**4.1. Acoustic framework**

Once the recordings had been made, different parameters of acoustic quality were obtained by signal processing. The following parameters were studied:

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

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

*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 sonority in the considered point.

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

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

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.

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

Evaluation between Virtual Acoustic Model and Real Acoustic Scenarios for Urban Representation

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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

*4.2.2. Speech clarity (C50)*

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

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