Bracing vs mass loading?

[duanebro]

So I finally ordered my drivers for InDIYana. While I can't talk about them until after the show, I wanted to ask about box damping in general. I don't think this will be a issue with the contest rules as it is a theoretical conversation. However we can use the limit of 12L bookshelf box size in this discussion. I have seen a very good example of a mass loaded box in Wolf's Stance speaker last year. And we all had heard about the importance of bracing. My thoughts for this design are drawn in each of these directions. For mass loading i would like to build a box and then line the inside with non shrinking concrete. Going the other direction is to use interlocking 1/4" bracing at 3-4" spacing. These would be laser cut. Which would be better? Or is this just over kill and a single brace tying the sides together will be fine? What are your thoughts?

[johnnyrichards]

Re: Bracing vs mass loading?

I am a recent convert to the "impossible to overkill" camp, so both.

[duanebro]

Re: Bracing vs mass loading?

I am a recent convert to the "impossible to overkill" camp, so both.

While I agree with you Johnny, I would think that it would be very difficult to do both at the same time.

[evilskillit]

Re: Bracing vs mass loading?

Has anyone built 2 or 3 identical speakers with the differences being only bracing and/or mass loading to see what the subjective difference is? I'm neither rich nor overburned with too much free time. But if I were I'd do it ;)

[billfitzmaurice]

Re: Bracing vs mass loading?

What are your thoughts?

Look at this picture, a representation of panel to panel braces, viewed end on:



Adding the red brace gives the same stiffening effect as doubling the panel thickness. Adding the blue braces gives the same effect as quadrupling the panel thickness. Either is a lot easier than using concrete.

As for polling, this is engineering fact that isn't influenced by opinion.

[Wolf]

Re: Bracing vs mass loading?

It would if you mass-load on the exterior, as I did. Damping (notice no 'en' there, no wet boxes apply) is one thing, typically of the absorbant variety. Mass-loading make the panel have a higher potential energy, and harder to resonate due to it being heavier. Bracing makes breaks the panels up into smaller sections between bracing parts, and shifts the resonant frequency into a high range where it won't interfere with the midbass region. All three together would be the trifecta.
Later,
Wolf

[johnnyrichards]

Re: Bracing vs mass loading?

While I agree with you Johnny, I would think that it would be very difficult to do both at the same time.

As easy as using two thinner walls with space between, backfill with something.

[Whitneyville1]

Re: Bracing vs mass loading?

My brain says there is a "better than brute force" solution here, probably a finite element design using materials and methods we don't have access to, but in the real world, mass and bracing may be all we can do.

[Pallas]

Re: Bracing vs mass loading?

Instead of just adding mass, why not be more sophisticated about it and use CLD? David Smith (Snell, PSB, KEF, McIntosh, JBL, etc.) mentioned on DIYA that the cabinets for his big Snell XA Reference speakers used two layers of MDF with car-fi noisekiller spray between them.

As for bracing, in KEF's LS50 "whitepaper" marketing doc they discuss mounting the cross-bracing to the cabinet via some sort of mastic rather than a rigid mounting system. No idea if that's more a marketing point than a substantive one, admittedly.

[jmb]

Re: Bracing vs mass loading?

Here is a link to a wiki that you might find interesting though the link to Tolvan seems to be dead http://www.diyaudio.com/oldwiki/inde...abinet+Bracing. Moriyasu did some actual testing and published in AES around a decade ago, if you can find the article. Here is another that also references the article: http://bellsouthpwp.net/l/j/ljfrank/Bracing.html. And finally, another discussion: http://www.hometheatershack.com/foru...materials.html
Jay

[skatz]

Re: Bracing vs mass loading?

What about stiffening ribs on the side panels. If placed assymetrically they spread the resonances, and they can be crosstied with bracing too.

[rkeman]

Re: Bracing vs mass loading?

Simple crossbracing with appropriate internal fill seems to produce good results in most situations. Shelf braces can yield particularly rigid and well damped larger cabinets and can be easy to implement. Mass loading of panels seems of more limited application and much more expensive if commercial products are employed over large surfaces.

[UGP]

Re: Bracing vs mass loading?

didn't answer the poll as I've only done shelf bracing, but I did a little experiment with 3 pieces of wood about 6"x12" one 3/4 mdf, one 3/4 H.D. plywood, one piece was two 1/2" pieces with a ~3/16 layer of urethane rubber between, the rubber won, so my next project will be that combo with bracing. though I should glue two pieces of 3/4 mdf together to compare.

[lorenmjones]

Re: Bracing vs mass loading?

What about stiffening ribs on the side panels. If placed assymetrically they spread the resonances, and they can be crosstied with bracing too.

This strategy plus fill or wall lining seems to make good sense to me and to be supported by some studies I have seen. I'm going to use hardwood ribs plus some crossbraces and then line walls with roxul on my current project.

[lorenmjones]

Re: Bracing vs mass loading?

What about stiffening ribs on the side panels. If placed assymetrically they spread the resonances, and they can be crosstied with bracing too.

This strategy plus fill or wall lining seems to make good sense to me and to be supported by some studies I have seen. I'm going to use hardwood ribs plus some crossbraces and then line walls with roxul on my current project.