Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Multi-Way Conventional loudspeakers with crossovers

Enclosure Bracing Simulation
Enclosure Bracing Simulation
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 9th January 2003, 08:07 PM   #1
Milzie is offline Milzie
diyAudio Member
 
Join Date: Oct 2002
Location: Barrie, Ontario, Canada
Default Enclosure Bracing Simulation

As a request by some others, I have created a "quick and dirty" site that outlines some FEA simulations on various bracing methods. If anyone has some feedback or suggestions let me know.

http://www.geocities.com/milzie/Index.htm

Jeff
__________________
The *** is a muscle that MUST be rested!
  Reply With Quote
Old 10th January 2003, 01:14 AM   #2
MJK is offline MJK  United States
Account disabled at member's request
 
Join Date: Feb 2002
Location: Clifton Park, NY
Hi Jeff,

Tried to view your vibration data, but it looks like you have overwhelmed Yahoo. I'll try again later and hopefully get a look at your simulations. Just out of curiousity, what FEM software are you using?
  Reply With Quote
Old 10th January 2003, 10:57 AM   #3
Milzie is offline Milzie
diyAudio Member
 
Join Date: Oct 2002
Location: Barrie, Ontario, Canada
I use catia V5 and unigraphics v18 at work for all solid modelling. I use catia for the fea simulations because its pretty basic and quick to use. It generaaly gives pretty good results as well. For what I have done its just fine.

I also have access to Ansys, Nastran, and Altair at work. I would need some tutorials from the structural engineers at work how to use these though as they are very complicated from what I understand.
__________________
The *** is a muscle that MUST be rested!
  Reply With Quote
Old 10th January 2003, 11:56 AM   #4
pinkmouse is offline pinkmouse  Europe
diyAudio Moderator
 
pinkmouse's Avatar
 
Join Date: Apr 2002
Location: Rotherham, England
Enclosure Bracing Simulation
Jeff

Great stuff, well done

Could you give us a bit more detail on how you did the simulations, i.e. exciting frequency, dimensions of the box, and what material you used for the box wall.

Cheers
__________________
Rick: Oh Cliff / Sometimes it must be difficult not to feel as if / You really are a cliff / when fascists keep trying to push you over it! / Are they the lemmings / Or are you, Cliff? / Or are you Cliff?
  Reply With Quote
Old 10th January 2003, 12:52 PM   #5
LaMa is offline LaMa
diyAudio Member
 
Join Date: Sep 2002
Location: NL
The greatest problem is to get proper material parameters, which is difficult because most materials behave isotropic. (in each direction other stresses and strains). How to measure these is another question.

It's great that you have taken the effort to model and insert it in a FEM package, the differences between the braces can be recognised, but the results of the calculation of the box without bracing gives only a maximum displacement of 1.54E-5 mm. That is nothing! Roughly you can say that displacement is cut in half when the box is proper braced.

The force you have applied is 10N/m2 if I read it correctly on your site. How did you came to this value?

I just want to add that if you want realistic output of a calculation the input has to be correct and that is the hardest part. Which parameters does your program need to calculate the displacement?
  Reply With Quote
Old 10th January 2003, 01:20 PM   #6
MJK is offline MJK  United States
Account disabled at member's request
 
Join Date: Feb 2002
Location: Clifton Park, NY
I finally made it into your site and looked at what you have analyzed and some of the plots you present.

You can find a lot of good info on different wood properties at the USDA site. One publication that I recently used at work to design wooden shipping crates is shown below. More info then you probably ever wanted to know!

US Department of Agriculture - Wood Handbook

http://www.fpl.fs.fed.us/documnts/FP.../fplgtr113.htm

If I understand what you have done, the displaced shape plots are for a unit pressure case and the results are only static deflections. While this is interesting data, these plots should not be mistaken for vibration plots that show natural frequencies and mode shapes. I would guess that when you run a modal analysis the deflected shapes will not look like those calculated by the static analysis. The change in the natural frequencies and the mode shapes will be very interesting as the different bracing schemes are applied.
  Reply With Quote
Old 10th January 2003, 03:33 PM   #7
Milzie is offline Milzie
diyAudio Member
 
Join Date: Oct 2002
Location: Barrie, Ontario, Canada
Quote:
Originally posted by LaMa
The greatest problem is to get proper material parameters, which is difficult because most materials behave isotropic. (in each direction other stresses and strains). How to measure these is another question.
Thats correct, because most materials behave the same, they will all deflect in a similar manner. I could have used steel and it would not have changed the results, only the value of deflection. I was not trying to determine the actual value of deflection.


Quote:
Originally posted by LaMa
It's great that you have taken the effort to model and insert it in a FEM package, the differences between the braces can be recognised, but the results of the calculation of the box without bracing gives only a maximum displacement of 1.54E-5 mm. That is nothing! Roughly you can say that displacement is cut in half when the box is proper braced.
That was in fact the purpose of the study, to determine how bracing effected to displacement of the enclosure walls and the reduction in deflection as a percentage from no braceing.

Quote:
Originally posted by LaMa
The force you have applied is 10N/m2 if I read it correctly on your site. How did you came to this value?
I pulled the number out my butt. The pressure is not important. I was not trying to calculate the actual deflection value, only compare the deflection between different styles of bracing. If you convert the deflection values to percentages relative to an unbraced enclosure, that may make the results more easily understood.


Quote:
Originally posted by LaMa
I just want to add that if you want realistic output of a calculation the input has to be correct and that is the hardest part. Which parameters does your program need to calculate the displacement?
To calculate displacement, I would need the modulus of elasticity as well as the poisson ration of MDF. I would then have to determine the actual pressure a loudspeaker exerts on the cabinet. This would be useful if I wanted to know how much the box deflected.

It really doesnt matter how much the box deflects in my simulation. What we are looking for is improvements from baseline (no bracing).



Quote:
Originally posted by MJK
If I understand what you have done, the displaced shape plots are for a unit pressure case and the results are only static deflections. While this is interesting data, these plots should not be mistaken for vibration plots that show natural frequencies and mode shapes. I would guess that when you run a modal analysis the deflected shapes will not look like those calculated by the static analysis. The change in the natural frequencies and the mode shapes will be very interesting as the different bracing schemes are applied.
I think you understand exactly what I have done. While this is not a modal analysis, and does not give us the resonant frequency of the enclosure, it does give us the relative stiffness of the enclosure walls and how various forms of bracing effect that stiffness.
I am in the process of building some models of loudspeakers as well as the mdf cabinet. I then plan to export the information to a more powerful FEA software such as Ansys to do some dynamic and modal simulations.


Jeff
__________________
The *** is a muscle that MUST be rested!
  Reply With Quote

Reply


Enclosure Bracing SimulationHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Subwoofer enclosure internal bracing rocko1290 Subwoofers 20 22nd February 2017 03:19 AM
Looking for ideas for bracing a lightweight enclosure owdi Subwoofers 3 15th September 2006 04:12 PM
Crossover, enclosure, simulation (dumb question I'm affraid) 00940 Multi-Way 4 30th August 2006 12:09 AM
Bracing an enclosure preiter Subwoofers 5 17th July 2006 10:54 AM
Curved enclosure simulation jouch Multi-Way 0 10th September 2003 08:26 AM


New To Site? Need Help?

All times are GMT. The time now is 09:36 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki