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-   -   LX521, the baffle (http://www.diyaudio.com/forums/multi-way/225158-lx521-baffle.html)

dewardh 7th December 2012 01:23 AM

LX521, the baffle
 
First impressions of the LX521 pretty much always include some comment about the baffle . . . usually its aesthetics. SL says that the shape was arrived at empirically, but clearly there is some “thinking” which justifies the departure from the more “normal” straight sides with steps, and many “empirical” solutions can be incrementally improved if there is a theoretical understanding of them, and why they work. That it does work (in the context of what a dipole baffle is supposed to do) I can attest from listening to it . . . the dipole null is pronounced and broadband, and extends vertically to the extent that I could determine, at least 45 degrees above the horizontal. The c-to-c spacing of the combined mids should lead to some dipole-like vertical beaming around the crossover frequency, and the undercut below the lower mid may extend vertical dipole behavior as well. But is it “optimum”? Is it possible to do better?

I intend to start with the basic LX521 baffle shape for my “clone” experiments (without the extension for the rear tweeter, which to my thinking could go anywhere), but I’m altogether open to suggestions for “improvements”. Any ideas ? ? ?

thomasjefferson 7th December 2012 06:21 AM

Years ago I thought about making a 4-way variation on Orion by adding a small upper midrange, and I always thought that would suggest bumping the 22cm midwoofer to a 26cm. The new LX521 baffle leaves the midbass driver pretty close to nude and its output will be limited toward the bottom if its range. A hybrid of Orion / LX521 / NaO Note II would have an Excel W26 midbass and Discovery 10F midrange. This would require a steep low-pass on the W26 which you could do with MiniDSP.

Melo theory 7th December 2012 06:47 AM

Quote:

Originally Posted by thomasjefferson (Post 3274173)
Years ago I thought about making a 4-way variation on Orion by adding a small upper midrange, and I always thought that would suggest bumping the 22cm midwoofer to a 26cm. The new LX521 baffle leaves the midbass driver pretty close to nude and its output will be limited toward the bottom if its range. A hybrid of Orion / LX521 / NaO Note II would have an Excel W26 midbass and Discovery 10F midrange. This would require a steep low-pass on the W26 which you could do with MiniDSP.

Why the 10f? The vifa tc9 is 1/10th the price and a better performer.
In fact, I would just use that for the top and forget about the dome tweeters!
I would put an acoustic reflector lens on the rear of the vifa to diffuse rear HF.

moep 7th December 2012 08:04 AM

Hi,

I have compared 2 variants of the LX521 lower baffle shape (eg. without tweeter part) to a rectangular baffle. The rectangular baffle is 256mm wide, the LX521 variants at the widest point 315 and 331mm. The measurements I made are a bit messy but if there is any interest it could upload them somewhere.

Regards

Rudolf 7th December 2012 11:07 AM

1 Attachment(s)
Quote:

Originally Posted by dewardh (Post 3273984)
First impressions of the LX521 pretty much always include some comment about the baffle . . . But is it “optimum”? Is it possible to do better?
I intend to start with the basic LX521 baffle shape for my “clone” experiments (without the extension for the rear tweeter, which to my thinking could go anywhere), but I’m altogether open to suggestions for “improvements”. Any ideas ? ? ?

Attachment 316253
The lower part of the midrange baffle has to work up to 1 kHz. That's a wavelength of 34 cm. I don't see how the specific shape of the baffle in that region would make a real acoustical difference compared to vertical sides.
Of cause it does have some aesthetical and marketing advantages over the rectangular baffle. ;)

The part around the tweeters isn't of too much acoustical concern either - regarding the crossover at 7 kHz. The tweeters already start to beam, which will control the radiation pattern increasingly more than the dipole null. If you would cut off the "excess" baffle around the tweeters (as indicated in the picture), I don't expect a tremendous difference - but would surely be interested whether I can be proofed wrong.

Now if you look at the "corrected" (red) baffle shape in my picture, it should strongly remind you of some other dipole 4-way speaker. :D I can't help but find the LX521 baffle as it is now more of a "statement". Its shape isn't dull, it calls for discussion and identification, it has a strong resemblance of "I am a piece of art on a pedestal".
I like it.

Rudolf

john k... 7th December 2012 11:17 AM

Equivalent Baffles

john k... 7th December 2012 11:28 AM

Quote:

Originally Posted by Melo theory (Post 3274187)
Why the 10f? The vifa tc9 is 1/10th the price and a better performer.


NOT!

dewardh 7th December 2012 11:48 AM

Quote:

Originally Posted by moep (Post 3274237)
The measurements I made are a bit messy

Wouldn't it be nice if reality weren't like that . . . ;)

Did you get any sense of "difference", or was it "lost in the noise"?

dewardh 7th December 2012 12:05 PM

Quote:

Originally Posted by Rudolf (Post 3274410)
I can't help but find the LX521 baffle as it is now more of a "statement". Its shape isn't dull, it calls for discussion and identification, it has a strong resemblance of "I am a piece of art on a pedestal".
I like it.

That was my first reaction as well, and I commented to that effect. But . . . (and despite his occasional flair for "marketing" ;)) I've learned a lot by looking for the "reasons" SL does the things he does . . .

I asked specifically about the "flair" at the top . . . the tweeters should be beaming enough for it not to matter . . . but he said that he observed interaction, and there was enough of it to make it worthwhile. I'm not going to co-locate the rear tweeter like that anyway, but still wonder about the overall effect of the "bigger" baffle.

dewardh 7th December 2012 12:25 PM

Quote:

Originally Posted by john k... (Post 3274423)

The implication of the "modeling" suggests that on average the difference isn't large enough to matter, but the models don't account for specific axial behavior (so far as I can see). A "rectangular" baffle may behave like a circular baffle of some specific dimension overall but differ significantly depending on whether you are looking across the short dimension or the long dimension (especially significant where the effective baffle may be extended by the bass box below it). Is the gap between the LX521 baffle and the structure it sits on large enough to divorce it from influence or does the lower enclosure act as a baffle extension?

Are there issues here that are lost in the model's simplicity that nevertheless have significance in the "real world"?


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