Speech is the main source of disturbance in offices. Task irrelevant speech causes annoyance, reduces performance, and increases physiological stress. Good acoustic design can reduce these adverse effects. Finnish building regulations require that the Speech Transmission Index (STI) in an unfurnished office space (furniture removed) is < 0.50. Our aim was to examine the benefits of good acoustic design regarding the room (building owner’s costs) and furniture (user’s costs) on cognitive performance, subjective experience, well-being, and stress (costs of employees). Identical laboratory experiments were performed in Finland and Germany. The conditions A-C were based on measurements in a real office during three stages of building, which differed in absorption, sound masking, and furniture. The simulated conditions were: A. Regulations violated (STI = 0.8); B. Regulations fulfilled (STI = 0.3), and C. Regulations surpassed (STI = 0.1). We measured cognitive performance, subjective experience, and physiological stress of participants. Finnish and German results were alike, and the samples were merged (N = 98). Conditions B and C appeared to lead to the best performance, and Condition C further improved subjective experience. Therefore, office design fulfilling Finnish regulations is useful for performance. Surpassing the regulations can improve work experience.