In Situ Acoustic Assessment of a Timber-Frame Floor: Airborne and Impact Sound Insulation Under ISO 717

Single-number ratings are widely used in building acoustics, but they are meaningful only when the reference-curve procedure is applied correctly and the reported descriptors are matched to the physical problem. This study re-evaluates accredited in situ measurements of airborne and impact sound insulation for a timber-frame interfloor construction at the Archaeological Museum of Istria, Croatia. Applying the measured one-third-octave spectra in 1 dB reference-curve steps according to ISO 717 gives R′w = 55 dB and L′n,w = 62 dB. Both values satisfy the historical Croatian requirements that applied at the time of measurement. For the meeting-room source context, the ISO 717-1 adaptation term C = −3 dB gives R′w + C = 52 dB; Ctr is not used in the internal-partition analysis because it represents a low-frequency-rich, traffic-oriented source spectrum. The impact receiving-room volume is 95.4 m3. A separate diffuse-field scenario estimates how certified broadband absorption would change the unnormalized receiving-room level Li(f); it is not treated as a change in L′n,w, and no band-by-band 60 dB compliance threshold is applied. A separate sensitivity analysis of floating-floor resonance gives f0 = 28–89 Hz over the selected mass–stiffness range, with an as-built estimate of about 53 Hz. The paper therefore distinguishes measured apparent sound insulation, source-spectrum context, receiving-room response, and analytical sensitivity without presenting the scenario calculations as validated acoustic optimization.