David Pelegrin Garcia – david.pelegringarcia@kuleuven.be
KU Leuven, Dept. Electrical Engineering
Kasteelpark Arenberg 10 – box 2446
3001 Leuven, Belgium

Monika Rychtarikova – monika.rychtarikova@kuleuven.be
KU Leuven, Faculty of Architecture
Hoogstraat 51
9000 Gent, Belgium

Lukaš Zelem – lukas.zelem@stuba.sk
Vojtech Chmelík – vojtech.chmelik@stuba.sk
STU Bratislava, Dept. Civil Engineering
Radlinského 11
811 07 Bratislava, Slovakia

Leopold Kritly – leopold.kritly@gmail.com
Christ Glorieux – christ.glorieux@kuleuven.be
KU Leuven, Dept. Physics and Astronomy
Celestijnenlaan 200d – box 2416
3001 Leuven, Belgium

Popular version of 1aAAa2 Auditory recognition of surface texture with various scattering coefficients
Presented Sunday morning, June 25, 2017 173rd ASA Meeting, Boston
Click here to read the abstract

When we switch on the light in a room, we see objects. As a matter of fact, we see the reflection of light from these objects, revealing their shape and color. This all seems to happen instantaneously since, due the enormously high speed of light, the time that light needs to travel from the light source to the object then to our eye is extremely short. But how is it with sound? Can we “hear objects”, or correctly said, sound reflections from objects? In other words, can we “echolocate”?

We know that sound, in comparison to light, propagates much slower. Therefore, if we stand far enough from a large obstacle and clap our hands, shortly after hearing the initial clapping sound, we hear a clear sound reflection from objects – an echo (Figure 1). But is it possible to detect an object if we stand close to it? And can the shape or surface texture of an object be recognized from the “color” of the sound? And how does it work?

Figure 1. Sound arriving at the ears after emitting a ‘tongue click’ in the presence of an obstacle. Credit: Pelegrin-Garcia/KU Leuven

It is widely known that bats, dolphins and other animals use echolocation to orient themselves in their environment and detect obstacles, preys, relatives or antagonists. It is less known that, with some practice, most people are also able to echolocate. As a matter of fact, echolocation makes a great difference in the lives of blind people who use it in their daily lives [1, 2], and are commonly referred to as “echolocators.”

While echolocation is mainly used as an effective means of orientation and mobility, additional information can be extracted from listening to reflected sound. For example, features about objects’ texture, size and shape can be deduced, and a meaning can be assigned to what is heard, such as. a tree, car or a fence. Furthermore, echolocators form a “map” of their surroundings by inferring where objects stand in relation to their body, and how different objects related to each other.

In our research, we focus on some of the most elementary auditory tasks that are required during echolocation: When is a sound reflection audible? Can people differentiate among sound reflections returned by objects with different shapes, fabric or surface textures?

In previous work [3] we showed that by producing click-sounds with their tongue, most sighted people without prior echolocation experience were able to detect reflections from large walls at distances as far as 16 meters in ideal conditions, such as in open field where there are no obstacles other than the wall that reflects the sound, and where one cannot hear any other noises like background noise. Blind echolocators in a similar study [4], nevertheless, could detect reflections from much smaller objects at nearby distances below 2 meters.

In the present study, we investigated whether sighted people who had no experience with echolocation could distinguish between walls with different surface textures by just listening to a click reflected by the wall.

To answer this question, we performed listening tests with 16 sighted participants. We played back a pair of clicks with an added reflection; the first click with one kind of wall and the second with another. Participants responded as to whether they heard a difference between the two clicks or not. This was repeated at distances of 1.5 meters and 10 meters for all possible pairs of simulated walls with various geometries (see in Figure 2 some of these walls and the echoes they produced).

Figure 2. Sample of the wall geometries that we tested (from left to right, top row: staircase, parabolic (cave-like) wall, sinusoid wall and periodic squared wall; bottom row: narrow wall with an aperture, broad wall, narrow wall, convex circular wall), with the echoes they produced at distances of 1.5 and 10 m. Credit: Pelegrin-Garcia/KU Leuven

We found that most participants could distinguish the parabolic wall and the staircase from the rest of the walls at a distance of 10 meters. The parabolic (cave-like) wall returned much stronger reflections than all other walls due to acoustic focusing. The sound emitted in different directions was reflected back by the wall to the point of emission. On the other hand, the staircase returned a reflection with a “chirp” sound. This kind of sound was also the focus of study at the Kukulcan temple in Mexico [5].

The results of our work support the hypothesis of a recent investigation [6] that suggests that prehistoric societies could have used echolocation to select the placement of rock art in particular caves that returned clearly distinct echoes at long distances.

[1] World Access for the Blind, “Our Vision is Sound”, https://waftb.org. Retreived 9th June 2017

[2] Thaler, L. (2013). Echolocation may have real-life advantages for blind people: An analysis of survey data. Frontiers in Physiology, 4(98). http://doi.org/10.3389/fphys.2013.00098

[3] Pelegrín-García, D., Rychtáriková, M., & Glorieux, C. (2017). Single simulated reflection audibility thresholds for oral sounds in untrained sighted people. Acta Acustica United with Acustica, 103, 492–505. http://doi.org/10.3813/AAA.919078

[4] Rice, C. E., Feinstein, S. H., & Schusterman, R. J. (1965). Echo-Detection Ability of the Blind: Size and Distance Factors. Journal of Experimental Psychology, 70(3), 246–255.

[5] Trivedi, B. P. (2002). Was Maya Pyramid Designed to Chirp Like a Bird? National Geographic News (http://news.nationalgeographic.com/news/2002/12/1206_021206_TVMayanTemple.html). Retrieved 10th June 2017

[6] Mattioli, T., Farina, A., Armelloni, E., Hameau, P., & Díaz-Andreu, M. (2017). Echoing landscapes: Echolocation and the placement of rock art in the Central Mediterranean. Journal of Archaeological Science, 83, 12–25. http://doi.org/10.1016/j.jas.2017.04.008

Jon G. Olsen – jon.olsen@musikk.no
Council for Music Organizations in Norway, Oslo, Norway

Jens Holger Rindel – jens.holger.rindel@multiconsult.no
Multiconsult, Oslo, Norway

Popular version of 2pAAb1, “The acoustics of rooms for music rehearsal and performance – the Norwegian approach”
Presented Monday afternoon, June 26, 2017, 1:20 pm.
173^rd ASA Meeting / 8^th Forum Acusticum, Boston, USA
Click here to read the abstract

Each week, local music groups in Norway use more than 10,000 rooms for rehearsals and concerts. Over 500,000 people sing, play or go to concerts every week. In Europe, over 40 million choir singers spend at least one evening in a rehearsal room. Professional musicians and singers use rehearsal rooms many hours a day. Most of the local concerts take place in rooms that are not designed for concert events, but are in schools, community centers, youth clubs and other rooms and spaces more or less suitable for playing music.

The size of the rooms varies from under 100 to over 10, 000 cubic meters. The users cover a broad variety of music ensembles, mostly wind bands, choirs and other amateur ensembles. Since 2009, the Norwegian Council for Music Organizations (Norsk musikkråd) has completed more than 600 acoustical room measurement reports on rooms used for rehearsal and concerts. All the reports are made available online with a Google Map of Norway (http://database.musikklokaler.no/map).

The results are depressing: 85 % of the rooms are not suited for the type of music for which they are used. A faulty type of acoustics can enforce the music ensemble to adapt to wrong balance between the instruments, making the musical interaction much more difficult and reducing the possibility for developing a good sound – both for each musician and for the orchestra or choir as a whole.

Unsuitable acoustics reduce the musical quality of the music group and give the conductor less possibility to work with and develop the musical quality. It also reduces the joy of playing or singing in a local music group. As the famous conductor Mariss Janssons used to say, “A good hall for the orchestra is as important as a good instrument is for a soloist.”

Different types of music need different types of rooms and different acoustical conditions. We can divide the music genres into three main groups:

• Acoustically soft music, such as singing and playing instruments that are relatively quiet, such as string instruments, guitars etc. and smaller woodwind ensembles.
• Acoustically loud music, such as playing brass instruments and percussion instruments, brass bands, concert bands, symphony orchestras and opera singing.
• Amplified music, such as pop/rock bands, amplified jazz groups etc.

The Norwegian Standardization Organization established a working group, with participants from the Council for Music Organizations in Norway, the music industry, municipalities, acoustic consultants, The Union of Norwegian Musicians and others. Together, this group has developed the National standard, “Acoustic criteria for rooms and spaces for music rehearsal and performance” NS 8178:2014.

The Norwegian standardization group has divided rooms into five categories and provided specific requirements for each:

• Individual practice room (1-2 musicians practicing)
• Small ensemble room (3-6 musicians, teaching rooms)
• Medium size ensemble room (up to 20 musicians/singers)
• Large ensemble room (for choir, school band, concert band, symphonic band with brass/percussion, acoustic big band)
• Performance rooms, subdivided into four types of rooms
  • Amplified music club scenes (small jazz, pop, singer/songwriter)
  • Amplified music concert rooms (pop/rock/jazz/blues)
  • Acoustic loud music (concert band, symphony orchestra, brass band, big band)
  • Acoustic quiet music (vocal group, string orchestra, folk music group, chamber music)

VOLUME – the most important criterion
Too small a volume turns out to be the main problem for many ensembles. A survey of Norwegian choir rehearsal rooms shows that 54% of the rooms are excessively small (less than half the size they should have been), 22% are too small and only 24% have more or less enough volume.

Figure 1.: Query Norwegian singer’s organization, spring 2016. Rehearsal room size.

For wind bands, we see more or less the same situation where the rooms are in general too small. In music schools, there are also many studios that are too small. The result is that the music is far too loud, and it is very difficult to work with sound quality and dynamic expression.

ROOM GEOMETRY – criterion number 2
This criterion poses not so many problems, apart from the fact that the room height is often too small, particularly in rehearsal rooms, but also in a number of concert rooms. A low ceiling is bad for the sound quality of the instruments and makes it difficult to hear each other.

REVERBRATION TIME – criterion number 3
There are often problems with the reverberation time, different for each of the three types of music. For acoustic soft music, the reverberation time should be relatively long in order to give support to the music, but it is very often too short in rehearsal and concert rooms. For acoustic loud music, the reverberation time should be moderate in order to avoid the music to be too loud, but it is often too long – or sometimes too short.

For amplified music, the reverberation time should be short, and this is quite often the case. However, it is especially important to have sufficiently short reverberation time in the bass (the low frequencies); otherwise the music makes an unpleasant booming sound.

The Norwegian standard provides a basis for better design of new music rooms. The systematic collection of acoustic reports of music rooms gives important background for recommendations on how to build or refurbish rooms for music in schools and cultural buildings.

Picture 1: Brass band rehearsal at Toneheim college, Norway, Credit: Trond Eklund Johansen, Hedmark/Oppland Music Council

Puglisi Giuseppina Emma – giuseppina.puglisi@polito.it
Bolognesi Filippo – filippo.bolognesi@studenti.polito.it
Shtrepi Louena – louena.shtrepi@polito.it
Astolfi Arianna – arianna.astolfi@polito.it
Dipartimento di Energia
Politecnico di Torino
Corso Duca degli Abruzzi, 24
10129 Torino (Italy)

Warzybok Anna – a.warzybok@uni-oldenburg.de
Kollmeier Birger – birger.kollmeier@uni-oldenburg.de
Medizinische Physik and Cluster of Excellence Hearing4All
Carl von Ossietzky Universität Oldenburg
D-26111 Oldenburg (Germany)

Popular version of paper 1aAAc3
Presented Sunday morning, June 25, 2017

The architectural design of classrooms should account for premises that influence the activities taking place there. As an example, the ergonomics of tables and chairs should fit pupils’ age and change with school grades. Shading components should be easily integrated with windows so that excessive light doesn’t interfere with visual tasks. Together with these well-known aspects, a classroom should also “sound” appropriate, since the teacher-to-student communication process is at the base of learning. But what does this mean?

First, we must pay attention must to the school grade under investigation. Kindergarten and primary schools aim at the direct teacher-to-student contact, and thus the environment should passively support the speech. Conversely, university classrooms are designed to host hundreds of students, actively supporting speech through amplification systems. Second, the classroom acoustics need to be focused on the enhancement of speech intelligibility. So, practical design must be oriented to reduce the reverberation time (i.e. reducing the number of sound reflections in the space) and the noise levels, since these factors are proved to negatively affect teachers’ vocal effort and students’ speech intelligibility.

Acoustical interventions typically happen after a school building is completed, whereas it would be fundamental to integrate these from the beginning of a project. Regardless of when they’re taken into consideration, it is generally due to the use of absorptive surfaces positioned on the lateral walls or ceiling.

Absorbent panels are made of materials that absorb incident sound energy because of their pores, like those found in natural fiber materials, glass or rock wool. A portion of the captured energy is transformed into heat, so the part of energy again reflected as sound into the space is strongly reduced (Figure 1). However, recent studies and standards updates investigated whether acoustic treatments should include both absorbent and diffusive surfaces, to account for the teaching and learning premises at the same time since an excessive reduction of reflections does not support speech and is proved to require higher vocal efforts to teachers.

Figure 1 – Scheme of the absorptive (top) and diffusive (bottom) properties of surfaces, with the respective polar diagrams that represent the spatial response of the different surfaces. In the top case (absorption), the incident energy (Ei) is absorbed by the surface and the reflected energy (Er) is strongly reduced. In the bottom case (diffusion), Ei is partially absorbed by the surface and Er is reflected in the space in a non-specular way. Note that these graphs are adapted from D’Antonio and Cox (reference: Acoustic absorbers and diffusers theory, design and application. Spon Press, New York, 2004).

Therefore, we found that optimal classroom acoustic design should be based on a balance of absorption and diffusion, which can be obtained by means of the presence of surfaces that are strategically placed in the environment. Diffusive surfaces, in fact, are able to redirect the sound energy in a non-specular way into the environment so that acoustic defects like strong echoes can be avoided, and early reflections can be preserved to improve speech intelligibility, especially in the rear of a room.

The few available studies on this approach refer to simulated classroom acoustics, so our work is a contribution to the research aiming to go further with new data based on measured realistic conditions. We looked at an existing unfurnished classroom in an Italian primary school with long reverberation time (around 3 seconds). We used software for the acoustical simulation of enclosed spaces to simulate the untreated room and obtain the so called “calibrated model” that gives the same acoustic parameters of the ones measured in-field.

Then, based on this calibrated model, in which the acoustic properties of the existing surfaces fit the real ones, we simulated several solutions for the acoustic treatment. This included the adjustment of absorption and scattering coefficients of surfaces to answer to characterize different configurations with absorbent and diffusive panels. All of the combinations were designed to reach the optimal reverberation time for teaching activities, and to increase the Speech Transmission Index (STI) and Definition (D50) parameters, which are intelligibility indexes that define the degree of support of an environment to speech comprehension.

Figure 2 – Schematic representation of the investigated classroom. On the left, it is represented the actual condition of the room with vaulted ceiling and untreated walls; on the right, the optimized acoustic condition is given with the use of absorptive (red) and diffusive (blue) panels that were positioned on the walls or on the ceiling (as baffles) based on literature and experimental studies. The typical position of the teacher (red dot) desk and position in the classroom is given in the figure.

Figure 2 illustrates the actual and simulated classrooms where absorptive (red) and diffusive (blue) surfaces were placed. The optimized configuration (Figure 3 for an overview of the acoustic parameters) was selected as the one with the highest STI and D50 in the rear area, and consisted in absorbent panels and baffles on the lateral walls and on the ceiling and diffusive surfaces on the bottom of the front wall.

Figure 3 – Summary of the acoustical parameters of the investigated classroom that are referred to the actual condition of the room. Values in italic represent the outcomes of the in-field measurements, whereas the others are obtained from simulations; values in bold represent the values that comply with the reference standard. If an average was performed in frequency, it is indicated as subscript. The scheme on the right represents the mutual position between the talker-teacher (red dot) and the farthest receiver-student (green dot), where the acoustic distance-dependent parameters of Definition (D50, %) and Speech Transmission Index (STI, -) were calculated. The reverberation time (T30, s) was measured in several positions around the room.

We evaluated the effectiveness of the acoustic treatment as the enhancement of speech intelligibility using the Binaural Speech Intelligibility Model. Its outcomes are given as speech reception thresholds (SRTs) to give a fixed level of speech intelligibility, set to 80% to account for the listening task that is related to learning. Across the tested positions that accounted for several talker-to-listener distances and noise-source positions (Figure 4), model predictions indicted an average improvement in SRTs up to 6.8 dB after the acoustic intervention that can be “heard” experimentally.

Here you can hear a sentence in the presence of energetic masking noise, or noise without an informational content, but with a spectral distribution that replicates the one of speech.

Here you will hear the same sentence and noise under optimized room acoustics.

Figure 4 – Scheme of the tested talker-to-listener mutual positions for the evaluation of speech intelligibility under different acoustic conditions (i.e. classroom without acoustic treatment and with optimized acoustics). The red dots represent the talker-teacher position; the green dots represent the listener-student positions; the yellow dots represent the noise positions that were separately used to evaluate speech intelligibility in each listener position.

To summarize, we demonstrated an easy-to-use and effective design methodology for architects and engineers of classrooms, and a case study that represents the typical Italian primary school classrooms, to optimize acoustics for a learning environment. It is of great importance to make a classroom sound good, since we cannot switch off our ears. The premise of hearing well in classrooms is essential to establishing the basis of learning and of social relationships between people.