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Chris Bolkan 20th April 2007 07:16 AM

Hi all,

I apologize in advance if this topic has been addressed previously. I looked but didn't find anything.

I have collected a set of old amt1 towers (with the TL bass box) and a set of regular ported box AMT1's, both the same vintage. Amazingly the AMT's work in both sets, so I don't have an immediate need to dive into replacement diaphrams.

I have two questions if someone will help me.

1) Are the signals out of the front and back of the AMT's in or out of phase? I can imagine it being either way depending on what is taking place with the motion of the diaphram. I just can't figure it out.

2) Both models came with the same woofer originally. One of the pairs has some el-cheapo replacement woofers that work, but not very well. The other set has original woofers with no surround left. I am looking for drop in replacement woofer recommendations. I've looked a bit but haven't been able to find TS parameters for the original woofer to help me find an adequate replacement.

Thanks in advance!

Chris Bolkan

SilverFox 20th April 2007 11:56 AM

I can't help you with the drop-in replacement question, but I can tell you that:

1. The Heils do indeed have a "phase", so if correctly wired, the front of the Heil should be facing the same direction as the woofer.
An easy way to tell if the Heils are wired correctly is to just trace the wire colors back to the Xover.

2. Speaker surrounds are really easy to do yourself, so if the cones are in good shape, just replace the surrounds rather than the whole driver.

And by the way, you're lucky that the AMT's have good diaphragms because there are NO equivilant replacements anymore.
The closest you can get would have to be ordered overseas, and that diaphragm's frequency specs are different than what you have and do not handle frequencies as low as yours.
Take care of them Heils. If you ruin 'em, that's it.

Chris Bolkan 21st April 2007 01:18 AM

Hi Mark,

So from what you say, I assume the diaphram acts as a dipole radiator with the front and back waves being out of phase, similar to a conventional speaker out of it's box, or a magnepan. The reason I care is it's good information to know when considering placement and room treatments.

As for the woofers, only one of the OEM woofers is refoamable leaving me with three slots to fill. I still need TS parameters, or recommendations on a suitable replacement woofer. Seems to me somebody must have done this homework considering the vast number of the OEM woofers have failed.

Still hoping someone can help.

BudP 21st April 2007 02:00 AM

Hi Chris,

Go to this specific link and look at what C2C Thomas is doing with his Heil tweeter. Not that you should do this, but he may still have the original woofers and you can PM him and ask to buy them. Nice fellow, very talented and thoughtful.


I am sorry that link seems busted. Go to post 200 of this same thread ,on page 20, at the bottom of the page.

rdf 21st April 2007 02:16 AM


Originally posted by Chris Bolkan
So from what you say, I assume the diaphram acts as a dipole radiator with the front and back waves being out of phase, similar to a conventional speaker out of it's box, or a magnepan.
Front and rear radiation are in phase, bipolar rather than dipolar. The tweeter works by squeezing and extending an accordian-like structure symetrical front and back. I don't know if other structural differences make for a prefered front face.
One suggestion, closely examine your diaphrams backlit. It wasn't usual for a bit too much high power exuberance to melt them.

BudP 21st April 2007 03:07 AM


And here is a different understanding of the Heil. The Heil is not exactly a dipole or a bipolar emitter, but mostly, since air is rarefied on one side while being pressurized on the other side of the mylar sheet, it is technically a Dipole, just as a permanent magnet is a Dipole. See this site for some descriptions and pretty good diagrams of a bit later production than the ESS model.

The Heil drivers actually perform their activity in a kind of swaying motion. All of the pleats open on one side while the pleats on the other side close. The diaphragm actually "sways" away from the pressure wave it is creating, which, to a degree negates both the positive pressure wave and negative pressure wave. This acts, ultimately as a sort of mechanical feed back mechanism and does linearize the emitted wave front, across the diaphragm, just as it emits into the air from the final edges of the pleats. Weird to wrap your head around for sure.


rdf 21st April 2007 04:05 AM

Not sure I see how the diaphragm can sway in the gap (it's been decades since I last repaired a driver) but it appears you're right about it being dipole. Describing it as an accordian is misleading.

Chris Bolkan 24th April 2007 07:17 AM

Yes got it. Pleats on one side close while those on opposite side open. Makes sense and the only way the device could have any sort of inherant linearity. So I vote dipole. Thanks for the help!

Now, does ANYONE have any information on suitable replacement woofers OR perhaps the specifications of the original 10 inch woofer? Or as an alternative does anyone have an original woofer they would be so kind as to measure the free air resonance of? I would really appreciate it!

Again, Thanks


frank ziel 24th April 2007 11:51 AM

try here, maybe they have what you are looking for:

c2cthomas 24th April 2007 03:59 PM

2 Attachment(s)
Hi Chris,

I have 1 10 inch spare woofer that is sitting on an ESS AMT2 that I scrapped the Heil tweeter off of for another project (see Walsh 5 remakes thread). Measures 9 inch's from cone edge to edge and 10.5 from frame edge to frame edge.

It is in working order and you can have it for shipping cost. :Present:
If interested PM me for details.

BTW - ESS speakers were never really renowned for their bass response and most people that wanted some "real bass" would slap in some JBL's and decent x-overs. But that was back in the '70's and there are more decent woofers to be had now - the problem being to match up that strange flat flange area ESS seemed to insist on using.

I always sort of suspected they did that so you had to use their woofers - but then I tend to suspect such things.

The towers were always my favorite model of the ESS line and had the best bass response and a fuller sound than the other models. They need good clean power (100 watts with good reserve) to sound their best.

As mentioned by others - be careful with the Heil's - ain't no replacement parts to be had!. :censored:

I see from your bio that you do QA. I even know how to spell QA! I go Q and then add and A! :joker: Ok - just shoot me! :headshot:
I ran the QA department at one of the places I worked at.

Hope this helps!


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