Subjective quality:

In concert halls, intimacy refers to the feeling of being close to the source of the music. This impression is usually present in smaller halls, but it is often difficult to achieve in larger spaces. In large halls that have not been designed with intimacy in mind, the audience may feel remote and detached from the performance.

Objective measure:

Intimacy is quantitatively measured by the initial time-delay gap (ITDG). This quantity is given by the time difference between arrival of the direct sound and arrival of the first significant reflection at a certain receiver position. If a space has a relatively short ITDG, it is said to be more intimate; a longer ITDG indicates less intimacy. In smaller halls, enclosing surfaces are closer together, so reflections occur more frequently than in large halls where surfaces are farther apart. Therefore, smaller halls generally have shorter initial time-delay gaps.

Because the initial time delay gap can depend on receiver position, it is standard to measure ITDG at a position roughly in the center of a hall for comparison purposes.

Listen to seats with different ITDG’s.

Optimum values:

Appropriate ITDG’s depend on the type of music for which a space is being designed. However, in general, concert halls are more successful if they have shorter ITDG’s, somewhere between 12 and 25 milliseconds.

Click for ITDG’s of famous concert halls.

How to design:

To increase ITDG, one should shorten the distance from the first reflecting surface to the audience area. In larger spaces, this may be accomplished by adding ceiling reflectors or protrusions from the walls.

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