Quote Originally Posted by S&W645 View Post
There are big differences in A weighed and D weighted reading over the spectrum. A weighted is the most commonly used but dB meters commonly have two or more scales and they do show some big differences depending on the frequency of the sound. Disturbing effects of low frequency sound immissions and vibrations in residential buildings Findeis H, Peters E - Noise Health

One of the measurements in the article showed a 66dB(A) reading while also producing an 84dB(B) reading. 85dB in either scale was our ear protection threshold.
In the section under Study Results I find what I think you are referring to, but as it is not exactly as you say it, I am left to wonder.
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:
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
The statement I suspect you were using and its continuation of what you were presenting is:
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.
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.