Optimizing the signal to noise ratio in classrooms using passive acoustics
Peter D’Antonio – firstname.lastname@example.org
RPG Diffusor Systems, Inc.
651 Commerce Dr
Upper Marlboro, MD 20774
Popular version of paper 1aAA4 “Optimizing the signal to noise ratio in classrooms using passive acoustics” Presented on Monday May 23, 10:20 AM – 5:00 pm, SALON I
171st ASA Meeting, Salt Lake City
The 2012 Program of International Student Assessment (PISA) has carried out an international comparative trial of student performance in reading comprehension, calculus, and natural science. The US ranks 36th out of 64 countries testing ½ million 15 year olds, as shown in Figure 1.
What is the problem? Existing acoustical designs and products have not evolved to incorporate the current state-of-the-art and the result is schools that are failing to meet their intended goals. Learning areas are only beginning to include adjustable intensity and color lighting, shown to increase reading speeds, reduce testing errors and reduce hyperactivity; existing acoustical designs are limited to conventional absorptive-only acoustical materials, like thin fabric wrapped panels and acoustical ceiling tiles, which cannot address all of the speech intelligibility and music appreciation challenges.
Figure 1 PISA Study
What is the solution? Adopt modern products and designs for core and ancillary learning spaces which utilize binary, ternary, quaternary and other transitional hybrid surfaces, which simultaneously scatter consonant-containing high frequency early reflections and absorb mid-low frequencies to passively improve the signal to noise ratio, adopt recommendations of ANSI 12.6 to control reverberation, background noise and noise intrusion and integrate lighting that adjusts to the task at hand.
Let’s begin by considering how we hear and understand what is being said when information is being delivered via the spoken word. We often hear people say, I can hear what he or she is saying, but I cannot understand what is being said. The understanding of speech is referred to as speech intelligibility. How do we interpret speech? The ear / brain processor can fill in a substantial amount of missing information in music, but requires more detailed information for understanding speech. The speech power is delivered in the vowels (a, e, i, o, u and sometimes y) which are predominantly in the frequency range of 250Hz to 500Hz. The speech intelligibility is delivered in the consonants (b, c, d, f, g, h, j, k, l, m, n, p, q, r, s, t, v, w), which occur in the 2,000Hz to 6,000 Hz frequency range. People who suffer from noise induced hearing loss typically have a 4,000Hz notch, which causes severe degradation of speech intelligibility. I raise the question, “Why would we want to use exclusively absorption on the entire ceiling of a speech room and thin fabric wrapped panels on a significant proportion of wall areas, when these porous materials absorb these important consonant frequencies and prevents them from fusing with the direct sound making it louder and more intelligible?
Exclusive treatment of absorbing material on the ceiling of the room may excessively reduce the high-frequency consonants sound and result in the masking of high-frequency consonants by low-frequency vowel sounds, thereby reducing the signal to noise ratio (SNR).
The signal has two contributions. The direct line-of-sight sound and the early reflections arriving from the walls, ceiling, floor and people and items in the room. So the signal consists of direct sound and early reflection. Our auditory system, our ears and brain, have a unique ability called temporal fusion, which combines or fuses these two signals into one apparently louder and more intelligible signal. The goal then is to utilize these passive early reflections as efficiently as possible to increase the signal. The denominator in the SNR consists of external noise intrusion, occupant noise, HVAC noise and reverberation. These ideas are summarized in Figure 2.
Figure 2 Signal to Noise Ratio
In Figure 3, we illustrate a concept model for an improved speech environment, whether it is a classroom, a lecture hall, a meeting/conference room, essentially any room in which information is being conveyed.
The design includes a reflective front, because the vertical and horizontal divergence of the consonants is roughly 120 degrees, so if a speaker turns away from the audience, the consonants must reflect from the front wall and ceiling overhead. The perimeter of the ceiling is absorptive to control the reverberation (noise). The center of the ceiling is diffusive to provide early reflections to increase the signal and its coverage in the room. The mid third of the walls utilize novel binary, ternary, quaternary and other transitional diffsorptive (diffusive/absorptive) panels, which scatter the information above 1 kHz (the signal) and absorb the sound below 1 kHz (the reverberation=noise). This design suggests that the current exclusive use of acoustical ceiling tile and traditional fabric wrapped panels is counterproductive in improving the SNR, speech intelligibility and coverage.
Figure 3 Concept model for a classroom with a high SNR
The Sound of the Sacred: The State of the Art in Worship Space Acoustics
David T. Bradley – email@example.com
124 Raymond Ave
Poughkeepsie, NY 12604-0745
Erica E. Ryherd – firstname.lastname@example.org
Durham School of Architectural Engineering and Construction
University of Nebraska – Lincoln
203C Peter Kiewit Institute
Omaha, NE 68182-0176
Lauren Ronsse – email@example.com
Columbia College Chicago
33 E. Congress Parkway, Suite 601
Chicago, IL 60605
Popular version of paper 3pID2, “The state of the art in worship space acoustics”
Presented Wednesday afternoon, May 25, 2016, 1:55 in Salon D
171st ASA Meeting, Salt Lake City
From the clanging of bells to the whisper of burning incense, sound is essential to the worship experience. It follows that the acoustic environment is paramount in the sacred place – the worship space – and thoughtful design is required to achieve a worship experience full of awe and wonder. The first intentional sacred spaces were constructed over 11,000 years ago  and, although architectural acoustics design practices have changed immeasurably since then, the primary use of these spaces remains essentially unchanged: to provide a gathering space for communal worship.
To meet this need, the four key acoustical goals that modern worship space designers must consider are to optimize reverberation time, eliminate acoustical defects, minimize ambient noise, and maximize dynamic range. These four goals are imperative in virtually all types of worship spaces around the world, despite vast differences in religious practices and beliefs. In the recent publication, Worship Space Acoustics: 3 Decades of Design , the application of these goals is seen in 67 churches, synagogues, mosques, and other worship spaces designed in the past thirty years. Each space and each religion has its own idiosyncratic acoustic challenges, from a visually translucent but acoustically transparent partition required to separate men and women in an orthodox synagogue in Brookline, MA (Figure 1) to the attenuation of a focused acoustic reflection from the dome of a mosque in Atlanta, GA (Figure 2). One space featured in the book, Temple Israel (Figure 3), shows the connectedness of acoustical design in worship spaces. It is part of a special project, the Tri-Faith Initiative, a 14-acre complex in Omaha, NE uniting three Abrahamic faith groups, Temple Israel, Countryside Community Church (United Church of Christ), and The American Muslim Institute. As each of these three worship spaces is constructed on the site, they all must have the four key acoustical goals considered.
In the past three decades, worship spaces have seen an increased need for multi-functionality, often hosting religious services with varying acoustical needs. For example, the Star Performing Arts Centre (Figure 4) in Singapore serves as the home of the New Creation Church, seats 5000 people, and supports programing ranging from traditional worship services to pop music concerts to televised national events. Some spaces must even serve more than one religion, such as the Sacred Space (Figure 5), a multi-faith house of worship constructed in the shell of an old Boston chapel that caught fire in the mid-90s, now used for meditation, private worship, and small gatherings. These varying usage requirements require careful consideration of the acoustic design, often relying on variable acoustics such as retractable sound absorption and the use of sophisticated electroacoustics systems.
Although the use of each space may vary, the most important acoustic goal remains to optimize the reverberation time. This is the time necessary for sound in a space to decay to one-millionth of its original intensity. Essentially, it describes how the sound energy decays, perceived as the fading away of sound over time. Typically, reverberation time decreases as more sound absorption is added, and increases as the size of the space increases. Figure 6 shows the mean reverberation times (500 Hz) for the various seating capacities of the 67 worship spaces. Seating capacity is generally directly proportional to size of the space, and the reverberation times here show the general trend of increasing with increasing size up to about 2000 seats. For 2000 seats and beyond, the data show a marked decrease in reverberation time. For these larger spaces, there tends to be a higher proportion of sound absorbing material used in the design, typically to allow for the use of electroacoustics systems that require a large number of loudspeakers. Spaces that rely heavily on electroacoustics to achieve the desired sonic environment require non-reflective surfaces and lower reverberation times for the microphone-loudspeaker systems to work properly.
Regardless of reverberation time, the goal remains the same, to create a gathering space for worship where the sound is sacred.
K. Schmidt, “Göbekli Tepe, Southeastern Turkey: A Preliminary Report on the 1995-1999 Excavations,” Paléorient, 26(1), 45-54, 2000.
D. T. Bradley, E. E. Ryherd, and L. Ronsse (Eds.), Worship Spaces Acoustics: 3 Decades of Design, (New York, NY, Springer, 2016).
Figure 1: Temple Young Israel, a 550-seat orthodox synagogue in Brookline, MA designed by Gund Partnership and Cavanaugh Tocci Associates, Inc. (Photo credit: Christopher A. Storch)
Figure 2: Al Farooq Masjid of Atlanta (interior view of main dome), a 1500-seat Islamic mosque designed by Lee Sound Design, Inc. and Design Arts Studio and EDT Constructors, Inc. (Photo credit: Wayne Lee)
Figure 3: Temple Israel, a 900-seat reform synagogue in Omaha, NE designed by Acentech Incorporated and Finegold Alexander + Associates. (Photo credit: Finegold Alexander + Associates)
Figure 4: The Star Performing Arts Centre, a 5000-seat multi-use space in Singapore designed by Arup (completed as Artec) and Andrew Bromberg of Aedas.
Figure 5: The Sacred Space, 150-seat multifaith house of worship in Boston, MA designed by Acentech Incorporated and Office dA.
Figure 6: Mean reverberation times at 500 Hz octave band center frequency for 67 worship spaces of varying seating capacity.
1 ADA Acoustics & Media Consultants GmbH, Arkonastr. 45-49, D-13189 Berlin / Germany
2 University of Architecture and Urbanism “Ion Mincu”, Str. Academiei 18-20, RO-010014 Bucuresti / Romania
Popular version of paper 4aAA5, “The National Opera in Bucharest – Update of the room-acoustical properties” Presented Thursday morning, November 5, 2015, 10:35 AM, Grand ballroom 3
170th ASA Meeting, Jacksonville
The acoustics of an opera hall has changed dramatically within the last 100 years. Until the end of the 19th century, mostly horseshoe-shaped halls were built with acoustically high-absorbing wall and even floor areas. Likewise, the often used boxes had fully absorbing claddings. That way the reverberation in these venues was made low and the hall was perceived as acoustically dry, e.g. the opera hall in Milan. 100 years later, the trend shows opera halls with more live and higher reverberation, preferred now for music reproduction, e.g. Semper Opera in Dresden.
This desire to enhance the acoustic liveliness in the Opera House in Bucharest led to renovation work in 2013-2014. The Opera House was built in 1952-1953 for around 2200 spectators and it followed a so-called style of “socialist realism”. This type of architecture was popular at the time, when communism was new to Romania, and the building has therefore a neoclassical design. The house was looking inside the hall like a theatre of the late 19th century. The conditions in the orchestra pit for the musicians, as far as mutual hearing is concerned, were bad as well. So, construction works took place in order to improve room acoustical properties for musicians and audience.
Fig. 1: Opera hall after reconstruction
The acoustic task was to enhance the room acoustic properties significantly by substituting absorptive faces (as carpet, fabric wall linings, etc.) by reflective materials:
Carpet on all floor areas, upholstered back- and undersides of chairs
Textile wall linings at walls/ceilings in boxes, upholstered hand rails
Textile wall linings at balustrades, upholstered hand rails in the galleries
All the absorbing wall and ceiling parts were substituted by reflecting wood panels, the carpet was removed and a parquet floor was introduced. As a result, the sound does not fade out anymore as in an open-air theatre but spaciousness may be perceived now.
The primary and secondary structures of the orchestra pit were changed as well in order to improve mutual hearing in the pit and between stage and pit. The orchestra pit had the following acoustically disadvantageous properties:
Insufficient ratio between open and covered area (depth of opening 3.5 m, depth of cover 4.7 m)
The height within the pit in the covered area was very small.
The space in the covered area of the pit was highly overdamped by too much absorber.
Fig. 2: new orchestra pit, section
The following changes have been applied:
The ratio between open area and covered area is now better by shifting the front edge of the stage floor to the back: Depth of opening is now 5.1 m, depth of cover only 3.1 m.
The height within the pit in the covered area is increased by lowering the new movable podium.
The walls and soffit in the pit are now generally reflective, broadband absorbers can be placed variably at the back wall in the pit.
After an elaborate investigation by measurements and simulation on site a prolongation of the reverberation time of 0.2-0.3 s was reached to actual values of about 1.3 to 1.4 s.
Together with alterations of the geometric situation of pit, the acoustic properties of the hall are now very satisfactory for musicians, singers and the audience.
Beside the reverberation time, other room acoustical measures such as C80, Support, Strength, etc. have been improved significantly.
Popular version of poster 5aMU1
Presented Friday morning, May 22, 2015, 8:35 AM – 8:55 AM, Kings 4
169th ASA Meeting, Pittsburgh
In this paper the relationship between musical instruments and the rooms they are performed in was investigated. A musical instrument is typically characterized as a system that consists of a tone generator combined with a resonator. A saxophone for example has a reed as a tone generator and a comical shaped resonator that can be effectively changed in length with keys to produce different musical notes. Often neglected is the fact that there is a second resonator for all wind instruments coupled to the tone generator – the vocal cavity. We use our vocal cavity everyday when we speak to form characteristic formants, local enhancements in frequency to shape vowels. This is achieved by varying the diameter of the vocal tract at specific local positions along its axis. In contrast to the resonator of a wind instrument, the vocal tract is fixed its length by the dimensions between the vocal chords and the lips. Consequently, the vocal tract cannot be used to change the fundamental frequency over a larger melodic range. For out voice, the change in frequency is controlled via the tension of the vocal chords. The musical instrument’s instrument resonator however is not an adequate device to control the timbre (harmonic spectrum) of an instrument because it can only be varied in length but not in width. Therefore, the players adjustment of the vocal tract is necessary to control the timbre if the instrument. While some instruments posses additional mechanisms to control timbre, e.g., via the embouchure to control the tone generator directly using the lip muscles, for others like the recorder changes in the wind supply provided by the lungs and the changes of the vocal tract. The role of the vocal tract has not been addressed systematically in literature and learning guides for two obvious reasons. Firstly, there is no known systematic approach of how to quantify internal body movements to shape the vocal tract. Each performer has to figure out the best vocal tract configurations in an intuitive manner. For the resonator system, the changes are described through the musical notes, and in cases where multiple ways exist to produce the same note, additional signs exist to demonstrate how to finger this note (e.g., by providing a specific key combination). Secondly, in western classic music culture the vocal tract adjustments predominantly have a correctional function to balance out the harmonic spectrum to make the instrument sound as even as possible across the register.
PVC-Didgeridoo adapter for soprano saxophone
In non-western cultures, the role of the oral cavity can be much more important to convey musical meaning. The didgeridoo, for example, has a fixed resonator with no keyholes and consequently it can only produce a single pitched drone. The musical parameter space is then defined by modulating the overtone spectrum above the tone by changing the vocal tract dimensions and creating vocal sounds on top of the buzzing lips on the didgeridoo edge. Mouthpieces of Western brass instruments have a cup behind the rim with a very narrow opening to the resonator, the throat. The didgeridoo does not have a cup, and the rim is the edge of the resonator with a ring of bee wax. While the narrow throat of western mouthpiece mutes additional sounds produced with the voice, didgeridoos are very open from end to end and carry the voice much better.
The room, a musical instrument is performed in acts as a third resonator, which also affect the timbre of the instrument. In our case, the room was simulated using a computer model with early reflections and late reverberation.
Tone generators for soprano saxophone from left to right: Chinese Bawu, soprano saxophone, Bassoon reed, cornetto.
In general, it is difficult to assess the effect of a mouthpiece and resonator individually, because both vary across instruments. The trumpet for example has a narrow cylindrical bore with a brass mouthpiece, the saxophone has a wide conical bore with reed-based mouthpiece. To mitigate this effect, several tone generators were adapted for a soprano saxophone, including a brass mouthpiece from a cornetto, a bassoon mouthpiece and a didgeridoo adapter made from a 140 cm folded PCV pipe that can be attached to the saxophone as well. It turns out that the exchange of tone generators change the timbre of the saxophone significantly. The cornetto mouthpiece gives the instrument a much mellower tone. Similar to the baroque cornetto, the instruments sounds better in a bright room with lot of high frequencies, while the saxophone is at home at a 19th-century concert hall with a steeper roll off at high frequencies.
If the MP’s speeches don’t put you to sleep, at least you should be able to understand what they are saying.
Using state-of-the-art audible simulations, a design team of acousticians, architects and sound system designers is working to ensure that speech within the House of Commons chamber of the Parliament of Canada now in design will be intelligible in either French or English.
The new chamber for the House of Commons is being built in a glass-topped atrium in the courtyard of the West Block building on Parliament Hill in Ottawa. The chamber will be the temporary home of the House of Commons, while their traditional location in the Center Block building is being renovated and restored.
The skylit atrium in the West Block will be about six times the volume of the existing room, resulting in significant challenges for ensuring speech will be intelligibility.
Figure 1: Existing Chamber of the House of Commons, Parliament of Canada
The existing House chamber is 21 meters (70 feet) long, 16 meters (53 feet) wide, and has seats for the current 308 Members of Parliament (to increase to 338 in 2015) and 580 people in the upper gallery that runs around the second level of the room. Most surfaces are wood, although the floor is carpeted, and there is an adjustable curtain at the rear of the MP seating area on both sides of the room. The ceiling is a painted stretched linen canvas over the ceiling 14.7 meters (48.5 feet) above the commons floor, resulting in a room volume of approximately 5000 cubic meters.
The new House chamber is being infilled into an existing courtyard that is 44 meters (145 feet) long, 39 meters (129 feet) wide, and 18 meters (59 feet) high. The meeting space itself will retain the same basic footprint as the existing room, including the upper gallery seating, but will be open to the sound reflective glass roof and stone and glass side walls of the courtyard. In the absence of any acoustic treatments, the high level of reverberant sound would make it very difficult to understand speech in the room.
ARCOP / FGM ARCHITECTS
Figure 2: Early Design Rendering of Chamber in West Block
In order to help the Public Works and Government Services Canada (PWGSC) and the House of Commons understand the acoustic differences between the existing house chamber and the one under design, and to assure them that excellent speech intelligibility will be achieved in the new chamber, Acoustic Distinctions, the New York-based acoustic consultant, created a computer model of both the new and existing house chambers, and performed acoustic tests in the existing chamber. AD also made comparisons of the two room using sophisticated data analysis and tables of data an produced graphs maps of speech intelligibility in each space.
An early design iteration, for example, included significant areas of sound absorptive materials at the sides of the ceiling areas, as well as sound absorptive materials integrated into the branches of the tree-like structure which supports the roof:
Figure 3: Computer Model of Room Finishes
The dark areas of the image show the location of sound absorptive materials, including triangularly-shaped wedges integrated into the structure which supports the roof.
Using a standardized measure of intelligibility, AD estimated a speech quality of 65% using the Speech Transmission Index (STI), a standardized measure of speech intelligibility, where a minimum of 75% was needed to ensure excellent intelligibility.
The computer analysis done by Acoustic Distinctions also produced colorful images relating to the degree of speech intelligibility that was to be expected:
Figure 4: Speech Transmission Index, single person speaking, no reinforcement
Talker at lower left; Listener at lower right
Dark blue to black color indicates fair to good intelligibility
While these numerical and graphical tools were useful in understanding acoustic conditions of the new room, in order to make it easier for the client and design team to appreciate the acoustic recommendations made by the consultant, Acoustic Distinctions also produced computer simulations of speech within the new room, enabling the team to hear the way the new room will sound when complete.
This approach, known as audible simulation or auralization, has been used to analyze a variety of room design options, and as the design progresses, new analysis and simulations are produced.
This first audible simulation is made using the room model shown above. The talker is an MP standing near the center of the bright yellow area in the STI map above. The listener is an MP seated in the opposite corner of the room, where the dark blue to black color confirms the STI value of just less than 0.70, corresponding to “good” intelligibility.
Audio file 1: Speech without Sound System. STI 0.68
(CLICK ON ABOVE LINK TO PLAY WAV FILE)
To increase the intelligibility to values above the 0.75 minimum design goal, we add the sound system, being designed by Engineering Harmonics, to our model. With the sound system operating, STI value are increased for the above talker/speaker pair to 0.85. Speech will sound like this:
Audio file 2: Speech with Sound System. STI 0.85
(CLICK ON ABOVE LINK TO PLAY WAV FILE)
While these examples clearly show the benefit of a speech reinforcement system in the Chamber, the design and client team were not satisifed with the extent of sound absorptive materials in the ceiling of the Chamber that were required to achieve the results of excellent intelligibility. An additional goal was expressed to reduce the total amount of sound absorptive materials in the room, to make the structure and skylight more visible and prominent.
Acoustic Distinctions therefore made changes to the model, strategically removing sound absorptive materials from specific ceiling locations, and reconfiguring the absorptive materials within the upper reaches of the structure supporting the roof. Computer models were again developed, and the resulting images showed that with careful design, excellent intelligibility would be achieved with reduced absorption.
Figure 5: Speech Transmission Index, single person speaking, with sound reinforcement
Talker at upper left; Listener at lower right
Bright pink to red color indicates excellent intelligibility
Not surprisingly, communicating this to the design team and House of Commons in a way that provided a high level of confidence in the results was required. We again used audible simulations to demonstrate the results:
Audio file 3: Speech with Sound System, reduced absorption. STI 0.82
(CLICK ON ABOVE LINK TO PLAY WAV FILE)
The rendering below shows the space configuration associated with the latest results:
ARCOP / FGM ARCHITECTS
Figure 6: Rendering, House of Commons, West Block, Parliament Hill
Proposed Design Configuration, showing sound absorptive panels
integrated into laylight and structure supporting roof
END OF PAPER
Audible Simulation in the Canadian Parliament The impact of auralization on design decisions for the House of Commons