Understanding soundscape

20th Jul 2021

Understanding soundscape

If we were to map the circuit to which our tasks carry us within corporate life, most -if not all- of our time and intellectual effort is consumed in offices and conference rooms. Regardless of surface and architecture, they have one thing in common:their default design value for human comfort has been established at 35 to 40dD, at least 25 dD below the usual soundscape and its distribution our performance has to overcome in our day to day projects.

As a parameter for comfort, soundscape may be too abstract to fully fathom. Though distress is perceived and acknowledged, one cannot accurately identify the value and intensity to which sound becomes a negative experience, much more as our cognitive abilities demonstrate different levels of irritation under a continued or sinusoidal manifestation of noise. However, a literature review of studies conducted on acoustic comfort in open space offices indicate 45 dBA as this limit. The exact same values from 35 to 45 dB can found in the EN 15251 industrial standard for acoustic comfort.

The conventional layouts within the corporate environment can be resumed to small, landscaped or office cubicles. Though one might presume that soundscape is influenced by the sources, frequency and intensity of noise, spatial geometry plays an even higher role to its manifestation, influencing its resonance and distribution. Contrary to individual or small office, landscape layouts exhibit an extreme height-length-width ration which amplify and distort sound transmission, imposing acoustic attenuation as a necessity. Additional environmental parameters which can affect the soundscape include the air conditioning or ventilation system, as well as the sound climate to which an office is exposed by its location. Office furniture can also redirect the natural transmission of noise.

The physical parameters characterising an interior lead to further variables for acoustic comfort in Reverberation time, Spatial decay, Sound pressure, Distraction distance and Speech transmission index.

Defining sound clarity in contrast to echoes, reverberation time is usually mentioned as the first parameter to classify acoustic quality within a room. Reverberation time becomes vital for conference rooms and auditoriums.

The rate of spatial decay indicates sound attenuation, as produced organically by physical distance. Offices are much more dependent of the rate of spatial decay than other facilities. However, studies conducted on offices point out that a distance of 3 to 16m is required in order to have levels of noise naturally fade. Sound absorbing screens can put a neutralising physical barrier to this transmission.

Acoustic experiments for quality standards use a 4m reference distance from the source of noise. Conventionally, the same 4m distance is used to set workstations within an open space office. The 4m distance proves efficient in attenuating speech.

A critical aspect amplifying acoustic discomfort is speech intelligibility which defines the degree to which a verbally transmitted content can be understood in synergy to the background noise levels. A fragmented comprehension of speech where words and phrases cannot deliver the expected coherence for cognitive assimilation is demonstrated exhaustive, as it instinctively channels concentration towards understanding and assimilating the content one is exposed to.

The fore-mentioned distinction between continued and discontinued sound remains fundamental, as the former type allows acclimatisation whereas the latter is perceived as a distressful alert by the human cognitive system. In an office environment, continuous noise can emerge from HVAC systems, computer operation or even ambient music. Discontinued noises which can elevate the office soundscape to 60 dB or even 65dB can be issued by phone rings, human voices or photo copiers.

Regardless of the investments one commits to when it comes to acoustic isolation, open layout office still require an acoustic space partitioning. Flexible and cost efficient, acoustic screens are praised as the most practical solution to redesign the office soundscape. However, a critical aspect should be taken in account when opting for an acoustic screen: its composition formula which shapes and guarantees its qualities. Sound absorbing screens are demonstrated to capture and neutralise noise. In contrast, sound attenuating screens are built to block the transmission of noise which will bounce off towards its source, highlighting a poor acoustic quality variation. Consequently, a sound absorbing certification should be the first aspect taken in account when selecting an acoustic screen.