The science of architectural acoustics is divided into room acoustics and building acoustics. A theoretical model and a calculation method for reverberation time were developed together with the first measurement method. Airborne sound insulation was measured with organ pipes as an extension of the method used for reverberation time. Another issue that would need attention was the impact sound from floors, especially footfall noise. New building technologies, new powerful sound sources in homes (hi-fi loudspeakers, home cinemas with subwoofers, etc.) and increased awareness of noise in the society have all contributed to the development of better sound insulation design. An important part of this development is the acousticians' understanding of the physical principles in sound insulation. Another important part of the development is the knowledge about how individuals react to noise from neighbours, and how the sound insulation of a building is related to the degree of satisfaction that can be expected among the inhabitants.