Quantity of damping material in cabinet - diyAudio
Go Back   Home > Forums > Loudspeakers > Multi-Way

Multi-Way Conventional loudspeakers with crossovers

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 15th July 2014, 06:42 AM   #1
diyAudio Member
 
Join Date: Aug 2010
Default Quantity of damping material in cabinet

Damping material is used for eliminating the unwanted waves radiated from rear of driver to the cabinet.

I think the waves radiated from the rear of driver is desirable to eliminate completely for reproducing sound with pure and accurate.

For that, IMO it is desirable to fill the damping material in as much as possible (but it should not block the air flow to the port), especially for the mid chamber in 3 way system.

Then, how much do you fill the damping material and why ?
  Reply With Quote
Old 15th July 2014, 09:27 AM   #2
Lojzek is offline Lojzek  Croatia
diyAudio Member
 
Lojzek's Avatar
 
Join Date: Feb 2012
You can calculate the wavelength of standing waves using formulas and
if your box is not treated with stuffing material, you should be able to see
small spike on impedance plot meaning it is alive and kicking. You would
also see it on FR plot too as an inconsistency around the same frequency.

You know you have put enough of the damping stuff when the spike and
FR issue dissapears. Dampen it further more if you feel you need to lower
the Qtc of the driver in the box which means you are reducing the spl around
Fb. Decide for yourself when it's enough. Simulation helps.
__________________
It is so good that you exist !
  Reply With Quote
Old 15th July 2014, 11:25 AM   #3
PLB is online now PLB  United Kingdom
diyAudio Member
 
Join Date: Sep 2008
Location: The backbone of England
Hi icsohn94,

This link should answer some of your questions.

http://www.nousaine.com/pdfs/Box%20Stuffing.pdf

Peter
  Reply With Quote
Old 15th July 2014, 12:55 PM   #4
IG81 is offline IG81  Canada
diyAudio Member
 
IG81's Avatar
 
Join Date: Feb 2008
Certain programs (MJK worksheets, Hornresp) can simulate filling/stuffing and actually tell you how much this should be in real life in grams of polyfill or similar material. Others like WinISD have a 'Qa' parameter, which represents absorption losses, you just have to guess at how much material this really is.

Lots of stuffing in a vented box can quickly kill the bass, so better use somewhat thick padding on the walls, to start at least, and then adjust as desired. Stuffing a vented box with a high Qt driver can tame the peaking response a bit, but this is only a band-aid on an already compromised situation.
  Reply With Quote
Old 15th July 2014, 02:05 PM   #5
diyAudio Member
 
Join Date: May 2012
Location: London
I think you should experiment. Do one speaker at a time and compare. I suggest you LISTEN.

For myself, I feel too much damping spoils the sound.
  Reply With Quote
Old 15th July 2014, 04:15 PM   #6
jReave is online now jReave  Canada
diyAudio Member
 
Join Date: Oct 2012
First you need to understand that acoustic absorption varies with frequency as well as with stuffing material, density and thickness. See here for the absorption coefficients of various materials. In a nutshell, to absorb increasingly lower frequencies, you need higher density material and more of it but what you want to use is going to depend on what driver it's for and where the xo is placed. Personnally, I like rigid rockwool of about RHT 60 if I can get my hands on it.

So for a sealed alignment, use a bigger box if you can get away with it so that Qtc ends up between .5 and .7 . This will allow for more stuffing but still allow enough volume to leave some nice breathing space behind the driver. Also if your design allows it, think about increasing the distance the backwave has to travel from the driver to the back wall and then back again by making the box longer and narrower so that, without increasing the internal volume, you have increased the effective thickness of your stuffing and thereby also increased the amount of absorption taking place.

I haven't worked that much with ported so I will leave that to others, but since more stuffing drops the bass response, you may again want to start off with a bigger box which will give you some peaking in the low bass to compensate for that absorption loss. And a bigger box means more stuffing again. And more absorption with a longer pathlength still applies as well.

But in both cases, I agree that you have to experiment to see what sounds best to you.
  Reply With Quote
Old 15th July 2014, 05:21 PM   #7
diyAudio Member
 
speaker dave's Avatar
 
Join Date: Nov 2009
Location: The Mountain, Framingham
Quote:
Originally Posted by icsohn94 View Post

Then, how much do you fill the damping material and why ?
Since you are specifically talking about internal standing waves, know 2 things.

Standing waves in a box (or equally inside a listening room) need a treatment equal to roughly 1/4 any cabinet dimension to absorb the lowest standing wave of that dimension. Treatment is more effective off the reflecting surface than it is on the reflecting surface.

BAF or Dacron materials are very crappy at absorbing standing waves. Fiberglass or rock wool are much better.

Okay, maybe that's 3 things.

David
  Reply With Quote
Old 15th July 2014, 07:16 PM   #8
badman is offline badman  United States
diyAudio Member
 
badman's Avatar
 
Join Date: Sep 2003
Location: Sunny Tustin, SoCal
Quote:
Originally Posted by speaker dave View Post
Since you are specifically talking about internal standing waves, know 2 things.

Standing waves in a box (or equally inside a listening room) need a treatment equal to roughly 1/4 any cabinet dimension to absorb the lowest standing wave of that dimension. Treatment is more effective off the reflecting surface than it is on the reflecting surface.

BAF or Dacron materials are very crappy at absorbing standing waves. Fiberglass or rock wool are much better.

Okay, maybe that's 3 things.

David
Totally agreed re: spacing off walls. Stuffing is most effective where pressure is lower- the middle of the box. Of course, you don't want to restrict the vent action overmuch in a tuned system, so what's to do? I used the bracing structure, and the ribs on the inside surface of the box hold the stuffing off the surface, while being held in place by the inner bracing structure, so the stuffing is closer to the middle of the box but still doesn't impede the pressure path for the vent operation.

https://imageshack.com/i/31img0530xfj

https://imageshack.com/i/jyimg0529rj
__________________
I write for www.enjoythemusic.com in the DIY section. You may find yourself getting a preview of a project in-progress. Be warned!

Last edited by badman; 15th July 2014 at 07:20 PM.
  Reply With Quote
Old 16th July 2014, 06:07 AM   #9
diyAudio Member
 
Join Date: Aug 2003
Location: Calgary on the Bow
Quote:
Originally Posted by speaker dave View Post
Since you are specifically talking about internal standing waves, know 2 things.

Standing waves in a box (or equally inside a listening room) need a treatment equal to roughly 1/4 any cabinet dimension to absorb the lowest standing wave of that dimension. Treatment is more effective off the reflecting surface than it is on the reflecting surface.

BAF or Dacron materials are very crappy at absorbing standing waves. Fiberglass or rock wool are much better.

Okay, maybe that's 3 things.

David

Dave is very right. For some reason most diy speaker builders seem to think that BAF Dacron and other Poly fills are gods gift and they are not they are very poor absorbers at low frequencies. HD fiberglass/rockwool are the best bang for the buck. S.A.E. rated Acoustical felts are excellent but costly. Dave is also correct about material application having a big impact upon how well different materials will work.

Thanks Dave for pointing this out. I make this case myself from time to time but always seem to end up with someone telling me how wrong I am and it gets to be a drag trying to tell people who don't want to hear. Best regards Moray James.
__________________
moray james
  Reply With Quote
Old 16th July 2014, 11:11 AM   #10
diyAudio Member
 
speaker dave's Avatar
 
Join Date: Nov 2009
Location: The Mountain, Framingham
Quote:
Originally Posted by moray james View Post

I make this case myself from time to time but always seem to end up with someone telling me how wrong I am and it gets to be a drag trying to tell people who don't want to hear.
Amen to that brother!
  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
Use of Lead (Pb) as damping material in loudspeaker cabinet nannoo Construction Tips 8 12th January 2014 05:45 AM
Damping material quantity pski Multi-Way 18 31st December 2011 10:24 PM
damping material Professor smith Multi-Way 18 31st December 2011 04:03 AM
Damping material BobA Multi-Way 7 8th November 2004 03:09 AM
Damping Material Jhovis Multi-Way 5 29th September 2003 08:35 AM


New To Site? Need Help?

All times are GMT. The time now is 04:53 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