So your thesis is that the phase reversal is not caused by a room reflection.
No.
The room modifies the arrival time at the listening position of the reflected soundwaves emanating simultaneously from the two speaker locations causing their sum at the listening position to cancel.
With either wave source operating alone the cancellation doesn't occur, or, is much less severe.
By modifying the launch time (phase) of one speaker or of the other, or splitting the difference between both, the relative time of arrival of the wave peaks and troughs from each source via reflective surfaces at the listening position can be adjusted, thereby adjusting the amount of cancellation occurring at the frequencies of interest.
Instead, you believe the right and left speakers played at the same time cancel each other at 47hz?
No.
Or Yes, with the following explanation.
The direct wave from both speakers is not the source of the cancellation.
The direct wave from left plus the reflected from left (causing some phase shift from the direct) does not cancel itself at the listening position.
The direct wave from right plus the reflected from right (causing some phase shift from the direct that is different from that of the left) does not cancel itself at the listening position.
The direct wave from both speakers, modified by the combined reflections from both speakers, at the listening position, does create a substantial null around 47hz.
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