Woofers' membrane modultion - 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 25th July 2012, 12:14 PM   #1
Legis is offline Legis  Finland
diyAudio Member
 
Legis's Avatar
 
Join Date: Dec 2009
Default Woofers causing membrane modulation in stats

I'm having a problem with my dipole line array subs, they modulate the membranes of the stats when I play bass heavy material loud. Moving the subs away from the stats seem to work to some extent, but for example the right subwoofer modulates the left (and right) stat for some reason.

Subs are U-frame dipoles with 18" drivers:

Click the image to open in full size.

The membrane is 3,5Ám and the lowest resonance is ~36Hz, so the tension is not the greatest but it can withstand 4,7kV bias with no problems, propably much more.

Is there any way around this problem other than moving to a bigger room and leave at least 1m distance between the stats and the woofers? Would 6Ám membrane with higher tension be less problematic or would it be almost just as unstanble at it's Fs? I'm really liking the sound with 3,5Ám, would not want to change them. Or are dipole woofers ultimately not the best partners for stats, because they generate more pressure changes (than box subs) or something that modulates the membrane?

Last edited by Legis; 25th July 2012 at 02:40 PM.
  Reply With Quote
Old 25th July 2012, 02:50 PM   #2
Legis is offline Legis  Finland
diyAudio Member
 
Legis's Avatar
 
Join Date: Dec 2009
I tested it with CB subwoofers and the result was the same - the membrane excites near it's Fs. So the reason is not the "eddy currents" around the dipole, but it's just the loud bass near the membrane's Fs (or loud, wide range transients like a bass drum).

I quess there is no way around this (without sacrificing SQ and/or sensitivity) than move to a bigger room and place the stats to dead angle on the side of the (dipole) subs and leave at least 0,5m distance between them.

On the other hand, the modulation is propably not going to kill the membranes, so should one worry about it too much; just turn a tad quiter when you hear the membranes hitting the stators.
  Reply With Quote
Old 3rd August 2012, 06:38 AM   #3
diyAudio Member
 
LineSource's Avatar
 
Join Date: Sep 2003
Location: SiliconValley
Legis,

You may find useful information by reading the Martin Logan Statement 1 and 2 manuals which you can download off the web. The ML Statement 1 is similar to your panels, but uses a monopole bass line array. ML recommends keeping the Statement 1 woofers near to the panels.(pdf) The ML Statement 2 woofer "balanced force" line array can be configured as dipole, bipole, or cardiod radiation. ML suggests putting these bass line arrays in the room corners with the null vector pointed toward the soundstage.(picture)

For fragile dipole ribbons I use an H-frame with 8" deep front/rear wings for a three woofer line array, and place it directly next to the ribbon linesources, but on the outside of the soundstage angled toward the side wall for extra time delay and bass room mode control. From my experience, the H-frame significantly reduced bass wind vibrating the ribbons over a flat dipole baffle. I use Ficus indoor trees as rear diffusors behind the ribbons. These trees both absorb and scatter the bass wave. I favor rear wave diffusion so the upper frequency energy is not absorbed, but scattered into several different vectors to enrich the room interaction.

Dipoles add the room into the listening equation. Horns subtract the room out of the listening equation. Modern controlled directivity monopoles with good diffraction control use long delay reflections for location clues.
Attached Images
File Type: jpg Statement_Bass_Tower.jpg (65.4 KB, 136 views)
Attached Files
File Type: pdf Manual_Statement.pdf (134.8 KB, 17 views)
  Reply With Quote
Old 3rd August 2012, 08:01 AM   #4
Calvin is offline Calvin  Germany
diyAudio Member
 
Calvin's Avatar
 
Join Date: Nov 2004
Location: close to Basel
Hi,

the chance of driving the ESL membrane into the stators is greatly reduced in the Statement2 design -which I similarly use in my design- by 3 mechanisms.
a) airgap between woofer and panel.
b) very high membrane tension. As a sideeffect this makes necessary a
c) dipole woofer-midrange between woofers and panel (which also reacts much less sensitive on the near placed woofer).
The dynamic driver dipole tower acts as a filler driver and kind of mechnical buffer between Panel and woofer. As with many aspects in ESL design, if all is done correctly, parameters fit into place, like pieces of a good mechanical watch. ML named this dipolar transistion tower. I think the name says it all.
Legis┤s design reminds of the earlier ML Statement, which featured a very large panel and a CB bass tower. ML probabely experienced the same problems as he does. The Panel was crossed over at very low 120Hz and was specced to reach down to 80Hz.

jauu
Calvin

ps:
Quote:
The ML Statement 2 woofer "balanced force" line array can be configured as dipole, bipole, or cardiod radiation.
Balanced Force implies bipolar or -because of the long wavelengths at such low freqs- monopolar distribution character. Apart from the first of the possible four stacked bass-modules per channel, the modules only featured two binding posts, hence no possibility to configure the single modules as dipoles or cardiods. The drivers within a module are simply paralleled

Last edited by Calvin; 3rd August 2012 at 08:14 AM.
  Reply With Quote
Old 3rd August 2012, 05:02 PM   #5
diyAudio Member
 
Andersonix's Avatar
 
Join Date: Jan 2004
Location: Silicon Valley
Legis, do you have space to arrange the woofers' axes so that they are in the same plane as the ESL panels? (to attempt to balance the F/R pressure on the ESL membrane)
  Reply With Quote
Old 3rd August 2012, 06:14 PM   #6
Legis is offline Legis  Finland
diyAudio Member
 
Legis's Avatar
 
Join Date: Dec 2009
Yes the best solution would be placing the woofers on the sides next to the panels, where the dipole has a null. This does not work in my small room however, the basses are under 1 meter away from the front wall and the null points do not build up on the sides. This apartment is not the final solution luckily, I need big dedicated listening room for these in the future, girl friend might also like it.
  Reply With Quote
Old 3rd August 2012, 07:01 PM   #7
diyAudio Member
 
Andersonix's Avatar
 
Join Date: Jan 2004
Location: Silicon Valley
Not just on the sides of the panels, but facing the edge of the panels, so that both front and rear sides of the panels get the same pressure from the bass.
  Reply With Quote
Old 3rd August 2012, 07:13 PM   #8
Legis is offline Legis  Finland
diyAudio Member
 
Legis's Avatar
 
Join Date: Dec 2009
I will try that setting.. So dipole's sides facing the spot, cannot really predict how it will sound. I have noticed that it's the air pressure that modulates the membrane (near the membrane's Fs). At first I though it was the eddy currents around the dipole, but it's not the only cause.
  Reply With Quote
Old 3rd August 2012, 09:52 PM   #9
diyAudio Member
 
Andersonix's Avatar
 
Join Date: Jan 2004
Location: Silicon Valley
I don't expect this arrangement to be ideal, but perhaps it will avoid unequal air pressure moving the ESL.

These eddy currents? ESLs are not affected by magnetism...
  Reply With Quote
Old 3rd August 2012, 10:40 PM   #10
Legis is offline Legis  Finland
diyAudio Member
 
Legis's Avatar
 
Join Date: Dec 2009
^I don't know the correct term in english, maybe acoustic eddy currents I mean the circulating waves/acoustic cancellation around the dipole. In other terms the air moving around the dipole that is not sound pressure per se, but just the air "moving".

Last edited by Legis; 3rd August 2012 at 10:44 PM.
  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


Similar Threads
Thread Thread Starter Forum Replies Last Post
Simulating the membrane arend-jan Planars & Exotics 6 27th March 2010 04:08 PM
Membrane keypads glen65 Everything Else 4 13th June 2007 09:05 PM
Membrane Coatings Martin Jay starz00700 Planars & Exotics 2 13th May 2007 02:05 PM
Zaphs B3S's with aperiodic membrane? GuyPanico Multi-Way 13 7th September 2006 06:33 PM
Tear in magnetostat membrane: What to do? Klimon Planars & Exotics 2 1st March 2006 11:33 PM


New To Site? Need Help?

All times are GMT. The time now is 11:04 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ę1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2