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Concentrix is a global customer-experience company with offices in more than 40 countries. Its Sofia office is a call centre on a whole floor – 208 workstations where staff are on the phone almost non-stop. They complained of noise, difficulty concentrating and headaches.
Desk separators, an acoustic ceiling and carpet were already in place. The problem remained, so the client commissioned an acoustic survey and proposals for a solution.
We divided the floor into 5 zones and measured them according to EN ISO 3382-3:2012 – in the empty office and during working hours.
| Parameter | Good value* | Measured |
|---|---|---|
| Distraction distance rD | ≤ 5 m | 13,5–14,8 m |
| Spatial decay rate of speech D2,S | ≥ 7 dB | 4,7–7,8 dB |
| Speech level at 4 m, Lp,A,S,4m | ≤ 48 dB | 50,2–51,2 dB |
| Reverberation time | 0,4–0,6 s | 0,50–0,60 s |
| Background noise without staff | < 40 dB(A) | 30–38 dB(A) |
| Noise during working hours | < 50 dB(A) | 55–65 dB(A) |
| Speech intelligibility (STI) | – | 0,85–0,92 |
*Indicative values according to EN ISO 3382-3 and the project.
Conclusion: there is enough absorption in the room – the reverberation time is within the norm. The problem is direct speech. The separators were low and had little absorption, so conversations were intelligible 14 m from the talker.
We built a computer model of the floor and calibrated it with the measurements – the difference was below 5%. We compared 6 screen options with different heights, layouts and absorption.
The best option: 1.5 m high screens around each group of 4 desks, with 50 mm sound-absorbing material (absorption coefficient about 1.0 at 500–1000 Hz).
| Parameter | Before | Option 6 (model) |
|---|---|---|
| rD | 13,5–14,8 m | 7,3–7,9 m |
| Lp,A,S,4m | 50,2–51,2 dB | 45,7–46,2 dB |
| D2,S | 4,7–7,8 dB | 8,0–8,6 dB |
With thinner screens (30 mm, like the existing ones) the result is 2–3 dB weaker. On site we also recommended active noise-cancelling headsets for the operators.
The report was handed over to the client; the choice and implementation of the measures were the client’s decision.
Similar project? See our service Acoustics and Soundproofing for Offices or contact us via the enquiry form.
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