Anechoic recordings of balloon bursts were systematically acquired for various conditions of balloon diameters, puncture location, and inflation pressure. The recordings were analyzed to derive the average frequency spectrum over the effective duration of the acoustic impulse. Although the data show the well-known limitations for the impulse responses (in terms of repeatability and directional behavior) when viewed at high resolution, the results are quite consistent when averaged over one-third octave bands and reveal that the diameter factor (the ratio between the diameter of the inflated balloon to that of its stated maximum), rather than the overall diameter of the balloon, is a good indicator of the sound pressure level, especially above 200 Hz. The study proposes some simple empirical formulas to predict the quantitative sound pressure level and the qualitative spectral response (using the spectral centroid & skewness) from balloon bursts, based on the inflation factor as a variable. The study also offers suggestions to maximize the value of the balloon-burst methodology in building acoustics measurements by describing an effective way to measure reverberation time while simultaneously acquiring useful directional information associated with the reflected sound.

The Chicago Transit Authority’s (CTA) Brown Line train is part of the Chicago ‘‘El’’ system and passes mostly through residential neighborhoods. Currently at maximum capacity, the Brown Line will be undergoing expansion, increasing the train length from six to eight cars. By taking sound-level measurements during morning peak hours and evening off-peak hours, this study analyzes the contribution of the Brown Line trains to the existing neighborhood noise floor. Data analysis reveals a significant disparity between the L90 and higher Leq readings. As the sole contributor to the L10 levels, this study finds that the Brown Line trains are highly influential to the elevated Leq. It is interesting to note that, while exempt from the city’s evening noise ordinance, the Leq is in excess of the prescribed level of 55 dB.