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7 Calculated Room Acoustical parameters This chapter will shortly describe the derivation of energy parameters for Single Point, Multi Point and Grid response calculations (for the Industrial edition only EDT, T 30 , SPL, SPL A and STI are available). All the parameters are derived on the assumption that the addition of energy contributions from different reflections in a response is valid. This manual will not cover the use of the individual parameters in depth and suggestions on ideal parameters choice should only be sought of as a first suggestion; instead refer to relevant literature e.g. some of the following references for a further discussion on parameters and design criterions: Auditorium acoustics as Concert Halls, Opera Halls, Multipurpose halls, etc. are dealt with in (Beranek, 1996) and (Barron, 1993), where different halls around the world are presented along with judgement of their acoustics and guidelines for design. Short guidelines on which values to expect for Clarity and G in concert halls based on some simple design parameters as width, height, floor-slope, etc. are given in (Gade, 1997). Some recommended values for room acoustical parameters are given in the following table. Objective parameter Symbol Recommended Subj. limen (symphonic music) Reverberation time T 30 1.7 - 2.3 seconds 5 % Clarity C 80 - 1 to 3 dB 5 % Level rel. 10 m free G > 3 dB 1 dB field Early Lateral Energy LF 80 > 0.25 5 % Fraction Early Support ST early > -13 dB Total Support ST total > -12 dB Recommended values for objective room acoustical parameters (ISO 3382-1, 2009) in large music rooms with audience, according to Gade (Gade, 2003). Subjective limen as given by Bork (Bork, 2000) and Bradley (Bradley, 1986). Early Decay Time and Reverberation time The energies of all the reflections received at the receiver point are collected in histograms, with class interval specified in the Room setup |Impulse response resolution. After completion of the response calculation, early decay time and the reverberation time are calculated according to (ISO 3382-1, 2009): The Reverberation time T 30 is calculated from the slope of the backward-integrated octave band curves. The slope of the decay curve is determined from the slope of the best-fit linear regression line between -5 and -35 dB, obtained from the backwardintegrated decay curve. Early Decay Time (EDT) is obtained from the initial 10 dB drop of the backwardintegrated decay curve. Sound Pressure Level, C 80 , D 50 , LF 80 , ST early , ST late and ST total The energy of each reflection is added to the appropriate terms in the formulas for all the energy parameters, according to its time and direction of arrival. After the response calculation, C 80 (Clarity), D 50 (Definition), Centre Time, SPL (Sound Pressure Level), LF 80 (Lateral Energy Fraction), ST early , ST late and ST total are derived. In the following formulae, E a-b is the sum of energy contributions between time a and time b after the direct sound, time t is the end of the calculated response, and t is, for the reflection 7-82