I don't think you really understand how diaphragmatic absorbers work. How about this: imagine removing a peak acoustically, instead of using EQ, also potentially addressing some nulls? For example, take the following thought experiment:Throwing away boundary reinforcement sounds like a daft idea to me I'm afraid. Possibly there is an upside if EQ isn't being used, but it should be.
You have a 20 foot wide room. This results in width modes due to axial standing waves at about 28.25 Hz, 56.5 Hz, 84.75 Hz, etc. (it's a little more complicated, but let's go with the simplest model). A person sitting in the midline of the room sits at the node of the first-order mode at 28.25 Hz so will experience a relative null at this frequency due to cancellation, especially if the bass source (like a single subwoofer) is positioned closer to a sidewall (unless you have two bass sources positioned close to the sidewalls, but let's stick with the single subwoofer until the next paragraph). They will experience a peak at 56.5 Hz since they're in the antinode for the second-order width mode, a null at 84.75, etc. You could bring down the 56.5 Hz peak with EQ. However, if this were a home theater, there might be multiple seats set up in a row, so a listener sitting near the end of the row, perhaps 5 feet to the side of the midline, is sitting in a node for this second-order width mode, so they were experiencing a null already, and the EQ that you just did to bring down the peak in the midline doesn't help them at all.
You could address the first-order node with two subwoofers, one positioned close to each side wall. This results in mode cancellation for the odd-order modes, but doesn't address the even-order ones. Alternatively, you could position two subwoofers along the midline of the room, maybe one in front and one in back. Because they're positioned in the nodes of the odd-order modes, they don't activate these standing waves, but they still activate the even-order ones because they're positioned in the antinodes for these
Now you take two very large diaphragmatic absorbers tuned to 56.5 Hz and position them along the sidewalls lateral to the listening position. These now address the second-order width mode so that the listener in the midline (who was experiencing a peak) and the listener at the end of the row (who was not experiencing much bass at the frequency at all) now experience much more similar bass levels at this frequency. The subwoofers still have boundary reinforcement, but the listeners are less subject to the frequency response irregularities due to standing waves at the frequencies relevant to the diaphragmatic absorbers.
Hope that makes sense.
Young-Ho
p.s. the first paragraph of the thought experiment goes part of the way towards explaining the 38% "rule" for listener positioning, since this is halfway between the nodes for the first-order and second-order length modes
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