboratory reference microphone.  
5.6.4.3.8 The tests described in 5.6.4.3.2 to 5.6.4.3.7 must be repeated in at least two other suitable 
location s or distances between the sound source and the microphone in the free -field test facility.  
5.6.4.3.9 At each test frequency, the measured frequency weighting must be calculated from the 
arithmetic mean of the frequency weightings determined at various dis tances and in various locations 
between the sound source and the microphone.  
5.6.4.4 Tests in the comparative coupler  
5.6.4.4.1 At frequencies lower than the lower limit frequency of the free -field test facility, the frequency 
weightings must be measured at third -octave intervals from 10  Hz to the lower limit frequency in the 
case of class  1 sound level meters and from 20  Hz to the lower limit frequency in the case of class  2 
sound level meters. In tests in the comparative coupler, the microphone of the sound level meter and the 
laboratory reference microphone must be exposed to the effect of the sound field in the compara tive 
coupler or in an equivalent device. The sound pressure level measured by the sound level meter and the General Measure No  0111 -OOP -C087 -18 
51 sound pressure level measured by the laboratory reference microphone must be recorded. If a wind 
protection cover is installed, it can be removed be fore the tests in the comparative coupler are initiated.  
5.6.4.4.2 If the tube for equalising the static pressure beneath the diaphragm of the microphone is 
exposed to the effect of a sound field in the comparative coupler, at frequencies lower than 
appro ximately 250  Hz, it is permissible to assume that the pressure frequency characteristics of the 
microphone inserted into the comparative coupler will be the same as the corresponding frequency 
characteristics of the microphone in a free field or in a field  with random sound incidence. If the upper 
limit frequency exceeds approximately 250  Hz in tests in the comparative coupler, it is recommended 
that the laboratory ensure the equivalence between the pressure frequency characteristic measurements 
and the cor responding measurements in the reference direction in the free -field test facility and with 
sound incidence in a random direction. If the microphone tube to equalise the static pressure is not 
exposed to the sound field in the comparative coupler, the labo ratory must clarify the difference between 
the microphone’s pressure frequency characteristics and frequency characteristics in a free field and in 
a field with random sound incidence.  
5.6.4.4.3 The measurement of the frequency weightings in the comparativ e coupler must be conducted 
at least three times. In each test, the microphones must be disconnected from the comparative coupler 
and reinstalled. In each test frequency, the frequency weighting measurement results must be calculated 
as the arithmetic aver age of the separate determinations.  
5.6.4.4.4 The sound level meter’s linearity range must be greater than 70  dB in order to carry out tests 
of frequency weighting A toward low frequencies down to 10  Hz. If necessary, tests of frequency 
weighting A must be  conducted down to the lowest frequency at which a sound pressure level of 5  dB 
higher than the lower limit of the linearity range is indicated.  
5.6.4.4.5 In tests in the comparative coupler, the measured frequency weighting must be calculated from 
the fre quency -weighted sound pressure levels indicated by the sound level meter minus the 
corresponding sound pressure level measured with the laboratory reference microphone.  
5.6.4.5 Conformity  
The measured deviations in frequency weightings from the correspondi ng nominal frequency 
weightings must not exceed the applicable acceptance limits specified in the technical requirements for 
sound level meters. The nominal values of the frequency weightings must be identical to the values 
specified in this Measure or the  values calculated according to the equations specified in it and rounded 
to the nearest tenth of a decibel.  
5.6.4.6 Sound incidence in a random direction  
5.6.4.6.1 The tests must be carried out with sound incidence in a random direction with a cover and 
without a wind protection cover installed around the microphone in order to verify the corrections for 
the wind protection cover with sound incidence in a random direction.  
5.6.4.6.2 The average frequency -weighted response to random sound incidence must be  determined at 
third -octave internals in a frequency range from the lower limit frequency of the free -field test facility 
up to 16  kHz in class  1 sound level meters and from the lower limit frequency up to 8  kHz in class  2 
sound level meters. At frequencie s lower than the lower frequency limit, the frequency weighting upon 
sound incidence in a random direction must be determined with the above -described method for tests in 
the comparative coupler.  
5.6.4.6.3 The directivity factors upon random sound incidenc e must be determined with the use of the 
data obtained in directional characteristics pursuant to 5.6.3. The measured directivity factors must be 
used when determining the measurement of the relative frequency -weighted response upon random 
sound incidence as the sum of the relative frequency -weighted response in a free field in the reference 
direction and the corresponding directivity factors.  
5.6.4.6.4 The measured frequency weightings upon random sound incidence constitute the relative 
frequency -weighted response to random sound incidence at each test frequency. The measured 
deviations in frequency weightings upon random sound incidence from the nominal frequency General Measure No  0111 -OOP -C087 -18 
52 weightings must not exceed the applicable acceptance limits specified in the technical require ments for 
sound level meters.  
NOTE Until higher -quality data are available, it is essential to consider the maximum permissible measurement 
uncertainties specified in the technical requirements for class  1 sound level meters as the valid uncertainties for 
frequency weighting measurements in the case of sounds with random incidence.  
5.6.5 Frequency weighting tests via electrical signals  
5.6.5.1 General  
5.6.5.1.1 Tests with electrical signals must be carried out for all frequency weightings incorporated in 
the sound level meter for which nominal values and acceptance limits are specified in the technical 
requirements for sound level meters or in the user manual. Sinusoidal input signals of the same test 
frequencies as used in tests pursuant to 5.6.4 must be us ed in all tests, with the exception that increases 
in frequencies may not be greater than one -third of an octave. All tests specified in this article must be 
conducted with the sound level meter set to the measurement range which was used in the tests purs uant 
to 5.6.4.  
5.6.5.1.2 Two alternative procedures are provided for the tests of frequency weightings with electrical 
signals. The first procedure requires the input signal level at each test frequency and frequency weighting 
to be set so that the display  device shows the same indication when acoustic signals and electrical signals 
are used. This procedure minimises the influence of amplitude characteristic linearity errors, but may 
make it impossible to measure the frequency weighting at certain frequenci es because the high voltage 
of the input signal may cause overexcitation in certain frequency weightings. If the preliminary test 
reveals that overexcitation is caused in certain frequency weightings at certain test frequencies, then a 
second alternative t est procedure will have to be used in all tests.  
5.6.5.1.3 There must be no attempt made to determine amplitude characteristic linearity errors in the 
sound level meter’s response in either of the two test procedures.  
NOTE If the linearity range in the sel ected measurement range is sufficiently broad, then the second test procedure 
enables measuring frequency weighting at any desired test frequency, but the influence of amplitude characteristic 
linearity errors may be somewhat greater than in the first test  procedure.  
5.6.5.2 First alternative test procedure (variable input signal level)  
5.6.5.2.1 The test is initiated with frequency weighting selected in tests with acoustic signals pursuant 
to 5.6.4; at each test frequency, the input electrical signal level  must be adjusted so that the indication 
on the sound level meter’s display device is the same as that obtained at the relevant frequency in the 
tests with acoustic signals pursuant to 5.6.4. The test must then be repeated for the other frequency 
weighting s. The input signal levels and corresponding indications on the display device must be 
recorded.  
NOTE The input signal levels can be measured as effective voltage values or the settings for the input signal 
attenuator expressed in decibels can be recorded.  
5.6.5.2.2 Frequency weightings via equivalent weighting which were obtained with acoustic signals 
must be calculated by the following means. The differences expressed in decibels between the input 
signal level recorded for the frequency weighting and the input signal level recorded for the frequency 
weighting which was selected in the tests with acoustic signals pursuant to 5.6.4 must be calculated at 
each test frequency. In order to obtain equivalent frequency weightings in the tests with electrical 
signa ls, the differences in the input signal level must be subtracted from the frequency weightings 
determined in the tests with acoustic signals.  
NOTE The difference between the electrical input signal levels may be determined from the differences in the 
atten uator settings of the input signal or according to the relation 10  lg(V2/ V1)2 dB, in which V2 and V1 are the 
effective voltage levels measured during frequency weighting, or during the frequency weighting which was 
selected in the tests with acoustic signals.  General Measure No  0111 -OOP -C087 -18 
53 5.6.5.3 Second alternative test procedure (constant input signal level)  
5.6.5.3.1 The test is in itiated with the frequency weighting used in the tests pursuant to 5.6.4; the input 
signal level must be adjusted at a frequency of 1  kHz so that the indication is 5  dB lower than the upper 
linearity range limit at a frequency of 1  kHz. The input signal le vel at any other test frequency must be 
identical to the signal level at a frequency of 1  kHz. The input signal levels and corresponding 
indications on the display device must be recorded.  
5.6.5.3.2 The differences between the indications on the display de vice obtained pursuant to 5.6.5.3.3 
and the indications obtained pursuant to 5.6.5.3.1 must be calculated at each test frequency. In order to 
obtain equivalent frequency weightings in the tests with electrical signals, these differences in indicated 
levels  must be attributed to the corresponding frequency weighting measured with acoustic signals.  
5.6.5.3.3 In all further frequency weightings, the input signal level at each test frequency must be the 
same as the level recorded in the tests pursuant to 5.6.5.3.1. The indications on the display device must 
be recorded.  
5.6.5.4 Conformity  
The measured deviations in equivalent frequency weightings from the nominal values must not exceed 
the applicable acceptance limits specified in the technical requirement s for sound level meters or in the 
user manual, depending on what is suitable.  
5.6.5.5 Frequency weightings C or Z  at 1 kHz 
5.6.5.5.1 A sound level meter which is equipped with frequency weightings C or Z must be tested with 
continuous sinusoidal electrica l signals with a frequency of 1  kHz. The input signal must be set so that 
the reference sound pressure level is indicated in the reference measurement range with classified 
frequency weighting A, and the indication must be recorded. The sound pressure leve l with time 
weighting F or S, the equivalent sound pressure level or sound exposure level indicated with weighting 
functions C and Z must then be recorded at the same input signal.  
5.6.5.5.2 The measured deviations in the measurement quantity level weighte d with function C and Z 
from the corresponding measurement quantity level weighted with function A must not exceed the 
applicable acceptance limits specified in the technical requirements for sound level meters.  
5.6.6 Correction for the effect of reflectio ns from the body of the sound level meter and sound 
deflection around the microphone  
5.6.6.1 The tests listed in this article are intended to verify the corrections and associated measurement 
uncertainties which are specified in the user manual for the typ ical effects of reflections from the body 
of the sound level meter and sound deflection around the microphone on the frequency characteristics 
of the microphone. The tests must be carried out with the sound level meter set to the ordinary operating 
mode sp ecified in the user manual, with the exception that no microphone or wind protection cover is 
installed.  
5.6.6.2 Corrections must be verified with constant sinusoidal electrical signals. The frequency weighting 
must be identical to the weighting which was selected in the tests with acoustic signals. The corrections 
must be verified for a microphone of the same type specified in the user manual for use with a sound 
level meter for which different corrections for the effects of reflections and sound deflectio n are 
specified.  
5.6.6.3 The input signal with a frequency of 1  kHz must be set so that the indicated sound pressure level 
is the same as that which was indicated in the same measurement range in the tests with an acoustic 
signal with a frequency of 1  kHz pursuant to 5.6.4. The electrical input signal levels and corresponding 
signal level indications must be recorded.  
5.6.6.4 The input signal frequencies must be at third -octave intervals for class  1 sound level meters in a 
range from a frequency greater tha n the lower frequency limit of the free -field test facility up to 16  kHz General Measure No  0111 -OOP -C087 -18 
54 and, for class  2 sound level meters, in a range from a frequency greater than the lower frequency limit 
up to 8  kHz.  
NOTE In the case of an electrical input signal, the level corresponding to the effective voltage value or input signal 
attenuator setting expressed in decibels can be recorded.  
5.6.6.5 Under the condition that the input signal is kept constant, the signal level indicated by the sound 
level meter must be recorded at all test frequencies other than 1  kHz.  
5.6.6.6 The relative frequency weighting of the electrical signal must be calculated from the level 
indicated at the test frequency minus the level indicated at a frequency of 1  kHz.  
5.6.6.7 At each test frequency,  the measured effects of reflection from the body of the sound level meter 
and sound deflection around the microphone must be calculated from the frequency weighting of the 
acoustic signal determined in accordance with the method specified in 5.6.4 minus t he relative frequency 
weighting of the electrical signal determined in accordance with 5.6.6.6.  
5.6.6.8 At each test frequency, the differences between the measurement of the effects of reflections and 
sound deflection and the corresponding data specified  in the user manual must not exceed the uncertainty 
values specified in the user manual for the correction for reflections from the body of the sound level 
meter and sound deflection.  
NOTE This method of verifying the effects of reflections and sound defle ction does not apply to any kind of non -
linearity of amplitude characteristics between the sound pressure levels measured in the free -field test facility and 
the signal levels indicated in the response to the electrical signals.  
5.6.7 Corrections for obtai ning sound pressure levels in a free field and sound pressure levels in a 
field with random sound incidence  
5.6.7.1 If the user manual recommends the use of a multi -frequency acoustic calibrator, comparative 
coupler and electrostatic actuator to control th e frequency weighting during verification, then it is 
essential for the user manual to specify data on correcting the indicated sound pressure levels for the 
equivalent sound pressure levels which were indicated in the response to plane sound waves from th e 
reference direction in a free field or, if applicable, in the response to sound waves in a field with random 
sound incidence. The data on the correction for a free field and the associated uncertainties must be 
verified as part of the type tests.  
5.6.7.2  If necessary, the sound pressure indication levels must be corrected for the difference between 
the sound pressure level created by the acoustic calibrator at the test frequency and the sound pressure 
level created at a frequency of 1  kHz, or according to  the corresponding difference expressed by the 
relative frequency characteristics level when the comparative coupler or electrostatic actuator is used. 
In order to determine the equivalent sound pressure level in a free field with sound incidence in the 
reference or, if applicable, equivalent sound pressure level in a field with random sound incidence, the 
correction data specified in the user manual must be used to correct the sound pressure levels. The 
relative equivalent sound pressure level A must then be calculated at each frequency in relation to the 
equivalent sound pressure level A at a frequency of 1  kHz. The result is the relative equivalent frequency 
characteristic weighted with function A.  
5.6.7.3 Before the tests for verifying the data on corrections specified in the user manual are carried out, 
it must be verified that the measured deviations in the measured frequency weighting A from the nominal 
value at a frequency of 1  kHz, which was verified in the tests of the frequency weighting with  acoustic 
signals pursuant to 5.6.4, do not exceed the applicable acceptance limits specified in the technical 
requirements for sound level meters. Sound pressure level A indicated in the response to the effect of 
the acoustic calibrator, comparative coupl er and electrostatic actuator must then be recorded for each 
frequency for which data on corrections are specified in the user manual.  
5.6.7.4 At frequencies different from 1  kHz, the measured deviations of the relative equivalent frequency 
characteristics  weighted by function A, determined in the use of the acoustic calibrator, comparative 
coupler or electrostatic actuator from the arithmetic mean of the relative frequency characteristics 
weighted by function A, which was measured in a free -field test faci lity or from frequency weighting in General Measure No  0111 -OOP -C087 -18 
55 a field with random sound incidence measured in accordance with 5.6.4.6 must not exceed the values of 
uncertainty specified in the user manual for data on corrections.  
5.6.7.5 The procedure for verifying the data on corr ections specified in the user manual must be repeated 
with each model of microphone specified for the sound level meter for which different data are provided 
on corrections in a free field and in a field with random sound incidence.  
5.6.8 Amplitude charact eristic linearity  
5.6.8.1 Tests at air temperatures close to the reference air temperature  
5.6.8.1.1 The amplitude characteristic linearity must be tested with the help of continuous sinusoidal 
electrical signals. The air temperature must be 18  °C and 23  °C at any suitable relative humidity and 
static pressure. The signal frequencies must be 31.5  Hz, 1  kHz and 12.5  kHz for class  1 sound level 
meters and 31.5  Hz, 1  kHz and 8  kHz for class  2 sound level meters.  
5.6.8.1.2 The amplitude characteristic linearity  must be tested with the sound level meter set to indicate 
sound pressure level A with time characteristic F, if available, and with the sound pressure level set to 
indicate equivalent sound pressure level A, if available. If only sound exposure level A is  displayed, the 
amplitude characteristic linearity error must be determined according to the equivalent sound pressure 
levels A calculated from the indication of sound exposure levels A, as specified in the technical 
requirements for sound level meters, fo r any suitable integration time.  
5.6.8.1.3 For all input signals, the amplitude characteristic linearity error is given by the deviation in the 
indicated sound pressure level from the corresponding anticipated sound pressure level. At any test 
frequency an d any measurement range, the anticipated sound pressure level must be calculated from the 
sound pressure level in the starting point specified in the user manual in the reference measurement 
range plus the difference between the input signal level and the input signal level which caused the 
sound pressure level at the starting point to be displayed.  
NOTE 1 The zero error of amplitude characteristic linearity is at the starting point in the reference measurement 
range at any test frequency.  
NOTE 2 The change s in input signal level in decibels can be determined from the changes in input signal attenuator 
settings or calculated from the levels of the ratio of two consecutive measurements of the effective voltage values 
of the input signals.  
5.6.8.1.4 At any tes t frequency, the amplitude characteristic linearity tests must begin with the input 
signal set so that the sound pressure level at the starting point is displayed in the reference measurement 
range. Amplitude characteristic linearity errors must be measure d in input signal level steps which are 
not greater than 1  dB. The tests must continue from the starting point upwards to the first indication of 
overexcitation and then back downwards through the starting point to the first indication of the lower 
signal level. The tests must then continue back upwards up to the starting point. The same input signal 
must be used in measurements with a rising and falling signal level.  
5.6.8.1.5 In measurement ranges other than the reference measurement range, the amplitude 
characteristic linearity errors must be measured toward the specified upper linearity range limit and then 
back downwards toward the lower limit in input signal level steps which are not greater than 10  dB. At 
each of the other measurement ranges, the test s for the amplitude characteristic linearity error must begin 
at the sound pressure level indicated with the input signal at which the starting point was displayed in 
the reference measurement range, and must be set according to the nominal change of the m easurement 
range switch in relation to the settings for the reference measurement range. Within a range of 5  dB 
from the specified upper limit and 5  dB from the specified lower limit, there must not be any steps in 
input signal levels toward the first indi cation of overexcitation or toward the first indication of low signal 
level greater than 1  dB in each measurement range.  
NOTE In measurement ranges other than the reference measurement range, the zero error in amplitude 
characteristic linearity need not ne cessarily be at the starting point at any test frequency (see 5.6.8.1.3, note  1). General Measure No  0111 -OOP -C087 -18 
56 5.6.8.1.6 At each test frequency and in the entire spread of the linearity range specified in the user 
manual for each measurement range, the measured amplitude characteristi c linearity errors must not 
exceed the applicable acceptance limits specified in the technical requirements for sound level meters.  
5.6.8.1.7 The measured amplitude characteristic linearity errors corresponding to the changes in input 
signal level from 1  dB to 10  dB must not exceed the applicable acceptance limits specified in the 
technical requirements for sound level meters.  
5.6.8.1.8 At each test frequency, the dynamic range of sound pressure levels A in which the measured 
amplitude characteristic linear ity errors do not exceed the applicable acceptance limits must not be 
narrower than the corresponding dynamic range specified in the user manual.  
5.6.8.2 Tests at increased air temperatures  
5.6.8.2.1 As specified in 5.4.6.9, the amplitude characteristic linearity errors must also be measured at 
increased air temperatures. This test must be carried out with the help of continuous sinusoidal electrical 
signals with a frequency of 1  kHz. In this test, components of the sound level meter which are intended 
for use under a wide range of ambient conditions must be exposed to the effect of an air temperature 
which is within a range of 2  °C from the applicable maximum temperature specified in 5.4.6.4, but does 
not exceed this temperature. The relative humidity and  static pressure may have any suitable values.  
5.6.8.2.2 The measured amplitude characteristic linearity errors must not exceed the applicable 
acceptance limits specified in the technical requirements for sound level meters. The dynamic range of 
sound pres sure levels A in which the measured amplitude characteristic linearity errors do not exceed 
the applicable acceptance limits also must not be narrower than the corresponding dynamic range 
specified in the user manual.  
5.6.8.2.3 The procedure specified in 5 .6.8.1 must be followed in these tests at increased air temperatures, 
except that the amplitude characteristic linearity errors must only be measured at the reference 
measurement range and only in steps of 10  dB from the starting point upwards to the speci fied upper 
linearity range limit, downwards to the lower limit and back to the starting point, and must encompass 
the lower and upper limit.  
5.6.9 Low signal level indication  
In each measurement range and at each frequency used in the amplitude characteristic linearity tests, it 
must be verified that the low signal level indication is not displayed under conditions in which the level 
of the time -weighted acoustic pressure, equivalent sound pressure level or sound exposure level is 
greater than or  equal to the lower limit of the linearity range specified in the user manual. If the low 
level signal is indicated, it must be verified that the low signal indicator is functioning as specified in 
the technical requirements for sound level meters.  
5.6.10 Internally generated noise level  
5.6.10.1 The internally generated noise level must be measured with the microphone attached to the 
sound level meter. The sound level meter must be placed into a sound field with a low sound pressure 
level in a configuratio n which is specified in the user manual for normal operating mode. If a microphone 
stand is specified for normal operating mode, it is not necessary to place all parts of the sound level 
meter on the opposite side of the stand from the microphone into the sound field with a low sound 
pressure level. The internally generated noise levels must be measured with each type of microphone 
which is specified in the user manual for use with the sound level meter. The internally generated noise 
levels must also be me asured if the microphone is replaced with a specified electrical input device and 
the input is loaded by the means specified in the user manual.  
5.6.10.2 The internally generated noise levels must be measured in the measurement ranges in which 
the maximum internally generated noise levels are anticipated pursuant to the data specified in the user 
manual.  
5.6.10.3 The air temperature and relative humidity must not exceed the ranges specified in 5.6.1.5 during 
measurements of internally generated noise levels . General Measure No  0111 -OOP -C087 -18 
57 5.6.10.4 The internally generated noise levels must be recorded for all available frequency weightings 
and frequency characteristics. The sound pressure levels with time weightings F and S must be 
determined from the arithmetic mean from ten measurements  distributed randomly at intervals of 60  s. 
In measurements of equivalent sound pressure levels, the averaging time must be the same as the period 
specified in the user manual for maximum internally generated noise levels.  
5.6.10.5 With each type of microp hone and in tests in which the microphone is replaced by an electrical 
input device, the measured internally generated noise levels should not exceed the corresponding 
maximum anticipated internally generated noise levels which the user manual specifies in  the 
measurement range by more than 10  dB. 
NOTE The specified internally generated noise level is only for the user ’s information and is not used for assessing 
conformity with the requirement.  
5.6.11 Time constants of decline for time weightings F and S  
5.6.11.1 The exponential time constants of decline F and S must be tested with continuous sinusoidal 
electrical signals with a frequency of 4  kHz. The signal level must be set so that the sound pressure level 
indicated is 3  dB lower than the upper limit spe cified for the linearity range in the reference 
measurement range. The continuous signal must be active for at least 10  seconds.  
5.6.11.2 The signal must be abruptly switched off and the speed of decline of the displayed sound 
pressure level must be measur ed from the initial switching off. The measured speeds of decline of time 
weightings F and S must not exceed the acceptance limits specified in the technical requirements for 
sound level meters.  
NOTE The exponential decline speeds may be measured by visually observing the sound pressure levels indicated 
on the display device and simultaneously determining the corresponding times which have elapsed since it was 
initially switched off, determined by a stopwatch or the equivalent timing device or from th e speed of sampling 
specified as the data refresh speed when displaying digital signal levels. Another method consists of using a video 
camera or equivalent device for recording the sound pressure levels indicated on the display device and digital 
clocks w hich simultaneously display time in milliseconds.  
5.6.11.3 With sound level meters equipped with time weighting S, a continuous sinusoidal electrical 
input signal with a frequency of 1  kHz must be set so that it indicates the reference sound pressure level  
in the reference measurement range during time weighting F. Sound pressure level A must be recorded. 
The indicated sound pressure level A with time weighting S must then be recorded at the same input 
signal.  
5.6.11.4 The measured deviation in the sound pr essure level measured with time weighting S from the 
sound pressure level measured with time weighting F must not exceed the acceptance limits specified 
in the technical requirements for sound level meters.  
5.6.11.5 If the sound level meter is able to disp lay the indicated sound pressure level as a function of 
time with the appropriate resolution, this function may be used when verifying the time constants of the 
decline.  
5.6.12 Response to a tone impulse with sound level meters which measure the time -weigh ted sound 
pressure level  
5.6.12.1 Response to a tone impulse in sound level meters which measure sound pressure levels with 
time weightings F and S must be tested in the reference measurement range with the help of sinusoidal 
electrical signals with a freq uency of 4  kHz.  
5.6.12.2 Tests of response to a tone impulse must begin with a continuous signal being sent to the sound 
level meter set with the frequency weighting A. When setting to time weighting F, the input signal must 
be set so that the indication i s 3 dB lower than the specified upper limit of the linearity range. The 
indication of the sound pressure level with time weighting F must be recorded. If the sound level meter 
is equipped with time weighting S, the procedure must be repeated for the sound pressure level with the 
time weighting S.  General Measure No  0111 -OOP -C087 -18 
58 5.6.12.3 Tone impulses derived from a continuous signal must be used for all periods of tone impulse 
duration specified in the applicable standard for the time weighting F and, if integrated, for the time 
weighting  S. Indications of the maximum sound pressure levels must be recorded in the response to the 
tone impulses.  
5.6.12.4 Tone impulse tests must be repeated with the indicated continuous signal level reduced in steps 
of 20  dB, whereby one begins with the indic ation specified in 5.6.12.2. The steps of 20  dB must be 
repeated until a sound pressure level indication is reached during the last step which is less than 20  dB 
higher than the specified lower linearity range limit. The responses must also be measured to tone 
impulses during a continuous signal which results in an indication which is 10  dB higher than the 
specified lower linearity range limit.  
5.6.12.5 In each step, the indications of the sound pressure level with time weighting F and sound 
pressure level with time weighting S must be recorded for the tone impulses as well as the corresponding 
indications of the maximum sound pressure level with the time weighting F and the maximum sound 
pressure level with the time weighting S. In each step, the responses to tone impulses must be measured 
for all periods of tone impulse duration specified in the technical requirements for sound level meters 
for which the maximum sound pressure levels with time weighting F and maximum sound pressure 
levels with time weightin g S can be observed on the display device with indications which are at least 
16 dB higher than the anticipated internally generated noise levels of weighting function A which are 
specified in the user manual for the reference measurement range.  
5.6.12.6 The response to tone impulse measurement results must be calculated from the maximum sound 
pressure level with time weighting F and the maximum sound pressure level with time weighting S, 
which are indicated in signals with tone impulses minus the correspon ding sound pressure level with 
the time weighting F and with the time weighting S indicated in the corresponding continuous signals.  
5.6.12.7 Tone impulse response tests must also be conducted in a mode in which the indicated 
continuous signal level is inc reased in steps of 1  dB above the level of the signal specified in 5.6.12.2 
until the first indication of overexcitation appears. The tone impulse duration times must be the shortest 
valid duration times pursuant to the applicable standards for time weight ings F and S.  
5.6.12.8 Deviations in the measured responses to tone impulses from the corresponding reference 
responses to tone impulses specified in the technical requirements for sound level meters must not 
exceed the applicable acceptance limits specifi ed in this Measure.  
5.6.13 Response to a tone impulse with sound level meters which measure the sound exposure level 
or equivalent sound pressure level  
5.6.13.1 Response to a tone impulse in sound level meters which measure the sound exposure level or 
equivalent sound pressure level, or both levels, must be tested in the reference measurement range with 
the help of sinusoidal electrical signals with a frequency of 4  kHz. If only sound exposure levels are 
being measured, the equivalent sound pressure lev el of the continuous signal must be calculated from 
the measurement of the sound exposure levels and integration time. If only the equivalent sound pressure 
levels are measured, the sound exposure levels from the tone impulses must be calculated from the 
measurement of the equivalent sound pressure level and the averaging time.  
5.6.13.2 Tests with tone impulses must begin with a continuous signal being sent to the sound level 
meter set with the frequency weighting A. The input signal must be set so that the  indication is 3  dB 
lower than the upper limit of the linearity range specified in the user manual. If the sound level meter 
only displays the sound exposure levels, the input signal must be set so that the sound exposure level is 
indicated at which the co rresponding equivalent sound pressure level corresponds to the specifications. 
An integration time of 10  s is recommended, in which the sound exposure level is 10  dB higher than the 
corresponding equivalent sound pressure level. The equivalent sound pressu re level and averaging time 
or sound exposure level and integration time must be recorded. If available, the averaging time or 
integration time must be identical to the periods indicated on the display device.  
5.6.13.3 Tone impulses derived from a continuo us signal must be used for all tone impulse duration 
times which are specified for sound exposure levels in the technical requirements for sound level meters. General Measure No  0111 -OOP -C087 -18 
59 The indicated sound exposure levels or equivalent sound pressure levels and averaging times must be 
recorded for every test. The integration times for sound exposure level indications must be sufficiently 
long to include all contributions from the tone impulse. If the sound level meter only displays the 
equivalent sound pressure level, then the sound exposure level of the tone impulse must be determined 
from the equivalent sound pressure level and corresponding averaging time as specified in the technical 
requirements for sound level meters. The averaging times for equivalent sound pressure level 
measu rements must be longer than the tone impulse duration time.  
5.6.13.4 The test with tone impulses must be repeated with the indicated continuous signal levels 
reduced in steps of 20  dB, whereby one begins with the indication specified in 5.6.13.2. The steps  of 
20 dB must be repeated until an equivalent sound pressure level indication is reached during the next 
step which is less than 20  dB higher than the specified lower linearity range limit. The responses to tone 
impulses must also be measured during a con tinuous signal which results in an indication which is 10  dB 
higher than the specified lower linearity range limit. The indication of the equivalent sound pressure 
level of the continuous signal and the sound exposure level of the tone impulse must be reco rded for 
each step. Responses to tone impulses must be measured for all tone impulse duration times specified 
in the technical requirements for sound level meters for which sound exposure levels or equivalent sound 
pressure levels are defined and these lev els are not lower than the lower linearity range limit at a 
frequency of 4  kHz.  
5.6.13.5 The response to tone impulse measurement results must be calculated from the sound exposure 
levels indicated or calculated from the tone impulse signals minus the equi valent sound pressure level 
indicated or calculated from the corresponding continuous signals.  
5.6.13.6 Tone impulse response tests must also be conducted in a mode in which the indicated 
continuous signal level is increased in steps of 1  dB above the leve l of the signal specified in 5.6.13.2 
until the first indication of overexcitation appears. The duration times of the tone impulses must be 
0.25 ms. 
5.6.13.7 Deviations in the measured responses to tone impulses from the corresponding reference 
responses t o tone impulses must not exceed the applicable acceptance limits specified in the technical 
requirements for sound level meters.  
5.6.14 Response to a series of repeated tone impulses with sound level meters which measure the 
equivalent sound pressure level  
5.6.14.1 Response to a series of repeated sinusoidal electrical tone impulses with a frequency of 4  kHz 
with sound level meters which measure the equivalent sound pressure levels must be tested in the 
reference measurement range.  
5.6.14.2 Tests of responses to a series of repeated tone impulses must begin with a continuous signal 
being sent to the sound level meter set with the frequency weighting A. The input signal must be set so 
that the indication of the equivalent sound pressure level is 3  dB lower than the upper limit of the 
linearity range specified in the user manual. The equivalent sound pressure level and corresponding 
averaging time must be recorded.  
5.6.14.3 The series of repeated tone impulses must be derived from a continuous signal. In dividual tone 
impulses from a series of repeated tone impulses must have duration times which are specified for sound 
exposure levels in technical requirements for sound level meters. In order to ensure the stable 
measurement of the equivalent sound pressu re level, each series of repeated tone impulses must contain 
a sufficient number of tone impulses. Each individual tone impulse in the series must begin and end at 
the zero transition point. The period between the individual tone impulses in the series mus t be at least 
three times longer than the duration time of the individual tone impulse. The equivalent sound pressure 
level must be recorded in each series. The averaging time must be equal to the period used when 
determining the equivalent sound pressure level of the continuous signal.  
5.6.14.4 Tests of responses to a series of repeated tone impulses must be repeated with a continuous 
input signal which results in the indication of an equivalent sound pressure level which is 10  dB higher 
than the specified  lower limit of the linearity range. Tests of results to a series or repeated tone impulses General Measure No  0111 -OOP -C087 -18 
60 must be carried out in all duration times of individual tone impulses, specified for sound exposure levels 
in the technical requirements for sound level meters in w hich the indications of the equivalent sound 
pressure levels are specified. The equivalent sound pressure levels and corresponding averaging times 
of the continuous signals and the series of repeated tone impulses must be recorded.  
5.6.14.5 The response me asurements for a series of repeated tone impulses must be calculated from the 
equivalent sound pressure level series minus the equivalent sound pressure level corresponding to the 
continuous signal.  
5.6.14.6 Deviations in the measured responses to the seri es of repeated tone impulses from the 
corresponding theoretical responses to tone impulses must not exceed the applicable acceptance limits 
specified in the technical requirements for sound level meters for sound exposure level. The theoretical 
responses m ust be determined as specified in these requirements.  
5.6.15 Overexcitation indication  
5.6.15.1 Overexcitation is partially tested in measurements of amplitude characteristic linearity or the 
response to tone impulses. The additional overexcitation indicat ion tests are described here.  
5.6.15.2 The overexcitation indication must be tested in the reference measurement range with the sound 
level meter set so as to display the level of time -weighted sound pressure A or equivalent sound pressure 
level A. The ove rexcitation indication must be verified for the time -weighted sound pressure level with 
the time weighting F and, if available, with the time weighting S. The positive and negative half periods 
of sinusoidal electrical signals with frequencies of 31.5  Hz, 1 kHz and 4  kHz. At each test frequency, 
the signals with a half period derived from continuous signals must be of the same level and must begin 
and end at the zero transition points.  
5.6.15.3  At each test frequency, the overexcitation indication test must  begin at the time -weighted or 
equivalent sound pressure level indicated for a continuous input signal which corresponds to a level 
1 dB lower than the specified upper linearity range limit. The level of the input signals with a positive 
half period which were derived from a continuous signal must be increased by steps of 0.1  dB until the 
overexcitation appears. The same procedure must be repeated for signals with a negative half period. 
The levels of the input signals with a half period which result in the  first indication of overexcitation 
must be recorded with a resolution to one tenth of a decibel.  
NOTE The relative levels of input signals with a half period may be determined from the input attenuator setting.  
5.6.15.4 The measured differences between input signals with a positive and negative half period which 
first results in the overexcitation indication being displayed must not exceed the acceptance limits 
specified in the technical requirements for sound level meters.  
5.6.15.5 If the sound level me ter enables measurements of peak sound pressure levels C, the 
overexcitation indication measurement must be repeated with signals with positive and negative half 
periods in the sound level meter setting for measurement of peak sound pressure levels C.  
5.6.15.6 If the sound level meter is used to measure sound pressure levels with the time weighting F or 
S, it must be verified that the overexcitation indication appears in accordance with the specification 
listed in the technical requirements for sound level meters. If the equivalent sound pressure levels, sound 
exposure levels, maximum sound pressure levels or peak sound pressure levels C are being measured, 
it must be verified whether, after the condition for overexcitation has appeared, the overexcitation 
indicator remains blocked in accordance with the specifications listed in the technical requirements for 
sound level meters.  
5.6.16 Peak sound pressure level C  
5.6.16.1 The indication of the peak sound pressure level C must be tested with continuous sinusoi dal 
electrical signals and electrical signals with one period and a half period. Signals with one period and a 
half period must be signals described in the technical requirements for sound level meters and must be 
derived from continuous signals. Signals w ith one period and a half period must begin and end at the 
zero transition point.  General Measure No  0111 -OOP -C087 -18 
61 5.6.16.2 The measurement of peak sound pressure level C must be tested at the levels of the three 
continuous input signals in the reference measurement range and in the measu rement ranges with the 
lowest sensitivity. The first continuous signal is a signal which gives an indication of the sound pressure 
level C with the time weighting F or equivalent sound pressure level C which is 4  dB lower than the 
upper limit specified in the user manual for the range of peak sound pressure levels. The second 
continuous input signal is a signal which gives an indication of the sound pressure level C which is 1  dB 
higher than the lower limit specified for the range of peak sound pressure lev els. The third continuous 
input signal is the signal which causes the indication, rounded to 1  dB, in the middle of the range of the 
peak sound pressure levels C specified in the user manual for the upper and lower limit of the range of 
peak sound pressure  levels.  
5.6.16.3 Peak sound pressure levels C must be measured on the three signal levels specified in 5.6.16.2 
with the signals with one period and a half period which are specified in the technical requirements for 
sound level meters. The equivalent sou nd pressure levels or sound pressure levels with the time 
weighting F must be measured with corresponding continuous signals. The differences must be 
calculated between the indications of peak sound pressure level C for signals with one period and a half 
period and the indications of the equivalent sound pressure level or sound pressure level with time 
weighting F of the corresponding continuous signals.  
5.6.16.4 The differences in the measured differences between peak sound pressure levels C and the 
corres ponding sound pressure levels of the continuous signal from the corresponding nominal 
differences specified in the technical requirements for sound level meters must not exceed the applicable 
acceptance limits specified in these technical requirements.  
5.6.16.5 It must be verified whether there is any indication of overexcitation for all of the measured peak 
sound pressure levels C conducted in accordance with the above -mentioned procedure.  
5.6.17 Zeroing  
If a zeroing function is integrated, it must be veri fied whether the activity of the zeroing device interferes 
with the previous indication on the display device. It must also be verified whether or not the activity of 
the zeroing device causes any inaccurate indications on any display device.  
5.6.18 Electrical output  
A sinusoidal electrical signal with a frequency of 1  kHz must be connected to the electrical input device 
of the sound level meter. The sound level meter must be set to measure sound pressure level A with the 
time weighting F or the equiv alent sound pressure level A. The signal must be set so that the indication 
of the reference sound pressure level appears in the reference measurement range, and the indication 
must be recorded. A shorting circuit must successively be connected to all anal ogue electrical outputs 
and all indications must be measured. The measured difference between the indicated sound pressure 
levels must not exceed the acceptance limits specified in the technical requirements for sound level 
meters.  
5.6.19 Timing devices  
It must be verified whether or not the shortest averaging times when measuring equivalent sound 
pressure levels or the shortest integration times when measuring sound exposure levels are longer than 
the corresponding shortest periods specified in the user m anual. It must be verified whether or not the 
longest averaging times or integration times are shorter than the corresponding longest periods specified 
in the user manual. The longest averaging time or integration time to be verified pursuant to this Measu re 
must not exceed 24  h. 
5.6.20 Crosstalk in multi -channel sound level meter systems  
5.6.20.1 The crosstalk between any pairs of channels in a multi -channel system must be tested with 
continuous electrical signals connected to the electrical input device o f one channel from the given pair 
at frequencies of 31.5  Hz, 1  kHz and 8  kHz.  General Measure No  0111 -OOP -C087 -18 
62 5.6.20.2 The input signal must be set at each test frequency so as to result in an indication at the upper 
limit of the linearity range specified in the user manual. The signal l evel indicated in the given channel 
and all other channels must be recorded. The differences between the indicated signal levels must not 
be lower than the applicable lowest differences specified in the technical requirements for sound level 
meters. The fr equency weighting must be the weighting function C or Z or, if necessary, the weighting 
function A.  
5.6.21 Power supply source  
5.6.21.1 The sound level meter must first be tested under conditions in which its power supply source 
supplies the nominal voltag e specified in the user manual. The acoustic calibrator supplied with the 
sound level meter must be attached to the microphone and the sound level meter must be placed in the 
reference measurement range. The indication of the sound pressure level A with th e time weighting F 
or equivalent sound pressure level A must be recorded. The test must be repeated under conditions when 
the power supply source is supplying the highest and the lowest voltage specified in the user manual.  
5.6.21.2 The measured deviations  in the sound pressure level indicated at the highest voltage and at the 
lowest voltage from the sound pressure level indicated at nominal voltage must not exceed the 
acceptance limits specified in the technical requirements for sound level meters.  
NOTE Th e term ‘power supply source ’ includes batteries.  
6 Initial verification  
The initial verification procedure is identical to the follow -up verification procedure.  
7 Follow -up verification  
The instruments specified in Chapter  1 of this Measurement may be verified separately. Microphones 
must be type -approved together with the sound level meter.  
7.1 Submission for testing  
7.1.1 The user manual of the applicable model and version of sound lev el meter must be submitted for 
verification together with the sound level meter.  
7.1.2 The sound level meter must be submitted for verification together with all components and/or 
accessories with which it is to be tested. The device specified in the user manual for connecting electrical 
signals equivalent to signals from the microphone must also be submitted.  
7.1.3 The data required to conduct verification must be available and the laboratory must record and 
note the origin of the data. The data must inclu de all relevant information required in the technical 
requirements for sound level meters and in the specifications on the correction methods for obtaining 
the sound level meter’s frequency characteristics in a free field.  
7.1.4 An acoustic calibrator must  be available. If the acoustic calibrator is supplied by the user, it must 
be used to determine the absolute acoustic sensitivity of the sound level meter.  
7.2 Conformity  
7.2.1 Conformity with the technical requirements is demonstrated if both of the following criteria are 
met:  
a) the measured deviation from the nominal value does not exceed the applicable acceptance limit; and  
b) the corresponding measurement uncertainty does not ex ceed the corresponding maximum 
permissible measurement uncertainty specified in the technical requirements for sound level meters 
for the same probability of coverage of 95  %.  General Measure No  0111 -OOP -C087 -18 
63 7.2.2 If the actual measurement uncertainty during verification exceeds the cor responding maximum 
permissible uncertainty, then the test result must not be used to assess conformity with the 
electro acoustic  requirements for sound level meters during verification.  
7.2.3 The actual measurement uncertainty during verification without in cluding the uncertainty of the 
data on corrections in a free field or in a field with random sound incidence specified by the manufacturer 
must not exceed the corresponding maximum permissible uncertainty specified in the technical 
requirements for sound l evel meters. If, however, the uncertainty of the data on corrections specified by 
the manufacturer is figured in, it is possible that the actual measurement uncertainty during verification 
may only exceed the corresponding maximum permissible uncertainty b ecause the uncertainty of the 
data on corrections specified by the manufacturer was a significant part of the sum of uncertainties 
during verification. In this case, the test may continue, but the documentation on verification must 
contain a statement expl aining the causes why the test results do not meet the technical requirement 
specified in the technical requirements for sound level meters.  
7.3 Preliminary inspection  
Before any kind of measurement, the sound level meter and all accessories must be visual ly inspected, 
with special attention paid to any damage or accumulation of foreign matter on the protective screen or 
diaphragm of the microphone. All of the important control elements must be functional and it is 
necessary to verify that they are in good working order. If the control elements, display and other basic 
elements are not in good working order, then no tests may be conducted.  
7.3.1 If the sound level meter does not bear the markings required in the technical requirements for 
sound level meters or there is no evidence that the sound level meter was originally marked that way, 
then verification must not be carried out. At least the model marking and serial number must be visible 
on the sound level meter.  
The sound level meter must be powered from its preferred source or suitable alternative in all tests. 
Before and after conducting the set of tests with acoustic signals and before and after conducting the set 
of tests with electrical signals, the voltage supplied by the power supply source to the s ound level meter 
must be checked using the method specified in the user manual and it must be ascertained that it is within 
the specified operating limits. If the voltage or equivalent indication of the power source status is not 
within the operating limit  range and the reason cannot be attributed to a partially drained battery or 
improper voltage setting on the power supply source connected to the public electrical grid, then no tests 
may be conducted due to an indication of improper functioning.  
NOTE: Cha nges at the output of the power supply source may be determined as changes in the percent of voltage of a fully charged 
battery or by an equivalent procedure.  
7.5.1 Verification must be conducted in the following ranges of ambient conditions: static pressu re of 
80 kPa to 105  kPa, air temperature of 20  °C to 26  °C and relative humidity of 25  % to 70  %. 
7.5.2 The static air pressure, air temperature and relative humidity must be measured and recorded at 
least at the beginning and end of the test.  
7.5.3 If dat a on the influence of deviations under the prevailing ambient conditions from the reference 
ambient conditions are not available, then, during tests of frequency weightings conducted at static 
pressure under 97  kPa, the laboratory must assign a standard un certainty of 0.09  dB to measurements at 
frequencies lower than or equal to 3  kHz and assign a standard uncertainty of 0.14  dB to measurements 
at frequencies higher than 3  kHz.  
NOTE: Both standard uncertainties are intended for use if the values of standard  uncertainties from the potential sources specified 
in 7.10.6 are not available. Both values were determined from estimates of 0.15  dB and, respectively, 0.25  dB of the maximum 
influence of static pressure on the frequency characteristics of the models of microphones which have the greatest resistance to air 
in the rear cavity.  
7.6.1 The tests described in the following articles only apply to those design characteristics which are 
required in the technical requirements for sound level meters and which are a ccessible in the sound level 
meter when it is submitted for the test. All such characteristics must be tested.  General Measure No  0111 -OOP -C087 -18 
64 7.6.2 In all tests pursuant this chapter, the configuration of the sound level meter must be in accordance 
with the user’s requirement and must b e as specified in the user manual for one of the normal modes, 
including all required accessories. With sound level meters which enable elective settings of corrections 
to the relative frequency characteristics for the influence of any kind of accessories and for other sound 
level meter configurations, the tests must be carried out with the use of the settings which are suitable 
for the configuration of the sound level meter in its normal operating mode. Any such settings must not 
be changed during the test . 
7.6.3 Electrical signals must be delivered to the sound level meter with the help of an input device or by 
the means specified in the user manual. The deviation in frequency of the input signal from the specified 
frequency must not exceed ±0.25  % of the specified frequency  
7.6.4 In the case of a sound level meter with an electrical output which is to be used during verification, 
it must be confirmed that the indication obtained from the electrical output and corresponding indication 
on the display device of the sound level meter are consistent in the range of acceptance limits specified 
in the technical requirements for sound level meters. If there are multiple outputs and if one output is 
specified in the user manual for the test, this output must be used  during verification.  
An acoustic calibrator specified in the manual must be used with the sound level meter or an acoustic 
calibrator generating the same nominal sound pressure level and frequency as the model specified in the 
user manual must be used. In  the second case, publicly available data must be used from either the sound 
level meter manufacturer or from the manufacturer of the acoustic calibrator on any kind of settings on 
the sound level meter which must be applied after connecting the given mode l of calibrator to the given 
model of microphone.  
NOTE: It is possible that publicly available data for the model of acoustic calibrator which are not specified in the user ma nual 
have not been verified or type -tested in accordance with this Measure.  
NOTE  1: The sound pressure level indication is influenced by background noise as well as by internally generated noise.  
NOTE  2: Sound pressure level A corresponding to the internally generated noise is only given as information and is not used for 
assessin g conformity with the requirement. The internally generated noise level is specified without the associated uncertainty.  
NOTE: The internally generated noise level is only given as information and is not used for assessing conformity with the 
requirement. The internally generated noise level is specified without the associated uncertainty.  
7.10 Frequency weighting tests via acoustic signals  
NOTE  1: If pertinent data are available on corrections in a free field or in a field with random sound incidence, it i s preferable to 
conduct these tests with the help of a multi -frequency acoustic calibrator, comparative coupler or electrostatic actuator in order to 
minimise testing time.  
NOTE  2: A microphone which meets the requirements specified in the technical requir ements for laboratory reference microphones 
also meets the requirements in the technical requirements for operating reference microphones.  
 equivalent frequency characteristics of a sound level meter in a free field or in a field with random 
sound incidence , if the source of sound or simulated sound of a pressure field is in a multi -
frequency acoustic calibrator, in a comparative coupler or from an electrostatic actuator;  
 average influence of the wind protection cover and any accessories which are part of t he sound 
level meter’s configuration in ordinary use on the frequency characteristics of a typical 
microphone.  
NOTE: It is possible that publicly available data which are not specified in the user manual have not been verified or type -tested 
in accordance with this Measure.  
NOTE: At frequencies lower than 1  kHz, the measured frequency weighting during the use of the electrostatic actuator will not 
show the effects of defects such as openings in the diaphragm of the microphone.  
7.11 Tests of frequency weighting via electrical signals  
 in tests of class  1 sound level meters:  
nine nominal frequencies in octave intervals from 63  Hz to 16  kHz;  General Measure No  0111 -OOP -C087 -18 
65  in tests of class  2 sound level meters:  
eight nominal frequencies in octave intervals from 63  Hz to 8  kHz;  
 deviation in frequency characteristics of the microphone in the reference direction in a free field 
or in a field with random sound incidence from stable frequency characteristics;  
 average effects of reflections from the body of the sound level meter and s ound deflection around 
the microphone and pre -amplifier;  
 if relevant, the average influence of the wind protection cover and any accessories of the wind 
protection cover which are part of the sound level meter’s configuration in normal use on the 
frequency  characteristics of a typical microphone.  
7.12 Frequency and time weighting at 1  kHz 
7.13 Long -term stability  
7.14 Amplitude characteristic linearity in a reference measurement range  
7.15 Amplitude characteristic linearity including a measurement range swi tch  
7.16 Response to tone impulses  
 maximum sound pressure level with  time weighting F;  
 maximum sound pressure level with  time weighting S; or  
 sound exposure level.  
7.17 Peak sound pressure level C  
7.18 Overexcitation indication  
NOTE: The relative levels of input signals with a positive and negative half period may be determined from the setting of the input 
signal attenuator.  
7.19 Stability at high levels  
7.19.1 The stability of a sound level meter to work continuously in response to a high signal level without 
significant changes in sensitivity is evaluated from the difference between the sound pressure levels A 
indicated in the response to a continuous signal with a frequency of 1  kHz connected at the beginning 
and end of a long -term exposure period wit h a signal lasting 5  minutes.  
7.19.2 The level of the continuous electrical input signal must correspond to the level required when 
displaying a sound pressure level which is 1  dB lower than the upper limit of the linearity range at a 
frequency of 1  kHz in  the measurement range with lowest sensitivity. It is permissible for the indicated 
sound pressure level to be the equivalent sound pressure level for 10  seconds, the sound pressure level 
with time characteristic F or sound pressure level with time charact eristic S.  
7.19.3 The difference measured between the initial and final indication of sound pressure level A must 
not exceed the acceptance limits specified in the technical requirements for sound level meters.  General Measure No  0111 -OOP -C087 -18 
66 8 Examination of the specified measuring instrument  
During examination of verified measuring instruments conducted in accordance with §  11a Act on 
Metrology, this examination shall, at the request of a party whose interests may be affected by improper 
measurement, be conducted in the same range a s the follow -up verification pursuant to Chapter  7. 
9 Notified standards  
For the purposes of specifying the metrological and technical requirements for measuring instruments 
and specifying the testing methods for their type approval and verification arisin g from this General 
Measure, the CMI shall notify Czech technical standards, other technical standards or technical 
documents of international or foreign organisations, or other technical documents containing more 
detailed technical requirements (hereinaft er ‘notified standards’). The CMI shall publish a list of these 
notified standards attached to the relevant measures, together with the general measure, in a manner 
accessible to the public (on www.cmi.cz ). 
Compliance with notified standards or parts thereof is considered, to the extent and under the conditions 
stipulated by a general measure, to be compliance with the requirements stipulated by this measure to 
which these standards or parts thereof apply.  
Compliance wi th notified standards is one way of demonstrating compliance with the requirements. 
These requirements may also be met by using another technical solution guaranteeing an equivalent or 
higher level of protection of legitimate interests.  
II. 
G R O U N D S 
The CMI issues, pursuant to §  14(1)(j) of the Metrology Act, for the implementation §  6(2), §  9(1) and 
(9) as well as §  11a(3) of the Metrology Act, this General Measure, stipulating metrological and 
technical requirements for specified measuring devices an d test methods for type approval for 
verification of the following specified measuring devices – ‘sound -measuring instruments of classes  1 
and 2, bandwidth filters, measurement microphones’.  
Under item  6.1.1 Class  1 and 2 Sound -measuring instruments, furt hermore under item  6.1.2 Bandwidth 
filters and under item  6.1.4 Measurement microphones in the Annex ‘List of the Types of Specified 
Measuring Instruments’ to Implementing Decree  No 345/2002 specifying the measuring instruments 
whose verification is mandat ory and measuring instruments subject to type approval, as amended, this 
type of measuring instrument is classified as an instrument subject to mandatory verification.  
This legislation (General Measure) will be notified in accordance with Directive  (EU)  2015/1535 of the 
European Parliament and of the Council of 9  September  2015 laying down a procedure for the provision 
of information in the field of technical regulations and of rules on Information Society services.  
III. 
I N S T R U C T I O N S 
In accordan ce with §  172(l) APC, in conjunction with §  39(l) APC, the CMI has stipulated a time limit 
for comments of 30  days from the date of posting the draft on the official notice board. Comments 
submitted after this time limit will not be considered.  
The person s concerned are hereby invited to comment on this general draft measure. With regard to the 
provisions of § 172(4) APC, comments are to be submitted in writing.  General Measure No  0111 -OOP -C087 -18 
67 Pursuant to the provisions of § 174(1) APC, in conjunction with the provisions of § 37(1) APC, it must 
be clearly stated who is submitting the comments, which general measure the comments concern, how 
the draft contradicts legislation or how the general measure is inaccurate. The comments must also 
contain the signature of the person making the comm ents.  
The supporting documents for this draft General Measure may be consulted at the Czech Metrology 
Institute, Legal Metrology Department, Okružní 31, 638 00 Brno, after making arrangements by 
telephone.  
This draft General Measure shall be posted for 15  days.  
 
 
 
 
 
 
 
 ................................ .......................   
RNDr. Pavel Klenovský  
Director -General  
 
 
 
Person responsible for accuracy: Mgr. Tomáš Hendrych  
 
Posted on:  
Signature of the authorised person confirming posting:  ................................ ..............    
 
Removed on:  
Signature of the authorised person confirming removal:  ................................ ............