Diy AMT

[båndsei]

I have been inspired from this tread in a Danish site:HIFI4ALL Forum: Lyd laboratoriet
And have made this one:

My second attempt:

Here how the magnets are placed on two 10x10mm.square iron.

More later.

Bernt

 

[tyu]

Thank for the info...an pic...vary cool......goodluck

 

[studiotech]

Nice work! Did you buy the diaphragm already made?

Greg

 

[båndsei]

Yes, I bought 2 diaphragms from ESS amt 1 app.100 euro. each.
Magnets are the same as i always use 6x10x70mm. 8 pcs. app.3 euro each.
Bernt.

 

[Lgrau]

Hi Båndsei,

Cool project ;-), did you already make a stereo set? and how's the sound compared to your Bipole Ribbon speaker?

 

[båndsei]

I like them.They added more "air" on top,and a bit "cleaner".Sensivity increased by at least 6-8db.Impressive for the amount of magnets.My omnipole´s used 24 magnets each.
Yes i have a stereo set,it`s not that difficult to build.I would like to attach immages from FEMM directly,but how is it done?

Bernt Båndsei.

 

[båndsei]

Here is mesurement at 40cm.distance.
Distortion increaces below 1.1khz.Mesurement is limited at 500hz. 48db.

Bernt.

 

[solhaga]

Very interesting.
How varies the flux in the gap?

I would like to attach immages from FEMM directly,but how is it done?

If you are on Windows, Snipping tool?

 

[båndsei]

This shows fieldstrength across the diaphragm 40mm. width.
Be free to ask other questions,I am willing to share.
Is snipping Tool part of office pack?

Bernt

 

[solhaga]

The Flux variation in the gap is more or less what I got in a narrower 25 mm gap with N42 NEOs:

I assume that the ribbon comprises aluminium strips, do the widths of the strips vary with were there are in the gap so that the force will be more even through the gap?

The frequency response doesn't seem to have the 2 to 6 kHz hump, this is probably due to the wider gap and the tilted positioning of the NEOs together with the pipe isolation leaving no narrow cavity as with ordinary ribbon drivers.

What resistance do they end up with?

Snipping Tool is a part of Windows Vista and 7

 

[Jack Caldwell]

Here is mesurement at 40cm.distance.
Distortion increaces below 1.1khz.Mesurement is limited at 500hz. 48db.

Bernt.

Nice work! I like the way it looks, especially on your omni type speakers. The measurements look very good also. Have you been able to quantify the sensitivity at 2.83V?

 

[båndsei]

It´s a prefabricated diaphragme and th with of the strips all the same.
The magnetic field is different from the one used for ribbons.

The magnetic lines does not cross the gap,I hope the picture helps.
Resistance is 7.2 ohm.

Bernt

 

[båndsei]

This shows Aurasound NSW2 2" unit and my diy Amt.
Recorded at same level and settings.It is messured at 40cm.distance.Amt is a dipole and level should be compared at 2-3m. distance.
Aurasound has a sensivity of 84db, 1w. 1m. 1000hz.

Bernt.

 

[solhaga]

It´s a prefabricated diaphragme and th with of the strips all the same.
The magnetic field is different from the one used for ribbons.

The magnetic lines does not cross the gap,I hope the picture helps.
Resistance is 7.2 ohm.

Bernt

Yes, it would seem that the flux is even in the y-plane at any given point in the x-plane, at least for any practical excursion. That's really great

If you have access to the strip's terminals you could have the outermost strips, the ones in the strongest flux, coupled in parallell.
I don't know how many strips there are, but let's say the pattern can be 3 3 2 2 1 1 1 1 2 2 3 3 to get an even force along the diaphragme.
You would still be above 4 ohms?
But perhaps the diaphragme is rigid enough, so it doesn't flex as it moves in the field.

 

[båndsei]

Here is a nude model!!

My latest one.It performs almost like the ones with "horn"

Mesurements with and without "horn"
I can´t make changes to the wiring of the diaphragm as it is bought from ESS Heill amt.
Bernt

 

[solhaga]

Quite interesting setup. I'm sure the sound stage is great.
Have you considered moving somewhat away from the corner?
In my setup the ribbons are 1,5 meters from the back and 1 meter from the side wall.

 

[båndsei]

My room is only 3 meters wide,and i use it for TV as well,so I must make compromises.

Bernt

 

[paulfx]

Side Flux AMT

Nice!
I love the way it eliminates diffraction from a diaphragm that is usually buried under iron prongs. From the other comments on this thread, more consistent output from each diaphragm pleat could be had if we could flow less current through the outers and more through the inners. To do that would require constructing the diaphragm. Could the resistance of each conductive strip vary with the flux levels shown in the graph, so each pleat has about the same loudness?
By the way, Neil Davis has written in Audio Amateur magazine on the topic of putting together custom AMT diaphragms. Calling Mr. Davis?
Also by the way, we have an Lgrau from Denmark here on diyAudio. Gentlemen?

 

[solhaga]

..Could the resistance of each conductive strip vary with the flux levels shown in the graph, so each pleat has about the same loudness?..

Perhaps we are saying the same thing, but if the strips are in series, the same current will flow in each strip no matter its individual resistance.
A wider strip means less current density and thus maybe the same force to the diaphragm in a higher flux as a narrow strip in a lower flux.

I was also wondering if there are any DIY AMTs out there.

 

[båndsei]

Here even more nude.

And seen from the top.

I have the same thought´s:can i improve the design?I don´t think i can.I would like to go deeper,but i think all have been tried, as it is what everyone wants.
It performs perfect and messures good too.

Bernt