Did Siegfried Linkwitz miss a trick?

[xrk971]

They have these 12" beach tires on ebay, $50 - $75 a piece.

What’s in the middle of it and if you take out the central wheel, is it all soft and floppy since it doesn’t hold air?

The $100 stainless steel 12in donut seems only a little more but more rigid.

 

[scottjoplin]

Vituixcad?

Is that where your avatar is from?

 

[Juhazi]

^No, it's from Dayton OmniMic unregistered test version. I exported REW measurements. I'm too dumb and lazy to learn Vituixcad, sorry!

I searched for my measurements of nude cone's backside, but couldn't find any. They were so ugly that I didn't save them!

One more Edge sim, dipole vs. monopole baffle

 

[scottjoplin]

Oh well A mock up would probably be the simplest to see whether there's actually anything in this. I think member jameshillj is keen to give it a try

 

[xrk971]

6in inside dia and 13in OD. Wheelbarrow inner tube.

AR-PRO 13 x 4.00-6'' Heavy Duty Replacement Inner Tube with TR-13 Straight Valve Stem (4-Pack) - for Wheelbarrows, Mowers, Hand Trucks and More https://www.amazon.com/dp/B0819D842F/ref=cm_sw_r_cp_api_i_6XYJFbZ50B7V3?_encoding=UTF8&psc=1

 

[scottjoplin]

It could be used deflated for comparison

 

[GM]

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

Dunno about SL, but as I alluded to here, I designed a rectangular one using horn theory decades ago now on a long gone forum, so round is in theory even a better solution, but at the time 'we' didn't think the extra woodworking would yield enough audible improvement: Torus

GM

 

[GM]

6in inside dia and 13in OD. Wheelbarrow inner tube.

Right, 'we' initially discussed using the biggest inner tube available in Costa Rica, which turned out to be not large enough to go as low as he wanted, but could get down into the mid-bass here in the USA.

GM

 

[DonVK]

Like this...
.

 

[xrk971]

Nice work DonVK! Can you show an on axis frequency response plot? Just wondering if there is a cancellation dip from the front to back round trip.

 

[scottjoplin]

Hi Don, thanks for doing that. Does the pattern hold well across the spectrum?

 

[DonVK]

If the model is close to what we are talking about, then I'll generate the polars and FR. This is currently in 4pi space.

The torroid is 150mm dia circle with sweep radius 150mm . Close to XRK971's wheel barrow inner tube or that SS torroid. Currently using an ideal flat membrane driven by a DSA175 motor.

 

[scottjoplin]

Yes, a pure torus is the initial idea, an "OS type" waveguide between the driver and torus has also been mooted

 

[DonVK]

Here's a quick look. Keep in mind the driver is not ideal (flat membrane+DSA175 motor). The polar is normalized w.r.t 0 deg (axis).
.

 

[GM]

If the model is close to what we are talking about, then I'll generate the polars and FR. This is currently in 4pi space.

FWIW,the rectangular one I mentioned earlier was 2pi, so vertically 1/2 size.

GM

 

[scottjoplin]

That's given me a bit more faith in the ripple tank simulation at what distance is the "mic" in your second attachment?

 

[Juhazi]

Don, please make sim of a flat baffle same radius too! And show spectrogram to +/- 180deg of both! Looks like directivity transition is pretty smooth with minimal ripples!

 

[scottjoplin]

So what's actually happening? Earl has been explaining it to me here, https://www.diyaudio.com/forums/mul...d-diffraction-baffle-edge-10.html#post6382802 but I'm not sure I'm grasping it properly, I'm pretty sure I'm not......

 

[scottjoplin]

Don, please make sim of a flat baffle same radius too! And show spectrogram to +/- 180deg of both! Looks like directivity transition is pretty smooth with minimal ripples!

I'm not sure same radius would be the best comparison? I've made the flat baffle larger as an approximation of the same distance around the torus curve.

 

[Juhazi]

Scott's right, same radius in 2D is not right, it's about pathlength to the edge.