Room sound

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Illustration of the multiple reflections on the walls.
Without sound absorption , the unrest increases.

Room sound R , also diffuse sound or diffuse field , is the sound in a closed room which - in contrast to direct sound  D - has already experienced several reflections when it arrives at the listening or measurement location .

Relation to direct sound

The ratio of the total reflected to the direct sound is important for the audibility of a room. The sound engineering Raumbeschreibungs- and sensorineural concepts of space sound field (R> D) and direct field or open field (R <D) through the room radius  r H separately. This is the distance to the sound source in a closed room at which the sound level of the room signal corresponds to the size of the direct signal (R = D). When describing a room for sound recordings , one speaks of a sound-determining R / D or D / R ratio ( reverberation measure ).

If the microphones are set up within the reverberation radius for sound recordings , the reverberation effect that arises when the room sound component predominates is avoided , and soloists or individual groups of instruments in an orchestra can be controlled largely independently of one another. The missing room sound can be recorded with room microphones and added to the recording as desired.

The terms diffuse field and direct field are not always clearly distinguished from the terms near field and far field . While the diffuse field and direct field are determined by the properties of the surrounding space, the far field and near field are characterized by the sound source itself (the interferer), and the spatial effect is not considered - i.e. virtually anechoic space .

Propagation delay

Delayed (reflected) signals of the same signal effect to a propagation delay of Δ t = 50 ms at the same level of discard (!) A desired sound reinforcement . In contrast, with transit time delays Δ t > 50 ms and the same level, the direct signal D and the reflected signal R can be perceived as separate auditory events ( echo which is undesirable for room acoustics ); with a lower reflection level, the propagation delay can be increased further.

Initial time gap

Room noise is associated with the initial time gap ( Predelay also useful) to create the illusion of depth stepping in stereo recordings and surround sound to reach shots. A dry "foreground" made of direct sound is helpful here.

If the initial time gap is greater than 30 ms and less than about 60 ms, the result is a spacious and transparent sound impression . If, on the other hand, the time gap is less than 15 ms, a small-scale impression is created. It is therefore advisable to set the start time gap large and only shorten it if necessary.

In a room, each sound source creates its own initial time gap, which depends on the location of the sound source and the location of the listener or the measurement location. In contrast, the pre-delay in a reverberation device is a fixed time setting, so it does not correspond to the natural conditions in the room. Accordingly, it is incorrect to call the initial time gap a space constant, as can be read in textbooks.

See also

Individual evidence

  1. Eberhard Sengpiel: Initial gap and predelay (pdf; 149 kB)