The arrangement of natural and physical features on the earth’s surface are a few among the countless items that govern the airborne acoustic transmission at boundary layers. In particular, if the acoustic waves are attributes of live concerts at open-air theatres, without losing the sheen and quality, the audience should certainly receive the unbroken depth of the performance. Hence, at all times, it is advisable to analyse the auditory receptiveness, particularly in all intended recreational spaces. The current pandemic circumstances and the mandated COVID-19 prevention protocols encourage gatherings in naturally ventilated outdoor regions than confined indoors. This work predicts and quantifies the acoustic experience at the naturally carved amphitheatre at SAINTGITS, an autonomous institution at the down South-West of the Indian Subcontinent. The entire recreational space at SAINTGITS AMPHI was separately modelled as a Base case and Advanced case, and were analysed using the acoustic modelling module of EASE Focus, a renowned simulation freeware, which is in strict adherence with the International standards. The variation in loudness received at the nearest and farthest ends of the amphitheatre was between 67 to 80 dB. Though the Zero frequency SPL (Z-weighting) exhibited the loudness in the range of 81 to 85 dB and could maintain a safer auditory level for any human ear, it was confined to a hemispherical region near the sound source. A vertical beam angle of −4.0° was found to be effective throughout. The procedures and analyses will certainly help the future organizers and stakeholders to effectively plan the resources to reap rich acoustic experience at terrain-centric locales. The surface topography and contours were plotted with another set of freeware, the CADMAPPER and the QUIKGRID, to compare terrain gradient with the known data. Furthermore, this interdisciplinary research exhibits the extensive simulation capability of both EASE Focus and QUIKGRID and demonstrates the modelling versatility and deliverable potential of these freeware to benefit the budding architects and researchers.
Any topographical maps that represent the surface configuration of the earth in multiple dimensions are widely referred and accepted [
In ancient days, during the Roman regime, people gathered at the open-air theatres (amphitheatres) for entertainment, performance and sports [
A modest and appreciable research effort was nurtured and taken care of at SAINTGITS, an Autonomous Engineering institution in South India (
The lush and green campus encompasses the iconic amphitheatre, SAINTGITS AMPHI. An exclusive and novel study was conducted to analyse the airborne acoustic transmission pattern at SAINTGITS AMPHI and to correlate it with its naturally carved terrain (
The recreational facilities at the scenic campus of SAINTGITS are plenty, both for the mind and body of every individual associated with the campus (
The amphitheatre at SAINTGITS, one of the common places for recreation, is centrally located between the Centre Lecture Complex (CLC) and the Administrative Block (AB). It has a modest gradient from CLC to AB, evenly distributed at 12 levels to comfortably accommodate the gathering. Therefore, the acoustic design of audience seating at amphitheaters includes an inherent altitude gradient between the front-most and rear most seating, scientifically christened as the mechanism of the seat-dip attenuation [
This paper expounds and analyses the airborne acoustic transmission over the entire SAINTGITS amphitheatre with the aid of the auditory module of the simulation freeware, the EASE Focus-3, conceived and rolled out during the year 1999. The final phase elaborates the terrain topology over the locale.
EASE Focus-3 is the third version of the acoustic simulator which integrates the acoustic simulation program for 3D modelling of line arrays, sub arrays, digitally steered columns and conventional loudspeakers [
In this work, the modelled acoustical layout at the entire SAINTGITS AMPHI consists of 12 stair seating for the audience, the performance stage and the backstage. The initial analysis and simulation (termed as Base case from hereafter) assume the airborne acoustic transmission to occur in three regions namely (a) the audience module as rectangular with dimensions of 100 m (width) × 80 m (depth), (b) the main stage as a regular trapezoid (25 m front width, 80 m back width and 15 m depth) and (c) the backstage as a perfect square of size 80 m (
Whilst the two sound sources (make: Renkus-Heinz IC08) were positioned horizontally 40 m apart to achieve wide auditory transmission, sixteen microphones were aligned at various altitudes to collectively emulate the presence and perception of the audience (
In the Advanced case model, the terrain-centric variations were accommodated. The twelve stair amphitheatre was modelled, taking into account the level difference of each stair. Furthermore, sector-wise divisions were performed to analyse the in-depth perception of the auditory level. Three main sectors (Sector angle = 60°) were demarcated (Sectors A, B & C) and each main sector contained six exclusive sub-sectors (
Though the sector-wise segregation improvises the ease of analyses, more footfalls were witnessed in the main sector B. To be more specific and to remain realistic, at the entire twelve stair amphitheatre, the enthusiastic live audience always occupied the initial three sub-sectors in the main sector B (Bf. Bm & Br, respectively). The arc-shaped three-storied built structure (Centre Lecture Complex) occupied the ‘
An overview of the sub-sector categorized sector-wise, and the gradient details are indicated in
Sectors A, B & C | ||||||
---|---|---|---|---|---|---|
Sub-sector | Af/Bf/Cf | Am/Bm/Cm | Ar/Br/Cr | |||
Radial width in metres | 14 | 6 | 6 | 24 | 15 | 25 |
Gradient | 1:4.3 | 1:4.3 | 1:4.3 | Nil | Nil | Nil |
Abbreviations used: f-Front; m-Mid; r-Rear; max-Maximum; clc-Centre Lecture Complex; out-Outside.
Though the tabulations in
The culmination of this work includes the topography analyses of SAINTGITS campus, in particular, the terrain topography of SAINTGITS AMPHI. A broader perception of the entire campus and its surroundings were generated, both as axonometric view and topology plots from CADMAPPER, an instant CAD file generator for any location on earth (
The satellite imagery over the campus was accessed from Google Earth Pro (GEP). The terrains over SAINTGITS AMPHI were traced, both in the longitudinal and transverse direction, using GEP’s ‘Add Path’ feature. The trace covered the entire twelve stair amphitheatre. The embedded terrain data points were retrieved and displayed with QuikGrid, a freeware to represent the terrain, either as two or three-dimensional contours. Further, the results were analysed to reiterate the reliability of the obtained terrain gradient plots.
This novel study at SAINTGITS was done to exhibit the immense simulation potential and versatility of the two freeware, EASE Focus and QUIKGRID. The airborne acoustic transmission and terrain topography were analysed in detail. For a detailed discussion, the results are categorized into five subsections: (3.1) influence of vertical beam angle on SPL(A) & SPL(Z) in the Base case model, (3.2) SPL
In the Audience module of the Base Case model, two Renkus-Heinz (IC-08) sound sources were chosen to provide the required auditory perception. The perception of loudness by the human ear was scientifically emulated with the help of orderly arranged microphones (
By analysing the SPL(A-Weighting) at a zero-degree beam angle, the recorded value of average SPL(A) was 74.9 dB. Though the entire range of SPL(A) was between 68 and 79.5 dB, the maximum (78 dB) and minimum (68 dB) were recorded respectively for 10% and 1% of the total SPL(A) distributions. The SPL(Z-Weighting) or ZERO frequency-weight was first introduced in the year 2003 as the International Standard IEC 61672: 2003. It is currently christened as IEC 61672-2 and is followed worldwide [
Whilst the physical hearing capability of a human being is represented by the A-Weighting curve, the Z-Weighting mainly focuses to analyse the sound source. The former is commonly used as an instant scientific measure of loudness. It also has the flexibility to interpret itself as sound power or sound pressure levels [
Furthermore, at the Audience module of the Base case model, a wide range of beam angles (varying from −4.0° to +4.0°) for sound source S1 (see
The beam angle of Sound Source |
Max SPL (A) | Min SPL (A) | Average SPL (A) |
Max SPL (Z) | Min SPL (Z) | Average SPL (Z) |
---|---|---|---|---|---|---|
−4.00 | 79(7.6%) | 76.5(1.5%) | 76.00 | 80.5(6.8%) | 85.5(0.6%) | 79.40 |
−3.00 | 79(8.3%) | 81(1.3%) | 75.80 | 80(7.2%) | 85.5(0.6%) | 79.20 |
−2.00 | 78.5(9.5%) | 76(1.3%) | 75.50 | 80(7.4%) | 85.5(0.5%) | 79.10 |
−1.00 | 78(10%) | 79.5(1.1%) | 74.90 | 79(7.1%) | 85.5(0.4%) | 78.80 |
0.00 | 78(10%) | 79.5(1.1%) | 74.90 | 79(7.1%) | 85.5(0.4%) | 78.80 |
1.00 | 78(9.6%) | 75.5(2.3%) | 74.70 | 78.5(7%) | 85(0.7%) | 78.60 |
2.00 | 77.5(9.5%) | 75(2.6%) | 74.40 | 78(6.9%) | 85(0.6%) | 78.50 |
3.00 | 77.5(9.5%) | 75(2.6%) | 74.40 | 78(6.9%) | 85(0.6%) | 78.50 |
4.00 | 77.5(9.2%) | 73.5(3%) | 74.00 | 78(6.9%) | 85(0.6%) | 78.30 |
U.S. Occupational Safety and Health Administration (OSHA) has reported the comfortable and safest level of sound pressure that any human ear can perceive for longer durations as less than or equal to 85 dB [
If the beam is inclined more to the other direction (positive side), the sound dispersion too happens upwards. Therefore, to experience the richness of auditory performance (at safer upper limits of 85 dB throughout the line of ear position) with the current configuration at the Audience module of the Base case model (see
After analysing the effects of vertical beam angle on sound dispersion, the succeeding session explores the influence of distance on the behavioural pattern of both SPL(A) and SPL(Z).
The Audience module of the Base case model has an auditory depth (usually the distance from the sound source to the audience at the farthest point) of 80 m. Hence, in the most ideal case, the audience is believed to be stationed at random locations inside a total area of 80,000 m2 (
where,
A well-focused comparison of the values of SPL(A) and SPL(Z), analysed individually for a range of beam angles (−4.0° to +4.0°), are plotted against the linear depth (0–80 m, an indicator for expected occupancy at amphitheatre) of the Audience module of Base case model (
The plotted values of SPL(A) confirm the adherence of the auditory level to the safer threshold of 85 dB, irrespective of the beam angle. At certain negative ranges of beam angles (−4.0°, −3.0° and −2.0°), the SPL(A) at halfway from the sound source (40 m) hovered at the same level as the values at a quarter distance (20 m). While the distance varied from 20 to 40 m, the decaying of SPL(A) for beam angles ranging from −4.0° to 0.0° was negligible (<0.15° dB). However, the rate of decay was prominent from 40 m until the farthest point (80 m).
A source-centric analyses of the sound pressure level (Z-Weighting) exhibits a steep decline, right from the source point until the farthest end of the Audience module in the Base case model. At every 20 m after quarter distance from the sound source, for all the modelled beam angles, the average decay was 1.67 dB. An overall view of the drop in sound pressure level had displayed the least drop as 1.68 dB at −4.0° beam angle. The maximum decay was recorded as approximately 2 dB (4.0° beam angle).
To comprehend, irrespective of weighting procedures, the range of SPL concerning the beam angles and the linear distance from the sound source, a beam angle of −4.0° will render richer acoustic transmission throughout the length and breadth of the Audience module in the Base case model.
As the last parameter to analyse in the Base case model, the frequency responses of ten centrally arranged microphones are comprehended in the following session.
The frequency response of any receiving device (mainly microphones) symbolizes its sensitivity to varying levels of frequencies [
Both A and Z weightings recorded their respective maximum sound pressure levels at octave frequencies of 1000 and 250 Hz. However, SPL(Z) had two more frequencies (125 and 250 Hz) which were nearer to its maximum SPL. Though the average SPL for A-weighting and Z-weighting experienced similar trends throughout, the variations were more significant for frequencies 31, 5, 63 and 125 Hz. At all octave frequencies from 1 to 8 kHz, there were subtle differences in the respective values of sound pressure levels. To be more specific, at exact 1000 Hz, the difference in average values of SPL(A) and SPL(Z) was merely 0.05 dB. Interestingly, even the maximum values of the SPL(A) and SPL(Z) were well inside the safer and sustainable auditory level of human ears.
In a nutshell, irrespective of the weightings (SPL(A) and SPL(Z)), the general trend of frequency responses of the receiving instruments in the Audience module of the Base case model were almost similar.
Having discussed enough the basic parameters in the base case model, now the discussion proceeds to consider the realistic acoustic space as the Advanced case model.
A realistic analysis and discussion on the airborne acoustic transmission over the amphitheatre at SAINTGITS can be elucidated by modelling the entire recreational locale as the Advanced case model. Whilst the Base case model assumed the Audience module as a single entity rectangular region, the Advanced case replicated the geometrical form of the twelve stairs SAINTGITS AMPHI as major sectors and sub-sectors (
Since SPL(A) predominantly takes care of the auditory perception by any human ear (audience-centric), the prime focus in the Advanced case model was to follow with the A-Weighting, rather than the source-centric SPL(Z).
The arc segment “
Twelve stairs of the naturally carved amphitheatre (SAINTGITS AMPHI) are lodged within the complete arc segments “
In-depth scrutiny of the overall values of SPL, collectively for these three sub-sectors found that at a vertical beam angle of −4.0°, the range of SPL(A) was within the band of 81.9 to 88.1 dB (
Furthermore, the sub-sector
The analyses were extended to the immediately advanced phase by substituting the Renkus-Heinz loudspeakers with a BOSS professional 4-array system (
The same scenario had been recreated with two array type loudspeakers (S1 & S2), arranged 10 m away from the audience module and stationed 40 m apart. The horizontal beam angles are set at −10.0° and +10.0°, respectively for S1 & S2 (
Whilst 27.7% of the total distributions had their SPLs within the safer hearing threshold (82–85 dB), more than 5.5% of SPLs were equal to or more than 100 dB (100 to 107 dB). The average SPL was almost 89 dB. The safer limits could be observed only at the most unoccupied sub-sectors
A modified configuration for the Audience module was suggested to address the issues concerning the perpetuation of sustainable auditory levels. The two 4-array loudspeaker systems (S1 & S2) were set 40 m away from the Audience module, 80 m apart and maintained the horizontal beam angle of −10.0° and +10.0°, respectively for S1 & S2 (
The acoustic analyses revealed that nearly 48% of the total SPL distributions (81.5 and 93 dB) hovered below the safer auditory level (85 dB) and the average SPL(A) was approximately 86 dB (
Since the outdoor acoustic transmission is highly influenced by the physical structure at the boundary layers, a quantifiable overall discussion on the same follows in the immediate session.
The propagation of outdoor sound is dependent on two broad factors: (i) attenuation due to the influence of the earth’s surface and (ii) the atmospheric absorption of the sound [
The application of acoustics is being practiced and further explored to analyse the stability of rivers and hydraulic structures: monitoring the sediment transport processes in rivers is one of the applications [
Higher levels of sound pressure are attributes of increased mean wind speeds. Interestingly, the distance between the sound source and the audience zone also affects the SPLs. The wind effect is prominent for larger distances [
The meteorological data for the month of January 2021 was retrieved from the archives of
The satellite imagery of SAINTGITS, in particular, the imagery above SAINTGITS AMPHI was accessed from Google Earth Pro (GEP) and the two dimensional and three-dimensional plots of the contour were generated and analysed (
A two-dimensional trace of the longitudinal contour plot had a span of 0.026′ to the East (horizontal) and 0.052′ to the North direction (Vertical). These values make an approximate linear measurement of 38 and 96 m in the East and North directions, respectively. The physical unerring measurements of the amphitheatre at SAINTGITS are 39.5 m to East and 86 m to North. Hence, the decoded values from GEP had been validated with the real measurements. A three-dimensional plot of the contour had the altitude varying from 25.95 to 31.26 m (5.3 m) (
In the case of the transverse trace, the resultant altitude was found to be at par with the value of the longitudinal contour plot (5.3 m). The values in the East and North directions were 53.62 and 88.85 m, respectively (
An overall analysis reiterates the robustness of the GEP data, irrespective of the direction of the contour plot (
A set of orthographic projections were developed to visually analyse the altitude gradient of longitudinal and transverse plots (
Whilst a stark comparison recapitulates the similarity of altitude gradient in both longitudinal and transverse plots, beyond any iota of doubt, these orthographic projections summarize the independence of the projected terrain gradient on the YZ plane. To remain specific, the orthographic projection of terrain gradient obtained on the XZ plane does not depend on the number of data points and the direction of plot progress (
An exclusive analysis of the acoustic characteristics and the comparison of terrain topography at the naturally carved landmark of SAINTGITS have revealed promising results that would certainly benefit the sound designers and event managers at all levels. This work has addressed both the recreation aspects and technical know-how of airborne acoustic transmission over SAINTGITS AMPHI. In a nutshell, it is encouraged to interpret the values of Sound Pressure Level as audience-centric (A-Weighting) than source-centric (Z-Weighting). This piece of research also reiterates the significance of beam angle. Among the modest range of beam angles analysed in this manuscript, a vertical beam angle of −4.0° was found to deliver the richness of any live performances at SAINTGITS AMPHI. Since the airborne sound transmission is a function of the surface textural attributes, meteorological conditions and terrain topography, the contour plots were traced for two distinct patterns. A visual inspection of the orthographic projection reaffirms that the terrain gradient (YZ plot) is independent of the direction of plot progress (longitudinal progress or transverse progress). To conclude, this work constructively exploited the immense research potential of the freeware: CADMAPPER, QUICKGRID and EASE Focus. Since sustainable practices are always at the forefront, let this research enlighten the practicing engineers and budding architects trans world.