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Old 16th November 2012, 10:54 PM   #121
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I think his Watson idea is much more interesting and innovative.
That thread got a lot less action than this one.
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Old 16th November 2012, 11:11 PM   #122
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Originally Posted by Melo theory View Post
Posted today on SL's website

"The shape of the midrange/tweeter baffle is the result of acoustic requirements, as is the woofer baffle. They are angular and not hidden behind grill cloth. The acoustic impedance of grill cloth rarely matches the acoustic field impedance near the radiator, causing frequency dependent reflection and transmission loss, which can also be angle dependent. The LX521 is meant to be used without grill cloth with the exception of a light fabric table runner over the woofer baffle to partially cover its front and rear openings."

I don't think grill cloth will impede performance that much.
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.
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Old 16th November 2012, 11:15 PM   #123
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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.
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Old 16th November 2012, 11:22 PM   #124
dewardh is offline dewardh  United States
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Originally Posted by Melo theory View Post
Why is this a hot topic now?
Because SL is doing it?
Hasn't this been done for a long time now?
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 . . .
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Old 16th November 2012, 11:27 PM   #125
ScottG is offline ScottG  United States
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Originally Posted by Melo theory View Post
Why is this a hot topic now?
Because SL is doing it?
Hasn't this been done for a long time now?
In fact I remember him protesting the idea of dipole action to such a high freq.


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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Old 16th November 2012, 11:29 PM   #126
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Originally Posted by dewardh View Post
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 . . .
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.
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Old 16th November 2012, 11:30 PM   #127
dewardh is offline dewardh  United States
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Originally Posted by john k... View Post
The rest is spin.
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 . . .
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Old 16th November 2012, 11:33 PM   #128
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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!
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Old 16th November 2012, 11:38 PM   #129
dewardh is offline dewardh  United States
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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.
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 . . .
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Old 17th November 2012, 12:38 AM   #130
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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.
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.
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