The comments regarding grill cloth are generally accurate, but a change in acoustic impedance isn't necessarily a bad thing. It can be used to advantage. Look at the Geddes speakers for example. In his wave guides us uses foam, which certainly has a different acoustic impedance than air, to reduce what he refers to a HOMs generated by reflections in the wave guide. The old BBC LS3/5a is another example of a speaker designed to be used with the grills in place. So, while it is true that the grills offer an acoustic impedance different than air that isn't necessarily a bad thing if it is part if the design consideration. The relevant part of the statement is, "The LX521 is meant to be used without grill cloth." The rest is spin.
John K, would you withdraw your objection to the first order high-pass on the 10cm upper midrange if the bass section extended an octave higher, say 240 Hz or 250 Hz? Then the "area under the curve" would be reduced on your diagram for excess excursion required of the 10cm driver. This assumes the bass baffle would be shallow enough to stay clean past 250Hz. That would also allow the midbass driver to drop a size, from 22cm to 18cm, or else have greater headroom.
Yes, and yes. People have been experimenting with narrow-baffle dipoles (all the way down to no-baffle, with the driver frames being the only "baffle" element) for a while now. SL added a rear radiator (for the upper mid/tweeter range) to ORION years ago as well, as have many others on their dipole designs. And SL has just introduced a new design that combines those two things, which naturally enough raises interest and attracts attention. It sounds good, too . . . arguably better than ORION, which is itself already arguably better than almost anything else. Maybe without the "almost".
It probably should be a much "hotter" topic than it is . . .
He has protested multiple ideas (though not in any major respect), and yet (in several instances) later on incorporated them in one fashion or another.
Oddly the one constant isn't what he is often known for.
Most people think "dipoles" with SL. The real constant isn't that at all - rather "active" crossover. I don't think that will ever change.
(..and now JohnK is going all "active", or at least providing that opportunity, which probably wasn't something he had originally envisioned.)
-got's to be flexible.
I think the "hot topic" aspect of this build is a *potential* shift from the wider-baffle Orion format to this new narrow baffle format. Perceptually it might leave those who have invested heavily in the Orion design saying: "what?" (..I don't think it will happen with this design, but alterations to it down the road may well be declared "better" than the Orion.)
On top of that there is the oddity of the top baffle shape (..hmm, wonder if Canadians will go all the way with it and just cut-out a Maple Leaf?)
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Well, the BG neo3 planar dipole tweeter has been used for a long time on these baffleless speakers. Which I think is a better solution anyway.
Not so much "spin", I think, as prophylactic against all the inevetable "can I use upholstry fabric as grill cloth" and "are you going to design a grill frame for it" questions.
Which I'm sure you've heard too . . .
On top of that there is the oddity of the top baffle shape (..hmm, wonder if Canadians will go all the way with it and just cut-out a Maple Leaf?)
hahaha!
It's been tested, and tried. Works as a "supertweeter", with the disadvantage of no independent control of the rear radiation, which can be an issue on the high end, depending on the characteristics of the front wall. Costs as much as the dual domes used in LX521. And it has horrible impulse performance if used below 3-4kHz.
Not to mention that the domes just sound better . . .
Certainly raising the crossover to the woofer to 250 would help address the mechanical issues. However, there are still the acoustic issues of the relatively broad overlap of the 1st order crossover. I can not speak to that regarding the LX521. I guess no one can unless SL tries the mod. But for my design, and to my ear and taste, higher order sounded better, aside from the other issues. So, to answer you question, from a mechanical point of view I would agree that a higher woofer/low mid crossover would be beneficial.
As for the use of an 18cm lower mid, that is basically what I have in the original Note and I see no advantage to it if the crossover to the upper mid is to remain at 1k hz. The problem with a shallower bass H frame (or what ever) is that it would shift the monopole vs dipole frequency higher, requiring more EQ and more excursion. So any headroom gained in the mid would be lost on the bottom.
I have configuration files for the revised Note for 1st, 2nd and 4th order lower to upper mid crossovers. I plan on supplying all three to anyone who builds my system. They can decide for themselves which sound better.
(..and now JohnK is going all "active", or at least providing that opportunity, which probably wasn't something he had originally envisioned.)
Can't let that slide by without a comment. Please recall that the NaO II has been offered in both hybrid and fully active since 2006. It's not a "now" thing. The "NOW" thing is that I'm going digital. And that's not so much for performance but cost. Plus, digital makes it easy to issue update (even though I generally don't issue them very frequently). I still stand by my position that most of the hype about fully active is just that. There are pluses and minuses on both sides. Choose your poison!
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..Doh, didn't know that.
But it was "a thing", no?
I think it's only been fairly recent with a much larger array of good inexpensive solid-state amp kits and cheap ready-made class D amps that active becomes more of a factor with respect to value (and as a result - actual use). 6 years ago.. not so much. It would be interesting to see SL's base sales/purchaser numbers (over the past 12 years).
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He has protested multiple ideas (though not in any major respect), and yet (in several instances) later on incorporated them in one fashion or another.
Oddly the one constant isn't what he is often known for.
Most people think "dipoles" with SL. The real constant isn't that at all - rather "active" crossover. I don't think that will ever change.
(..and now JohnK is going all "active", or at least providing that opportunity, which probably wasn't something he had originally envisioned.)
-got's to be flexible.
I think the "hot topic" aspect of this build is a *potential* shift from the wider-baffle Orion format to this new narrow baffle format. Perceptually it might leave those who have invested heavily in the Orion design saying: "what?" (..I don't think it will happen with this design, but alterations to it down the road may well be declared "better" than the Orion.)
On top of that there is the oddity of the top baffle shape (..hmm, wonder if Canadians will go all the way with it and just cut-out a Maple Leaf?)
I first met SL at the Las Vegas CES show in the early Nineties, back when he was the designer of the Beethovens. I was surprised the Beethoven's had a sonic balance similar to my loudspeakers, with balance that favored vocal and orchestral music. We had fun discussing the differences in our approaches - he's more comfortable with complex loudspeakers than I am, and gives less weight to arcane audiophile issues like capacitor and amplifier coloration.
His designs have evolved in the direction of more complexity since the Beethoven days - stacks of amplifiers, and pretty heavy equalization in the active crossover unit that the dipoles require. I've gone in the other direction - not as far as the full-range driver crowd, but certainly chasing down every part in the passive crossover, signal path in the amplifier, and the I/V converter in the DAC.
Compared to the Beethoven's, which had a pretty lush, warm sound, SL's newer speakers are drier (tonally) but also more spacious sounding (as you would expect from dipoles). But I can hear the op-amps in the crossover/EQ unit and the solid-state amps and that's not for me.
But the subjective spectral balance is still very much SL, which is a lot more musical than the edgy, hard sound that dominates the commercial high-end business. The real dividing line is how you feel about transistor amps and op-amps; if you're cool with them, SL's your man.
I haven't heard John K's speakers, so I have no idea how they're balanced, but there's certainly plenty of good engineering there.
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How extended is the rear radiation of the mid range drivers used in dipoles by SL and JohnK ? I am very hesitant to believe that the rear radiation from the two midrange drivers of the LX521 is uniform as high as 7K, before the 2 tweeters kick in.
The magnets on the rear of the drivers would never allow the higher frequencies to be radiated at the same magnitude leave alone the polar pattern as the front side radiation.
Sure, but it's very, very difficult to get true dipole behaviour above 3-4k. You get sort of a "dipolar" response but not true figure of eight. You would need an incredibly small tweeter back to back on a really narrow baffle to achieve that. But.. at the end of the day the rear wave is meant to be diffracted anyway. As long as you get some sort of cancelation at 90°..
I'd rather have a true dipole in the low highs, this you can probably clearly hear, and the LX probably achieve that compared to the Orions. One interesting thing would be to compare a 45° toed in Orion next to an LX521. Despite all qualities the Orions have, I myself never been totally happy with the tweeter going so low, especially after hearing the B&G RD-75.
I'd rather have a true dipole in the low highs, this you can probably clearly hear, and the LX probably achieve that compared to the Orions. One interesting thing would be to compare a 45° toed in Orion next to an LX521. Despite all qualities the Orions have, I myself never been totally happy with the tweeter going so low, especially after hearing the B&G RD-75.
lolo, I completely concur.
As far as I understand it, the "problem" of the Orion never has been the figure 8 per se, but the bloom of the tweeter radiation pattern. And that mainly regarding the frontal hemisphere.
So what we should be adressing in the first place is not a front-back symmetry, but constant directivity in the front of the loudspeaker.
Since directivity can't be kept constant ad infinitum, we should make sure that it at least increases with frequency.
As far as I understand it, the "problem" of the Orion never has been the figure 8 per se, but the bloom of the tweeter radiation pattern. And that mainly regarding the frontal hemisphere.
So what we should be adressing in the first place is not a front-back symmetry, but constant directivity in the front of the loudspeaker.
Since directivity can't be kept constant ad infinitum, we should make sure that it at least increases with frequency.
There is no "theory" demanding 4 ways. If we had a 1" device, which could move litres of air, a one way dipole would be no problem. It is just the technical limitations of cone/dome drivers which demands a 4 way for "perfect" dipoles.
I object this point !
There is no psychoacoustic requirement for increasing directivity with freq for sound reproduction in a small room. I think it should do just the opposite, smoothly decrease with freq. In other words, the radiation pattern should get wider with incresing freq.
- Elias