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PURIFI finally did a fully purified passive speaker design! The SPK 16 prototype is here - with a PTT tweeter

I want to stress what Fluid mentioned earlier: the magnitude of these effects really depend on the waveguide and baffle in question. A well-designed +-40 degree waveguide that is as wide as the baffle will see relatively minor benefits from roundovers (benefits still exist, of course) as the ratio of on-axis sound pressure and sound pressure at the edge is high, the same is not at all true for a +-70 degree pattern like on the SPK16. In those cases a roundover is more or less mandatory.

To take some examples mentioned in this thread:
The Kali LP-6 has a baffle that is much wider than the waveguide - generally not ideal, even if the baffle is a little curved.
I made this mistake in one of my speakers, the baffle for the waveguide was too wide, and even retroactively adding a large roundover as an extension to the baffle couldn't solve the issue. I later confirmed in simulation that making the baffle slimmer around the tweeter waveguide would in fact solve the issue, even without any roundovers!

KEF manage this issue by making their speakers as slim as possible for a given driver size. On the KEF R-series the shadow flare (which is a waveguide, make no mistake) ends almost right at the edge. On the LS60 the baffle is barely wider than the driver itself. It's not the best solution (that would be something like the Blade), but it's a very good compromise all things considered.

Buchardt do things similarly to KEF, and again we see that it's not perfect, but the magnitude of the issue is much, much smaller than a direct-radiating or smaller waveguide speaker of similar dimensions.

There's also the fact that you have to treat the waveguide and baffle as a system, so it's not necessarily easy to pinpoint the exact culprit of certain directivity issues. It's entirely possible (very easy, in fact) to create waveguides that have major diffraction/interference issues. Often due to suboptimal termination at the mouth of the waveguide. See Geddes' speakers for an example of this. They have a large suckout on-axis in the 5-10kHz range due to the waveguide design.
 
Dennis Murphy said:
I know that watts are cheap
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Yes...but not really. Significantly more power than an AVR is >$1000 which is a lot of money for many people. So I'll join the "give me a more sensitive solutions" bandwagon. Although most all of the time you could play those pretty loud I suppose. On a radically different note I wonder if I could morph those into in-walls...
 
Ktacos said:
Finally at a computer. Time to make way too long of a post.

I gathered up a few speakers mentioned earlier that had spins and the typical combo of a ~6.5" with a roughly 6" circular waveguide, with the exception of the Kali lp6 v2 which are oblate spheroid but still similar in width and exhibits the issues I mentioned previously. Some are worse than others, most people probably wouldn't care about these problems but after hearing speakers with 3" radius round overs I'm kind of a convert and the problem just really bugs me now. Subjectively I find the issue smears the sound of music when the content gets is a little "busy" or dense if that makes sense. Ever listen to a song with a clear vocal that gets kind of drowned out when the music picks up? That very well could be diffraction getting in the way. A distcint aspect I noticed in speakers with 2-3" radius round overs is that you don't lose track of song elements at any given time, reverb is rendered much better and the tails seem to stick around longer and in a more convincing way. This makes sense to me as a dense track and reverb are generally going a more sustained aspect of music so they will be more prone to exhibiting audible interference from edge diffraction. More staccato/pizzacato/percussive stuff doesn't seem to be affected much. One user on this forum whom I shared my experiences with was on the same page as me and described diffraction as sounding "restless" and I agree. It's a sound that makes you want to get up and try to fix something with the speaker.

First up, a Buchardt speaker. These have no round over, just a hard edge. Based on my own testing with a similar waveguide, I expect to see some diffraction artifacts at around 5khz, and that's exactly what we see. There's some lower stuff but probably not as annoying as a secondary source at 5khz.

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Next up Kali LP6 v2. These have a taper to the baffle on both sides and a very small round over. You can see that the lack of a hard edge helps in the region the buchardt has trouble, but you still get issues around 3khz as you generally need around a 1" radius to avoid that. This speaker is also a good example of how diffraction works it's way down to the woofer region as well, it's not just about helping the tweeter.

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Here's the Kef LS50 meta. It has largely no roundover but does have a vertical taper. The woofer does a good job of preventing the tweeter from having much trouble, but the woofer around 1-2k is a diffraction factory.

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Here's probably one of the worst examples I've ever seen, the criton 1td. It has no round over and no waveguide for the tweeter. The wilson tunetot has similar problems but I really do not care to share that speaker as it's kind of just a joke of a product. I am not identifying the diffraction in the graph because it's so obvious.

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Now for my own measurements, which are not going to be as accurate but display some things I wanted to share.

Here's a 6" waveguide I had placed on a baffle with hard edges, then on a one with a 3/4" round over. Not the best data but you can clearly see how the response has been smoothed out from the round over. Top is hard edges, bottom is rounded. In the top graph we can see a few issues, such as the depression off axis at 3khz, an on axis dip at 5khz, and a big dip axis at 10k. We can see on the bottom graph most of the issues are alleviated with the roundover. These may appear to be small differences I can tell you that these speakers sounded completely different from each other, the speaker with the hard edges was just annoying to listen to.

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For fun I wanted to share my most beautiful speaker I've ever made, some cnote drivers and box with some PVC around it and active filters. Not really much going on with the tweeter filter here, the round overs make the response very smooth and easy to work with. There is a 2nd order high pass and a tilt EQ from 4k-20khz on the tweeter, and I think a low pass at the top end at 15khz (stuff above that kind of annoys me). My current goal is trying to find a way to manufacture this in a visually pleasing manner.

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Anyway, those are my thoughts on the importance of proper edge termination, there's definitely a bit more to it all, but so far in my experience the larger the round over the better the speaker sounds. There's plenty of better info out there on the topic and as a DIY'er, I do find a lot of DIY is people finding an aspect they don't like about speakers and obsessively pursueing solutions to that one problem, so I'd say edge diffraction is that for me.
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Infinity style! ;)

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JohnnyNG said:
Those were the days! Wouldn’t those slits add a bunch of individual edges, though?
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Or would removing a third of the edge material be beneficial? My intuition suggests that if the waves hit each edge, they would lose energy / amplitude with each impact. But honestly, at this point, I'm merely guessing.
 
Matias said:
The cabinet is almost identical to Sointuva AWG, so roundeovers the same.

As for wider x narrower treble dispersion, IMO it is secondary to the end result of having better linearity in predicted in-room response. I would (and did) prefer a narrow dispersion with very linear tilted response (Sointuva AWG), over a wide dispersion which possibly/probably will have a treble boost in response (SPK 16). Let's wait and see to be sure, but I fear the SPK 16 is going to be like that.
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I think the emergence of the so-called “PIR” average has caused a lot of listening with the eyes. I suspect blind listening would bust a bunch of myths about this average. Recall that Dr. Olive’s “curve drawing” study showed that trained blind listeners characterized speakers with curves more like their on-axis/lIstening window response.

IME, in a normally furnished room wide and constant HF dispersion is not bright. (Admittedly my personal experience limited to 100 or 110, whatever JBL 7-series does, or less wide than Purifi’s tweeter.) It just expands the area that sounds spectrally “right.”
 
Head_Unit said:
Yes...but not really. Significantly more power than an AVR is >$1000 which is a lot of money for many people. So I'll join the "give me a more sensitive solutions" bandwagon. Although most all of the time you could play those pretty loud I suppose. On a radically different note I wonder if I could morph those into in-walls...
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not to nitpick but this isn't accurate and besides, if you're buying speakers using $500+ Purifi drivers you're paying thousands for the speakers to begin with, but anyway, here's >250 wpc at a state of the art quality for $720. There are cheaper options and there are more powerful options for about the same money as well with a little elbow grease:
 
Any tweeter sightings in the wild yet?
 
What's up with the Purifi woofer surrounds? Why do they look uneven like that? From afar it looks damaged almost.
 
Buckchester said:
What's up with the Purifi woofer surrounds? Why do they look uneven like that? From afar it looks damaged almost.
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There's a whitepaper on it somewhere, but basically (IIRC) they work in such a way as to keep the moving area of the surround consistent as the cone moves in and out. Apparently normal symmetrical surrounds create modulation distortion because the effective radiating area of the cone changes throughout the stroke.

They look really ugly but apparently improve the sound very measurably.
 
kemmler3D said:
There's a whitepaper on it somewhere, but basically (IIRC) they work in such a way as to keep the moving area of the surround consistent as the cone moves in and out. Apparently normal symmetrical surrounds create modulation distortion because the effective radiating area of the cone changes throughout the stroke.

They look really ugly but apparently improve the sound very measurably.
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Cool, thanks. But it does beg the question, if it provides an actual improvement, why isn't anyone else doing it? Is it actually practical, or simply marketing?
 
Emlin said:
In what way have I shown that I'm obviously convinced? I was merely pointing out the flaw in your logic.
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With due respect, I wouldn't say inventing the first airplane to fly is the same as inventing a new type of speaker surround. Especially if it doesn't lead to a meaningfull difference.
 
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