Background

The interaural level difference is the difference in loudness and frequency distribution between the two ears. As sound travels, its strength dissipates. For example, if you are very close to a loud sound, it will sound loud to you. But if you are some distance from the same loud sound, it will not be as loud. Think of a dog barking. If it is right in front of you, it will sound loud, but if the same dog barks across a big grassy field, the sound will be much less loud to you. Amazingly, our ears can detect loudness differences between the left and right ears. However, more important for sound localization is that the head casts an acoustic shadow, which changes the loudness and frequency distribution of sound going to each ear. We can define the acoustic shadow as the area on the side of the head opposite from the source of a sound in which the loudness of a sound is less because of blocked sound waves. The acoustic shadow is much more prominent for high-frequency sounds than it is for low-frequency sounds.

In this activity, you can explore how sounds arising from different direction lead to this auditory space cue.

Instructions

Full Screen Mode

To see the illustration in full screen, which is recommended, press the Full Screen button, which appears at the top of the page.

Illustration Tab

Settings

Below is a list of the ways that you can alter the illustration. The settings include the following:

Start: Start an animation that traces the sound from the source to the two ears. This travel time will be plotted on the screen as well.
Sound Source X Position: Move the sound source left and right across the screen.
Sound Source Y Position: Moves the disparity object up and down on the screen.
You can also move the sound source by clicking and dragging on the screen with a mouse or by touching the screen.

Reset

Pressing this button restores the settings to their default values.