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In Reply to: RE: Subwoofer with ESL 63 posted by josh358 on March 17, 2017 at 12:16:29
Yup Josh, Linkwitz uses a "W" style open baffle frame, which is what I used before the guy in Canada started making his H frame. They're both good, each having advantages and disadvantages over each other. The H has better structural bracing, the W having a large expanse of unsupported panel on each side, leading to resonance. But the W does purportedly provide some reduction in harmonic distortion due to the opposing force relationship between the two drivers, created by them being mounted on baffles 90 degrees to each other.But both posses dipole characteristics, with nulls to either side, loading the room in one less direction (side wall to side wall), resulting in less room boom. Being dipoles, their SPL drop-off rate with increasing distance also matches the dipole speakers they are mated with, keeping the balance between the two the same regardless of listening distance.
Edits: 03/17/17Follow Ups:
... should be same as with a W-frame by physically and electrically reversing one driver. Both drivers move in the same direction but any asymmetry in the summed output is reduced (this reduces even-order distortions but doesn't help with odd-order).
13DoW
Right Duke, that I heard of first. But then someone (Linkwitz?) claimed an additional related benefit resulting from the 90 degree differential between the two drivers in a W-frame in particular. Anybody know more about this?
I did read his Phoenix dipole woofer design papers but that was some time ago. I wonder if the advantage is that with the two woofers opposite each other and moving in the same direction that cancels vibration in the frame
(as well as reversing one woofer to cancel cone movement asymmetry)?
In an H-frame that would not be the case as the frame will be rocking in opposition to the drivers.
Regards
13DoW
In a W-frame, the two woofers are always mounted in opposite directions (typically with the woofer on the bottom baffle facing forward, the one on the top baffle facing the rear of the frame, it's backside being visible listener). In an H-frame, the two woofers can be mounted facing in opposite directions (one forward, one rearward), but they don't HAVE to be. Danny Richie recommends doing so to balance the weight/mass of the woofers in the frame, the magnets being far heavier than the front end of the driver. When so mounted, the two woofers are wired in opposite polarity, of course. Ric Schultz of EVS uses the Rythmik amp and GR Research 12" woofers in his version of the OB/Dipole sub with the two drivers mounted on a flat baffle, both facing forward. He feels by doing so the woofers are in exact time alignment, the sub sounding better as a result. Richie argues that the wavelengths are so long at bass frequencies, that time alignment of woofers in an OB sub is not critical. But as to force-cancellation and harmonic distortion reduction, I'm not sure about the difference between the H-frame (with opposing drivers) and W-frame.
Edits: 03/21/17
I think some folks are getting confused on the frame designations here.
And there are variations on each (basic) configuration as well.
The "W"-frame was initially a label applied to the full force-cancelling configuration of the Linkwitz Phoenix dipole woofer. However, later (hybrid) configurations actually look more like a "W".
It can get a bit confusing.
The even-order distortion reduction comes primarily from having the cones always moving in opposite directions relative to their magnet assemblies. You can do that with any of the double-woofer configurations.
Dave.
The W I was referring to is that found in the Linkwitz LX521 loudspeaker---the two woofer baffles being at 90 degrees/right angle to each other (and 45 degrees to the floor), with the bottom woofer facing the listener, the top woofer's rear magnet facing him (or her). It seems to me it could just as easily be called an M frame! In an H frame the baffles are in the same plane, perpendicular to the floor. The woofers in the H frame can be mounted facing in opposite directions (as Danny Richie does), or both facing the same direction, thereby losing the opposing force cancellation and even-order harmonic distortion reduction provided by opposite-direction mounting.Davey, does the mounting of the woofers in the 521 (90 degrees apart, rather than 180) and same-direction mounting of woofers in an H frame not create opposing force cancellation and harmonic distortion reduction?
Edits: 03/23/17 03/23/17
No, it doesn't create optimum force cancellation because the cones are not moving in 180 degree opposite directions.
However, one cone is always moving inward towards the basket while the other is always moving outward away from the basket. So, there is even-order distortion cancellation associated with that.
But, some could probably make the case even-order distortion reduction is not beneficial......subjectively.
Many, terrific sounding speakers are asymmetrical in their construction and operation. You need only look at most of the Magnepan lineup of speakers. :)
Dave.
Thanks for the clarification, Dave. Isn't it also true that harmonic distortion is less perceivable at bass frequencies than at higher ones? On the question of force cancellation, I imagine the H frame and the mounting of two woofers on opposing baffles and wired in opposite polarities (Seaton Submersive, for instances) in a sealed sub provide about the same degree of opposing force cancellation and harmonic distortion reduction, all else being equal.
The Seaton Submersive is a sealed-box design with opposing woofers wired with opposite polarity??
What's the point of that????? To shake the woofer box all over the floor and not generate any bass??? :)
Dave.
It is just a bipolar sub. Not a self cancelling construct.
Now I get it---the two woofers in the Submersive are wired in same polarity, which I think I use to know! Demonstrations of the sub have included a coin being set on edge on the top of the enclosure, the coin remaining motionless, proof of the benefit of apposing woofers. It was THAT that was the point of my query---is a reduction in harmonic distortion one benefit of Seatons design. I don't think Seaton makes that claim, instead focusing on the design resulting in less enclosure resonance.
Edits: 03/26/17
A bipolar sub with two drivers at opposite ends IS a force-cancelling construction.
Do you understand the concepts involved with these types of double-woofer schemes???
Dave.
Yes, force cancellation on the geometrical on axis vibration transferred by the structure, not cancelling the acoustic output, which is what I presumed you were referring to..
So, I have no idea how putting drivers at 90 degrees affects distortion.
13DoW
Interesting, hadn't considered the effect of the unsupported panels on the side.
Also, not only will a dipole woofer trigger fewer room modes, the ratio of direct/reflected sound will be the same as with the line source.
However, the SPL drop-off will still be inverse square since they're point sources, and won't match the 1/R falloff of a line source. Depending on crossover frequency you don't need too many woofers to create a line source, if they're spread out. Two per wavelength, taking into account floor reflections. And if you sit the same distance from the rear wall as the woofers are from the front, the first rear wall bass reflection will be cancelled -- I tried that back when I had 1-D's and it really did work.
Thanks for the clarification and additional info Josh. I forgot to mention that Danny Richie recommends the side panels of a W-frame made from the plans he provides on his site be doubled---an extra 3/4" layer of MDF be added to each side---to stiffen those side panels and prevent audible resonance. Either that or put in a brace connecting the two panels together, running across the open cavity of the "W". Of course, there is nothing preventing one from doing both!---Eric.
Edits: 03/19/17 03/19/17
You're very welcome!
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