Franssen Effect

(see AUDIO FILES for information on the *.wav files)

(The effect can only be heard if the sounds are presented to two loudspeakers. The loudspeakers should be placed at about +45 degrees (right) and -45 degrees (left), where 0 degrees is straight ahead. The listener should be about 3 feet from the loudspeakers. The exact configuration is probably not important, as long as the loudspeakers are not too close together and the listener either too close or too far away).

The Franssen Effect (see references below) is a strong auditory illusion demonstrating the power of the first arriving information in establishing the location of a sound source. The general stimulus configuration for the Franssen Effect is shown in the Figure. A sound is turned on abruptly at one loudspeaker and is then turned off slowly (with a 100-ms linear offset ramp). As this sound is going off, the sound is turned on at the other loudspeaker with the same envelope (with a 100-ms linear onset ramp). In this demonstration, this tone is left on for 5 seconds at this loudspeaker.

In the Noise Demonstration a broadband noise is used as the carrier sound for the temporal conditions shown in the Figure and explained above.

In this case, you should hear a sudden noise appear at one loudspeaker and then "jump" to the other loudspeaker, where the source of the sound remains for the rest of the five seconds. This is what the temporal diagram in the Figure shows.

In the Tone Demonstration, a 1000-Hz tone is used as the carrier.

In this case, almost all listeners report that the sound is always located at one loudspeaker. And this is the loudspeaker to which the brief tone was presented (the same loudspeaker from which you heard the short noise burst in the Noise demonstration). That is, you hear the full five seconds of sound coming from the location of the loudspeaker that only presented the sound for 100 ms. Or put another way, you hear the tone coming from a loudspeaker that is no longer presenting any sound. However, the location that you perceived as the sound's source is the loudspeaker that presented the sound first, and thus its location seems to dominate your perception of the sound's location.

In public demonstrations the tone is often left on for many seconds while the person presenting the demonstration removes the wires from the loudspeaker that everyone is pointing to as the source of the sound. Even with no wires going to the loudspeaker (or in some cases, even with the loudspeaker removed from the room), the audience still reports that the source of the sound is at the location of the (missing) loudspeaker.

The acoustics of the room in which the demonstration is being played will affect the strength of the illusion. For instance, it does not work in an anechoic room (see Hartmann and Rakerd in the references below).

Suggested References:

Blauert, J., Spatial Hearing. Cambridge, MA: MIT Press, 1983.

Hartmann, W. M., & Rakerd, B. (1989). Localization of sound in rooms IV: The Franssen effect. Journal of the Acoustical Society of America, 86(4), 1366-1373.

Yost, William A. and Guzman, Sandra J. Sound Source Processing: Is There an Echo in Here?, Current Directions in Psychological Sciences, invited paper-under review.