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

The effect of road traffic noise spectrum on sleepValtteri HONGISTO1,2; Saana MYLLYNTAUSTA3
1

Finnish Institute of Occupational Health, Turku, Finland
2Turku University of Applied Sciences, Turku, Finland
3

University of Turku, Turku, Finland.

ABSTRACTPURPOSE. Two façades having nominally equivalent sound insulation declaration, such as Rw+Ctr value,
may have very different frequency behaviors leading to different spectrum of road traffic noise (RTN) indoors.
Because spectrum affects annoyance of sound, spectrum may also affect sleep quality. Our purpose was todetermine, how the spectrum of RTN affects sleep.
METHODS. Twenty-one participants slept three nights in a sleep laboratory in three different conditions: LF(low frequency prominence, 37 dB), HF (high frequency prominence, 37 dB), and Q (control, quiet, 19 dB).
Conditions LF and HF were created by filtering an outdoor recording of RTN through two filters
corresponding to two different sound insulation spectra but equal value of Rw+Ctr = 37 dB. Sleep quality wasmeasured both objectively (polysomnography) and subjectively (questionnaires).
RESULTS. Subjective sleep quality was worse in conditions LF and HF than in Q. Duration of slow wave
sleep (deep sleep) was shorter in LF and HF than in Q. LF and HF did not differ from each other. After theexperiment, most of the participants rated condition HF as the most disturbing for sleep.
CONCLUSIONS. High frequency RTN may be more adverse for sleep than low frequency RTN, but more
research is needed.
Keywords: Sleep, environmental noise, façade sound insulation

1. INTRODUCTIONNighttime noise level regulations concern usually the upper limit for the A–weighted equivalentsound pressure level (SPL) during the nighttime, such as LAeq22-07 . In addition to that, penalty is often
applied if the sound contains specific properties which may increase the annoyance of sound, such as
impusivity or tonality. According to several studies, also the spectrum of sound affects annoyance(25). This suggests that the spectrum could also affect sleep disturbance.
Proper façade sound insulation is the most important way of protecting residents fromenvironmental noise. The dimensioning of the façade is usually made in Europe by a dimensioning aminimum value for the sound insulation using a single-number quantity of ISO 717-1 standard (6).
Different single-number quantities are, however, used in different countries. In Finland, the target
value for the entire façade and for façade components are described by R w+Ctr. The sound insulation
spectrum of two different façade constructions having the same value of Rw+Ctr can, however, differ
drastically (Figure 1a). The frequency dependence of sound insulation may, therefore, affect sleep.
There is at least one study which has studied the sole effect of spectrum (7) on sleep quality. They
found that ground-borne noise from railway tunnels having larger emphasis on high frequencies
affected sleep more than similar sound having larger emphasis on low frequencies with the same LAeq .
Studies about the effects of the spectrum of road traffic noise (RTN) do not exist.
Our purpose was to determine, how the spectrum of RTN affects sleep when LAeq = 37 dB.

1valtteri.hongisto@turkuamk.fi
3saakar@utu.fi
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2. MATERIALS AND METHODSWe conducted a sleep study in laboratory conditions. The participants were recruited from student
organizations. The inclusion criteria were normal hearing, a fairly regular sleep-wake rhythm, andbeing a normal sleeper (e.g. absence of sleep apnea). The participants were also required to live in anapartment building close to or nearby a busy road, as we wanted to avoid volunteers who are notaccustomed to neighbor or environmental noise. It was also required that the participants did not doshift or night work, or take naps regularly.
The study sample consisted of 21 healthy volunteers (19 women). Their mean age was 25 years.
The participants were given 60 Euro gift token for their participation. The experiment was approvedby the ethics committee of the Hospital District of Helsinki and Uusimaa.
Our study involved three sound conditions, LF, HF, and Q. The spectra are shown in Figure 1b.
Each of them were presented in three different rooms (Figure 2). Sound condition LF consisted ofRTN having more emphasis on low frequencies (37 dB LAeq,8h ) than sound condition HF (37 dB LAeq,8h ).
Sound condition Q was a reference condition representing full silence (17 dB LAeq,8h ).
RTN for the laboratory experiment was recorded at a busy urban crossroads between 10 p.m. and7 a.m. (Figure 1b, outdoor noise). The SPL of sound condition LF (Lin,LF) was obtained by reducing
the the sound reduction index (RLF of Figure 1a) from the SPL of outdoor RTN (Lout ), i.e. Lin,LF=Lout RLF. Similarly, Lin,HF=Lout – RHF. The resulting sound conditions LF and HF had, therefore, drasticallydifferent spectra but the same A-weighted SPL (Figure 1b). The time profile of nocturnal RTN isshown in Figure 1c.
The study was conducted in the sleep laboratory of Finnish Institute of Occupational Health (Figure2a) during fall 2014. The participants slept in the laboratory for 4 successive nights (MonFri). The
first night was reserved for habituation. Repeated measures design was applied so that each participant
slept one night from 11 p.m. to 7 a.m in each room. The order of the rooms (sound conditions) wascounter-balanced. Sound was produced into the room using loudspeakers hidden behind fake windows.
The target spectrum of Figure 1b in the position of sleeper’s head in the room was obtained byapplying one-third-octave filtering (Adobe Audition).
Objective sleep quality was measured using polysomnography. Subjective sleep quality wasdetermined using questionnaires on mornings and evenings. Furthermore, the sound conditions withrespect to their sleep disturbance were ranked retrospectively after the whole experiment by aquestionnaire.
Statistical analysis was done using ANOVA or Friedman’s test. Paired comparisons between twosound conditions were done with paired-samples t-test or Wilcoxon signed-rank test.
70
LF

80

HF

60

70

50

60

45

30

40
30

LAeq,10min [dB]

LF
HF
Q
Outdoors

50

40

LZ,eq,8h [dB]R' [dB]

40

35

30

20
20
25

10100b)20
23:00 0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00

4000

500

63

125

250

f [Hz]

2000

f (Hz]

1000a)

31.5

20
31.5
50801252003155008001250
20003150
50000c)TimeFigure 1. (a) Sound reduction index R’ as a function of frequency, f, for two façade constructions having
nominally the same airborne sound reduction index against road traffic noise, Rw + Ctr = 37 dB. (b)Unweighted 8-hour equivalent SPL, LZeq,8h, as a function of frequency for sound conditions LF, HF, and Q.
(c) The 10-minute equivalent A-weighted SPL of RTN as a function of time in the experimental room.

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Number of 1st ramks

201510504170LF

HFSound condition

QFigure 2. Left: the layout of the laboratory indicating three rooms for each sound condition LF, HF, and Q.
Right: retrospective ranking of the three sound conditions with respect to their sleep disturbance.

3. RESULTS
Duration of slow wave sleep (SWS) was shorter in sound condition LF and HF than in Q. Soundcondition did not have other effects on objective measures (Table 1). Subjective sleep quality wasworse for many measures in sound conditions LF and HF than in Q (Table 2). However, soundconditions LF and HF did not differ statistically significantly from each other for any measure. RTN
was the only environmental factor notably affecting sleep quality after the first night when theparticipants habituated to the environment (Table 3). After the experiment, 81% of participants rated
the sound condition HF worst with respect to sleep disturbance (Figure 2b, p<0.001).

4. CONCLUSIONS
RTN presented at a level of 37 dB LAeq had an adverse effect on sleep both with subjective andobjective measures compared to silence (17 dB). The finding concerned both studied RTN spectra, i.e.
LF (low frequency content higher) and HF (high frequency content higher). Statistically significant
differences were not found between the two RTN spectra. However, the retrospective ranking of thethree sound conditions indicated that spectrum HF was the most adverse for sleep. Smith et al. (7)found that ground-borne noise from railway tunnels having high emphasis above 100 Hz led to greater
elevations of heart rate and arousal probability than similar noise having high emphasis below 100Hz. Smith et al. found objective evidence and we found retrospective subjective evidence. It is, thus,
possible that high frequency RTN could be more adverse for sleep than low frequency RTN. Moreresearch is needed in this field.
Table 1. The results of objective sleep quality measures.
Condition
HF
M (SD)Q
M (SD)

p

Variable

LF
M (SD)

Sleep latency [min]WASO duration [min]No. of arousals
N1 duration [min]N2 duration [min]SWS duration [min]REM duration [min]14 (13)19 (15)49 (23)29 (14)228 (28)
86 (30)104 (24)

13 (10)18 (13)54 (24)32 (17)225 (28)
89 (25)104 (24)

13 (11)15 (16)47 (24)27 (13)218 (43)
97 (27)111 (27)

>0.1
>0.1
>0.1
>0.1
>0.1
0.01
>0.1

M= mean, SD = standard deviation, SWS= Slow wave sleep,
REM= rapid eye movement sleep, WASO=wake after sleep onset

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Table 2. The results of subjective sleep quality measures. Means (M) and standard deviations (SD).

Subjective variable
Satisfaction with sleepaSubjective sleep latencybSubjective sleep difficulties
Subjective recoverybb

Sound condition
LF
HFQ
M (SD)
M (SD)
M (SD)
0.1 (1.1) 0.3 (1.0) 1.0 (1.0)

0.02

2.1 (1.1)

1.9 (1.1)

1.5 (0.9)

0.01

2.2 (1.0)

2.1 (1.1)

1.6 (1.0)

0.01

3.2 (1.0)

3.2 (0.9)

3.5 (1.2)

0.29

aResponse range: -2 Very dissatisfied, +2 Very satisfiedbResponse range: 1 Not at all, 5 Very muchpTable 3. The disturbance caused by different environmental factors on sleep.
Sound condition
1st night
LF
HF
Q
M (SD)
M (SD)
M (SD)
M (SD)
Item
1.2 (0.5)
2.5 (1.2)
2.8 (1.1)
1.1 (0.2)
Road traffic sound***1.9 (1.3)
1.0 (0.0)
1.0 (0.0)
1.2 (0.5)
Silence
1.9 (0.9)
1.4 (0.7)
1.6 (0.9)
1.3 (0.7)
Cold
1.8(1.0)
1.4(0.7)
1.3(0.6)
1.2(0.5)Hot
1.1 (0.3)
1.1 (0.3)
1.1 (0.5)
1.1 (0.5)
Bed quality
2.8 (1.0)
1.1 (0.3)
1.2 (0.5)
1.2 (0.5)
Apparatus on my body
1.5 (1.2)
1.1 (0.4)
1.1 (0.2)
1.2 (0.6)
Darkness
2.5 (1.2)
1.3 (0.5)
1.3 (0.6)
1.4 (0.7)
Unfamiliar place
1.5(0.9)
1.3(0.7)
1.1(0.5)
1.2 (0.5)
Monitoring camera*** Significant difference between sound conditions LF, HF, and Q (p<0.001).

ACKNOWLEDGEMENTS
This study was a part of ÄKK project (2012-2014) mainly funded by Tekes (Grant 2296/31/2011).

REFERENCES
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Part 1: Airborne sound insulation, International Organization for Standardization, Geneva, Switzerland.
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