Academic journal article Psychomusicology

The Preferred Level Balance between Direct, Early, and Late Sound in Concert Halls

Academic journal article Psychomusicology

The Preferred Level Balance between Direct, Early, and Late Sound in Concert Halls

Article excerpt

The auditory perception of a symphony orchestra playing in a concert hall can be understood with respect to two main percepts: the source presence and the room presence (Kahle, 2013). The source presence is the continuous perception of the sound sources in the hall, whether it be through a unified source perception (i.e., the full orchestra as one auditory entity), groups of instruments, or each instrument as a separate entity in the perceptual domain. The formation of the auditory streams comes about through stream segregation (Griesinger, 1997) and is subject to the perceptual grouping laws therein (Moore, 2012). The early reflections are perceptually grouped with the source streams through the precedence effect (Litovsky, Colburn, Yost, & Guzman, 1999), and affect the width, loudness, and timbre of the auditory events (Blauert, 1997). In this way, the direct sound of the orchestra and the early reflections of the hall combine to make up the source presence. The late reflections form the room presence, that is, the context and space for the music which lends the music support, embellishment, and a sense of depth, and provides the listener with a sense of envelopment.

The balanced relationship of the early sound (i.e., direct sound and early reflections) and the late reflections is a necessary requirement for a concert hall (Meyer, 2009). It is usually expressed with the concept of "clarity" and the corresponding standard parameter C80 (ISO 3382-1:2009, 2009), which measures the amount of early sound energy against that of late energy. Adequate clarity is needed for appreciation of musical detail (Barron, 2009), but it is also known that the late reflections enhance the blending of the instruments of the orchestra into a "closed overall sound" (Meyer, 2009).

The crossover time for early and late reflections is often taken to be 80 ms, as is also the case for the ISO 3382-1 parameters. However, it is a simplification. In terms of the source presence, an early reflection is one which contributes to it. From the studies concerning the precedence effect, it is known that the limit of fusion is dependent on the nature of the sound stimuli (Litovsky et al., 1999). The limit is shorter for transients such as clicks, and longer for less abrupt and more continuous sounds, such as speech. The significance for concert hall acoustics is that the limit is more or less dependent on program material. It has also been suggested that the fusion limit for early reflections depends on frequency (Soulodre, Lavoie, & Norcross, 2003), with low frequency limits longer than 80 ms and high frequency limits somewhat shorter. However, the 80 ms limit may be seen as a plausible perceptual average for most symphonic music.

The relationship of the direct sound to the early reflections is also of interest. The direct sound is afflicted by the seat dip effect (Schultz & Watters, 1964; Sessler & West, 1964), which is caused by interference from diffracted and reflected sound from the audience seats. It is often seen as a broad region of attenuation in the low frequencies with a center between about 100 Hz to 300 Hz and a maximum attenuation of about 10 to 20 dB. The early reflections contribute to fill the dip in the frequency response (Pätynen, Tervo, & Lokki, 2013). Lateral early reflections also broaden the width of the auditory sources, which is a crucial effect for good concert halls (Barron & Marshall, 1981). The extent of this effect is measured by the early lateral energy fraction (standard parameter JLF), which is the fraction of sound energy arriving from lateral directions within 5 to 80 ms compared with the whole sound energy arriving within 0 to 80 ms.

While the ISO 3382-1 standard parameters are useful for classifying concert halls and establishing optimum criteria for guidance, several studies point toward shortcomings of the parameters (Bradley, 2011; Kirkegaard & Gulsrud, 2011; Lokki, Pätynen, Tervo, Siltanen, & Savioja, 2011). …

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