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

If speech is the source of noise, how can the source be eliminatedor reduced?
Andreas LIEBL 1; Noemi MARTIN 2; Benjamin Johannes MUELLER2
1

HSD Hochschule Döpfer, Germany
2

Fraunhofer IBP, Germany

ABSTRACTThe exposure to noise can be reduced by eliminating the source of noise (if possible), substituting the sourcewith a quieter one, applying engineering modifications, using administrative controls, and by using protectiveequipment. It is generally agreed that the solutions controlling the source are more cost effective than thosecontrolling noise along the propagation path. Administrative controls and the use of personal protective
equipment are measures that control the noise at the receiver and are supposed to be applied only if measuresat the source are not possible. However, in this line of argumentation human beings are usually only treatedas receivers of noise but not as noise sources. Results are reported in which an inverse Lombard effect orrather the Fletcher effect is used to reduce the speech effort and thus the speech level of persons. A feasibility
study shows that the speech level can be lowered by up to 3 dB without the necessary manipulation being
perceived to be distracting.
Keywords: room acoustics, open plan offices, sidetone, speech effort

1. INTRODUCTION
It has been shown numerous times, that lack of acoustic privacy and disturbance caused bybackground speech rank among the least satisfying parameters of the indoor environmental quality inoffice buildings (1, 2). Acoustic privacy refers to not being able to prevent others from overhearing
your own conversations or to prevent overhearing the conversations of others. It follows from thisthat the presence of background speech is closely related to acoustic privacy.
Occupational safety and health (OSH) aims to promote and maintain the highest degree of safety
and health at work, therefore creating conditions to avoid the occurrence of work accidents and illhealth. To achieve such goal employers have to implement safety and health measures based on risk
assessments and legislation. Since OSH applies a holistic approach to promote the social, mental andphysical well-being of employees, it also addresses non-auditory effects of noise like increased stress,
cardiovascular function, annoyance, performance, sleeping problems, and mental health. These effects
can be triggered by rather low noise levels which cause no direct harm to the hearing system (auditoryeffects). The presence of background speech is well known to impair subjective well-being and work
performance (3, 4).
OSH usually applies a hierarchy of prevention and control measures, which starts by avoiding risks
and eliminating hazards. If this is not possible, hazards have to be reduced and minimized or separated
from the employees. However, if a colleague is the source of speech noise, separating him from theother employees is not easy or not wanted. Because this would be mean, providing single offices or
sufficient acoustically separated spaces for communication or concentrated work but also
disconnecting people.
Preventive measures which aim to reduce the likelihood of occurrence of a hazard can be applied.
Those incorporate engineering or technical measures (designed to act directly on the risk source, inorder to remove, reduce or replace it) and organizational or administrative measures (meant to force2475

changing of behaviors and attitudes and promote a safety culture). Thus reducing the vocal effort of aspeaker and therefor the level of disturbing background speech for his colleagues is a desirable goal.
Preventive measures can be followed by protection measures which include collective measures(designed to enclose or isolate the risk, for instance through the use of physical barriers, organizationalor administrative measures to diminish the exposure duration) and individual measures (any adequate
Personnel Protective Equipment designed to protect the worker from the residual risk).
The OSH approach has been very successful for example in reducing the background noise level
in offices caused by technical noise sources. However, doing so the impairment caused by backgroundspeech may even have increased since the disturbing background speech is no longer masked bybackground sound from technical sources. The consideration of work colleagues as potential noise
sources has so far found no adequate consideration. Many guidelines and recommendations
specifically ignore this kind of noise which is caused by the presence of other people in the room.
For this reason, a feasibility study is presented here, which investigates whether electro-acoustic
measures on the technical equipment of the source of background speech, namely the speaker, canreduce the vocal effort of the speaker and thus also reduce background speech. For this purpose, theso-called sidetone settings of five different headphone systems were systematically manipulated andthe effects on the speech sound level of the speakers was examined. The sidetone settings are intended
to intervene directly at the source of the disturbing noise, namely the speech sound caused by thespeaker. A system was developed which reproduces the speaker´s own speech sound on theheadphones as a sidetone during a simulated conversation with a headset. By means of this technique
it is attempted to reduce the speech level by psychoacoustic measures. The effectiveness of thedevelopment was validated in an experiment by measuring the speech levels and also the acceptanceof the development was tested by questionnaires. Only the effects on speech levels will be reported
here.

2. METHOD
2.1 Procedure
Participants were instructed to read aloud sentences of the HSM-sentence test (5) while wearing
different types (SH HD 600, SH HD 600 mono, SH HD 280, SH CHAT, SH MB 660 UC) ofheadphones (Sennheiser) and being exposed to three different conditions of background sound(SILENCE, ONE SPEAKER, SOME SPEAKERS) and to eight different sidetone settings as well asa baseline condition with no sidetone (0, 49, 55, 61, 67, 73, 79, 85, 91 dB). Thus a factorial design
with the independent variables type of headphone (5 levels), sidetone setting (8 levels) and conditionof background sound (3 levels) was applied. The headphones differ with regard to their characteristics
as described in Table 1.
Table 1 – Headphone Characteristics
TypeDesign TypeSidetone

SH HD 600

over-ear open-back headphones

both ears

SH HD 600 mono

over-ear open-back headphones

one earSH HD 280

over-ear closed-back headphones

both ears

SH CHATearpad headphones

both ears

over-ear closed-back headphones with active noise cancellingboth ears

SH MB 660 UC

The background sounds were presented via the headphones and differed with regard to level (levelsin brackets correspond to the level with active noise cancelling switched on) and the number of voices
as described in Table 2.

2476

Table 2 – Background Sounds
Condition

Level dB (A)SILENCE~One Speaker

53.6 (40.63)

Some Speakers

53.9 (41.49)

The sidetone settings were varied in steps of 6 dB in gain (0, 49, 55, 61, 67, 73, 79, 85, 91 dB)
which means that every participant received different sidetone levels depending on her/his own speech
level. The reduction of the speech level during each sidetone setting was compared to the speech levelwith no sidetone.
2.2 Participants
Data were collected from N = 20 participants. Most of the subjects were students of various disciplines.
The subjects were between 21 and 69 years old (M = 28.65 years, MD = 25 years). Ten female and 10
male subjects participated in the listening test.

3. RESULTS
The results of this feasibility study have to be interpreted with caution since plenty of individual
data points were lost due to technical problems during recording of individual speech levels. In order
to be able to conduct the statistical analysis in a factorial manner, the missing data was substituted by
the mean of the experimental condition. The ANOVA was calculated with de-logarithmed levels.
Additionally the factors HEADPHONE and SIDETONE were treated as between-subject factors
because of problems with the data protocol even so each participant wore each headphone and was
exposed to each sidetone setting.
3.1 Statistical Analysis
A three-way (HEADPHONE, SIDETONE, BACKGROUND SOUND) repeated measures ANOVA
with two between-subject factors (HEADPHONE, SIDETONE) and one within-subject factors(BACKGROUND SOUND) was conducted and is reported in Table 3 (Between Subjects Effects) andTable 4 (Within Subjects Effects).
Table 3 – Between Subjects Effects
Sum of Squares

df

Mean SquareFp

HEADPHONE

11.88

42.971

12.632<ௗ

SIDETONE

5.75

70.821

3.492

0.001

HEADPHONE ٝ SIDETONE

6.29

28

0.225

0.956

0.532

165.57704

0.235

Residual

The analysis reveals significant main effects of the factors HEADPHONE (F(4,704)=12.63, p<.001,Șð=.014) and SIDETONE (F(7,704)=3.49, p<.01, Șð=.007) but no significant interaction of bothfactors.

2477

Table 4 – Within Subjects Effects
Sum ofSquares

dfMeanSquareFp

BACKGROUND SOUND

8.80

24.39820.779ௗ

BACKGROUND SOUND ٝ HEADPHONE

6.47

80.8093.820

ௗ

BACKGROUND SOUND ٝ SIDETONE

2.47

140.176

0.833

0.634

8.29

56

0.148

0.699

0.955

298.02

1408

0.212

BACKGROUND SOUND ٝ HEADPHONE ٝSIDETONE
Residual

The analysis reveals significant main effects of the factors BACKGROUND SOUND(F(2,1408)=20.78 S Șð 0). The interaction between BACKGROUND SOUND andHEADPHONE is also significant (F(8,1408)=3.82SȘð 08).
3.2 Descriptive Analysis
Figure 1 depicts the reduction of the speech level depending on the sidetone settings compared tothe condition with no sidetone collapsed over all headphones. It appears that for the higher sidetone
gains the speech level decreases but only during the ONE SPEAKER and SOME SPEAKERS
condition.

Figure 1 – Reduction of speech level during different sidetone settings and background sound conditions
collapsed over all headphones.
Figure 2 depicts the reduction of the speech level depending on the sidetone settings compared tothe condition with no sidetone for the SH HD 600 headphone. It appears that for the higher sidetone
gains the speech level decreases but only during the SOME SPEAKERS condition.

2478

Figure 2 – Reduction of speech level during different sidetone settings and background sound conditions
for the SH HD 600 headphone.
Figure 3 depicts the reduction of the speech level depending on the sidetone settings compared tothe condition with no sidetone for the SH HD 600 headphone but with monaural sidetone presentation.
There seems to be no pattern of results.

Figure 3 – Reduction of speech level during different sidetone settings and background sound conditions
for the SH HD 600 headphone but with monaural sidetone presentation.
Figure 4 depicts the reduction of the speech level depending on the sidetone settings compared tothe condition with no sidetone for the SH HD 280 headphone. It appears that for the higher sidetone
gains the speech level decreases for all background sound conditions.

2479

Figure 4 – Reduction of speech level during different sidetone settings and background soundconditions for the SH HD 280 headphone.
Figure 5 depicts the reduction of the speech level depending on the sidetone settings compared tothe condition with no sidetone for the SH CHAT headphone. There seems to be no pattern of results.

Figure 5 – Reduction of speech level during different sidetone settings and background soundconditions for the SH CHAT headphone.
Figure 6 depicts the reduction of the speech level depending on the sidetone settings compared tothe condition with no sidetone for the SH MB 660 UC headphone. There seems to be a reduction ofspeech level for all levels of sidetone gain but only for the SOME SPEAKER condition.

2480

Figure 6 – Reduction of speech level during different sidetone settings and background soundconditions for the SH MB 660 UC headphone.

4. DISCUSSION
Since the results of the analysis have to be treated with caution the discussion of the results has tobe preliminary. As there were problems with the recording of the speech levels during the different
experimental conditions the technical setup of this feasibility study needs to be improved. However,
the results seem to be promising with regard to the possibility to impact upon the speech level of aspeaker during a headset conversation by means of manipulating the sidetone settings of theheadphone. However, the results seem to vary depending on the background sound situation anddepending on the headphone being used.

5. CONCLUSIONS
Since background speech usually ranks among the least satisfying parameters of the indoor
environmental quality in office buildings even so common room acoustical measures are applied, newsolutions have to be found. This feasibility study yields that the speech level of a speaker can beinfluenced by applying certain sidetone settings to the headsets being used. However, the effect islimited in quantity and the results of this feasibility study have to be treated with caution due to limits
to the statistical protocol.

REFERENCES
1. Liebl, A.; Drotleff, H.; Sedlbauer, K.; Schleuniger, F.; Uygun, A. (2011): Raumakustische Zielgrößen undMaßnahmen zur Optimierung der kognitiven Leistungsfähigkeit sowie des akustischen Komforts in
Mehrpersonenbüros. In: Bauphysik 33 (2), S. 87–93.
2. Frontczak, M.; Schiavon, S.; Goins, J.; Arens, E.; Zhang, H.; Wargocki, P. (2012): Quantitative
relationships between occupant satisfaction and satisfaction aspects of indoor environmental quality andbuilding design. In: Indoor air 22 (2), S. 119–131. DOI: 10.1111/j.1600-0668.2011.00745.x.
3. Liebl, Andreas; Assfalg, Alexander; Schlittmeier, Sabine (2016): The effects of speech intelligibility andtemporal-spectral variability on performance and annoyance ratings. In: Applied Acoustics 110, S. 170–175.
4. Venetjoki, N.; Kaarlela-Tuomaala, A.; Keskinen, E.; Hongisto, V. (2006): The effect of speech and speech
intelligibility on task performance. In: Ergonomics 49 (11), S. 1068–1091. DOI:
10.1080/00140130600679142
5. Hochmair-Desoyer, I.; Schulz, E.; Moser, L.; Schmidt, M. (1997): The HSM sentence test as a tool forevaluating the speech understanding in noise of cochlear implant users. In: The American journal ofotology 18 (6 Suppl), S83

2481