If this is what you were referring to, it is based upon the vibrations resulting in a 33Hz range so you might have continued reading to understand that though there is a physiological effect that it is not one that really effects hearing. Thus the statement of:The statement I suspect you were using and its continuation of what you were presenting is:vibration velocity level of 66 dB with a frequency of 33 Hz. Vertical vibrations of this magnitude are as a rule not perceptible as ground-borne vibrations
In this specific case it was not the sound effecting the hearing so much as the resonance of the vibration much like how even deaf people can suddenly become or get sick when exposed to high intensity base vibrations that they can't hear but can feel.In the centre of the room 26 dB(A) resp. 66 dB(lin), and near to the wall surfaces 44 dB(A) resp. 84 dB(lin).
The exposed persons stated that the vibrations near to the walls left an uneasy feeling in their stomachs which very quickly increased to the point of feeling sick. The measuring staff experienced similar symptoms. The highly exceeding level values near the to walls were in all probability promoted by the fact that the distance between the window and the opposite wall was 5 m which was equal to exactly half the wave length of the airborne sound, or resonance.