Simple Explanation

A sound curve used in the film industry, defining how sound should be distributed in a theater or dubbing situation, with a gradual roll-off above 2 kHz.

Concise Technical Definition

The X curve (or extended curve) is a standard used in the film sound industry, particularly for playback in movie theaters. It is designed to produce a flat response up to 2 kHz, with a gradual roll-off of 3 dB per octave above that frequency. The X curve is defined by ISO Bulletin 2969 and is commonly used for listening positions in dubbing situations or approximately two-thirds of the way back in a theater. A variation, the small-room X curve, is used for smaller rooms (under 150 cubic meters or 5,300 cubic feet), with a flat response to 2 kHz, rolling off at 1.5 dB per octave, or a modified curve starting the roll-off at 4 kHz with a 3 dB per octave rate.

Layman-Friendly Analogy

The X curve is like the way a concert sounds better as you move away from the stage. Near the stage, the sound is bright, but further back, the higher frequencies start to fade, making the sound feel more balanced. In theaters, the X curve helps replicate this effect, so the sound is more natural for listeners seated away from the speakers.

Industry Usage Summary

The X curve is primarily used in the film and movie sound industries, where it defines the ideal frequency response for cinema sound systems. It ensures that sound levels remain consistent and natural across a theater, especially for seated listeners in the back rows. The X curve is also used in smaller rooms, such as those with less than 150 cubic meters of space, and is essential for achieving a balanced sound that doesn't sound too bright or harsh, especially in rooms with less acoustic treatment. This curve is often compared with the Academy curve, which has similar but slightly different specifications.

Engineering Shortcut

A standardized frequency response curve used in the film sound industry to ensure balanced sound with a gradual high-frequency roll-off starting at 2 kHz.

Full Technical Explanation

The X curve is a standard curve used in film sound reproduction, particularly in movie theaters and dubbing situations. According to ISO Bulletin 2969, the curve specifies that the sound should be flat up to 2 kHz at the listening position, with a roll-off starting at that frequency. Above 2 kHz, the sound drops by 3 dB per octave, providing a smooth, natural reduction in treble frequencies. The small-room X curve is designed for smaller spaces, such as those with less than 150 cubic meters, and has a slightly different roll-off rate of 1.5 dB per octave. A modified version of this curve may begin the roll-off at 4 kHz and roll off at a rate of 3 dB per octave. The X curve ensures that sound is consistent for listeners at different distances in a theater, replicating how human hearing naturally diminishes high frequencies with distance. It is often used as a reference in the film industry for achieving natural, immersive sound in both large and small spaces.