The Neil Davis Heil AMT

[srinath]

OK so how is the block magnet in the right 1/2 of the first pic sitting inside the unit on the left 1/2 of the first pic.

Also how did you arrive at the third pic from the second.

Anyway the heil I have has the grill in front and the slots on the steel inside the thing perfectly staggered, the holt in the front hits the crest in the back one, and vice versa.
Anyway drown the ribbon in magnetic field is the name of the game.
Cool.
Srinath.

[Steve M]

Originally Posted by srinath

OK so how is the block magnet in the right 1/2 of the first pic sitting inside the unit on the left 1/2 of the first pic.

Also how did you arrive at the third pic from the second. Srinath.

The large ferrite bar magnet sits flat stuck magnetically to the steel housing of the whole tweeter assembly, directly behind the ribbon.

The second and third pics are to simply show the two alternatives discussed, the first shows the steel threaded pole piece, the second the alternative where the pole piece is substituted with five magnets - both setups work and sound good.

Steve.

[paulfx]

Crzy8z:
"How much more would the latest magnets offer over the ceramic/ferrite ones I have now?"

4 or 5 times the flux you have now, my friend!

[paulfx]

Srinrath,
Hello from Containment Area for Relocated Yankees, as they call Cary, NC! May I quote you?
“1. They are a tweeter I guess ? They compare to a emit ? I am thinking along those lines cos they too have a diaphragm.”
The Heil is a tweeter first. (What's an emit?) Midrange territory gets expensive and soul-trying, although crzy8z’s upper mid AMT made my pupils expand when I saw the pictures. Making one’s own diaphragm seems to be a rite of passage, but I saved a bunch of nerve-wracking time by buying a stock replacement.
“2. The basic idea is magnetic north and south poles staring at each other in a tight space with a electrically energized diaphragm in the middle. It vibrates and makes sound. How would it work with a thinner wall steel tubing. The reason I ask that, it will be a lot easier to work with a thinner walled steel piece than the thick wall one.”
Your first sentence is correct, and it vibrates and makes sound out both the front and the back. The eternal paradox of the Heil AMT is the need to have magnetic poles and emitted sound exist in the same volume. Here’s where the dome tweeters have the advantage. In the front at least, I want nothing, but I can’t have that, there has to be a pole. Most working Heils have pole pieces that are deep but not wide to block as little of the fluid, extruded sound as possible, which explains why thin walled tubing might not be loud enough. Then you need to have the pole pieces as ferric as possible to direct the magnetic flux to each side of the diaphragm, so aluminum is out. They have to be thick for the same reason. If I could have gotten my hands on iron tubing and bars I would have used them. I used the soft steel because that was the softest ferrous metal that Metals Depot sells in small quantities. If you could get iron, not steel but iron, with your background you could whittle an AMT like a good walking stick.
“3. The steel tube, if you had left one wall a little longer instead of cutting it off @ 3, say it was 3.5 inches for that front side and 3 inches for the back side it would have made it easier to mount. No need for the extra angle piece on the sides. Would that work.”
Oh…actually that would have worked famously! Fastener on the top, fastener on the bottom. Too late now!

[srinath]

Oh well ... the points are well taken and will be shamelessly used when I cobble up my heil.
So yes, neodymium magnets put in fat way horizontal, reverse magnetism contained by a couple steel strips bent into hair pins, or I'd use 304 stainless which is magnetic but stainless.
Excellent, infinity emit ribbons were my tweeters of reference, of course I got my own emit killer of late.
Cool.
Srinath.

[paulfx]

Steve,
I'm gonna quote you -
"I just came across this thread. Is anyone still interested in electromagnets for speakers? I have done this, and may be able to answer some of your questions."
We're definitely interested in keeping from getting hurt from the NIB magnets that are so tempting but so dangerous. Magnetic door locks designed for large doors and gates might be cheaper than an array of NIB's.
Your experience would be applicable to AMT's even if your emag speaker was electrodynamic or otherwise conventional so -
Did you experiment with different current levels, and what happened?
How stiff was the voltage source? There's been some mention of power supply quality and wether it matters.
Were turn-on transients a problem?
How did this thing sound, Man?
Paul

[Steve Dunlap]

I built a ribbon using electromagnets. I was working in the product development lab at a company that wound their own transformers, so I had access to pre wound coils of different sizes. So, what I observed:

The more turns on a coil, the more ampere turns you get for a given current. I used 4 800 turn coils wired in series for one ribbon to give me 6,400 ampere turns total. I will try to draw up a picture so you can get an idea what it looked like. I will post that later.

You want to use the lowest voltage that will allow your current to flow to keep heat dissipation as low as possible.

I used a 2 amp current source for the supply, and the magnetic field was very high. I had no way to measure it, so I don't know how high, but you could not remove the pole piece while the current was on.

Turn on transients were not a problem because of the constant current source. I don't think the choice of iron is very important, but I used transformer laminates.

It sounded like a ribbon, why wouldn't it?

[Steve Dunlap]

Here is a crude drawing of what I did. The drawing on the left shows a front view with a faceplate for mounting. The second is a side view and the third is the back view.

[paulfx]

To do a powered AMT midrange. I really should finish my other audio projects first. As big as that other beauty from the nineties on this thread. What I's like to do is try to design it for a resonant frequency. Come to think of it, has anyone seen any research on Thiele-Small parameters for these beasties?