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In concert halls, the spectrum of direct sound (here 0 to 15 ms) is influenced by the seat-dip effect that causes selective low frequency attenuation. The seat-dip effect has been considered to be detrimental to the acoustic quality of halls, yet there is little evidence about the perceptual significance of the effect. This paper studies the discrimination and preference of seat-dip effect related changes in the direct sound, with realistic auralization of multichannel anechoic orchestra recordings in halls measured with the loudspeaker orchestra. Comparisons are made with a free-field direct sound and direct sound magnitude changes typically associated with the seat-dip effect. Overall, the differences were not significantly audible, except with a subgroup of participants in one out of four halls, and two out of three comparisons. Furthermore, participants' preference for the uncolored direct sound was significant in the halls with less reflected energy, but non-significant in the halls with more reflected energy. The results imply that for most seats in adequately reverberant halls, typical seat-dip effect related coloration in the direct sound can be perceptually negligible.

It is known that the perception of a warm and full sound in a concert hall requires a rich bass. However, earlier research offers an incomplete understanding on the perception of bass in concert halls, especially regarding how the excess attenuation of low frequencies due to seats affects the perception of musical instruments with low-frequency fundamentals. This article studies the level of perceived bass and its clarity in 4 concert halls via paired comparison listening tests. The results suggest that the perceived level of bass is strongly related to the seat-dip effect, in particular to its main attenuation frequency with both short musical excerpts and individual notes. Moreover, the perceived clarity of bass seems to depend on the musical content and instruments. The results also indicate a complicated relationship between level and clarity of bass, as clarity can be enhanced with an increased level of bass in some cases.

The low-frequency attenuation in the direct sound due to the concert hall seats, i.e., the seat-dip effect, is studied with the help of a scale model comprising an adjustable seating area and an enclosed box. More particularly, different seat underpass sizes and floor raking angles are studied, and the results are averaged over multiple source positions. With the measurements on the seating area only, the main seat-dip frequency is found to depend on the seat back rest height, and on the degree of obstruction of the seat underpass. The attenuation bandwidth is found to depend mainly on the floor raking. The differences become less clear when seating area is enclosed by concert hall walls and ceiling because the early reflections from the concert hall geometry compensate the low-frequency attenuation in the direct sound. In addition, the low frequencies below the main seat-dip frequency are found to increase in the presence of unobstructed seat underpasses, and such seats are recommended for the maximal bass response in a concert hall.

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