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Old 20th March 2013, 09:59 AM   #221
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Join Date: Sep 2007
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When the 1.5 volt battery test are performed you can use your ears...
The "sound" when the battery are connected should be equal to the "sound" when you disconnect, and also the "sound" (this is difficult to describe..) itself should be "clean" (a pulse that start and stop without ringing..).

With my own AMTs I can get a similar "sound" when I connect a coil in parallel and thus changing the "properties"..
Then the physical movement of the diaphragm are more similar and the "sound" similar and best described as "ringing" - like when you tap on a tight drum skin and not like when you tap on a solid surface.

Both my AMTs and dynamic 8" drivers are made for DC operation and the 1.5 volt battery moves the diaphragm / cone and it stays there till the 1.5 volt are removed - then the diaphragm / cone moves back to "neutral" - changing the polarity - then the diaphragm / cone moves in the opposite direction and stays there till the 1.5 volt are removed..

This behavior you will not find in ordinary designed AMTs or dynamic drivers.
What happen there are that the 1.5 volt will try to move the diaphragm / cone (to the intended position the DC voltage was supposed to cause), but mechanical and electrical properties of the design will cause the diaphragm / cone to be repositioned back to closer to the neutral position (creating a spike / pulse with possible ringing at start and stop of the movement). When the 1.5 volt voltage are removed the diaphragm / cone will not just return to the neutral position, but the "forces" that have caused the misalignment will create ringing as the diaphragm / cone are forced to cross back over the neutral position etc. etc..

The properties / "forces" that destroys the DC performance are part of what limits the LF response.
I have observed that most AMT designs are created with basis in the Heil patent and are thus mostly limited in LF to between 1kHz and 2kHz with both SPL and THD under control. By tweaking the Heil design I have not really seen any AMT that can manage to have both SPL level and THD under control below 1kHz. There are designs that can go lower than 1kHz, and I have tested what they are good for in reality.
As Mark & Daniel made AMTs based on the Heil patent that was good sized and should run well below 1kHz I bought a pile of them and made a OB / line source baffle where I connected them in series / parallel with first 8 units pr. side and then 16 units pr. side. As 500 or 700Hz (if I remember correctly) was the LF response of one unit - then the increased surface area should extend the usable LF response at least down to around 200 - 300Hz in theory.. But that was in theory as in practical use I ended up with 2kHz (using -6dB/oct filter) as the lowest usable LF extension.. Trying to play as full range without filter was a complete disaster due to the diaphragm was shorting "all over the place"..

I ripped a couple of them open and the folding style and resulting very low xmax would cause shorts between the folds and thus prevent any real low frequency use. There was other properties that also would limit the low frequency response.

As I never have made any copy of the Heil patent I do not really know the limitations and possibilities of that design...

Last edited by RayCtech; 20th March 2013 at 10:06 AM.
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Old 20th March 2013, 10:55 AM   #222
solhaga is offline solhaga  Sweden
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Thanks for your elaborate reply, RayCtech.
Again you put it in words what I only have a hunch about.

DC characteristics is a good indicator for the LF response and/or max excursion.
One shouldn´t need to put together a whole diaphragm to evaluate different solutions.
It should also be possible to make a simple "magnetometer" comprised of a probe coil that is moved at a constant speed through the field.
Connect to a voltmeter or a VU-meter and you can do some relative measurement. Like how sparse the rods shall be or if the field is un-even.

So what does a non Heil AMT look like then? Anything you would like to share?
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Old 20th March 2013, 12:45 PM   #223
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Quote:
Originally Posted by solhaga View Post
So what does a non Heil AMT look like then? Anything you would like to share?
The exterior looks are quite similar due to the used slot loading principle and the basic electro magnetic engine principle, but every single property of the design are a factor of 2 to 10 different - so a 1:10 / 10:1 or maybe closer to 100:1 / 1:100 overall design difference are a reality.

To extend the LF response alone 10 to 20 times (from 1 - 2kHz to 100Hz) cannot be achieved without some radical changes. I will soon power up the first bass AMTs where the goal was to reach 20Hz with full SPL. From the design view they should work as intended, but who knows - there may be some practical limitations I have not foreseen that comes into play and become a "show stopper". The bass AMT design was finished a long time ago and the 100 diaphragms that was made then have never been folded or tested. It is not due to I expect the bass AMT to be a failure I have not finished them, but due to I already have both a pure AMT setup that plays full range, and also a hybrid setup with my 8" taking care of the lowest frequency octaves, and it is simply more fun to design something new and totally different then to do time consuming assembly works.
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Old 22nd March 2013, 03:11 PM   #224
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I used to glue the diaphragm with melt glue:
[IMG]Click the image to open in full size.[/IMG]
[IMG]Click the image to open in full size.[/IMG]
I have mounted a small tube and pressed it to 0 shape.
In my newest diaphragms the pleats only have a with of 1mm. ,and I want to glue it in the folding tool.
I have tried several types of glue,but the problem is either it is too thin or too heavy.
Silicone is ok,but needs to be pressed to get all in.
Now i use this:
[IMG]Click the image to open in full size.[/IMG]
[IMG]Click the image to open in full size.[/IMG]
I have grindet the needle and pressed it.It is the largest 1.2mm. and a small pump 2ml.

Bernt

Last edited by båndsei; 22nd March 2013 at 03:14 PM.
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Old 26th March 2013, 06:23 PM   #225
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Someone´s got a bigger brother:
[IMG]Click the image to open in full size.[/IMG]
Have not measured yet.
It is a 40x170x6,5mm diaphragm.

Bernt
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Old 29th March 2013, 10:35 AM   #226
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I have decided to make a pair of this one:
[IMG]Click the image to open in full size.[/IMG]
Magnetsystem is made from 2" iron pipe (60mm.)and 12x12 mm. iron
Magnets 70x10x6mm 8 pcs.and 30x10x6mm 4pcs.
[IMG]Click the image to open in full size.[/IMG]
I have to make 2 new diaphragms too.

Bernt
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Old 30th March 2013, 10:31 AM   #227
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My jealousy is overwhelming. I am hoping and praying to have time to build when I move back to Australia in the next 3 months - the opportunity keeps getting pushed back.

But at least I will have learnt some new tricks from you by then.
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Old 30th March 2013, 11:11 AM   #228
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It seems you are allright,although you are a bit jealouse.Pardon my English.
I like to share all my ideas,some are not a ceeper,but I think I am close to what is possibly to make with this size of diaphragm.
The change in my last,or maybe latest diaphragm is 30 stripes or leads,in a 40x170x6,5mm frame.I will show how the frame is build later.And the folding tool too.


Bernt
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Old 30th March 2013, 01:26 PM   #229
WrineX is offline WrineX  Netherlands
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looking good again Bandsei, i only could not figure out what the glue is for?
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Old 30th March 2013, 04:35 PM   #230
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The glue is used to keep the pleats aligned,they are only 1mm wide.
I glue it in the tool to keep distances right.Might have to glue both sides.

Bernt
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