How speech in acoustically different offices influences a working person? – Experiments in two countries

•The strictest office room acoustic regulations were applied in Finland in 2018.•Occupant benefits of surpassing the regulation were inspected in our study.•Experience, performance and stress were examined with an experiment in two countries.•Room acoustic solution meeting the regulation improved experience and performance.•For best occupant experience even stricter room acoustic solutions are beneficial. Working during task-irrelevant speech influences workers. Adequate room acoustic design can reduce the negative effects in open-plan offices, but harmonized target values do not exist. Our purpose was to examine the effects of room acoustic design levels on a working person during the exposure to task-irrelevant speech. The Finnish room acoustic regulation was chosen as a reference, as it is one of the strictest worldwide. Three room acoustic conditions were examined: regulation violated (Reg-) (Speech Transmission Index, STI=0.71), regulation fulfilled (Reg0) (STI=0.37), and regulation surpassed (Reg+) (STI=0.16). To examine the generalizability of the results, a similar experiment was performed in two countries (two languages and laboratories): Finland and Germany (FinGer study, N = 98). Experience was measured with questionnaires, performance with visual and auditory serial recall tasks, and physiological stress with heart rate variability. Results did not depend on the country, suggesting that our findings could be similar also in other countries. Speech annoyance and perceived concentration difficulty differed in each condition. With other experience measures, only Reg+ improved experience compared to the two other conditions. Visual serial recall performance was more accurate and faster in Reg+ than in Reg-. Accuracy was also improved in Reg0 compared to Reg-. The physiological stress levels did not depend on the condition. Our study shows that Reg0 was better than Reg- with respect to experience and performance but experience was further improved from Reg0 to Reg+. Therefore, it is beneficial to design room acoustics better than the Finnish regulation to maximize work performance and experience.