Dissatisfaction with acoustic conditions is a common problem in open-plan offices, as documented by numerous researchers over several decades. 1-6 Similar problems are also encountered nowadays in activity-based offices, albeit to a lesser extent. 7-9 Of the different noise sources in open-plan offices, speech is the main source of noise annoyance, 3,5,10 correlating highly with the general perception of disturbing noise. 11 The acoustic problems are not restricted to subjective discomfort but have more direct implications for the productivity of workers. Background speech that is irrelevant to the listener (later in the text: speech) is known to objectively decrease human performance in several areas of information processing, including particularly verbal short-term memory, 12 but also more complex tasks, such as writing 13 and proofreading. 14 Thus, the noise control