Haas effect
The Haas effect is for the room acoustics and especially for the sound system is of great importance.
Method
The dissertation by Helmut Haas, " On the influence of a single echo on the audibility of speech " (1951), Acustica 1, pages 49-58, the following is postulated:
The first arriving at the listener direct sound alone is decisive direction. This gives only an auditory event. Those with a propagation delay of Δ t> 2 ms incoming reflection increased in the auditory event the volume, changing the tone and increases the impression of greater spatial extent. Even if the subsequent signal (reflection ) has a higher level and with a propagation delay within Δ t < 35 ms arrives, only the first incoming signal determines the perceived direction of incidence.
Although Haas two speakers for its tests used, which were placed in a listening angle of ± 45 ° from the listener, his work does not relate to today's Stereofonieverfahren. The localization of phantom sources on the speaker base by runtime differences 0-3 milliseconds at the Laufzeitstereofonie or Äquivalenzstereofonie has nothing to do with this Haas effect.
The Haas effect is brought also with other terms " law of the first wavefront " or " precedence effect " relating to or often equated. See: The " precedence effect" ( Wallach et al, 1949. ) - The " Haas effect", after Haas (1951 ) - The "law of the first wave front" ( Blauert, 1997).
Law of the first wavefront
Two similar signals coming from different directions (eg direct sound and a discard ), will be localized from the incident direction from which arrives the first wavefront. This situation is called the law of the first wavefront or precedence effect. However, the delay of the second signal can not exceed a certain threshold ( the echo threshold ), since the receiver in this case, two individual signals (e.g., direct sound echo) perceives. The echo threshold is dependent on the delay time and the level of (! ) Of the second signal. If the delay of the second signal is less than 3 ms, the result is a different phenomenon, the summing localization in the direction of localization.
The precedence effect shows that the hearing the arriving first at the hearing direct sound in determining the direction of an auditory event ( an auditory object) given more consideration than the time arriving later discards. A few milliseconds after the direct sound arriving discards are not perceived as a single auditory events. Recent studies have shown that habituation to a reflection -prone environment the precedence effect amplified (Structure of Präzedenzeffekts ), while certain changes in the auditory scenarios reset the precedence effect again (burglary of Präzedenzeffekts ).
If a listener has become accustomed to an auditory scenario, be back litters that do not provide relevant information for the listener, is suppressed. New " unexpected " discards are less strongly suppressed because they also contain new information about the environment. An alternative explanation holds that the structure of the Präzedenzeffekts occur selectively for the directions from which discards arrive at the listener.
The spatial sense of localization of sound sources depends essentially on the time of arrival of the sound signals. This delay times 2-30 ms are used. If the delay is longer than 50 ms, so two separate sounds are audible. Mostly a delay between 10 and 30 milliseconds is used as the Haas effect in the PA systems.
The studies of Haas do not describe the Precedence Effect in full width. They deal mainly so that the conditions under which a delayed sound, which has a higher level than the undelayed sound is still perceived from the direction of the instantaneous sound. Only under these conditions are met, if the reflection is "louder" than the direct sound, the specified Haas delay time range applies 10 to 30 ms. This effect is referred to in the test with Trading, in contrast to the use in the stereo recording as equivalent.