Originally Posted by LTD02
speed of sound across the room is not infinity.
most sound waves are less than the length of the room.
as a result, your "mechanically in phase" subs at the front and rear of the room are not actually in phase.
when the driver at the front of the room "pushes" air as it begins to make some sound, the driver at the rear of the room will begin to "pull" some air. BUT that air is not coupled together like it would be in a shoe box. as a result, a high pressure peak starts moving from the front of the room, and a low pressure trough starts moving into the room from the rear. with no delay, they will meet in the middle of the room and cancel each other out.
Good explanation. But I don't think the speed of sound is the issue, it is the coupling or compliance of the air.
Take a plastic shoe box and fill it half way with water, the water representing the air in the room. Create coordinated waver-fronts (south-south) in the water, and create opposing wave-fronts (north-south). I suspect when opposing waves collide in the middle, you will get a larger wave, but only at that one point.
When the Front Sub pushes
and the Rear Sub pulls
, the rear Sub is not sending a rarefied wave into the room, rather it is pulling air toward the speaker, or I suppose within a limited context, pulling air into the speaker.
When the driver rebounds and pushes compressed air into the room, at the same time, the other driver is pulling on the air in the room creating a ratification on the other side of the room. (south-south)
Rather than think of the air in the room as individual compression fronts moving through the air, think of the air in the room as one mass of air that you are trying to move in a given direction.
Again, I've only tried this for a couple of days with two near identical speakers, both 3.5-way with 2x8" drivers each, placed about 13 feet apart. That is the only time in decades of using my turntable that I ever had a problem with it. At some point, the turntable platform was literally bouncing around making it impossible for the stylus to stay in the groove. Four speakers in front, or four speakers front and rear but electrically in phase
didn't create this substantial resonance problem.
I attribute this to the mechanically in-phase
the air more effectively.
Again, easy enough to try.