Falling coins, striking matches, and whispering voices to demonstrate the acoustics of an open air amphitheatre

Abstract

Part of the Ancient Acoustics research project was to measure a dense grid of impulse responses in three ancient amphitheatres in accordance with the ISO 3382 standard. In this conference paper, the measurements performed in the theatre of Epidaurus at 264 receiver positions are used to study the “signal” to “noise” ratios (SNR) for typical low energy sound sources such as falling coins, striking matches and whispering voices, described in travel guides and used by tourists to confirm or disclaim the exceptional acoustical quality of open air amphitheatres. The “signal” is obtained from sound powermeasurements of these sources in a reverberation room, combined with the measuredSound Strength G at every position in the theatre. To determine G, asynchronous impulse response measurements were carried out using two dodecahedron sound sources playing stimulus signals simultaneously. The measured background noise was used as the “noise” in the SNR. Besides, speech intelligibilitymeasurements have been carried out in accordance with IEC 60268-16 using a special “speech source,” that could be used to determine the SNR of a whispering voice. Using the sound sources mentioned, no evidence of the often claimed exceptional sound transmission was found.

Full text

Constant Hak
Niels Hoekstra
Bareld Nicolai
Remy Wenmaekers
University of Technology Eindhoven
Department of the Build environment
Unit Building Physics and Services
Falling coins, striking matches and whispering voices
to demonstrate the acoustics of an open air amphitheatre
Project: Ancient Acoustics
Acoustics ’17 Acoustical Society of America & Forum Acusticum Boston June 2017
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Herodes Atticus, Epidaurus and ArgosHerodes Atticus, Epidaurus and Argos
Acoustics ’17 Acoustical Society of America & Forum Acusticum Boston June 2017
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Impulse response measurements
Project Ancient Acoustics
Acoustics ’17 Acoustical Society of America & Forum Acusticum Boston June 2017
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microphone positions:
source positions:
measurements:
240
2
2400
Epidaurus number of
: S1, S2
(5 rotations)
: S1

Measurement and analysis
IR
Setup
Process Result
Acoustics ’17 Acoustical Society of America & Forum Acusticum Boston June 2017
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Average
5 angles
C80 1000 Hz
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[dB]
Sound source directivity
Measurement and analysis
Example

Impulse response and quality
Measurement and analysis
Acoustics ’17 Acoustical Society of America & Forum Acusticum Boston June 2017
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Percentage of the measured impulse responses that exceed a certain decay range (INR)

Acoustics ’17 Acoustical Society of America & Forum Acusticum Boston June 2017
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Hak, C.C.J.M., Hoekstra, N., Nicolai, B. & Wenmaekers, R.H.C. (2016). Project Ancient
Acoustics Part 1of 4:amethod for accurate impulse response measurements in large
open air theatres.23rd ICSV, 10-14 July 2016,Athens, Greece (pp. 1-8).
Hoekstra, N., Nicolai, B., Peeters, B.P.A., Hak, C.C.J.M. & Wenmaekers, R.H.C.
(2016). Project Ancient Acoustics Part 2of 4 : large-scale acoustical measurements in
the Odeon of Herodes Atticus and the theatres of Epidaurus and Argos.23rd ICSV, 10-
14 July 2016,Athens, Greece (pp. 1-8).
van Loenen, R.C., van der Wilt, M., Diakoumis, A., Wenmaekers, R.H.C. & Hak,
C.C.J.M. (2016). Project Ancient Acoustics Part 3of 4 : influence of geometrical and
material assumptions on ray-based acoustic simulations of two ancient theatres.23rd
ICSV, 10-14 July 2016,Athens, Greece (pp. 1-8).
Wenmaekers, R.H.C., Nicolai, B., Hoekstra, N. & Hak, C.C.J.M. (2016). Project Ancient
Acoustics Part 4of 4 : stage acoustics measured in the odeon of herodes atticus and
the theatre of argos.23rd ICSV, 10-14 July 2016,Athens, Greece (pp. 1-8).
Download via:
www.ancient-acoustics.nl
Four papers presented at ICSV 2016
More background info?

Do amphitheatres have
extraordinary acoustics?
Acoustics ’17 Acoustical Society of America & Forum Acusticum Boston June 2017
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“........Wonderbaarlijk is de akoestiek.Tot op de achterste rij, 59 mverwijderd
van het midden van de orchestra, waar de gids fluistert, enkele stappen zet,
een papiertje scheurt, een lucifer aanschrapt, op de borst slaat, met de
vingers knipt, een blad van een boek omslaat, een geldstuk laat vallen en
diep zucht, zijn duidelijk alle geluiden te horen! Op de weekeinden in de
zomermaanden worden er klassieke stukken opgevoerd;overal zijn de
spelers duidelijk te verstaan, alleen is er dan wat nagalm........”
Dominicus reisgids ‘Griekenland’ 1989
Acoustics ’17 Acoustical Society of America & Forum Acusticum Boston June 2017
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‘Epidaurus described in a travel guide’
Extraordinary acoustics?

“........The acoustics are extraordinary. Even on the back row, at adistance of
59 meters from the centre of the orchestra, where the tour guide whispers,
walks around, tears apiece of paper, lights amatch, beats his chest, snaps
his fingers, turns apage of abook, drops acoin and sighs heavily, all sounds
are clearly audible! During the summer weekends, classical plays are
performed there:the players can be heard everywhere, although there is abit
of reverb........”
...You could hear a pin drop...
‘Epidaurus described in a travel guide’
Dominicus travel guide ‘Greece’ 1989
Extraordinary acoustics?
Acoustics ’17 Acoustical Society of America & Forum Acusticum Boston June 2017
e

“........The acoustics are extraordinary. Even on the back row, at adistance of
59 meters from the centre of the orchestra, where the tour guide whispers,
walks around, tears apiece of paper,lights amatch,beats his chest, snaps
his fingers, turns apage of abook, drops acoin and sighs heavily, all sounds
are clearly audible! During the summer weekends, classical plays are
performed there:the players can be heard everywhere, although there is abit
of reverb........”
...You could hear a pin drop...
‘Epidaurus described in a travel guide’
Dominicus travel guide ‘Greece’ 1989
Extraordinary acoustics?
Acoustics ’17 Acoustical Society of America & Forum Acusticum Boston June 2017
e

“........The acoustics are extraordinary. Even on the back row, at adistance of
59 meters from the centre of the orchestra, where the tour guide whispers,
walks around, tears apiece of paper,lights amatch,beats his chest, snaps
his fingers, turns apage of abook, drops acoin and sighs heavily, all sounds
are clearly audible! During the summer weekends, classical plays are
performed there:the players can be heard everywhere, although there is abit
of reverb........”
...You could hear a pin drop...
Dominicus travel guide ‘Greece’ 1989
Extraordinary acoustics?
Acoustics ’17 Acoustical Society of America & Forum Acusticum Boston June 2017
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not truetrue don’t know

Measurement set for amfitheater acoustics
‘The small suitcase of the guide’
?
Acoustics ’17 Acoustical Society of America & Forum Acusticum Boston June 2017
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Epidaurus background noise level 35 dB(A)
Sound source versus background noise
Acoustics ’17 Acoustical Society of America & Forum Acusticum Boston June 2017
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Just Noticeable
(JN+10 dB)
Recogniseable
Dry

‘match’ 45
35
25
15
5
-5
-15
dB(A)
Sound level
Acoustics ’17 Acoustical Society of America & Forum Acusticum Boston June 2017
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(just noticeable)
LwA = 57,1 dB(A)
Impulse 30 ms

‘match’ 45
35
25
15
5
-5
-15
dB(A)
Sound level
Acoustics ’17 Acoustical Society of America & Forum Acusticum Boston June 2017
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(recogniseable)
LwA = 57,1 dB(A)
Impulse 30 ms

‘coin’ 45
35
25
15
5
-5
-15
dB(A)
Sound level
LwA = 60,4 dB(A)
Acoustics ’17 Acoustical Society of America & Forum Acusticum Boston June 2017
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Impulse 30 ms
(Just noticeable)

‘coin’ 45
35
25
15
5
-5
-15
dB(A)
Sound level
LwA = 60,4 dB(A)
Acoustics ’17 Acoustical Society of America & Forum Acusticum Boston June 2017
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Impulse 30 ms
(recogniseable)

‘paper’ 45
35
25
15
5
-5
-15
dB(A)
Sound level
LwA = 61,3 dB(A)
Acoustics ’17 Acoustical Society of America & Forum Acusticum Boston June 2017
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Impulse 30 ms
(just noticeable)

‘paper’ 45
35
25
15
5
-5
-15
dB(A)
Sound level
LwA = 61,3 dB(A)
Acoustics ’17 Acoustical Society of America & Forum Acusticum Boston June 2017
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Impulse 30 ms
(recogniseable)

‘whispering’ 45
35
25
15
5
-5
-15
dB(A)
Sound level
LwA = 52,2 dB(A)
Acoustics ’17 Acoustical Society of America & Forum Acusticum Boston June 2017
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Impulse 30 ms
(just intelligible)

‘needle’
Sound level
45
35
25
15
5
-5
-15
dB(A)
LwA = 21,4 dB(A)
Acoustics ’17 Acoustical Society of America & Forum Acusticum Boston June 2017
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(hearing threshhold)

“........The acoustics are extraordinary. Even on the back row, at adistance of
59 meters from the centre of the orchestra, where the tour guide whispers,
walks around, tears apiece of paper,lights amatch,beats his chest, snaps
his fingers, turns apage of abook, drops acoin and sighs heavily, all sounds
are clearly audible! During the summer weekends, classical plays are
performed there:the players can be heard everywhere, although there is abit
of reverb........”
...You could hear a pin drop...
Dominicus travel guide ‘Greece’ 1989
Extraordinary acoustics?
Acoustics ’17 Acoustical Society of America & Forum Acusticum Boston June 2017
e
not truetrue don’t know

“........The acoustics are extraordinary. Even on the back row, at adistance of
59 meters from the centre of the orchestra, where the tour guide whispers,
walks around, tears apiece of paper, lights amatch, beats his chest, snaps
his fingers, turns apage of abook, drops acoin and sighs heavily, all sounds
are clearly audible! During the summer weekends, classical plays are
performed there:the players can be heard everywhere,although there is abit
of reverb........”
Dominicus travel guide ‘Greece’ 1989
Extraordinary acoustics?
Acoustics ’17 Acoustical Society of America & Forum Acusticum Boston June 2017
e
not truetrue don’t know

Avond ‘Infinite’ silence
0,1 0,6 0,7 0,8 0,90,2 0,3 0,4 0,5 1,0
excellent
good
poor
bad fair
Evening
Speech intelligibility
Measurement result
Acoustics ’17 Acoustical Society of America & Forum Acusticum Boston June 2017
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Normal voice
Very loud voice

“........The acoustics are extraordinary. Even on the back row, at adistance of
59 meters from the centre of the orchestra, where the tour guide whispers,
walks around, tears apiece of paper, lights amatch, beats his chest, snaps
his fingers, turns apage of abook, drops acoin and sighs heavily, all sounds
are clearly audible! During the summer weekends, classical plays are
performed there:the players can be heard everywhere,although there is abit
of reverb........”
Dominicus travel guide ‘Greece’ 1989
Extraordinary acoustics?
Acoustics ’17 Acoustical Society of America & Forum Acusticum Boston June 2017
e
not truetrue don’t know
•Theater performance at a historic place in the open air/nature
•More than 10,000 silent people
•The ease with which players speak very loudly

Adonia
Constant
Niels
Chris
Bareld
Bas
Remy
Marco
Diakoumi
Hak
Hoekstra
Van Loenen
Nicolai
Peeters
Wenmaekers
van der Wilt
www.ancient-acoustics.nl
Argos
Epidaurus
Herodes
Attucus
Acoustics ’17 Acoustical Society of America & Forum Acusticum Boston June 2017
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Thanks for your attention!