Originally Posted by KidHorn
You obviously don't understand yourself. There's no way the initial wave will not be the strongest. It's basic thermodynamics. Every reflection will result in less energy because some of the energy is lost at the boundary.
I'm not saying anyone is right or wrong. What I'm saying is the only way to tell optimal placement is through trial and error. There are way too many variables involved in a real world application.
I've written many computer models that use finite element analysis to model real world behavior. You can only go so far. In order for any model to work you have to setup boundary conditions that in reality will almost never be correct. For a final design, you have to build a real model and collect empirical data. This is true in acoustics, air flow, heat transfer and anything else that involces particle motion and transfer of energy.
But hey, I don't have a website with drawings of subwoofers, I just have college degrees and years of experience modeling things, so what do I know about it.
When you place a subwoofer in a room, the room becomes the biggest factor in the reproduction of the bass. Period. Direct wave theory is useless in a room. The wavelengths are so long at bass frequencies that small distance discrepancies are immaterial. It is the modal response of the room that totally dominates. If you get an SPL meter and play a single frequency tone and walk around the room, you can measure the peaks and nulls throughout the room. These peaks and nulls are caused by constructive/destructive interference from the REFLECTED waves off the room boundaries combining, sometimes in-phase, sometimes out-of-phase. The in-phase combinations will add SPL; the out-of-phase combinations will decrease SPL.
With multiple subwoofers placed separately around the room, the peaks and nulls appear at different points in the room and they tend to cancel each other, yielding smoother response.
Here is the baseline response of one of my subwoofers measured outdoors with the mic placed on the ground one meter away from the side of the sub:
Bass frequencies propagate omnidirectionally, so that would be a measurement of the "direct wave" from the subwoofer.
Take that same subwoofer and place it in my room, and this is the response at the listening position:
Place it somewhere else and you get this:
Put 3 of them in the room, all daisy chained off one Subwoofer output, all placed randomly, at different distances to the LP, and EQ'd with Audyssey XT32, and you get this:
The *point* that Bill was trying to make to you was that, when you stack 2 of the subs, you forego an opportunity to spread them out and improve the smoothness of the response in your room. The "direct wave" is inconsequential when you're dealing with bass frequencies. The reflected sound has it's way with the direct sound and produces the final response you *HEAR*, which is the only response that matters. You can blather on about modeling and direct waves and thermodynamics all you want, but this is the only important aspect of optimizing multiple subwoofers.
With that, I will do what Bill did, and bow out of this thread.