Room acoustics is the field of acoustics, which deals with the effect of a rooms physical conditions on the sound events occurring in it. In this respect rooms can be concert halls, theaters, classrooms, studios, churches, but also offices, call centers or conference rooms where acoustic performances (language or music) or communication in general take place.
The central question of room acoustics adresses which surfaces can be used to create optimal hearing conditions in a room. The decisive property of the materials in this context is their sound absorbing ability.
SOUND ABSORPTION COEFFICIENT
The sound absorption coefficient α of a material indicates the absorbed portion of the total sound impact.
α = 0 meaning that no absorption takes place; the incidental sound is completely reflected. At α = 0.5, 50% of the sound energy is absorbed and 50% is reflected. At α = 1 the sound gets completely absorbed; a reflection no longer takes place.
Reverberation time is the key criterion for the assessment of rooms from a room acoustical viewpoint. In simplified terms it indicates the duration of time required for a sound event to become inaudible. Technically, the reverberation time T is defined as the time duration for a 60 dB decrease of the sound pressure level in a room.
The optimal reverberation time depends on the usage of a room. The so-called acoustic quality of a room signifies its suitability for a certain usage. Acoustic quality is determined by the condition of the spatially demarcating surfaces (wall, ceiling, floor), furnishings and the persons present.
The frequency specifies the number of sound pressure changes per second. Sound events with a high frequency are perceived as high notes by the human ear, low frequency sound events as deep sounds.
Sounds such as noise, road traffic etc. usually include a variety of frequencies. The measuring unit of frequencies is hertz (Hz), 1 Hz = 1 / s. Human speech ranges from 250 Hz to 2000 Hz. The human hearing range is between 20 Hz and 20000 Hz.
REVERBERATION CHAMBER METHOD
The reverberation chamber method is used to determine the frequency-dependent sound absorption degree. A sample of a to be tested material is placed into a reverberation chamber. The sound absorption ability of this material can be calculated based on the change in reverberation time in the chamber.
Sound absorption or sound attenuation describes the ability of materials to absorb sound or respectively convert sound energy into other forms of energy, ultimately into heat energy (see also "sound damping").
Sound damping specifies the limitation of sound propagation through space limitations. Sound damping is thus a measure for the acoustic separation of rooms or areas from undesired sound from adjacent rooms or areas. This has nothing to do with the required acoustic sound attenuation in the room (see also "sound absorption").
Airborne sound damping and impact sound damping are differentiated. Airborne sound is generated by sound sources in the room, which do not have a direct connection to the spatial damarcation, eg. speaking people. On the other hand impact sound is generated by structure-borne noise (steps, knocking), which in turn stimulates walls or ceilings to emit airborne sound.
Variations of the air pressure caused by sound events are called sound waves. The length of the sound waves defines the frequency, the height of the sound waves their level. Long sound waves have a low frequency and are perceived as deep sounds. Short sound waves have a high frequency and are perceived as high notes.
A 100 Hz wave has an expansion of 3.40 meters in the air, a 5000 Hz wave has an expansion of approx. 7 centimeters.
Source: bso Verband Büro-, Sitz- und Objektmöbel e.V.