Infinity in some of their old kappa series speakers use a peculiar structure in the edges of the baffle(together with felt), what's the operational principle of such a design?
I remember those speakers, some of the kappa line were very large.
I imagine the rounded edge was made by cutting kerfs (slots) in a sheet of material, such as veneered plywood, and then bending the flat sheet into a curve. At the time, CNC machines were too expensive for ordinary manufacturers, so this was the best way to achieve a large radius edge. It is very similar to the method used to make tambour doors for a cabinet. It was also quite attractive, and it was a unique look for Infinity. Today, a CNC router could mill the baffle edge to any sort of circular, elliptical, or parabolic shape the designer might want.
The small size of the ridges/gaps in the rounded edge are smaller than a 20 kHz wavelength, so Arnie & co. probably expected those small ridges/gaps to have no diffraction effect. Now we know that small features of that size do have a measurable diffraction effect, but it is open to debate on whether this kind of very low level diffraction would be audible.
That cabinet you are showing probably dates from the late 1980's or early 1990's. Infinity was quite advanced compared to most other speaker makers of that vintage.
j.
I imagine the rounded edge was made by cutting kerfs (slots) in a sheet of material, such as veneered plywood, and then bending the flat sheet into a curve. At the time, CNC machines were too expensive for ordinary manufacturers, so this was the best way to achieve a large radius edge. It is very similar to the method used to make tambour doors for a cabinet. It was also quite attractive, and it was a unique look for Infinity. Today, a CNC router could mill the baffle edge to any sort of circular, elliptical, or parabolic shape the designer might want.
The small size of the ridges/gaps in the rounded edge are smaller than a 20 kHz wavelength, so Arnie & co. probably expected those small ridges/gaps to have no diffraction effect. Now we know that small features of that size do have a measurable diffraction effect, but it is open to debate on whether this kind of very low level diffraction would be audible.
That cabinet you are showing probably dates from the late 1980's or early 1990's. Infinity was quite advanced compared to most other speaker makers of that vintage.
j.
The speaker in the photo is a kappa 5, I've inherited a pair but even though I look at them every day I've never questioned the edge design.
Regarding the construction, to me it doesn't look like its made by cutting kerfs, The sticks(?) have a slightly conical shape and they are completely painted in the inside, i can't capture it on photo but they each seem to be independent from one another.
After reading this paper on edge diffraction I find it hard to imagine how they could work, especially after the first slot, maybe on lower frequencies? To me it looks more like a diffuser. Well, it's hard to test if this actually works.
Maybe they did it more for the looks, and they do look very well put together.
Regarding the construction, to me it doesn't look like its made by cutting kerfs, The sticks(?) have a slightly conical shape and they are completely painted in the inside, i can't capture it on photo but they each seem to be independent from one another.
After reading this paper on edge diffraction I find it hard to imagine how they could work, especially after the first slot, maybe on lower frequencies? To me it looks more like a diffuser. Well, it's hard to test if this actually works.
Maybe they did it more for the looks, and they do look very well put together.
Perhaps they're trying to create multiple diffraction points to introduce smaller diffractions to enhance the width of the stereo image?
The ridges may leave a slight edge effect that would only affect the highest frequencies. Sometimes a full diffraction-less baffle doesn't produce a response as good as possible with good edge placement. But there is not necessarily much HF energy reaching the edge to interact with those small features.
If you want to test out the difference you can cover the notches with tape, that will be enough to block the effect.
If you want to test out the difference you can cover the notches with tape, that will be enough to block the effect.
In my opinion, the Infinity round over approach would work pretty good. Up to about 6k it would be no different than a smooth roundover. I estimate the size of the ridges/gaps to be about 1/4 inch, and at 6k that would be about 1/8 wavelength. A feature, bump, or gap needs to be about 1/4 wavelength in size before it has the full diffraction effect of an edge. It will have an effect that is measurable, but it will not be the full effect. At the baffle step frequency, I don't think the Infinity approach would be any different than a smooth roundover of the same radius.
j.
j.
The ridges look to be wood, as in not plywood, as you can see the grain in the photo. Shaping the ridges after cutting isn't that difficult. If I were to speculate, I'd think that section may have been steamed to get it to bend without breaking, and the fastened after drying. It hardly seems worth the effort given the probable negative effect on sound.
I’d think that that treatment would increase edge diffraction, but would also make it more chaotic so probbaly less of an issue..
dave
dave
Fluting is a cosmetic moulding/paneling, though in this case it in theory makes for a smoother baffle polar response, i.e. has less stiction as the wavelengths are whipsawing back 'n forth at > baffle width WLs.
The felt actually works, but the kerfed corners are more likely something from the marketing department.
There seems to be slight differences but time gating on the measurements and off-axis responses would be useful.
So I'm not gonna tell you the difference between the two.
It's just like a particular mix for car tyres: you gotta make the race, and someone tells you " it's just for making the wheel turning, that's ok!? why care?"
It's just like a particular mix for car tyres: you gotta make the race, and someone tells you " it's just for making the wheel turning, that's ok!? why care?"
If you post the REW file somewhere like Google Drive or Dropbox, we can drill down with the impulse windowing and see if there are tiny differences. But they will be very tiny. Ideally you would want the tape to be as round as possible, not pushed into the gaps.
Also, the tape needs to smooth the step from the baffle to the corner, because this is the first step encountered by the wavefront and will have the most dramatic effect.
and don't forget the waves coming from the room to the baffles...
and: the slots are there for a reason, why would anyone cover them?
and: the slots are there for a reason, why would anyone cover them?