Hello - I'm looking for some guidance from anyone who has seen this wave guide in person (or the JBL 2380A).
I'm modelling the wave guide at the moment with the aim of getting it CNCd from MDF and integrated into the baffle of the speaker i'm building so it looks seamless - only thing is, there has been some guess work on my part as I haven't laid eyes on one in real life.
My question is, is my construction of the base (where the driver attaches) to the top of the throat, correct, see image attached.
Thanks for any help,
Steve
I'm modelling the wave guide at the moment with the aim of getting it CNCd from MDF and integrated into the baffle of the speaker i'm building so it looks seamless - only thing is, there has been some guess work on my part as I haven't laid eyes on one in real life.
My question is, is my construction of the base (where the driver attaches) to the top of the throat, correct, see image attached.
Thanks for any help,
Steve
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Steve,
Yours doesn't look right, vertically too short and too wide.
If I recall correctly, JBL 2" is actually ~49mm.
The JBL 2380A diffraction slot appears to be about 1" wide, 4.5" tall.
It's throat expands from ~3.14 square inches to ~4.5 square inches at the diffraction slot.
Your vertical expansion looks to be straight.
I'm not 100% positive, but I think the vertical arc radius of the throat section matches the initial portion of the bi-radial horn.
I think the only part of the horn without a curve is the mounting flange.
Art
Yours doesn't look right, vertically too short and too wide.
If I recall correctly, JBL 2" is actually ~49mm.
The JBL 2380A diffraction slot appears to be about 1" wide, 4.5" tall.
It's throat expands from ~3.14 square inches to ~4.5 square inches at the diffraction slot.
Your vertical expansion looks to be straight.
I'm not 100% positive, but I think the vertical arc radius of the throat section matches the initial portion of the bi-radial horn.
I think the only part of the horn without a curve is the mounting flange.
Art
Thanks for your help, I should have pointed out my drawing was not to scale or accurate, I was simply demonstrating my modelling method of creating the shape by using the circle extruded to the rectangle and asking if that is how the inside of the wave guide would be constructed.
There's multiple ways of interpolating a surface body between the circle and the rectangle in a CAD. Those methods will have their own names. Some of them take a tangent coefficient. So the answer isn't yes or no, as we don't know which of these interpolation methods you used.
Should be 49,2 mm.
so indeed not 2" by the international standard of today.
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I have this Paudio horn (JBL2380 copy) and from what I can see into it, your guess about the throat morphing into the slot is mostly correct, except for the size of the slot, which is 4" x 0.75".
A 3D model is available from JBL but it appears to have low polygon count and the throat portion is not modelled accurately, need to check again using Autodesk software.
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This might help as well not the same horn but it shows how they do the transition. They have bumps before the slot that narrow it in the horizontal plane.
https://www.audioheritage.org/vbulletin/showthread.php?14933-Walnut-H9800&highlight=array+horns
https://www.audioheritage.org/vbulletin/showthread.php?23297-H9800-CAD-Data&p=232914#post232914
https://www.audioheritage.org/vbulletin/showthread.php?14933-Walnut-H9800&highlight=array+horns
https://www.audioheritage.org/vbulletin/showthread.php?23297-H9800-CAD-Data&p=232914#post232914
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From what I see here, there is a shaft inside the throat of the PAudio PH-2380 which the JBL may not have. However, over the years, a lot of speakers (Calpamos etc.) have made use of this Paudio version of the 2380, so all the best !!
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OK so they don't match the JBL throats. None of them have pronounced slots that are larger than the driver exit. Also no hard internal edges they are all "blended" with some slightly raised mold marks. This is a much easier way to see the transitions of a typical modern JBL biradial. This is a 1 thread on throat adaptor goes to 1.5". You would bolt a 1.5 " horn to the adaptor. Don't know what this was used on. It's cast aluminum, molded in halves and bolted together.
Rob 🙂
Rob 🙂
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Wow! Thank you for all your replies it’s a massive help, I’ll finish modelling it and post the results.
This is where i'm at - I think it should work well but now Ive seen all these new images, I have another question:
What do you think this extra rectangle is adding to the wave guide here - is it for strength, acoustics? any ideas. I have left it out of my model but Ill add it in if it is essential.
What do you think this extra rectangle is adding to the wave guide here - is it for strength, acoustics? any ideas. I have left it out of my model but Ill add it in if it is essential.
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It is probably easier to mold. Doing cast aluminum in haves makes sense. The 2380A is one piece don't quite understand how JBL did the molds assuming the throats are exactly the same as what I posted.
Rob : )
Rob : )
It's probably an artefact of the moulding process or the mould itself, as mentioned by Robh above. This rectangular slot is only along the vertical axis of the horn.
Paudio 2380s from the internet also show this slot and the serial number 42011067 which probably indicates the model.
http://www.poweraudio.ro/horn_p-audio_PH-2380
https://vaudioshop.tarad.com/products_detail/view/3534446
Those who already have the Paudio horn (Calpamos users etc.) need not become excessively paranoid about this slot as it is too small to make any audible issues. As shown below, the slot measures the same as the throat exit (red) and maybe smoothed off into a circle (if desired) by filling in the hollows with auto body filler, followed by some sanding.
Absolutely not, it maybe better to go with JBL's version, which is considered geometrically superior, due to the absence of any sharp edges. Note that the circular shaft is also absent in the JBL photographs, besides the rectangular slot.
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The rectangular slot extending past the driver exit weakens the horn and increases unwanted diffraction artifacts.
It was only done that way to simplify (cheapen) making the mold.