PROCEEDINGS of the23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

The preliminary study on subjective rating of different floors
characterised by Ln,w+CI,50-2500
Vojtech CHMELÍK1; Jakub BENKLEWSKI2; Monika RYCHTÁRIKOVÁ3; Dominik KISIĆ4; Kristian
JAMBROŠIĆ5; Marko HORVAT6; Herbert MUELLNER7
1

Department of Architecture, Faculty of Civil Engineering, The Slovak University of Technology, Bratislava,Slovakia.
2,7
3

TGM Versuchsanstalt, Fachbereich Akustik & Bauphysik, –Wexstraße 19 – 23, A-1200 Wien, Austria

KU Leuven, Faculty of Architecture, Hoogstraat 51, 9000 Gent/ Paleizenstraat 65, 1030 Brussel, Belgium

4,5,6

Department of Electroacoustics, University of Zagreb, Faculty of Electrical Engineering and Computing,
Unska 3, 10000 Zagreb, Croatia

ABSTRACTThe problem of noise in dwellings is topic of large discussions nowadays. Not only airborne noise but also
impact noise are responsible for decreased comfort of living. The subjective evaluation of impact noisesounds in dwellings are described in this paper. Listening tests based on method of adjustment (1) withstatistically sufficient sample of tested subjects were performed in a listening test room in the laboratory of
TGM where subjects compared the performance of acoustically presented floors. Impact noise stimuli weremeasured as the sound coming through various floor constructions with similar Ln,w values, sorted into threemain groups: (i) masonry concrete structure, (ii) cross laminated timber (CLT) structure and (iii) light-weighttimber structure. Comparisons of listening test performance with calculated single number quantities for eachconstruction were prepared in order to understand the perception of presented sounds by dwellers. The resultsfrom this preliminary study are meant as a basis for adjusting of currently applied reference curve also withparticular focus on the low frequency range.
Keywords: Sound insulation of floors, sound transmission, impact noise, listening tests, psychoacoustic

1. INTRODUCTION
The impact sound with majority of sound energy in low frequencies, is nowadays perceived as oneof the most unwanted noise sources in dwellings. The main reason is the serious impact of noise on
human health (2-4). The disturbance of people by impact noise in dwellings was proved also in a largescale study in the framework of the Swedish research project AkuLite, which was running in the years
2009-2013. In one of the performed experiments, walking neighbours were identified as the mostannoying noise sources (5). Various single number quantities (SNQs) assessing impact noise
performance of floors has been proposed after the study of Bodlund (6) and some of them wereintroduced in ISO 717-2:2013 (7). Later, modified version of Ln,w+C I,50-2500 with increased weight(importance) in frequencies below 50 Hz and above 400 Hz was introduced (8). The questions about
subjective perception of impact noise have arisen in the last decade and in 2012 a study of Ljunggren
et al dealt with matching of acoustic measurements with subjective judgements (9). In 2017 Kylliäinen
1

vojtech.chmelik@stuba.sk
jbenklewski@tgm.ac.at3monika.rychtarikova@kuleuven.be4
dominik.kisic@fer.hr
5marko.horvat@fer.hr
6
kristian.jambrosic @fer.hr
7hmuellner@tgm.ac.at25134

et al performed an experiment aimed on the impact sound insulation of concrete floors. This
experiment showed inconsistency of subjective perception of loudness of impact noise with calculated
single number quantities which are standardized in ISO 717-2 – L’n,w, L’n,w+C I, L’n,w+C I,50-2500 (10).
In this paper, results of a preliminary study are presented, that show the influence of low frequency
content of sound signals on human’s perception and judgement of loudness of sounds.

2. DESCRIPTION OF LABORATORY LISTENING TESTS
2.1 Tested subjects
Listening tests were performed by 45 listening subjects. The age of participants ranges between 14and 63 years. (13 female and 32 male). None of them reported hearing problems. Each listener got thesame instruction and explanation prior to the test to ensure the same conditions among them.
2.2 Stimuli used in listening tests
The stimuli were based on sounds recorded in receiving rooms, composed out of 6 steps of awalking person, coming through 9 different floor constructions. These constructions can be sorted into
three different groups based on the main bearing structure as (i) heavy-weight concrete ceilingconstruction, (ii) floor construction based on cross laminated timber (CLT) panels and (iii)light-weight timber beam ceiling construction. The recordings were done under laboratory conditionsin test stand for impact noise measurements at the facilities of TGM Vienna Acoustic Center Austria
and in situ situations with low noise microphones placed 1 m from the ceiling:
1“-Condensermikrophon (Type Brüel & Kjaer 4179 with Preamp Typ 2660) recorded on a SQuadriga
II (Code 330), from Head Acoustics. Reverberation time in receiving room was adopted (if necessary)by sound absorption material to mimic conditions of an ordinary living room, i.e. T30 = 0.36 s. List anddescription of all measured ceilings is shown in Table 1. The recordings were arranged into the pairs
according to the similar performance in terms of parameter Ln,w+C I,50-2500 , with maximal difference of
1 dB, since the so called just noticeable difference of sound level for low levels does not exceed 1 dB
(11). Frequency spectra of considered ceiling sorted into pairs are shown in Figure 1.
Table 1 – Ceiling constructions used as “filters” for sound recordings
CodeType of construction

L n,w /dB

L n,w +C I,50-2500 /dBCON1CON2Concrete
Concrete standard floor with floating concrete floor with different kind of impact soundinsulation material (polystyrene or mineral-wool) and gravel pouring

5456

5152

50

5450

56

425250

5350

56

4352

41

54

CON4BSP1BSP3

CLT
Cross laminated timber with different kind of floating floors ( dry screed or concrete) withmineral-wool impact sound insulation slabs on gravel pouring, without suspended ceiling

BSP4
HBD7HBD8HBDSLight weight timber frame
Light weight timber frame floor constructions with different kind of floating floors (concreteor dry screed elements) on mineral-wool impact sound insulation slabs and different kind ofsuspended ceilings

2.3 Description of room used for listening tests
Laboratory listening tests were performed in a silent environment in the listening test room at TGM– Die Schule der Technik, Vienna, Austria. To ensure the low background noise level the use of
professional high-quality perception room is essential, since low level stimuli were presented during
the listening test. The measured overall A-weighted background noise level inside the room wasLA,eq = 17 dBA (measurement performed with Norsonic NOR 840 real time sound level analyser witha class 1 and B&K low-noise microphone). This room is furnished to be like a pleasant environment ofa living room. All equipment which could possibly emit disturbing noise is placed outside in aneighboring control room – computer, second screen, etc. Thanks to that, the operator could stayoutside of the room and was able to control the whole listening tests procedure. The 2 nd orderambisonic loudspeaker system which allows to choose any combination of presenting loudspeakers is5135

installed in this room.
2.4 Listening tests procedure
The performed listening tests were based on method of adjustment (1). The sound stimuli werepresented via loudspeakers from the installed ambisonic system (EVE Audio SC204) to reproduce
sound coming from the ceiling to tested subjects. The low frequency content of the played stimuli waspresented via two low frequency loudspeakers (EVE Audio TS110) hidden behind the test person.
During the listening test, pairs of signals were played and subjects were asked to adjust the loudness ofa second stimulus to sound as loud as the reference signal. Altogether 13 comparisons were presented
in one test set - six were formed by pairs according to the above described rule played in random order
twice as A-B, B-A, to avoid a possible bias. An additional 7 th pair contained two identical stimuli(HBD8) which were used for “calibration reason”, in other words, to understand the uncertainty ofmeasurement by asking people to adjust two identical sounds to the same loudness.
Each test subject was seated inside the listening room and was able to control the whole test with atablet connected to the computer in the control room using graphical user interface (GUI) of theprepared test routine showed in Figure2. Each test set took around 15 -20 minutes. Each subject has
performed the listening test only once.

Figure 1 – Frequency spectra for impact sound level Ln of used floor constructions

Figure 2 – Graphical users interface of listening test5136

3. RESULTS AND DISCUSSION
Distribution of answers obtained from listening tests shown below are expressed in percentage ofgiven answers (Figures 3-5). The x axis shows values of sound pressure level in dB as following: The
red line indicates the objectively measured value of Ln,w+C I,50-2500 and the blue bars shows answers ofsubjects, obtained as adjusted sound level of given signal to reference signal (to be perceived equallyloud). Data are analyzed per each pair (defined earlier in this paper) one by one.
Results for the so called “calibration pair” which consists of two identical stimuli (HBD8) are
shown in the Figure 3. Ideally all answers should be identical with the red line, since the two sounds
were equally loud. Based on the obtained answers it can be concluded, that the data form a nicegaussian distribution around the “correct answer” and a slight shift towards lower values is observed,
which means that people have adjusted the signal slightly louder (in average 1 -2 dB) than the reference
signal. It can be concluded, that almost all subjects were able to set the loudness of the second stimuli
almost correctly to Ln,w+C I,50-2500 = 53 dB, with a deviation of max. 5 dB. Almost half of the people
made an error less than 1 dB. Answers of all persons with error > 5 dB in the calibration test wereexcluded from the final analysis.

Figure 3 – Distribution of answers for “test” of test subjects which were taken into account for the analysis
compared with calculated values of Ln,w+CI,50-2500

Figure 4 Left - Distribution of answers for pair BSP4 - HBDS compared with calculated values ofLn,w+CI,50-2500, Right - example of HBDS – BSP45137

Figure 5 Left - Distribution of answers for pair CON2 – CON4 compared with calculated values ofLn,w+CI,50-2500, Right - example of CON4 – CON2
When analyzing pairs one by one, different trends were observed. In several cases a large spread indata was seen.
The comparison between BSP4 and HBDS is given in the Figure 4. The reference signal (HBDS)
Ln,w+C I,50-2500 = 52dB is drawn in red and the sound signal that subjects were adjusting (BSP4) isindicated in black color. Answers of people are in blue.
Based on the obtained results, and the large spread of answers it cannot be concluded, that single
number quanity Ln,w+C I,50-2500 corresponds with subjective perception the best.
Furthermore a number of research questions arises, such as :On which bases people take decision about the loudness of 6 consequently arriving impulsive
sounds? Do they take the average value, or do they take the loudest step or the last they hear into
comparison?
The statistical distribution of all answers (from all pairs) shows two groups of answers. First one
from people who were deciding about the loudness level based on low frequency components andsecond one, that decided based on differences in high frequencies. Deeper analysis is therefore
necessary in more detail, in which also individually recorded steps need to be analysed, maybe
compared with recorded sound from standardized rubber ball.

ACKNOWLEDGEMENTS
The
authors
acknowledge
financialsupportby
theEuropean
Commission,(H2020-MSCA-RISE-2015 project 690970, "Advanced physical-acoustic and psycho-acoustic
diagnostic methods for innovation in building acoustics (PAPABUILD)", COIN Project “AkustikCenter Austria” and Project VEGA 1/0050/18.

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