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Multi-Way Conventional loudspeakers with crossovers

Cloning a 00 Speaker for 0
Cloning a 00 Speaker for 0
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Old 10th August 2017, 04:17 PM   #121
Greebster is offline Greebster  United States
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Patrick,
Did not rush out and buy a 3D printer, took my time choosing as was on my bucket list. Recently the situation presented itself not just for a printer but a whole shop full of tools. This is just the lastest addition. Not quite fully setup yet, Creality CR-10 S4 3D printer (tinymachines3d.com). Used it a bit, very happy. Will print upto 400mm cube, eg ~15.75". Currently undergoing upgrades, should have OctoPrint up and running in couple of days. Adding a 7" touch screen, camera, more modding etc eg having fun.

Bought this for the express purpose of testing waveguide design. Making the bloody difficult transition region between the tweeter and a mid(woofer), esp hard in an mtm arrangement. Everything being discussed right here

Very tempted to buy the smaller but still rather large, new CR-10S. Has a 300mm square build area and a 400mm Zaxis. Not bad for $625

Cheers
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Old 11th August 2017, 04:57 PM   #122
Megalomaniac is offline Megalomaniac  United States
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Does this imply that the narrower the exit angle the higher the freq may pass thru only, like does the highpass adjust to a higher number ?Click the image to open in full size.
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Old 11th August 2017, 11:17 PM   #123
gedlee is offline gedlee  United States
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I don't think that the attachment that you show has much, if any, to do with exit angle on a compression driver. Trying to find some relevance is just going to mislead you.
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Old 18th February 2018, 08:41 PM   #124
Patrick Bateman is offline Patrick Bateman  United States
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I was pondering a new waveguide this weekend, and noticed that this one from a few months back performed REALLY well:

Cloning a $3200 Speaker for $400

No, it doesn't perform as well as the big QSC waveguide, but one of the things that I love to tinker with is "how do I get big waveguide performance in a small package?"

I think that one of the things about the SAW lens is that it's quite easy to get the tweeter to play down low. Here's why:

Click the image to open in full size.
Nearly all the time, these things are being placed on a big flat surface. With a big flat surface underneath the lens, the tweeter is only radiating into half space, or less. (The radiation angle gets narrower at high frequency.)

Click the image to open in full size.
With your typical bookshelf or desktop speakers, the speaker is only radiating into half space down to about 2000-25000Hz. (This is because the baffle is about as wide as 2000Hz is long.)

So if you have a tweeter with a 2nd order rolloff at 2000Hz in a bookshelf speaker like this, the tweeter is REALLY struggling at the xover point. Obviously, a good designer will juggle the variables so that the woofer and tweeter are directivity matched, and the baffle is a sufficient width to keep this from happening.

Click the image to open in full size.
Click the image to open in full size.
While looking at the Beolab 50, and my grey lens from a few years back, it occurred to me that there's a possible improvement that's a bit reminiscent of both.

Click the image to open in full size.
The idea that I had was to use a sphere for one of the waveguide walls.

Click the image to open in full size.
JBL has been using spheres for decades now, going back to the biradial horns. The spheres are present in their "progressive transition" waveguides and in their "image control" waveguides. (All of these waveguides share DNA)

Here's an explanation of what's going on from their designer:

"“The Bi-Radial horn that we have had for decades was a 90x60 horn, and not the best match for the low frequency device in the M2,” Sprinkle says. “This horn is 120 degrees horizontal and 110 degrees vertical. We knew that if we wanted a good directivity transition between the woofer and the high frequencies, we had to have that amount of pattern, so the waveguide was designed to have a pattern consistent with what the woofer was doing with no discontinuity at the crossover point, which is 800 Hz.

“The second thing we did was use a blending geometry—there are no straight lines, you’ll notice—that has a generally decreasing radius,” he continues, “forming an infinite number of reflections, and the net effect is that it smears the reflections coming back down the horn and negates them."


Click the image to open in full size.
Using a sphere for the top wall of the waveguide, it's possible to get a near perfect match between the exit angle of the diffraction slot and the sphere. You could also get a perfect match with a cone. The use of a sphere here is what Sprinkle described, basically create an infinite series of paths, for reducing radiation back down the horn. I would also argue that it's good for the frequency and impulse response, because equal pathlengths create resonances.

Another 'neat' thing about the SAW lenses in general is that you can mount them very very low. When I first built one, the first thing that I noticed is that the image from the stereo seems to hover about a foot above where the loudspeaker is. I think this is caused by two things:

1) In a waveguide like the grey one pictured in this post, the listening axis is pointed UP. It behave like a conventional waveguide that's been tilted backwards. This is because the bottom wall of the waveguide is flat, while the upper wall of the waveguide is tilted UP. The net effect is that the soundstage is higher than the speaker.

2) In a conventional speaker, you often get diffraction off the cabinet edges, and I believe that has the effect of 'anchoring' the sound to the cabinet.
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