The area between the ramps will connect the back volumes of both drivers.
Wow! That's really innovative, djk! Thanks for sharing your insight!
The inner driver is still firing into the slot, right? So will there be sufficient space between drivers, or does the area with the ramp have to be 'broadened'? (I'm guessing it's gonna mess with the horn dimensions, but...
)And the wedge for bifurcation? Can it be omitted?
What about the outer driver's front chamber? You said the back volume will be connected by the area between the ramps - the 'V's' - so how much volume should the outer driver have?
I guess I'm still confused how the secondary driver will be mounted. Can you please explain it a little bit more?
This is my 12 inch size La Scala with your port mod(only upper 2 ports are in use) and loaded with quad 8 inch PPSL plenum per side. (Thanks for the design!)
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"The inner driver is still firing into the slot, right?"
There will be no slot in practice. I recycled pictures of the Belle type product to show the ramps.
"So will there be sufficient space between drivers, or does the area with the ramp have to be 'broadened'?"
The 12PE32 is 120mm deep behind the mounting plane (front mounted). The mounting board is 18mm, so the magnet is 102mm deep. If the inner driver is mounted behind its mounting board that is another 18mm, so we are down to 84mm. I was thinking of making the passage 75.5mm (like the stock LaScala), so the magnet sticks into the cone of the other driver by 8.5mm, plenty of room for cone travel.
"What about the outer driver's front chamber? You said the back volume will be connected by the area between the ramps - the 'V's' - so how much volume should the outer driver have?"
As little as possible. The optimum back volume for both drivers is only 20L, it will be hard to get it down that low.
"And the wedge for bifurcation? Can it be omitted?"
It's not there.
The effective divider is the centerline of the drivers, and the ramps will come right up to this centerline and define where the bifucation starts.
http://www.parts-express.com/pedocs/tech-diagrams/294-660-bc-speakers-12pe32-technical-diagram.pdf
The mounting hole is 281mm, and the width of the passage is about 75.5mm, so the area at the effective throat is about 212cm (the design calls for 231cm, close enough).
Going either direction from the throat about 32cm (the middle of the 90° bend), and then moving forward 55cm to the mouth gives us a total length of about 82cm (the design calls for 84cm).
With the cabinet about H610mm x D610mm x W760mm the mouth is a bit bigger than required (better a bit big than a bit too small).
There will be no slot in practice. I recycled pictures of the Belle type product to show the ramps.
"So will there be sufficient space between drivers, or does the area with the ramp have to be 'broadened'?"
The 12PE32 is 120mm deep behind the mounting plane (front mounted). The mounting board is 18mm, so the magnet is 102mm deep. If the inner driver is mounted behind its mounting board that is another 18mm, so we are down to 84mm. I was thinking of making the passage 75.5mm (like the stock LaScala), so the magnet sticks into the cone of the other driver by 8.5mm, plenty of room for cone travel.
"What about the outer driver's front chamber? You said the back volume will be connected by the area between the ramps - the 'V's' - so how much volume should the outer driver have?"
As little as possible. The optimum back volume for both drivers is only 20L, it will be hard to get it down that low.
"And the wedge for bifurcation? Can it be omitted?"
It's not there.
The effective divider is the centerline of the drivers, and the ramps will come right up to this centerline and define where the bifucation starts.
http://www.parts-express.com/pedocs/tech-diagrams/294-660-bc-speakers-12pe32-technical-diagram.pdf
The mounting hole is 281mm, and the width of the passage is about 75.5mm, so the area at the effective throat is about 212cm (the design calls for 231cm, close enough).
Going either direction from the throat about 32cm (the middle of the 90° bend), and then moving forward 55cm to the mouth gives us a total length of about 82cm (the design calls for 84cm).
With the cabinet about H610mm x D610mm x W760mm the mouth is a bit bigger than required (better a bit big than a bit too small).
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If you were to use a narrow flat board on the front (like the Belle does) the exact mouth area could be realized, and the exit angles reduced (dispersion narrowed at the upper crossover point). I would probably opt for the larger mouth and wide exit angles, easier build too.
The rear cover over the rear 12 will need only be about 25mm deep or so. I would place some sort of pad on it (foam or pehaps a piece of fiberglass celing tile) to reduce midrange reflections from coming back through the cone. This cover will need to be removeable to load the driver.
There will need to be a loading hatch (removeable cover) similar to the LaScala (or Belle) to load the internal driver. The 'V' shaped volume behind the interior driver will have to be block off and/or stuffed with non-porus material to hit the target of 20L.
While a straight corner reflector is shown, a curved section could be used (1/4 section of a 150mm plastic pipe or paper tube). The 1/4W of 1130hz is 75mm, so a straight corner reflector should be OK here.
The rear cover over the rear 12 will need only be about 25mm deep or so. I would place some sort of pad on it (foam or pehaps a piece of fiberglass celing tile) to reduce midrange reflections from coming back through the cone. This cover will need to be removeable to load the driver.
There will need to be a loading hatch (removeable cover) similar to the LaScala (or Belle) to load the internal driver. The 'V' shaped volume behind the interior driver will have to be block off and/or stuffed with non-porus material to hit the target of 20L.
While a straight corner reflector is shown, a curved section could be used (1/4 section of a 150mm plastic pipe or paper tube). The 1/4W of 1130hz is 75mm, so a straight corner reflector should be OK here.
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Thanks for the detailed explanation, djk!
I have few more questions...
1. "Normally the depth of the mounting plenum for PPSL determines how high it can go, but I have figured out how to eliminate the plenum for a Belle type horn."
So, if this version doesn't have the limitations from the plenum, then what do you expect the usable upper limit to be?
2. Also, compared to say, a 'standard' quad 8 inch manifold, what pros does this version have over the old version? (besides ease of construction and the case above?)
3. "The 'V' shaped volume behind the interior driver will have to be block off and/or stuffed with non-porus material to hit the target of 20L."
So, does this mean no ported mod for this version?
4. "I would probably opt for the larger mouth and wide exit angles, easier build too."
Kind of like the Peavey FH-1?
5. Can you use an alternate driver besides the 12PE32?
If you can, what are the main specs to look for? (similar dimensions, of course)
"For minimum size and maximum bass extension, I suggest a driver with a Qts around 0.312, and 6th order tuning."
And does this advice still apply when the drivers get smaller? (10 or 8 inches... etc)
6. Can this be down scaled to be used as a mid-horn?(using 6 or maybe even 8 inches for midrange) Or does the LS folding has limitations on the upper frequency even when its size get shrunk?
(it would be so cool to have a PPSL loaded mid horn... I thought it wasn't possible because of the plenum limiting the highs, but perhaps with this design?)
7. And finally, despite of all it's shortcomings(lack of bass... etc), why do you keep building LS cabs? What kind of merits do you see in them? (compared to even a K-horn, for that matter)
I thought someone with your experience would use... I don't know, anything other than a La Scala! (because lots of horn guys don't seem to take the LS seriously...)
I have few more questions...
1. "Normally the depth of the mounting plenum for PPSL determines how high it can go, but I have figured out how to eliminate the plenum for a Belle type horn."
So, if this version doesn't have the limitations from the plenum, then what do you expect the usable upper limit to be?
2. Also, compared to say, a 'standard' quad 8 inch manifold, what pros does this version have over the old version? (besides ease of construction and the case above?)
3. "The 'V' shaped volume behind the interior driver will have to be block off and/or stuffed with non-porus material to hit the target of 20L."
So, does this mean no ported mod for this version?
4. "I would probably opt for the larger mouth and wide exit angles, easier build too."
Kind of like the Peavey FH-1?
5. Can you use an alternate driver besides the 12PE32?
If you can, what are the main specs to look for? (similar dimensions, of course)
"For minimum size and maximum bass extension, I suggest a driver with a Qts around 0.312, and 6th order tuning."
And does this advice still apply when the drivers get smaller? (10 or 8 inches... etc)
6. Can this be down scaled to be used as a mid-horn?(using 6 or maybe even 8 inches for midrange) Or does the LS folding has limitations on the upper frequency even when its size get shrunk?
(it would be so cool to have a PPSL loaded mid horn... I thought it wasn't possible because of the plenum limiting the highs, but perhaps with this design?
)7. And finally, despite of all it's shortcomings(lack of bass... etc), why do you keep building LS cabs? What kind of merits do you see in them? (compared to even a K-horn, for that matter)
I thought someone with your experience would use... I don't know, anything other than a La Scala! (because lots of horn guys don't seem to take the LS seriously...)
After reading that soundforums thread the SynTriPP looks so much attractive to me. Spent some more time studying and I think I now see the hardest part is the BR porting. Looks like Art revised it since I didn't notice until recently.
You guys are way over my head with the PP Belle/LaScala stuff. Just recently figured out what the VOTT acronym stands for
You guys are way over my head with the PP Belle/LaScala stuff. Just recently figured out what the VOTT acronym stands for
DJK anymore news on your dual 12" new design?
Curious if there is anymore progress or not. I can try and fold it on my end and then go from there.? BUT figured I will just wait. Still have to order some BC 12's. I found the horn locally so maybe in the next month or two I can try and build it. BUT I dont want to do anything without your blessings either.
Curious if there is anymore progress or not. I can try and fold it on my end and then go from there.? BUT figured I will just wait. Still have to order some BC 12's. I found the horn locally so maybe in the next month or two I can try and build it. BUT I dont want to do anything without your blessings either.
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