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In Reply to: RE: DMW posted by timm on March 09, 2017 at 19:13:55
As others have pointed out, what appears to happen is that the panels couple acoustically, creating a larger baffle, and to the proximate side wall as well. In some cases, this reduces dipole cancellation, increasing bass output and extension.
The magnitude of the effect depends on room and setup, which is why Magnepan doesn't advertise it -- it works in their listening room, and it apparently worked in Chris Martens', but Magnepan has no way of knowing whether it will work in yours. I would think that proximity of your mains to the sidewalls is important.
If you're using a model that goes lower than the DWM's, you could model it by making two barriers the size of the DWM and placing them between your speakers and the sidewall, then measuring with the barriers in different positions. A full height barrier that completely coupled the speaker to the wall would give you a 6 dB increase in bass output. These barriers aren't full height, but then, most of the lowest frequencies are produced at the bottom of the Maggie, so a DWM-height barrier may have a disproportionately large effect. (Remember when visualizing this to think of the floor and walls as mirrors -- any baffle is "reflected" and becomes twice as wide or tall.)
Follow Ups:
Josh,
Nobody is denying that it increases bass output. I am denying that it makes any material difference in low end extension in any room I have tried it in. I have measured it in three different rooms with countless set ups and two different sets of main speakers.
If you have measured the differences objectively then share your data. Seriously, exactly how much extra gain did you get with DWMs added at 32 or 40 hz? I will share my number and it rounds to zero. Please share your numbers with us.
I didn't try it myself, this is what Wendell found when he was first experimenting with the DWM/large maggie combination. (I'm using a barrier now on my left woofer panel to bridge a gap caused by a radiator and there is a lot of bass reinforcement since not only does it extend baffle width it gives me the full 6 dB dB of proximity gain, but that isn't sufficiently analogous since it runs about 2/3 the length of a speaker and there are no large gaps between it and the wall.)
IIRC, Wendell was astonished to discover while tweaking the DWM arrangement at an audio show that he was measuring response into the 20's from two speakers that didn't go that low, so when he got back to Magnepan, he conducted some experiments in the listening room at Magnepan and was able to reproduce the phenomenon and modulate the effect by moving the DWM in an arc between the speaker and the wall. However, since the effect was room and setup dependent, they couldn't use it as a specification or selling point.
I don't know why specifically it worked in Christ Martens' and Magnepan's setups but not the ones you tried -- it would be interesting to find out.
If you add another bass driver with a similar response, it will not change the extension but it will for sure add more bass.
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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