Call Center Acoustics: Sources, Room Acoustics, And Design Guidelines

Acoustics includes both desirable and undesirable sounds. As listeners, we all experience a wide variety of sounds in our environment. To a degree, we can ignore undesirable sounds; but there is some level above which we cannot ignore undesirable sounds, which we usually term ‘noise’. Noise may include the sounds of vehicular traffic, mechanical systems, slamming doors, footsteps, conversations between other persons, and even music to which we are not sympathetic. The interior acoustic environment is more complex than the exterior one because it is associated with a greater variety of activities within an enclosed space. In order to improve the acoustic environment, it is important that a systematic evaluation be conducted to understand the acoustic condition.

1. Consider producing an evaluation criteria which will act as a guide or program towards the production of an environmental assessment guide for acoustics. You will be given reading materials including case studies to develop these criteria, in addition to your classes. You are expected to read these and engage in active discussions during the tutorial sessions. Attendance in tutorial is very important in order to complete this assignment task (online discussion section is provided for off-campus students).

2. Apply your guide to critically evaluate (objectively and subjectively) the acoustics performance of the space (see material below) and consider possibilities of new alterations in design and materials. Give a critical analysis and reasoning in accordance to the grading criteria of the project.

General sources of sound in the space and their frequency ranges

Call centers serve a significant role when it comes to the daily operations of utility, financial as well as technology companies besides public bodies. Reliable and relevant information is needed among the workers in the call centers on the levels of risks as well as the hazards associated with the working environment.

General sources of sound in the space and their frequency ranges

The main source of sound in the space is the air supply at the lighting fixture that is located in the ceiling of the working place. The noises from the air supply fixture which finally get to the workers in the working place are composed of:

• Low-frequency fan noise-fans often generate sound in 16 Hz via 250 Hz octave bands
• Mid-frequency airflow also called turbulence-generated noise in the duct of the system which range from 31.5 Hz through 1000 Hz (Le Muet, 2012).
• High frequency damper or otherwise diffuser noise which often contributes to the general noise in the 1000 Hz through 4000 Hz octave. The air supply system

Room acoustics in terms of sound absorption and reflection, and the characteristics of internal finishes

Reflection of sound waves takes place in the same manner as those of light waves with the angle of incidence being equal to the angle of reflection (Moeller, 2016). Among the properties of reflection of sound include:

Upon the reflection of sound from a flat surface, there is formation of special shape by the wave fronts and the center of curvature tends to be the source of sound

Sound waves become magnified when reflected from a convex surface and hence tending to be thinner and weaker. Convex surfaces can thus be used in the reduction of the impact of sound in the interior spaces.  Sound is amplified when reflected from a concave surface as they are dense and compressed. Curved surfaces should thus be avoided in the interior surfaces since the results are not desirable (Postma, Jouan and Katz, 2018).  Some of the sound that strikes a surface is absorbed by friction and materials which absorb sound are known as absorbents. Absorption in the call center occurs through three main ways:

Air: Such absorption occurs as a result of friction between any two molecules in as much as it is very small.

Audience: Clothes serve as absorbents. In the call center, sound absorption takes place through the clothes of the people working inside. The higher the number of people working in the call center the greater the absorption that occurs (Moeller, 2016)

Furniture and furnishing: Materials used in the finishing and furnishing of the building are capable of absorbing sound for example the curtains and carpets.

Reverberation time defines the amount of how much taken is take for sound to undergo decay in a space and this property has the ability to influence how well a speech is understood and even change the way voices sound. The speech transferred across a room by an individual is not always received at the position of listening as an exact reproduce of the initial signal. There is no only an additional of the background noise but also distortion of the signal by the reverberant as well as reflective features of the room (Reinten, Braat-Eggen, Hornikx, Kort and Kohlrausch, 2017). In most cases, a direct consequence of such distractions is lowering of the intelligibility speech.

Room acoustics in terms of sound absorption and reflection, and the characteristics of internal finishes

The speakers of the room are in most cases adapting their speech in such a way that they suit the room. This is attained through talking slowly in a room perceived to be very reverberant or in a room that has dead-spots.

Through specifying the quantity of speech intelligibility and taking its measurement within a room, the degree of acoustical treatment in needed in the solution of such changes is established. Among the main approaches that can be used in the enhancement of the clarity of speech include: reduction of reverberation time in the rooms used for meeting, reinforcement of sound in the room, reducing reverberation time in the meetings that are used for meeting as well as the prevention of echoes in voluminous enclosures (Postma, Jouan and Katz, 2018).

Among the features perceived to be of importance with regards to the acoustical comfort are as described:

• The personnel who serve in space perform their roles at tables which are linked in groups of four
• Celling is made of plasterboard
• All staff are provided with headphones
• The windows are not covered with any materials

The most significant sources of noise in the space include air supply fixture, office equipment and telephone signals. There is not significant noise coming from the outside or from the other sections of the building.

Over 30 measurement points were chosen considering the seating plan. The measurement of the levels of noise were taken twice a day since the number of personnel serving in the call center and once the major sources of noise  do not undergo any alterations in the course of the day (Osses, Kohlrausch, Lachenmayr and Mommertz, 2017). Besides the equivalent continuous noise level, determination was also done on the statistical levels. The findings are as shown in the figures below

The noise levels can be significantly reduced for the neighbouring personnel by making adjustments to separators that are used on the tables which would be experienced. This will go hand in hand with increasing the heights of the separators as well as changing their shapes in order to generate better acoustical shadow.  Such a simple modification may be attained by joining an extension board to each of separators which have a congruent inverse slope. While this modification would result in enhanced sound adoption effectiveness of the separators, it would result in visual connection loss for the personnel and hence it would be recommendable to use separators that are made of glass for the case of the working personnel (Moeller, 2016).

Each of the sides of the tables may as well be enclosed using turn-rounds that are sound absorbent and are linked to separators to enhance effectiveness of such barriers. The total absorption of the place may be attained through lowering the boards to the ground surface. Such modifications are predicted to be able to decrease the levels of sound by about 10 dB

Absorption of sound in the call center through three main ways

Enhancing quantity of absorption of sound that cover on walls as well as ceiling could be another strategy for reducing the sound levels in the call center (Dunne, 2019). The sound absorbing features of internal surfaces of call center are established at various stages. Among the main recommendations include:

• Addition of sound absorption to the entire celling area to enable achievement of a reduction in noise of about 9 dB often at frequencies of 250 Hz, 500 Hz as well as 1000 Hz that were most dominant speech sound frequencies
• Having the internal walls covered using absorbing materials (Le Muet and Chevret, 2015)
• Having the entire ceiling covered using sound absorbing surfaces as well as the adoption of double sided sound absorbing barriers which would offer noise reduction levels to the tune of between 10 and 20 dB t frequencies of 250 Hz, 500 Hz as well as 1000 Hz
• Having both the walls and the ceiling covered using absorbing surfaces to offer between 5 to 10 dB of levels of noise reduction at frequencies of 250 Hz, 500 Hz and 1000 Hz (Petersen and Rasmussen, 2018)

The levels of noise or sound in the open plan spaces may be lowered through the introduction of barriers which will serve to lower direct sounds as they form acoustic shadows. Should the barriers be made sound absorbing, they will be able to lower reverberant sound as well as reflected sound (Vervoort and Vercammen, 2015). The placement of the barriers at the correct positions in the call center would serve as one of the most effective ways of attenuation of direct and indirect sound between the personnel.

The quality of the working space can be enhanced by reducing the number of the staff that works in the call center. This would serve to enhance the acoustical quality of the space as there will be a significant reduction in sources of noise which include both people as well as phone signals. Modifications to the telephone equipment may as well be conducted in order to achieve a further reduction in the levels of sound (Dehlbæk, Brunskog, Petersen and Marie, 2016).

References

Dehlbæk, T.S., Brunskog, J., Petersen, C.M. and Marie, P., 2016, August. The effect of human activity noise on the acoustic quality in open plan offices. In INTER-NOISE and NOISE-CON Congress and Conference Proceedings (Vol. 253, No. 4, pp. 4117-4126). Institute of Noise Control Engineering

Dunne, J., 2019, March. Room & Architectural Acoustics-A New Approach to the Design & Delivery of Critical Acoustic Facilities. In Audio Engineering Society Convention 146. Audio Engineering Society

Le Muet, Y. and Chevret, P., 2015. Acoustics of Open Spaces–Towards a New French Standard. Euronoise 2015, pp.1192-1196

Le Muet, Y., 2012, April. Acoustic of open spaces-Overview of standardization work. In Acoustics 2012

Moeller, N., 2016. Acoustic Privacy within the Built Environment. Architect, 105(10), pp.82-85

Osses Vecchi, A., Kohlrausch, A., Lachenmayr, W. and Mommertz, E., 2017. Predicting the perceived reverberation in different room acoustic environments using a binaural auditory model. The Journal of the Acoustical Society of America, 141(4), pp.EL381-EL387

Petersen, C.M. and Rasmussen, B., 2018. Acoustic design of open-plan offices and comparison of requirements in the Nordic countries. In Baltic-Nordic Acoustics Meeting 2018 (pp. 1-8). Nordic Acoustic Association

Postma, B.N., Jouan, S. and Katz, B.F., 2018. Pre-Sabine room acoustic design guidelines based on human voice directivity. The Journal of the Acoustical Society of America, 143(4), pp.2428-2437

Reinten, J., Braat-Eggen, P.E., Hornikx, M., Kort, H.S. and Kohlrausch, A., 2017. The indoor sound environment and human task performance: A literature review on the role of room acoustics. Building and Environment, 123, pp.315-332

Vervoort, T. and Vercammen, M., 2015. Background noise level to determine the speech privacy in open plan offices. Proceedings of Euronoise, Maastricht, The Netherlands, pp.1209-1214