Something that has been a long running mystery is why some subs tend to produce more physical effects than other subs even when the SPL is kept the same.
A recent and rather striking experiment was conducted here:
In essence, a near-field subwoofer produced much greater physical effects than a far-field subwoofer as measured by an accelerometer, even though SPL was kept the same.
This is not the first time that this observation has been made.
So what is going on?
One hypothesis relates to the way sound wave propagate. In the near field, or even out doors, the sound wave moves in one direction first compressing the air molecules on one side of the listener, then moving across the listener's position, and finally increasing pressure on the opposite side of the body. The pressure change is in ONE DIRECTION ONLY. As the pressure wave moves across the body, following compression of the air is rarefaction of the air--a negative pressure zone. As this rarefaction of air creates a negative pressure zone, the listener is then "pulled" back toward the sound source.
So, positive pressure gives a linear "push" and it is then followed by a negative pressure which gives a linear "pull". Thus the listener is rocked back and forth as the sound wave passes by. This creates the physicality.
Now, take a subwoofer placed in a car or in a home room. When a tone is played, the wave will begin to propagate in one direction. However, it will then be met with reflections off the boundaries. So what actually ends up hitting the listener are bass waves from ALL DIRECTIONS. The air molecules are compressed and rarefied, which creates the SPL, but there is no directional change. That is the key. Integrated across the entire body of the listener, there is no net directional change in pressure
. It pushes in all at the same time, then it sucks out (rarefied) all at the same time. As a result, the pressure goes up and down. SPL is measured, but there is no movement back and forth of the listener. No physicality, at least in some sense.
A further ramification of this is that various subwoofer designs could have more or less physicality depending on the extent to which they produce linear bass waves. Horns, for example, are frequently described as having more punch than direct radiators all other things equal. Within this model of physicality, this could be explained by the fact that a sound wave must travel some distance before exiting the horn, thus putting the listener effectively into the "far field" where bass waves are nearly planar even while standing directly in front of the horn itself.
The same might also be true of large radiators and/or large numbers of them relative to small diameter radiators, as the former creates something much closer to the planar wave of the far-field.