# Haas effect

The Haas effect is of great importance for room acoustics and especially for sound reinforcement technology.

## method

In Helmut Haas ' dissertation , On the Influence of a Single Echo on the Audibility of Speech , the following is postulated:

The direct sound that reaches the listener first is solely directional. Only one auditory event occurs here . With a propagation delay of incoming reflection increased in the auditory event the volume , changing the tone color and increases the impression of greater spatial extension. Even if the following signal (reflection) has a higher level and arrives with a transit time delay within , only the signal arriving first determines the perceived direction of arrival. ${\ displaystyle \ Delta t> 2ms}$${\ displaystyle \ Delta t <35ms}$

Even if Haas used two loudspeakers for his tests, which were set up at a listening angle of ± 45 ° from the listener, his work does not refer to today's stereophony method . The localization of phantom sound sources on the loudspeaker base through time differences between 0 and 3 milliseconds in the case of time stereophony or equivalent stereophony has nothing to do with this Haase effect.

The Haas effect is also associated or often equated with other terms “law of the first wave front” or “ precedent effect ”.

## Law of the first wavefront

 The articles Precedence Effect and Haas Effect # Law of the First Wavefront overlap thematically. Help me to better differentiate or merge the articles (→  instructions ) . To do this, take part in the relevant redundancy discussion . Please remove this module only after the redundancy has been completely processed and do not forget to include the relevant entry on the redundancy discussion page{{ Done | 1 = ~~~~}}to mark. SK ( discussion ) 09:07, Jun 21, 2020 (CEST)

For two similar signals that arrive at a listener from different directions (e.g. a direct sound and its wall reflection), the perceived location of the sound source is assigned to the direction of incidence from which the first wavefront arrives.

This fact is called the law of the first wavefront or precedence effect. However, the delay of the second signal must not exceed a certain threshold (echo threshold), because in such a case the listener perceives two individual signals (e.g. direct sound and echo).

The echo threshold depends on the delay time and the level of the second signal. If the delay of the second signal is less than 3 ms, another phenomenon occurs, the cumulative localization in the directional localization .

The precedent effect shows that the hearing system takes into account the direct sound first arriving at the ear when determining the direction of an auditory event (auditory object) than the reflections that arrive later. Throws arriving a few milliseconds after the direct sound are not perceived as individual auditory events. Recent studies have shown that getting used to a reflective environment increases the precedence effect (build-up of the precedence effect), while certain changes in the auditory scenario reset the precedence effect (collapse of the precedence effect).

Once a listener has got used to an auditory scenario, discards that provide no relevant information for the listener are suppressed. New "unexpected" discards are suppressed less strongly because they also contain new information about the environment. An alternative attempt at an explanation states that the building of the precedence effect takes place selectively for the directions from which discards arrive at the listener.

The spatial perception of the localization of sound sources depends largely on the time at which the sound signals arrive. Here be Delay -times 2-30 ms used. If the delays are longer than 50 ms, two separate sound events are audible. A delay of between 10 and 30 milliseconds is mainly used as a Haas effect in the PA system.

Haas' research does not fully describe the precedence effect. They focus on the conditions under which a delayed sound, which has a higher level than the instantaneous sound, can still be perceived from the direction of the instantaneous sound. The specified Haas delay time range of 10 to 30 ms applies only under this boundary condition, when the reflection is “louder” than the direct sound. This effect is called trading in the experiment , in contrast to the use of stereo recording as equivalence .

## literature

• Jens Blauert : Spatial hearing. S. Hirzel, Stuttgart 1972, ISBN 3-7776-0250-7 .
• Helmut Haas: About the influence of a single echo on the audibility of speech . Göttingen 1949, DNB  481794824 (dissertation at Braunschweig Technical University, March 14, 1950).
• Helmut Haas: About the influence of a single echo on the audibility of speech . In: Acustica . tape 1 , no. 2 . S. Hirzel, 1951, ISSN  0001-7884 , p. 49-58 .