big AMT Diy - diyAudio
Go Back   Home > Forums > Loudspeakers > Planars & Exotics

Planars & Exotics ESL's, planars, and alternative technologies

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 29th August 2008, 01:10 PM   #1
diyAudio Member
 
Join Date: Mar 2008
Location: Uzhgorod
Default big AMT Diy

Did anyone here tried to make DIY AMT fullrange (wideband) driver?

Is it possible at least from 200-300 Hz?

I know that there are projects for fullrange magnetostats (Jamesbos), but what about making the same - long and narrow AMT panel instead of common magnetostat?

10 cm wide x 1,5 meters heigh for example.

Is it possible at all? Whta`s your opinion?
  Reply With Quote
Old 30th August 2008, 10:07 PM   #2
diyAudio Member
 
Join Date: Dec 2004
Location: Reston, Virginia
Default Re: big AMT Diy

Quote:
Originally posted by Charcoal

Is it possible at all? Whta`s your opinion?
Possible, hard to do, but not worth it.

I made a 22" tall Heil many years ago. The diaphragm gets increasingly hard to fold as the length increases. The caption for this picture on my website is: "This is a great project to recommend to your worst enemy."
Click the image to open in full size.

An unfortunate fact of the Heil is that the design doesn't scale well for low frequencies. At low frequencies you have large excursions, and the restoring force of the diaphragm isn't linear for large excursions. If you browse some of Heil's other patents you can see that he was working on "hinged" suspension systems for folded diaphragms that would be suitable for large excursions. But no products used these ideas, as far as I know.

One way to appreciate the Heil driver is to think of it in terms of the distortion modes that Klippel describes. Klippel identifies 3 primary distortion distortion components that affect sound quality (these aren't the only sources of distortion, but they are probably the most important ones). These are:

--Bl-product versus displacement x
--Voice coil inductance Le(x) versus displacement
--Stiffness Kms(x) versus voice coil displacement x

The first of these, the BL product versus displacement, is a problem for planars and some ribbons, but this problem is close to totally non-existent in the Heil. This needs to be explained with a picture, but the bottom line is that the pleats in the Heil move in a uniform magnetic field, and even large displacements don't suffer from this distortion mode.

The second distortion mode is voice coil inductance versus displacement, and like ribbons, the Heil design is immune to this this mode of distortion (there simple isn't much "voice coil" inductance to worry about)

However, the final distortion mode is stiffness versus displacement, and this is where the Heil suffers, particularly at lower frequencies. The diaphragm material provides the restoring force, and at lower frequencies where the excursion becomes large this restoring force is probably not a simple linear relationship. So getting the Heil to scale to work at lower frequencies is going to be a challenge.

But for frequencies where the excursion is relatively small, the Heil is amazing. If you look at the distorion figures published by A.D.A.M, it looks like the region where excursion becomes a problem is around 1-2K. Above that, the distortion is very low. Below that, you are best off with a cone driver, in my opinion.

Click the image to open in full size.
  Reply With Quote
Old 4th September 2008, 05:40 AM   #3
diyAudio Member
 
Join Date: Mar 2008
Location: Uzhgorod
Thanks for detailed advice. A lot of reasons to think before starting DIY.

Do you think that in case of tall narrow wideranger I should better think about common planar than AMT?
  Reply With Quote
Old 5th September 2008, 02:19 PM   #4
diyAudio Member
 
Join Date: Dec 2004
Location: Reston, Virginia
Quote:
Originally posted by Charcoal
Thanks for detailed advice. A lot of reasons to think before starting DIY.

Do you think that in case of tall narrow wideranger I should better think about common planar than AMT?
I just don't think either of these designs--Heil or planar--work well at lower frequencies. There may be a ribbon/planar design that actually does work well at lower frequencies, but I'm not aware of it.

A planar has a similar problem as the Heil with linear suspension for high excursions, so the "trick" is to have enough surface area to keep excursion low. The planar has the additional problem of having a linear magnetic field--that is, as the conductive path moves it may or may not cut through a constant amount of magnetic flux. A "push-pull" magnetic structure helps ensure a symmetrical magnetic field, but even though it may be symmetrical it might not be linear throughout the entire excursion.

I believe that the most promising configuration for lowest frequency would be a circular or cylindrical Heil. This topology provides a relatively large surface area so that suspension non-linearities are minimized, and the Heil structure ensures a symmetrical and linear magentic field. Moreover, it can be made to be omnidirectional, which has some nice benefits.

Of course, it sounds like you are asking about a tall narrow configuration instead, so that probably doesn't help you.

Click the image to open in full size.
  Reply With Quote
Old 6th September 2008, 09:34 PM   #5
el`Ol is offline el`Ol  Germany
diyAudio Member
 
Join Date: May 2005
Location: Bavarian Forest
This magnetostat does what you demand:
http://www.soundimage.dk/Friends/Andre.htm
Andre is active here as ABJensen.
  Reply With Quote
Old 8th September 2008, 05:14 AM   #6
diyAudio Member
 
Join Date: Mar 2008
Location: Uzhgorod
I read about Andre`s planar. It realy looks promissing. Is it corrugated like: UU (just two curves) or UUUUU?

Omni low frequensy Heil is interesting (magnets available to buy?), but at first I should do wide ranger.
  Reply With Quote
Old 8th September 2008, 04:33 PM   #7
el`Ol is offline el`Ol  Germany
diyAudio Member
 
Join Date: May 2005
Location: Bavarian Forest
André´s magnetostat has a flat diaphragm that rests on foam stripes. The conductor has no turn.
Some years ago I thought about an AMT-like onmi myself, but my doubt was that the contraction of the whole construction overlays the air motion coming out of the folds. I can think of two solutions: textile/rubber across the folds or foam on the cylindrical parts.
Attached Images
File Type: jpg omni.jpg (20.3 KB, 1057 views)
  Reply With Quote
Old 8th September 2008, 06:22 PM   #8
el`Ol is offline el`Ol  Germany
diyAudio Member
 
Join Date: May 2005
Location: Bavarian Forest
Today I don´t like the idea of coupling the segments any more. I would build single segments like this and arrange them planar or cylindrical, as desired.
Attached Images
File Type: jpg neoheil.jpg (10.6 KB, 1026 views)
  Reply With Quote
Old 8th September 2008, 06:24 PM   #9
el`Ol is offline el`Ol  Germany
diyAudio Member
 
Join Date: May 2005
Location: Bavarian Forest
This kind of magnetic circuit is quite linear:
But probably Neil Davis will tell us that the mechanical linearity is a mess.
Attached Images
File Type: jpg heoheilmag.jpg (68.3 KB, 777 views)
  Reply With Quote
Old 9th September 2008, 03:45 AM   #10
diyAudio Member
 
Join Date: Dec 2004
Location: Reston, Virginia
Quote:
Originally posted by el`Ol
Some years ago I thought about an AMT-like onmi myself, but my doubt was that the contraction of the whole construction overlays the air motion coming out of the folds.
Why do you think there will be contraction? Half of the pleats move one direction and the other half move in the opposite direction. There is no net contraction, unless I'm missing something here. BTW, this isn't a new idea--look at Figure 11 and 12b in the original Heil patent:
http://www.google.com/patents?id=Yjw...zoom=4#PPA3,M1


Quote:
Originally posted by el`Ol
This kind of magnetic circuit is quite linear:
But probably Neil Davis will tell us that the mechanical linearity is a mess.
Only if that is true
It may be possible to design a linear suspension for ribbons that will allow higher excursions. But the simple design used in the conventional planar, using the tension of the diaphragm as the restoring force, probably isn't going to ever give good results for large excursions.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



New To Site? Need Help?

All times are GMT. The time now is 05:13 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2