Wiki on bracing - Page 3 - 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 4th May 2007, 08:52 PM   #21
frugal-phile(tm)
diyAudio Moderator
 
planet10's Avatar
 
Join Date: Oct 2001
Location: Victoria, BC, NA, Sol III
Blog Entries: 5
Quote:
Originally posted by rick57
Is it mostly your point about energy available, but also that a greater amount of energy is needed to excite it?
I don't know if more of less energy is required to excite a higher frequency panel resonance, but, as Svante's graph clearly shows, as the frequency goes up there is a lot less enegy available to excite a panel resonance.

dave
__________________
community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi
p10-hifi forum here at diyA
  Reply With Quote
Old 4th May 2007, 08:54 PM   #22
frugal-phile(tm)
diyAudio Moderator
 
planet10's Avatar
 
Join Date: Oct 2001
Location: Victoria, BC, NA, Sol III
Blog Entries: 5
Quote:
Originally posted by rick57
My statements are drawn from the experience of others, mostly dave.
Keep in mind that my comments reflect my particular speaker building philosophy and that there are perfectly competent speaker builders who would never consider my approach.

With this in mind, you may end up having to have a couple parallel articles.

dave
__________________
community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi
p10-hifi forum here at diyA
  Reply With Quote
Old 4th May 2007, 09:01 PM   #23
frugal-phile(tm)
diyAudio Moderator
 
planet10's Avatar
 
Join Date: Oct 2001
Location: Victoria, BC, NA, Sol III
Blog Entries: 5
Quote:
Originally posted by Ron E
http://bellsouthpwp.net/l/j/ljfrank/Bracing.html
That looks like it is a good reference -- i'll comment more once i have a chance to properly read it -- a couple quick comments.

I see he experimentally validates the longitudanal brace, and that there is an indication that a brace should reach across to th eopposite panel.

With respect to Jim Moriyasu from AudioExpress (Feb. 2002) entitled, Panel Damping Studies: Reducing Loudspeaker Enclosure Vibrations, this has somewhat limited application as he made the classic error of placing the praces exactly in the middle of the panels. I chatted with him about this, and he said he didn't see himself getting around to exploring the subject further.

dave
__________________
community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi
p10-hifi forum here at diyA
  Reply With Quote
Old 4th May 2007, 11:04 PM   #24
Tenson is offline Tenson  United Kingdom
diyAudio Member
 
Join Date: Feb 2006
Location: Kent
Most of what you need for practical examples is probably here.

http://www.exdreamaudio.de/Boxen-Bau...umaterial.html

Thorsten posted a quick summery of what the page says for those (like me) who can't read German.

Quote:
A brief summary:

1) 19mm MDF (7.5kg):

Click the image to open in full size.

The upper response trace is the signal before inserting the test wall into a speaker (so the actual stimulus) the lower is the output after inserting the testwall. Observable is a main resonance around 170Hz which takes long to decay, as the "lossy" mechanism in MDF includes energy storage.

2) 18mm Plywood (6kg):

Click the image to open in full size.

Same as above, we note that despite having less mass (which would suggest a high resonance) the resonance with plywood has shifted down to 150Hz suggetsing less stiffness, but more crucially, the decay of the resonance is much quicker and very rapid initially and thus suggest a loss mechnism without much energy storage.

3) 44mm coarse fibre board (a little coarser than MDF) 14kG:

Click the image to open in full size.

The much thicker and heavier material isolates a little better and again due to the coarse and heterogenous structure decay is rapid.

4) For reference - 18mm plywood, 12mm sandfilling, 16mm plywood sandwich (18.5kg):

Click the image to open in full size.

Only marginally better than cheap, generic thick woodfibre board for a lot of effort.

5) For reference - 20mm Marble (26kg):

Click the image to open in full size.

Overall, as we can see, attenuation and suppression of the resonance somwhere between 100Hz and 300Hz (paradoxically the resonance seems to go up with added weight, but instead it is actually the increased stiffness from increasing the acthive thickness that does it and outweights the added weight) seems mainly related to weight and thickness (few surprises).

Equally though, going from 19mm MDF to 44mm coarse fibre board does not seem to bring much improvement.

The only real surprise is that Plywood (good grade) decays much quicker than more amorphous and homogenus materials, meaning despite a strong initial resonance peak when excited the audibility of this will be much less as (unlike MDF) Plywood seems to "drone on" much less long.

Okay, what if we apply simple re-inforcements (10cm 18mm board glued on plate edge on):

Click the image to open in full size.

No material improvement.

How about bitumen Damping Mats (quite expensive in Car Audio Shops):

Click the image to open in full size.

No material improvement. You need to go to the length the BBC did where they used equal thickness of Bitumen and Plywood to see real improvements.

What if we brace the plate against the opposite board like this?

Click the image to open in full size.

This is a starting point BTW to the matrix bracing B&W use and which I also recommend.

Click the image to open in full size.

Wow, now we are cooking with GAS! This is WAY better than 44mm of the same stuff!

What is the upshot?

At similar thickness all materials (except stone and metal - metal was not tested, I used this myself before) resonante in a similar fashion. Plywood will have a less audible and objectionable resonance due to it's lossy nature, if you use a really good grade, (building grade plywood is bad though - see figure 7).

Damping mats and the like improve little. Bracing to opposite walls majorly improves things. If you tie the bracing together in the center of the box so all walls connect together (matrix style) thing get even better.

So, use sensible thickness of Plywood (18 - 22mm) of good grade and brace the heck out of the box will result in the most economical solution.

"Exotic" enclosure materials such as stone and metal are vastly superior but usually not applicable in DIY.
Hope that gives some info for your wiki. Since it is from that website you had better contact them about permissions though.
  Reply With Quote
Old 4th May 2007, 11:38 PM   #25
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
 
EC8010's Avatar
 
Join Date: Jan 2003
Location: Near London. UK
Default Circles.

I've just looked through this thread and am amazed to find no mention of the seminal Stephens JAES paper. For maximum rigidity, you position your brace so as to minimise the diameter of circles that can be inscribed. That means that a rectangular panel should have a brace running centrally along the long dimension, rather than diagonally or across the width. It's why transmission line loudspeakers work well - their dividers inevitably end up in this orientation. To work well, a brace needs to be a panel going all the way to the opposite wall. To prevent it turning into a transmission line, it needs large holes in it. Now you know where B&W's "Matrix" idea comes from.
__________________
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
  Reply With Quote
Old 5th May 2007, 01:30 AM   #26
Ron E is online now Ron E  United States
diyAudio Member
 
Ron E's Avatar
 
Join Date: Jun 2002
Location: USA, MN
Default Re: Wiki on bracing

More time tonight....

Quote:
Originally posted by rick57
The goal of bracing is to push panel resonances higher.
Perhaps a semantic issue, but the goal of bracing is to reduce cabinet talk, the practical result is to increase resonant frequency and/or increase damping rate. This is perhaps more generally true of cabinet construction rather than simply bracing.

Quote:
Originally posted by rick57
Also damping materials attenuate higher frequencies better.
Good observation. Perhaps true both for acoustic and structural vibration.

Quote:
Originally posted by rick57
As mass stores energy, the releases it with a time delay, a well braced single layer box is better than a non-braced two layer box.
I mostly agree with this, bracing is certainly more economical on material. I have never been of the thick wall camp.

Quote:
Originally posted by rick57
Theory
From "Vibration Analysis for Electronic Equipment", by David S. Steinberg (p 267):
I'll look at this and the other resonance question later....

Quote:
Originally posted by rick57
Spacing
· The largest panels resonate at the lowest frequencies, so they are the most important to divide up
· Linkwitz’ rule of thumb from years ago: no unbraced distances should be greater than 4" ie 100 mm.
Can't argue with that.

Quote:
Originally posted by rick57
· GM for void free plywood suggests the points where bracing around the driver is required:
- for 5/8" ply: 0.75 ft^2 CSA (cross sectional area), ie equivalent to 10” ^2, ie 25 mm^2.
- For 3/4" ply: for 1.0 ft^2 ie 30 mm^2.
This doesn't make sense (perhaps you were too brief) and the dimensions in mm are incorrect conversions.

Quote:
Originally posted by rick57
Shape
· the strongest (bracing) structure is a triangle . .
While it is true that trangles make stiff structures, make sure that you clarify that diagonal panel braces are ineffective. The advice for triangular bracing structures should be considered advice as to what the cutouts in braces should look like (i.e. trusses make very stiff, light structures). Square cutouts will "shear" easier.

Quote:
Originally posted by rick57
Placement
· Bracing the short dimension creates a larger number of panels that are closer to square, with same or similar resonances. It’s better to run them along the long dimension of a panel.
· the middle is the worst place, as energy at divisor frequencies can feed panel resonances - the panel can actually be worse after bracing. To spread resonances, bracing should never be at equidistant intervals, eg instead 1 ft intervals - 11", 13" & 12" would be better.
· So that the 1st resonance is killed instead of enhanced - place them offset and/ or oblique ~ by at least X? degrees
· brace so that you move the dimensions away from each other
· endeavour to brace the driver magnets to the box.
I agree with most of this. Bracing magnets to the box, I am a little iffy on. Seems like a recipe for rattle/buzz.

Note that Weems in his ancient and deceptively simplistic books recommends a longitudinal rib just off center.

Quote:
Originally posted by rick57
Materials
· plywood or hardwood, because they are stiff and not heavy (mass absorbing energy, then releasing it later).
· A good size is 3/4" x 1 1/2" ie 18 * 36 mm.
· mount edge-on, ie deeper side attached to the box.
· metal braces or steel rods are stiffer so even better
I think you mean 3/4" side attached to box, not "deeper side".

Metal braces I agree with, but steel rods as point braces are not likely to be effective.

Quote:
Originally posted by rick57
Tips for attaching braces
· Butt joints with glue & screws is fine.
· Ideally each bracing sheet is connected to other bracing sheets(?)
· If the bracing also ties the box walls together, that is better
· Best - run rods all the way thru, and add compression to the panels (ie try to bend the walls into a dish shape).
Doubting that stressing the panels will have a beneficial effect. MDF and particle board especially and all materials to some extent will creep, or relax under stress. What was once tight, might end up loose and rattle. Whether rods are good or not depends on implementation.

Quote:
Originally posted by rick57
Shape
http://www.diyaudio.com/forums/showt...ht=#post832740
· holes in the braces - are to . . . ?
· Approx 30 - 60% is a good proportion of holes
· Shelf braces ( . . . . . ) are not effective because . .
· Instead, braces should divide the panels into long thin unequal, preferably trapezoidal sub-panels
Boxes for full-range or midrange-&-above : . . . .
Needs development.

Quote:
Originally posted by rick57
And for subs (XO < 100 Hz):
At 100 Hz, as long as the biggest box dimension is < 1.7 m (5.6’), there is no benefit to bracing, as potential panel resonances will be above the panel size.
This confuses acoustic with panel resonances. Subwoofers are just as important to brace, but bracing only needs to put the resonances out of band.


~16 years ago, a friend made a 10 cubic foot box (I think it was golden ratio-my first box design) out of 3/4 ply with one shelf cutting it into two 5 cube boxes. That thing vibrated a LOT even though it was limited to below 80Hz. 2x PYLE 12" drivers. Sure was loud, and no rattles , except the furniture and the drywall, and the cupboards upstairs, etc.... ahh, the folly of youth. 120dB at 15 feet with a 80 watt onkyo receiver.....
__________________
Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan
Armaments, universal debt, and planned obsolescence--those are the three pillars of Western prosperity. —Aldous Huxley
  Reply With Quote
Old 5th May 2007, 03:03 AM   #27
frugal-phile(tm)
diyAudio Moderator
 
planet10's Avatar
 
Join Date: Oct 2001
Location: Victoria, BC, NA, Sol III
Blog Entries: 5
Default Re: Circles.

Quote:
Originally posted by EC8010
That means that a rectangular panel should have a brace running centrally along the long dimension,
aka longitudinal brace...

dave
__________________
community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi
p10-hifi forum here at diyA
  Reply With Quote
Old 5th May 2007, 03:06 AM   #28
frugal-phile(tm)
diyAudio Moderator
 
planet10's Avatar
 
Join Date: Oct 2001
Location: Victoria, BC, NA, Sol III
Blog Entries: 5
Default Re: Re: Wiki on bracing

Quote:
Originally posted by Ron E

Quote:
Originally posted by rick57
The goal of bracing is to push panel resonances higher.
Perhaps a semantic issue, but the goal of bracing is to reduce cabinet talk, the practical result is to increase resonant frequency and/or increase damping rate. This is perhaps more generally true of cabinet construction rather than simply bracing.
The goal for bracing is to push the panel resonant frequencies up where there is less energy to excite them, which helps achieve the desired result of less cabinet talk.

dave
__________________
community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi
p10-hifi forum here at diyA
  Reply With Quote
Old 5th May 2007, 03:36 AM   #29
Ron E is online now Ron E  United States
diyAudio Member
 
Ron E's Avatar
 
Join Date: Jun 2002
Location: USA, MN
Default Re: Re: Re: Wiki on bracing

Quote:
Originally posted by planet10
The goal for bracing is to push the panel resonant frequencies up where there is less energy to excite them, which helps achieve the desired result of less cabinet talk.
Perhaps a (where am I standing) deal, but the way I look at it you are focused on the brace when perhaps you should be focused on the cabinet.

What we want is a cabinet that doesn't talk.
Our options:
-Try different materials: heavy light, stiff, floppy,lossy, resonant....
-Use different shapes - e.g. sonotubes have inherent advantages/disadvantages
-Use braces and/or ribs
-composite panel construction methods.
-any or all of the above
__________________
Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan
Armaments, universal debt, and planned obsolescence--those are the three pillars of Western prosperity. —Aldous Huxley
  Reply With Quote
Old 5th May 2007, 05:19 AM   #30
diyAudio Member
 
Join Date: Dec 2002
Location: dry ol Melbourne Australia
My apologies, I fess up, I need a rap on the knuckles for my inability to comprehend the How to create & edit wiki pages http://www.diyaudio.com/wiki/index.p...dit+wiki+pages which is just now v 1 of the Wiki on bracing . .

if need be, I have the original text on my hard disc.

I plead for leniency in that I thought I’d jump in, thinking I’d hopefully do more good than harm.

Maybe there should be a point “creating a wiki from prepared text”, or how to create “new wiki pages for dummies”

On the content, thanks for the further material, I haven’t time to look it at properly yet, but that Thorsten via Tenson material looks good, the sooner the wiki is going in the right place, the better.
  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 A Box Like This Need Bracing? sdclc126 Subwoofers 10 12th May 2006 01:31 AM
how much bracing is enough gwgjr31 Subwoofers 1 5th May 2006 06:57 AM
do I need bracing for a 15L BR? RockysDad Full Range 12 11th August 2005 07:18 PM
enough bracing?? Chris8sirhC Multi-Way 3 31st January 2004 08:16 PM
OT (badly) Wiki Wiki jackinnj Everything Else 0 26th June 2002 04:50 AM


New To Site? Need Help?

All times are GMT. The time now is 04:44 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