Originally Posted by FOH
Bosso, what is this? What parameters changed?
Sub 'A' is placed in the front right corner of the room.
Sub 'B' is placed in the front left corner of the room.
Microphone is at the LP and its position remains unchanged.
Sweep is played through sub 'A' sub only (RED TRACE)
Sweep is played through sub 'B' only (BLUE TRACE)
Sweep is played through both subs simultaneously (BLACK TRACE)
The pressure pot theory dictates that room gain below the modal region occurs because the drivers cone moving into the room makes the rooms volume smaller, thus increasing the ambient air (barometric) pressure of the room. There is no escaping the fact that when both subs are playing at the same time, there is an exact doubling of cone displacement of the rooms volume.
Therefore, the summed sub black trace measurement should show a perfectly uniform increase in dBSPL in the pressure pot region, if there were such a thing.
Instead, we see evidence that there is no such phenomenon. As well, we see that the law of reflection holds true across the entire sweep bandwidth.
I believe I'm the only person on earth to have performed this simple exercise with accurate measurement capability to 4 Hz. I did this measurement nearly 4 years ago, posted the results and commented that phase still matters, regardless of frequency vs the modal region.
When I open a door or a window, it changes the pattern of wave propagation at the LP in a positive way. Opening a window may just as well cause a destructive pattern of propagation at the LP, depending on where the window is, how big it is, etc. Changing the listening position or the subwoofer positions can also place the listener in a more constructive or destructive pattern.
This is all only relative to a measurement and not so much the listening experience because a) if the subwoofer system is correctly scaled to the room and desired listening levels it is presenting an accurate playback and those frequencies in discussion are inaudible and b) that slice of bandwidth that is below the modal region is almost exclusively sensed by other than hearing and mostly through tactile responses generated by the reaction of the room (or seat, or your body) to the pressure waves, so that it does not matter where you sit in relation to the propagation pattern.
The 'both' graph, the 'window open vs closed' graph, the 'door open vs closed' graphs, the 'mic at progressively farther from the sub' graphs and the 'room gain profile' graphs I've posted over the years are all strong evidence against the pressure pot theory and serious clues as to how to attain optimal ULF playback and they were always accompanied by accurate in-room FRs from the LP showing flat-to-3 Hz or 4 Hz results.
The response has been:
Your measurements are wrong.
It's the measurement rigs noise floor.
You're using the wrong measurement window and the result is all noise.
It must be you have a magic room.
It must be your magical subwoofers.
LOL, that's not how it works at all.
That's because when you have no topical reply, you change the discussion to something else and pour on reams of verbiage and data.
The point is that I get results. But, I could very well not get results (SEE THE BLACK TRACE) and post that my room has no gain below 20 Hz but that I don't miss it anyway or some such typical sentiment.
Obviously, I didn't do that.