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

Acoustics of multipurpose halls in Croatia
Marko HORVAT; Kristian JAMBROŠIĆ
University of Zagreb, Faculty of Electrical Engineering and Computing, Croatia

ABSTRACTIn the modern-day era, halls are usually built to host a variety of events that can range from movie projections,congresses and meetings, theatre plays, sporting events, music performances in various genres, etc., all of itwith or without sound reinforcement. Each type of event requires specific acoustical conditions in the hall,which makes the acoustics of a multipurpose hall a challenge to be dealt with mostly by making compromises.
In smaller communities, there is often only one hall large enough to accommodate all the visitors interested inattending an event, usually a cultural center or a sports hall of a school. However, the trend of building
multipurpose halls is present in cities as well, in order to use such spaces as much and as often as possible, tomaintain their self-sustainability. To address the acoustics of multipurpose halls in Croatia and make an
overview, this paper gives a comparison of basic acoustical parameters of 16 different halls. The parameters
were either measured as a way of acoustical analysis, or simulated during the acoustic design process. The
acoustics of these halls is analyzed with regard to their size, intended use, and the values of relevant
acoustical parameters.
Keywords: Room acoustics, Multipurpose halls

1. INTRODUCTION
The design of public performance spaces rarely aims to serve a single purpose, i.e. these spaces are
required to host many different types of events. Big cities can afford to build dedicated concert halls,
conference centers, etc., but even they resort to building multipurpose halls or using existing ones forany number of events. Smaller communities do not have much of a choice, as there is often only one
public space at their disposal. For example, a small town will want to use the sports hall of its
elementary school, or a small concert hall of the local music school, or a movie theater for different
kinds of program. Private investors, who build halls almost exclusively for commercial use, often
demand to have an acoustically favorable space for different types of events.
The challenge in designing a multipurpose hall is reflected in identifying all possible uses, i.e.
types of events the hall is to host, in adding weight to each individual use according to its frequency,
importance, and other factors, and, finally, in deciding on a compromise that is required to obtain themost favorable acoustics for all considered cases. The design of single-purpose spaces allows thedesigner to aim for optimal acoustics of the space they are designing, whereas the designers ofmultipurpose halls will strive to achieve the least-objectionable acoustic conditions for all intended
uses.
The main motivation for this paper are the challenges the authors have dealt with over the years in
the area of multipurpose hall design. A similar paper (1) was written by the authors on the acoustics ofchurches in Croatia and its changes over time. The encouraging trend is the growing interest thearchitects show for the acoustics of the spaces they design, multipurpose halls included. This
improvement has happened over the years, starting from the situation where visual appeal was highly
appreciated, but acoustics was often completely ignored, resulting in a space with visually spectaculararchitectural design, but unusable in practice due to bad acoustics.
The data that contains the values of the most common acoustical parameters was either measured or
simulated for all included spaces, or both, depending on the task laid out before the authors in eachparticular case. The said data was obtained by simulation in the acoustic design process, or measured
in either the initial stage or the control stage of these projects. Reverberation time was chosen as themost relevant parameter for assessing the acoustical conditions in examined halls, especially because
relevant standards and recommendations use reverberation time as the parameter of interest, andstipulate its optimal values for any given situation. Size (volume) and purpose(s) of the investigated8031

spaces are also taken into account. The seating or standing capacity of a given hall is also recognized
as an important parameter, leading to the specific volume, i.e. volume per person.

2. THE DESCRIPTION OF THE INVESTIGATED HALLS
Due to a variety of uses that can be defined for each investigated hall, the halls were sorted together
in the following way: firstly, they were divided based on their purpose. This division took into accountthe primary purpose of the halls, i.e. whether the dominant program content in their most common use
is speech or music. The music group was further subdivided to classical music and modern music, andthe speech group was subdivided to sports and other speech content. The secondary purpose of thehalls is complementary to the primary one, i.e. if the primary purpose of a hall is to host music -based
events, then its secondary purpose is to be able to host speech-based events as well, and vice versa. The
following subsection give a short description of the investigated halls. If a facility has several halls,
their descriptions are grouped together in the same subsection.
2.1 The concert hall of Albert Štriga Music School in Križevci
This concert hall is frequently used for teaching and concert performance. It is a part of theaforementioned music school located in the Croatian House building in Križevci, built in 1914. The
hall was measured in its current state, with the intent of the school to implement some kind of acoustic
treatment in the future. The hall is quite small and made mostly of hard materials. The exception arelarge windows and the ceiling that provide some absorption of low frequencies, and the upholsteredseats that introduce some absorption at middle and high frequencies. As a space primarily used forteaching purposes, the hall requires acoustics treatment to shorten the reverberation, thus making thecommunication between teachers and pupils easier, and providing the clarity required to hear all fastnotes clearly.

Figure 1 – Albert Štriga hall (left), and Croatian House hall (right) in its present state
2.2 The Croatian House hall in Split
The Croatian House hall in Split is meant to become the representative concert hall for the city of
Split, with the primary purpose of hosting all kinds of chamber music ensembles. The building itself
and the hall within was built in 1908 and has suffered a number of changes since then. Acoustic
conditions in the hall were measured in 2014, in what was then the current state, i.e. the hall and theentire building were in a quite run-down state, and in need of restoration. The building is being
restored, and it is expected to host the concert season in the year 2020/2021. The values ofreverberation time presented here are the ones simulated for the purpose of thorough restoration. Dueto the status of the building as a cultural and architectural monument, only discrete acoustic treatment
was possible. Therefore, appropriate chairs were selected as a mean of treatment. The hall is a classic
shoebox type. Besides its primary purpose as a concert hall, the hall is to host different kinds ofspeech-based events, such as celebrations, meetings, presentations, etc.
2.3 Blagoje Bersa concert hall of the Music Academy in Zagreb
This concert hall was opened in 2016 as a space that would be used primarily for all kinds of student
projects and classical concert performances. However, initial demands on acoustic design were
overwhelming; to ensure financial sustainability, the wish of the investors was that the hall be able tohost just about any event and/or performance imaginable, serving as a movie theater, theater, opera
house, concert hall, conference hall, etc. In 2018, an organ was installed in the hall. Although theinitial acoustic design was aiming at a reverberation time of about 1.5 seconds, the final state of the2804

hall, as measured just before the grand opening, is characterized with a much shorter reverberation
time. The hall itself has a changeable configuration that allows the size of the stage to be c hanged asneeded, and even the orchestra pit to be opened for opera performances. These changes demand that apart of the audience area be sacrificed, so number of seats varies. The net volume of the hall also
depends on its configuration.

Figure 2 – Blagoje Bersa concert hall (left) (2), and Vatroslav Lisinski concert hall (right) (3)2.4 Vatroslav Lisinski concert hall in Zagreb
Vatroslav Lisinski concert hall was opened in 1973 as the first concert hall in Zagreb designed
exclusively to host symphonic music performances. To this day, it is still the most representative spacefor classical music performances, despite some drawbacks regarding its design. Extensive
measurements of acoustical parameters were made, on request of the management of the hall. Apartfrom classical music, the hall hosts modern music performances, as well as all kinds of large meetings,
conferences, and various ceremonies as speech-based events. Ballet and opera performances are
sometimes organized as well.
2.5 Pogon - Zagreb Centre for Independent Culture and YouthThis facility strives to promote out-of-mainstream cultural and other events. The facility has threespaces that were encompassed in the acoustics design project made by the authors. Two of them,
namely, the great and the small hall are in use, while the club as the third space requires renovation.
The facility hosts a variety of events, from festivals and concerts , theater performances, to lectures,conferences, movie projections, workshops, etc.
The great hall is the largest of the three spaces, used mostly for popular music concerts.
The small hall is adequate for small events, such as workshops, rehearsals, presentations, etc.
The club space was also included in the acoustic project, as the intention is for it to be used mostly
for club music performances.

Figure 3 – The great hall (left) and the small hall (right) of Pogon (4)2.6

Stara mehanika – Educational center for entrepreneurship and lifelong learning in

PulaThis facility is still in the design stage. The intent is to create a representative facility in the townof Pula for hosting a variety of different events, from theater to modern music, but also entertainment
event such as stand-up comedy, puppet shows, magicians, cabaret, as well as congresses, lectures,round tables, fashion shows, etc. Two spaces are to be built, namely, the great hall and the small hall.

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The great hall is to become a facility to host large-scale indoor events, mainly concerts involving
various modern types of music.
The small hall is designed primarily for small-scale events, from entertainment to various kinds ofmeetings, presentations, etc.
2.7 Bunker hall in Samobor
The Bunker hall was originally a warehouse within a military installation that was eventually
abandoned and its facilities made available for public use. It was built almost exclusively out ofreinforced concrete, and its initial reverberation time of 7 seconds was inappropriate for any kind ofuse. The desire of the town council was to have a hall that would be used primarily for concerts,
hosting performers from different genres of modern music. The hall was acoustically treated, and thereverberation time, as shown below, has been significantly reduced.

Figure 4 – Bunker hall
2.8 The hall of the Diplomat hotel in Zagreb
The grand hall of the Diplomat hotel is to be used mainly for weddings and other types ofcelebrations where modern music performances are expected. Its secondary use is extended toconferences, meetings, presentations, etc. The hall consists of the main space, a side annex, and agallery, which can be connected or function separately. The configuration shown here assumes that all
three spaces are used together as a whole.
2.9 The Croatian House hall in Glina
This hall is to be renovated, and appropriate acoustic treatment has been proposed. Its primary
purpose is to serve as a venue for different kinds of meetings, presentations, etc. Additionally, the hall
is to be used for small ensemble performances, and any other events important to a small town such as
Glina.
2.10 The movie theater hall in Samobor
The freshly renovated public hall in Samobor has always been used as a central place for all kindsof public happenings. It is most commonly used as a movie theater, but it also hosts various musicalevents that are of considerable importance to the town and its people. In light of that, the hall has beenrenovated and acoustic treatment has been applied. A control meas urement of acoustical parameters
has been made.

Figure 5 – Movie theater Samobor (left), and the hall in St. Thomas church (right)

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2.11 The hall in St. Thomas church in Mostar
The hall of St. Thomas Church in Mostar, Bosnia and Herzegovina, is another example of amultipurpose hall designed primarily for speech-based events, but also as a performance space for all
kinds of small-ensemble shows. The hall is in the design stage and is to be constructed.
2.12 The Ivan Benković sports hall in Dugo Selo
This sports hall is used primarily for teaching in physical education, and the occasional matches indifferent kinds of team sports. The floor is large enough to hold a full -size handball court. It can bedivided into three equal-sized sections, each of them large enough to hold a full-size basketball court.
Due to space restriction, the hall only has small, foldable bleachers. As the largest indoor space in the
town of Dugo Selo, it is frequently used for all kinds of public gatherings. The reverberation time in its
initial state was excessive, so some acoustic treatment was applied, thus reducing the reverberation.
However, the reverberation time is still too long, and further steps are required. Both cases arepresented in the paper.
2.13 The Ljudevit Modec sports hall in Križevci
This sports hall meets the same criteria as the one described in the previous section, regarding its
size and the most common uses. The main difference is in the design of the roof, which is made of lightsandwich material, as opposed to the roof of the Ivan Benković hall that is made of p re-fabricatedconcrete plates. Consequently, low-frequency absorption is quite high. The hall has both fixed stands
and foldable bleachers that extend along the length of the hall on both sides . To house the audiencearea, the hall has been enlarged, and it is the largest space considered in this investigation.

Figure 6 – Ivan Benković sports hall (left), and Ljudevit Modec sports hall (right)

3. ACOUSTICAL PARAMETERS OF THE HALLS AND DISCUSSION
This section presents the most important parameters that characterize the investigated halls. The
halls were grouped according to their primary purpose. Four groups were established: halls forclassical music, halls for modern music, halls for speech, and sports halls. Location was given for eachhall, along with its volume as a measure of size, the mid-frequency single-number reverberation time
as defined in (5), the bass ratio as the measure of reverberation balance between low and middle
frequencies, the seating or standing capacity. For brevity, the primary and secondary purpose of thehalls was roughly divided into speech-based events and music-based ones, without further details.
The described data is shown in Table 1.
Table 1 – Relevant parameters of the investigated halls. The halls are sorted by their primary purpose, andthen by size.
Hall

Town

Volume RT60500 - 1k Bass
(m3)
(s)
Ratio

Capacity(persons)

1 Albert Štriga concert hallKriževci

660

2.15

1.25

91

2 Croatian House concert hall

Split

1650

1.63

1.09

250

3 Blagoje Bersa concert hall

Zagreb

2350

0.91

0.92

246

PurposePrimary

SecondaryClassical music

Speech8075

4 Vatroslav Lisinski concert hall

Zagreb

16000

1.78

0.83

1850

5 Pogon - small hall

Zagreb

404

0.57

1.51

50

6 Pogon - club

Zagreb

671

0.57

1.15

334

7 Stara Mehanika - small hall

Pula

918

0.89

0.97

120

8 Diplomat hotel - wedding hall

Zagreb

2040

0.72

1.48

221

9 Bunker hallSamobor

2600

1.12

1.37

1000

10 Pogon - great hall

Zagreb

3339

1.27

0.84

1200

Pula

11 Stara Mehanika - great hall

10500

1.18

1.03

600

Dugo Selo 13800

6.44

0.86

100

Dugo Selo 13800

4.57

0.90

100

Križevci

18600

5.41

0.56

600

15 Croatian House hall

Glina

1536

0.89

1.11

244

16 Movie theater hallSamobor

2095

0.81

1.21

225

17 Hall of St.Thomas church

Mostar

2140

0.89

1.08

300

12 Ivan Benković sports hall –before treatment
13 Ivan Benković sports hall –after treatment
14 Ljudevit Modec sports hallModern music

SpeechSportsMusic

SpeechMusic

Figure 7 shows the mid-frequency single-number reverberation time vs. room volume for all
investigated halls. To assess the adequacy of each hall for its primary purpose, the r ecommendations
from DIN 18041:2016 (6), usually used in defining the optimal acoustic conditions for a given space,
are taken as guidelines. All the halls were eventually grouped in three groups: halls for unamplified
music, halls for speech and amplified music, and sports halls. For clearer display of the data, the data
for sports halls was not shown in the figure, as it greatly exceeds the recommended value of 2 seconds
for sports halls larger than 10000 m 3.

Figure 7 – Mid-frequency single number reverberation time vs. room volume for classical concert halls (redcircles), modern music halls (blue circles), and speech halls (blue diamonds).
As shown in Figure 7, the reverberation time in the halls intended primarily for speech andamplified music does not deviate much from the values recommended by DIN 18041. The exception ishall 10, i.e. the great hall of Pogon, in which there were limitations as to what materials can be appliedin the hall. As the result, a reverberation time higher than recommended was obtained. In all othercases, the designed reverberation time was achieved using common materials, and the designed values
match quite closely to the recommended ones. The four concert halls, on the other hand, show
considerable differences when it comes to meeting the DIN 18041 recommendations. Hall 1, i.e. theconcert hall of Albert Štriga Music School is the smallest one, yet it has the longest reverberation time.
The wish of the users is to shorten it by implementing acoustic treatment, as they report problems bothin teaching, when good communication between the teacher and the student is crucial, and in preparing
the students for performance. The main complaint is that the students love excessive reverberation

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because it conceals certain mistakes in playing or singing, and they do not have to make an effort toplay or sing loud, both of which only makes it more difficult for them when they play in a moreacoustically controlled (damped) hall. Hall 3, i.e. Blagoje Bersa concert hall of the Music Academy in
Zagreb has too short a reverberation time to be a true concert hall, due to certain technical issues that
resulted in too much sound absorption introduced in the hall. While the players of wind and brass
instruments seem to love such acoustics, the players of string instruments often complain about thehall being too “dead”. The hall serves quite nicely for all kinds of speech -based events, but also as apractice hall for orchestra rehearsals, as the short reverberation is quite unforgiving and reveals all
mistakes made during playing or singing. Short reverberation also enables reasonably dry recordings
to be made in the hall.
Figures 8 and 9 present the reverberation time as a function of frequency. The reverberation time
was normalized to its mid-frequency single-number value so that similar halls can be directlycompared, regarding their frequency-dependent behavior. Figure 8 shows the normalized
reverberation time in concert halls and sports halls, whereas Figure 9 shows the same for small (<1000m3 ) and large (> 1000 m 3 ) halls for modern music, and for the halls for speech.

Figure 8 – Normalized reverberation time vs. frequency, shown for concert halls (red lines), and sports halls(green lines). The numbers in the legend correspond to the number of the hall as listed in Table 1

Figure 9 – Normalized reverberation time vs. frequency, shown for small modern music halls (blue lines),larger modern music halls (cyan lines), and halls for speech (magenta lines). The numbers in the legend
correspond to the number of the hall as listed in Table 1
The data shown in Figure 8 reveals that the concert hall of Albert Štriga Music School suffers fromserious imbalance between low- and high-frequency reverberation. Additional steps have to be taken
in order to shorten the reverberation time at low and middle frequencies, thereby achieving the8097

required balance, and shortening the overall reverberation time. The Croatian House concert hall is in
the implementation stage, and the data shows a well-balanced design that will yield a proper
reverberation time and the required warmth for classical, mostly chamber music, while maintaining
enough speech intelligibility for speech-based events. The remaining two concert halls, i.e. theBlagoje Bersa and the Vatroslav Lisinski concert hall, seem to suffer from the same problem, with their
low-frequency reverberation not being long enough to provide the warmth that classical musicrequires.
The reverberation in both sports halls, as shown in Table 1 and Figure 8, is excessive, and reaches
its highest values at middle frequencies. This finding is a very fortunate circumstance, as any
additional absorption will have to be introduced in the form of mid-frequency absorbers. In alreadyfinished halls, this is far easier to achieve than to have to deal with excessive low-frequency
reverberation. During the measurements conducted in these halls, it was found that direct speechcommunication across the hall was very difficult, but still possible in the Ljudevit Modec hall (hall 14),due to relatively short low-frequency reverberation. In Ivan Benković hall (two cases; hall 12 before
treatment, and hall 13 after treatment), such communication was impossible before treatment, andbarely manageable after it. Both findings suggest that further acous tic treatment measures have to betaken, if the halls are to meet the relevant criteria regarding their acoustics.
The data shown in Figure 9 reveals that the halls designed primarily for speech -based events (halls
15, 16, and 17) have a well-balanced reverberation throughout the entire frequency range, as intended,with the values of the bass ratio of around 1.1 to 1.2.
The halls designed primarily for modern music performance (halls 5 to 11) over electroacoustic
systems, i.e. amplified music, should follow the same criterion applied for halls for speech -based
events, as amplified music requires reasonably short and well-balanced reverberation. In some cases,
it was not possible to meet these criteria in full due to technical and financial limitations on available
space and choice of finishing materials. As a result, these halls have considerably long reverberation,
especially in the 63 Hz octave band, which is usually not even considered, and it should be, given thatthe energy content of modern music material is considerable in this particular frequency band. In thenext design step, further steps will need to be taken to correct this issue, if possible.

4. CONCLUSIONSThis paper collects the results of the efforts made by the authors to design and/or evaluate different
halls in Croatia over the past ten years. Originally, many of them were intended to be used for a single
type of events, but their use has been extended to a number of different programs over the years. The
reasons for this range from technical to financial, and in many cases, it is a mere question ofavailability of a given space. Acoustic design of multipurpose spaces depends on the range offoreseeable purposes, and is rarely aimed at achieving optimal acoustics for one particular purpose.
Instead, the design process heavily relies on compromise, resulting in “equally bad” acoustics for all
intended types of program. The design process also suffers from further limitations imposed byarchitects, fire safety experts, and other experts involved in the overall design process. Theselimitations result in narrowing the range of materials to be used, and the range of surfaces on whichthese materials can be placed. As a part of further work, the intent of the authors is to promote
cooperation between all interested parties in multipurpose hall design in as early stage as possible.

REFERENCES
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Adria Acoustics Association; 20-21 September 2018; Zagreb, Croatia 2018. p. 186-94.
2. http://www.muza.unizg.hr, last accessed on 29 May 2019
3. http://www.lisinski.hr, last accessed on 29 May 2019
4. http://www.pogon.hr, last accessed on 29 May 2019
5. ISO 3382-1:2009 - Acoustics - Measurement of room acoustic parameters - Part 1: Performance spaces
6. DIN 18041:2016 - Acoustical quality in rooms - requirements, recommendations and instructions forplanning

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