**4.2. Acoustics quality parameters in the environments**

## *4.2.1. Reverberation time (T60)*

In Sant Felip Neri square (top left from **Figure 4**) we can observe an increase in reverberation time when we step away from the source. The Ts values vary from a conference hall (T60 = 0.7–1.9: point 1), an opera theatre (T60 = 1.2–1.5: point 2), a chamber music concert hall (T60 = 1.3–1.7: points 3 and 4) and a symphonic concert hall (T60 = 1.8–2.0), according to the recommended values of Carrión [42]. Plaça del Rei (top right) presents typical values of a symphonic hall when we step away from the source. Meanwhile, Plaça Sant Iu (bottom left) shows a typical curve of a speech hall in all the interior points of the square, except for the point in the

**Figure 4.** Reverberation time (T60) of the different environments: Sant Felip Neri (top left), Plaça del Rei (top right), Plaça Sant Iu (bottom left), and Carrer Santa Llúcia (bottom right).

alley, which presents Ts values like a chamber music hall. Carrer de Santa Llúcia (bottom right) presents some features of an opera theatre for points 1, 2 and 3, that is, in the frontal points to the source, whilst in the rear part to the source, some symphonic hall features are presented.

#### *4.2.2. Speech clarity (C50)*

**4.1. Acoustic framework**

ity in the considered point.

*4.2.1. Reverberation time (T60)*

is, the worse quality is the acoustics [3].

Once the recordings had been made, different parameters of acoustic quality were obtained

*Reverberation time (T60)*: when a sonorous source that is continually radiating suddenly stops in a determined enclosure, a listener in the hall will continue to hear the sound for a period of time in which its energy is being absorbed by the surfaces of the enclosure's limits [39]. The T60 value corresponds to the falling time of the sound associated with the angle for the first 60 dB decrease. The T60 for an empty hall varies with the frequency. Generally, for music halls, the Ts is higher for low frequencies and decreases when the frequency increases.

*Early decay time (EDT)*: this considers the reverberation time for the first 10 dB of decrease. EDT is more closely related to the subjective impression of the reverberation in an enclosure than Ts [40]. To ensure good diffusion of sound in a hall, it is imperative that EDT correspond-

*Speech clarity (C50)*: registered C50 values vary with the listening point. According to Carrión Isbert [39], the recommended value of C50 associated with each point in an occupied hall must fulfill C50 > 2 dB. The higher the value, the greater is the speech intelligibility and sonor-

*Definition (D50)*: if the definition increases, the hall is better prepared for speech, as may be the case in theatres or conference halls. Thus, a D50 value that is over 65% is an appropriate value for this kind of hall. A concert hall with good acoustics has a definition index lower than 50% in central frequencies of 500 and 1000 Hz. In concert halls, the higher the definition index

*Musical clarity (C80)*: registered C80 values vary with the listening point. Beranek [41] recommends an average of −4 ≤ C80 ≤ 0 dB for C80 in the 500 Hz, 1 kHz and 2 kHz frequencies

*Strength (G)*: G values remain similar at each of the measurement points. They approximately correspond to a decreasing line from low frequencies (G = 30) to high frequencies (G = 10).

In Sant Felip Neri square (top left from **Figure 4**) we can observe an increase in reverberation time when we step away from the source. The Ts values vary from a conference hall (T60 = 0.7–1.9: point 1), an opera theatre (T60 = 1.2–1.5: point 2), a chamber music concert hall (T60 = 1.3–1.7: points 3 and 4) and a symphonic concert hall (T60 = 1.8–2.0), according to the recommended values of Carrión [42]. Plaça del Rei (top right) presents typical values of a symphonic hall when we step away from the source. Meanwhile, Plaça Sant Iu (bottom left) shows a typical curve of a speech hall in all the interior points of the square, except for the point in the

by signal processing. The following parameters were studied:

50 From Natural to Artificial Intelligence - Algorithms and Applications

This typical spectrum of reverberation is known as the *tonal curve*.

ing to 500 Hz and 1 kHz is in the same order as Ts [40].

for an empty hall. Values over +1 dB should be avoided.

**4.2. Acoustics quality parameters in the environments**

UNE-EN ISO 3382 [40] recommends G values between 4 and 5.5.

In Plaça de Sant Felip Neri (top left from **Figure 5**) only the recordings at points 1, 2 and 3 exceed 2 dB of C50 for high frequencies. Note that Points 1, 2 and 3 are the nearest points to the source and it is natural that clarity is better near the speaker. Thus, we can deduce that this is not a square with clear acoustics for speech in most of the recording locations and frequencies. In Plaça del Rei (top right) we find a similar situation at first glance. However, clarity is very appropriate at point 1 for mid-high frequencies. Moreover, as we step away from the source, that is, at points 1, 2 and 3, clarity is restricted only to high frequencies, whilst in lateral points, the clarity is below accepted levels. Plaça de Sant Iu (bottom left) presents a similar scheme to those seen above: a lack of clarity for low-mid frequencies and better clarity for high frequencies. Note that point 4 is the only one that does not follow the typical curve of the other points. This is due to its position in the access alley to the square rather than inside the enclosure. Thus, its behavior is different from the others. In Carrer de Santa Llúcia (bottom right) we can observe a progressive decrease in speech clarity from point 1 to point 5 for

**Figure 5.** Speech clarity (C50) of the different environments: Sant Felip Neri (top left), Plaça del Rei (top right), Plaça Sant Iu (bottom left), and Carrer Santa Llúcia (bottom right).

mid-high frequencies. This knowledge indicates that speech clarity at points 1 and 2 is only acceptable for mid-high frequencies. Considering that this environment is generally used by opera singers, and that most of the audience occupies the zone in points 1 and 2, we can say that the acoustics of this space are extremely favorable to its use.

is correctly understood, although music is not underprivileged. Finally, Carrer de Santa Llúcia (bottom right) has better musical clarity at points 3, 4 and 5. Curiously enough, these points are the same that held the aforementioned bad speech clarity (C50). This fact suggests that the points with better qualities for speech are not the optimum ones for music, and

**Figure 6.** Music clarity (C80) of the different environments: Sant Felip Neri (top left), Plaça del Rei (top right), Plaça Sant

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In Plaça Sant Felip Neri (top left from **Figure 7**), we can see that D50 values were below 50% for low frequencies, but above 50% for high frequencies (from 500 Hz). This was true particularly at points 1, 2 and 4. Thus, this square is very appropriate for music at points 3 and 5 (lateral and distant from the source) and better for speech at points 1, 2 and 4 (points near to or centered with the source). Similarly, the Plaça del Rei (top right) had D50 parameters that exceeded 50% for high frequencies at points 1, 2 and 3 (these points were aligned frontally with the source). The lateral points maintained D50 values under 50%. Thus, these lateral points are appropriate for music. These data, together with those revised about C50 and C80, again indicate that this square has good acoustics for music and worse acoustics for speech. Conversely, Plaça Sant Iu (bottom left) had a similar tendency for almost all the measured

vice-versa.

*4.2.4. Definition (D50)*

Iu (bottom left), and Carrer Santa Llúcia (bottom right).

## *4.2.3. Musical clarity (C80)*

In Sant Felip Neri Square (top left from **Figure 6**) we can see that all the C80 values remain above −4 dB, but they are higher than +1 dB from 2 kHz at points 1, 2 and 4. If we compare C50 and C80 values, we can deduce that this square is clearer for music than for speech. In Plaça del Rei (top right), C80 values at points 2, 4 and 5 are within the desired limits. However, at points 1 and 2, C80 values exceed +1 dB, thus those points are not optimum for musical clarity. This square holds good musical clarity at the points furthest from the source, that is to say, points that belong to the reverberant field and not to the direct field. In contrast, Plaça de Sant Iu (bottom left) only shows C80 values within the desired limit when we consider low and mid frequencies. These recommended frequencies hold C80 values exceeding the +1 dB criteria. These data, compared with C50, make us think that the square is more appropriate for speech than for music. It is a square in which the spoken word

**Figure 6.** Music clarity (C80) of the different environments: Sant Felip Neri (top left), Plaça del Rei (top right), Plaça Sant Iu (bottom left), and Carrer Santa Llúcia (bottom right).

is correctly understood, although music is not underprivileged. Finally, Carrer de Santa Llúcia (bottom right) has better musical clarity at points 3, 4 and 5. Curiously enough, these points are the same that held the aforementioned bad speech clarity (C50). This fact suggests that the points with better qualities for speech are not the optimum ones for music, and vice-versa.

#### *4.2.4. Definition (D50)*

mid-high frequencies. This knowledge indicates that speech clarity at points 1 and 2 is only acceptable for mid-high frequencies. Considering that this environment is generally used by opera singers, and that most of the audience occupies the zone in points 1 and 2, we can say

**Figure 5.** Speech clarity (C50) of the different environments: Sant Felip Neri (top left), Plaça del Rei (top right), Plaça Sant

In Sant Felip Neri Square (top left from **Figure 6**) we can see that all the C80 values remain above −4 dB, but they are higher than +1 dB from 2 kHz at points 1, 2 and 4. If we compare C50 and C80 values, we can deduce that this square is clearer for music than for speech. In Plaça del Rei (top right), C80 values at points 2, 4 and 5 are within the desired limits. However, at points 1 and 2, C80 values exceed +1 dB, thus those points are not optimum for musical clarity. This square holds good musical clarity at the points furthest from the source, that is to say, points that belong to the reverberant field and not to the direct field. In contrast, Plaça de Sant Iu (bottom left) only shows C80 values within the desired limit when we consider low and mid frequencies. These recommended frequencies hold C80 values exceeding the +1 dB criteria. These data, compared with C50, make us think that the square is more appropriate for speech than for music. It is a square in which the spoken word

that the acoustics of this space are extremely favorable to its use.

*4.2.3. Musical clarity (C80)*

Iu (bottom left), and Carrer Santa Llúcia (bottom right).

52 From Natural to Artificial Intelligence - Algorithms and Applications

In Plaça Sant Felip Neri (top left from **Figure 7**), we can see that D50 values were below 50% for low frequencies, but above 50% for high frequencies (from 500 Hz). This was true particularly at points 1, 2 and 4. Thus, this square is very appropriate for music at points 3 and 5 (lateral and distant from the source) and better for speech at points 1, 2 and 4 (points near to or centered with the source). Similarly, the Plaça del Rei (top right) had D50 parameters that exceeded 50% for high frequencies at points 1, 2 and 3 (these points were aligned frontally with the source). The lateral points maintained D50 values under 50%. Thus, these lateral points are appropriate for music. These data, together with those revised about C50 and C80, again indicate that this square has good acoustics for music and worse acoustics for speech. Conversely, Plaça Sant Iu (bottom left) had a similar tendency for almost all the measured

**Figure 7.** Definition (D50) of the different environments: Sant Felip Neri (top left), Plaça del Rei (top right), Plaça Sant Iu (bottom left), and Carrer Santa Llúcia (bottom right).

**5.** *How* **is it evaluated?**

Sant Iu (bottom left), and Carrer Santa Llúcia (bottom right).

brief discussion of what usability means is mandatory.

students [44, 45].

Quantitative approaches are the main methods of scientific research. They focus on analysing the degree of association between quantified variables, promulgated by logical positivism. Therefore, possible answers need to be constrained in order to evaluate results objectively [43]. Some evaluation investigations have already been done with architecture

**Figure 8.** Early decay time (EDT) of the different environments: Sant Felip Neri (top left), Plaça del Rei (top right), Plaça

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Qualitative research is less common in education areas, because it focuses on detecting and processing intentions. Unlike quantitative methods, qualitative approaches require deduction to interpret the results. The qualitative approach is subjective, because it is assumed that reality is multifaceted and cannot be reduced to a universal parameter. Interviewers are passive observers, they take notes and classify them [46]. These methods have traditionally been related with social sciences, due to their association with human factors and the user's experience. In fact, *User Experience*, UX, is a discipline focused on the study of behavioral patterns in working environments. Our case study is framed in teaching process usability [47]. Thus, a

points, except for the point measured in the alley. In particular, D50 was above 65% for high frequencies and under 50% for mid and low frequencies. Therefore, we restate that this square works better for speech and has too much definition for music. Perhaps for this reason, and because of its size, the square is ideal for solo singers or those accompanied with chamber instruments. Finally, Carrer de Santa Llúcia (bottom right) has an inherent tendency to lower definition when we move away from the source or we are behind it. Particularly, points 1 and 2 are more suitable for speech or opera, whilst points 3, 4 and 5 have better features for music. Again, we can note that the audience zone belongs to points 1 and 2.

## *4.2.5. Early decay time (EDT)*

In Plaça de Sant Felip Neri (top left from **Figure 8**) we can see that EDT values for 500 Hz and 1 kHz are similar to Ts values, except for the Ts peak at point 5, which is the result of a measurement error due to the high amount of background noise at that time. Similarly, in Plaza del Rei (top right), Sant Felip Neri (bottom left) and Carrer Santa Llúcia (bottom right), the EDT levels are very similar to the Ts levels, which indicates that there is a good sound diffusion in these environments.

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**Figure 8.** Early decay time (EDT) of the different environments: Sant Felip Neri (top left), Plaça del Rei (top right), Plaça Sant Iu (bottom left), and Carrer Santa Llúcia (bottom right).
