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Old 4th May 2013, 07:49 AM   #111
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You could cower more surface with alu,it might reduce resonances.Weight on a normal diaphragm lowers resonance and eficiensy.
How effective is your Amt?
How wide are the traces without alu?
Do you know how to attach measurements ?

Bernt
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Old 4th May 2013, 03:03 PM   #112
solhaga is offline solhaga  Sweden
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Quote:
Originally Posted by båndsei View Post
You could cower more surface with alu,it might reduce resonances.Weight on a normal diaphragm lowers resonance and eficiensy.
I don´t think that I can have more percentage alu and besides the efficiency is good enough as it is.
What about low frequency response?

Quote:
How effective is your Amt?
I don´t know in absolute numbers as I have no calibrated microphone or SPL-meter. But I´d say they are 3 to 6 dB better than my line arrays.
Quote:

How wide are the traces without alu?
It is 7 mm alu with 3 mm gaps.

Quote:
Do you know how to attach measurements ?
Yes, and I will post some soon (just gonna make just one more adjustment ...)
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Old 4th May 2013, 04:21 PM   #113
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I dont have ideas for improvment yet.
If you want a calibrated mic, Mini DSP have one,and you can buy it from Norway:
AVshop.no / minidsp UMIK-1 USB målemikrofon
It is able to measure SPL with REW.
More details here:http://www.minidsp.com/images/docume...20-%20Umik.pdf

Bernt

Last edited by båndsei; 4th May 2013 at 04:24 PM.
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Old 5th May 2013, 06:39 AM   #114
solhaga is offline solhaga  Sweden
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Still problem with resonances.

These are only due to the cavity´s dimensions, it´s a whole lot of air being compressed and decompressed.

The frequencies I´ve noticed to produce unwanted vibrations are around 230, 460 and 510 Hz.
The cavity is 160 high and 120 mm broad. The iron rods in front and back of the element is 10 mm times 3 mm and the gap between them is also 3 mm.

I´ve discovered that putting my hand in front or at the back of the element reduces the vibrations, maybe som cloth behind the element can be a remedy.

For now the membrane will be glue completely at the top and the bottom; the vibrations are hardly noticeable during listening.
But of course, knowing that they are there is annoying enough to hinder the listenening to be completely relaxed.
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Old 5th May 2013, 07:19 AM   #115
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Location: Outside Copenhagen
Hi Solhaga,

Some AMT´s have a thin piece of felt placed at the back of the AMT to cope with unwanted movements of the diaphragm.

As you have discovered, this might be worth trying-out. If possible, you could try with, say, 2-5 pieces of felt with different thickness.

It´s cheap and worth trying. Hopefully it will bring you closer to the finished DIY AMT.

Karsten
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Old 5th May 2013, 08:02 AM   #116
solhaga is offline solhaga  Sweden
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Thanks Karsten for your insight.

At the least I now know that I am not barking up the wrong tree. Click the image to open in full size.
Felt it is then, hopefully it isn´t going to ruin the soundstage too much.
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Old 5th May 2013, 08:40 AM   #117
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Can it be breakup of diaphragm, distortion ?
If you use a tone generator,and hit the frequense ,it might be easïer to locate the bussing or vibrateings.

Bernt
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Old 5th May 2013, 08:46 AM   #118
solhaga is offline solhaga  Sweden
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I´m using REW as a tone generator in order to find the vibrations as you suggests.
It is always the same frequencies on both speakers.
Just putting my finger on the spot source of vibration dampens it.

Last edited by solhaga; 5th May 2013 at 08:51 AM.
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Old 5th May 2013, 09:59 AM   #119
solhaga is offline solhaga  Sweden
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The felt is dampening the unwanted vibrations but not enough.
It is the fastening of the membrane on the sides that are the main problem.
The first and last pleats doesn´t adhere to the motor enough.
If I could get some glue between the iron rods the vibrations will probably get away.
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Old 5th May 2013, 07:46 PM   #120
solhaga is offline solhaga  Sweden
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Default Bummer

Not coming to terms with the unwanted vibrations made me re-evaluate the membrane.
Should I make in slimmer, perhaps 6 mm in the 10 mm gap?
Should I make the folds further apart, perhaps 4 mm between the pleats?

Then I came to think of the current in the magnetic field thus producing the forces that makes the pleats compress and de-compress.

What about the forces on the part of the aluminium conductor that are not supposed to produce any sound?

At any given moment, that is direction of the current, every other pleat moves left and the other right thus producing the every other fold to either compress or de-compress the air, but the horizontal conductors at the top and the bottom moves in the same direction, let´s say down. When the current switches the horizontal conductors at the top and the bottom move in the other direction, that is up.
The membrane is being moved up and down with the music.
That shouldn´t do any harm if it wasn´t for the fact that the membrane is fixed at the top and the bottom.

So either the membrane should be free to move up and down, but that is difficult to accomplish as the membrane needs to be fixed so it doesn´t touch the iron rods, or the horizontal conductors must be out of the magnetic field.

So I need a wider membrane and thus a wider film or make some other arrangements to get the horizontal conductors out of the magnetic field.

Back to the drawing board...

(Please correct me if I am wrong!)
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