Methods to measure stage acoustic parameters: overview and future research

Transcription

1 Methods to measure stage acoustic parameters: overview and future research Remy Wenmaekers Constant Hak Maarten Hornikx Armin Kohlrausch Eindhoven University of Technology (NL)

2 Stage acoustics ST late T 30 Support Ease of Ensemble Reverberance EEL ST early Timbre PAGE 1

3 Perception vs physics perceptive physical/objective? T 30 ST early PAGE 2

4 State of the art Past research Marshall et al. (1978) Early insights into stage acoustics Gade ( ) Suggestions for stage acoustic parameters Dammerud (2010) Architecture, acoustics and musicians preference Guthrie (2014) Spatial parameters to describe stage acoustics Schärer Kalkandjiev (2015) How musicians adjust to acoustic conditions Current status - Some relations between perceptual attributes and physical parameters have been found, but these appear to be highly individual. - Optimal ranges for acoustic parameters are not confirmed or non-existent. - Researchers have doubts whether the standardised method used to measure physical stage acoustic parameters is sufficiently accurate and appropriate. / Department of the Built Environment - Unit BPS PAGE 3

5 Overview of our work Topics that have been investigated: Time windows for early and late reflected sound Measurements over various distances Reference level at 1 m or the sound power of the sound source Directivity of the dodecahedron sound source Impulse response quality (decay range) Occupied stage measurements Directional transducers Wenmaekers, Hak, Hornikx, Kohlrausch (2017). Sensitivity of stage acoustic parameters to source and receiver directivity: Measurements on three stages and in two orchestra pits. Appl. Acoust. 123, Wenmaekers, Hak and van Luxemburg (2012) On measurements of stage acoustic parameters - time interval limits and various source-receiver distances Acta. Acust. united Ac. 98, Wenmaekers and Hak (2015) The sound power as a reference for Sound Strength (G), Speech Level (L) and Support (ST): uncertainty of laboratory and in-situ calibration. Acta. Acust. united Ac.101, Hak, Wenmaekers, van Luxemburg (2012) Measuring room impulse responses: impact of the decay range on derived room acoustic parameters. Acta. Acust. united Ac. 98, Wenmaekers, Hak, Hornikx (2016). How orchestra members influence stage acoustic parameters on five different concert hall stages and orchestra pits. J. Ac. Soc. Am. 140(6), / Department of the Built Environment - Uit BPS PAGE 4

6 TIME WINDOWS AND DISTANCE / Department of the Built Environment - Unit BPS PAGE 5

7 Time windows (18 x 12 m 2 stage) Source Self Source Other Source Self Source other 1 Source other 2 Source other n Receiver Self time [ms] Direct sound Self, time is 3 ms at 1 m distance Early reflected Self, +/- 5 to 100 ms after direct sound Self Direct sound Others, +/- 3 to 60 ms after direct sound Self Early reflected Others, +/- 5 to 100 ms after direct sound Self Late reflected Hall, +/- > 100 ms to infinite after direct sound Self R.H.C. Wenmaekers, C.C.J.M. Hak, and L.C.J. van Luxemburg, (2012), On measurements of stage acoustic parameters - time interval limits and various source-receiver distances Acta Acustica united with Acustica, 98, PAGE 6

8 Optimised acoustic parameters 103 ms delay 10 ms after delay Sound power measurement delay = time for direct sound to arrive at receiver R.H.C. Wenmaekers, C.C.J.M. Hak, and L.C.J. van Luxemburg, (2012), On measurements of stage acoustic parameters - time interval limits and various source-receiver distances Acta Acustica united with Acustica, 98, PAGE 7

9 SOUND POWER OF THE SOURCE PAGE 8

10 Reference level / sound power Precision methods ISO methods Diffuse field Sound Intensity Single plane Free field In-situ Direct or with ref. *: The maximum uncertainty over all octave bands is shown, which is dominated by the 125 Hz octave band. **: The uncertainty presented for STI holds for the worst case scenario when the room acoustics has no influence. ***: The two figures represent the offset and the random deviation. R.H.C. Wenmaekers and C.C.J.M. Hak (2015) The sound power as a reference for sound strength (G), speech level (L) and support (ST): uncertainty of laboratory and in-situ calibration. Acta Acustica united with Acustica, 101(5), PAGE 9

11 DIRECTIVITY OF THE DODECAHEDRON / Department of the Built Environment - Unit BPS PAGE 10

12 Directivity of dodecahedron source Sound pressure level (free field) Made by Johannes Klein (ITA) f (Hz) 500 1,500 4,000 9,000 22,000 ISO rotations (40 degrees) ISO rotations Of 12.5 degrees Equi-angular steps 2 to 8 rotations Suggested by Martelotta J. Acoust. Soc. Am. 134 (2013) PAGE 11 Repeatibility Measurement every 5 degrees, 72 steps R.H.C. Wenmaekers and C.C.J.M. Hak (2015) The sound power as a reference for sound strength (G), speech level (L) and support (ST): uncertainty of laboratory and in-situ calibration. Acta Acustica united with Acustica, 101(5),

13 IMPULSE RESPONSE QUALITY / Department of the Built Environment - Unit BPS PAGE 12

14 Impulse response quality Decay range estimated by the room Impulse to Noise Ratio (INR) - Calculate the Reverberation Time - Determine the backwards integrated energy curve S(t). - Calculate the level of the impulse response at t=0, L IR (based on an exponential decay) - Calculate the noise level L N - Calculate the decay range INR Stage acoustic parameters: The decay range should be 30 db or more for determining ST early or ST late with an error < JND C.C.J.M. Hak, R.H.C. Wenmaekers, L.C.J. van Luxemburg (2012) Measuring room impulse responses: impact of the decay range on derived room acoustic parameters. Acta. Acust. united Ac. 98, PAGE 13

15 THE OCCUPIED STAGE / Department of the Built Environment - Unit BPS PAGE 14

16 Occupied stage, direct sound Attenuation of direct sound with floor reflection Dammerud and Barron, J. Acoust. Soc. Am. 128, (2010). R.H.C. Wenmaekers, C.C.J.M. Hak, M.C.J. Hornikx (2016). How orchestra members influence stage acoustic parameters on five different concert hall stages and orchestra pits. J. Ac. Soc. Am. 140(6), PAGE 15

17 Occupied stage, reflected sound - ST early at 1 m distance varies by 2 db with/without orchestra members, close to the estimated JND - ST early,d at various distances significantly reduced as a function of distance by the orchestra members - ST late significantly reduced above 2 db, more than expected based on reduction of reverberation time - Mannequin orchestra accurate substitute but not practical - A musician friendly measurement with a real orchestra performed within 10 minutes R.H.C. Wenmaekers, C.C.J.M. Hak, M.C.J. Hornikx (2016). How orchestra members influence stage acoustic parameters on five different concert hall stages and orchestra pits. J. Ac. Soc. Am. 140(6), PAGE 16

18 DIRECTIONAL SOURCE AND RECEIVER / Department of the Built Environment - Unit BPS PAGE 17

19 Directive receiver: HATS Omni source and HATS receiver The EDT tends to be lower and STearly,dhigher for the ear directed towards the sound source. (average deviation well below the estimated JND of 2 db) RWenmaekers, Hak, Hornikx, Kohlrausch (2017). Sensitivity of stage acoustic parameters to source and receiver directivity: Measurements on three stages and in two orchestra pits. Appl. Acoust. 123, PAGE 18

20 Directive source: 12 loudspeakers 250 Hz 1 khz 4 khz * ** * Behler and Pollow (2008) J. Acoust. Soc. Am. 123(5) ** Pätynen and Lokki (2010) Acta. Acust. united Ac. 96, ST early,d (2-4 khz) RWenmaekers, Hak, Hornikx, Kohlrausch (2017). Sensitivity of stage acoustic parameters to source and receiver directivity: Measurements on three stages and in two orchestra pits. Appl. Acoust. 123, PAGE 19

21 Directive source: 12 loudspeakers The the EDT tends to be lower and STearly,dhigher when the sound source is directed towards a surface causing a first order reflection. (on average just below the estimated JND) ST early,d (2-4 khz) RWenmaekers, Hak, Hornikx, Kohlrausch (2017). Sensitivity of stage acoustic parameters to source and receiver directivity: Measurements on three stages and in two orchestra pits. Appl. Acoust. 123, PAGE 20

22 CONCLUSIONS / Department of the Built Environment - Unit BPS PAGE 21

23 Summary of conclusions The time limits used in ST early and ST late are reasonable. To measure reflected sound levels over distance the ST time window can be modified using a variable time point 103-delay. Distance averaged results for ST early,d highly correlate with ST early at 1 m. Reference measurement at 1 m in situ should be avoided. Sound power preferably measured in the reverberation room instead of anechoic room. For single position, frequency band results the source should be rotated 5x. The decay range should be sufficient, with INR > 30 db. ST early at 1 m is only moderately influenced by presence orchestra. Orchestra should be present when measuring over distance. Chairs and stands hardly effect the sound field (might as well empty). Removing objects close to the source/receiver is not necessary. Source and receiver directivity have an influence on ST early,d and ST late,d with a value just below the estimated JND. PAGE 22

24 FUTURE RESEARCH / Department of the Built Environment - Unit BPS PAGE 23

25 Recommendations for future research Very different stages can have equal ST values but are evaluated differently. ST might only be comparable among stages with similar architectural properties and similar basic acoustic conditions (RT). The effect of design elements (reflectors, diffusors, dimensions, etc.) on parameter values could be further investigated. The just noticeable difference for ST needs to be established. Studies using simulated sound fields could include the full orchestra, both in terms of transmission of sound through it, the number of sources. To find preferred values for acoustic parameters, it is necessary to develop new research methods that can substantially increase the amount of included stages and participating musicians (either in field or laboratory studies). PAGE 24

26 More info : R.H.C.Wenmaekers@tue.nl / Department of the Built Environment - Unit BPS PAGE 25

27 Annex: Design guidelines The hall should have a suitable acoustics for symphonic music as preferred by the audience. The stage should not be too wide or too deep (17-18 m x m is a good range) and the total surface area should not be based on 2 m 2 per musician (200 m 2 for a full orchestra). Larger stages should have variable means to reduce its size by flexible walls. Risers should be present, a semi-circular shape is liked by strings players. The walls of the stage should be oriented in such a way that sound is reflected back to the stage. The upper parts of the walls should be tilted to direct sound over the heads of players. Sound from the loud woodwinds and brass should not be trapped on stage. This could be avoided by playing the walls in the back and by adding sound scattering or sound absorbing elements to walls. Reflectors above the orchestra might be necessary, however care must be taken that sound from loud woodwinds and brass is not reflected to the softer strings. A typical height is 6 to 10 m. Above 10 meters reflectors are not effective. / Department of the Built Environment - Unit BPS PAGE 26

28 Annex: Examples of good stages Left shows the concert stage that is preferred by the musicians in Dammerud s study (The Anvil Basingstoke) and the stage in our study that had the best balance of early and and late reflected sound (Muziekgebouw Eindhoven). Both stages fulfil the requirements mentioned in the guidelines: moderate stage dimensions, large tilted upper side walls, risers and a high ceiling (the ceiling reflectors in these halls project sound to the audience). Possibly, this is a rather safe stage design that is generally liked by musicians. However, these concert halls are of moderate size with room volumes around 14,000 m 3. / Department of the Built Environment - Unit BPS PAGE 27

29 Annex: New concert stages Looking at large concert halls with room volumes of 25,000 m 3 or more, left: Philharmonie Paris (2015), right: Elbphilharmonie Hamburg (2017), one also recognises the architectural features mentioned in the guidelines. However, the stages in these large concert halls are wider than 18 m and deeper than 12 m resulting in a floor area above 250 m 2. The reflectors are positioned high above the stage, only moderately influencing early reflected sound levels. There is a risk that time delays are too long and early reflected sound levels are too low on these large stages. / Department of the Built Environment - Unit BPS PAGE 28