Of course it adds some diffraction but this is actually what we gan get this way: https://www.diyaudio.com/community/...-design-the-easy-way-ath4.338806/post-7056696
Could it be improved further? Sure it could. Is it already good enough? That's the question. I tend to think so.
Could it be improved further? Sure it could. Is it already good enough? That's the question. I tend to think so.
Inspired by recommendations for boxes with sides in an irrational ratio, we could try an irrational number close to 3, maybe π... Oh wait...
Jokes aside, Marcel's latest work looks very feasible to cut sides from a polystyrene foam slab with a simple hot wire cutter.
Use the foam for fast prototypes, or assemble the male off-cuts as a mould for more serious and robust products.
Carbon fibre in solvent-less epoxy would look nice and doesn't dissolve polystyrene.
It wouldn't be too expensive if just a face layer, backed with cheaper material.
Any one tried either technique?
Best wishes
David
Initial thoughts on this:
1) not sure what a R-OSSE is, but one way to get a easy roll back in a tight radius is to stick to easy available diameters of pipe (64mm for drain, 3 inch, 4 inch etc) I can put together a list of internationally common sizes if this helps. We can then avoid the radius limit of the ply or kerfed MDF.
On that note: kerfed MDF may be preferable as it can be purchased in a RAL finish, so requires no finishing on the main surface. The downside is that it has a lower limit on bend radius than Flexi-ply. I will investigate and get back to you. If this was possible, making one would be a 30 min job. 3D printed throat insert, laser main walls, PVA/masking tape corners (same way you make a violin) and use a skirting board pin gun to hold.
2) Is a roll back on the mouth preferable to flush mounted when in a corner horn Vs infinate baffle? I would guess it is as less energy would reach the edges between the baffle and the room walls... No idea.
3) 20 Deg listening window would be too narrow, however, I assume when mounted, the boundary would make this wider? But how much?
Guys, are we not talking about 3 dimensional symmetry, a completely different kettle of fish all together than 2D symmetry? A horn, like the one Mabat has shown can of course be highly asymmetrical throughout even with rectangle for a mouth.Well, flat boards don't seem to work well. You would really have to bend them (OSSE works fine). And then perhaps no mouth rollback would be necessary, who knows.
- BTW, isn't such triangle more symmetric than a rectangle, after all?
I also have great difficulties in understanding what AllenB is trying to show us btwy.
I think what people are trying to get at, (but the language is elusive) is path length.
In a round horn, the path length is the same in all radial directions.
In an oval horn, there is gentle change in path length.
In a square horn there is more sudden change.
The JBL M2 has little or no change in path length if I understand correctly but is square.
The data MBAT shows for the response of a square horn is not intuitive.
You would intuitively expect odd effects from lower compression ratios and distance to the throat in the corners (for instance), but I don't know if this is a reality or not. If it did turn out to have a measurable effect of significance (say at high SPL?) Then a 8 petal version would presumably be less affected.
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If I had to take a guess,
Rectangle horn should do even better as there's even more of a timing difference.
I'd say even with a rectangle horn it should pay off to add the proper edge termination. Unless cost of building it becomes a factor (not likely in DIY, just spend more time).
My theory being it should always be better to (be able to) avoid diffraction than to smear it out over time.
Hoping to see an optimized rectangular horn with these R-OSSE curves as the base of a MEH at some point... It should do better than the flat (stepped) wall versions, right?
The ports would be the next challenge and the driver fit on a curved wall.... but for those who like challenges
Which makes the timing of the reflection back to the throat from the mouth edge all the same (at all angles)...
Timing will vary in this case, so even without a roll back it will look prettier than the round horn (with the same edge termination).
A square horn will have variable timing of the reflection from the mouth edge back to the throat. Making it smeared out in time and less severe.
Rectangle horn should do even better as there's even more of a timing difference.
The above is about looking at diffraction effects at the mouth... (and a resulting reflection back to the throat)
I'd say even with a rectangle horn it should pay off to add the proper edge termination. Unless cost of building it becomes a factor (not likely in DIY, just spend more time).
My theory being it should always be better to (be able to) avoid diffraction than to smear it out over time.
Hoping to see an optimized rectangular horn with these R-OSSE curves as the base of a MEH at some point... It should do better than the flat (stepped) wall versions, right?
The ports would be the next challenge and the driver fit on a curved wall.... but for those who like challenges
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To add to this earlier comment, I just calculated the angles for my room in CAD.
Corner wall angle is 15degrees, so way off the 45 Deg of the average corner speaker.
At worst I would sit 20 degrees off axis vertically and horizontally, and am limited to 575mm wide for the horn (corner wall width), but unlimited vertically. Driver is capable of playing down to 500hz, but 600hz+ is lower distortion.
the alternative JBL M2 horn is 90/100 degree coverage before dropping SPL. This isn't ideal either, as I assume the side walls will get more energy than the listening seat would, so it's too wide.
~20 degree listening angle is fine, 45 degree toe in with roughly equilateral stereo listening triangle. Just tune the speaker response for it, ~20 degree of axis as the main listening axis.
This is how you get stable phantom center, big sweetspot, tight imaging and still some envelopment, good rejection to the nearest walls for reduced early reflections. Its not bad, its about best there is for roughly constant directivity speakers.
edit. read your post again and I probably misunderstood it so if this probably wasn't relevant info so carry on
This is how you get stable phantom center, big sweetspot, tight imaging and still some envelopment, good rejection to the nearest walls for reduced early reflections. Its not bad, its about best there is for roughly constant directivity speakers.
edit. read your post again and I probably misunderstood it so if this probably wasn't relevant info so carry on