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Room Acoustical Parameters

CadnaR the following room acoustical parameters are calculated from the backward-integrated RIR-Evaluation.

  1. T30 (reverberation time from 30 dB decrease of level): linear regression from -5 to -35 dB (based on the method of least squares)

Example: RIR-Evaluation for 500 Hz-octave with regression line for reverberation time T30 (500 Hz)

  1. T20 (reverberation time from 20 dB decrease of level): linear regression from -5 to -25 dB (based on the method of least squares)

Example: RIR-Evaluation for 500 Hz-octave with regression line for reverberation time T20 (500 Hz)

  1. T10 (reverberation time from 10 dB decrease of level): linear regression of -5 dB to 15 (based on the method of least squares)

Example: RIR-Evaluation for 500 Hz-octave with regression line for reverberation time T10 (500 Hz)

  1. EDT (Early Decay Time): linear regression from 0 to -10 dB (based on the method of least squares)

Example: RIR-Evaluation for 500 Hz-octave with regression line for early decay time EDT (500 Hz)

All four quality measures are determined from the slope of the integrated RIR-Evaluation. For each of the above listed parameters what level range of the decay curve was used to generate the regression line.

  1. D50 (Deutlichkeitsgrad or Deutlichkeit / Definition or Clarity, for speech):

where W is the sound energy (applies also to all further equations).

Note

The starting point at 0 ms corresponds with switching off the source, i.e. this and other energy based parameters include the direct sound.

  1. C50 (Deutlichkeitsmaß / Clarity Index, for speech):

  1. C80 (Klarheitsmaß / Clarity Index, for music):

  1. TS (Center Time or Center of Gravity Time, for speech):

  1. ALcons (Articulation Loss of Consonants, for speech):

The definition is based on the RIR-Evaluation, but does not consider a background noise level. In general, ALcons% is not specified in frequency bands. In CadnaR, the following values are provided:

  • ALcons_2k (2000 Hz)
  • ALcons_500_2k (average from octaves at 500, 1000, 2000 Hz)
  1. STI (acc. to IEC 60268-16:2011)

Two values result from the calculation scheme:

  • STI_male
  • STI_female

The calculation according to IEC 60268-16:2011 may consider or not the effect of background noise. In CadnaR, this depends on the settings on the "RIR-Evaluation" tab (see Configuration).

  1. STIPA acc. to IEC 60268-16:2011 (Speech Transmission Index for Public Address Systems)

  2. CIS (Common Intelligibility Scale acc. to Barnett):

    CIS results from STIPA according to:

    \(CIS=1+\lg(\text{STIPA})\)

    This equation holds provided STIPA>0.126.

Typical Value Ranges

From the available literature Literature, Literature, Literature, Literature] the following value ranges for each of the room acoustical parameters can be quoted:

Parameter Freq. Range Optimum for Speech ... for Music
T30
T20
T10		 500-1000 Hz ca. 1 s *) ca. 1.5 s *)
EDT 500-1000 Hz - ca. 2,2 s *)
D50 500-1000 Hz > 0.5 -
C50 500-1000 Hz > 0 dB -
C80 500-1000 Hz - -1 to +3 dB
TS 500-1000 Hz < 80 ms 100-150 ms
ALcons_2k 2000 Hz <=12%
Ranges:
< 3% ideal intelligibility
3..8% very good i.
8..11% good i.
11..20% poor i.
> 20% worthless i.		 -
ALcons_500_2k 500-2000 Hz
STI_male 125-8000 Hz >=0,5
Ranges:
0..0,3 poor intelligibility
0,3..0,45 satisfactory i.
0,45..0,6 good i.
0,6..0,75 very good i.
0,75..1,0 excellent i.		 -
STI_female 250-8000 Hz
STIPA 125-8000 Hz see STI -
CIS 125-8000 Hz >= 0,7 (STI>=0,5) -

*) depending on the room volume V and type of use (values above hold for V=ca. 1000 m³)

Literature

  • Fasold, W.; Veres, E.: Schallschutz + Raumakustik in der Praxis, HUSS-MEDIEN GmbH, Verlag Bauwesen, Berlin, 2. Auflage 2003.
  • Ahnert, W.; Tennhardt, H.-P.: Kapitel 5 - Raumakustik, in: Handbuch der Audiotechnik (Hrsg.: S.Weinzierl), Springer Verlag, Berlin/Heidelberg, 2008.
  • DIN EN ISO 3382-1, Akustik - Messung von Parametern der Raumakustik, Teil 1: Aufführungsräume, 2009-10.
  • DIN 18041, Hörsamkeit in kleinen bis mittelgroßen Räumen, 2016-03.