Most design choices are made, given time constraint, i started with the production of the baffle shapes using 3D-printer, and also supports for the enclosure to "lay" on its back.
Overall picture:
The gey part will be printed with PLA+
The blue rings with a soft material, probably TPU, covering the PTT8.0X08 woofers including their frames.
The lighter blue is the basic design for the ring for the PTT4.0M08 Midrange including its frame
The roze-red is the preliminary tweeter, its mounting to be decided upon.
The baffle shape to print:
Cut into parts:
The ring for a woofer:
And very important, the supports:
The 3D-printing is like Dutch&Dutch 8C a cover over the baffle made of hartpapier/pertinax, where for the mid/twwet part it needs to be remade
The 3D printed baffle will be glued to this main construction. (i left out the holes for the units, and made sure a gap of 0.5-1mm for glue)
Whilsth modeling in 3D (Rhino3D) for me is like coming home after a very long journey, as usual i also use sketches to validate contemplations:
As you can see from the loads of Tipp-Ex, this went through a lot of iterations and alternatives ;-)
For the woofers it is almost literally a drop-in replacement, at least size-wise. I will add some reinforcements inside the cavities, and have to drill 6 holes, as the circular centerline is different.
The biggest challenge is the midrange-tweeter area of the enclosure/baffle. In red the cross-section of the existing encl;osure & baffle, in blue/black the design considerations. Clearlty seen is the huge reduction in needed enclosure volume for the midrange. This allows for filling the excess volume with hartpapier/pertinax glued with a epoxyglue of about the same Young's modulus. Thus providing a very massive "ground" to support the magnet ;-)
(the arched red part to the left and top is mainly layers of MDF stacked, the other parts are hartpapier/pertinax, where layered a cld in between.
The tweeter is just a guestimate for its total depth. Its faceplate diameter and mounting depth are already known.
Nevertheless i wait final design in that part till i have it confirmed. ;-)
As soon as the supports are ready, i can start preparing the current enclosures, luckily, the final design for mid-tweet area is needed as last part ;-)
To be continued !
Overall picture:
The gey part will be printed with PLA+
The blue rings with a soft material, probably TPU, covering the PTT8.0X08 woofers including their frames.
The lighter blue is the basic design for the ring for the PTT4.0M08 Midrange including its frame
The roze-red is the preliminary tweeter, its mounting to be decided upon.
The baffle shape to print:
Cut into parts:
The ring for a woofer:
And very important, the supports:
The 3D-printing is like Dutch&Dutch 8C a cover over the baffle made of hartpapier/pertinax, where for the mid/twwet part it needs to be remade
The 3D printed baffle will be glued to this main construction. (i left out the holes for the units, and made sure a gap of 0.5-1mm for glue)
Whilsth modeling in 3D (Rhino3D) for me is like coming home after a very long journey, as usual i also use sketches to validate contemplations:
As you can see from the loads of Tipp-Ex, this went through a lot of iterations and alternatives ;-)
For the woofers it is almost literally a drop-in replacement, at least size-wise. I will add some reinforcements inside the cavities, and have to drill 6 holes, as the circular centerline is different.
The biggest challenge is the midrange-tweeter area of the enclosure/baffle. In red the cross-section of the existing encl;osure & baffle, in blue/black the design considerations. Clearlty seen is the huge reduction in needed enclosure volume for the midrange. This allows for filling the excess volume with hartpapier/pertinax glued with a epoxyglue of about the same Young's modulus. Thus providing a very massive "ground" to support the magnet ;-)
(the arched red part to the left and top is mainly layers of MDF stacked, the other parts are hartpapier/pertinax, where layered a cld in between.
The tweeter is just a guestimate for its total depth. Its faceplate diameter and mounting depth are already known.
Nevertheless i wait final design in that part till i have it confirmed. ;-)
As soon as the supports are ready, i can start preparing the current enclosures, luckily, the final design for mid-tweet area is needed as last part ;-)
To be continued !
@JanRSmit
Please have a look at my directivity study, if you haven't already seen it:
https://www.diyaudio.com/community/...s-of-hf-mf-and-lf-drivers-in-cabinets.409660/
You may be able to visualize the pros/cons of different forms of directivity control...
Please have a look at my directivity study, if you haven't already seen it:
https://www.diyaudio.com/community/...s-of-hf-mf-and-lf-drivers-in-cabinets.409660/
You may be able to visualize the pros/cons of different forms of directivity control...
For the midrange, the cross-section :
This game me in sim a very nice response on and off-axis, and testing a printed version with real driver proved a close correlation on the horizontal axis. The real thing actually a bit better as the real response extends a bit in the response, the off-axis response being quite linear up to 3.5kHz before the directivity increases..
Would be nice to have a tweeter for sim the baffle shape as "seen" by the tweeter. In the mean time i will see if what leeway i have w.r.t. curvature variation.
This game me in sim a very nice response on and off-axis, and testing a printed version with real driver proved a close correlation on the horizontal axis. The real thing actually a bit better as the real response extends a bit in the response, the off-axis response being quite linear up to 3.5kHz before the directivity increases..
Would be nice to have a tweeter for sim the baffle shape as "seen" by the tweeter. In the mean time i will see if what leeway i have w.r.t. curvature variation.
A quick check on the curvature to reduce and more even spread, within the space constraints i have, but without lowering the tweeter:
The current one is moved up and shows that curvature. The one in place is altered and shows a better looking curvature.
Assuming some similar waveguide shape, this looks like a better transition.
Bear in mind this is only on the centerline cross-section.
The current one is moved up and shows that curvature. The one in place is altered and shows a better looking curvature.
Assuming some similar waveguide shape, this looks like a better transition.
Bear in mind this is only on the centerline cross-section.
Adapted the top edge of the baffle (was the area where i decided to drop Fusion 360 and go for Rhino 3D ;-)), more round using the modified curve in above post:
Note: for the time being the diameter of the opening for the tweeter is 2mm more in diameter than the frontplate, this to provide some space to add some vibration isolation room in the mounting of the tweeter. Not sure if i will do something
Note: for the time being the diameter of the opening for the tweeter is 2mm more in diameter than the frontplate, this to provide some space to add some vibration isolation room in the mounting of the tweeter. Not sure if i will do something
That is smart. 2mm clearance is enough. I have tried routing driver recess with 1/32" clearance (0.8 mm), and it was not quite enough. Changes in temperature and humidity would create an interference fit. It is very frustrating to trial fit a driver and it becomes wedged into the recess. Now I use 1/16" (1.6 mm) clearance. It is a very close fit, it looks perfect visually. I have never had a geometric interference, and I have confidence the driver is sitting fully flush in the recess.
j.
j.
@JanRSmit - in your graphics of the baffle curvature, you show lines emenating from the surface of the curve. I am not sure what those are, but I would guess that the length of the line is inversely proportional to the radius... perhaps?
I agree with @lrisbo. If you could make the radius above the tweeter at least a 30mm radius, that would be very nice.
I agree with @lrisbo. If you could make the radius above the tweeter at least a 30mm radius, that would be very nice.
Crossed the Rubicon, as a matter of speak:
Glueing was still perfect. A lot of careful chiseling needed ;-)
@hifijim , 30mm radius is not possible given the constraints i have, see image, as i need to lower the tweeter by some 11mm to achieve this.:
(orange is the curve i used, red is a circle with 30mm radius)
LIke @lrisbo said a post ago, I will model a tweeter in LEM and BEM (Akabak) and work out a shape. And just for the comparison do one model with a 30mm radius.
The shape i posted last was the one i developed already, but when switching from F360 to Rhino, i deviated from that shape.
(From my naval architecture background i rather use splines instead of arc's, as arc to straight line by definition is a disruption in curvature.
Do not know if it is that of an issue with sound wave propagation though ;-))
Glueing was still perfect. A lot of careful chiseling needed ;-)
@hifijim , 30mm radius is not possible given the constraints i have, see image, as i need to lower the tweeter by some 11mm to achieve this.:
(orange is the curve i used, red is a circle with 30mm radius)
LIke @lrisbo said a post ago, I will model a tweeter in LEM and BEM (Akabak) and work out a shape. And just for the comparison do one model with a 30mm radius.
The shape i posted last was the one i developed already, but when switching from F360 to Rhino, i deviated from that shape.
(From my naval architecture background i rather use splines instead of arc's, as arc to straight line by definition is a disruption in curvature.
Do not know if it is that of an issue with sound wave propagation though ;-))
Inspection of empty enclosure, all ok, no glued joints failures, the other side of the rubicon looks nice!
This part once housed the xo filter ;-)
The connectors will be replaced by Speakon's , no more of this WB crap.
As the aim is a hybrid active/passive , an option is to place the 2-channel Purifi Eval1 amplifier inside this space. If time is an issue(look like it) , i consider 3-way active. Choices, choices.
A serious setback is the 3D printed baffle shapes, they keep shape distorting after 1 day , and even at 40' C they start to distort their shape, and when cooled to 20' C they become stiff again. The crossections are variing in thickness from 11mm to 2mm, apparently this is too much variation. The more thick prints for the testing shapes with real speaker, stayed more in shape.
So back to adding another layer of hartpapier(pertinax) with a CLD layer in between, and some thin layers on the side, then followed by some serious sanding to make the rounded shape. Bummer.
But then again, been there, done that, so, with crossections printed and cut from stiff carton, it can be done ;-)
This part once housed the xo filter ;-)
The connectors will be replaced by Speakon's , no more of this WB crap.
As the aim is a hybrid active/passive , an option is to place the 2-channel Purifi Eval1 amplifier inside this space. If time is an issue(look like it) , i consider 3-way active. Choices, choices.
A serious setback is the 3D printed baffle shapes, they keep shape distorting after 1 day , and even at 40' C they start to distort their shape, and when cooled to 20' C they become stiff again. The crossections are variing in thickness from 11mm to 2mm, apparently this is too much variation. The more thick prints for the testing shapes with real speaker, stayed more in shape.
So back to adding another layer of hartpapier(pertinax) with a CLD layer in between, and some thin layers on the side, then followed by some serious sanding to make the rounded shape. Bummer.
But then again, been there, done that, so, with crossections printed and cut from stiff carton, it can be done ;-)