At a spherical dome’s focal point one can hear one’s own voice concentrated to an extraordinary extent, but the focus shifts away from oneself at other locations. The spherical Mapparium (Boston, USA) provides access to the sphere’s focus, entertaining tourists and especially acousticians with the sound of their own or each other’s voice, ]. In many domed buildings the geometric focus is not accessible, but whispering wall phenomena are well-known at St Paul’s Cathedral (London, UK) and Gol Gumbaz (Bijapur, India). Using these approaches to investigate reflections in the polytrihedral dome, this paper documents retroreflective acoustic design that, on a larger scale, might ameliorate sound focussing problems in domed room designs.ĭomes and curved surfaces in architecture have been noted for the way they capture and concentrate sound through whispering wall and focussing phenomena. Average voice output between the two environments as measured by a contact microphone differ by 9 dB while the level at the ears remains approximately the same. In-situ field measurements of singing practice show reduced voice levels ( room effect) from the dome’s voice support, contrasted with increased voice levels ( Lombard effect) at a second practice setting, a waterfall. The polytrihedral dome was installed at a remote acoustically pristine location for sustained use in singing practice. This value is substantial partly because the on-axis singing energy is greatest in the 2 kHz octave band where retroreflection is particularly evident. The power spectrum of singing is measured and used to weight voice support, yielding measured mean values of + 3.5 dB (maximum + 6 dB).
Oral-binaural measurements of voice support exhibit a 4 dB/octave spectral slope from the 500 Hz to the 4 kHz octave bands.
Measurements and FDTD simulations show that the polytrihedral dome is retroreflective, especially in the 2 kHz octave band and higher, and provides high levels of voice support. The polytrihedral dome is investigated with laboratory measurements, field recordings of singing practice, and by finite-difference time-domain (FDTD) simulation of sound reflections within the polytrihedral dome and other kinds of domes for comparison. This paper examines acoustic retroreflection from a polytrihedral dome that was used in creative-arts practice-led research as a unique, high voice support singing practice space.
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