ESL with acoustic foam - 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 11th December 2010, 02:08 PM   #1
diyAudio Member
 
Join Date: Dec 2010
Question ESL with acoustic foam

Regarding bass on ESLs.
"Bass. At low frequencies, as wavelengths become large relative to panel width, the out-of-phase signals from opposite sides of the diaphragm tend to wrap around and cancel each other. So like all true dipole speakers (not to be confused with conventional-driver quasi-dipole surrounds), electrostatics are prone to weak bass. Increasing panel size helps with this, as well as with the output/efficiency problem discussed above, but there's a practical limit."
-Martin Logan website
Would it be possible to place lots of acoustic foam on one side of a electrostatic loudspeaker to absorb the out of phase signals?
Would that increase the bass or is there some problem that will crop up?
  Reply With Quote
Old 11th December 2010, 05:45 PM   #2
diyAudio Member
 
bolserst's Avatar
 
Join Date: Jun 2005
Location: Fort Worth, Texas
Quote:
Originally Posted by andrelim View Post
Regarding bass on ESLs.
Would it be possible to place lots of acoustic foam on one side of a electrostatic loudspeaker to absorb the out of phase signals?
Would that increase the bass or is there some problem that will crop up?
In general acoustic foam is not very affective at absorbing low frequencies, below about 300 Hz.
To block the out of phase bass from the rear of the ESL you pretty much have to use a physical barrier.
For their full range model Martin Logan adds a large baffle extension on the side nearest the bass panels to increase the bass output.
Adding an additional baffle extension on the other side of the panel would have increased the bass output further,
but the response and radiation pattern of the curved mid-treble panel would be adversely affected.
Also, with two large side baffle extensions, a cavity would be formed behind the panels which would potentially add an undesirable cavity resonance.

One other possibility was mentioned in the Williamson-Walker US patent 3008013:
Replace the baffle extensions with active ESL panels that are only driven at low frequencies where the phase cancellation is most problematic.
At higher frequencies, these panels will be essentially acoustically transparent so they will not induce a cavity resonance or adversely affect the mid-treble response.
Attached Images
File Type: jpg CLX_baffle.jpg (79.1 KB, 310 views)
File Type: jpg Williamson_Walker_active_baffle.jpg (19.6 KB, 300 views)

Last edited by bolserst; 11th December 2010 at 05:56 PM.
  Reply With Quote
Old 12th December 2010, 08:22 AM   #3
Calvin is offline Calvin  Germany
diyAudio Member
 
Calvin's Avatar
 
Join Date: Nov 2004
Location: close to Basel
Hi,

as bolserst already said, foam layers of sufficient effectiveness would be of unpractical huge physical size and terrible optics too. But besides reducing the SPL on the foamed side this could lead to a positive shaping of the distribution character towards a ´kidney´. But still it wouldn´t help with the main problem, which is that an ESL is no good bass in first place.

jauu
Calvin
  Reply With Quote
Old 12th December 2010, 08:51 AM   #4
diyAudio Member
 
Join Date: Dec 2010
What about installing a ESL panel in a wall?
The out of phase signals would be blocked by the wall.
  Reply With Quote
Old 12th December 2010, 09:31 AM   #5
DaveG is offline DaveG  United States
diyAudio Member
 
DaveG's Avatar
 
Join Date: Feb 2007
Location: Grease
Beveridge speakers absorb the rear wave. Model 2 are about 18" deep.
  Reply With Quote
Old 12th December 2010, 06:54 PM   #6
Calvin is offline Calvin  Germany
diyAudio Member
 
Calvin's Avatar
 
Join Date: Nov 2004
Location: close to Basel
Hi,

installing a panel into a wall would basically mean the same as to put a dynamic driver into a cloased box. But while the high mass of the drivers moving system leads only to an acceptable rise in resonance frequency the Fs of the ESL could rise undue high. Because of the diaphragm beeing virtually acoustically transparent utmost care needed to be taken that no internal reflected soundwaves could pass the membrane (something I dislike about the simple flat Beveridge casing). Peter Walker suggested rather deep shallow casings with lots of wadding and possibly open to the end.

jauu
Calvin
  Reply With Quote
Old 13th December 2010, 09:53 AM   #7
diyAudio Member
 
Join Date: Dec 2010
If acoustic foam doesnt absorb frequencies below 300hz, then what about mineral wool insulation boards used in bass traps? Would around 18" of it behind a ESL panel sufficiently absorb the out of phase signals?
  Reply With Quote
Old 13th December 2010, 10:58 AM   #8
diyAudio Member
 
Join Date: Dec 2010
What about micro perforated plates? I know the stators are made of perforated metal but would additional layers behind absorb sound? Since each plate is 0.5mm - 2mm, it would be possible to stack many layers without reaching unpractical sizes and making the ESL unsightly.
  Reply With Quote
Old 13th December 2010, 02:09 PM   #9
expert in tautology
diyAudio Member
 
bear's Avatar
 
Join Date: Apr 2002
Location: New York State USA
Metal plates will reflect strongly at HF, and not absorb at LF... I think you are thinking of a Helmholtz resonator. That is a possibility, although problematic because of the inevitable reflection at some frequency related to the distance to the diaphragm...

Mineral wool, or any other absorptive material, sure, but you'd need about 3 feet or better of whatever that is back there to be effective down to useful bass freqs... go for it...

Or you could go listen to some Acoustats - ESL dipoles with plenty of bass.

There have been discussions of DIY Acoustats here and elsewhere...

_-_-bear
__________________
_-_-bear
http://www.bearlabs.com -- Btw, I don't actually know anything, FYI -- [...2SJ74 Toshiba bogus asian parts - beware! ]
  Reply With Quote
Old 14th December 2010, 07:25 AM   #10
diyAudio Member
 
Join Date: Dec 2010
I was referring to Micro perforated plate - Wikipedia, the free encyclopedia
"A Micro Perforated Plate (MPP) is a device used to absorb sound, reducing its intensity. It consists of a thin flat plate, made from one of several different materials, with small holes punched in it. An MPP offers an alternative to traditional sound absorbers made from porous materials...When the oscillating air molecules penetrate the MPP, the friction between the air in motion and the surface of the MPP dissipates the acoustical energy."
-Wikipedia
  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
Does foam-lined deadsheet affect acoustic volume? AntM Multi-Way 7 30th November 2009 08:15 PM
acoustic foam and Box volume mcmahon48 Multi-Way 2 6th March 2009 01:46 AM
Convoluted Acoustic foam skooter Car Audio 3 18th November 2007 05:45 PM
acoustic foam vs. box volume?? help dste6 Multi-Way 2 27th September 2006 07:31 PM
conductability of acoustic foam sberube Multi-Way 2 27th August 2004 07:18 PM


New To Site? Need Help?

All times are GMT. The time now is 12:33 AM.


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