Metodología de aprendizaje: el aula invertida

Overall, six types of water sounds were used in this study. These included small sized water features that were designed to be installed in outdoor settings as well as indoor environments. The water features were designed and constructed in the laboratory by Galbrun and Ali (2013) and are representative of a wide range of water features that could be used to mask noise. The water features differed in design as well as flow rate and impact materials. The original study examined the effectiveness of these water sounds in masking road traffic noise.

The water features were originally classified into 3 categories, namely, waterfalls, fountains with upward jets, and streams. Galbrun and Ali (2013) suggested that water sounds categorised as waterfalls tend to be disliked by people. Another study (Galbrun and Calarco, 2014) confirmed the same finding. On this ground, it was decided to exclude water sounds categorised as waterfalls in the current study. Furthermore, the natural shallow stream sound, which was highly preferred in previous research (Galbrun and Ali, 2013; Galbrun and Calarco, 2014) was also excluded, owing to the fact that it is not practical to have a stream in an open-plan office. In the original study, water was preferred as an impact material, while hard impact surfaces tended to be disliked by participants.

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Thus, one more water feature was excluded as a result of using a hard surface as impact material. Six water features remained in the pool of data after excluding the above water features. These were all considered as small in size and practical to be used in an open- plan office. The water features that were selected were, a cascade with four steps (CA), a dome fountain (DF), a foam fountain (FF), a fountain with 37 upwards jets (FTW), a narrow jet (NJT) and a large jet (LJT). The design properties and acoustic/psychoacoustic characteristics of these water features are given in Table 3.1.

Table 3.1 Acoustic and psychoacoustic parameters of the water sounds normalised at 55 dBA (Galbrun and Ali, 2013).

Sound

code Water feature Impact material Fl. LAx-x LC-A Sh. Ro. Pi. CA Cascade (4 steps) Stone (pebbles) 15 -1.30 1.20 2.21 0.10 0.05

DF Dome fountain Water 30 0.31 1.60 1.96 0.07 0.14

FF Foam fountain Stones and Boulder 30 -0.25 2.30 1.91 0.09 0.05

FTW Fountain (37 jets) Water 30 -0.90 1.40 2.21 0.07 0.10

LJT Large jet Water 15 4.94 4.90 1.73 0.28 0.08

NJT Narrow jet Water 15 -0.96 1.90 2.09 0.19 0.07

Fl. = Flow rate (l/min). LAx-x = LA10-LA90 (dB). LC-A = LCeq-LAeq (dB). Sh. = Sharpness (acum).

Ro. = Roughness (asper). Pi. = Pitch strength

3.2.1 Test structure

The water features described above were generated using a test structure built in the Building Services laboratory of Heriot-Watt University and configured to meet the design properties of each water feature. The test structure is shown in Figure 3.1.

The structure consisted of a sump tank (2.0 m long  1.2 m wide  1.2 high) encased in the floor, and a tank (1.5 m long  0.5 m wide  0.5 m high) fixed to a structural frame at a higher level. Two submersible low noise water pumps were placed in the sump tank and used to circulate water to the upper tank or to the fountain extensions. Sound reflections were minimised through using absorption panels and bass traps around the structure. The original study examined a variety of waterfalls and the tank was crucial for configuring the structure to resemble waterfalls. However, since waterfalls were excluded in this study, the only water feature that used the upper tank was the four-step cascade (CA). The remaining water features were mainly fountains and were created using different fountain extensions attached to the water pumps via a pipe. Photographs of the selected water features are shown in Figure 3.2.

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Figure 3.1 Laboratory structure used to test the water generated sounds (Galbrun and Ali, 2013) (Fig. reproduced).

Figure 3.2 Photographs of water features selected in this study, taken at the Building Services laboratory of Heriot-Watt University. (a) Cascade (4 steps). (b) Fountain (37 jets). (c) Large jet. (d) Dome fountain. (e) Narrow jet. (f) Foam fountain. (Galbrun and

Ali, 2013). (a) (b) (c) (e) (d) (f) Absorbers Structural frame Tank Pipes Sump tank Submersible pumps Microphone position

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Audio recording of the water sounds was carried out with a Zoom H4n digital sound recorder connected to Brüel and Kjær Type 4190 ½ microphones, which in turn were attached to a dummy head. The dummy head was placed 0.5 m away from the impact area of the falling water at a height of 1 m above the ground. Given the large size of the laboratory (20 m 15 m  7 m), recordings at the dummy head’s position was considered as being free from reflected sounds from the boundaries of the space. The result of the audio recordings was a 20-second long binaural recording for each of the water features. A 20-second-long audio recording was considered long enough to cover the operation cycles of the water features (i.e., steady water sounds for all water features tested apart from the large jet, LJT). Seven-second-long audio samples were then extracted from the binaural recordings and were used in the tests run by Galbrun and Ali (2013). Given the steady nature of the sounds, the 7-second period was considered long enough by Galbrun and Ali (2013) to allow for the calculation of the acoustic and psychoacoustic parameters of the water sounds. In the current study, the short audio recordings (i.e., 7-second) were used in the sound level preference test (Chapter 4) and the audio-only and audio-visual preference and perception tests (Chapter 5). The longer recordings (i.e., 20-second) were used in the cognitive performance tests (Chapter 6). More details on the water sounds and their spectral properties are given in their corresponding chapters.

Psychoacoustic parameters such as sharpness, roughness, and pitch strength, were calculated by Ali (2012) using the module PsySound3 in MATLAB. The following default time steps were used in the calculations: 2 ms for sharpness, 186 ms for roughness, and 10 ms for pitch strength. More specific information on the water features and their sounds can be obtained from Ali (2012).