PROCEEDINGS of the
23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

The new Italian standard UNI 11532 on acoustics for schools
Arianna ASTOLFI1; Linda PARATI2; Dario D’ORAZIO3; Massimo GARAI3
1

Department of Energy, Politecnico di Torino, Turin, Italy23

Acustica Parati & Co., Crema, Italy

School of Engineering and Architecture, University of Bologna, Italy

ABSTRACTIn Italy, the new UNI 11532 standard introduces requirements for acoustic comfort in different
building typologies such as schools, offices and hospitals. In March 2018 the UNI 11532 - Part 1"General requirements" was published, which includes the main descriptors related to noise, room
acoustics and speech intelligibility to be considered for the design and verification phases. The
drafting of Part 2, dedicated to schools, is now completed. This standard is voluntary for private
constructions, but mandatory in the public sphere following the issue of the Ministerial Decree“Minimum Environmental Criteria (Criteri Ambientali Minimi or “CAM”) for the awarding of designand construction services for new construction, renovation and maintenance of public buildings”,
dated 11 October 2017. The Decree explicitly refers to the UNI 11532 standard for the requirements to
be guaranteed in public procurement. The underlying principles and criteria of the new standard in thecase of schools, as well as comparisons with other standards in Europe, will be presented and discussed
in this work.
Keywords: Classroom acoustics, Italian standard, Acoustic comfort, Speech intelligibility

1. INTRODUCTION
At the beginning of 2017 a new regulation has been issued in Italy for public buildings, making, forthe first time, a distinction between public and private ones. It is the Ministerial Decree “Minimum
Environmental Criteria (Criteri Ambientali Minimi or “CAM”) for the awarding of design andconstruction services for new construction, renovation and maintenance of public buildings”, dated 11
October 2017.
The new regulation goes more deeply into details distinguishing sound insulation and acoustical
comfort and recalling technical standards, whose contents become compulsory. This standard isvoluntary for private constructions, but mandatory in the public sphere.
Specifically, it explicitly refers to the Technical Standards UNI 11367 “Acoustic classification ofbuildings units – Evaluation procedure and in situ measurements” [1] for sound insulation and to the
UNI 11532 “Internal acoustical characteristics of confined spaces” for acoustical comfort.
Just after the publications of the new CAM regulation in 2017, it was immediately clear for theexperts at the Italian standardization body that the T.S. UNI 11532:2014 needed to be reviewed forbetter complying with the new regulation expectations. Moreover, the public tenders are based on the
C.A.M.; this means that their contents must be explicit, that is i) clear goals, ii) specific predicting
methods and iii) practical verification methods.
Due to the requirements listed above, the review transformed the original standard into a package ofstandards. Part 1 (published in 2018) is devoted to general issues, while part 2 (expected to be
published in October 2019) is intended for schools, where the main goal is to achieve a good speech
intelligibility. The end users will be teachers (vocal effort reduced) and students (attention
encouraged).
The main indices to be verified are Reverberation Time (RT) and STI (Speech Transmission Index),
12
3

arianna.astolfi@polito.it
l.parati@acusticaparati.it

dario.dorazio@unibo.it, massimo.garai@unibo.it

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but in order to achieve the goals, background noise level must be also considered. The suitable values
for RT are those listed in the DIN 18041:2016 [2], while for STI they have been referred to the UNI
technical committee experience.
Background noise is a complicate issue in educational buildings. Basically, it can be defined as “allthe other signals (noise) different from the one of interest”. In literature few information is given, suchas the Student Activity Noise [3]; basically, background noise is due to environmental noise (external
noise), students’ behavior, and noise from service equipment.
Background noise is one of the most important factors affecting speech intelligibility. As a matterof fact, STI depends on the signal to noise ratio (SNR). Here is the main point: the new UNI 11532
standard will be the reference document for public tenders, being cited in the CAM decree, and thus
everything in it must be clear, predictable and measurable. On the other hand, service equipment andenvironmental noise are the only predictable aspects of background noise, whi le activity noise isneglected at the design and verification phases.
What seems to be the best way to solve the problem is to consider the teacher's vocal effort asNormal based on ANSI 3.5 [4], i.e. having LAeq equal to 60 dB(A) at 1 m, for rooms below 250 m3,
increased up to Raised, i.e. 70 dB(A) , for rooms above 250 m 3, with and without amplification
systems; then, the room is designed so that, thanks to the optimal values of reverberation time andsound pressure level from service equipment (i.e. HVAC systems) and outdoor noise, a STI value
suitable for special hearing or communication needs can be expected.

2. REQUIREMENTS
In relation to the activities the room is designed for, interventions are defined and, in cascade, thelimit values, which already include the measurement uncertainty.
2.1 Identification of the environment in relation to its use
Table 1 shows the categories of the school environments in relation to their use covered by the UNI
11532 Part 2 Standard, with the objectives to be reached according to the activity carried out in side therooms. Table 2 shows the detailed description of use for the categories from A1 to A5.
Table 1 – Categories of the school environments in relation to the use
Category

Activity

Interventions

A1

Music

Objective achieved with integrated

A2

Speech/Conference rooms

design of geometries, furnishings,

A3

Teaching/Speech communication/Convention

control of residual noiserooms/Interaction rooms
A4

Teaching/Speech communication, Special rooms
included

A5

Sport

A6

Areas and spaces not intended for learning andObjective achieved with soundlibraries

absorption and control of residual
noise

2.2 Reference values for sound insulation and noise from service equipment
Reference values for the following acoustic descriptors are shown in UNI 11367, and correspond tothe values identified as “superior performance”:- weighted apparent sound reduction index, R ’ w ;- weighted standardized sound level difference of a façade, D 2m,nT,w ;- weighted standardized sound level difference D nT,;
- weighted normalized impact sound pressure level in field, L ’ nw ;- equivalent A-weighted sound pressure level in a room due to the sound produced by6970

continuously operating equipment or machinery in the building (e.g HVAC systems), installedout of the room under consideration, standardized to a reference reverberation time, L ic ;- A-weighted maximum sound pressure level in a room due to the sound produced by
non-continuously operating equipment or machinery in the building, (e.g. waste water flow, liftsetc.), installed out of the room under consideration, standardized to a reference reverberation
time, Lid .
Table 2 – Detailed description of use for the categories from A1 to A5
Detailed description of use
Category
A1

Description of use

Qualitative objective

Examples

Music

Good

Mostly musicalnon-amplified

music;

performances

limitedspeechacoustics

forMusic teaching rooms with live
playing of music and singing

comprehension
A2

Speech/Conferences

High

grade

Speech presentations whereintelligibilityofspeechClassrooms, lecture theatresofspeechClassrooms, lecture theatres

there is a frontal speaker
A3

A3.1

Class A2 environments forHighpeople who have hearing

intelligibility

impairment or non-native

peoplespeakers

impairment or non-nativeor

specialclassrooms

degree

even

with

for

hearing

speakers or with language
differences

A3.2

SpeechHighdegreeCommunication with theintelligibility

simultaneous presence ofmultipleseveral people speaking insimultaneouslyofspeechClassrooms,

classrooms

for

even

with

interviews,

classroomsforspeakers

seminars, classrooms for study
or work groups, laboratories,

the classroom

administrative offices, teachers’
rooms and similar

A4

More people talking in theHighspeechClassrooms,

classroomsforroom (like Category A3.2)

intelligibility with multiple

interviews,

classrooms

forand intended for people

speakers

simultaneously,

seminars, classrooms for study

with special needs (special

and for people with hearing

or work groups, laboratories,classrooms)

impairment or non-native

administrative offices, teachers’

specialspeakers or with language

rooms and similar. Rooms forvolumedifferences

videoconferences

Excludingclassrooms

withdegreeofover 500 m3, or for musicalactivities
A5

Sports: swimming pools andSpeechcommunication

Pool and gyms for use as sports

gyms and similar

possiblebut

environments in general

at

short

distances6971

2.3 Reference values for STI
This descriptor applies to the categories A1, A2, A3 and A4 in Table 1 and Table 2. For
environments smaller than 250 m 3 as an alternative to STI the descriptor C 50 can be used. The
reference values for STI in furnished and unoccupied environments are shown in Table 3. These values
refer to the arithmetic average of the measured values in the measurement positions as shown in Figure
1 and Table 5.
For STI and C 50 measurements, a sound source with a directivity approximating that of a humanspeaker should be used, in compliance with ITU RECOMMENDATION P.58 [5], or ITU-T P.51
-compliant speakers [6].
Table 3 – Reference values for STI
V< 250 m3

V≥ 250 m3

Without amplification system≥ 0.55 with source output at 1 m≥ 0.50 with source output at 1 m

or with system off

on axis equal to 60 dB(A).

on axis equal to 70 dB(A).

With amplification system≥ 0.60 with source output as in normal conditions of operation of theamplification system

2.4 Reference values for C50
The C50 descriptor can be used as an alternative to STI for categories A1, A2, A3 and A4
exclusively for environments smaller than 250 m 3 . For environments with V ≥ 250 m 3 only STI isapplicable. The reference values for C 50 are shown in Table 4. They refer to furnished and empty rooms.
The limit values refer to the arithmetic average of the measured values in the measurement positions
shown in Figure 1 and Table 5. The C50 values in each single measurement position are obtained as thearithmetic average of the measured values in the octave bands 500-1000-2000 Hz.
Table 4 – Reference values for C50< 250 m3
Without amplification system or with system off≥ 2 dB

Figure 1 – Examples of measurement positions in classrooms with and without amplification system

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Table 5 – Mandatory and optional measurement positions for speech intelligibility

Positions

V< 250 m3

V≥ 250 m3

STI – C50

STI

Without amplification system orWithout amplification system orWith amplification

with system off

with system off

systemoptional

mandatory

mandatory

x

x

x

x

x

x

x

x

x

mandatory

1
2

x

3
4

x
x

5

x

2.5 Reference values for reverberation time
The optimal reverberation time, T ott , corresponding to a conventional room occupation of 80%,
with the exception of category A5, is determined according to the specific room activity as a functionof the room volume, according to the formulas shown in Table 6. Figure 2 shows the dependence of the
optimal reverberation time from the volume, and Figure 3 shows the T ott frequency dependence.
Formulas and graphs derive from DIN 18041.
Table 6 – Tott (s) calculation formulas for categories from A1 to A5
Category

80% occupied room

A1

Tott,A1 = (0.45logV + 0.07)

30 m3 ≤ V < 1000 m3

A2

Tott,A2 = (0.37logV – 0.14)

50 m3 ≤ V < 5000 m3

A3

Tott,A3 = (0.32logV – 0.17)

30 m3 ≤ V < 5000 m3

A4

Tott,A4 = (0.26logV – 0.14)

30 m3 ≤ V < 500 m3

Category
A5

Unoccupied room
Tott,A5 = (0.75logV – 1.00)

200 m3 ≤ V < 10000 m3

Tott,A5 = 2.00

V ≥ 10000 m3

As said, for categories A1, A2, A3 and A4 the requirements for the reverberation time refer to thefurnished and occupied state at 80% of the capacity. The conversion between the values in theoccupied status to the values in the unoccupied but furnished state, as at the time of the verification,must be carried out in accordance with Eq. 1, in the octave bands between 125 Hz and 4000 Hz:ܶ௜௡௢௖௖ ൌܶ௢௖௖ο‫ܣ‬௣௘௥௦ͳ െ ܶ௢௖௖
ͲǤͳ͸ܸ

(1)

where:
Tocc is the optimal reverberation time for the room occupied at 80%, in s;
Tinocc is the optimal reverberation time for the unoccupied, furnished room, in s;
V is the volume of the room, in m3;
Δ‫ܣ‬pers is the area of equivalent absorption of persons, in m2.
For the category A5 only the octave bands between 250 Hz and 2000 Hz are considered. For the6973

category A6, the reference values are always considered for furnished and unoccupied conditions andthe optimal value of the reverberation time is a function of the equivalent absorption area, in m2, and of
the geometric characteristics of the environment (volume and height).

Figure 2 – Dependence of the optimal reverberation time Tott from the volume and the mode of use

Figure 3 – Target range for Tott, as a function of frequency for the categories from A1 to A4
Table 7 – Reference values for Lic,int, NC and Lamb.
Lic,int

Mode of use

dB(A)

Lamb
dB(A)

3

Classrooms and libraries with V < 250 m

≤ 34

≤ 25

≤ 38

3

Classrooms and libraries with V ≥ 250 m

≤ 38

≤ 30

≤ 41

Single office

≤ 35

≤ 25

≤ 38

Exhibition environments, rooms for studying

≤ 45

≤ 35

≤ 48

Gyms, swimming pools, administrative offices, laboratories,

≤ 45

≤ 35

≤ 48

areas open to the public, canteens, corridors, reception / area

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NC

desk
2.6 Reference values for noise from continuous operation systems inside the room
In UNI 11532-2, the noise due to continuous operation systems, i.e. from HVAC systems, isexpressed by the descriptor L ic,int, which is defined as the energy spatial average of the L pu,c values
obtained at the measurement positions shown in Figure 1. L pu,c is the equivalent A-weighted soundpressure level at a specific position in a room due to the sound produced by equipment or machineryinstalled in the room under consideration, standardized to a reference reverberation t ime. Alternatively,
NC [7] limit values can be ensured. Table 7 shows the reference values for L ic,int and NC.
2.7 Reference values for environmental noise
The determination of the overall noise that occurs in the furnished and unoccupied room, isessential for a clear understanding of speech in the teacher-student relationship and of the speech
among pupils. The overall noise level in an environment, Lamb , is determined by:
1. Noise due to sources outside the school (noise from vehicular or railway traffic, noise fromcommercial or industrial activities, etc.);
2. Noise from continuous operation systems serving the environment (mechanical ventilation
systems, heating, cooling, vents, etc.).
The noise coming from continuously operating systems in the building, installed out of the room
under consideration, is subject to compliance with UNI 11367. The environmental noise level in theroom, Lamb , must comply with the limit values in Table 7.

3. PREDICTION AND VERIFICATION METHODS for STI, C50, T, Lpu,c and Lamb
3.1 Prediction methods
The prediction methods for STI, C 50 and reverberation time are reported in UNI 11532-1.
The prediction methods for STI refers to CEI EN 60268-16 [8]. Two methods are available: (1)calculation based on a predicted direct field, combined with an exponential reverberant decay;
statistically calculated reverberation times may be used here; (2) prediction based on a simulated
impulse response of the system in the acoustic space. Predictions based on simulated impulse response
offer a higher degree of precision. For the STI descriptor, the values obtained in the 4 kHz octave band
will also be extended to the 8 kHz octave band if data are not available.
C 50 can be determined as a function of the volume, V, of the reverberation time, T, and of t hesource-receiver distance, r, with the Barron & Lee theory [9], according the formula:(2)

The prediction method for calculating the reverberation time is described in EN 12354-6, while for
Lpu,c the reference standard is the EN 12354-5.
The indoor sound pressure level due to noise sources outside the school, i.e. the residual noise level,
is obtained from the external noise level, the sound insulation property of the façade and thereverberation time, according to Eq. (E.2) of EN 12354-3. Lamb is obtained from the logarithmic sum of
the residual noise level and the noise due to continuous operation systems in the room, Lic,int .
3.2 Verification methods
The verification method for STI is described in CEI EN 60268-16 [8], while for C 50 and T in EN
ISO 3382. The procedures and conditions for measuring the noise from HVAC systems for ordinary
environments are described in UNI 8199 [10].
The measured values of each quantity, before being compared with the reference values, must be
corrected with the measurement uncertainty as specified in the Standard. The comparison with the NC
curves must be carried out as usual without considering the measurement uncertainty.
The assessment of the measurement uncertainty is based on the experimental approach in terms of
repeatability and reproducibility, which leads to an evaluation of the typical uncertainty of a given

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measurement method based on inter-laboratory tests.

4. FINAL REMARKSThe new UNI 11532-2 builds on the previous experience in other European countries. For example,
the classification of the different spaces in relation to their use and the determination of the optimal
reverberation times are taken from DIN 18041 [2]. BB93 was a reference for many concepts andprocedures and also gave input the for establishing some limit values, like the indoor ambient noiselevel. However, all this was fitted to the Italian situation. For example, UNI experts had to consider thecase of a school building in the city center, exposed to high traffic noise levels, where windows cannot
be opened, and thus mechanical ventilation systems are installed. Regarding equipment noise, there no
single international standard covering all issues: limit values for both equipment external or internal to
the room under consideration, calculation procedures to be used at design stage consistent withprocedures for verification of the installed equipment etc. Therefore, prescriptions from national (e.g.
UNI 8199) and international (e.g. EN 12354-6) standards were harmonized. It was considered thatverifications must be done in empty rooms, because according to the law they can be used only after apositive verification, and thus an unambiguous link between the unoccupied and o ccupied conditions
had to be specified. Limit values were specified considering that in Italy most classrooms lack of a PA
system and many surfaces are not sound absorbing: linoleum or ceramic tiles on the floors, smoothwall for water cleaning etc. Last but not least, single parts of the standard are applicable to (partial)refurbishments of schools.

REFERENCES[1] UNI 11367 (2010) “Acustica in edilizia - Classificazione acustica delle unità immobiliari - Procedura divalutazione e verifica in opera”. (“Building acoustics - Acoustic classification of building units Evaluation procedure and in situ measurements”).
[2] DIN 18041 (2016). “Hörsamkeit in Räumen—Anforderungen Empfehlungen und Hinweise für die
Planung” (“Acoustic quality in rooms—specifications and instructions for the room acoustic design”)(German Institute for Standardisation, Berlin).
[3] Hodgson M, Rempel R, Kennedy S. Measurement and prediction of typical speech andbackground-noise levels in university classrooms during lectures. J. Acoust. Soc. Am. (1999);
105(1):226-233.
[4] ANSI/ASA S3.5-1997 (R2017). “Methods for Calculation of the Speech Intelligibility Index”.
[5] ITU Recommendation P.58 (1994) “Head and torso simulator for telephonometry”.
[6] ITU-T P.51 (1996), “Telephone transmission quality – Objective measuring apparatus – Artificial
mouth”.
[7] Schaffer ME. A Practical Guide to Noise and Vibration Control for HVAC Systems (SI), 2nd ed.,ASHRAE, 2011.
[8] CEI EN 60268-16 (2012). “Sound system equipment Part 16: Objective rating of speech intelligibility
by speech transmission index”.
[9] Barron M, Lee L-J. Energy relations in concert auditoriums, J. Acoust. Soc. Am. (1988);
848(2):618-628.
[10] UNI 8199 (2016). “Acustica in edilizia - Collaudo acustico di impianti a servizio di unità immobiliari Linee guida contrattuali e modalità di misurazione all’interno degli ambienti serviti.” (“Building
acoustics - Acoustic testing of service equipment in buildings - Contractual guidelines and measurement
methods inside served buildings”)

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