Investigations on the Development of the Frequency Response over Time in Concert Halls

The subjective impression of the concert hall acoustics is usually formed around various descriptors, such as clarity and definition, and envelopment in the sound field. While room acoustics is evaluated from room impulse responses with several standardized objective parameters1, such as G, T60, C80, EDT, and LF, the frequency response of the hall is sometimes left for lesser importance. The overall frequency response commonly depends on the surface properties. Although the direct sound frequency response could be intuitively thought as flat, the "seat dip" phenomenon affects to the direct sound by attenuating low frequencies. The effect is noticed mainly around 100-300 Hz, but it can span up to 1000 Hz. The seat dip effect was first introduced with real and model measurements at different distances from the stage by Schultz and Watters, and Sessler and West in 19642,3. The attenuation was noticed at approximately one-quarter wavelengths of the seat heights, when the sound is diffracted from the seat backs to the floor, and later integrates with the actual direct sound causing destructive interference. The effect was observed to increase with longer receiving distances up to 19 m. Subsequently, multiple papers have been published on the subject with measured and experimental data.