## 4 Acoustic Measurements  
### Acoustic Measurements of the Monte Castello di Vibio Theatre  
Acoustic measurements were carried out in the Monte Castello di Vibio theatre to understand the acoustic response of the hall by the requirements of the standard set out in ISO 3382-1 [3], which is considered the international reference standard for objectives of acoustic parameters. During the survey, thermal and humid conditions were taken into account [7]. The equipment involved in the study and how the signals they recorded were used to calculate the relevant acoustic parameters were as follows:  
* Equalized omnidirectional loudspeaker: a light yet powerful sound source for measurement applications in the room and building acoustics. It is built from twelve specially developed dynamic drivers that ensure a uniform emission of the acoustic test signal. This speaker was used to reproduce the ESS signal in the theatre;  
Figure 4: View of the main hall from the stage [1]. Figure 5: Interior view of the 1763 theatre [6]. * Binaural dummy head: a professional dummy head made by [PERSON]. It is a binaural stereo microphone, and two omnidirectional condenser capsules are built into artificial ears mounted on an enclosure resembling a human head. The [PERSON] dummy head has very low self-noise and can handle high sound pressure levels of up to 135 dB without audible distortion. This head was used to record binaural stereo files, which were used to calculate interaural cross-correlation (IACC early);
* B-Format microphone: it is a Sennheiser Ambeo microphone to record 360\({}^{\circ}\) spatial audio. The Ambeo is an Ambisonics microphone fitted with four matched KE 14 capsules in a tetrahedral arrangement. This unique design lets users capture the surrounding sound from one single point. The capsules of the Sennheiser Ambeo deliver A-format, a raw four-channel output that has to be converted into a new set of four channels, the Ambisonics B-format. B-format is a W, X, Y, and Z representation of the sound field around the microphone. W is the sum of all four capsules, whereas X, Y, and Z are three virtual bi-directional microphone patterns representing front/back, left/right, and up/down. In this study, only the W and Y signals were used to compute Lateral Fraction (LF) and Lateral Efficiency (LE);
* Omnidirectional microphone: a Bruel & Kjaer \(\frac{1}{2}\) inch preparised free-field microphone. It is an ultra-linear condenser microphone for measurement and recording applications, ideally suited for room equalisation, high-resolution studio recording, and live applications. It has a flat frequency response from 15 Hz to 20 kHz and an actual omnidirectional pattern. The omnidirectional microphone was used to record mono signals, which were used to calculate other main acoustic parameters (in this survey, the Reverberation Time (T\({}_{20}\)), Early Decay Time (EDT), Clarity indexes (C\({}_{80}\) and C\({}_{50}\)), and Definition (D\({}_{50}\)) were included);
* Audio interface: a Zoom F8 audio interface was used to record the signals coming from microphones, with 8-input/10-track recording, super low-noise preamps, and support for 24-bit/192 kHz audio. Through it, seven channels of audio files were recorded, with tracks from one to four for the Ambeo microphones, 5-6 for the binaural recordings of the dummy head, and the last channel for the mono recording from the omnidirectional microphone. The sound source was placed 1.6 m above the finished floor. In comparison, the receiver was mounted at 1.4 m across the stalls and inside several boxes to cover the spectator area and the complete setup was composed of a dummy head, a B-Format microphone, and an omnidirectional microphone, as shown in Figure 6. The receiver points chosen for the measurements were sufficient to understand the acoustic response of the hall, taking into account the axisymmetry of the volume. The excitation signal feeding the sources was an Exponential Sine Sweep (ESS) with a duration of 15 s at a constant sound pressure level from 40 Hz to 20 kHz [8].