SLAM

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SLAM!

On the last pages in my old thread, Yet another DIY AMT, I were on the verge of starting to work on a new AMT motor.

But now when I'm actually starting, I want to make a clean start with a new thread.

This motor will be 150 cm long, that is how far my stash of pole pieces and magnets takes me.

I still have my doubts of an AMT line source, but the motor can be used for other configurations.

So Solhagas Long AMt is finally coming up!

First I need to do some OnShaping...
 
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Do you have pole pieces for 2 AMT´s ?
Yes I have. But I'll will not mount any pole pieces on the back.
I haven't measured or heard any drawbacks of that approach.

This must be 3 or 4 membrane´s ,or what
Bernt
It'll probably be a MMTMM configuration. The four Ms might be my usual full range membrane but cut off in the highs.
The tweeter will then be a new 45x45 mm AMT.
Hopefully this configuration deals with the vertical dispersion better.

Nice to hear from you again.

Bernt

Thank you, Bernt. Been busy building my CABS (Controlled Acoustic Bass System) system. Like all good things in loudspeakers - it's Danish.
 
Yes I have. But I'll will not mount any pole pieces on the back.
I haven't measured or heard any drawbacks of that approach.


It'll probably be a MMTMM configuration. The four Ms might be my usual full range membrane but cut off in the highs.
The tweeter will then be a new 45x45 mm AMT.
Hopefully this configuration deals with the vertical dispersion better.



Thank you, Bernt. Been busy building my CABS (Controlled Acoustic Bass System) system. Like all good things in loudspeakers - it's Danish.
Would a series of smaller AMT "stacked" have the same characteristics as a single large verdion?
 
The result of a days work with OnShape.

Magnet and pole piece:

magnet.jpg
pole%20piece.jpg


I'm doing a section of four pole pieces and then I'll multiply to the full AMT, so I need a smaller part of the frame:

main%20frame%20short.jpg


Pole piece hold:

pp%20hold.jpg
.

Spacer to hold a bar between the magnets and the bar itself:

spacer.jpg
magnet%20hold.jpg


There's a big chance that I can get 3D printed pole piece holders:

pp%20hold%20mold.jpg


All the above in one four pole pice section:

four%20pp%20assembly%20front.jpg
four%20pp%20assembly%20back.jpg


And...

SLAM!

slam%20front.jpg
slam%20back.jpg
 
SLAM!

Got some prototypes made of the pole piece holders:

first%20prototype%20pp%20hold.jpg


Some minor errors: fillet where the vertical part ends in the horisontal part should have had a larger radius and there should be no fillet on the bottom plate.

First try of the mounting:

first%20assembly%20pp%20hold.jpg


The holders should have the same contour as the pole piece at membrane.

The backside, where the magnets will be mounted:


first%20assembly%20pp%20hold%20back.jpg



It could of course be good to cover the nuts with some snap-in so it'll be the same contour towards the membrane/gap all the way.

Test mount in the frame:

first%20assembly%20in%20frame.jpg


 
SLAM prototype v2

I'll replace the small aluminium parts with 3D printed:

second%20prototype%20parts.jpg


I can then premount a complete two pole piece section (you'll have to ignore the aluminium part here):

second%20prototype%20two%20pp%20assembly.jpg


Another angle:

second%20prototype%20two%20pp%20assembly%20flip.jpg


I'll force the sections down the aluminium frame "rail":

second%20prototype%20slam.jpg


When in place I'll secure the section at the aluminium frame with a screw though the section and frame.

Hopefully will this be a lot faster and much more secure.
 
While waiting for the printer, I'll need some advice from the forum expertise.

The ideal motor looks like this:

An externally hosted image should be here but it was not working when we last tested it.


Simulated flux density:

An externally hosted image should be here but it was not working when we last tested it.


Horisontal plot:

An externally hosted image should be here but it was not working when we last tested it.


Linear and even through the gap.


But the reflexion of the back wave produces all sorts of distortion both in time and frequency when it is mixed with the front wave.

So after a couple of measurements with different back pole pieces, I decided to skip the back pole pieces all together.

An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


The flux density is now un-linear and varies a lot over the gap.


Now I'm wondering if there a way to disperse the reflexion.

An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


Considerably better linearity over the gap.

But is the back pole piece curved the right way to make the desired dispersian?
Shall it have a larger radius? (Larger radius means greater variation.)
Other thoughts?
 
Hi Solhaga

I don´t use back pole for my AMT´s.
Using back pole increases sensivity and give a much more linear magnetic field.
My idea is to use round bars to omit reflexions .
Use a angle grinder to cut the ends like this: View attachment 641975

Bernt

Yeah, that's a great idea.
Instead of using a grinder, a 5x5 mm square rod can be used that can have your suggestion glued to it or a concave or a convex or a ...
 
As the configuration is MMTMM, the section where the four mid membranes are can have back pole pieces.
This as the reflections have little impact for that frequency interval.
I'm also considering to make the mid membranes to go lower, let's see what properties that will have to change - pleat depth, pleat width and/or foil thickness/width.

Then I will see if the small tweeter membrane in the middle can cope with back pole pieces.
That membrane's properties will of course be changed as well, apart from being shorter of course.

Back pole piece:

An externally hosted image should be here but it was not working when we last tested it.


I will test this in my current motor.
Simulations looks good!

An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.




SLAM! two pole piece complete assembly:

An externally hosted image should be here but it was not working when we last tested it.
 
Hi Solhaga

I have tried to become member at faktisk.se to make a comment to your SLAM project.
At the registration site you are given a security question to prevent spambots
In SWEEDISH.

A comment to the other site. You can increase the field strength in the tweeter gap using this bar: solhaga bar tweeter.PNG
Are the iron bars saturated ?

Bernt
 
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