Ling time ago I experimented with dual woofers, in bipolar and dipolar arrangement. I liked dipolar, where the enclosure have seen almost no pressure changes. I am still using it till today. Was inspired by Emerald Physics.
I do not understand the need for any delay.
Here are some old pages.
Audio Pages
I do not understand the need for any delay.
Here are some old pages.
Audio Pages
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Elac has a good designer so the sub should work well, although I don't quite agree with coupling the magnets to cancel the forces. In principle the driver frame could still be applying force to the baffle. All I care about is that there is zero forces at the baffle, since that will be communicated to the outside as unwanted sound. I don't care about magnet vibration since it is inside the box and presumably less noticeable since it can be damped by fibrefill. In fact, assuming symmetry such as a cylinder or sphere, even the internal pressure forces at the baffles should be equal and opposite and therefore cancel if connected rigidly.
I just conducted an experiment with reversing the phase of one of the subwoofers in the pairs of speakers in my post #25. Since I listen directly on the mid-line, there was now perfect cancellation of low bass. It just disappeared. The stereo image also because unfocussed. If I moved off-axis the bass cancellation was now not so evident but the stereo image was not good. Presumably off-axis the cancellation is frequency dependent and variable. Since I am now a different distance from each of the subwoofer drivers, this is equivalent to delay of one of the drivers relative to the other. This is why I argue that to get any bass requires a path length difference to the listener for out-of-phase woofers. i.e. time delay if seated mid-line. However as I mentioned previously, out-of-phase woofers negates all the benefits of force cancelling.
Going push/pull can also have benefits. Reverse the phase of driver 2, but also remount it magnet out so it's still acoustically in phase. Depending on the particular non linearities of the drivers there can be some even harmonic cancellation. Potential negatives are aesthetics and mechanical noise from the magnet out driver.
If you design a box enclosure correctly, in my experience there isn't much real world advantage over the cylinder in terms of enclosure vibration.
I agree. The cylinder was available for free, so why not? It was such an easy build compared to an mdf rectangular box. I did not know what to expect with a wall thickness of only 8mm. An mdf enclosure would have wall thickness at least 25mm and significant internal bracing (see my sub enclosure in #25), hence much heavier. The paint prep for plastic cylinder was a breeze compared to mdf too. For the time and materials investment, the result was very rewarding. Don't pay retail for 6m of pipe though!
I am a big fan of push-push woofers. We built a pair of dual SDX10 woofers out of 15mm BB to test how well the force cancelation removes the load on the box… it turned out very well. One could pick the boxes (both of them) with a couple fingers using the driver cut-outs as handles. After the drivers were instaled it was near a 2-man lift.
I also have the 12”PVC pipe cut and drivers for a push-push push-pull (isobarik) pr of woofers using vintage 12” Foster woofers.
IMO not taking advantage of the huge gains in removing the box from the equation is short-sited.
dave
I also have the 12”PVC pipe cut and drivers for a push-push push-pull (isobarik) pr of woofers using vintage 12” Foster woofers.
IMO not taking advantage of the huge gains in removing the box from the equation is short-sited.
dave
Years ago, I built a sub with 4 x 12". One to each side of a square cross-section box. 3/4" ply with bracing in all directions. It worked very well, and filled a quite large room with excellent bass. I still have it, but it's doing service as a table right now, the 4 subs are mounted into columns in the walls.... Tied to the concrete-filled walls.
Just reviving this thread.
When designing a force cancelling dual opposed subwoofer am I correct in understanding the cabinet has to be twice as big as for one woofer? Because there are 2 woofers. And is the SPL gain +6dB?
What are the pros/cons then, compared to using the 2 drivers in 2 separate enclosures (that take up the same volume space), but can be scattered throughout a room?
When designing a force cancelling dual opposed subwoofer am I correct in understanding the cabinet has to be twice as big as for one woofer? Because there are 2 woofers. And is the SPL gain +6dB?
What are the pros/cons then, compared to using the 2 drivers in 2 separate enclosures (that take up the same volume space), but can be scattered throughout a room?
Yes, 2 woofers, 2 x as big for the same alignment.
2 cabinets will take up more space due to more build material, and because the build needs to be stouter.
I successfully used 15mm for a dual 10” sub, if i was only putting 1 driver in the box no less than 18mm and more bracing.
2 boxes have the advantage eof being able to placed in 2 places. I built 2 push-push subs.
dave
2 cabinets will take up more space due to more build material, and because the build needs to be stouter.
I successfully used 15mm for a dual 10” sub, if i was only putting 1 driver in the box no less than 18mm and more bracing.
2 boxes have the advantage eof being able to placed in 2 places. I built 2 push-push subs.
dave
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