Early reflections
In room acoustics, early reflections are understood to be the portion of the reflected sound that arrives at a listener within 15 milliseconds of the direct sound .
Characteristic
Early reflections are sound thrown back by a solid body, which often reaches the ear immediately after this one or a few more reflections. The time interval between the individual early reflections is still relatively large. The early reflections pass seamlessly into the reverberation as the time interval increases from the direct sound, from approx. 15 ms .
Room acoustic design
The early reflections have a decisive influence on the room acoustics assessment of a room. Since the human ear can still determine the direction of early reflections , they contribute significantly to the spatial impression. In addition, they change the sound perceived by the listener, since their frequency response often does not match the direct sound. If they arrive at the listener less than 60 milliseconds after the direct wave, they increase the subjective impression of volume and the speech intelligibility measured in Alcons . Later we no longer assign them to the direct wave and they blur the sound impression. Therefore, when planning the halls, care must be taken that the sound detour between the direct wave and the first reflections does not exceed about 20 meters. Efforts are also being made to build concert halls in such a way that the early reflections are distributed as well as possible across all directions. This is intended to achieve a high degree of "spatiality" in the concert hall: the listener should also have a musical spatial experience.
Sound engineering applications
In audio engineering, the time interval between the arrival of the direct sound and the first reflection early indoors "is initial time gap " (or ITDG = Initial Time Delay Gap ) mentioned. By changing the predelay value of a delay device, the subjectively perceived distance to the sound source can be influenced. The perceived characteristics of a simulated room depend on the level, the temporal course, the sound and the directional distribution of the early reflections, as well as the level and time behavior of the denser reverberation. If the phantom sound sources are generated with panpots alone , there is no difference in direction between the direct wave and the first reflections. Up to now, these acoustic conditions can only be reconstructed spatially correctly using the method of wave field synthesis .
Web links
- Early reflections below 15 ms are undesirable in stereo recordings (PDF file; 36 kB). Accessed on May 20, 2013.
Individual evidence
- ↑ Stefan Weinzierl: Handbuch der Audiotechnik , p. 869. Retrieved on May 17, 2013 .