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In Reply to: RE: DMW posted by josh358 on March 12, 2017 at 07:03:15
If you add another bass driver with a similar response, it will not change the extension but it will for sure add more bass.
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I think there are several effects here. One, the additional driver will increase bass levels and if the two speakers have similar low frequency cutoffs (not at all certain) that in and of itself will lower the frequency of the 3 dB point, so give you a bit more bass extension. Two, the coupling of the two baffles which will increase baffle area. This will have the effect of reducing the frequency at which the 6 dB/octave rolloff begins and that will increase bass extension.
Of course, the baffle itself is a complex shape and reflections from the room surfaces have to be taken into account as well, so it's really more complex than that. But suffice it to say that adding baffle area will lower the 3 dB point, as long as it's near enough to couple effectively, and that the baffles themselves will interact with their reflections in proximate surfaces, possibly resulting in a disproportionate increase in bass output and extension if the large speaker is coupled to the wall by the smaller speaker -- keeping in mind that the deepest bass is emitted at the bottom of the speaker where the lowest resonance segment is. This assumes that the diaphgrams will impede bass frequencies effectively despite the fact that they're underdamped. Since they are, there may also be some resonant coupling between drivers.
As I see it, anyway -- it's others who have measured the effect, I'm just trying to account for it.
I don't want to reorganize my room to repeat my DWM experiments from years ago but here are a couple of REW sweeps I took today both without any smoothing and with the sub off. The key in the first is the level at 60 db. That shelf drops off at 24 HZ and moving the 1.7s +DWMs around can move that level much higher. The second is just a sweep with the mic as close to the rear wall as I could get it which just illustrates some more extension below 40 HZ. Earlier some one mentioned a 'big German amp' with a 'grip' issue. My little 1.7s +DWMs in parallel run steady just below 2 ohms. Crown amps are unaffected. I also got more extension from the DWM by using DSP to cut them off above 50 HZ.
Edits: 03/14/17
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