Previous research on the “missing 6 dB”, i.e., the loudness mismatch between loudspeaker and headphone presentation reported a non-explainable discrepancy between the experimental outcome from Aachen and Oldenburg anechoic rooms even with the same subjects and acoustic compensation methods. To examine the influence of the visually presented scene and other possible causes, a headphone-only study was performed with stimuli that were binaurally recorded in the free field through a KEMAR and were presented or diotic. A visual presentation via a head-mounted display provided 360° photos either of the respective anechoic rooms or a black screen. Subjects performed a loudness comparison task by indicating via footswitch which presentation is louder. The results indicate that the mismatch was not at all dependant on the visually perceived rooms. Further experimental parameters that were tested with and without visual presentations include the usage of a handheld controller in comparison to the footswitch as well as synthesised signals generated by convolution of the different third-octave band noise signals with the binaural room impulse response (BRIR). The results and possible magnitude of bias will be discussed in comparison to the possible bias in the original HRTF-recordings in the standing position (Aachen) vs. sitting position (Oldenburg).