Remedy for ribbons' limited vertical dispersion??

[rick57]

I would think that this or similar had been thought of before, but I haven't seen it; though to be frank 'til recently I thought little about directivity. (But I do have some ribbons that I want to employ to their best, and many other technical challenges . .

I may have overlooked a fundamental of waveguides and/ or directivity theory, but just in case:

To improve vertical dispersion, waveguides on the sides of ribbons, forward of the their side axes, that reflects some of the wide horizontal dispersion inwards, and up and/ or down.

I have no idea how large the waveguides should be, or if they would be better flat or curved etc.

To get the 'correction' best for the room/ listener/ system would require adjustment. Waveguides could be mounted close to the ribbon on pivots, starting with them e.g. about 30 degrees forward of the ribbon's side axes. By reducing horizontal dispersion, much of it bouncing off side walls, image width would probably decrease, but image 'specificity' increase.

The key idea: the waveguides would be divided in two horizontally, with the upper part, folded back, diverting sound up. The % of the waveguide folded up, depending on how much energy you want to divert up. I would think usually more than half, with typical directivity focused on a listener who is seated, but wants more even response when standing or walking around.

If the split of the waveguides' upper and lower parts is hinged, the amount of diversion up or dowm could be fine tuned.

Any merit?

[ackcheng]

you mean like this?

http://www.raalribbon.com/products_flatfoil_140-15.htm

[rick57]

Basically, yes.

Though my idea could be - probably with **? experimantaion - be used on any other less $ ribbons, and by the vertical and horizontal pivots, be adjusted to the room/ listener/ system

Cheers

[bear]

Ummm... no.

First off, that's not a waveguide in the linked site.

That's a cheezy way to change the effective length of the ribbon with respect to frequency. Foam isn't terribly effective, but it might help some.

At higher freqs only the open area radiates, but then the level is also dropped due to the absorption of the other 2/3 of the ribbon not radiating (if the absorption works).

They tapered the wedges to try to make the ribbon "change size" wrt freq.

A waveguide is a sort of horn. This is not a sort of horn.
A waveguide will do nothing to improve the vertical dispersion of a ribbon, but it could control the horizontal directivity, and or pop up the energy at or below the F3 point...

_-_-bear

[Jim Griffin]

The longer ribbons (about 5" long) like the Aurum Cantus G3, Fountek Neo2.0, and similar are the ones with more limited vertical response if you just use one. These ribbons need to be at ear level for best results.

The shorter ribbons (3" long) I have used such as the A-C G2 or G2si, Fountek Neo3.0 and similar have enough vertical dispersion so that they sound OK at listening distances in normal situations.

I wouldn't think that any attempt to use waveguides and such would be successful with any of these ribbons. The ribbon element is already embeddedd somewhat so you'll quickly screw up their horizontal dispersion. All of the ribbons mentioned above have exceptional wide horizontal dispersion and sound great when used properly.

[Bill F.]

Foam isn't terribly effective, but it might help some.

I can't point to empirical data on these, but at the frequencies in question, I believe the foam wedges may be quite effective at widening vertical coverage.

Depending on the formulation and pore size, the foam will supply not only absorbtion but also a form of physical acoustic delay proportional to its thickness (actually slowing the speed of the sound passing through it), creating a lensing effect much like the perforated metal "potato masher" lenses on the front of some vintage horns.

[ShinOBIWAN]

Originally posted by Bill F.


I can't point to empirical data on these, but at the frequencies in question, I believe the foam wedges may be quite effective at widening vertical coverage.

Whilst Bear is right that they are a little cheesy(I kinda like 'em though) there's no denying they are effective. So your right Bill, I've seen with and without the foam and the results aren't subtle confirming that the foam is indeed effective.

Bear was thinking about it like I originally did ie. progressive attenuation of HF along the extremes of the ribbon. Whereas you correctly state that sound passing through the foam gets delayed in relation to that which is unimpeaded. So you get an offset in the time domain where the frequencies on the extremes of the ribbon are less likely to create the typical line source characteristic.

There are downsides of course but my pair of RAAL's should arrive within the week and I'll be testing with and without the foam to see just what happens, what improves and how this relates to overall performance.

[Cloth Ears]

Based on the similarities in design between the RAAL and the Aurun Cantus G3, (and the cheapness of creating the foam wedges), I might just have to try this.
The G3s have a measured (on the website) 15+dB drop-out at 10 degrees off vertical at 15kHz - where the RAALs have 15dB drop-out at 20 degrees off vertical at 15kHz.
I'm not going to hack out the saw edge baffle though.

[rick57]

It was reading of the RAALs’ good dispersion in ShinOBIWAN’s 'Tarantism' Construction Diary thread that triggered my initial post.

If you could get half way from the Aurum Cantus to the RAAL's vertical dispersion .

[jeff mai]

Originally posted by rick57
If you could get half way from the Aurum Cantus to the RAAL's vertical dispersion

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