[steve f]

Hi Albert,
I feel like a student in one class asking the teacher in another class for help with my homework. It involves the workings of the Heil driver. You are the authority, and were Dr. Heils assistant. I tried the web but couldn't find indisputable evidence. I believe the Heil driver is a dipole. Others claim it to be a bipole driver. I couldn't even find a polar response chart except for one that had a speaker with an eclosed the back wave. Help please.

Steve

[JackD201]

Here's a wiki link for you Steve

http://en.wikipedia.org/wiki/Air_Motion_Transformer

edit. Oops you wanted non-disputable. Sorry. I'll look some more.

[JackD201]

In the product literature of ESS the open backed Great Heil it says it is a dipole. Funny. I would have thought that it was a bipole.

http://www.parts-express.com/pe/showdetl.cfm?partnumber=264-600

[steve f]

Thank you Jack. At first glance, I thought it was a bipole too. I now believe that the round portions of the U shaped pleats act as surrounds for the contracting and expanding parts.  As some expand the other side contracts. Therefore a dipole, I think. A polar response chart, or the words of Albert or Nelson Pass, both worked with Heil, would settle a friendly dispute. The only chart I found was of a closed back unit. I appreciate your participation.

Steve

[Norman Tracy]

Steve,

I believe the answer to your question is "it depends".

Specifically the basic pleated structure that is the heart of Dr. Heil's invention is a dipole. Like a flat ribbon or even a cone while the front is pressurizing air the back is rarefying it and on the second half of the cycle front is rarefying air and back is pressurizing.

The "it depends" part comes into play when you go from the basic operating principle to the implementation of an actual driver. The original model in the AMT-1 floorstander was very much a dipole sitting on top of the woofer box with it's big horn'ish shaped pre-neodymium magnet structure open on the front and back. Later models from Heil (the company) had unipolar Heil drivers as tweeters in bookshelf/stand mount designs. The drivers available today come in both dipole and unipolar models. Of course the unipolar versions have chambers like a dome tweeter that catch and absorb the rear wave (we hope, in the real world some will bounce back out the front).

[wisnon]

That is my understanding too Mr Tracy and I got the same info from Martin, the close friend of Dr Heil and the owner of the Heil AMT brand, known as Oskar in North America.

[Albert Von Schweikert]

Sorry I didn't see this thread quickly as I have been working 18-hr days getting ready for RMAF. 

Mr. Tracy describes the driver correctly. The original AMT-1 was a 12" two-way with a crossover point of approximately 1kHz, so the large AMT was actually a low-range tweeter that sounded very dynamic, and it was indeed a dipole.  The 12" woofer on the front was "loaded" by a rear mounted passive radiator, so the bass system was also an interesting device.  Unfortunately, that passive radiator wasn't quite as clean and fast we we would have liked and sounded a bit boomy at times.
That first version of the AMT-1 is available from Parts Express as shown in the link above. Unless you need extension above 17kHz, the original AMT is a fabulous device, with high output and fairly wide bandwidth (800-Hz to 17kHz). The sensitivity was higher than a dome tweeter and it handled quite a bit of power before burning.  It was eventually horn loaded and used in PA systems, but the failure rate was excessive and eventually was discontinued.  The PA version used a sealed back and thus could not be considered to be dipolar or bipolar, and as Mr. Tracy explains, was a monopole.

Towards the end of my tenure at ESS Laboratory, I built a prototype using a smaller AMT which behaved as a super tweeter which was placed on top of the larger standard folded ribbon, extending the response to above 30kHz, but it was never put into production.   Oskar also asked me to design a 3-way system using a cone midrange driver and a smaller version of the folded ribbon that had a sealed back, and that was the best sounding version of all of the various ESS models that I worked on.  Unfortunately, that 3-way version wasn't put into production either, due to various economic issues and the departure and eventual death of Dr. Heil.  He was one of the most influential transducer designers that ever lived, in my humble opinion. If you're a part time speaker builder, you owe it to yourself to try the AMT device! 

[steve f]

I thank you, both for your reply, and historical insight. I had an early pair of the AMT drivers, and they are a fascinating driver. I hope RMAF was a great success for Von Schweikert Audio. 

Steve

[sebrof]

That first version of the AMT-1 is available from Parts Express as shown in the link above. Unless you need extension above 17kHz, the original AMT is a fabulous device, with high output and fairly wide bandwidth (800-Hz to 17kHz). The sensitivity was higher than a dome tweeter and it handled quite a bit of power before burning. 

Great stuff Albert, thanks for the information. Your post is screen-shotted and saved in my Heil folder on my hard drive for future reference 
I got a used pair of the original (I assume, look like the PE linked) and used them with a 15" Altec 416. Crossed in 3rd order at 1200 Hz I find them to be a fantastic driver. I had never heard them before but a friend recommended them to me, quite glad he did.

[James Romeyn]

Thanks to Albert for sharing his experience with Dr. Heil.

I had the rare pleasure of having lunch with the late Dr. Heil, who I met through a mutual acquaintance named Albert Brown, a long time friend of Oskar.  Dr. Heil was a kind and gentle person and I enjoyed my brief meeting with him.  Albert mentioned that ESS (absolutely no association with the current ESS company) may not have quite lived up to the full spirit of their financial obligation to Oskar. 

The AMT-1 may have been the greatest high-end audio icon of its day.  I practically drooled over the spot-lit AMT-1, in the otherwise dark Pacific Stereo high end rooms in the back.  IIRC a sales man had to escort you into those rooms.   

Albert: is it correct that any single driver must be a dipole?  I don't see any mechanical way one driver could be a bipole.  All the bipoles I can think of employ separate drivers for rear radiation: Definitive Technology, Bose 9, Audience, Mirage...

Also, a brief history of the terms "dipole" and "bipole" would be appreciated.  I always wondered about the "b" vs. "d" and the history behind the terms.  One manufacturer confused the terms and labeled their bipole a dipole. 

Thanks! 

 



 

[wisnon]

I think bipole vs Dipole has to do with the sound wave propagation???

In any case, here is more interesting info on the Heil transducer:
http://www.precide.ch/eng/eheil/eheildetails.htm

and the current speakers made by his close pal and executor of his will
http://www.precide.ch/eng/eheil/eheil.htm

D vs B

In a dipolar speaker, the two sets of speakers are out of phase with each other, while the drivers are one side are pushing, the opposite side is pulling. The result is that there is a null or a dead zone of sound in the area along the 90 degree axis of the speaker (see illustration on right). Why is that good? When properly set up, a pair of dipole speakers used as surround speakers will provide a very open, enveloping rear effects soundstage without allowing you to pinpoint the location of the speakers themselves. That’s a good thing. But for all this to work properly, the speakers need to be positioned in-line with the listening position as shown on the illustration. If you are sitting out of the null area, the effect is ruined. What if you can’t or don’t want to place your surround speakers and listening position as required? That’s where bi-poles come in handy.
 
In a bipolar speaker, the two sets of drivers are in phase with one another - both sides push air at the same time. The result is greater sound output where the dipolar speaker’s null would be. Theoretically, a bipolar speaker approaches a 360° sound field - it disperses the sound all around the room. That’s a good thing if you need to position your surround speakers behind your listening position or anywhere outside of the null area. Some people prefer the greater localization of bipolar speakers when used in digital discrete (Dolby Digital 5.1, DTS) systems.
http://www.polkaudio.com/polk-university/faq/what-is-dipole-and-bipole-and-how-are-they-different

also


A dipole is a speaker which has matched drivers facing in opposite (really about 90 degrees) directions. So in a 2-way setup you will have two midrange/woofer drivers set opposite each other and two tweeters set opposite each other. None of the speakers should be directed to the prime listening area. In addition the speakers should be out of phase with one another (unlike all other drivers in your system, which should all be ‘in-phase’).

All of this is so that the sound is diffuse, or not easy to localize. The object is to recreate a theater environment, where the surround effects seem to come from everywhere.

 In some cases we get speakers that are termed adaptive dipoles, which simply means that the tweeters are not in-phase, but the woofers are. This is to provide more mid-range and bass (due to the drivers being in-phase) while allowing for the diffuse effect, as the tweeters (with their easily localized high frequencies) are still out-of-phase.

 Some persons write bipole when they really mean dipole.

 Some other people make a distinction of changing a dipole to a bipole by rewiring the all drivers to be ‘in-phase’. So in this case a bipole physically looks like a dipole but provides somewhat more localization due to all drivers being ‘in-phase’. There are some other reasons to rewire the drivers to be in-phase, depending on the exact location of the speakers in the listening area.

 In this context the term for speakers, whose drivers are intended to provide a localized sound (or point source) is monopole.

 Hope that this helps and did not make things more confusing.