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This experiment investigates the effect of images of differently colored sports cars on the loudness of a simultaneously perceived car sound. Still images of a sports car, colored in red, light green, blue, and dark green, were displayed to subjects during a magnitude estimation task. The sound of an accelerating sports car was used as a stimulus. Statistical analysis suggests that the color of the visual stimulus may have a small influence on loudness judgments. The observed loudness differences are generally equivalent to a change in sound level of about 1 dB, with maximum individual differences of up to 3 dB.

Abstract:The reduced noise of electric and hybrid electric vehicles has been of particular concern because of the potential danger that these vehicles pose to pedestrians when their approach is inaudible against background noise. To address this issue, the use of additional warning sounds in such vehicles is being considered in various countries. The aim of this study was to examine the feasible level of the warning sounds in some urban environments. The levels of three candidate warning sounds (sound of car horn, engine sound, and band-pass noise) were adjusted by the study subjects against four types of urban background noise presented in a laboratory environment. The subjects were asked to adjust the level of the warning sounds so that they were reliably audible or just detectable. The results showed that the level of background noise and type of warning sound significantly affected the perception of the warning sounds, but there was no significant cross-cultural difference between the German and Japanese subject groups. The observations showed that a warning sound that was reliably audible in a particular environment might be inaudible in another environment approximately 10 to 20 dB noisier. The results were also compared with current recommended levels of warning sounds for quiet vehicles.

Acoustics 08 Paris 2165Previous experiments showed that images of differently colored trains and sports cars can influence the loudness ratings given by subjects via free magnitude estimation. Red vehicles caused subjects to rate the loudness of simultaneously presented train or car sounds higher relative to green vehicles. To investigate whether these loudness differences correspond to shifts in absolute threshold, subjects' threshold in quiet was measured via Békésytracking while viewing red, green, and neutral color patches. Also, the influence of color on the loudness of broadband noise was measured using a method of adjustment, in which subjects had to adjust the level of a test sound until it was perceived as loud as a reference sound. In both cases, no influence of color on either absolute threshold or loudness perception measured via adjustment could be found. These results support the hypothesis that, compared to previously used methods like magnitude estimation, methods that require subjects to concentrate on the auditory stimulus do not seem to be as applicable for measurements of audio-visual interactions.

The free-field response of NordicNeuroLab AudioSystem electrostatic headphones for use in functional magnetic resonance imaging (fMRI) is determined by loudness comparisons with freefield equalized Beyerdynamic DT 48 headphones. Based on these measurements, an active equalizer with resonances at 0.55, 1.5, and 6.9 kHz is developed, realized, and tested. A free-field equivalent level independent of frequency within AE3 dB between 63 Hz and 10 kHz is obtained when using the AudioSystem headphones with the described free-field equalizer.