The Missing 6 dB: Perceptual or Procedural Effect?
Résumé
Several studies have shown that, to produce the same loudness, a sound must be played 6 dB louder by headphones than by loudspeaker. Thus, a sound is louder when reproduced by loudspeaker compared to headphones, while the level at the ears are the same in both cases. This phenomenon was called the "missing 6 dB". It was found using methods of direct comparison between loudspeaker and headphone reproductions. In most studies, to make the comparison, the listener had to listen to a sound played by a loudspeaker, then to put the headphones on to listen to the sound played by the headphones, then remove the headphones to listen again to the sound played by the loudspeaker and so on. The purpose of the current study was to test whether the missing 6 dB is found using a procedure that does not require a direct comparison of the two reproducing systems. We measured the loudness functions of one-ERB band of noise centered at 250 and 500 Hz (the missing 6 dB is observed at low frequencies). We used a scale, derived from G. Borg's work, with verbal anchors (from extremely weak to extremely loud, with a special anchor for inaudible). This scale makes it possible to compare the loudness functions measured with the headphones and loudspeaker. The at-ear level was measured individually using a small microphone inserted into an ear plug that blocked the ear canal. The experiment took place in an anechoic room. The loudspeaker was visible from the subject in all experiments. We did not found any differences in the loudness functions for the two center frequencies. Thus, for the same at-ear level, the sounds had the same loudness in both reproduction conditions.
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