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Did Siegfried Linkwitz miss a trick?
Did Siegfried Linkwitz miss a trick?
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Old 19th October 2020, 12:29 PM   #1
scottjoplin is offline scottjoplin  Wales
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Default Did Siegfried Linkwitz miss a trick?

Take a look at figure d below, from here Electro-acoustic models

It appears to be possible, using a torus-like baffle, to spread the interference nulls in space and time, so does something similar to this diagram actually become a viable option?
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Old 19th October 2020, 12:36 PM   #2
CharlieLaub is offline CharlieLaub  United States
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I think you should, for your own sake, explain your idea in a little more detail. Please do. I don't want to put words in your mouth about what you are thinking here, exactly.

What you are showing is just a "thought experiment" showing how a tube can be squashed into an equivalent planar, circular baffle, and how the front-to-back distances compare.
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Old 19th October 2020, 12:43 PM   #3
scottjoplin is offline scottjoplin  Wales
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"For my own sake"? Sure, it's a combination of ideas. According to Earl Geddes a torus mitigates edge diffraction This is either very wrong or I have still not understood diffraction from baffle edge
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Old 19th October 2020, 01:05 PM   #4
CharlieLaub is offline CharlieLaub  United States
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Ah, I see what you are talking about. Take a "donut" torus. Install a baffle inside of the hole in the middle, then install a driver in that. Is that correct? Like this:
Click the image to open in full size.

Earl Geddes, from what I recall, is opposted to open baffle speakers because he feels they have "twice the diffraction" of a regular speaker: diffraction off of the baffle edge once from the front radiation, and diffraction off of the baffle edge once from the rear radiation. I find that argument rather academic and specious.

Firstly, diffraction is not what gives rise to oscillations in the on or off axis response from a dipole. In a boxed loudspeaker that IS what is causing the oscillations at the top of and above the baffle step, and the more regular the distance to the edge the worse these will be. In a dipole speaker it is front-to-back pathlength differences that give rise to cancellation or addition of the front and rear waves, and these result in the oscillations. Using a toroidal baffle shape will not change that. Also, the old two-monopole-source model of a dipole has shown to be INVALID at and above the dipole peak. From the page on SL's web site that you linked to just look at the difference between the two figures, below. The first is the two-monopole model, and the second is a more complete simulation that I find matches actual driver measurements very well. These are not at all the same at and above the dipole peak regarding the "oscillations" in the responses.

Click the image to open in full size.
Click the image to open in full size.

Regarding the diffraction of the edge being problematic, the diffraction is opposite in polarity from front and rear, and I would like to think that there is quite a lot of, if not complete, cancellation. This would be more true at low frequencies than higher ones I suppose. I also feel that the sonic influence of diffraction, just like jitter in digital music, is so over blown and concerns are so over-hyped that it is laughable. So maybe I am a little jaded about the whole thing.
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Old 19th October 2020, 01:17 PM   #5
scottjoplin is offline scottjoplin  Wales
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Do you know what's going on here, Allen's sim appears to be showing no on axis nulls? What is the polar response of "L-frame" OB speakers
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Old 19th October 2020, 01:45 PM   #6
CharlieLaub is offline CharlieLaub  United States
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Quote:
Originally Posted by scottjoplin View Post
Do you know what's going on here, Allen's sim appears to be showing no on axis nulls? What is the polar response of "L-frame" OB speakers
If I use a driver, without baffle (nude), it doesn't have any on axis nulls either. You can easily confirm this with the Edge when the driver radiating surface and baffle edge are close together. If diffraction is a problem, why would it not be worst in this case with a circular, sharp edge?

Using, for example, a nude 15" driver I only measure very smooth responses all the way up until the cone breakup region. Here is a measurement with better than 50Hz resolution to prove it:
Did Siegfried Linkwitz miss a trick?-15inch-nude-dipole-png

If the torus shape seems to be worth pursuing then someone should definitely build it, possibly in a couple of difference sizes, and perform some high resolution (e.g. outdoor) measurements that will show what is going on in more detail than Allen's sims.
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Old 19th October 2020, 01:46 PM   #7
Just Dave is online now Just Dave  United States
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@Scottjoplin,

Would you please post a link or just the address of where you got that SL drawing that was in your post #1. SL's website is quite extensive, and it sure would help to not have to poke around looking for it.

Thanks.
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Old 19th October 2020, 01:49 PM   #8
scottjoplin is offline scottjoplin  Wales
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Would it be possible to sim it with better software? I think the ripple tank simulation is probably limited.
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Old 19th October 2020, 01:50 PM   #9
scottjoplin is offline scottjoplin  Wales
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Quote:
Originally Posted by Just Dave View Post
@Scottjoplin,

Would you please post a link or just the address of where you got that SL drawing that was in your post #1. SL's website is quite extensive, and it sure would help to not have to poke around looking for it.

Thanks.
Did the link I posted not take you there?
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Old 19th October 2020, 02:37 PM   #10
ErnieM is offline ErnieM  United States
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Similar idea to the roll backs on large stand alone horns.

I can see an advantage for open baffle if you want to gain more acoustic output from a wider baffle...but you also increase center to center distance to the next driver. It might be interesting for a full-range driver or coaxial.
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