Diy AMT

[solhaga]

So you will the stack 3x15 mm rods where every other rod is prolonged over the gap?

 

[solhaga]

Thanks for the link.
Supermagnete has a N42 15x15x8. For 40 pieces incl shipping to Sweden: EUR 74.

 

[båndsei]

Every second layer is shorter.

Bernt

 

[solhaga]

Looks great! The way you stack them makes the pieces easy to make by cutting.
Have you simulated 20 mm width (3x20 mm steel) as well?
The air has long way to travel with 30 mm.

 

[båndsei]

My drawing has not the right measures.Diaphragm is 40mm.,and fieldstrength is measured at 30mm.length.
I have tried 20mm width,fieldstrength decreases.
Air has only to travel 15mm. with the 15mm steel i use.
I have ordered the magnets from Polen.
Bernt

 

[solhaga]

Yes, I got the dimensions of the magnets and the iron mixed up 😱

15x3 mm steel will be perfect.

I have some 10x4 mm from an abandoned bass panel project.
Thought I might give it a try along with the favourite magnet dimension 40x20x10 N42.
FEMM says the same field strenght as yours above.

 

[RayCtech]

Yes, I got the dimensions of the magnets and the iron mixed up 😱

15x3 mm steel will be perfect.

I have some 10x4 mm from an abandoned bass panel project.
Thought I might give it a try along with the favourite magnet dimension 40x20x10 N42.
FEMM says the same field strenght as yours above.

What field strength do you get with 10 mm and N52 ?
And with N52 and 6 mm ?

I bought some N35 because they was very cheap, but I did never test them due to they was only a fraction of the strength in practical use...

 

[solhaga]

The difference between the N:s is the square root of the division if I remember it correctly.
So N52 is 1,22 times stronger than N35. But you must analyze every circuit as there can be saturation (for iron it is 2T) that minimizes the fields.

 

[solhaga]

I have just ordered 9meter 3x15mm iron to make my new magnetsystem.

I was wondering if the iron you ordered has a perfect square profile or has it got rounded edges like mine.
If they are rounded and you stack them, the surface to the magnetes will not be flat.
Do you plan to sand the iron in order to have an even surface?

BTW, I finally decided to go ahead with this. Just placed an order of 40 pieces of 40x20x10 N42s.

 

[båndsei]

The iron i ordered has perfekt square profile and it is not much more expensive.App.150 dkr for 12meter.

Bernt

 

[RayCtech]

The difference between the N:s is the square root of the division if I remember it correctly.
So N52 is 1,22 times stronger than N35. But you must analyze every circuit as there can be saturation (for iron it is 2T) that minimizes the fields.

What field strength do you get with 6 mm and 10 mm iron and N52 ?

The interesting issues are:
1. How much iron are needed if N52 are used ?
2. How weak magnets can be used for a given iron to get maximum field strength ?

 

[solhaga]

I guess you are asking me to do the analysis.
Have you tried to use FEMM yourself?

To avoid cluttering this thread, perhaps I can mail you? I´ve sent you a PM.
Also uploading pictures to the forum takes time, so a mail conversation is better.
Maybe the end result can be posted here.

 

[båndsei]

I have made a "Kithara" model:

I have used my 6x10x70mm neodynium magnets,and tried with a 4mm thick diaphragm.
Sensivity is much higher,but I hane not made any measurements yet.
I am waiting for my new magnets to arive.

Bernt

 

[solhaga]

Looking great!

 

[solhaga]

@båndsei: I sent you a PM.

 

[båndsei]

I got my magnets from Polen.

I have tested the new magnetsystem with the 7,5mm thick magnets and 5mm.thick diaphragm.
It does not seem to improve the performances regarding THD and FR.
I have to make more measurements to be sure.

Bernt.

 

[solhaga]

Did you get higher excursion?

 

[båndsei]

It is not posibly to see any motion of the diaphragm course of the magnetsystem.

Bernt

 

[RayCtech]

It is not posibly to see any motion of the diaphragm course of the magnetsystem.

Bernt

I tested a Mark & Daniel AMT with a 1.5 volt battery and I cannot see any movement even if I used a 10x magnifying lens..
The Mark & Daniel AMT have ca. 700Hz lower bandwidth and ca. 89dB sensitivity.

With my AMTs the lower (-3dB SPL) bandwidth are ca. 100Hz (due to limited diaphragm area), but are designed for DC operation...
So there I can se the movement of the diaphragm with the naked eye as 1.5 volt moves the diaphragm ca. half xmax, and as every second fold / pleat moves in opposite direction the movement are then very easy to see..

 

[solhaga]

Perhaps it is the pleat folds themselves.
If a foldering "machine" with thinner plates where used, much sharper edges would be the result.
Shouldn´t it result in better compliance and also a more V-shaped folds of the diaphragm rather than U-shaped with your current method?
And as such compressing/decompressing the air better giving a higher SPL?