I suspect it’ll be pretty much the same as PM2 Mk1 ie same size magnet as PM4.
But PM4 had the permendur pole pieces & a higher gap flux density (2.4T)
Using the 5 mm o-ring in situ and a height guide I’ve just been pushing up on the underside of the cone to see how high the foam reaches - I would say the spacer needs to be 6mm to allow full clearance
Post 39 above has my attempt at HornResp. The parameters should be fine, the only change from that is that S1 should be 60 as it measures 6x10cm.
Post 44 shows the entrance to the front horn; you can see that the sound bounces off some plaster buttocks and out the front. No idea of dimensions, might be a bit of guesswork involved!
That’s one of the horns. What about the other?
Need to ensure the vertical alignment of the pot is adjusted.
TBH, the only thing you can sensible change is the volume of pot, so not much point simulating. Just make the pot larger that you think it needs to be and you can add blocks to shrink it while measuring. Remember that the magnet and cone use up some of the volume.
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Kermit
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Kermit the pig. 
I had naively assumed that giving these dimensions on their plan implied that there was 4-way symmetry.
Reader, there was not.
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@Ruprecht um, just asking…
The speakers (and the helmets), they are identical, aren’t they? Not, say, mirror images internally or anything. Knowing this kind of thing now is definitely better…
The Enclosures are a stereo production pair - Hand made of course long before CNC, so there may be hand made ‘fun’ ! The BD5’s should be the same (modern production pair)
As long as the enclosures are basically the same, as opposed to being mirror images of each other (pun intended), it should be fine.
“Construction piece 1” is now on the printer. This is to help me to understand if I have the basics right - are things where I expect them to be, are there any things in the way, are the angles that should be right angles actually 90 degrees, etc. It will also help us to make the small adjustments to get close to a perfect fit.
I’ll send it out tomorrow. Probably.
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Sounds like operation helmet is engorging
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Well it would be if my 3d printer hadn’t just shat the bed 
About four hours ago I had a conversation with Claire about whether I should get a new one, and she said that I should. So I will. Then this one broke.
Anyway this does mean that everything will be delayed by a week, sorry!
Pics please!
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Well I’ve given away the old 3d printer and bought a new one because of reasons.
@Ruprecht service will be resumed shortly.
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Construction model number 1 is on its way, in a fetching green (came free with the printer).
There’s another gasket as well, should be a better fit.
Finally, a surprise bonus. Not sure if good or trolling tbh. You’ll want to move to St Albans.
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(I’m moving this back to the thread rather than PM so people can laugh and bitch)
Here is construction piece #2…
The idea here is that the horizontal piece is the exact size of the driver, and the vertical should match up to the horn throat and screw holes. And it should fit inside the funny angle, without having to be cut!
The AER driver is 202mm in diameter at its narrowest, whereas the helmet chamber is 200mm. What this means is that there will be a slight misalignment between the centre of the driver and the (170mm diameter) hole for the front horn. This will have no acoustic impact.
The final solution will be as follows:
- TPU gasket, 7mm deep, that will be the same as the horizontal green part of this construction piece
- Driver
- TPU gasket probably 1mm deep (depends how well it prints)
- New helmet chamber, which will also be the same shape as the horizontal green part at the bottom, and marry up nicely with the rectangle of the horn throat.
The mounting will be as follows:
- Four holes will be drilled in the top to the Lowther cabinet, and all four items above will be squeezed together by four bolts that go all the way through the bolt holes from top to bottom. (I recommend using nice threaded inserts in the cabinet.)
- For the horn throat, there will be a 1mm gasket cut from a rubber sheet. The side screws will go through holes in the helmet chamber and there will be nuts to bite onto.
This should end up better than the original, as there will be four contact points at the bottom. Although the chunky cast iron chamber is quite a thing, needing less to keep it in place!
In terms of size of compression chamber I might print 3 versions:
- The natural size that comes from the geometry (this will be slightly lower volume than the original Lowther chamber, despite being the same height)
- One that will look rather bulbous, where it should be the same volume as the Lowther one.
- One that has a smaller volume
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