Diy AMT

[båndsei]

Hyab magnets Sweden.

This is from my new horn and 38x170mm diy amt.
I have a little problem with distortion.I think it can ´be solved with a new fixture for diaphragm,li´ke the one from Adam.

Bernt

 

[ticovski]

This is from my new horn and 38x170mm diy amt.
I have a little problem with distortion.I think it can ´be solved with a new fixture for diaphragm,li´ke the one from Adam.

Very nice! What is the sound impression?

How far was mic from AMT during measurement?

If I recalls correct horn is better with very smooth surface.

From this article:

http://profesional.beyma.com/ingles...ributions_improvement_Pleated_Loudspeaker.pdf

comes that AM1 and AM2 have fs around 1000 Hz so seems that is the main reason for not going below that fq. If we want to go lower we need more emitting area and more mass.

Are there any particular reason(s), apart from usable magnetic field, why AMT can not be wider? Eg. 10 cm wide or so?

 

[solhaga]

Yeah, I know about Hyab. Hard to get to their online web catalogue though.

Anyway, according to Hyab's product sheet they got Neodym blocks with:

lenght [mm] 2,0-120
width [mm] 2,0-50
thickness [mm] 2,0-15,0


I was thinking of the link you supplied that included this picture of an AMT motor:

Wouldn´t for example a 5x5x40 mm block be too fragile to be in front?

 

[båndsei]

I measured at 1meter and a bit off axis.I have not listened to music yet.
Neo's are not that fragile ,more like ceramic,so dont smack them.
You could try to simulate a system with 5x5 iron in front and back,and neos in betwene.

Bernt

 

[solhaga]

Yes, iron in front is one thing.

I was curios about the configuration SEdwards was talking about with "planks of neos across the front" and I thought the picture showed just that.

According to my first simulations it is hard to get an even field in the gap.
It is much simpler with iron pole pieces. But I would really like to be proven wrong.

Anyway, keep up the good work båndsei!

 

[SEdwards]

One thing that I would like to try is to have less field strength at the edges of the diaphragm where it is fixed. I think that less distortion may be possible this way. Plus if the loudest sound is from the center dispersion should be better. That's one of the reasons to consider neo planks.

The horn looks really cool.

 

[solhaga]

Sorry for the crappy ascii art, but could a formed iron pole piece do?
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At the edges the field will be farther away and thus weaker.

Or you can make a compound "plank" suspended with non-magnetic steel screws in the beginnng and at the end.

Just my 10 öre (Swedish for cent).

 

[solhaga]

"Or you can make a compound "plank" suspended with non-magnetic steel screws in the beginnng and at the end"

Sorry about that, it won´t obviously not work.

 

[båndsei]

I have bee able to make this tool:

By mistake it is made with 2mm alu,my idea was 1,5mm. Maybee good for large amt's
Depth is variable, length max 175mm.
I have listened and adjusted the horn/sub system 800 hz 48db crossover.I might have another bas/sub,this one is too slow.

Bernt.

 

[SEdwards]

Love all the progress. I was looking at plexiglass as a possibility for the planks, since you can score and snap it with straight lines.

Any update with the THD? 2 and 1/2 weeks and I should be able to start building stuff, can't wait.

 

[båndsei]

I had forgotten that measurement.Here it is:

Green is covered 20mm at each end.
Very small difference.
I made a test with my new tool.Plates are too thick.2mm gives a spacing off 4-5mm.,and it have to bee app.2,5mm.
The fixture with the diaphragm has to be in the oven 20min. at 175 c.
Plexiglass gets soft and bendy at that temperature.

Bernt.

 

[båndsei]

I have made a new diaphragm with 1mm. alu plates for the tool

It is very symetrical .And it keeps shape,meening i have to drag a bit to fit 32mm.with.

Bernt

 

[solhaga]

Impressive!

So you have alufoil across to keep the shape?

 

[båndsei]

No.Not nesesery.The mylar keeps shape as it is warmed up and cooled again.The stripes is there because tape is double there .My tape is 50mm.wide and i use 4 to get 160mm.

Bernt

 

[solhaga]

So you have 50 mm wide mylar tape? How thick?

The mylar keeps shape as it is warmed up and cooled again.

Yes of course. That´s how it used when making wings and fuselage for air plane models. In fact, I order my mylar from a micro flight diy supplier here in Sweden.

How do you heat it up, bake the whole package in the oven?

 

[båndsei]

Mylar is the same as polyester or PET.My tape is 12my with 8 my adhesive.I place it all in a oven for 20min. at 175' c.

Bernt.

 

[solhaga]

Thanks, Bernt.
Do you buy the tape or make it yourself?

When I saw your method I thought of nail strips. They have predrilled holes, can be down to 0,7 mm thick and can be cut in any length:

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

 

[båndsei]

I bought it here:Specialtape & klæbestoffer
Nail strips might do it.

Bernt

 

[solhaga]

Great. I´ll check if it can be obtained in Sweden.

Looking at the site it says:
"We can supply tape in standard widths as indicated below or in widths according to specifications."
and according to the data sheet:
"Widths from 1/4” to 15.5"

So then you can have the tape oriented along with the gap and you don´t need to overlap.

 

[jay53]

Mylar is the same as polyester or PET.My tape is 12my with 8 my adhesive.I place it all in a oven for 20min. at 175' c.

Bernt.

Bernt,

This is very interesting. I just bought AMT diaphragms to build the Tweeters.

Are you using the Photoresist to develop the aluminum traces on the PET or using Aluminum adhesive backed tapes ? I presume the Mylar 3M tapes are to protect Aluminum traces.

Jayant