Comparative acoustic analysis of treated and untreated small recording rooms using vocal and room-response measurements

This study investigates the influence of small-room acoustics on sung vocal quality by comparing two adjacent recording environments of nearly identical dimensions: a professionally treated room (Room A) and an untreated room (Room B). Exponential sine-sweep measurements were conducted using calibrated studio equipment, and room impulse responses were analysed using reverberation metrics (EDT, Topt, RT60), clarity indices (C50, C80), definition (D50), modal behaviour, decay characteristics, and total harmonic distortion (THD). Room A incorporates broadband absorption at primary reflection points, corner bass trapping, rear-wall diffusion, and a double-layer wall structure for low-frequency damping. In addition to room-response measurements, three sustained sung vocal phrases were recorded in both rooms at microphone distances of 10, 30, and 60 cm and analysed using spectrograms and formant trajectories. The results reveal acoustic differences between the two environments. The untreated room exhibits prolonged mid-band decay times (Topt ≈ 1.3–1.9 s), elevated EDT values, reduced clarity (C80 between −5 and +8 dB), low definition (D50 ≈ 30–40%), strong low-frequency modal buildup, and increased harmonic masking. In contrast, the treated room shows studio-appropriate decay times (Topt ≈ 0.20–0.30 s), high clarity (C80 ≈ 15–25 dB), excellent definition (D50 ≈ 90–100%), and smooth decay behaviour. Time–frequency analysis of the vocal recordings confirms that acoustic treatment stabilises temporal and spectral response, yielding cleaner harmonic structure, sharper transient articulation, improved intelligibility, and greater formant precision across all microphone distances. These findings demonstrate the critical role of acoustic treatment in achieving reliable, high-fidelity vocal recordings in small-room environments.